A.S.T.M.24, Metallographic and Materialographic Specimen Preparation-2006

Metallographic and Materialographic Specimen Preparation, Light Microscopy, Image Analysis and Hardness Testing Kay Geels In collaboration with Daniel B. Fowler, Wolf-Ulrich Kopp, and Michael Rückert

ASTM International 100 Barr Harbor Drive PO Box C700 West Conshohocken, PA 19428-2959

Printed in U.S.A. ASTM Stock No. MNL46

Library of Congress Cataloging-in-Publication Data Metallographic and materialographic specimen preparation, light microscopy, image analysis and hardness testing Kay Geels; in collaboration with Daniel B. Fowler, Wolf-Ulrich Kopp, and Michael Rückert p. cm.—共Manual; 46兲 ASTM stock number: MNL 46. Includes bibliographical references. ISBN 978-0-8031-4265-7 E-book ISBN 978-0-8031-5691-3 1. Metallography. 2. Metallographic specimens. TN690.G3785 2006 2006103391 669⬘.95028—dc22

I. Title.

Copyright © 2007 ASTM International, West Conshohocken, PA. All rights reserved. This material may not be reproduced or copied, in whole or in part, in any printed, mechanical, electronic, film, or other distribution and storage media, without the written consent of the publisher. Photocopy Rights Authorization to photocopy item for internal, personal, or educational classroom use, or the internal, personal, or educational classroom use of specific clients, is granted by ASTM International „ASTM… provided that the appropriate fee is paid to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923; Tel: 978-750-8400; online: http:// www.copyright.com/. The Society is not responsible, as a body, for the statements and opinions expressed in this publication. ASTM International does not endorse any products represented in this publication. Printed in City, State Month Year

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Preface This book is written both for the experienced and unexperienced metallographer 共materialographer兲 who wants specific advice and information. It is also for persons seeking a broader knowledge of metallographic/materialographic specimen preparation and the examination methods, light microscopy, image analysis, and hardness testing. Special emphasis has been made on relations between ASTM standards and metallography/materialography. The book will be useful for students in courses devoted to practical metallography and materialography. The scope of the book is to give relevant information, in an efficient and clear way, covering the daily work in a metallographic/materialographic laboratory.

Metallographic/Materialographic Preparation Kay Geels and Michael Rückert 共Sections 13.5/6兲 Part I is a description of sectioning, mounting, grinding, polishing, and etching of specimens for examination in reflected light, enabling the reader to understand the mechanisms of the entire preparation process. This is combined with practical advice on specimen preparation and an introduction to existing equipment and consumables. Part II is a “Hands-on” Manual guiding the metallographer/materialographer to the correct preparation method, based on the material to be prepared and the purpose of examination. More than 150 methods are indicated covering practically all types of materials, describing the preparation process from sectioning to etching. This part also includes a section on Trouble Shooting, covering all stages in the preparation process and artifacts developed during the preparation.

Light Microscopy Wolf-Ulrich Kopp Part III is a description of the optical reflected-light microscope with photomicroscopy giving the reader both an introduction to the subject and a manual for the daily work. Also, a short introduction to electron microscopy and scanning probe microscopy can be found in this part of the book.

Quantitative Metallography/Materialography—Automatic Image Analysis Daniel B. Fowler Part IV gives an introduction to quantitative microstructural analysis and automatic image analysis, both theoretically and practically, with emphasis on the examinations based on ASTM standards and other types of commonly used analyses.

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Hardness Testing Wolf-Ulrich Kopp Part V gives a description of the hardness testing methods, Brinell, Vickers, Rockwell, microhardness and instrumented 共nano兲 indentation testing based on ASTM standards, both theoretically and as a practical guide.

The Metallographic/Materialographic Laboratory Kay Geels Part VI gives directions on how to establish and maintain a modern metallographic/ materialographic laboratory. The important rules and regulations covering occupational safety are described and commented on. The authors of this book, representing more than 100 years’ experience with practical metallography and materialography, have tried to make this book a practical tool and helpful source of information to all who are involved in the noble art/science of metallography/materialography—Kay Geels.

Acknowledgments The authors wish to acknowledge the four reviewers, who brought forward valuable insight for improvement. Special thanks to R. C. Nester, for his advice and suggestions on extension and shortening of the chapters. Thanks to G. Petzow, F. Mücklich and L. E. Samuels for permission to use a number of illustrations, and to B. Ottesen and W. Taylor for reading the manuscript and giving good advice. A special acknowledgement goes to fellow-metallographers/materialographers for support and advice through the years and directly connected to the book. The list includes U. Täffner, S. Glancy, E. Weidmann, A. Z. Jensen and A. Guesnier. A special thanks to L. Bjerregaard for her very important advice on many of the preparation methods, and to H. Hellestad for her invaluable support in making the illustrations. Also, thanks go to W. Taylor and Struers GmbH for providing important micrographs. The authors acknowledge the following companies for supply of information and illustrations, Buehler Ltd., Carl Zeiss AG, DoAll Company, Emco-Test GmbH, Leica Microsystems AG, Olympus Optical Co. Inc., and Struers A/S. Particular thanks to G. E. Totten and K. Dernoga at ASTM International for establishing and maintaining the project of making this book. Last but not least, thanks to B. Freiberg and J. Hestehave for support and encouragement during the years of making the book.

Abbreviations AFM BF CBN DF DIC

Atomic Force Microscope Bright Field Cubic Boron Nitride Dark Field Differential Interference Contrast

v

EBSD EDS EPMA FIB MFM PCB POL SEM SPM STM STEM TEM

Electron Backscatter Diffraction Energy Dispersive Spectroscopy Electron Probe Microanalyzer Focused Ion Beam Magnetic Force Microscope Printed Circuit Board Polarized Light Scanning Electron Microscope Scanning Probe Microscope Scanning Tunnel Microscope Scanning Transmission Electron Microscope Transmission Electron Microscope

Contents Part I: The Metallographic/Materialographic Preparation Process 1 1.1 1.1.1 1.2 1.3 1.3.1 1.3.2 1.4 1.4.1 1.5 1.5.1 1.5.2 1.5.3 1.5.4

Introduction Metallographic/Materialographic Preparation—The True Microstucture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Henry Clifton Sorby 共1826–1908兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The True Microstructure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Selection of Preparation Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Artifacts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preparation Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Metallographic/Materialographic Specimen. . . . . . . . . . . . . . . . . . . “Specimen” or “Sample”. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Preparation Process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sectioning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mounting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preparation of the Surface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Etching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 5 6 6 7 7 7 8 9 10 11 11 13

2 2.1 2.1.1 2.1.2 2.1.3 2.1.4 2.1.5 2.2 2.3 2.3.1 2.3.2 2.3.3 2.3.4 2.3.5 2.3.6 2.3.7 2.3.8 2.4 2.4.1 2.4.2 2.5 2.5.1 2.5.2 2.6 2.6.1 2.7 2.7.1 2.7.2 2.7.3 2.7.4 2.7.5

Sectioning Selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General Studies or Routine Work. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Study of Failures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Research Studies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Type of Section. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reporting of Locations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sectioning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wet Abrasive Cutting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Cut-off Grinding Process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Cut-off Wheel—Abrasives and Bond Materials. . . . . . . . . . . . . . . . Grinding Mechanics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanical Damage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermal Damage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cut-off Wheel Wear. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cutting Fluids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Metallographic/Materialographic Cutting Operation. . . . . . . . . . . Abrasive Cut-Off Wheels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Consumable Wheels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Slow Consumable Wheels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Abrasive Cut-off Machines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Principles of Wheel—Work Piece Contact. . . . . . . . . . . . . . . . . . Machine Designs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Advice and Hints on Wet Abrasive Cutting. . . . . . . . . . . . . . . . . . . . . . . . Cut-off Wheel Selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Other Sectioning Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fracturing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sectioning by Melting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shearing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sawing—Table 2.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wire Cutting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

14 14 14 14 14 15 15 15 15 16 21 22 23 25 26 29 32 32 34 36 36 39 43 44 45 45 46 46 47 52

3 3.1 3.1.1 3.1.2

Mounting Purpose and Criteria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Purpose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Criteria for a Good Mount. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

54 54 54 vii

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Metallographic and Materialographic Specimen Preparation

3.1.3 3.2 3.2.1 3.2.2 3.2.3 3.3 3.3.1 3.3.2 3.3.3 3.4 3.4.1 3.4.2 3.5 3.5.1 3.5.2 3.5.3 3.6 3.6.1 3.7 3.7.1 3.7.2 3.7.3 3.8 3.8.1 3.8.2 3.8.3 3.9 3.9.1 3.9.2 3.10 3.10.1 3.11 3.11.1 3.11.2 3.11.3 3.11.4 3.11.5 3.11.6 3.12 3.13 3.13.1

Surface Flatness—Edge Retention. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mounting Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Clamping. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hot Compression Mounting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cold 共Castable兲 Mounting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hot Compression Mounting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Advantages of Hot Compression Mounting. . . . . . . . . . . . . . . . . . . . . . . Disadvantages of Hot Compression Mounting. . . . . . . . . . . . . . . . . . . . . MSDS 共Material Safety Data Sheets兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hot Mounting Resins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermoplastic Resins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermosetting Resins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mounting Presses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Heating/Cooling Unit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Hydraulic Press. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Air-operated Press. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Advice and Hints on Hot Compression Mounting. . . . . . . . . . . . . . . . . . Selection of Resins for Hot Compression Mounting. . . . . . . . . . . . . . . . Cold 共Castable兲 Mounting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Advantages of Cold 共Castable兲 Mounting. . . . . . . . . . . . . . . . . . . . . . . . . Disadvantages of Cold 共Castable兲 Mounting. . . . . . . . . . . . . . . . . . . . . . . MSDS 共Material Safety Data Sheets兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cold Mounting Resins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acrylics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polyesters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Epoxies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Accessories for Cold 共Castable兲 Mounting. . . . . . . . . . . . . . . . . . . . . . . . . Mounting Molds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Clips. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vacuum Impregnation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dyes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Special Mounting Techniques. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Taper Sectioning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Edge Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mounting of Very Small Parts, Foils, and Wires. . . . . . . . . . . . . . . . . . . . Mounting of Powders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mounting of PCB Coupons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conductive Mounts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Recovery of Mounted Specimen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Advice and Hints on Cold Mounting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Selection of Cold Mounting Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . .

54 57 57 58 58 58 59 59 59 60 60 61 62 62 63 65 65 66 67 68 68 68 68 68 69 69 70 70 71 71 72 72 73 74 75 76 76 77 77 78 79

4 4.1 4.1.1 4.1.2 4.1.3 4.1.4 4.2 4.3

Marking—Storage—Preservation Marking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Marking with Waterproof Ink. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Identification Tag. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Engraving. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stamping. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Storage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preservation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

80 80 80 80 80 81 81

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5 5.1 5.1.1 5.1.2 5.2

Cleaning and Cleanliness Cleaning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cleaning Before Start of Preparation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cleaning During and After Preparation. . . . . . . . . . . . . . . . . . . . . . . . . . . Cleanliness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

82 82 82 84

6 6.1 6.1.1 6.1.2 6.2 6.2.1 6.2.2 6.2.3 6.2.4 6.2.5 6.3 6.3.1 6.3.2 6.4 6.4.1 6.4.2 6.4.3 6.4.4 6.4.5 6.4.6 6.5 6.5.1 6.5.2 6.5.3 6.5.4 6.6 6.6.1 6.6.2 6.6.3 6.7 6.7.1 6.7.2 6.7.3 6.7.4 6.7.5 6.7.6 6.7.7 6.7.8 6.8 6.8.1 6.8.2

Mechanical Surface Preparation—Grinding Grinding—A Basic Process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plane Grinding 共PG兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fine Grinding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Material Removal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rake Angle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grain Shape—Contacting Points. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grain Penetration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Force on Specimens. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grinding/Polishing Fluids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Deformation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Metals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Brittle Materials—Ceramics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grinding Abrasives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aluminum Oxide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Silicon Carbide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diamond—Diamond Products. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cubic Boron Nitride 共CBN兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Boron Carbide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hardness of Abrasives and Materials—Table 6.1. . . . . . . . . . . . . . . . . . . Grinding/Polishing Fluids—Lubricants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Water-Based Lubricant. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Alcohol-Based Lubricant. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Water-oil Based Lubricant. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oil-Based Lubricant. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Traditional Grinding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grinding Stones/Disks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SiC Wet Grinding Paper—Table 6.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Alumina—Zirconia Alumina Wet Grinding Paper. . . . . . . . . . . . . . . . . . Contemporary Grinding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Magnetic Fixation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Resin-Bonded Diamond Grinding Disks. . . . . . . . . . . . . . . . . . . . . . . . . . . Resin-Bonded SiC Grinding Disks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Metal-Bonded Diamond-Coated Disks. . . . . . . . . . . . . . . . . . . . . . . . . . . . Diamond Pads. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diamond/CBN/ Al2 O3 /SiC Film. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rigid Composite Disks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fine Grinding Cloths. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grinding/Polishing Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plane Grinding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fine Grinding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

85 85 86 86 87 88 89 89 89 89 89 92 93 93 93 94 97 97 97 97 97 97 98 98 99 99 100 105 106 106 107 108 109 109 109 109 116 117 117 119

7 7.1 7.1.1 7.1.2

Mechanical Surface Preparation—Polishing Polishing: Producing the True Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . 120 Rough Polishing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 Polishing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

x

7.2 7.2.1 7.2.2 7.3 7.3.1 7.3.2 7.4 7.4.1 7.4.2 7.4.3 7.5 7.5.1 7.5.2 7.5.3 7.5.4 7.5.5 7.5.6 7.6 7.7


7.11.1 7.11.2 7.12 7.12.1 7.13 7.13.1 7.13.2 7.14

Material Removal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Influence of Polishing Abrasive on Removal Rate. . . . . . . . . . . . . . . . . . Force on Specimens. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Deformation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Beilby Layer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Influence of Polishing Abrasive, Cloth, and Fluid on Deformation... Polishing Cloths. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Edge Retention—Relief. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cloths for Fine Grinding and Rough Polishing. . . . . . . . . . . . . . . . . . . . . Cloths for Polishing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polishing Abrasives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diamond Suspensions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diamond Spray. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diamond Paste. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Alumina. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Silica. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Other Oxides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polishing Lubricants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Metallographic/Materialographic Preparation Methods— Method Parameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RPM of Grinding/Polishing Disk. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RPM of Specimen Holder. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Direction of Specimen Holder. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Force on Specimens. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Process Time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stock Removal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grinding/Polishing Equipment—Manual Preparation. . . . . . . . . . . . . . . Grinding/Polishing Equipment—Automatic Preparation. . . . . . . . . . . . Machine Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polishing Dynamics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Semiautomatic and Fully Automatic Systems. . . . . . . . . . . . . . . . . . . . . . Special Preparation Techniques. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PCB Coupons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microelectronic Materials—Nonencapsulated Cross Sections. . . . . . . . Microelectronic Packages—Table 7.2—Target Preparation. . . . . . . . . . EBSD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Field Metallography/Materialography—Nondestructive Mechanical Preparation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Portable Grinder/Polishers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Replication. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chemical Mechanical Polishing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Protection—Corrosion at CMP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thin Sections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thin Sections of Petrographic/Ceramic Materials. . . . . . . . . . . . . . . . . . . Thin Sections of Plastics/Polymers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microtomy—Ultramilling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8 8.1 8.1.1 8.1.2

Electrolytic Polishing/Etching The Electrolytic Polishing/Etching Process. . . . . . . . . . . . . . . . . . . . . . . . . 156 The Polishing Cell. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 Smoothing and Brightening. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157

7.7.1 7.7.2 7.7.3 7.7.4 7.7.5 7.7.6 7.8 7.9 7.9.1 7.9.2 7.9.3 7.10 7.10.1 7.10.2 7.10.3 7.10.4 7.11

120 121 121 122 122 123 124 126 126 127 129 129 129 130 130 131 132 132 132 133 133 134 134 134 134 135 135 135 139 140 143 143 143 147 149 150 150 150 151 152 152 152 153 155

xi

8.1.3 8.1.4 8.2 8.3 8.3.1 8.3.2 8.4 8.4.1 8.5 8.6 8.7

Electrolytic Etching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Advantages and Disadvantages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electrolytes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electropolishing in Practice. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Factors Influencing Electrolytic Polishing. . . . . . . . . . . . . . . . . . . . . . . . . . Example of Electrolytic Polishing/Etching. . . . . . . . . . . . . . . . . . . . . . . . . . Electrolytic Polishing Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electropolishers for Laboratory Use. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Field Metallography—Nondestructive Electropolishing. . . . . . . . . . . . . Electrolytic Thinning for TEM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chemical Polishing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

159 160 163 164 164 165 165 165 166 167 168

9 9.1 9.2 9.2.1 9.2.2 9.2.3 9.2.4 9.3 9.3.1 9.3.2 9.3.3 9.3.4 9.4 9.4.1 9.4.2 9.4.3 9.5 9.5.1 9.5.2 9.5.3 9.6 9.6.1 9.6.2 9.6.3 9.6.4 9.6.5 9.7

Etching Microetching—Contrast. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Contrast Without Surface Modifications—Microscope Techniques... Dark-Field Illumination 共DF兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Differential Interference Contrast 共DIC兲. . . . . . . . . . . . . . . . . . . . . . . . . . . Polarized Light 共POL兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fluorescence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Contrast with Surface Modification—Etching. . . . . . . . . . . . . . . . . . . . . . Grain Contrast Etching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grain Boundary Etching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reproducibility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Safety Precautions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Classical Etching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chemical Etching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Precipitation 共Color兲 Etching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Heat Tinting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electrolytic Etching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Anodic Etching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Anodizing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Potentiostatic Etching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Physical Etching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Relief Polishing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ion Etching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermal Etching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vapor Deposition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sputtering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Macroetching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

169 169 169 169 169 170 170 170 171 171 172 172 172 172 172 172 172 173 173 173 173 173 174 174 174 174

Part II: Metallographic/Materialographic Specimen Preparation—A Hands-On Manual 10 10.1 10.2 10.3

Introduction Specimen Material. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Purpose of Examination. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Specimen Preparation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179

11 11.1 11.2 11.3

Specimen Material—Table 11.1 Classification of Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 How to Use Table 11.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 Table 11.1—Materials/Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182

xii


12 12.1 12.2 12.3 12.4 12.4.1 12.4.2 12.4.3 12.5 12.5.1 12.5.2 12.5.3

Purpose of Examination Purpose in General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Purpose: ASTM Standards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 12.1: Purpose/ASTM Standards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ASTM Standards—Metallography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ASTM Standards in this Book. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ASTM Standards—Document Summaries. . . . . . . . . . . . . . . . . . . . . . . . . . Chemical Microetching—Table 12.2—Table 12.3. . . . . . . . . . . . . . . . . . . Etching Practice. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 12.2—Numerical List of Etchants. . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 12.3—Etchant Names. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13 13.1 13.2

Specimen Preparation Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanical Preparation—The “Traditional” and “Contemporary” Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Material/Preparation Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Method Tables—Generic Methods—Parameters/Consumables— Table 13.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Material/Preparation Tables—Methods C-01/T-01 to C-68/T-68. . . . . . . Manual Preparation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electrolytic Polishing and Etching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electropolishers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electrolytes—Methods for Electropolishing—Table 13.2. . . . . . . . . . . . Table 13.2—Electrolytes for Electropolishing/Etching. . . . . . . . . . . . . . . Mechanical Preparation for Electropolishing. . . . . . . . . . . . . . . . . . . . . . Electropolishing—Method Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electropolishing—Methods El-01 To El-25. . . . . . . . . . . . . . . . . . . . . . . . . Field Metallography/Materialography—Nondestructive Preparation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanical Preparation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electrolytic Polishing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Replication. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Trouble Shooting—How to Improve Preparation Results. . . . . . . . . . . Sectioning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mounting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanical Preparation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electrolytic Polishing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General Rules—“The Metallographer’s Rule of Thumb”. . . . . . . . . . . . Trouble Shooting—How to Overcome Preparation Artifacts. . . . . . . . Preparation Artifacts—Flow Charts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sectioning—General Problems—Flow Charts. . . . . . . . . . . . . . . . . . . . . . Mounting—General Problems—Artifacts. . . . . . . . . . . . . . . . . . . . . . . . . . Grinding and Mechanical Polishing—Flow Charts. . . . . . . . . . . . . . . . . . Electropolishing—General Problems—Artifacts. . . . . . . . . . . . . . . . . . . .

13.2.1 13.2.2 13.2.3 13.2.4 13.3 13.3.1 13.3.2 13.3.3 13.3.4 13.3.5 13.3.6 13.4 13.4.1 13.4.2 13.4.3 13.5 13.5.1 13.5.2 13.5.3 13.5.4 13.5.5 13.6 13.6.1 13.6.2 13.6.3 13.6.4 13.6.5

188 188 188 188 188 190 193 194 194 195 217 218 218 218 219 222 450 453 454 454 454 456 456 456 475 475 475 475 476 477 479 482 483 483 484 484 485 495 498 521

Part III: Light Microscopy 14 14.1 14.2

Introduction Visible Light–Table 14.1–Table 14.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525 The Human Eye. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 526

xiii

14.3 14.4

Magnifying Lens and Microscope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 527 Magnification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 527

15 15.1 15.2 15.2.1 15.2.2 15.2.3 15.3 15.4 15.4.1 15.5 15.6 15.6.1 15.6.2 15.7 15.7.1 15.7.2 15.7.3 15.7.4 15.7.5 15.8 15.8.1 15.8.2 15.8.3 15.8.4 15.8.5 15.8.6 15.8.7 15.9 15.10 15.10.1 15.10.2 15.11

The Optical Reflected Light Microscope The Path of Light Rays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Objective. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Numerical Aperture—Resolution-Magnification–Table 15.1–Table 15.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aberrations in Image-Formation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Available Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Eyepieces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Illumination. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Koehler’s Illumination System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microscope Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Reflected-Light Microscope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Upright Type of Reflected-Light Microscope. . . . . . . . . . . . . . . . . . . . . . . Inverted Type of Reflected-Light Microscope. . . . . . . . . . . . . . . . . . . . . . Optical Examination Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bright-Field 共BF兲 Illumination. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dark-Field 共DF兲 Illumination. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polarization Contrasting 共POL兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Differential Interference Contrasting 共DIC兲. . . . . . . . . . . . . . . . . . . . . . . . Fluorescence in Reflected Light. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Practical Use of the Microscope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Setting up the Microscope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Working with the Microscope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Correct Adjustment of the Microscope. . . . . . . . . . . . . . . . . . . . . . . . . . . . Focusing and Practical Use. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Measurements of Length. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Measurements of Height Differences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maintenance of the Microscope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Documentation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Confocal Laser Scan Microscope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Function of Confocal Laser Scan Microscope. . . . . . . . . . . . . . . . . . . . . . Applications of Confocal Laser Scan Microscope. . . . . . . . . . . . . . . . . . . Stereo Microscopy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

528 532 533 535 536 536 537 538 538 538 540 541 541 542 544 545 546 546 547 548 548 549 550 550 550 552 552 554 555

16 16.1 16.1.1 16.2 16.2.1 16.2.2 16.2.3 16.3 16.4

Electron Microscopy—Scanning Probe Microscopy The Transmission Electron Microscope 共TEM兲. . . . . . . . . . . . . . . . . . . . . . The Scanning Transmission Electron Microscope 共STEM兲. . . . . . . . . . . . The Scanning Electron Microscope 共SEM兲. . . . . . . . . . . . . . . . . . . . . . . . . . Energy Dispersive Spectroscopy 共EDS兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electron Backscatter Diffraction 共EBSD兲. . . . . . . . . . . . . . . . . . . . . . . . . . . The Electron Probe Microanalyzer 共EPMA兲. . . . . . . . . . . . . . . . . . . . . . . . Focused Ion Beam 共FIB兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scanning Probe Microscopes 共SPM兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

558 558 558 559 559 560 560 560

528 528

Part IV: Quantitative Metallography/Materialography— Automatic Image Analysis 17 17.1 17.1.1

Quantitative Metallography/Materialography—An Introduction Quantitative Metallography/Materialography. . . . . . . . . . . . . . . . . . . . . 565 Stereology–Table 17.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565

xiv

17.1.2 17.1.3 17.1.4 17.2 17.2.1 17.3 17.3.1 17.3.2 17.3.3

17.4 17.4.1 17.4.2 17.4.3 17.4.4 17.5 17.5.1 17.6 17.6.1 17.7 17.7.1 17.7.2 17.7.3 17.7.4 17.7.5 17.8 18 18.1 18.2 18.2.1 18.2.2 18.3 18.3.1 18.3.2 18.3.3 18.3.4 18.3.5 18.3.6 18.3.7


Specimen Preparation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Calibration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Field Selection—Bias. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Volume Fraction—Point Count. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ASTM Test Method for Determining Volume Fraction by Systematic Manual Point Count 共E 562兲. . . . . . . . . . . . . . . . . . . . . . . . . . . Inclusion Rating. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ASTM Standard Test Method For Determining the Inclusion Content of Steel 共E 45兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ASTM Practice for Obtaining JK Inclusion Ratings Using Automatic Image Analysis 共E 1122兲共withdrawn 2006, replaced by E 45兲. . . . . . . ASTM Practice for Determining the Inclusion or Second-Phase Constituent Content of Metals by Automatic Image Analysis 共E 1245兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grain Size. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ASTM Test Methods for Determining Average Grain Size 共E 112兲. . . ASTM Test Methods for Estimating the Largest Grain Observed in a Metallographic Section 共ALA Grain Size兲共E 930兲. . . . . . . . . . . . . . . . . ASTM Test Methods for Characterizing Duplex Grain Sizes 共E 1181兲.. ASTM Test Methods for Determining Average Grain Size Using Semiautomatic and Automatic Image Analysis 共E 1382兲. . . . . . . . . . . . Banding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ASTM Practice for Assessing the Degree of Banding or Orientation of Microstructures 共E 1268兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Porosity in Thermal Spray Coatings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ASTM Test Methods for Determining Area Percentage Porosity in Thermal Sprayed Coatings 共E 2109兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Decarburization—Case Depth—Coatings. . . . . . . . . . . . . . . . . . . . . . . . . . Specimen Preparation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ASTM Test Methods for Estimating the Depth of Decarburization of Steel Specimens 共E 1077兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case Depth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ASTM Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of a Cross Section 共B 487兲.. ASTM Test Methods for Thickness of Diffusion Coating 共C 664兲. . . . . Other ASTM Standards for Quantitative Materialography. . . . . . . . . . Automatic Image Analysis Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Qualitative and Quantitative Metallography/Materialography. . . . . . The Transition to Quantitative Standards. . . . . . . . . . . . . . . . . . . . . . . . . Structure, Stereology, and Statistics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Principles of Digital Imaging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What is Digital Image Analysis?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Image Acquisition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Image Digitization—Gray Scale. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Histogram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Effects of Brightness and Contrast on Illumination Distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Image Processing and True Microstructure. . . . . . . . . . . . . . . . . . . . . . . . Image Calibration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

567 568 568 569 569 570 570 570

570 571 571 573 573 573 574 574 574 574 575 575 575 575 576 576 576 577 577 577 578 579 579 579 580 581 581 586 595

xv

18.4 18.4.1 18.4.2 18.5 18.5.1 18.5.2 18.5.3 18.5.4 18.5.5 18.5.6 18.6 18.6.1 18.6.2 18.7

Image Measurement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Manual Measurements 共Operator Defines Points, Lines, or Areas兲... Automatic Measurements 共Objects Defined by Image Segmentation兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Digital Imaging Applied to Quantitative Materialography. . . . . . . . . . Percent Area 共Volume Fraction兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Inclusion Rating. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grain Size. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Degree of Banding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Depth or Thickness Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Graphite in Iron Castings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Digital Imaging Technology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hardware. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Software. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Digital Imaging System Implementation. . . . . . . . . . . . . . . . . . . . . . . . . .

19

Digital Image Management „Archiving…

598 599 600 602 602 603 606 608 608 610 613 613 616 617

Part V: Hardness Testing 20 20.1 20.2

Introduction Indentation Hardness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 623 ASTM Standards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625

21 21.1 21.1.1 21.1.2 21.2 21.2.1 21.2.2 21.3 21.3.1 21.4 21.4.1 21.4.2 21.5 21.5.1 21.5.2 21.5.3 21.5.4 21.5.5 21.6 21.6.1 21.7 21.8

Static Hardness Testing Procedures Brinell Hardness Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Calculations and Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Brinell Hardness Testers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vickers Hardness Testers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Calculations and Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vickers Hardness Tester. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Knoop Hardness Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Calculations and Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rockwell Hardness Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Calculations and Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rockwell Hardness Testers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microindentation Hardness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Specimen Preparation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Taking the Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microindentation Hardness Testers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Examples of Indentations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Universal Hardness—Martens Hardness—Instrumented Indentation Testing—Nano Indentation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Instrumented Indentation Testing—Nano Indentation. . . . . . . . . . . . . Precision of Hardness Values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conversion of Hardness Values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

22

Dynamic Hardness Testing Procedures

23

Special Methods for Hardness Testing

626 626 628 628 628 632 633 633 634 634 636 636 636 637 638 639 639 639 641 642 642

xvi


Part VI: The Metallographic/Materialographic Laboratory 24 24.1 24.2 24.3

Introduction Establishing a Metallographic/Materialographic Laboratory. . . . . . . . 649 Running a Metallographic/Materialographic Laboratory. . . . . . . . . . . . 649 Occupational Safety and Health. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649

25 25.1 25.1.1 25.1.2 25.1.3 25.2 25.2.1 25.2.2 25.3 25.3.1 25.3.2 25.4 25.4.1 25.4.2 25.5 25.5.1 25.5.2 25.5.3

How to Build a Metallographic/Materialographic Laboratory Purpose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Quality Control 共QC兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Research and Education. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Testing and Inspection Laboratories—Failure Analysis. . . . . . . . . . . . . . Rationalization and Automation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reproducibility—Standards—Occupational Safety. . . . . . . . . . . . . . . . . . Productivity—Cost Per Specimen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Planning the Metallographic/Materialographic Laboratory. . . . . . . . . Basic Planning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Detailed Planning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Equipment and Laboratory Layout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Equipment—Table 25.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Layout—Furniture—Installations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Organizing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cleaning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Servicing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

26

Occupational Safety and Health in the Metallographic/ Materialographic Laboratory Dangers in the Metallographic/Materialographic Laboratory. . . . . . . Sectioning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mounting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanical Preparation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electrolytic Polishing/Etching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Etching—Etchants—Electrolytes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dust. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cold 共Castable兲 Mounting Resins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Standard Guide on Metallographic Laboratory Safety 共E 2014兲. . . . . Safety Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Identification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Material Safety Data Sheet 共MSDS兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Standard Operating Procedure 共SOP兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Job Safety Analysis 共JSA兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Disposal of Chemicals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Occupational Safety in General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Standards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Training. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maintenance and Service. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Standards and Regulations—Organizations. . . . . . . . . . . . . . . . . . . . . . . Designations and Abbreviations Used to Describe a Chemical Substance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ASTM Standard. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OSHA—OSHA Standards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

26.1 26.1.1 26.1.2 26.1.3 26.1.4 26.1.5 26.1.6 26.1.7 26.1.8 26.2 26.2.1 26.2.2 26.2.3 26.2.4 26.3 26.4 26.4.1 26.4.2 26.4.3 26.5 26.5.1 26.5.2 26.5.3

650 650 651 651 651 652 653 654 654 655 656 656 660 662 662 662 663

664 664 664 665 665 665 667 667 668 668 668 670 672 672 672 673 673 673 673 673 673 674 674

xvii

26.5.9 26.5.10 26.5.11 26.5.12 26.5.13 26.5.14 26.6

National Institute for Occupational Safety and Health 共NIOSH兲. . . . . International Chemical Safety Cards 共ICSCS兲. . . . . . . . . . . . . . . . . . . . . . . Environmental Protection Agency 共EPA兲. . . . . . . . . . . . . . . . . . . . . . . . . . National Technical Information Service 共NTIS兲. . . . . . . . . . . . . . . . . . . . . American Conference of Government Industrial Hygienists 共ACGIH兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . National Toxicology Program 共NTP兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Agency for Toxic Substance and Disease Registry 共ATSDR兲. . . . . . . . . . National Fire Protection Association 共NFPA兲. . . . . . . . . . . . . . . . . . . . . . . National Paint and Coatings Association 共NPCA兲—HMIS. . . . . . . . . . . . BSI—ISO. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . EU. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Literature on Laboratory Safety. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

27 27.1 27.2

Literature Books. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 685 Periodicals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 686

26.5.4 26.5.5 26.5.6 26.5.7 26.5.8

681 682 683 683 683 683 683 684 684 684 684 684

Appendixes Appendix I: Other Standards on Metallography/Materialography . . . . . . . . . . . . . 686 Appendix II: Other Standards on Hardness Testing . . . . . . . . . . . . . . . . . . . . . . . . . . 691 Appendix III: Hardness Conversion Tables for Metals 共E140兲 . . . . . . . . . . . . . . . . . . 694 Appendix IV: SI Quick Reference Guide: International System of Units 共SI兲 . . . . 694 Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 695 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 727

Part I: The Metallographic/Materialographic Preparation Process

1 Introduction “METALLOGRAPHY” or “MATERIALOGRAPHY”? IN MODERN TECHNOLogy and Materials Science we are examining the microstructure of all solid materials; therefore, materialography seems to be the correct word instead of the traditional metallography. In 1968, Crowther and Spanholtz1 suggested this and it now seems appropriate to use the word “materialography” to cover the examination of the infinite number of existing and future materials. Also, the term “metallographer” should be changed to “materialographer.” Changes of this kind, however, take time, and therefore the terms “metallography” and “metallographer” are used in this book, except in contexts where materials other than metals are discussed. G. Petzow2 defines Materialography 共metallography兲 as “an investigative method of materials science. It encompasses the optical examination of microstructures, and its goal is a qualitative and quantitative description of the microstructure.” The term materialography includes ceramography 共ceramics兲, metallography 共metals兲, plastography 共polymers兲, and mineralogy 共minerals兲, in this way covering the microstructural examination of most materials. Metallography/materialography includes a wide field in material investigation; it bridges the gap between science in new and existing materials and engineering using the materials in modern technology. Figure 1.13 shows how materialography covers the examination of parts from the centimetre and metre 共in and ft兲 range to atomic dimensions in the nm and sub nm range. The microstructure is characterized through size, shape, arrangement, amount, type, and orientation of the phases and the defects of these phases, as schematically

Fig. 1.1—Metallography/materialography can be described as a bridge between engineering and science, covering the examination of the part in cm and m to the examination of the single atom in Å.

3

4

METALLOGRAPHIC AND MATERIALOGRAPHIC SPECIMEN

Fig. 1.2—The constituents of a microstructure and the factors affecting them.

shown in Fig. 1.23. Each material contains many millions of microstructural features per cubic centimetre and these features strongly influence many of the properties of the material. As seen in Fig. 1.1, the microstructural features can exist in sizes of at least ten orders of magnitude. There are many instruments today that visualize nearly all of the features across this range. The image we see in the typical microscope is two-dimensional, but we should not lose sight of the fact that the constituents in a material are three dimensionally arranged. A photomontage shows the prepared surface of a silicon nitride alloy superimposed on a pile of silicon nitride crystals 共see Fig. 1.3兲.3 It shows that the true size of the crystals cannot be deduced directly from the microstructure. A statistical extrapolation of the two-dimensional surface shows that approximately 80 % of the crystals are relatively short and have an equiaxial shape. Stereological calculations, however, show a much higher variation in crystal length. The average crystal length is larger, corresponding to the three-dimensional characteristics shown in Fig. 1.3. It can be concluded that the analysis of the microstructure plays an important role in modern materials science and engineering, and consequently, the metallographic/ materialographic preparation. It is important to secure the true microstructure because without this the best examinations and inspired interpretations will be of no avail. As stated in the Preface, this book concentrates on metallographic/ materialographic preparation and the most commonly used examination methods. For a comprehensive, in-depth coverage of metallurgy and microstructures, including interpretation of the microstructures, ASM Handbook, Volume 9, Metallography and Microstructures,4 is recommended. This part of the book concentrates on the preparation of the specimen surface for examination in the reflected-light optical microscope. This preparation can also be used frequently for the scanning electron microscope 共SEM兲. The mechanical removal

Chapter 1

Introduction

5

Fig. 1.3—Photomontage of a microsection of silicon nitride alloy superimposed upon a pile of silicon nitride crystallites.

of material will be described and discussed rather intensively because it is the central process in abrasive cutting, sawing, plane/fine grinding, and polishing, as will the problems involved in obtaining the true microstructure. The machines and consumables available will also be described and discussed. Etching, often performed after the specimen preparation process to obtain a contrast to highlight or clearly reveal certain features, will be described in theory and practice.

1.1 Metallographic/Materialographic Preparation—The True Microstructure The goal of the metallographic/materialographic preparation is to obtain the true microstructure or “The True Structure,” meaning an undisturbed material surface, which can be analyzed in an optical 共light兲 microscope or an SEM. The basic problem for a metallographer preparing a specimen is that the preparation process itself modifies the specimen surface and, theoretically, a “true structure” completely without artifacts can never be obtained. Consequently, a preparation process should be used that creates the smallest amount of artifacts, making it possible, in practice, to analyze a microstructure in a satisfactory way.

1.1.1 Henry Clifton Sorby „1826–1908… In the 1860s, because he understood that to obtain a “true structure” he had to remove the irregularities of the material surface, H. C. Sorby was able to produce what is con-

6


Fig. 1.4—Original specimen prepared by H. C. Sorby, 1863, Bessemer steel 0.2 % carbon. BF, 450:1. Preparation Method—Rough grinding: Emery paper from coarse to fine. Fine grinding: “Fine grained” water-of-Ayr stone. Rough polishing: “Finest grained” crocus 共Fe2O3 used for industrial polishing兲. Polishing: “Very best and finest washed” rouge 共Fe2O3, jeweler’s rouge兲.

sidered the first true microstructure. In 1863 he prepared a specimen of Bessemer steel by using a preparation method with several steps, a method similar to the mechanical preparation used today. Figure 1.45 shows the microstructure, which was prepared in several steps, a rough polishing step and a fine polishing step.

1.2 The True Microstructure Based on studies by Vilella and Samuels,6–8 the true structure can be defined as: No deformation—The plastically deformed layer created by the preparation should be removed or be negligible. No scratches—Scratches normally indicate a surface that is not yet sufficiently prepared, but small scratches might be allowed if they do not disturb the examination. No pull-outs—Especially in brittle materials, particles can be pulled out of the surface leaving cavities that can be taken for porosity. No introduction of foreign elements—During the preparation process, abrasive grains can be embedded in the surface. No smearing—With certain materials, the matrix or one of the phases might smear 共flow兲, resulting in a false structure or covering of structure details, or both. No relief or rounding of edges—Relief can develop between different constituents of the surface, caused by different hardness or other condition. Edge retention is important if the edge has to be examined.

1.3 Selection of Preparation Method The preparation process will always influence the prepared surface, creating artifacts. Artifacts are defined as false structural details introduced during the preparation.

Chapter 1

Introduction

7

The choice of preparation is usually between using mechanical or electrolytic polishing, but chemical and chemical-mechanical polishing are also used.

1.3.1 Artifacts A number of artifacts are already stated above under the true structure, but a few more can be added. Microcracks, comet tails, pitting, contamination, and lapping tracks are all caused by the preparation process. Artifacts can also be introduced during chemical etching of the surface. Most of these artifacts can be readily observed under the microscope. In some cases, artifacts can be accepted and the metallographer can decide whether, for example, a scratch is acceptable as it does not disturb the structural analysis, or whether the specimen surface should be reprepared. In some cases it can be very difficult to establish the true structure, e.g., a smeared layer can cover pores. It is important that the metallographer pay attention to this possibility when analyzing a structure 共see Section 13.5兲.

Artifacts of Mechanical Polishing With mechanical polishing, it is possible to obtain an approximate true structure when the correct procedures are followed, even with very heterogeneous materials. Figure 1.5 shows the following most common artifacts: relief between phases caused by difference in hardness; embedded abrasive grain; inclusion protruding 共it could also be missing兲; pull-out looking like a pore; rounding of the edge; and deformation of the matrix.

Artifacts of Electrolytic Polishing With electrolytic polishing, the electrolysis might create problems if more than one phase is present in the structure. Figure 1.6 shows the most common artifacts. Relief between phases caused by a difference in electrochemical potential: in some cases one phase will be removed much faster than another phase, in other cases a phase might not be electrically conductive and, as such, will not take part in the polishing process. Inclusions might react in the same way; they will often be dug out during the process. Pitting might develop if the electrolytic process is not controlled correctly. Also, a pronounced rounding of the edge will take place because the current density is always stronger at the edge.

1.3.2 Preparation Methods Because most materials are heterogeneous 共or even nonconductive兲, the conclusion must be that mechanical polishing is by far the most commonly used method. For certain materials, however, electrolytic polishing gives very good results. Alternatives to the above-mentioned methods are chemical polishing and chemical-mechanical polishing. Chemical polishing is not used much, although recipes for polishing of a number of materials are developed. Chemical mechanical polishing or attack polishing can be seen as an extension of mechanical polishing and, when relevant, recipes will be stated in connection with the specific material. For recipes on chemical and chemical mechanical polishing, see Refs. 2, 4, and 9.

1.4 The Metallographic/Materialographic Specimen In practice, the total work piece normally cannot be prepared and examined. For this reason, a small part of the work piece, the sample 共specimen兲 must be extracted. For

8


Fig. 1.5—Mechanical polishing: the most common artifacts shown schematically.

both specimen preparation and examination, using an optical microscope or an SEM, the ideal specimen size is 12– 40 mm 共0.5– 1.5 in兲 square or cylindrical, with a height of 12– 30 mm 共0.5– 1.2 in兲. There are, of course, exceptions like welds, where larger specimens have to be prepared. With the specimen being only a small part of the material to be examined, if the interpretation is to be valuable, it is very important that the specimen be representative of the material to be studied. This usually happens by cutting out the specimen from a correct location and in the correct direction 共see Section 2.1兲. Most ASTM standards covering examination of a metallographic/materialographic specimen offer guidance in selection and sectioning of specimens 共see Section 12.4兲. The preparation can be performed once the specimen is established.

1.4.1 “Specimen” or “Sample” The two words are often used indiscriminately, describing the object prepared and examined. The “sample” can be defined as the piece of material in its “raw” state, as taken

Chapter 1

Introduction

9

Fig. 1.6—Electrolytic polishing: the most common artifacts shown schematically.

from the original material 共work piece兲. As soon as the “sample” is treated 共prepared兲 and described, it turns into a “specimen,” and for this reason only the word “specimen” is used in this book, except in a few cases where “sample” is the correct description.

1.5 The Preparation Process As mentioned above, several polishing methods are available, but in the diagram, Fig. 1.7, only the two methods used for almost all preparation, mechanical and electrolytic, are shown. The diagram gives an overview of the total process, of which each step will be discussed further in this part of the book.

10


Fig. 1.7—Diagram showing the total preparation process based on mechanical and electrolytic preparation.

1.5.1 Sectioning To obtain a specimen, some kind of sectioning from the basic material 共work piece兲 is necessary. If this sectioning could take place without disturbing the specimen surface, the specimen could be examined without further work, but unfortunately all the known sectioning methods will leave some kind of irregularities on the surface. Abrasive wet cutting using a precision cut-off machine is considered as a sectioning method giving a low deformation of the specimen surface. Figure 1.8 shows a surface from a specimen cut on a precision cutter and measured with an atomic force microscope 共AFM兲, and the irregularities of the surface are evident. Abrasive wet cutting is the most frequently used sectioning method, but other

Chapter 1

Introduction

11

Fig. 1.8—Surface cut with a precision cut-off machine in a very careful way to avoid irregularities in the cut surface. Measurements with an atomic force microscope 共AFM兲 give the peak-to-valley value of irregularities: higher than 1000 nm 共1 ␮m兲. This shows that even with the most gentle sectioning technique, the cut surface will have deformations which have to be removed in the following preparation steps.

methods, such as shearing, sawing, and punching are used as well 共see Section 2.7兲.

1.5.2 Mounting In some cases, the sample taken from the base material can be handled and treated directly as a specimen, but often a mount must be made to secure the handling and a satisfactory preparation. The mounting can be made by clamping the specimen between two pieces of a material compatible to the specimen material. This way of mounting has a number of drawbacks 共see Section 3.2.1兲; therefore mounting mainly takes place as hot compression or cold 共castable兲 mounting in a mounting plastic 共resin兲. Figure 1.9共a兲 shows three mounts made with hot mounting, giving mounts with very precise dimensions. Figure 1.9共b兲 shows three mounts made with cold mounting; these mounts, made in molds, are less exact than the hot mounts.

1.5.3 Preparation of the Surface The goal of the preparation is to obtain the true microstructure or at least a microstructure in a condition that makes a satisfactory examination possible. This means that the number of irregularities 共artifacts兲 in the surface must be kept at a minimum. The preparation is done through a number of steps, either mechanical or electrolytical 共see Fig. 1.7兲.

12


Fig. 1.9—Mounts made with hot compression mounting 共a兲 and cold 共castable兲 mounting 共b兲.

A mechanical preparation method will normally contain a plane grinding step, one or more fine grinding steps, and one or more polishing steps. Electrolytic polishing usually takes place as one electrolytic step, performed on a mechanically ground or polished surface.

Chapter 1

Introduction

13

Fig. 1.10—Copper unetched 共a兲 showing a bright, reflecting surface and color etched with Klemm III45 共b兲, revealing the microstructure.

1.5.4 Etching The prepared surface often reacts as a mirror when examined in the microscope, not showing all phases of the microstructure. For this purpose, the surface can be etched chemically or electrolytically or treated in other ways to discriminate between phases, grains, grain boundaries, and other details. Figure 1.10 shows a copper specimen 共a兲 in an unetched condition, giving very little information; and 共b兲 one that is etched, showing the microstructure.

2 Sectioning 2.1 Selection IT IS VERY IMPORTANT THAT THE SPECIMEN IS SELECTED CORRECTLY SO that the specimen material is representative of the material to be studied. The intent or purpose of the examination will usually dictate the location of the specimen. With respect to the purpose of the study, metallographic examination may be divided into three classifications, as stated in ASTM Practice for Preparation of Metallographic Specimens 共E 3兲共see Section 12.4兲.

2.1.1 General Studies or Routine Work Specimens should be chosen from locations that are most likely to show the maximum varieties within the material being studied. For example, specimens should be taken from a casting in the zones wherein maximum segregation should occur, as well as specimens from sections where segregation should be at a minimum. In the examination of strip or wire, test specimens should be taken from each end of the coils.

2.1.2 Study of Failures Specimens should be taken as closely as possible to the fracture or to the initiation of the failure. Before taking the specimens, study of the fracture surface should be complete, or, at the very least, the fracture surface should be documented. In many cases, specimens should be taken from a sound area for a comparison of structures and properties.

2.1.3 Research Studies The nature of the study will dictate the specimen location, orientation, etc. Sampling usually will be more extensive than in routine examinations.

2.1.4 Type of Section After establishing the location of the specimen to be studied, the type of section to be examined must be decided. For a casting, a section cut perpendicular to the surface will show the variations in structure form the outside to the interior of the casting. In hot-worked or cold-worked metals, both transverse and longitudinal sections should be studied. Special investigations may at times require specimens with surfaces prepared parallel to the original surface of the product. In the case of wire and small rounds, a longitudinal section through the center of the specimen proves advantageous when studied in conjunction with the transverse section. Cross sections or transverse sections taken perpendicular to the main axis of the material are more suitable for revealing the following information: • Variations in structure from center to surface • Distribution of nonmetallic impurities across the section. • Decarburization at the surface of a ferrous material, see ASTM Test Methods for 14

Chapter 2

• • •

• • •

•

Sectioning

15

Estimating the Depth of Decarburization of Steel Specimens 共E 1077兲, Section 12.4. Depth of surface imperfections. Depth of corrosion. Thickness of protective coatings and structure of protective coating. Longitudinal sections taken parallel to the main axis of the material are more suitable for revealing the following information: Inclusion content of steel, see ASTM Test Methods for Determining the Inclusion Content of Steel 共E 45兲 and other ASTM standards, Sections 12.4 and 17.2. Degree of plastic deformation, as shown by grain distortion. Presence or absence of banding in the structure, see ASTM Practice for Assessing the Degree of Banding or Orientation of Microstructures 共E 1268兲, Sections 12.4 and 17.5. The quality attained with any heat treatment.

2.1.5 Reporting of Locations The locations of surfaces examined should always be given when reporting results and in any illustrative micrographs. A suitable method of indicating surface locations is to make a sketch of the work piece with an indication of the location.

2.2 Sectioning The goal is to extract the specimen to be prepared from the material to be studied 共work piece兲. This should be done so that the specimen is representative of the work piece material and it should be done with a minimum amount of damage to the surface that is to be prepared. In principle, all methods, including sawing with a hacksaw, shearing, flame cutting, fracturing, etc., can be used to separate a specimen from the work piece. It is, however, important that the surface being prepared is only influenced mechanically or by heat to a degree that is suitable for a rational preparation that follows. This limits the sectioning methods to wet abrasive cutting and a few other methods that will be described in the following sections.

2.3 Wet Abrasive Cutting Abrasive cutting is a cut-off grinding process.

2.3.1 The Cut-off Grinding Process The cut-off grinding 共abrasive cutting兲 is a special operation following the general principles of the machining process, grinding. Within the spectrum of machining processes, the uniqueness of grinding is found in its cutting tool. Grinding wheels are generally composed of two materials: abrasive particles called grains that do the cutting and a softer bonding agent to hold the countless abrasive grains together in a solid mass. During most grinding processes the surface of the work piece is treated to obtain a given accuracy or surface finish. In cut-off grinding, a very thin grinding wheel 共normally the thickness of the wheel is 1 / 100 of the wheel diameter, or less兲 grinds its way through a work piece. In metallographic/materialographic cutting, this is to separate a

16


sample suited for further preparation from the work piece. Although there isn’t a demand for high accuracy, the surface quality concerning mechanical damage, thermal damage, and planeness is important. Cut-off wheels are made by cementing together abrasive grains with a suitable bonding material. Each grain is a potential microscopic cutting tool. The grinding process uses thousands of abrasive points simultaneously and millions continually. By choosing a cut-off wheel with the correct abrasive and bond and using it on a suitable machine, both the mechanical and thermal damage and the planeness can be kept inside narrow limits. This will shorten and facilitate the following preparation process. Figure 2.1 shows the surface roughness of mild steel after cutting, after grit P220 SiC grinding paper, and after P320 grinding paper. It can be seen that the irregular scratches from the cut-off are removed by the grinding papers, and for most materials a grinding with grit P220 after cutting will give a satisfactory surface for further preparation; this will be discussed further below. For certain materials P320 paper can be used as the first step after cut-off, omitting plane grinding with grit P220.

2.3.2 The Cut-off Wheel—Abrasives and Bond Materials The cut-off wheels belong to the category of “bonded abrasive tools.” Such tools consist of hard abrasive grains held in a weaker bonding matrix. Depending on the particular type of bond, the space between the abrasive particles may only be partially filled, leaving voids and porosity, resulting in an open bond. A dense bond is the result of completely filled spaces between the grains. Aside from abrasive and bond material, fillers and grinding-aid material may also be added. The correct combination of abrasive and bond is important to ensure the right cut-off process. Every abrasive particle has a number of cutting points with each removing a tiny chip from the work piece. Eventually the cutting edge becomes blunt and it must bear a larger force in order to remove the chip from the work piece. The force rises until it causes the grain to fracture and present a new, sharp edge to the work piece. In this way the grain reduces its size until finally the cutting force 共see Section 2.3.3兲 causes it to be completely torn out of the wheel, exposing new grains. This “self-sharpening” process is highly controlled by the combination of abrasive material and bond material 共see Fig. 2.2兲 that schematically shows the abrasive grains in the bond with voids 共pores兲 in between. Depending on how the wheel is breaking down, the wheels are defined as either “Consumable Wheels” or “Slow Consumable Wheels” 共see Section 2.4兲.

Cut-off Wheel Specifications The basic specification of a consumable cut-off wheel defines the following parameters: 1. The type of abrasive, expressed with a number and a letter 共aluminum oxide: A, silicon carbide: S兲. 2. The size of abrasive grains, expressed with grit number 共see Section 6.6.2兲. 3. The grade 共hard/soft兲 of wheel bond expressed with a letter. 4. The wheel’s structure expressed with numbers. 5. The bond material expressed with a letter. 6. A code in numbers to express the maker’s details of manufacture. In the following sections parameters 1–5 will be described in detail.

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Fig. 2.1—共a兲 Steel after wet abrasive cutting. An abrasive grain 共arrow兲, embedded in the surface during the cutting, can be seen, 共b兲 after grinding with grit P220 SiC paper, and 共c兲 after grinding with P320 grinding paper.

18


Fig. 2.2—Schematic drawing of cut-off wheel showing abrasive grains and bond material with voids 共pores兲.

Type of Abrasive For cut-off wheels four types of synthetic abrasives, aluminum oxide 共Al2O3兲, silicon carbide 共SiC兲, cubic boron nitride 共CBN兲, and diamond are used 共see Table 6.1 and also Section 6.4兲. Al2O3—Although this is the softest of the abrasive materials, it is the abrasive used in most cut-off wheels. This is due to the fact that Al2O3 is best suited for ferrous materials, from mild steel to high-strength materials, i.e., alloy steels. Al2O3 is not suited for cast iron 共see SiC below兲. Al2O3 is made synthetically in different types with varying hardness and friability, and is used for cutting of different materials. It is used in consumable cut-off wheels. SiC—This synthetic material is harder and tougher than Al2O3, but dulls and glazes rapidly when used with steels. It is well suited for cutting of softer materials like nonferrous metals, and it is also suited for cast iron. SiC is made in two varieties, black and green; normally the black type is used in cut-off wheels. It is used in consumable wheels. CBN—This very hard, synthetic abrasive 共superabrasive兲 is used for cutting of hard materials that are not to be cut with Al2O3 and SiC. CBN is rather expensive; the price is comparable to the price of diamond, but CBN has the advantage that it cuts ferrous materials that cannot be cut with diamond. CBN has a very high thermal stability and will work for a very long time before getting dull and needs little dressing 共see Section 2.3.6兲. It is used in slow consumable wheels where the wheel consists of a metal body, and CBN is only part of the rim in a very stable bond 共see Section 2.4兲. CBN grains tend to be blocky shaped with sharp edges and smooth faces, which makes bonding difficult. Therefore CBN, as diamond, normally is coated before being used in a resin bonded cut-off wheel. Diamond—Diamond is the hardest abrasive 共see Table 6.1兲 and is used for cutting of the hardest materials. In spite of its extreme hardness, diamond has been found to be unsuitable for cutting ferrous materials. This is due to graphitization and carbon diffusion into the iron causing excessive diamond wear.10 Diamond is found as natural diamonds, but mostly synthetic diamonds are used in cut-off wheels. The diamond grains

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Fig. 2.3—Schematic drawing of the cut-off process. The rotating cut-off wheel is cutting into the fixed work piece.

are normally coated to improve the fixation of the grain in the bond. Diamond is only used in slow consumable wheels as described under CBN above 共see Section 2.4兲.

Grain Size The grain size is expressed as a grit number 共#兲. This number refers to the number of openings per linear inch in a mesh screen through which the grain is just able to pass. The grit sizes are standardized by ANSI 共American兲 and FEPA 共European兲共see Table 6.2 and Section 6.6兲. For cut-off wheels, grit sizes between 50 共336 ␮m兲 and 120 共125 ␮m兲 are normally used. Generally speaking, large grains will have a higher material removal rate, but a rougher finish. Large grains also allow for a more open bond structure because the pores 共voids兲 between the grains can be relatively large 共see Fig. 2.2 and Structure below兲. An open bond structure allows room for the chips created during the cutting process so that they can be removed without disturbing the process. For this reason cut-off wheels with large grains, which enable an open structure with large pores, are suited for cutting of large work pieces. This creates a large contact area 共arc of contact兲 between cutoff wheel and work piece 共see l in Fig. 2.3兲. In the long contact area, chips and bond particles will be accumulated before they are removed from the wheel outside the work piece, and this accumulation takes place in the large pores. If not accumulated in the pores, the chips and particles will take room in the interface between wheel and work piece, reducing the cutting action and creating heat. Fine grains have a lower removal rate, but a better surface finish. Fine grains will give a relatively dense bond structure 共small pores兲, and therefore a fine-grained cut-off wheel is most suited for brittle materials 共very small chips兲 and smaller work pieces

20


with a short arc of contact.

Grade The grade expresses the degree of retaining grip exerted on each grain by the bonding material that corresponds to the cutting force needed to dislodge the grain Figure 2.2 shows the grains bonded together with voids 共pores兲 in between. When the cutting force has increased to a certain point, the grain will be dislodged from the bond. Wheel grades are expressed with letters from E 共very soft兲 to X 共very hard兲. Cut-off wheels are mostly in the range K to R. A soft grade of bond has a weak hold in the abrasive grain Blunt grains will be torn away easily, thus the self-sharpening action will be pronounced. This is desirable when cutting hard materials expressed in the rule: Hard Material—Soft Wheel. A relatively soft wheel is used if the arc of contact is very large because the long arc will normally reduce the force per grain 共see Sections 2.3.3 and 2.3.8兲. If the wheel is too soft for a given material it will in most cases cut very well, but the wheel wear will be excessive causing a bad economy. In principle, the hardest possible wheel for a given material should be used to secure the most economical sectioning. A hard grade has a stronger hold in the abrasive grain, making it suited for softer materials expressed in the rule: Soft Material—Hard Wheel. A hard wheel is also used with a short arc of contact 共see Section 2.3.6兲. A hard bond gives a longer wheel life, but if it is too hard the blunt grains may be retained for too long, leading to a condition called glazing of the edge of the wheel. In this condition the wheel might stop cutting completely and will only generate heat. A wheel may be made to act harder or softer by varying the forces acting on the grains. Decreasing the wheel speed or raising the feed speed will increase the cutting forces. This will cause the wheel to shed grains and wear quicker so it will appear to be acting as a softer grade of wheel. Increasing the wheel speed or reducing the feed speed will decrease the cutting forces and the wheel will act as a harder wheel. This can be used in cut-off machines with variable speeds 共see Sections 2.3.3 and 2.3.8兲.

Structure The structure is a measure of the relationship between the grain size and porosity of the bond. Wheels can be manufactured to give specific structures ranging from very dense to very open. Structure is expressed as a numerical value between 1 and 15, 1 being very dense and 15 very open. The porosity, the voids deliberately built into the wheel 共see Fig. 2.2兲, are designed to take the chips away, to avoid clogging the wheel edge 共glazing兲, and to allow grains to cut efficiently. A dense structure has closely spaced, relatively small grains and small pores so that only a small amount of material is removed. An open structure with larger grains and larger pores can cope with higher rates of material removal as described in Grain Size above.

Bond Material The bond material keeps the abrasive grains together. In general, the bond must be strong enough to withstand grinding forces, high temperatures, and centrifugal force. Consumable 共abradable兲 cut-off wheels most often have a phenolic 共bakelite兲

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21

bond. It is produced by mixing abrasive grains with phenolic thermosetting resin and plasticizers, molding to shape and baking 共curing兲 at 150– 200° C 共300– 400° F兲. The bond hardness and porosity are varied by controlling the amount of plasticizer and by adding fillers. Phenolics are also used for cut-off wheels of the slow consumable type, using CBN and diamond. These wheels are soft compared to the metal bonded wheels 共see below兲 and will give a smooth cut on very hard materials, but the wheel wear will be relatively high. Bakelite wheels are sensitive to prolonged exposure to cutting fluids. The fluid lowers the strength of the wheel so that it wears quicker; therefore cut-off wheels must be kept out of the fluid when not in use and stored in a dry place. Rubber bonds consist of vulcanized natural or synthetic rubber. They are stronger than phenolics and are often used for extra thin cut-off wheels. Bakelite rubber bond is a mixture giving a stronger bond than pure bakelite that allows for a thinner wheel. The disadvantage with rubber as part of the bond is a strong smell, even with an efficient cooling during the cutting process. Metal bonds are used for CBN and diamond wheels. The most common metal bond is sintered bronze that is produced by powder metallurgy methods. Other metal bonds that are generally stronger include iron and nickel. A low-cost diamond wheel is made with the diamond grains fixed through an electroplating process. Metal bonds and electroplating are used for slow consumable wheels 共see Section 2.4.2兲.

2.3.3 Grinding Mechanics Abrasive cutting is a grinding process where the material removal takes place when the abrasive grains interact with the work piece. The mechanics of the process highly influence the result and the economy of the cut-off process; the most important parameters will be discussed below. Grinding forces, power, and specific energy forces are developed between the wheel and the work piece 共see Fig. 2.3兲. The total force against the wheel, F, can be separated into a tangential component Ft and a normal 共radial兲 component Fn.10–12 The grinding power P associated with the force components in Fig. 2.3 can be written as: P = Ft · v

共1兲

where Ft is the tangential force and v is the wheel velocity. An important parameter is the energy per unit volume of material removal 共specific energy兲, u. u = P/d · l · b

共2兲

where d is down feed rate (feed speed), l is length of cut (arc of contact), and b is width of cut (width of wheel). The mean force per grain Ft⬘ is another important parameter since it determines the tendency to cause grain fracture and therefore plays a major role in relation to wheel wear 共self sharpening兲. Ft⬘ = u · d · l · b/v · l · b · C = 共d/v兲u/C

共3兲

where C is the number of active cutting points per square mm/in of the wheel surface.

22


Fig. 2.4—Schematic drawing of an abrasive grain producing a chip from a metal work piece.

It can be seen from Eq 共3兲 that the ratio 共d/v兲, feed speed, and wheel velocity plays a major role. At a higher force per grain, Ft⬘ a given wheel should wear faster. It can be expected that Ft⬘ in a given cut-off operation will increase until the grain fracture strength is reached, then the worn grain will either be sharpened 共fractured兲 or forced from the wheel 共see Section 2.3.6兲.

Chips, Sliding, and Plowing Some of the energy used in the grinding process is used for creating chips. These very small chips are comparable to chips made by other cutting processes such as turning and milling. The grinding chips are irregular, probably because of the variation in abrasive grains and the negative rake angles 共see below and Section 6.2.1兲. Part of the energy is expended by mechanisms other than chip formation. One such mechanism could be flattened parts of the abrasive grain sliding against the work piece surface without removing any material, as shown in Fig. 2.4. Another part of the energy will be used for plowing, only displacing the material without cutting 共see Fig. 6.3, Section 6.2兲. The high energy used for grinding compared to other cutting processes can be explained with the energy used for sliding and plowing. The specific energy used for grinding is virtually the same as the melting energy of the removed material.10

2.3.4 Mechanical Damage Abrasive cutting generates a surface with scratches that are produced by interaction of abrasive cutting points with the work piece, as shown in Figs. 2.4 and 2.5. Both figures show chips being removed from the surface of the work piece. Both the making of chips and the plowing will create deformation in the specimen surface 共see Section 6.3兲 and the depth of the deformed layer will depend on the material, cut-off wheel, feed speed, and other factors. According to the literature7,13–17 the general deformation depth at wet abrasive cutting will be so that it is easily removed by plane grinding with grit 220 SiC grinding paper. For annealed polycrystalline 70:30, brass, the damage depth has been measured to 700 ␮m 共maximum depth Dd, see Section 6.3兲 and significant deformation depth to 16 ␮m.7 For carbon steel the damage depth has been measured to 125 ␮m and for electrolytic copper 250 ␮m.14 In case of precision cutting with very thin wheels, a low force on the wheel and lower cutting speeds, the damage is lower, in the range of 50 ␮m.14 For annealed steel 共AISI/SAE 4130兲 deformation of below 10 ␮m has been measured at conventional wet cutting and less than 2 ␮m at precision cutting.16 Very often the unplaneness of the cut surface will be in the range of 300– 500 ␮m

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Fig. 2.5—Schematic drawing of fractures taking place in the abrasive grains and the bond of the cut-off wheel during cutting.

共see below兲, which means that at least the same amount of material should be removed to obtain a plane surface. The damaged layer will be removed during this process for most materials.

Waviness—Unplane Surface It is important to avoid waviness during the cut. Overloading the cut-off wheel so that it does not cut straight can cause waviness. This is due to the flexibility of the wheel that allows for cutting without breaking even if the wheel body is curved because of an excessive force 共Fn in Fig. 2.3兲. The wheel also might cut in a curve if the point of attack between wheel and work piece is not straight 共perpendicular兲, forcing the wheel out of the line of movement between wheel and work piece. The same effect can develop if the cooling fluid is unevenly distributed to the wheel, causing a chisel-shaped edge of the wheel 共see Sections 2.6 and 13.5.1兲. Correct clamping is also important 共see Section 2.3.5兲. In a normal routine-cut specimen, the surface might be unplane with variations up to several hundred ␮m.17 The variation is strongest at the entry and the exit of the cutoff wheel; therefore, the feed speed should be regulated often at the start and the finish of the cut 共see Section 2.6兲.

2.3.5 Thermal Damage As described in Section 2.3.3 the total grinding energy input includes chip formation, sliding, and plowing. Peak “flash” temperatures approach the melting point of the material being ground. These very high temperatures, however, are of extremely short duration and highly localized on the shear planes of the microscopic grinding chips. Just beneath the surface the work piece feels nearly continuous heating. This heating, at cut-off grinding, will mainly take place in the material under the wheel 共see below兲. Specimen burn can take place if the cut-off conditions are not correct. Visible burns with steels are characterized by bluish temper colors 共see Fig. 2.6兲 and might

24


Fig. 2.6—Macro photograph of a steel specimen cut with thermal damage. “Blue burn” can be seen.

cause a metallurgical transformation in the heat-affected zone 共see Section 13.6.2兲. The models developed for heat transfer at cut-off are for dry cutting used for industrial purposes, but materialographic cutting with cooling should follow the same patterns, but with lower temperatures. The heat is developed in the arc of contact and it will move downwards in the material under the wheel. This means that the heated material is continuously removed and only a relatively small part of the heat is transferred to the cut surfaces of work piece and specimen. This process, however, will take place at the end of the cut when the wheel is about to break through since no work piece material remains to conduct the heat downwards. To avoid this it is recommended by manual cutting to decrease the feed speed a moment before the wheel is through the work piece. At automatic cutting a suitable low feed speed should be chosen for the total cutting process. Heat is also developed through friction between the sides of the wheel and the work piece/specimen surfaces because of thermal expansion of the material under the wheel not yet cut. The cutting parameters should be kept so that this expansion is reduced to a minimum 共see Section 2.3.8兲. Also, a correct clamping can reduce the friction between wheel and work piece 共see below兲.

Clamping It is important that the forces developed by clamping do not influence the microstructure of the clamped work piece. This is mostly not the case when using a standard vice

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25

for parts with a stiff cross section, but in the case of sensitive materials, bending and deformation of the work piece should be avoided. Clamping is often made by using two vices and clamping both the work piece and the specimen, which-avoids a burr. When the wheel is completing the cut, and there is little stock beneath the wheel, the temperature rises rapidly and the uncut material expands thermally. This forces the already cut surfaces against the sides of the wheel and appreciable additional torque is involved. This, combined with internal stresses in the work piece might cause the “disk brake effect” in which the two sides of material clamp the wheel so hard that the rotation stops and most often the wheel breaks 共see Section 2.6兲.

Wet Cutting During materialographic cutting it is important to keep the temperature low. For this reason the process takes place with a strong supply of a grinding fluid, usually water with an additive 共see Section 2.3.7兲.

2.3.6 Cut-off Wheel Wear The cut-off wheel wear is decisive for the efficiency of the wheel. If the wear is too low the cutting edge will grow dull causing glazing and the cutting will stop. If the wear is too high, the economy of the process is not correct and the quality of the cut might be good, but the number of cuts made with one wheel is too low. The wheel wear involves three parameters: attritious wear, grain fracture, and bond fracture 共see Fig. 2.5兲.10 Attritious wear involves dulling of abrasive grains and the growth of wear flats by rubbing against the work piece 共see Fig. 2.4兲. Grain fracture refers to the removal of abrasive fragments by fracture within the grain, and bond fracture occurs by dislodging the abrasive from the binder 共see Fig. 2.2兲. Both attritious wear and the two types of fracture depend on the tangential force, Ft 共Fig. 2.3兲. If the force is too low, the process will stop and the grains will be blunt, resulting in glazing and overheating of the cut. A Ft that is too high might cause an increase in the temperature in the cut which leads to an excessive bond fracture. Wheel wear is measured by the total weight of abrasive worn away during the process. Experiments show that attritious wear is very little, grain fracture is only a small part of the total wear, and bond fracture is the dominant part. Attritious wear, altogether negligible, is probably the most important type of wear because it controls the grinding forces and thus governs the probability of bond fracture and the overall rate of wheel wear. The grinding ratio 共G兲 is a convenient measure of wheel wear and is expressed as follows: G = Volume ground away 共Qw兲/Volume of wheel consumed 共Qs兲 The G-ratio needs to be as high as possible to secure a good economy of a cut. The best G-ratio is obtained when the cut-off wheel and process parameters are chosen correctly in relation to the material and shape of the work piece. Experiments12 have shown that the arc of contact 共l in Fig. 2.3兲 is important to obtain a high G-ratio. If l is too high the longer cuts give chip interference, the space 共pores兲 between the grains in the cut are not able to accommodate the chips that causes larger lumps to be broken from the wheel edge, resulting in a lower G-ratio. It seems that the ideal length of l is around 12– 20 mm 共0.5– 0.75 in兲. If l is smaller, the G-ratio also drops, probably due to a very high load on the wheel edge due to the very short arc of contact. In practical

26


work, l can be up to around 15–20 % of the wheel diameter without problems, depending on the material11 共see Section 2.3.8兲. Another important factor regarding the G-ratio is the down feed rate 共feed speed兲 d in Fig. 2.3.12 It seems that at a too low d, excessive heat is generated, probably because of the lack of sufficient chips to take the heat away that causes the wheel to wear too fast because of the high temperature in the bond. At a certain optimum value of d the temperature drops and the G-ratio increases. If the feed speed is further increased the G-ratio drops because there no longer will be sufficient chip clearance to handle the chips, the temperature increases, and the wheel edge breaks down, as described above. In practical work the G-ratio is in the range 0.5 to 1.5 depending on the hardness of the cut-off wheel and the material to be cut. For a material like medium-carbon steel 共40 mm 共1.50 in兲 diameter兲 cut with a medium hard wheel 共250 mm 共10 in兲 diameter兲, this gives around 40 to 50 sectioned specimens.

Truing and Dressing Truing and dressing are both connected to wheel wear. Truing is a process to be performed when the grinding wheel is shaped incorrectly because wheel surface is worn. Cut-off truing is done to an unround wheel, making it run concentrically. This is done automatically with consumable wheels during the process, but truing might be necessary at slow consumable wheels. In metallographic/materialographic preparation using grinding disks having a plane surface, truing is done to make the disk plane, and it implies that an amount of the disk is removed to establish the original flatness of the disk surface. Dressing is a process to reinstate the cutting ability of the grains. If the grains are glazed or the edge/surface of the wheel/disk is clogged, the surface is opened by removing a small amount of bond material with a dressing stick, normally a piece of ceramic bonded aluminum oxide or silicon carbide. Dressing should be limited because it causes wheel/disk wear. In cut-off, dressing is only done on CBN and diamond wheels 共see Section 2.4.2兲.

2.3.7 Cutting Fluids Materialographic cutting is always performed as wet grinding, using a grinding fluid or coolant. The fluid has the following simultaneous functions: cooling the work piece/ cut-off wheel interface; lubrication; flushing away the chips; protecting against corrosion of work piece and machine; and preventing development of bacteria and fungi. Because water is a very good cooling medium, it is used as the main ingredient. However, an additive that contains a number of components is needed to obtain the mentioned functions.

Lubrication and Cooling As described in Sections 2.3.3 and 2.3.5, heat is developed during the grinding operation due to chip formation and friction forces in the cut. For these reasons it is important that a relatively high lubrication takes place, reducing the power required to remove a given volume of material and thereby keeping the heat generation as low as possible, and at the same time cool the work piece to avoid a heat buildup.

Synthetic Grinding Fluids—Oil-Based Fluids The so-called synthetic or chemical fluids used as additives to water are used for cut-off grinding. These fluids, generally defined as grinding fluids contain no mineral oil and are typically clear, but may be dyed.

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27

The simplest fluid only contains some inorganic chemicals that protect against corrosion and bacterial attack. This fluid can be described as “water that doesn’t make rust,” producing a very good cooling, but no lubrication. The most frequently used type of synthetic fluid has surface active components 共for better wetting of the surfaces兲 and other components that improve the lubrication, cooling, and corrosion inhibition. The synthetic fluid is mixed as an additive in ratios of 1:30 to 1:50 with water. Semisynthetic fluids have 3–30 % oil and give a stronger lubricating action than the synthetic fluid. It can be used instead of emulsions for band sawing and other processes with high friction. Emulsions, emulsifiable oil in water and typically milky white are not normally used for cut-off grinding, but are suited for other cutting processes, such as band sawing, hacksawing, etc. Oil-based fluids are, however, often used for cutting with precision cutters using diamond cut-off wheels. This fluid can be used without mixing. Water-soluble 共emulsifiable兲 oils, that mix with water in ratios of 1:5 to 1:20 are also available. Grinding fluids normally have a high pH and can cause skin problems 共see Chapter 26兲 and skin contact should be kept to a minimum 共see below兲.

Application of Grinding Fluid It is very important that the fluid is taken as close as possible to the area of contact between work piece and wheel. Caused by the rotation of the wheel, a layer of air is moving along with the sides of the wheel. It is important that the cooling fluid penetrates this layer and gets in contact with the sides of the wheel so that a laminar stream of fluid is established along the sides of the wheel. In this way the centrifugal force of the wheel takes the fluid into the wheel/work piece contact area. On most cut-off machines there are two nozzles positioned, one on each side of the wheel, that directs the fluid under a certain pressure towards the wheel sides. In some cases other nozzles will lead fluid to the work piece for extra cooling. Systems with the work piece totally submerged in fluid have also been used. These systems should, however, only be used as a supplement to the nozzles previously described because the coolant covering the work piece will not be able to get in contact with the wheel sides due to lack of pressure.

The Cooling System The most important parts of the cooling system are the pump and tank. The pump should have a sufficient capacity to supply the fluid, normally from 10– 15 L / min 共2.6– 4 gal/ min兲 for tabletop machines with 200– 250 mm 共8 – 10 in兲 cut-off wheels and 20– 25 L / min 共5.3– 6.6 gal/ min兲 for larger machines with 300– 500 mm 共12– 20 in兲 cut-off wheels. The tank should have a sufficient size, containing 25– 30 L 共6.6– 7.9 gal兲, and 80– 150 L 共21.2–39.7 gal兲, respectively. If the tank is too small the fluid might heat up during use, and the tank will fill up too fast with ground-off material. The tank should have a number of weirs and baffles so that the swarf and grit settle on the bottom of the tank and are not circulated in the system. Very long chips may be floating on the surface of the fluid and may eventually clog the pump. Often a simple filter positioned near the outlet of the machine will collect these chips. This filter should be cleaned relatively often. Larger filters and filter conveyor swarf removal systems, originally developed for industrial machine tools, can be used.

28


Maintenance of Cooling System and Grinding Fluid Considering the importance of a sufficient cooling, both the cooling system and the fluid should be maintained regularly. The flow to the cut-off wheel should be checked daily to assure that the flow is uniform on both sides of the wheel. Depending on the use of the machine, the tank should be emptied and cleaned in regular intervals, at least yearly. The tank should be emptied regularly for sludge to prolong the lifetime of the grinding fluid. Often the content cannot be taken directly to the sewer because local environmental restrictions will forbid this 共see below and Chapter 26兲. The machine, cutting chamber, and piping should also be cleaned regularly with a detergent cleaner to prevent development of bacterial attack 共see below兲.

Water Quality The quality of the water is important to the performance of aqueous grinding fluids. The hardness of the water 共content of carbonates兲 affects the fluid very often and the amount of additive should be adjusted accordingly based on the advice of the additive supplier. Water with a high calcium or magnesium content, or both, above 7.0 gpg 共120 ppm兲, is considered to be hard and precautions should be taken. Either a higher percentage of additive can be used or the water can be softened. Hard water also increases the bacteria/fungi growth 共see below兲. Very soft water might cause development of foam that often can be suppressed by reducing the amount of additive in the coolant. Other minerals, such as metal salts also may be present in the water, disturbing the action of certain components in the additive.

Concentration of Grinding Fluid During use, water evaporates and the concentration of additive and minerals will increase 共see below兲. This can be checked by measuring the pH and using a refractometer for exact measurements. According to the advice of the supplier, additive or water, or both, should be added. Generally straight water should not be added, but always mixed with additive in a higher or lower concentration so that the correct values are reinstated. A rule of thumb is to add water with half of the normal concentration to compensate for evaporation. The concentration of the minerals originating from the water also will rise to maybe three to four times that of the original water during use. Therefore, the more pure the water used for mixing with the additive and added during use, the longer the fluid can be used before problems might develop.

Bacteria and Fungi Bacterial growth in the cooling system often develops if a machine has not been used for a period of time or the cleaning has not been done for quite a while. Two types of bacteria are found in the fluid: aerobic, which grow in the presence of oxygen, and anaerobic, which grow in the absence of oxygen. The anaerobic bacteria that might develop in the sludge in the bottom of the tank, produce hydrogen sulfide that can cause dark staining of the work piece and machine and has a strong, unpleasant odor. The growth of fungus 共mold兲 in the fluid can be a larger problem than bacteria, depending upon the type of fluids used for cut-off. The presence of fungi can be seen in the form of slimy, semisolid deposits that cling to the walls of the tank and the machine. Development of fungi can be avoided by regular maintenance of the system as mentioned above. In case of serious attacks the supplier of the additive should be contacted. In case of strong development of microorganisms, a biocide can be added to the

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29

fluid, or in severe cases, the system must be emptied, completely cleaned, and treated with a biocide 共germicide兲 before it is filled up with new grinding fluid. The choice of biocide should be done according to information from the supplier of the original additive because the biocide added should not be antagonistic to the biocide already in the formulation.

Disposal of Grinding Fluids A number of components in a used grinding fluid might be dangerous to the environment and therefore should be treated with special care. These can be: components in the original fluid 共additive兲, bactericides, and fungicides used for cleaning, sludge consisting of metal particles, and particles from cut-off wheels. It is very important that all these substances are listed and checked with the local authorities regarding their disposal. Since disposal is often very troublesome and expensive, the advantage of good maintenance is evident; by constantly removing sludge and keeping the fluid clean, the disposal of the fluid can be done relatively seldom.

Health and Safety Aspects of Grinding Fluids The operator working with wet abrasive cutting can be affected in one or more of the following ways: skin contact, oral ingestion, inhalation, and eye contact. The fluids used mostly for cutting are of the water-miscible synthetic 共chemical兲 type having a high pH 共8.5–9.5兲 and a low surface tension. If skin is exposed to this fluid for a long period of time it loses its protective oily layer and, in seldom but some cases, dermatitis can develop. This can be avoided by careful prevention and the operator should not come in contact with the fluid by using gloves, barrier creams, etc., and by maintaining the fluid so that it is clean and the concentration is correct. Inhalation of mist and fumes can be avoided by having the cutting chamber connected to a ventilation system. The operator should use protective glasses to avoid eye contact.

ASTM Standards A number of ASTM standards are related to grinding fluids, the most important are: • Standard Practice for Selecting Antimicrobial Pesticides for Use in Miscible Metalworking Fluids 共E 2169兲 • Standard Method for Evaluation of Antimicrobial Agents in Aqueous Metal Working Fluids 共E 686兲 • Standard Test Method for Evaluating the Bacteria Resistance of Water-Dilutable Metalworking Fluids 共D 3946兲 • Standard Practice for Safe Use of Water-Miscible Metal Removal Fluids 共E 1497兲

2.3.8 The Metallographic/Materialographic Cutting Operation The metallographic/materialographic cutting operation has the following goals: 1. Produce a specimen surface with lowest possible deformations and scratches. 2. The surface should be without any thermal damage. 3. The surface should be flat without waviness and without a burr. 4. The cut-off should be done with lowest possible costs, meaning lowest possible wheel wear 共high G-ratio兲 and in the shortest period of time.

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Fig. 2.7—Schematic drawing of wet abrasive cutting process. The cut-off wheel is fed into the work piece. The work piece being with a circular cross section, the arc of contact between wheel and work piece, l, will vary from a “point” when the wheel touches the work piece to the total diameter of the work piece, when the wheel is half way through.

The Parameters The following parameters are available for the operator when cutting with a normal cut-off machine 共see Section 2.5 and Figs. 2.3 and 2.7兲:

Cut-off Wheel rpm This is normally in the range of 2000–3000, depending on the diameter of the wheel 共see below and Section 2.4.1兲.

Wheel Velocity Based on the rpm, the velocity 共v兲 can be calculated. This should be in the range of 30 to 50 m / s 共6000– 10 000 fpm兲. On most cut-off machines the rpm, and consequently, the velocity, is a fixed value that the operator will not be able to change. The velocity will decrease with the decrease of the wheel diameter caused by wear. On some newer models of cut-off machines the rpm is made variable, making a variation in wheel velocity possible. This changes the forces on the wheel 共see Section 2.3.3兲 and therefore also strongly influences the wheel wear, meaning that a “hard” wheel can be changed to a “soft” wheel by reducing the rpm and vice versa.

Force The force 共F兲 is an important parameter relating to wheel grade 共hard/soft兲, work piece material, and length of cut 共arc of contact兲. Normally the force is not used as a controlling parameter, but made available to accommodate the selected feed speed, even at long arcs of contact 共see Section 2.3.6兲.

Feed Speed The feed 共d兲 will vary according to material, length of cut, etc. It is usually in the range of 0.005– 5 mm/ s 共0.0002 to 0.2 in/ s兲. This parameter can be controlled by the opera-

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Fig. 2.8—The work piece should be placed correctly to obtain the shortest area of contact between cut-off wheel and work piece. 共a兲 This position will give a short area of contact; 共b兲 this position will give a longer area of contact and should be avoided.

tor and is very important to obtain a correct cut 共see below兲.

Power The electric motors available in the cut-off machines range from 15 W to 10 kW. The power consumption expresses the tangential force, Ft in Fig. 2.3. The operator will often be able to observe the power consumption on an amp meter, and, if necessary, adjust the feed speed up for a higher power consumption and down for a lower consumption.

Arc of Contact The contact area 共l兲 between work piece and wheel plays an important role in the process. Preferably the arc should be in the range of 12– 50 mm 共0.5– 2 in兲, but it is often longer. As a general rule, the work piece should always be placed so that the arc is the shortest possible 共see Fig. 2.8兲. When cutting large work pieces, it is helpful to use an oscillating movement of the wheel or work piece, or to rotate the work piece 共see Section 2.5.1兲.

Free Cutting Based on the relations discussed earlier in this chapter, the expression “Free Cutting” can be used as a “Rule of Thumb.” Free cutting is achieved when the correct balance is obtained between force 共wheel against work piece兲, feed speed, and power consumption, giving a correct cut with the highest G-ratio. The balance is reached at a feed speed corresponding to the optimum chip removal. If the feed speed and force are too low, the wheel edge gets blunt and heats up the work piece, stopping the process. On an automatic machine, if the feed speed is set to a certain value, and a lower feed or no feed is obtained, the same will happen because the wheel is too hard for the given material. If the force is increased without a corresponding increase in feed speed, the cut becomes too hot, causing the bond to fracture, and the wheel will start to break down at a rapid rate or bend.

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Free Cutting by Hand When cutting a work piece by hand, first a notch is made in the work piece with low force to secure a straight cut. Then the force is increased until the feed speed is constant, being the free cutting state. Free cutting is when an increase in force does not increase the feed speed. If a reasonable feed speed is not obtained, even with a relatively strong force, the wheel is too hard for the given material. If a relatively high feed speed can be obtained without a reasonable force, the wheel is probably too soft.

Free Cutting—Automatic Cut-off machines often have a hydropneumatic or electric 共electronic兲 feed system, enabling the operator to establish an automatic feed 共see Section 2.5兲. To obtain a “free cutting,” feed speed and power consumption are compared, the consumption expressing the force in the cut. The feed speed is increased, and as long this increase has a corresponding increase in power consumption, the situation is correct and free cutting is made, provided that a sufficient force is available. When adjusting to a higher feed speed, no increase can be observed but the power consumption goes up, the feed speed should be reduced because the force in the cut is too high. The wheel will start to break down at a too high rate or bend. The operation described is assuming that a sufficient force between wheel and work piece is available. If the force is not adequate for a given arc of contact, the feed will, of course, stop or be too low 共see Section 2.5.1兲.

2.4 Abrasive Cut-Off Wheels Two types of wheels are used for metallographic/materialographic cutting: consumable wheels and slow consumable wheels. Consumable wheels are based on inexpensive abrasives, whereas slow consumable wheels are made with diamond or CBN.

2.4.1 Consumable Wheels With consumable cut-off wheels, the whole wheel is made from a resin 共bond兲, bakelite or rubber, or a combination of these, with mixed-in abrasive grains, either aluminum oxide 共Al2O3兲 or silicon carbide 共SiC兲共see Fig. 2.9 and Section 2.3.2兲. The consumable wheel functions by wearing down during the cut-off process, the wear being related to the wheel grade. The wheel grade goes from soft to hard, allowing cutting of hard materials 共up to HV 700–800兲 with a soft wheel and soft materials with a hard wheel. Al2O3 is used for cutting of most ferrous materials and SiC for nonferrous and cast iron. There are normally six to seven different grades available based on either Al2O3 or SiC. Typically the grades are specified according to material type and hardness, spanning from soft nonferrous materials to very hard ferrous materials. When cutting larger work pieces with a long arc of contact, a wheel with a relatively coarse abrasive should be used and a soft grade might be needed 共see Section 2.3.2兲.

Wheel Velocity The consumable wheels, being rather brittle, are not to be used with wheel velocities higher than stated on the wheel, normally a maximum of 50 m / s 共9800 fpm兲 or 60 m / s 共11 800 fpm兲. The wheel velocity depends on the rpm of the wheel and the wheel diameter. The velocity can be calculated from:

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Fig. 2.9—Consumable cut-off wheel. The entire wheel is made of a resin bond with an abrasive 共Al2O3 or SiC兲 and will be totally worn down during the process.

Velocity =

rpm · ␲ · Diameter of wheel 共mm兲 m/s 60 · 1000

or Velocity =

rpm · ␲ · Diameter of wheel 共in兲 fpm 12

The velocity for consumable wheels is typically 35– 50 m / s 共6900– 9800 fpm兲. Most cut-off machines for general use have a fixed rpm 共except precision cut-off machines 共see Section 2.5兲, setting the wheel velocity. Because the wheel velocity, even with consumable wheels for general use, has an important impact on the cut-off process, newer machines can be made with variable rpm 共see Section 2.5兲.

Wheel Dimensions The consumable wheels are normally available in diameters: 100 mm 共4 in兲, 125 mm 共5 in兲, 150 mm 共6 in兲, 175 mm 共7 in兲, 200 mm 共8 in兲, 235 mm 共9 in兲, 250 mm 共10 in兲, 300 mm 共12 in兲, 350 mm 共14 in兲, 400 mm 共16 in兲, 432 mm 共17 in兲, 450 mm 共18 in兲. Thickness of the wheels varies from 0.5 mm 共0.02 in兲 at the smallest diameters to 3.0 mm 共0.12 in兲 at the largest. Arbor 共shaft兲 diameter is normally 32 mm 共1.25 in兲. For small wheels for precision cutting: 12.7 mm 共0.5 in兲.

Storing Consumable wheels should be stored in a dry atmosphere and laid flat on a stiff flat surface to prevent bending of the wheel. To safeguard the wheels it is useful to have a

34


Fig. 2.10—Slow consumable cut-off wheel, continuous rim. The body of the wheel is metal and the rim is a bond 共metal or bakelite兲 with diamond or CBN. The wear is very low, caused by cutting and dressing.

vertical shaft protruding from the holes in the wheels and a weight may be placed on the top. Bakelite wheels especially will deteriorate when stored in a humid environment.

2.4.2 Slow Consumable Wheels As indicated in the designation, these cut-off wheels are worn during the process, but not to the same degree as consumable wheels. The abrasives used in consumable wheels are the super abrasives, diamond and CBN 共see Section 2.3.2兲. The single grain is worn very slowly and therefore a very stable bond is used, either metal or resin 共bakelite兲. This secures that the abrasive stays in place and is not torn away from the wheel, as is the case with consumable wheels. The slow consumable wheels are usually made with a metal body and the abrasive with the bond is placed around the periphery of the body 共see Fig. 2.10兲. The abrasive/ bond layer can be a continuous layer around the periphery 共continuous rim兲 or in segments. The metal body allows for very thin wheels, down to 0.15 mm 共0.006 in兲 suited for precision cutting. In cutting wheels with electroplated abrasives, the abrasives are placed in a band along the periphery of a metal body and covered with a metal layer. These wheels only have a thin layer of abrasive; they are less expensive than the wheels described above and their lifetime is shorter.

Truing and Dressing Because the slow consumable wheels have a very stable bond, the abrasive grain does not readily break away even when very worn. Also, the edge of the wheel may clog up

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with abraded material that stops the cutting action. Therefore, truing or dressing must be done. With truing, the shape of the wheel is corrected 共see Section 2.3.6兲 and this is normally not necessary for a slow consumable cut-off wheel. Dressing is important, because it exposes new abrasive grains in the edge by removing bond material and to a certain degree removes worn down grains. Dressing is done with a dressing stick made from hard materials such as sintered Al2O3 and SiC that is held against the edge of the wheel for 5 – 10 s. Attention: Dressing should not be overdone because it wears down the relatively expensive wheel.

Use Slow consumable wheels are used frequently when consumable wheels are not suitable. Cut-off in general: For cutting of ferrous metals with hardness higher than approximately HV 500–700 and up to HV 1400, CBN wheels are used. For sintered carbides, ceramics, and other very hard materials, diamond wheels are used. Tough 共ductile兲 materials like sintered carbides are cut with a bakelite bond and most hard and brittle materials with a metal bond.

Precision Cut-off This operation, done on precision cut-off machines 共see Section 2.5兲 often calls for very thin wheels below a thickness of 0.5 mm 共0.02 in兲; therefore, slow consumable wheels are used. Normally, when cutting hard materials and composites, metal bond is used with either high or low diamond concentration. High concentrations are used for the softer materials and low concentrations for the hardest materials like ceramics. At low concentrations the cutting action is high because of the fewer abrasive grains, creating a higher force on each grain 共see Section 2.3.3兲. If possible, ductile materials, like most metals, should not be cut with slow consumable wheels. The ductile metal will constantly clog up the edge of the wheel, the cutting action will be very low, and the wheel will “wear” its way through the work piece. When cutting most metals on a precision cut-off machine, a thin resin bonded consumable wheel should be used if a thickness of 0.5 mm 共0.02 in兲 can be allowed.

Wheel Velocity The wheel speed should be approximately 25 m / s 共4900 fpm兲. This can be established with most precision machines 共see Section 2.5兲, but often the heavier machines for general cutting will not be able to accommodate this relatively low wheel velocity. At lowspeed cutting with small precision cutters, very low wheel speeds in the range of 2 m / s 共395 fpm兲 are used 共see Section 2.5.2兲.

Wheel Dimensions Slow consumable wheels for general use are available in diameters from 200– 400 mm 共8 – 16 in兲. Thickness from 1 – 2.2 mm 共0.04– 0.09 in兲. Shaft diameter 共arbor兲 is normally 32 mm 共1.25 in兲. Wheels for precision cutting 共wafering兲 are available in diameters from 75– 200 mm 共3 – 8 in兲. Thickness varies from 0.15– 0.9 mm 共0.006– 0.035 in兲. Shaft 共arbor兲 is normally 12.7 or 22 mm 共0.5 or 0.87 in兲.

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Storing Slow consumable wheels should be stored laid flat on a stiff, flat surface. Especially thin wheels should be treated with utmost care because of the risk of bending the wheel. The boxes in which the wheels were supplied should be used for storage.

2.5 Abrasive Cut-off Machines Metallographic/materialographic cut-off machines are made for wet abrasive cutting of a work piece to obtain a sample 共specimen兲. The machine is normally built for a certain size of the cut-off wheel, deciding the power of the electric motor driving the wheel. It is important that the cut-off wheel and work piece are sealed off from the operator during the cutting to avoid damage to persons in case of wheel breakage. The machine has a system for moving either work piece or wheel to establish a feed movement 共see below兲. It also has a system for adding cooling/lubricating fluid to the cutting area. The work piece is normally placed on a table to allow for fixing the work piece before cutting. The spindle carrying the wheel should be without play and the machine design should be stable to avoid vibration. During the cutting, mist and fumes are developed, and the machine should have an outlet for an exhaust system.

2.5.1 Design Principles of Wheel—Work Piece Contact As described in Sections 2.3.3 and 2.3.8, the arc of contact 共or contact area兲 between work piece and cut-off wheel should be kept around ideally 12– 50 mm 共0.5– 2.00 in兲, and preferably kept constant during the whole operation. This is often not possible at “direct” or “chop” cutting where the contact area will vary strongly with the shape and the size of the work piece 共see below兲. To avoid this, a number of designs have been developed to keep the contact area constant.

Direct Cutting The wheel and work piece contact is dependent on the shape of the work piece as shown in Fig. 2.7 and 2.12共a兲. If a 50 mm 共2 in兲 shaft is cut, the length of the contact area will vary from a “point” when the wheel first touches the work piece to more than 50 mm when the diameter of the work piece is reached. This means that the force between cut-off wheel and work piece can be very low at the beginning but has to increase to ensure a sufficient force on the abrasive grains at the long arc of contact 共see Section 2.3.6兲. This is normally solved by operating with a sufficiently high force and controlling the feed speed, keeping it constant through the whole cut. With the correct cut-off wheels and machine data, a direct cut can be made on almost all materials, even up to large sections. A rule of thumb would be that a dimension up to 15–20 % of the wheel diameter can be cut directly, depending on the material and the type of wheel.

Oscillating Cutting During oscillating cutting, the feed movement between the work piece and the wheel is combined with a relative movement between the two. This means that the arc of contact is kept low and dependent of the length of the total cut only to a certain degree so the cutting force can be kept at an optimum value. For metallographic/material-

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Fig. 2.11—Principle of oscillating cutting; the cut-off wheel moves relative to the work piece.

ographic cutting the oscillating movement also has the advantage of making room for the cooling fluid, improving the cooling in the cut. Oscillating cutting can be made with an oscillating wheel or an oscillating work piece as shown in Figs. 2.11 and 2.12共b兲. In most cases, the arbor 共spindle兲 carrying the wheel is moved in a circle 共ellipse兲 or a horizontal 共lateral兲 movement in the same plane as the wheel, in this way creating a movement relative to the work piece, as shown in Fig. 2.12共b兲. Only a small amplitude, 1 – 2 mm 共0.04– 0.08 in兲, a in Fig. 2.11, is necessary to limit the arc of contact. When oscillating the work piece, the table with work piece is moved in a tilting or reciprocating movement. Figure 2.12共b兲, shows an oscillating wheel but it can easily be imagined that the work piece has a movement giving the same effect. Oscillating cutting makes it possible to cut very large work pieces even from difficult to cut materials. The short arc also makes it possible to work with harder wheels, thus reducing the costs.

Fig. 2.12—Comparison between direct cutting 共a兲 and oscillating cutting 共b兲. At oscillating cutting the cut-off wheel can be moved relative to the work piece, as shown, or the table with the work piece can have a tilting or reciprocating movement, not shown.

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Step Cutting Another way of avoiding the long arc of contact is step cutting 共Fig. 2.13兲. In this principle the wheel is moved in increments into the work piece, or vice versa, while moving the wheel back and forth, performing the process in steps. The depth of each step 共increment兲 dictates the contact arc and this depth can be selected according to the hardness of the work piece material and the hardness of the wheel. The advantage of step cutting is that very long work pieces can be cut independently of the size of the wheel and very hard and tough materials can be cut.

Fig. 2.13—Schematic drawing of step cutting. The cut-off wheel is fed into the work piece in a step of 1 – 5 mm 共0.04– 0.2 in兲 and moved along the work piece to the end where a new step is made.

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Fig. 2.14—Schematic drawing of a rotating work piece showing complementary 共⬎⬎兲 and contra 共⬎⬍兲 rotation. With a rotating work piece, the cut-off wheel and work piece only touch in a “point,” and the specimen will be cut off when the wheel reaches the center of the work piece; this will double the cutting capacity of the machine.

Rotating Work Piece In the case of a rotating work piece, the arc of contact is only a point where work piece and cut-off wheel are touching each other 共see Fig. 2.14兲. In some cases this is the only way to cut very hard materials like sapphire, and by cutting of coatings, the coating is supported all the way around, avoiding peel-off. This way of cutting also will give double cutting depth because the cut-off wheel will only reach halfway through the work piece. Complementary rotation should be preferred 共see Fig. 2.14兲. The figure shows a work piece with a circular cross section, but other shapes can be rotated and cut. However, this usually causes some cutting in air because the wheel will first touch the corners of the work piece. A rotating work piece is mostly used at precision cutting but special rotating chucks are also available for general use machines.

2.5.2 Machine Designs Cut-off machines can be designed according to different principles regarding movement of work piece/wheel 共see Fig. 2.15兲.18 The wheel is either moved towards the work

Fig. 2.15—Design principles for the metallographic/materialographic cut-off machines. At a, b, and c, the cut-off wheel is fed into the work piece. At d, e, and f, the work piece is fed into the cut-off wheel.

40


Fig. 2.16—Standard manual laboratory cut-off machine for chop cutting with dual vices to clamp samples on both sides of the cut-off wheel. A 3 kW motor and 254 mm 共10 in兲 cut-off wheels with cut capacity 76 mm 共3 in兲 in diameter.19

piece, a, b, c, or the work piece is moved towards the wheel d, e, f. In the case of the radial in-feed shown in a, c, d, and f, the depth of the cut is limited to the part of the wheel outside the flange. At b and e, the work piece is attacked tangentially, and a larger work piece can be cut if the movement of the cut-off wheel b or the work piece e allows for it. Most modern machines are built according to c, where the cut-off wheel is moved into the work piece that is fixed on a stationary table, or e, where the work piece, fixed to a movable table, is moved into the stationary cut-off wheel which in most cases is placed on the motor shaft. In some machines the two principles are combined, giving more flexibility.

Cut-off Machines for General Use Smaller machines for wheels of 200– 250- mm 共8 – 10- in兲 diameter are mostly table top models with an external recirculation system for the cooling fluid. Most of these smaller machines are hand-operated, and the cut is a direct cut 共see Section 2.5.1兲. The motor power for these machines is in the range of 1 – 4 kW. An example of a handoperated table-top machine is shown in Fig. 2.16. Machines for wheels of 300 mm 共12 in兲 and larger are mostly floor models with recirculation systems included in the machine, with motor power ranging from 4 – 10 kW. These machines are usually automatic, meaning that the feed speed is controlled by hydropneumatics or by electric means. In the case of electrically driven feed, this can be controlled by a microprocessor, allowing for adaptive control so that the optimum feed speed in relation to motor power is found 共see Section 2.3.8兲. An example of an automatic, floor-based machine is shown in Fig. 2.17.

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Fig. 2.17—Automatic cut-off machine with oscillating cutting and step cutting for obtaining the minimum contact area. A 10.5 kW motor and 432 mm 共17 in兲 cut-off wheels with cut capacity 160 mm 共6.3 in兲 diameter, cutting length 450 mm.20

Most machines have tables with T-slots for flexible positioning of the work piece, often with quick clamping devices. The cutting compartment should be closed according to the rules of safety. It shall not be possible for the operator to open into the compartment before the wheel has stopped. The compartment should be easy to clean, without too many components and corners. It is also an advantage if electrical parts, such as the motor, are not placed in the cutting compartment. An efficient cooling system is important, taking the grinding fluid effectively into the cut, with easy access to cleaning. Large machines should have a system for reducing the arc of contact between wheel and work piece 共see Section 2.5.1兲.

Precision Cut-off Machines Precision cut-off machines are defined as machines being able to cut with relatively high precision, the work piece being placed in a fixture, moved with a micrometre screw or automatically. Where machines for general use are mostly used for metals, the precision machines are often used for other 共hard兲 materials such as ceramics and electronic parts to be cut with diamond cut-off wheels. Most of these cutters have variable speed, from very low 共50 rpm兲 to 5000 rpm. The wheels are from 75 to 200 mm

42


Fig. 2.18—Low speed precision saw for low volume applications. A 15 W motor, 0 – 300 rpm and up to 125 mm 共5 in兲 diamond wheels, 32 mm 共1.25 in兲 cutting capacity.19

共3 to 8 in兲 in diameter and often very thin, securing a very low loss of material 共kerf loss兲 which can be important when cutting materials of high value. On most modern machines both consumable and slow consumable wheels can be used. The work pieces, electronic parts, optical parts, and other parts where a precision cut is needed, are normally of a size up to 50– 75 mm 共2 – 3 in兲.

Fig. 2.19—Precison cut-off machine for automatic precision cutting of larger specimens. Adjustable vertical position of the cut-off wheel makes use of small wheels, 75 mm 共3 in兲, and large wheels, 200 mm 共8 in兲, easier to work with. Automatic feed speed adjustment and 5 ␮m specimen positioning. An 800 W motor, up to 5000 rpm. Cutting capacity 60 mm 共2.3 in兲, cutting length 190 mm 共7.5 in兲.20

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Precision machines are built according to the same principles as the general purpose machines 共see Fig. 2.15兲. The smallest machines are built according to f in Fig. 2.15, with the work piece being fed into the wheel by a weight 共constant force兲. These machines are made for use with slow consumable wheels 共diamond兲 because consumable wheels cannot be used with the very simple feed system without getting unround. The speed is low, in the range corresponding to 300 to 600 rpm, and the motor power is very low, 15– 100 W. An example of a low-speed cutting machine is shown in Fig. 2.18. The larger machines typically have a table with the fixed work piece moving linear into the rotating cut-off wheel, Fig. 2.15, d and e. The motor power is in the range of 500– 1000 W. The feed, “y-movement,” can be hand-operated or automatically controlled by a microprocessor. The fixture, placed on a table carrying the work piece, can be with a micrometre or with automatic control of the “x-movement,” positioning the work piece. An example of an automatic precision cutter is shown in Fig. 2.19. All machines have a system for cooling fluid to be taken into the cut. With machines running more than approximately 300 r / min, the cutting compartment is protected by a hood and it should be secured that the wheel is stopped if the hood is opened.

2.6 Advice and Hints on Wet Abrasive Cutting When working with cut-off, it is possible to routinely make a number of precautions to secure a good cut and, therefore, a good specimen. • Fix the work piece securely before cutting. Take care that the cut-off piece 共the specimen兲 is not squeezed against the wheel during the cutting. Preferably the specimen should be lightly clamped to avoid a burr. • When clamping sensitive work pieces, place some soft material, such as plastic, between the work piece and the clamp to avoid damage. • When introducing the wheel into the work piece at manual cutting, do it slowly and stop the feed for 2-–3 s to allow a notch 共kerf兲 to be formed. This secures a straight cut. This is especially important at tapered or rounded work pieces. If the wheel is not cutting straight from the beginning it will cut sideways and ultimately break. • Pay attention at manual cutting when the cut-off wheel is almost through the work piece. Lower the feed speed to avoid overheating of the edge of the specimen or pinching of the wheel. • Check the edge of the cut-off wheel. It should be flat 共square兲 when cutting medium thick sections, flat with rounded corners 共large sections兲, or concave 共thin sections兲, indicating that the proper cut-off wheel is used and normally giving a burrfree cut. If the edge is strongly rounded 共convex兲 or pointed, the wheel is probably too hard for the material and a softer wheel should be used. A glazed edge indicates a wheel that is too hard, which requires a too high force and therefore develops excessive heat. If the edge is chisel shaped, the flow of cooling fluid to the wheel is uneven, giving a crooked cut possibly causing wheel breakage 共see Section 13.6.2兲. • Disk brake effect: In some materials having internal stresses the work piece will tend to pinch the wheel, very often when the cut is almost finished. This can cause a breakage of the wheel because the pressure between the two parts of the work piece is so high that the rotation stops. This effect might be avoided when working with a very low feed speed, 0.5 mm/ s 共0.02 in/ s兲 or lower, and preferably oscillating/step movement, minimizing the development of heat.

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•

•


When cutting a material for the first time, check that the feed speed and power consumption 共force in the cut兲 are in reasonable balance. If yes, the wheel is “freecutting” 共see Section 2.3.8兲. If the force on the wheel increases, shown by an increase in power consumption, without a visible increase in feed speed, the setting of the feed speed is probably too high and it should be reduced. If the force is allowed to mount, the wheel might bend and a straight cut 共plane surface兲 is not obtained, or the wheel might break. Cutting of a work piece with a coating: Take care that the cut-off wheel is moving through the section of the coating to be examined and into the base material. In this way the coating is preserved, because it is in compression and not torn away from the base material. Mounting before cutting: In some cases it is an advantage to mount the specimen before sectioning to be able to establish a correct cutting plane or avoid breakage. This can be failure analysis with cracks/corrosion, electronic parts, small specimens of plastic, or very brittle specimens. The mounting is done mostly with a cold mounting resin, preferable epoxy 共see Section 3.8兲. To avoid clogging of the edge see electronic parts below. Cutting of electronic parts: Often these parts contain soft 共copper兲 and very hard 共brittle兲 materials 共ceramics兲. Use an electroplated diamond wheel 共precision cutting兲; this wheel has diamonds on both the edge and the sides, and it will cut through ductile and brittle materials without clogging 共see Dressing below兲. When the wheel is too hard 共glazing兲, and a softer wheel is not available, try a worndown wheel which causes a lower cutting speed and thereby a softer acting wheel, or use a thinner wheel. In the case of hand cutting, “pulse cutting,” by beating the wheel into the work piece will create a wheel wear and the wheel will start cutting; only the lifetime of the wheel is reduced. Another possibility is to make incisions in the periphery of the wheel, using a pair of pliers to break out small pieces with 50– 75 mm 共2 – 3 in兲 in distance. This also increases wheel wear. Cutting may cause harmful gases derived from the phenolic bond and a rubber bond will normally develop a strong smell. Therefore, the cut-off machine should be connected to an exhaust system. The hood of the cutting machine should be left open after use so that the machine and cut-off wheel can dry out, reducing corrosion of the machine and prolonging the lifetime of the wheel. Dressing: Diamond and CBN wheels can have a material build-up on the edge of the wheel 共clogging兲, reducing the cutting ability. The edge is dressed, “cleaned,” using a dressing stick of Al2O3, for about 5 – 10 s. For Trouble Shooting, see Section 13.5.

2.6.1 Cut-off Wheel Selection Rule of thumb: Use a soft wheel for a hard material or a large work piece and a hard wheel for a soft material or a small work piece. Both hardness and ductility of the material must be evaluated. A soft material will not wear out the abrasive very fast, therefore a hard wheel can be used. A ductile material might clog the wheel rim so that a softer wheel must be used. On the other hand, a ductile material might pull out the grains, causing excessive wear. A hard material will wear out the grains fast, therefore the wheel should break down, releasing new grains.

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General Use Nonferrous metals—These are relatively soft 共up to HV 350兲. Use a hard bakelite 共phenolic resin兲 wheel with SiC. Soft ferrous metals—共Up to HV 350兲. Use a hard bakelite or rubber-resin wheel with Al2O3. Medium hard ferrous metals—共Up to HV 550兲. Use a medium hard bakelite or rubber-resin wheel with Al2O3. Hard ferrous metals—共Up to HV 950兲. Use a soft bakelite or rubber-resin wheel with Al2O3. Very hard ferrous metals—共Harder than HV 950兲. Use a slow consumable CBN wheel with bakelite bond. Sintered carbides/hard ceramics „relatively ductile…—Use a slow consumable diamond wheel with bakelite bond. Ceramics/minerals „relatively brittle…—Use a slow consumable diamond wheel with metal bond. Precision Cutting Soft and medium hard materials—Use a medium hard bakelite wheel with Al2O3. Medium hard and hard materials, hard, ferrous metals—Use a medium soft bakelite wheel with Al2O3. Very hard ferrous metals—Use a slow consumable CBN wheel with high concentration, metal bond. Extremely hard ferrous metals—Use a slow consumable CBN wheel with high concentration, bakelite bond. Ceramics, minerals, very hard materials, general use—Use a slow consumable diamond wheel with high concentration, metal bond. Brittle materials „ceramics, minerals兲—Use a slow consumable diamond wheel with low concentration, soft metal bond. Electronic parts, hard tough materials, medium to soft ceramics, structural ceramics—Use a slow consumable diamond wheel with low concentration, metal bond. Polymers and other soft materials—Use a slow consumable diamond wheel with high concentration and metal bond, or a toothed saw blade. Soft and ductile nonferrous metals—Use a medium hard bakelite wheel with SiC.

2.7 Other Sectioning Methods As described earlier, wet abrasive cutting is the dominating cut-off method for materialographic specimens. Other methods, however, are used either because they are simple and effective like fracturing, shearing, punching, and sawing, or because they give a gentler treatment of the cut surface, like wire cutting, than can be obtained with wet abrasive cutting.

2.7.1 Fracturing Fracturing can be done on brittle materials like hardened tool steels, ceramics, etc. Often a notch is made to control the fracture. Less brittle steels and cast iron can be cooled in liquid nitrogen before fracturing.

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2.7.2 Sectioning by Melting Cutting using methods based on melting the material to be cut is not recommended for metallographic specimens. The melting process always develops zones affected by heat and changes the material, often far from the cut surface.16,21 As some of these methods are used in spite of the drawbacks, the most important methods should be mentioned.

Oxyacetylene Torching This method should only be used when no other method is available and it should only be used for obtaining a relatively large work piece for further cutting in the laboratory with other means. When cutting-off steel specimens it should be considered that a zone of at least 25 mm 共1 in兲 has been affected by heat during the torch cutting,21 but often the affected zone is wider 共see Fig. 13.1兲.

Plasma Torching This method also creates a heat-affected zone with material changes and microcracks,16 and should only be used for cutting a work piece for further cutting.

Laser Cutting During laser cutting the heat-affected zone is the range of 0.5 mm 共0.02 in兲 for an annealed steel 共AISI/SAE 4130兲,16 and care should be taken to remove enough material at the grinding stage if laser cutting is used for the specimen.

Electric Discharge Machining Electric discharge machining 共EDM兲, or spark machining, is a process that uses sparks in a controlled manner to remove material from a conducting work piece in a liquid dielectric.22 The sparks melt the specimen material creating craters in the surface and a heat-affected zone below the surface. With certain materials that have been melted and then solidified, the molten material may absorb extraneous alloying elements from the surroundings.7 A layer containing cracks also may develop immediately beneath the surface. Both the craters and the heat-affected zone can be several hundred ␮m deep, and care should be taken, especially in heat-sensitive materials, so that the damaged layer is removed during the grinding process.

2.7.3 Shearing A shear can be used for cutting of sheets and other flat products of not very hard materials. The edge of the produced specimen will be heavily damaged by cold work and a burr often develops. The cold work will alter the microstructure in a layer of the specimen in most cases, and it is important that this material is removed during the plane grinding and fine grinding process. For this reason, shearing is not recommended for materials that are sensitive to mechanical twin deformation.9 A hand shear can be used for cutting work pieces up to 4 – 6 mm 共0.15– 0.25 in兲, depending on the type of material. For shearing of stock up to 13 mm 共0.5 in兲 a power shear is needed. The power shear is built with a table for placing the work piece and a lower blade integrated in the table and an upper blade moved mechanically or by hydraulics. The work piece is fixed during the shearing process by a hold down foot very close to the lower blade. The upper blade is not attacking the work piece in its full length, but the blade has a slope called the rake. The rake is given by the design of the shear. The load required to shear the work piece material depends on the thickness and

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type of material and the rake. In normal shearing a portion of the material is sheared and the rest is broken through due to the shearing action. As an example, in mild steel up to 6 mm 共0.25 in兲, one-half will be sheared and the rest will break. The shearing load increases strongly with the thickness of the work piece, although mild steel of 9.5 mm 共0.38 in兲 is only approximately 50 % thicker than 6 mm 共0.25 in兲; the load needed is 225 % higher. For this reason, a shear should not be used for cutting of metallographic material thicker than the rated capacity, even in narrow pieces. On most power shears the upper blade will move in a plane 0.5–1° away from vertical, allowing the upper blade to contact the work piece immediately above the edge of the lower blade. When the upper blade moves downwards and edge contact is obtained, the correct clearance is developed and this clearance will increase when the blades overlap. In principle, the blades should be adjusted according to the thickness of the work piece, but at most modern shears the blades can be set for a wide range of thicknesses. If shearing of both thin and thick products are made, the shear should be adjusted to minimum clearance to avoid thin stock wedging between the blades. It is very important that the clearance setting is correct and accurate grinding of the blades is maintained. If the edges of the blades are rounded by wear, or the clearance is too high, the burr mentioned above will increase. The shear is a safe tool to use as long the operator follows the given rules. The shear is a precision machine tool and should be kept in good working order according to the instructions of the supplier.

Punching Punching is shearing using a die and a punch and it is used for foils and thin plates to make circular or rectangular specimens. An example of a circular specimen is the punching of samples for electrolytic thinning 共see Section 8.6兲. Rectangular specimens are used for printed circuit boards 共PCBs兲共see Section 7.10.1兲. Rectangular specimens also are used for steel sheet because the long edge of the specimen can be aligned to the rolling direction of the sheet. As with shearing 共see above兲, cold work and a burr will be developed in the process and this should be removed during the grinding stage of the preparation.

2.7.4 Sawing—Table 2.1 Sawing is a machining process using a circular blade or a straight band having a series of small teeth for cutting of most materials. By sawing, material is removed from the work piece in chips as described in Section 6.2 and shown in Figs. 6.1 and 6.2. When sawing, the rake angle 共see Fig. 6.2兲 is always neutral 共0°兲 or positive, up to 10° for power hacksawing and bandsawing and 18° for circular sawing. The distance between adjacent teeth on the saw blade is called the pitch, normally expressed in number of TABLE 2.1—Recommended Band Pitches for Sawing of Work Pieces of Different Thickness. Work Piece Thickness Less than 25 mm 共1 in兲 25– 75 mm 共1 – 3 in兲 75– 150 mm 共3 – 6 in兲 150– 300 mm 共6 – 12 in兲 Over 300 mm 共12 in兲

Band Pitch 10 or 14 6–8 4–6 2 or 3 1 1 to 3 2

48


teeth per inch, and it depends primarily on the cross section area of the work piece to be cut and to a lesser degree on the type of material. As a rule, two or three teeth should be engaged with the work piece at all times during sawing. Under Bandsawing, below, the tooth geometry, pitch, etc., are further discussed. Sawing should be performed with a cutting fluid 共see Section 2.3.7兲. The surfaces created by sawing normally are rather rough, but if correctly treated in the following specimen preparation, sawing can be used for sectioning of metallographic/materialographic specimens.

Hacksawing The hand-held hacksaw often can be used for cutting of a work piece from a large part, maybe placed outside the materialographic laboratory, the work piece later to be sectioned by wet abrasive cutting to produce a specimen. If the hacksaw is used for cutting a specimen from a work piece, the surface should be carefully prepared, often with an extended plane-grinding step to remove cold work and deformation 共see Fig. 13.2兲.

Power Hacksawing Power hacksawing is characterized by the reciprocating action of a relatively short, straight-toothed blade that is drawn back and forth over the work piece in much the same manner as a hand hacksaw. Hacksawing machines consist of a supported reciprocating frame and saw blade mounted to a base for supporting the work piece. The machines are made as both horizontal and vertical designs, horizontal machines being the most popular. The blade is fed into the work piece with a feed mechanism and a flow of cutting fluid is led to the cutting area. Because of the limited possibilities for clamping the work piece, power hacksawing is well suited for cutting of stock material, tubing, etc., but less suited for cutting of more complicated parts. The surfaces produced with power hacksawing are very rough and the problems mentioned above with cold work and deep deformation are evident. Therefore, this cutting method should only be used for cutting of a work piece from a larger part, the specimen to be cut later from the work piece by wet abrasive cutting.

Circular Sawing Circular sawing is a process using a rotating, continuous cutting blade with teeth on its periphery to cut most materials under a flow of cutting fluid. A circular saw produces better surfaces than power hacksawing, but the limitations regarding cutting of other work pieces than stock material and tubes, etc., are the same.

Bandsawing Bandsawing uses a long, endless band traveling over two or more wheels in one direction. The band, with only a portion exposed, produces a continuous and uniform cutting action using a cutting fluid to improve the cutting, cool the work piece, and increase band life. In bandsawing the cutting takes place as a continuous, single-direction cutting, and this, combined with blade guiding and tensioning, gives the possibility of following a free cutting path, making contour cutting possible. In this way a specimen can be cut out from a work piece of odd form, a great advantage compared to other types of sawing mentioned above.

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A number of saw blade types are available for bandsawing, but only two of them are suited for cutting of metallographic/materialographic specimens. These types are “conventional sawing” with a bandsaw blade with teeth, used primarily for cut-off and contour cutting of most materials, and “saw-grinding” with a blade with continuous/ segmented edge for the cutting of very hard materials and composites 共see below兲. The quality of the cut is generally better than hacksawing, but still a relatively strong deformation caused by cold work is developed.16,21 At conventional properly performed bandsawing, the heat developed will not create an altered microstructure but this could happen if the cooling has not been efficient or the feeding pressure has been too high. Care should be taken so that cold work and heat-affected zones are totally removed during the grinding steps of the preparation process.

Safety at Bandsawing The dangerous area when bandsawing is the point of operation where the saw band traverses to process the work piece. It is very important that the operator is careful to keep his hands out of the immediate sawing area whenever the band is moving. The work piece should always be guided into the band with some kind of distance piece so that the hands will not be close to the band, even when the band has cut totally through the work piece.

Bandsaw Blades It is important to select the correct saw band 共blade兲 for the given work piece to be cut.23 Important factors are: • Type and hardness of the work piece material that determine the tooth form and composition of the band. • The size and variation in cross section of the work piece that determine the pitch of the teeth of the band. • Type of cut, is it straight, contoured or both? If cutting in small radii, the width of the band should be limited. • Type and condition of the machine to be used. • Whether a cutting fluid will be used. Different bandsaw blades with different width, thickness, and tooth geometries are available for cutting of different materials, ranging from relatively soft carbon steel bands for cutting of mild steel, cast iron, copper, and other relatively soft materials, to bi-metal and tungsten carbide-tipped blades for hard, very hard, and tough materials like work-hardening alloys, high temperature alloys, hastalloy, and titanium. Bandsaw blades with a grit edge are available with a tungsten grit for cutting hardened tool steel, titanium, nickel- and iron-based superalloys, glass fiber optics, low density ceramics, and composites. The more expensive diamond edge blades are used for very hard, brittle materials, such as minerals and ceramics. Figure 2.20 shows the terminology commonly used for saw bands. The cutting action of the band depends on the tooth geometry. There are three main types of tooth forms: precision, claw, and buttress, as shown in Fig. 2.21. The precision form normally has a 0° rake angle, but a positive rake angle is also available. It has a full-rounded gullet with a smooth radius; the gullet is taking up the chip as long as the tooth is in contact with the work piece. Bands with precision-form teeth are the most versatile, have a smooth finish, and are recommended for cutting of most metallographic/ materialographic specimens. The claw form has the same form as the precision except

50


Fig. 2.20—The terminology commonly used for bandsaw blades.

the gullet is more shallow with less chip capacity but greater backing strength and a 10° rake angle that requires less feed force. The claw form is recommended for the toughest materials that demand heavy feed and yield small chips. The buttress form also has a more shallow gullet and neutral rake angle and is a stronger, less aggressive variant of the claw form for cutting of wood and plastics. The band width should be as high as possible for the given cutting operation 共see Fig. 2.20兲. The wider the band, the greater its beam strength and the more accurate the cut. For straight cuts the widest band that the machine can accommodate should be used. Narrower bands should be used only for contour cutting. The band thickness is important for the strength of the band, especially if the band width is small. The tooth set is the distance between the outer corners of oppositely set teeth, determining the kerf 共width of the cut兲. The teeth are set by bending the single tooth to one side of the band. At straight set the bending alternates all teeth left and right. Raker set includes one unset tooth 共raker兲 in each sequence of 3, 5, or 7 teeth. The raker set is recommended for materialographic cutting of ferrous materials.

Fig. 2.21—The three main types of bandsaw blades.

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The band pitch, the number of teeth per inch of length 共see Fig. 2.21兲 is primarily determined by the thickness of the work piece to be cut. A thin work piece requires bands with a finer pitch 共more teeth per inch兲, thick stock a coarser pitch 共see Table 2.1兲. The work piece material and the surface finish required also must be considered when selecting the optimum pitch. It should, however, be assured that at least two teeth are in contact with the work piece at all times during sawing. Definitions, tooth form and set, pitch sizes, etc., regarding bandsaw blades are discussed in ASME Standard B94.51M, “Specifications for Band and Saw Blades 共Metal Cutting兲.”

Bandsawing Machines Bandsawing machines are built as vertical machines and horizontal machines. The vertical type23 having a vertical band and a horizontal table on which the work piece is moved into the band is the most versatile and typically used for cutting of metallographic/materialographic specimens 共see Fig. 2.22兲. The table often can be tilted to allow for cutting under an angle to the work piece, and the maximum work height is in the range of 300– 400 mm 共12– 16 in兲. Most machines have variable band speed in the range from 0.2– 28 m / s 共39– 5500 fpm兲, but most cutting takes place at speeds in the range of 0.6– 5 m / s 共118– 985 fpm兲, the speed varying with the hardness/ ductility of the work piece material and the cross section to be cut 共see below兲. Most metals are cut with speeds in the range of 0.4– 2 m / s 共847– 394 fpm兲 for a cross section of 25 mm 共1 in兲 reducing the speed to half or less at sections above 150 mm 共6 in兲. For soft materials like copper the speed can go up to 5 m / s 共985 fpm兲.

Cutting Fluids For cutting fluids, semisynthetic or emulsion type fluids are used because a relatively high mechanical lubricity is needed to prevent the chips from bonding to the tooth faces. A good cooling is also important to keep the teeth cool when they are in the cut, and the viscosity may also be important depending on the application 共see Section 2.3.7兲.

Advice and Hints on Bandsawing • •

•

• •

For a higher cutting rate, increase the blade velocity or use a band with a coarser pitch. A higher feeding pressure also will give a higher cutting rate. To increase the life of the blade, the blade velocity should be reduced or a band with a finer pitch should be used. Be careful that the feeding rate 共feeding pressure兲 is not too high. To improve the finish of the cut, precision bands 共0° rake angle兲 should be used 共preferably with a fine pitch兲. The band velocity may be increased and the feeding rate 共feeding pressure兲 may be reduced. To improve accuracy of the cut, the band velocity may be increased and the feeding rate may be reduced. A bandsaw is a relatively dangerous machine, and all precautions should be taken to avoid accidents when the work piece is guided towards the moving band, see above. For Trouble Shooting, see Section 13.6.2.

52


Fig. 2.22—General purpose contour bandsaw machines, Model 2013-V3 and Model 3613-1. Model 2013-V3 is designed for contour sawing, band filing and band polishing; it cuts metal, wood, plastics and other materials. It has a 660⫻ 660 mm 共26⫻ 26 in兲 table that tilts 45° right, and 10° left and a 330 mm 共13 in兲 work height. The band speed can be varied through a twospeed transmission from 17–97 or 292– 1585 m / min 共55–300 or 960– 5200 fpm兲. The band width capacity is 1.5– 27 mm 共1 / 16– 1 in兲 and the motor capacity is 2.25 hp.23

2.7.5 Wire Cutting When sectioning very sensitive materials with relatively small dimensions, wet abrasive cutting might be too rough; therefore, other methods have been developed. Among these, electro-erosive, chemical, and mechanical principles have been used, but only the mechanical sectioning, based on a wire with embedded diamond grains, has gained ground and is commercially available. Wire cutting uses a metal wire with diamond particles pressed into the metal, in this way anchored so that they can remove material from a work piece when the wire is drawn against the work piece under a certain force. The wire, the length up to 10– 20 m 共30– 60 ft兲, is rolled on two drums moving in two directions, the wire being rolled from one drum to the other. This gives a strong wire 共no welding兲 which can be highly tight-

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ened, securing a good precision of the cut. The force in the cut, creating the feed movement, is achieved using a weight. The wire is 0.2– 0.5 mm 共0.008– 0.02 in兲 thick and moves with up to 2.5 m / s 共493 fpm兲. The process runs without cooling because the removal rate is very low. A fluid is used only for cleaning the wire, keeping the diamonds free from swarf. Work pieces up to 50 mm 共2 in兲 can be cut. The advantages are a very low deformation of the cut surface and a low material loss 共kerf loss兲. The disadvantage is the long cutting time.

3 Mounting MOUNTING IS A PROCESS IN WHICH THE SPECIMEN, IN ONE WAY OR ANother, is encapsulated to facilitate and often improve the following preparation. The mounting normally takes place after sectioning 共for mounting before sectioning, see Section 2.6兲 and several methods are available.

3.1 Purpose and Criteria 3.1.1 Purpose Mounting is needed for a number of reasons: • The specimen is small and is difficult to handle. • The specimen has an awkward shape and mounting is necessary to secure the preparation of the correct surface. • Edge retention and flatness of the specimen is important for a correct examination. • The specimen is brittle or has cracks or pores, and the mounting 共impregnation兲 will stabilize the surface. Also the specimen could be a powder material or in a shape not fit for preparation. • A standard specimen size is required when using semiautomatic or automatic preparation equipment.

3.1.2 Criteria for a Good Mount If mounting is done only for handling a small, awkwardly shaped specimen, and the demands for the quality of the prepared surface are relatively low, a simple mounting, such as clamping, can be used 共see Fig. 3.4兲. In most cases, however, a mounting in plastic is performed 共see Fig. 1.9兲. This is to ensure a certain quality of the mount to avoid problems when cleaning the specimen 共see Fig. 3.1兲. The problem shown in Fig. 3.1 is due to a gap between the specimen and the mounting material, letting fluids 共etchants兲 or abrasives, or both, from the preparation leak onto the prepared surface after drying of the specimen. In case of an etchant, the objective of the microscope might be damaged. The gap develops because the shrinkage of the mounting material is too high or with a clamped specimen, a gap exists between the specimen and the clamp material. This gap also spoils the edge retention of the specimen which is one of the common advantages at mounting. To obtain a good mount the following criteria should be fulfilled: • No gap between specimen and mount material. • Rate of removal 共wear resistance兲 of mounting material should correspond to that of the specimen material. • No air bubbles in the mounting material or along the edge of the specimen. • The mounting material should be resistant to common etchants. • The mounting material should not pick up abrasive grains during the preparation.

3.1.3 Surface Flatness—Edge Retention To obtain a satisfactory examination in a light microscope the specimen surface has to be relatively flat. This is due to the depth of field of the microscope, the distance along 54

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Fig. 3.1—Fluid leaking from a gap between mounting material and specimen onto the prepared surface.

the optical axis over which details of the specimen surface can be observed with adequate sharpness. The depth of field decreases with increasing magnification, at 100, 250, and 500⫻ the distance is 20, 3, and 1 ␮m, respectively. This means that if a specimen should be examined at 250⫻ or higher, special care should be taken to obtain a plane specimen surface. This can be obtained by mounting as described below for edge retention, but another important factor is the use of the correct preparation process 共see Sections 6.6 and 6.7兲. When examining surface layers, a very good edge retention is definitely needed, even for low magnifications. However, also in other cases, a flat specimen surface without edge rounding is wanted. Figure 3.2 shows a specimen with 共a兲 a rounded edge due to a gap between mounting material and specimen. In 共b兲 there is contact between mounting material and specimen, which provides a good edge retention. To support the edge of the specimen, the mounting material must be in contact with the specimen, and ideally, the surface of the mounting material should be in the same level as the specimen 共no relief兲. To obtain this the mounting material should have the lowest possible shrinkage, good adhesion, and a removal rate 共wear resistance兲 corresponding to the specimen material. Plating the edges of the specimen, mostly with electroless nickel, is used also, but with modern preparation methods this relatively laborious process can be avoided. Attention: Although the edge retention to a high degree depends on a good support of the edge, the correct preparation process is even more important, using the right grinding/polishing surfaces 共see Chapters 6 and 7兲.

Shrinkage and Adhesion All mounting materials typically have a higher shrinkage than the specimen material. In case of hot mounting materials, using powder of polymers 共see Section 3.4兲, the shrinkage is due to the thermal expansion of the polymer during heating and the contraction during cooling. This means that hot mounting resins that usually have a higher thermal expansion than the specimen material will have a stronger contraction than the specimen. Therefore, they will “squeeze” the specimen, making a good contact. This means, however, that a gap will develop in a hole or cavity in the specimen.

56


Fig. 3.2—Edge retention: 共a兲 In case of a gap between mounting material and specimen, a rounding of the specimen edge is developed; 共b兲 with contact between specimen and mounting material, edge retention is obtained.

To ensure a good contact, hot compression mounting materials should always be cooled under pressure 共see Section 3.3兲. In cold 共castable兲 mounting resins, the shrinkage takes place during the polymerization of the components 共see Section 3.7兲 and a gap will develop if the shrinkage is high. The shrinkage of cold mounting resins can be reduced by mixing a mineral powder in the resin If the polymerization process is accelerated by heating, then the shrinkage is usually increased. High adhesion between the resin and the specimen material ensures the contact, but only epoxy has a strong adhesion.

Material Removal Rate—Wear Resistance During the preparation process, the specimen material and the mounting material are removed from the surface, expressed in the material removal rate 共see Sections 6.2 and 7.2兲. Ideally the removal rate should be equal for both materials. In most cases, how-

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Fig. 3.3—Relief at mounting: 共a兲 In case of a mounting material that is too soft, a positive relief is developed, and the edge of the specimen is rounded. 共b兲 With a mounting material that is too hard, a negative relief is developed.

ever, the mounting material 共resin兲, being relatively soft, has a much higher removal rate than the specimen. This could be critical because a positive relief is developed 共Fig. 3.3共a兲兲, and the edge of the specimen is not protected. In some cases, if the specimen material has a higher removal rate than the resin, a negative relief develops, with the specimen material being in a lower level than the resin 共Fig. 3.3共b兲兲. The removal rate of the resin, as it pertains to “wear resistance,” depends to a high degree on the hardness of the resin Tests have shown that when grinding on a P240 SiC grinding paper, the removal 共abrasion兲 rate of an acrylic or phenolic mounting material is 10 to 15 times as high as for soft metals like copper and brass. At rough polishing on a cloth with 4 – 6 ␮m diamond, however, the removal 共polishing兲 rate is only 2–3 times higher.7 It seems that not only the hardness of the mounting material plays a role, but also the machinability, meaning that at rough polishing the mounting material to a certain degree will be removed with the same speed as the sample material. Wear resistance can be regulated by adding hard fillers to the resin, and this type of resin should be used if a good edge retention is wanted 共see Sections 3.4 and 3.7兲. See also Sections 3.6.1 and 3.13.1 with indications of the material removal rate for the single mounting material. If the wear resistance of a resin is very high, as known from hot mounting epoxy with filler, it will influence the preparation process and probably a negative relief will develop, as mentioned above. The resin will behave like a hard material and if SiC grinding papers are used, these will wear out the same way as by hard materials. This also means that if a standard preparation time for a given specimen, mounted in normal phenolic resin, is 2 to 3 min, it might be doubled if the specimen is mounted in the epoxy resin with filler.

3.2 Mounting Methods 3.2.1 Clamping By clamping, the specimen is fixed mechanically without using a mounting material. For automatic preparation, the specimens can be clamped in a holder 共see Fig. 3.4共a兲 and Fig. 3.5共a兲 for flat specimens and Fig. 3.5共b兲 for circular specimens兲. In Fig. 3.4共b兲 a clamp, normally used for hand preparation, is shown. It has two flat pieces of soft steel or stainless steel which are kept together with two screws and the

58


Fig. 3.4—Clamping of specimens. 共a兲 Specimen holder for clamping of flat specimens for automatic preparation; 共b兲 six pieces of sheet metal clamped between two flat pieces of steel for manual preparation.

specimen 共often pieces of sheet metal兲 placed between the two pieces that should have rounded outer edges to avoid excessive wear of the polishing cloth. If possible, the clamp material and the specimen material should be compatible. Common for all clamping: it is difficult to avoid rounding, and often, when clamping several sheets, gaps will retain abrasives or fluids, creating problems during the examination.

3.2.2 Hot Compression Mounting Hot compression mounting or hot mounting indicates that the specimen is placed with an amount of resin in a cylinder in a mounting press and heated under pressure for a specified period of time. The resin polymerizes around the specimen, and after cooling, a mount can be ejected from the press 共see Section 3.3兲.

3.2.3 Cold „Castable… Mounting Cold mounting typically takes place at room temperature but often the temperature during the curing will reach 30– 130° C 共82– 265° F兲共peak temperature兲. During cold mounting, the specimen is normally placed in a mold 共mounting cup兲 and a mixture of a resin and a hardener is poured into the mold. After 5 min to 20 h the plastic will cure, and a mount can be taken from the mold 共see Section 3.7兲.

3.3 Hot Compression Mounting Hot compression mounting is based on the fact that certain plastics, such as powder, in the following called resins, can be formed to a given shape, usually cylindrical, when heated and cooled under pressure in a metallographic/materialographic mounting press.

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Fig. 3.5—Clamping in specimen holders without mounting: 共a兲 specimens of a flat shape; 共b兲 specimens of cylindrical shape.

3.3.1 Advantages of Hot Compression Mounting • • • •

The quality and wear resistance 共hardness兲 is generally superior to cold mounting. Fast method for making one single mount. A choice of diameters from 25 mm 共1 in兲 – 50 mm 共2 in兲. The diameter of the mount is very exact.

3.3.2 Disadvantages of Hot Compression Mounting • • • •

High initial cost for mounting press. Fragile and brittle specimens can be damaged by the pressure in the cylinder that is from 20– 30 MPa 共2.900– 4.350 psi兲. Heat sensitive materials can be damaged. The temperature is normally 120– 200° C 共250– 400° F兲 in the mounting cylinder. If mounting large series of specimens, hot mounting is slow because usually only a limited number of mounting presses will be available.

3.3.3 MSDS „Material Safety Data Sheets… Hot mounting resins are generally not hazardous, but the MSDS should always be obtained from the supplier and studied before use. Vapors from the heated material might be irritating; especially vapors from phenolics that might contain formaldehyde should be avoided. Prolonged skin contact with phenolic and epoxy materials may irritate the skin and cause a skin rash 共dermatitis兲, and, of course, all skin contact to very hot mounts should be avoided.

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Fig. 3.6—Schematic drawing of thermoplastic polymer, not cross-linked.

3.4 Hot Mounting Resins The resins for metallographic/materialographic mounting are used as powders and can be classified into two groups: thermoplastic and thermosetting. A thermoplastic resin is a polymeric material that can be formed on application of heat and pressure and is solidified by cooling. A thermosetting resin is a polymeric material that can be formed and cured by the application of heat and pressure but cannot be reformed on further heat and pressure. For selection of the correct hot mounting resin for a given purpose, see Section 3.6.1.

3.4.1 Thermoplastic Resins Thermoplastic materials undergo no permanent change on heating. They flow and may be molded into a shape which they retain on cooling. The material will flow again when reheated and can be remolded. Thermoplastic polymers contain linear molecules that are not cross linked; these are shown schematically in Fig. 3.6.

Acrylics A number of well-known plastics are thermoplastics. For metallography/materialography, acrylics 共polymethylmethacrylate 共PMMA兲兲 are used. Acrylics are known as sheets used instead of glass for many purposes. This transparency often is an advantage for mounting. Acrylics have to be heated to 150– 180° C 共300– 360° F兲 to flow 共melt兲 and cooled to obtain its shape. The pressure is in the range of 30 MPa 共4350 psi兲 like most other hot mounting resins. The pressure can be omitted or kept very low during a preheating period, and this can be of advantage when mounting porous specimens when the resin penetrates into the pores. Cooling under pressure should be performed down to 40° C 共104° F兲, preferably room temperature, before the mount is removed from the press. The total time for heating and cooling is 14– 24 min depending upon the diameter of the mount. Acrylics are resistant to water, alcohol 共when properly cured兲, solutions of most salts, diluted alkalies, hydrochloric acid, and sulfuric acid, but soluble in nitric and acetic acids, some ketones, and esters. Acrylics are notch-sensitive and cracks may develop if stress is too high 共see Section 13.6.3兲. The shrinkage is relatively high, hardness is medium, compared to other mounting resins, and wear resistance is low 共see Section 3.1.3兲.

Acrylics with Fillers Acrylics can be made electrically conductive by adding a metal powder, usually Fe or Cu, and the mount loses its transparency. This is done to create a conductive mount for electrolytic polishing. This type of conductive mounting material cannot be recommended for use with SEM because the metal powder 共Fe or Cu兲 can contaminate the

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Fig. 3.7—Schematic drawing of thermosetting polymer with a high degree of cross-linking.

specimen surface leading to false results. For SEM, a resin with graphite should be used 共see Section 3.4.2兲.

3.4.2 Thermosetting Resins Thermosetting resins for hot mounting are capable of a high degree of cross-linking shown schematically in Fig. 3.7. They are generally molded in a practically polymerized state so that they can flow by the application of heat and pressure. During the molding process further polymerization occurs, and the plastic becomes highly crosslinked and can no longer flow or be changed on further application of heat and pressure. The following three types of thermosetting resins are available for hot mounting: phenolics 共bakelite兲, diallyl phthalate, and epoxy.

Phenolics The phenolic resin is made from phenol and formaldehyde and a filler. Formaldehyde, being a critical solvent, should only be present in very low amounts 共below 1 %兲 in the finished resin The filler is important to obtain the right properties of the mount. Generally wood flour is used as a filler giving brown mounts. Added colors provide phenolic resins with a number of colors. The temperature for a correct polymerization is 150– 180° C 共300– 360° F兲, and although the thermosetting resin need not be cooled for curing, the mount should be cooled under pressure to approximately 60° C 共140° F兲 to reduce shrinkage. The pressure in the cylinder should be approximately 30 MPa 共4350 psi兲 and the total time for heating and cooling is in the range of 8 – 13 min. Phenolics have a number of drawbacks, but being the most inexpensive of the mounting resins, they are used for routine examinations. Phenolics are resistant to weak acids, organic solvents, hydrocarbons, detergents, and cleaning fluids, but attacked by strong alkalis, oxidizing acids, and hot 共boiling兲 etchants. Phenolics have good mechanical properties. The shrinkage is relatively high, the hardness is low, and the wear resistance is low 共see Section 3.1.3兲.

Phenolics with Conductive Filler Graphite can be added as a filler, making the resin electrically conductive. This resin is used for mounts to be examined in an SEM.

Phenolics in Tablet Form Tablets or premounts are made by pressing phenolic powder to form a “mount,” with dimensions slightly smaller than the diameter wanted. It is used for mounting of solid specimens, which are not influenced by the pressure, when the tablet is pressed on the specimen. The advantage is that working with a powder resin is avoided.

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Diallyl Phthalate The diallyl phthalate 共DAP兲 resin is a polyester with a filler. The filler strongly influences the strength of the resin, and for materialographic mounting, mineral and glass fiber 共short兲 are used with glass fiber-filled resin, the most all-round material. The temperature for a correct polymerization is 150– 180° C 共300– 360° F兲 and the pressure in the cylinder 25– 30 MPa 共3650– 4350 psi兲. The total time for heating and cooling is 8 – 13 min. Compared to phenolics, DAP has a number of advantages but it is more expensive than phenolics. DAP is resistant to most chemicals and the mechanical properties are excellent. The shrinkage is much lower than in phenolics, and the filler causes a relatively high hardness and a high wear resistance, securing a good edge retention 共see Section 3.1.3兲.

Epoxy Epoxy resin for hot mounting is made as a powder with a filler. Epoxy has a number of properties very suitable for mounting. The filler is a mineral like calcium carbonate ground to a very fine powder which to a high degree reduces the removal rate and consequently improves the wear resistance of the resin 共see Section 3.1.3兲. The temperature for a correct polymerization is 150– 180° C 共300– 360° F兲, and the pressure in the cylinder is approximately 10 MPa 共1450 psi兲, considerably less than for other resins. The total time for heating and cooling is 9 – 15 min. The resistance to all chemicals, even to hot etchants, is very high. The mechanical properties are excellent and the strong adhesion to the specimen and an extremely low shrinkage make epoxy resin the best resin for retention of edges. The strong adhesion can cause problems with adhesion to rams and cylinder walls in the mounting cylinder. These parts need to be treated with a release agent 共see Section 3.6兲.

3.5 Mounting Presses Heating, pressure, and cooling are needed when making a mount from a hot mounting resin The temperature should be in the range of 100– 200° C 共210– 400° F兲 and cooling should take place from the maximum temperature to approximately 60° C 共140° F兲 in a reasonable time. Cooling is necessary for thermoplastics, but even thermosetting resins should be cooled to around 60° C 共140° F兲 under pressure to secure the lowest possible shrinkage. The force between the lower and upper ram during the process should be in the range of 1 – 50 kN 共225– 11.235 lbf兲 making it possible to establish a pressure of 10– 30 MPa 共1450– 4350 psi兲 in the mounting cylinder at diameters from 25– 50 mm 共1 – 2 in兲.

3.5.1 The Heating/Cooling Unit The heart of the press is the heating/cooling unit consisting of mounting cylinder 共mold兲, lower ram, upper ram, top closure, heating coil, controlled by a thermostat, and cooling coil 共water cooling兲共see a schematic drawing in Fig. 3.8兲. The cylinder can be typically supplied in diameters of 25 mm 共1 in兲, 30 mm 共1.18 in兲, 31.75 mm 共1.25 in兲, 38.1 mm 共1.5 in兲, 40 mm 共1.57 in兲, and 50 mm 共1.97 in兲. The lower ram is moved up and down in the mounting cylinder by hydraulics 共or by air兲. Before the sample is placed in the cylinder, the lower ram is normally placed in

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Fig. 3.8—Schematic drawing of heating/cooling unit. The heating and cooling coils can be seen around the mounting cylinder with upper and lower ram.

the top to secure the right position of the sample. After moving down the lower ram, an amount of resin is put into the cylinder. This amount should cover the sample so that the upper ram should not be damaged when the resin is put under pressure, and therefore has a volume reduction. The upper ram with top closure is placed and secured, and the lower ram is moved upwards, building up pressure. Heating is switched on for a few minutes, followed by cooling, usually water cooling as shown in Fig. 3.8, but also air cooling with cooling blocks is used. After about 9 – 24 min, depending on the resin and the diameter, the mount can be pushed out of the top after removing the upper ram. Considering that both pressure and heating should be continuously adjusted during the process, an automatization is a great advantage for the operator 共see below兲. The heating/cooling unit is typically exchangeable so that one press can be used for a number of different mount diameters, or the cylinder can be exchanged in the heating/cooling unit. If the cylinder has enough space, two mounts can be made at the same time, using an intermediate ram 共piston兲 separating the two mounts. On modern units, the heating and water-cooling coils are totally integrated with the mounting cylinder, Fig. 3.8. This secures the best heat transfer, saving energy, water, and time.

3.5.2 The Hydraulic Press Hydraulic presses are the most frequently used way of obtaining the relatively high pressure needed. The first presses were car jacks operating inside a frame, the jack putting a pressure on the lower ram and the frame holding the cylinder and upper ram in place. Heating was done with a jacket containing a heating element with a thermostat placed around the cylinder and exchanged with a cooling block 共air cooling兲 or a jacket with water. From this simple setup, the hand-operated presses were developed, the pressure established through a hand pump, and the heating/cooling unit as part of the press 共see

64


Fig. 3.9—Hand-operated mounting press for mold sizes from 25– 38 mm 共1 – 1.5 in兲. The standard model is with air cooling, and water cooling is optional.19

Fig. 3.9 which shows a hand-operated mounting press for mold sizes from 25– 38 mm 共1 – 1.5 in兲兲. Heating is switched on and off manually and the temperature is controlled by a built-in thermostat. Water cooling is controlled by a water tap, and the operator has to be careful that the pressure in the mounting cylinder is maintained during the process. To avoid the requirement for an operator to be present during the whole process, automatic presses are available. The simplest automatic press uses a motorized hydraulic pump which automatically keeps the pressure controlled by an adjustable pressostat. The operator switches the heating and cooling on and off. With more advanced presses, all parameters, pressure, temperature, cooling 共cooling rate兲, and time, are microprocessor-controlled. In some cases, a number of methods for different mounting materials and mount sizes can be programmed and stored. Figure 3.10 shows an electrohydraulic, automatic, programmable press with two heating/cooling units with mold diameters from 25– 50 mm 共1 – 2 in兲.

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Fig. 3.10—Electrohydraulic, automatic, programmable press with two heating/cooling units with mold diameters from 25– 50 mm 共1 – 2 in兲.20

3.5.3 The Air-operated Press Compressed air has been used for establishing the pressure during hot mounting. An air-operated press could be made at a lower cost than a hydraulic press. The drawback is the compressibility of the air which makes the ejection of the finished mount difficult to control. The air presses seem to have vanished from the market.

3.6 Advice and Hints on Hot Compression Mounting •

• • • • •

• •

•

• • • •

Check that the specimen to be mounted is not too brittle, has brittle layers 共spray coatings might change the porosity under pressure兲, or is not suited for compression mounting or in other ways. If in doubt, use cold mounting. Check that the specimen material can be treated at minimum 150° C 共300° F兲. Take care that the specimen is clean and dry, without grease or other residues. Keep the mounting cylinder and rams 共upper/lower兲 clean. Mold release agent: Treat the upper and lower ram with a thin layer of agent. This is especially important for resins, like epoxy, sticking to metal surfaces. Process time depends upon the amount of resin; therefore, keep the amount low. On the other hand, the distance from the specimen to the cylinder wall should be not less than 3 mm 共0.12 in兲, and the resin should effectively cover the top of the specimen so that the upper ram will not touch the specimen. Save expensive resin: Only use the expensive resin in a thin layer around the specimen and fill up with a less expensive “back-up” resin Pressure: At phenolics and other thermosetting resins, apply the pressure at the same time as the heating. At acrylics and other thermoplastic resins, the pressure may be applied after a preheating period 共see below兲. Never use excessive pressure. Phenolic mounts: Cool the mount under pressure down to approximately 60° C 共140° F兲. Do not take out a very hot mount and cool it directly in water; the mounting material might crack or a gap along the specimen will develop, or both. Specimens with layers requiring a superior edge retention: Use an epoxy resin Porous specimens: Use a thermoplastic resin 共acrylics兲; if possible preheat the resin or use cold mounting. Small specimens: These can be supported during the process by using a clip 共see below兲. Electrolytic polishing: Use a conductive resin but apply a thin layer of nonconduc-

66


tive resin around the specimen to avoid an electrolytic reaction in the resin For Trouble Shooting see Sections 13.5/6.

3.6.1 Selection of Resins for Hot Compression Mounting

Purpose Glass clear mounts Porous specimens 共low pressure兲 Nonconductive surface for electropolishing

Routine examination Back-up resin Color marking Serial mounting of uncomplicated shapes Resin in tablet form

Good edge retention 共Thermal spray coatings兲 High planeness Chemical resistance

Temp., °C 共°F兲 Force KN 共lbf兲

Heat./ Cool. Time 共min兲

Price Range

Specific Property

Mounting Resin

Thermoplastic Transparent Low initial pressure, slow cure Medium shrinkage Low hardness High removal rate at grinding, medium at polishing Low chemical resistance Tendency to defects Thermosetting Fast cycle Medium shrinkage Medium hardness High removal rate at grinding, medium at polishing Medium chemical resistance

Acrylics, transparent without fillers

150–180 共300–360兲 15–50 共3375– 11250兲

Medium 6 / 8 at 25 mm 共1 in兲 to 12/ 12 at 50 mm 共2 in兲

Phenolics 共Bakelite兲 as powder with wood flour filler, with or without color Phenolics 共Bakelite兲 in tablet form Diallyl phthatalate with glass fiber or mineral filler

150–180 共300–360兲 15–50 共3375– 11 250兲

6 / 3 at 25 mm 共1 in兲 to 11/ 4 at 50 mm 共2 in兲

150–180 共300–360兲 15–50 共3375– 11 250兲

5 / 3 at High 25 mm 共1 in兲 to 9 / 4 at 50 mm 共2 in兲

Thermosetting Low shrinkage High hardness Low removal rate Medium/high chemical resistance

Low

Low

Chapter 3

Purpose Very good edge retention 共Thermal spray coatings, plated layers兲 Very high planeness

Electroytic polishing, to be used with a nonconductive resin as surface against electrolyte Examination in SEM

Specific Property

Mounting Resin

Epoxy with Thermosetting mineral Very low filler shrinkage Good adhesion High hardness Very low removal rate Medium/high chemical resistance Thermoplastics or Acrylics or phenolics thermosetting with metal Electrically or carbon conductive filler Low shrinkage Phenolics with carbon filler

Temp., °C 共°F兲 Force KN 共lbf兲

Mounting

Heat./ Cool. Time 共min兲

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Price Range

150–180 共300–360兲 5–50 共1125– 11 250兲


Medium

150–180 共300–360兲 15–50 共3375– 11 250兲


High

High

3.7 Cold „Castable… Mounting Cold mounting, or castable mounting, is used parallel to hot compression mounting. Normally cold mounting is not “cold” 共room temperature兲; often temperatures will reach 30– 150° C 共82– 265° F兲. In most cases with cold mounting, two components, either two liquids or a powder and liquid, are mixed. The components, resin and hardener, are measured either by weight or by volume with a relatively high precision. In the case of very small quantities, measurement by weight is recommended. The mixing of the components should be very careful to secure a total distribution of the hardener. The time after mixing until the curing starts, the pot life varies for the different resins, but as a rule the mixed resin should be used immediately, securing the lowest possible viscosity of the mixture. The mixture is preferably done in disposable paper cups which can be discarded after use. Normally the clean, grease-free specimen is placed in a mounting mold 共see below兲, and the mixture is poured carefully into the mold, avoiding entrapment of air, when the mold is filled. The low viscosity ensures that the resin flows into all irregularities of the specimen and air bubbles, if any, will be able to move to the top of the mount. To improve the penetration of the resin into the specimen, vacuum impregnation can be used 共see Section 3.10兲. A pressure chamber that creates a pressure with a small compressor, 0.2– 0.28 MPa 共30 to 40 psi兲, will help to avoid bubbles and improve the infiltration of the resin into the specimen. During the curing, the temperature increases to the peak temperature, depending on the type of resin Up to 130° C 共265° F兲 is measured. The temperature can be kept

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down if good heat conduction is established. The different resins have different peak temperatures 共see Section 3.13.1兲.

3.7.1 Advantages of Cold „Castable… Mounting • • • •

Low initial cost. Brittle and fragile specimens are not damaged. Specimens with cracks and pores, or both, can be impregnated. Large series can be made simultaneously, using inexpensive mounting molds.

3.7.2 Disadvantages of Cold „Castable… Mounting • • • • •

Some of the resins have a relatively high shrinkage. Some of the resins are relatively soft with a low wear resistance 共high removal rate兲. The shape 共diameter兲 is not very exact. Risk of bubbles and cracks around the specimen. Hazardous vapors and risk if skin is in contact with chemicals.

3.7.3 MSDS „Material Safety Data Sheets… Some cold mounting resins can be hazardous and special care should be taken during use. MSDS should be obtained from the supplier and studied carefully. Special precautions to be taken for the different resins are mentioned below.

3.8 Cold Mounting Resins Similar to hot mounting resins, cold mounting materials can be both thermoplastic and thermosetting 共see Section 3.4兲.

3.8.1 Acrylics Acrylics are thermoplastic and are supplied as a resin, a powder 共polyamized methyl methacrylate 共MMA兲兲 with an initiator, and a fluid, the hardener 共MMA monomer兲, with a promoter. The size of the single particles 共beads兲 of the resin has a specific importance. They vary from 5 – 50 ␮m. Figure 3.11 shows the beads and the grains of a filler. With small beads, the flow of the mixed resin is more viscous, and better able to penetrate into microcracks and pores. The peak temperature is 90– 110° C 共194– 240° F兲 and curing time 5 – 15 min 共see also Section 3.13.1兲. The acrylics 共without filler兲 are translucent and will cure in down to 5 – 10 min which makes it the fastest curing resin If the system is expanded with a filler, the shrinkage can be reduced considerably 共see below兲. Acrylics being thermoplastic have a tendency to melt during grinding, clogging up the cut-off wheel and grinding paper if not efficiently cooled. Acrylic cold mounting materials are not as chemical resistant as the hot mounting materials 共see Section 3.4.1兲. The shrinkage is relatively high and this material should not be used if a very good edge retention is wanted. The wear resistance is relatively low but both this and the shrinkage can be modified with fillers 共see below兲. Attention: Fumes from methyl methacrylates are considered hazardous and skin contact should be avoided so work should be done with gloves and under a fume hood.

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Fig. 3.11—Acrylic-mounting material with filler. The small gray particles between the beads of the polymer are the filler.

Acrylics with Fillers With hot mounting materials, the fillers usually are established during the manufacturing process, the filler being integrated into the polymer. With acrylics used for cold mounting, fillers like fine ground calcium carbonate are mixed into the powder and the grains of the filler will be integrated in the finished mount 共as shown in Fig. 3.11兲. Acrylics with fillers are opaque. Combinations of acrylics 共MMA兲 with styrene 共see below兲 have been developed having two liquid components and a powder component consisting mainly of filler material. This resin has a very low shrinkage and good edge retention. Attention: Grains from the filler can be released from the surface during preparation and cause scratches in the finished specimen.

3.8.2 Polyesters Polyester is a thermosetting resin that is supplied as two liquids: an unsaturated polyester resin and styrene acting as an accelerator with peroxide as the initiator. A polyester mount is transparent. The amount of accelerator is very small compared to the amount of resin, making the measurement of the two components relatively difficult, when small amounts should be used. The peak temperature is 50– 110° C 共122– 240° F兲 and curing time is from 45 min to 6 – 8 h 共see also Section 3.13.1兲. The shrinkage is high, and polyester should only be used for mounting of specimens with no need for edge retention. The price is relatively low, however, and the resin is often used for routine mounts. Attention: Styrene is considered a dangerous material and all work with measurement and mixing should take place under a fume hood using gloves. Polyester has a limited shelf life 共6 to 12 months兲; therefore, the container should be marked with the date of receipt to secure that the oldest material is used first.

3.8.3 Epoxies Epoxy is a thermosetting resin supplied as two liquids, a “resin” and a hardener. Epoxy is the cold mounting resin with the lowest shrinkage and the best grinding and polish-

70


ing properties. Epoxy adheres strongly to the specimen, and if the curing time is reasonably long, more than 6 – 8 h, the shrinkage is extremely low. If curing time is shortened, either by adding accelerator to the hardener 共30– 45 min兲 or by introduction of heat 共2 – 4 h兲, the shrinkage will be higher. By introduction of heat, the negative effect can be reduced by letting the epoxy cure in 1 h after mixing at room temperature and then complete the curing at 60– 70° C 共140– 158° F兲. Epoxies are supplied with a very low viscosity and a high boiling point, securing an efficient impregnation of porous specimens 共see below兲. Epoxies are transparent and cure through an exothermic reaction. The peak temperature varies with the curing time. Curing for periods from 6 to 20 h gives a peak temperature 40– 60° C 共104– 140° F兲, while curing for 45 min results in peak temperatures from 85– 100° C 共185– 220° F兲. The peak temperature can be kept low by placing the mold in a fridge. To avoid very high temperatures at mounts larger than the normal size, cooling with air using a fan is recommended. Epoxies for cold mounting are normally not supplied with fillers for metallographic/materialographic purposes, but fillers can be mixed in by the user 共see Section 3.11.2兲. The two parts, resin and hardener, should be measured in a precise manner because even a small variation can cause problems after curing 共see Section 3.13兲. The good adhesion properties of epoxy can result in problems with removal of the finished mount from the mounting mold. The mold should be made of a plastic material with low adhesion and certain flexibility, like POM 共see Section 3.9兲. Epoxies are not attacked by weak acids, weak alcohols, and organic solvents. Strong acids and strong alcohols give a slight attack. Resistance to heat: 90– 250° C 共200– 500° F兲. Epoxy has good mechanical properties and it is the strongest, most durable of the cold mounting resins. The shrinkage, as mentioned previously, is very low if the curing process is not shortened down. The hardness is relatively high and the wear resistance is relatively high 共see Section 3.1.3兲. Attention: Epoxies can cause allergies and all work should be done with correct gloves under a fume hood.

3.9 Accessories for Cold „Castable… Mounting In most cases it is important to have a relatively exact shape of the finished mount and therefore a mounting mold 共cup兲 is normally used. Clips are other accessories that support the specimen during the curing.

3.9.1 Mounting Molds In most cases these are cylindrical molds, made of a flexible plastic like POM or of silicone rubber 共see Fig. 3.12兲. The specimen is placed on the bottom of the mold and the liquid mounting resin is poured into the mold. Some molds have a removable bottom to allow the mount to be pushed out after curing. Molds made of silicone rubber are normally in one piece, the high flexibility of the silicone rubber allowing the mount to be removed from the mold. To secure the removal of the mount, the mold can be smeared with a silicone compound before the resin 共epoxy兲 is introduced. Reusable molds of a square or rectangular shape are also available. Disposable ring forms often made of phenolics remain as an integrated part of the mount after curing. The ring is placed on an adhesive film so that the resin will not leak

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Fig. 3.12—Mounting molds consisting of two parts, a bottom and a cylinder. The specimens are supported by clips.

during the curing. The specimen is placed inside the ring and, after curing, the ring with resin and specimen is taken for preparation. Another type of disposable mounting mold is an aluminum cup used for packaging of foods, etc. This is especially useful for large specimens of odd shapes.

3.9.2 Clips If specimens are small and flat, it helps to support the specimen during the curing. Plastic and metal clips that squeeze the specimen are available, being an integrated part of the mount 共see Fig. 3.12兲. The clips can be used for both hot and cold mounting.

3.10 Vacuum Impregnation Specimens like sintered materials and ceramics having pores, cracks, etc., are difficult to prepare without an impregnation 共infiltration兲 of the surface. If not impregnated the pores will increase in size and cause pullouts, resulting in a microstructure that is not showing the correct conditions of the material. Also, electronic parts or other parts of a complicated structure that should be kept in place during the preparation may be encapsulated using vacuum impregnation. Impregnation in depth can only take place in a material with open pores. In the case of closed pores, only the pores on the surface will be infiltrated. Normally the impregnation takes place after cutting, but to certain, very brittle materials, impregnation should be done before cutting. In the case of closed or very narrow pores, the impregnation should take place both after cutting and after plain grinding or even fine grinding. Impregnation is done in vacuum 共80– 120 mbar兲 using an epoxy resin with a low viscosity and a boiling point high enough to avoid boiling in the vacuum chamber. The impregnation takes place in a vacuum chamber which can be a normal labora-

72


Fig. 3.13—Apparatus for impregnation; the mounting molds are placed in a vacuum chamber and the epoxy is sucked into the chamber through a tube.

tory bell jar or an apparatus made for the purpose 共see Fig. 3.13兲. The specimen, carefully cleaned and degreased, is placed in a mold in the vacuum chamber and a vacuum is established for an appropriate time from a couple of minutes for not very porous specimens up to half an hour for very porous specimens. The impregnation is done by sucking the mixed epoxy into the mold through a tube until the specimen is covered. 共For best results, only a small amount of resin is taken into the mold, just covering the area of interest and then slowly returning the chamber to atmospheric pressure. The back pressure will further the penetration of the resin into the specimen. Repeat the evacuation of the chamber and let in epoxy to completely cover the specimen.兲 Now the mold can be removed for curing, or curing can take place in the vacuum chamber without vacuum. A simpler method, which can be used for materials with less pores, is to place the specimen in a mold with epoxy and immediately after pouring in the epoxy, the mold is placed in the vacuum chamber and vacuum is established. To obtain the best result, the first method should be preferred. Cold mounting can also be done under a low pressure 共see Section 3.7兲.

3.10.1 Dyes Dyes can be used in connection with vacuum impregnation of porous materials, the dye being mixed into a low viscous cold mounting epoxy resin By using a dye it is possible to contrast the voids into which the resin has penetrated against the surrounding structure. The contrast is created through fluorescence. Figure 3.14共a兲 shows a microstructure in bright field where the pores cannot be identified. In Fig. 3.14共b兲, the same structure in fluorescent light is shown and the pores filled with epoxy can be clearly identified. To obtain the fluorescence, a so-called short-pass filter in the microscope is needed to excite the areas with dye, and a long pass filter is needed to see the fluorescent light 共see Section 15.7.5兲. Dyes are commercially available.

3.11 Special Mounting Techniques For some materials special mounting techniques are necessary, i.e., examination of very thin layers, powders, wires, etc.

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Fig. 3.14—Use of impregnation with epoxy and dye. 共a兲 Microstructure in bright field; 共b兲 and the same structure in fluorescent light revealing the pores filled with epoxy.

3.11.1 Taper Sectioning This technique allows the examination of very thin layers and was highly developed by L. E. Samuels in his work with surface deformation at metallographic/materialographic preparation 共see Section 6.3兲.7 TABLE 3.1—Taper Sectioning: Enlargement Factor, f, with the Corresponding Taper Angle, ␣. f 100:1 50:1 25:1 20:1 15:1

␣ 0° 30⬘ 1° 20⬘ 2° 20⬘ 2° 50⬘ 3° 50⬘

f 10:1 5:1 3:1 2:1 1.5:1 1:1

␣ 5°40⬘ 11°30⬘ 19°30⬘ 30° 41°50⬘ 90°

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Fig. 3.15—Taper section with taper angle, ␣. The thin layer with thickness A can be analyzed and measured, B.

The specimen is placed under an angle to the plane of examination, in this way enlarging the width of the layer, when examined in an optical microscope 共see Fig. 3.15兲. If measured as a normal cross section in an optical microscope, the lower limit of a layer thickness is approximately 2 ␮m because below this the measurement uncertainty is too big, the limit of the optical microscope being 0.5 ␮m. Very thin layers can be examined or measured using taper sectioning because, depending on the taper angle, an enlargement of 1.5⫻ to 100⫻ can be obtained. Table 3.1 shows the enlargement factor, f, and the corresponding taper angle, ␣. If only the layer or the diffusion zone, or both, should be analyzed without measurement of layer thickness, a suitable angle can be established with a spacer, the angle not being exact. In case of measurement of the layer thickness, the taper angle should be known and exact, or the dimension of the specimen should be known. The angle can be established with a wedge. If the angle is known, the layer thickness A = B sin ␣, as shown in Fig. 3.15. If the dimensions X and Y are known, A = X B / Y, as shown in Fig. 3.16.

3.11.2 Edge Protection When examining layers, it is absolutely necessary to have a good edge retention. The edge retention depends very much on the type of preparation performed; it can to a very high degree be obtained by using the modern grinding and polishing methods and automatic polishing 共see Section 6.7兲. In some cases, especially if preparation has to take place with SiC grinding paper, some precautions can be taken to preserve the edge. Section 3.1.3 describes the use of the correct mounting resin to protect the edge and often this will be sufficient.

Fig. 3.16—Taper section with known dimensions X and Y.

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If further edge protection is needed there a number of methods available.

Plating During plating a thin layer of metal is deposited on the surface to be analyzed. The idea is that the edge rounding takes place on the plated layer, leaving the original layer plane. Plating can be done electrolytically, placing the specimen as cathode in a bath containing a Cu, Ni, or Fe salt. Electrolytic plating is laborious and the result is not often satisfactory for metallographic/materialographic examination. Electroless plating gives better results and is easier to perform. Electroless nickel is the most commonly used metal for metallographic/materialographic specimens. Most metals can be plated. Only bismuth, cadmium, tin, lead, and zinc cannot be plated.9 Other materials such as plastics, wood, glass, carbide, silicon, and porcelain can be plated. An example of a formula for electroless nickel: 45 g nickel chloride 11 g sodium hypophosphite 100 g sodium citrate 50 g ammonia chloride 1000 mL distilled water pH 8.5–9 Use the mixture at 90– 100° C 共194– 212° F兲. The plating rate will be in the range of 0.015 mm/ h. Instead of mixing the solutions yourself, different solutions for electroless plating are commercially available.

Fillers Many mounting resins are supplied with integrated fillers, in this way improving the edge protection 共see Sections 3.4 and 3.8兲. Fillers can be mounted together with the specimen, placed in the surface of the mount close to the edge to be protected, and preferably adjusted to correspond to the hardness of the specimen. The preferred filler is alumina used together with epoxy cold mounting resin to avoid shrinkage and increase hardness. The alumina should be made preferably as hollow nodules to secure the stability of the alumina grain in the resin If grains fall out during the final steps of the preparation this might create scratches in the specimen surface. Fillers are commercially available.

Back-up Materials A relatively simple way of securing the edge is to mount a piece of material similar to the specimen material close to the edge of the specimen. A metal foil can be wrapped around a cylindrical specimen, which, in the case of hot mounting, is pressed close to the specimen because of the high pressure in the mounting cylinder.

3.11.3 Mounting of Very Small Parts, Foils, and Wires Very small parts and foils can be difficult to place correctly for mounting. A solution would be to mount several at a time placed in a piece of tube.

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It can be advantageous to use a fast curing glue 共cyano acrylate兲 to fix the parts to the bottom of a mounting mold before the resin is poured into the mold. Clips for stabilizing the parts are commercially available 共see Section 3.9兲. Wires can be examined as cross sections or longitudinal sections. Longitudinal sections can be done, as mentioned above, but cross sections, especially at thin wires, can be difficult. If hot mounting is possible, Nelson24 recommends drilling holes in a mount made of thermoplastic resin without a specimen. The wires are put into the holes, the holes are filled with resin and some resin is placed over the top of the mount to avoid damage of the upper ram. Then the mount is reprocessed. Transparent mounts are to be preferred when working with small parts and wires, making it possible to observe the position of the specimen.

3.11.4 Mounting of Powders The most common method for mounting of powder is mixing the powder with epoxy resin The problem can be the settling of the particles because they either settle around the periphery of the mounting cup or, if the powder has a lower gravity, the setting is not efficient, the powder being suspended in the liquid epoxy. Metal powder will settle, but often irregularly, and Glancy25 suggests a method of filling a small plastic vial or plastic tube with powder. The vial is placed in a vacuum impregnation apparatus 共see Section 3.10兲 under vacuum and epoxy is added, the same as at a normal impregnation. Once the epoxy has cured, the plastic vial is cut lengthwise using a razor knife. Now the slug is mounted by hot or cold mounting. Care should be taken at cold mounting that the slug does not float. For powder with particles sizes under 2 ␮m, Petzow2 suggests the following: The powder is placed in a test tube in a low vacuum 共like at impregnation, see Section 3.10兲. It is then impregnated with a mixture of methacrylic acid methyl ester and 1 % 共wt %兲 of benzole peroxide. This mixture cures in 12 h at 50° C 共122° F兲 with the test tube closed. The test tube is then broken and the content is mounted as usual.

3.11.5 Mounting of PCB Coupons A test coupon, normally around 10 by 20 mm 共0.4 by 0.75 in兲 with two reference holes of 2 mm 共0.079 in兲 is needed if a PCB board should be inspected metallographically/ materialographically with an automatic system. In some cases the coupon is produced together with the board and it can be removed from the board and taken directly for mounting. Very often, the coupon has to be made from the finished board, in this way destroying the board. For hand preparation, the reference holes are not needed.

Test Coupon According to the American standard IPC-TM-650, the plated-through holes 共inspection holes兲 of a PCB board should be inspected metallographically. For this purpose a test coupon is produced and prepared so that the exact center of the plated holes can be inspected in a microscope. To obtain the exact position of the coupon during automatic preparation, two positioning 共reference兲 holes must be made in an exact distance from the inspection holes 共see Fig. 3.17兲. Often the coupon is produced through punching the board, risking deformations in the areas of the coupon later to be examined. If a router is used, this deformation is avoided and the two reference holes are made in the same operation.

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Fig. 3.17—PCB test coupon. It can be seen that the distance from the upper edge of the precision pins, placed in the positioning holes, to the center of the plated 共inspection兲 holes is 5 mm.

Mounting for Automatic Preparation A preparation system, made according to IPC-TM-650, Method 2.1.1.2, is typically used. As mentioned earlier, this means that two reference holes are drilled in the coupon. Two or more coupons are placed on two precision pins so that the pins are in a given distance from the holes to be measured. Now the coupons with pins are mounted, allowing the ends of the pins to be used as contact surface in a special specimen holder. Generally acrylics are used for mounting of PCB coupons but polyester and epoxy can be used also. It is important that the mounting resin is able to flow into the holes to be measured. When using acrylics, the coupon can be dipped in the monomere component ensuring a good penetration into the very small inspection holes, often down to 50 ␮m 共for preparation, see Section 7.10兲.

3.11.6 Conductive Mounts Conductive mounts can be necessary for electropolishing and for observation in an SEM. The simplest way of mounting is using a conductive resin, either thermoplastic or thermosetting 共see Section 3.13.1兲. The conductive resin should only be used to establish conductivity to the top of the mount. Around the specimen surface contacting the electrolyte, a nonconductive resin should be used. If the specimen should be cold mounted, the simplest way is letting the specimen protrude at the top of the mount. This is only possible if the specimen has a certain height. Another effective way is to drill a hole in the cold mount and insert a piece of metal or a screw to make contact to the specimen. Also, a wire can be soldered to the specimen before mounting and the wire taken outside the top of the mount.

3.12 Recovery of Mounted Specimen In some cases, the specimen cannot be etched or examined, or both, when mounted in a mounting resin The resin can be removed mechanically, chemically, or by heating. It

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is important that the prepared surface is not damaged. First, as much resin as possible is removed mechanically by sawing, grinding, and breaking the resin away from the specimen. When only a small amount of resin is left on the surface of the specimen, possibly impregnated in the surface, this can be removed chemically or by heating. M-Pyrol 共N-Methyl-2-Pyrrolidone兲 is a resin solvent, classified as a combustible liquid, which is less hazardous than other solvents used for removal of resin The stripped down specimen is placed in M-Pyrol at room temperature for 24 h and in most cases the remaining resin is dissolved or can be removed. An alternative is boiling N,N-Dimethyl-formamide 共approximately 150° C 共300° F兲兲 or in a laboratory furnace at 500– 600° C 共900– 1100° F兲. Epoxy can be dissolved by submerging the mount in methylene chloride. Methylene chloride is a strong, hazardous solvent and is carcinogenic. The mount can also be dipped in boiling glycerine for 1 or 2 h, which will soften the epoxy so that the specimen can be removed. All work should be done under a fume hood and with suitable protection. The relevant MSDSs should be studied carefully before commencing the work.

3.13 Advice and Hints on Cold Mounting Check that the specimen material is not being influenced by the mounting material, if the material is at all sensitive to heat, use epoxy curing in 6 – 20 h. • Ensure that the specimen is clean and dry without grease. • If using a mounting mold, take care that the material of the mold is suited for the mounting material. Relatively flexible molds should be used when using epoxy. • Be careful when mixing that the exact amount of each component 共by volume or by weight兲 is measured out. Stir for the time stated in the directions for use. It is very important that the components are totally mixed. • Specimens with layers requiring a perfect edge retention: Use an epoxy resin • In case of epoxy mounts larger than 50 mm 共2 in兲, the heat developed can accelerate the process causing shrinking. To avoid this the amount of hardener can be reduced or the mount can be cooled in a refrigerator for the first period of time, or both. • If using a filler mixed into the mounting material, this mixture need only be in a thin layer around the specimen. When this layer is partly cured, fill up with normal resin • Always use special gloves when handling epoxy. • Always use a fume hood for all cold mounting resins. • Cold mounting materials, especially polyester have a limited shelf life; take care to mark the containers upon receipt to ensure that the oldest material is used first. For long-term storage, use a refrigerator. For Trouble Shooting see Sections 13.5/6.

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3.13.1 Selection of Cold Mounting Materials

Purpose

Specific Properties

Thermoplastic Translucent Medium shrinkage Low hardness High removal rate Medium chemical resistance Thermoplastic Good edge Low shrinkage retention Serial mounting High/medium hardness Fast curing Low removal rate Medium chemical resistance Routine Thermosetting examination Transparent Serial mounting High shrinkage Medium hardness High removal rate Low chemical resistance Very good edge Thermosetting Transparent retention Low shrinkage Transparent Medium mounts Porous hardness specimens Medium removal Impregnation rate 共Plated layers, Low viscosity thermal spray coatings兲 Mineralogy Serial mounting Thermosetting Transparent Routine Medium shrinkage examination Low hardness Transparent Medium removal mounts rate Serial mounting Routing examination Fast curing Translucent 共Printed circuit boards兲

Mounting Material

Approximate Curing Time at 20 °C 共68° F兲

Peak Temp. °C 共°F兲

Price Range

Acrylics, resin 共powder兲 with one hardener Without filler

6 – 15 min

90–110 Medium 共194– 220兲

Acrylics, resin 共powder兲 with one hardener and with mineral filler

8 – 15 min

90 共194兲

Medium/ high

Polyester, resin 45 min to and hardener, 6– 8 h both liquids

50–110 Low 共122– 240兲

Epoxy, resin and hardener, both liquids

30–60 共86– 140兲

6 – 20 h

Medium

30– 45 min 85–100 High Epoxy, resin 共185– and 220兲 hardener, both liquids

4 Marking—Storage—Preservation 4.1 Marking MARKING OF METALLOGRAPHIC/MATERIALOGRAPHIC SPECIMENS IS very important because a proper identification of the specimen is the only thing that ensures that the result of the analysis is correctly used. This is true for both quality control and research, and it can be said that the specimen must be marked in all cases where a metallographic/materialographic analysis should be reported. The marking should not in any way influence the microstructure of the surface to be examined; therefore, this risk should be considered before marking is done. It should also be considered that the marking is placed where it is not disturbed or removed during the preparation process. The backside of the specimen/mount is usually used for marking. Considering the limited space, a code expressing job number, material treatment, etc., is used most often. If the final marking is done on the mount, special care should be taken that the specimen is identified at the stage after sectioning, before mounting, so that correct marking of the mount is assured. A number of methods for marking are available.

4.1.1 Marking with Waterproof Ink This cannot be recommended because the treatment of the specimen/mount will in most cases remove the ink. Marking ink or pencil can be used as an intermediate.

4.1.2 Identification Tag This works well if the tag 共carton or metal兲 is placed on the backside of the specimen and mounted in a reasonably transparent resin, the resin protecting the tag. A tag placed on the outside of the specimen/mount, however, might be removed during cleaning in water and alcohol.

4.1.3 Engraving One of the most widely used methods of marking is vibration engraving. A very hard vibrating needle induces a visible deformation of the surface of the mount/specimen. This method will stress the material layer below the surface and it should not be used for thin specimens like foils. Electro engraving gives less damage to the surface, but can only be used on electrically conducting materials. The engraving, on a clean and smooth surface, is done through the melting/evaporation of metal, caused by a high temperature spark. Hand engraving, using a hard needle, is also possible in most, not too hard, materials.

4.1.4 Stamping Stamping a number or code in the specimen is possible but because of the very strong deformation below the stamped surface this method should only be used in cases where it will not disturb the material to be examined. 80

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81

4.2 Storage It is important that the prepared surface of a specimen is not disturbed by attack from the atmosphere. Therefore, the prepared specimen is placed very often in a dessicator with moisture-absorbing material. Airtight cabinets are also commercially available. For long-term storage, often the specimen should be stored for several years, a direct preservation of the surface is recommended 共see below兲.

4.3 Preservation To absolutely protect the prepared surface a lacquer usually from a spray can is used. The microstructure can be examined through the lacquer, or the lacquer can be removed easily with acetone and the specimen resprayed after examination.

5 Cleaning and Cleanliness TO AVOID ARTIFACTS IT IS VERY IMPORTANT, ESPECIALLY IN THE POLISHing stage, that the specimen/specimen holder is carefully cleaned between each step. It is also important that the room in which the process takes place and the operator’s hands are clean to avoid contamination of the polishing cloths. Cross contamination: Considering that the preparation process often includes abrasives with grain sizes spanning from grit 180 共82 ␮m兲 grinding paper to 1 ␮m diamond suspension, it is evident that cross contamination, larger grains from an earlier step, cannot be tolerated. Cross contamination can be caused by an inadequate cleaning of the specimen, specimen holder, or by the operator’s hands. The polishing disk may become contaminated from airborne particles or excessive debris in the machine.

5.1 Cleaning 5.1.1 Cleaning Before Start of Preparation All greases, oils, and other residues on the specimen should be removed by water with a detergent or a suitable organic solvent. Failure to clean thoroughly can prevent cold 共castable兲 and hot compression mounting resins from adhering to the specimen surface. Also oxidation, etc., should be removed 共unless these products are to be examined兲. As some of the more rough cleaning methods, like shot blasting and wire brushing might damage the surface, it should be considered whether this might influence the final result of the preparation. In special cases, where normal procedures are unsuccessful, electrolytic or chemical cleaning can be used 共see ASTM Standard Practice for Preparation of Metallographic Specimens 共E 3兲, Section 12.4兲.

5.1.2 Cleaning During and After Preparation In principle, the specimen and the specimen holder 共fixed specimens兲 should be cleaned between every step in the grinding and polishing process, but at wet grinding on SiC paper, using a constant flow of water, a careful cleaning can be limited to after the last grinding step. When grinding on other media, like rigid composite disks and at polishing, a cleaning between each step is absolutely necessary. There are, however, some materials or some constituents in materials that will be preferentially attacked by water 共zinc coatings on steel, lead inclusions in machining steels, etc.兲, therefore, water must be avoided completely in the latter preparation steps.

Cleaning by Hand For cleaning of most metals and other materials without pores, cracks, etc., manual cleaning is the most effective method. The specimen or specimen holder is held under running lukewarm water and rinsed with a soft brush or cotton ball dipped in water with a detergent. In cases of soft materials and after the last polishing step, a cotton ball is used to clean the prepared 82

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Cleaning and Cleanliness

83

surface. The cleaning is finished with the spraying of ethylene alcohol from a spray bottle on the prepared surface and possibly wiping the surface before it is taken for drying. Ethanol containing a denaturation additive can be used as long as the additive does not leave a film on the specimen. In case of specimens with pores, cracks, etc., and mounts with a gap between mounting material and specimen, ultrasonic cleaning is recommended, except for fragile materials. In case the standard cleaning methods are inadequate, the cleaning solutions stated in ASTM Standard Practice for Preparation of Metallographic Specimens 共E 3兲, TABLE X1.1, can be used.

Ethanol Although ethanol 共ethyl alcohol兲 is taken by many persons in different forms, the ethanol used in a laboratory has the following Hazards Identification, Human Health: “Organic solvents may be absorbed into the body by inhalation and ingestion and cause permanent damage to the nervous system, including the brain. The liquid may irritate the skin, the eyes and the respiratory tract.”

Ultrasonic Cleaning Ultrasonic cleaning is efficient and relatively fast, removing dirt from pores, gaps, cracks, etc. The specimen or specimen holder is placed in a tank with a liquid, water with a detergent, alcohol, or an organic solvent like acetone. In cases of dirt difficult to remove, weak acids and basic solutions can be used. A transducer vibrates under the bottom of the tank, with 20– 40 kHz creating gas bubbles 共cavitation兲 in the liquid. These bubbles implode and a rubbing effect occurs which removes the dirt. The dirt contaminates the liquid and therefore a specimen must be rinsed, as mentioned above, before drying. Ultrasound penetrates glass so it is possible to place one or more beakers in the tank with water with a detergent around the beakers. When the specimens are only placed in the beakers, in a suitable liquid, this liquid can easily be exchanged when contaminated. Cleaning usually takes 0.5– 1 min. Some soft, very porous and brittle materials should not be cleaned ultrasonically or only for 10– 30 s. Using specimen holders, the whole holder can be placed in the tank.

Ultrasonic Apparatus Ultrasonic apparatuses are supplied with tanks of different size from 1.5– 10 L 共0.4– 2.6 gal 共U.S.兲兲 and with capacities from 80 W to 470 W. The ultrasound is produced mostly from a piezoelectric transducer but magnetostrictive transducers can also be used with large units. The frequency is 20– 50 kHz.

Drying Drying should take place in a stream of mild air. It is important that the layer of alcohol is not dried on the prepared surface but is blown away and evaporates from the sides of the specimen/mount. Air can be supplied from a fixed hair dryer type apparatus allowing both hands to be free to clean the specimen with soft cotton wool and alcohol. Compressed air can be used as well, in which case a clean, dry, oil free air must be secured. A hair dryer is recommended for the finished specimen to avoid possible oil drops from the compressed air.

84


Cleaning of Grinding Disks and Polishing Cloths Grinding disks based on diamond usually are used with water as a lubricant and cleaning shouldn’t be necessary. Rigid composite disks 共RCD兲, lubricated by a special lubricant, will be covered with swarf after use. This typically will not disturb the function, but if the swarf has dried and therefore filled up the openings between the segments of the disk, the disk should be cleaned. This is done with a brush, detergent, and lukewarm water. A cloth that has been contaminated can be cleaned in the same way but different brushes should be used for the grinding disks and the cloths because of the different grain sizes.

5.2 Cleanliness It has already been mentioned above that a high level of cleanliness is needed when preparing metallographic/materialographic specimens. The operator should be aware that no contamination takes place through transfer of debris from the hands of the operator. The room in which polishing takes place should be clean and should not contain dust in the air. The room for preparation, when possible, should not be part of a production environment. It is advisable that cutting does not take place in the same room as grinding and polishing, as the cutting produces large amounts of debris. The grinding/polishing machines should be kept clean according to a weekly schedule, securing that no contamination can take place from the sides of the machine, splash ring, etc. This also prolongs the lifetime of the equipment.

6 Mechanical Surface Preparation—Grinding 6.1 Grinding—A Basic Process AFTER SECTIONING AND POSSIBLY MOUNTING, THE METALLOGRAPHIC/ materialographic specimen is now to be prepared to obtain the true microstructure or a structure, which, in spite of certain defects 共artifacts兲, will give a true examination result. For a thorough description of artifacts and how to avoid them, see Sections 13.5/6. The true structure has been defined in Section 1.2, indicating a surface with no or few artifacts. In practice only two ways are open to obtain this, either mechanical preparation, grinding and polishing, or grinding, followed by electrolytic polishing 共see Fig. 1.7 to get an overview兲. In some cases a chemical attack can be included in the mechanical polishing, creating chemical mechanical polishing, and, more seldom, chemical polishing is used 共see Sections 7.12 and 8.7兲, but in all cases one or several grinding steps are performed before the polishing takes place. In this book, grinding is defined as an abrasive machining process with a fixed abrasive. The abrasive grain might be fixed from the start of the process, either by a bond 共ceramic, metal, resinoid兲 or placed on a flexible backing covered by a coating, like at SiC grinding paper, or covered by a thin layer of metal on a backing of metal plate. Also the abrasive grain, normally suspended in a liquid, can be added to the abrasive machining process taking place on a plane, prepared disk. In this case some of the grains will be forced into the disk surface, be fixed in the moment of cutting, and grinding takes place. In case the abrasive grain is not fixed but staying loose and rolling between the work piece and the disk surface a lapping process takes place. Consequently in this book, a disk to be used with loose abrasive grains is called a “grinding disk,” if the majority of the grains are fixed when the material removal takes place, producing a “ground surface,” and a disk where the majority of the grains are loose, producing a “lapped surface,” is called a “lapping disk” 共see also Section 6.7.7兲.

6.1.1 Plane Grinding „PG… Plane grinding, also called planar grinding, may be necessary for three reasons: 共1兲 To plane the surface after sectioning, depending on the sectioning method, the sectioned surface might not be plane. 共2兲 To remove the deformation caused by the sectioning and establish a known “start surface” of the specimen to secure a reproducible further preparation. 共3兲 When a number of specimens are fixed in a specimen holder, the specimen surfaces are not in the same plane, and material has to be removed to obtain this. Plane grinding is usually performed with relatively coarse abrasive grains and will be described further under the different grinding methods mentioned below 共see also Fig. 13.14兲. 85

86


6.1.2 Fine Grinding Fine grinding is the process used for establishing a specimen surface suited for the first polishing step. This means that the relatively rough surface from sectioning or plane grinding, through one or several steps with finer and finer grain sizes, is changed into a surface that can be treated by polishing. The fine grinding step共s兲 are needed because the material removal is relatively high, opposite to the polishing steps with a low material removal 共see below兲. Fine grinding is further described under the different grinding methods mentioned below 共see also Fig. 13.15兲. Grinding plays a major role in the preparation process and, therefore, it will be discussed in depth in the following. The mechanics of the grinding process, being a “cutting” process producing chips are the same as in wet abrasive cutting 共see Chapter 2兲, and they are basically the same in mechanical polishing. In mechanical grinding/polishing, the following two features should be considered.

Material Removal Material is removed from the specimen surface during the process. The amount of material removed can be expressed by the removal rate, often measured as ␮m per minute or ␮m per a certain travel in m 共metres兲 of the specimen on the preparation surface. The preparation process is controlled mostly by time, assuming that a certain amount of material is removed from the specimen per time unit. This assumption is often not correct because a number of parameters that are not totally controlled, such as preparation surface, abrasive, and lubrication, influence the removal rate. By the device, “stock removal,” sometimes used on grinding machines, the process is not controlled by time but through a constant measurement of the actual removed amount of material. In this way the process can be stopped when the amount of material planned for is removed 共see Section 7.7.6兲.

Deformation Deformation can be defined as the nature and depth of the plastically deformed layer that is produced in the specimen surface during material removal. In general, the removal rate should be as high as possible and the deformation as low as possible. This depends on the interaction between the abrasive grain and the specimen surface as described in the following.

6.2 Material Removal Grinding is defined as a process with fixed abrasive grains, acting like machine tools. Figure 6.1 shows a schematic drawing of a tool removing a chip from a work piece. The abrasive grains will remove chips from the specimen surface in the same way. Using a normal machine tool like a lathe for the cutting process, macroscopic chips in the form of ribbons or particles having a thickness of from about 0.025 to 2.5 mm 共0.001– 0.1 in兲 are produced. In grinding, the chips produced are much smaller, ranging in thickness from 0.0025 to 0.25 mm 共0.0001– 0.01 in兲. The reason for this is the shape and size of the abrasive grains, acting very differently as “tools.” During the cutting process the tool and work piece are forced against each other

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Fig. 6.1—Basic model of cutting process indicating shear zone.

and a compressive force is set up which causes the metal to deform in front of the tool point. The deformation will take place in a zone along the shear plane 共see Fig. 6.1兲 and the metal is forced to slide over the tool surface. In doing this, the stress will cause the material to separate as a chip, if the rake angle is correct 共see below兲. The cutting process is very complex, influenced by cutting speed, tool geometry, and feed rate. A mathematical model has been developed for abrasive machining of a work piece moving in a linear path across a planar abrasive device like grinding paper under a constant normal load 共L兲.7 In this model the material removal rate can be expressed as: m = f␳DL/共H␾m兲

共1兲

where m is the mass of material removed, f is the fraction of the contacting points that cut a chip, ␳ is the density of the work piece material, D is the distance traveled, L is the load, H is the indentation value of the surface layers of the work piece material and ␾m is a form factor expressing the shape of the contacting points. The most interesting aspect from a metallographic/materialographic viewpoint is that the material removal increases with increasing load and decreases with increasing hardness of the work piece material. This latter assumption, however, only covers hard metals where the removal rate can be expected to be relatively small, but the relative removal rates for metals of low and intermediate hardnesses are virtually unpredictable.7

6.2.1 Rake Angle The rake angle ␣ is the angle between the top face of the tool and a plane perpendicular to the work piece, as schematically shown in Fig. 6.2. Rake angles may be classed as positive, negative, or neutral 共tool face perpendicular to the work piece兲, as shown in Fig. 6.3. To create a chip, the rake angle has to be positive, neutral, or to a certain degree negative. With a positive rake angle, the area under shear decreases, leaving less deformation in the surface of the work piece, and the friction 共heating兲 is lower than with a neutral or negative angle. At a certain negative angle, the critical rake angle, the chip is not produced anymore and a “plowing” takes place as shown in Fig. 6.3.7 When plowing, the rake angle is so negative that only a groove is made in the work piece surface. A standing wave bulge forms in front of the tool, and material is dis-

88


Fig. 6.2—Basic model of cutting process indicating rake angle.

placed into a ridge on each side of the groove. The material removal approaches zero and the deformation of the surface increases.

6.2.2 Grain Shape—Contacting Points In cutting, using a machine tool like a lathe, the shape of the cutting tool is given with a fixed geometry. In grinding, using the abrasive grains as cutting tools, the shape of the grain and the number of edges and points vary extremely. Figure 6.13 shows the grains of a grit 220 SiC grinding paper. The most effective shape of the grain is a V-form creating an efficient chip provided that the rake angle is correct. If the grain is flat, the cross section of the chip is reduced and in the case of flat grains of a certain size the specific pressure between grain and surface will decrease and no cutting will take place, resulting in plowing or no action at all. It is very important that a high number of contacting points are available to obtain an efficient grinding. Only a small number of the visible contacting points make contact with the specimen surface. At coarser SiC papers like grit 220 only approximately 1 in 10 points make contact and at finer papers like grit 600 only 1 in 20.7

Fig. 6.3—Schematic drawing of possible rake angles with abrasive grains in different positions. Cutting is shown with a chip being removed from the work piece and plowing is indicated as a groove with ridges.7

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6.2.3 Grain Penetration The depth of penetration at the contacting points of an abrasive grain into the work piece is only a small percentage of its size. At grinding, the maximum value is in the range of 5 %, meaning that a grit 220 grain with an average size of 68 ␮m using a pressure of 40 kPa 共6 psi兲 will penetrate less than 3 – 4 ␮m into the specimen surface. In practice, at grit 220 SiC grinding paper the penetration 共scratch depth兲 at an annealed 30 % Zn brass will be up to 5 ␮m in the first seconds and drop to 2 – 2.5 ␮m.7

6.2.4 Force on Specimens In principle, the material removal increases linearly with the increase in specific pressure between specimen surface and grinding surface. This means that a certain force is needed to obtain a satisfactory high removal rate. It is, however, a problem with SiC paper that a too high specific pressure might cause stronger deformation in the specimen. This is especially important during the first few seconds when the paper has a few large grains causing a very aggressive attack 共see Section 6.6兲. At grinding, the force should correspond to a specific pressure from 30– 100 kPa 共4.35– 14.5 psi兲 depending on the material to be ground. In theory the specific pressure should be kept regardless of specimen size, but experience has shown that the force on the single specimen should not exceed 50 N 共11 lbf兲, and as compensation, to obtain the necessary material removal the preparation time is extended. A too high pressure might cause the grinding paper, in most cases held only by a water layer 共see Section 13.2.4兲 to be dragged off the support disk and the more expensive paper with adhesive backing or a double adhesive foil must be used. If a polishing cloth is used for “grinding” the cloth may overheat.

6.2.5 Grinding/Polishing Fluids The fluids used for metallographic/materialographic grinding/polishing has no lubricating effect regarding the actual cutting process taking place between the abrasive grain and the work piece 共specimen兲 material, creating chips.7 The fluid has a strong cooling effect and especially in case of grinding, the fluid, usually water, will remove the swarf. If the debris is not removed the grinding surface becomes clogged and it will create deformation in the specimen surface. At polishing the fluid, also called lubricant, is lubricating the surface of the polishing cloth, reducing the friction and heat developed between cloth and specimen, at the same time removing swarf from the cloth surface. For more details on fluids and lubricants see Sections 2.3.7 and 6.5.

6.3 Deformation 6.3.1 Metals In metals, being ductile materials, the separation of a chip during machining operations induces complex systems of plastic deformation in both the separating chip and the specimen material. An inevitable consequence is that a layer, plastically deformed during machining, is left in the new surface that is produced. In general terms, the strains in this layer are very large at the surface and decrease more or less exponentially with depth. See also Figs. 13.3–13.6 and Figs. 13.19–13.22. This deformed layer becomes important in metallography when the plastic deformation changes the microstructure of the specimen in a way that can be detected in the microscopic examination that is to be performed. The layer is then an important poten-

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Fig. 6.4—Section of a chip cut in 70:30 brass by an orthogonal tool with a highly negative rake angle.7

tial source of false structures, or preparation artifacts, the avoidance of which is one of the primary objectives of a metallographic preparation sequence. As mentioned above, the abrasive grains act as machine tools set at different rake angles. When a chip is separated from the surface, the shear strains are concentrated in the so-called shear zone in front of the tool. A region adjacent to this shear zone, and extending into the specimen in advance of the tool is also plastically deformed though to a lesser degree, as shown in Fig. 6.4. Samuels7 has done an exhaustive study of the deformation created in the specimen surface of metals, by using taper sections 共see Section 3.11兲. A taper section of annealed polycrystalline 30 % Zn brass ground on a 220 grit SiC paper, etched with different etchants shows the surface of the specimen with scratches and the deformation in Fig. 6.5. Samuels7 splits up the layers into two levels of deformation, the shear-band layer at the surface that has been subjected to large strains, and the deformed layer beneath the shear-band layer. The shear-band layer typically extends preferentially beneath individual polishing scratches for approximately twice the depth of the scratch with which it associates. In the deformed layer the material has been strained by simple compression, and the magnitude of the strains decreases with depth until a level is reached where the material is only elastically strained. This elastic-plastic boundary defines the lower limit of the deformed layer. An important difference between the shear-band layer and the deformed layer is that the presence of shear-band layer material is always apparent after etching with any etchant suited for the material, whereas the presence of the less deformed material becomes apparent in light microscopy only

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Fig. 6.5—Taper section of the surface of annealed polycrystalline 30 % Zn brass that has been ground on grit P220 SiC paper. The section has been etched by several methods that have different threshold strains for revealing deformation as follows. 共a兲 Ferric chloride reagent 共threshold strain: 5 % compression兲. 共b兲 Cupric ammonium chloride reagent 共threshold strain: 0.1 % compression兲. 共c兲 Low sensitivity thiosulfate etch 共threshold strain: 0.1 % compression兲. 共d兲 High-sensitivity thiosulfate etch 共threshold strain: elastic limit兲. In each case, the base of the layer, in which the manifestations of deformation have been developed, is indicated by an arrow. Taper ratio 8.2, 250:1.7

in a rather limited number of materials, and then, perhaps, only after etching by specific methods. Samuels splits the deformed layer into two depths, the total deformed layer Dd and the significant deformation Ds. This gives the following three levels of deformation in an abraded materialographic specimen: Depth of shear-band layer 共Dsb兲: The maximum depth beneath the root of the surface scratches of the shear-band layer. Depth of deformation 共Dd兲: The maximum depth beneath the root of the surface scratches to the elastic-plastic boundary. Depth of significant deformation 共Ds兲: The maximum depth beneath the root of the surface scratches of the deformation that would noticeably affect the observations to be made on the finished surface. The value of Ds is the most important one regarding metallographic preparation. It varies with materials and the etchant used and the level of the finished specimen surface should always be beyond Ds. Example: Annealed Polycrystalline 30 % Zn Brass7 SiC grinding paper, 220 grit, with water, hand abrasion Dsb 共scratches兲: 2 ␮m Dd: 77 ␮m Ds: 7.5 ␮m

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Fig. 6.6—Schematic drawing of surface damage to ceramic material. Because of the brittleness of the material, micro cracks and pull-outs 共surface fractures兲 are developed in the surface during the grinding. When a sharp point 共a兲 is pressed into the surface, a pseudo-plastic zone 共1兲 of irreversible deformation is produced beneath the indentation. A median vent crack 共2兲 in vertical direction may develop. By increasing force 共b兲 lateral vent cracks 共3兲 may develop. If an indentation is made with a spherical point, 共c兲 first a pseudo-plastic zone 共1兲 develops, at increasing force followed by a cone 共ring兲 crack 共2兲 and by further increase of the force also a median vent crack 共3兲 may develop. Pull-outs of whole grains or parts of grains, 共d兲 and smaller pull-outs 共e兲. Crack following grain boundary 共f兲.

6.3.2 Brittle Materials—Ceramics The above description covers ductile materials like metals, which when stressed, will plastically deform a significant amount before fracture occurs. This is not the case with brittle materials like most ceramics, which deform only elastically prior to fracture by propagation of a crack. To understand the effect often taking place at grinding of brittle materials, it can be seen how the indentation of a sharp point and a spherical point affects the surface of a specimen. When a sharp point, 共a兲 in Fig. 6.6, is pressed into the surface, a pseudo-plastic zone 共1兲 of irreversible deformation is produced beneath the indentation. This impression stays in the surface, and by increasing force a so-called median vent crack in vertical direction 共2兲 develops, and by further increase of the force lateral vent cracks develop 共b兲共3兲. When this lateral vent crack develops to the surface, a relatively large volume of material is removed which can be called a fracture chip, considerably larger than the chips earlier described under metals.7 If an indentation is made with a spherical point, 共c兲 in Fig. 6.6, first a pseudo-plastic zone 共1兲 develops, at increasing force followed by a cone 共ring兲 crack 共2兲 and by further increase of the force also a median vent crack develops 共3兲. The circular symmetry of the ring crack will be lost if the indenter is drawn across the surface as by grinding/polishing, and the crack might follow grain boundaries and cause pull-outs of whole grains or parts of grains, 共d兲 in Fig. 6.6. The same might happen with the crack formation shown in 共a兲, Fig. 6.6. As mentioned above the material removal in brittle materials to a high degree takes place with fracture chips, leaving cavities in the surface 共e兲 in Fig. 6.6, but according to Samuels7 this is mainly the case at the larger abrasive grain sizes, whereas below grit P1200 共approximately 15 ␮m兲 it seems that chip cutting without fracturing takes over. It can be seen in Fig. 6.6 that beneath the fracture cavities and pull-outs, a crack-

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containing layer develops, 共f兲, which extends to considerable depth. This layer must be removed during the preparation. A normal preparation procedure for ceramics and other hard and brittle materials is grinding with a bonded diamond grinding disk followed by grinding on rigid composite disks or very hard polishing cloths with diamond and a final polishing on a medium hard cloth with silica. The most serious problem is the development of pull-outs and cavities developed during the first grinding step共s兲 with bonded diamond disks. These artifacts, which as a mistake can be considered to be pores belonging to the true structure, must be effectively removed during the grinding on the rigid composite disks 共see Sections 3.10, 6.6.1, 6.7.7, and 13.5/6兲. Preparation of ceramics is stated in Material/Preparation Tables 02–06 in Section 13.2.3. For in-depth information on ceramics and preparation of ceramics, see Refs. 26 and 27.

6.4 Grinding Abrasives The abrasives already described in Section 2.3 for abrasive cutting are also used for grinding, but below a further description related to grinding/polishing is given.

6.4.1 Aluminum Oxide Hardness: 2500 HV Although Al2O3, alumina, has certain advantages, especially for grinding of steel, it is not used much for metallographic/materialographic grinding except in ceramic grinding stones and in connection with zirconia in wet grinding paper for plane grinding. Very fine alumina is used for polishing 共see Section 7.5兲. Aluminum oxide was the first grinding medium found in nature, typically emery 共about 50 % Al2O3 with other oxides, principally iron oxide兲 and corundum. Around 1900 a process was found to turn bauxite into Al2O3 and today it is the most used abrasive. Al2O3 is available in different crystals with the ␣ particles mostly used for grinding. Al2O3 easily forms substitutional solid solutions like the combination Al2O3 and ZrO2 mentioned above. Being made in many different types, Al2O3 also has very different surface structure. The types with relatively smooth surfaces are used for rough grinding operations. Types with a surface with sharp facets are used for finer grinding.

6.4.2 Silicon Carbide Hardness: 2700 HV SiC plays an important role in metallographic/materialographic grinding with SiC grinding paper being used for both plane grinding and fine grinding 共see Section 6.6.2兲. SiC is the first synthetic abrasive, made in the 1890s. There are two grades of SiC. The green type is relatively friable and has fewer impurities; the black type has the same hardness as the green type but is less friable. Most of the SiC used for grinding is of the black type. Silicon carbide is the second most widely used type of abrasive. The surface structure of an SiC grain is rather irregular, resembling fractured glass. This is an advantage when coated on an SiC grinding paper because the grain will be fixed firmly in the coating cement but the irregular surface combined with an irregular shape will give an increased deformation of the specimen surface 共see Section 6.6.2兲.

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6.4.3 Diamond—Diamond Products Hardness: 8000 HV Diamond plays an increasing role in metallographic/materialographic preparation. A number of products based on diamond are developed using diamond grains as fixed or loose abrasive for both grinding and polishing 共see below兲. Diamond, together with cubic boron nitride 共CBN兲, belongs to the superabrasives. Since the 1940s, natural diamonds have been used for grinding purposes. After many years of research, methods to make synthetic diamonds were developed in the 1950s– 60s and today almost all diamonds used for grinding and polishing are synthetic. Diamonds are made with two crystal structures: polycrystalline and monocrystalline. The polycrystalline grain, having many sharp edges, is relatively friable and will break down during use, giving a self-sharpening effect, as shown in Fig. 6.7. Polycrystalline diamonds are considered the most effective for materialographic preparation because of a higher removal rate than monocrystalline diamonds in most materials.7 Monocrystalline grains are stronger, having a blocky form with relatively few cutting edges and will not easily break down. If they break down, it takes place along straight lines, as shown in Fig. 6.8, not creating many new cutting edges.

Fig. 6.7—Schematic drawing of polycrystalline diamond grain before and after grain fracture creating many new cutting edges.

Fig. 6.8—Schematic drawing of monocrystalline diamond grain before and after grain fracture creating only a few new cutting edges.

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Fig. 6.9—Diamond grains 共2兲, uniform size 共a兲 and nonuniform size 共b兲, between grinding/ polishing disk 共3兲 and specimen 共1兲. The smallest grains 共b兲 are not active.

Diamond Products with Fixed Grains Diamond is used in a number of products, all having the diamond grains fixed in some kind of bond. These materials are used for grinding of metallographic/materialographic specimens, ranging from plane grinding with relatively coarse grits to extremely fine grits used in the diamond 共lapping兲 films 共see below兲. Diamond Grinding Disks—The diamond grains are placed in a metal or bakelite bond. Primarily used for “traditional” grinding of very hard materials 共see Section 6.6.1兲. Resin-Bonded Diamond Grinding Disks—The diamonds are placed in a thin layer in a resin bond 共not bakelite兲. This type of disk is used for “contemporary” grinding of all materials harder than 150 HV 共see Section 6.7兲. Metal-Bonded Diamond Disks—The diamonds are placed in a thin layer fixed by a nickel coating 共see Section 6.7.4兲. Diamond Pads—The diamonds are placed in a bond of metal or resin in a dot matrix on a self-adhesive backing. Used for plane and fine grinding of hard materials 共see Section 6.7.5兲. Diamond Film—The diamonds are coated to a very thin film 共lapping film兲. This product is used for grinding/polishing of electronic devices, wafers, etc. 共see Section 6.7.6兲.

Diamond Products with Loose „Free… Grains A number of products are available with the diamond grains mixed with a carrier, enabling grinding or polishing with free grains on the surface of the grinding/polishing disk 共see below兲.

Grain Size It is very important that the grains for a given grain size are selected with a narrow tolerance. If the grains are relatively uniform, as shown in Fig. 6.9 共a兲 a very high part of the grains are active, securing a high removal rate; Fig. 6.9 共b兲 shows diamond grains with a large difference in grain size and it can be seen that a high number of grains are present only as “filler” and with only a few acting grains. This causes the specific pressure on each grain to be high, possibly causing deeper scratches in the specimen surface.

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Diamond Suspensions The use of diamond suspensions 共slurries兲 is increasing because applying the abrasive in small quantities during the process is an advantage, giving a more constant removal rate than other types of diamond products.28 Suspensions are suited for being applied from a dosing unit, in this way making the charging of the grinding disk/polishing cloth, automatic. The automatic dosing can be performed as spray, creating aerosols, which are considered dangerous to health, or by pumps, supplying the suspensions in drops. Also the suspension can be conveniently applied by hand from a pump 共spray兲 bottle. Diamond suspensions can be based on water, alcohol, oil, or other hydrocarbons. Water-based suspensions are to be preferred, because of the nontoxic nature of water. To the suspension should be added an ingredient that stabilizes the diamond grains so that they do not sediment or only sediment very slowly. In case sedimentation takes place, the bottle with suspension can be placed on a stirring apparatus or in other ways be stirred during the process. In certain cases, when the material to be prepared is sensitive to water, a water-free suspension based on oil or preferably on alcohol, should be used. Diamond suspensions are available with both polycrystalline and monocrystalline diamonds in the range 45 ␮m to 0.05 ␮m. The grain sizes most used are 9 and 6 ␮m for fine grinding/ rough polishing and 3, 1, 0.25, 0.1, and 0.05 ␮m for polishing and final polishing. The polycrystalline suspension is preferred if the highest removal rate and best finish is wanted. This is due to the fact that the polycrystalline grains break down during the process and in this way creates new cutting edges. Monocrystalline suspensions are normally less expensive than polycrystalline, and the removal rate is considered to be lower. Normally the suspension is used in combination with a lubricant 共see Section 6.5兲. In this way the adding of new grains and the establishment of a lubricating film are separated, making it possible for a more exact dosing of both. Diamond suspensions, also acting as lubricants, however, are available. Using these, only one product is added to the grinding/polishing disk, establishing both a sufficient number of active grains and a lubricating film.

Diamond Sprays Both polycrystalline and monocrystalline diamonds are available in spray cans. The advantage of using spray is the very small amount of “other material” introduced to the process that are opposite of suspensions and pastes which contain a high amount of carrier. Diamond sprays are available in the grain sizes 45, 25, 15, 9, and 6 ␮m for fine grinding/rough polishing and 3, 1, and 0.25 ␮m for polishing.

Diamond Pastes This is the original way of distributing the diamond, by rubbing a small amount of diamond paste into the polishing cloth. For this reason diamond cannot be added during the process and in certain cases, like working with a rigid composite disk 共RCD兲, the paste will disturb the process. A variation of paste is the stick, where the diamonds are placed in a harder wax; this is easier to apply than paste. Pastes are available with both polycrystalline and monocrystalline diamonds. The grain sizes available are 15, 9, and 6 ␮m for fine grinding/rough polishing and 3, 1, and 0.25 ␮m for polishing

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6.4.4 Cubic Boron Nitride „CBN… Hardness: 4500 HV CBN is made along the same lines as diamond, with high pressures and high temperatures. The main reason why CBN is of interest as an abrasive is that it is much more chemically stable than diamond in the presence of hot iron 共see Section 2.3兲. CBN crystals are relatively smooth which makes bonding difficult. Therefore, the grains are often coated with metal, suck as nickel. CBN can be used in grinding disks in a metal or bakelite bond for very hard ferrous metals.

6.4.5 Boron Carbide Hardness: 2800 HV Boron carbide 共B4C兲 was developed for grinding purposes, but for different reasons the use is limited. It is used as a suspension for lapping purposes, the grain having a porous structure with many sharp edges. B4C is seldom used in metallographic/ materialographic grinding and polishing.

6.4.6 Hardness of Abrasives and Materials—Table 6.1 Table 6.1 gives a comparison between the Vickers hardness of a number of materials to be prepared and the abrasive materials used in the preparation process.

6.5 Grinding/Polishing Fluids—Lubricants The most commonly used fluid for “traditional grinding” 共see Section 6.6兲, with grinding stones and SiC wet grinding paper, is water with or without an additive. If the water is recirculated, an additive should be used to prevent corrosion and reduce bacterial growth in the water 共see Section 2.3.7兲. For “contemporary grinding” 共see Section 6.7兲, using grinding disks with fixed grains, water is also used, but in the case of fine grinding on rigid composite disks 共RCDs兲, lubricants, also called extenders 共normally used for polishing兲, are used. They are described below.

6.5.1 Water-Based Lubricant This lubricant is to be used if possible because it has no environmental effects. It is suited for polishing of most materials using polishing cloths. In case of fine grinding on rigid composite disks, the water-based lubricant should be dosed in small amounts to avoid “aqua planing” where the specimen is planing on the fluid layer, not getting into contact with the surface of the disk. For polishing of certain soft, ductile materials, a water-oil based lubricant should be used 共see below兲.

6.5.2 Alcohol-Based Lubricant This type of lubricant gives a high removal rate and a good cooling due to the fast evaporation of the alcohol. For this reason this lubricant can be used as an alternative for a water-based lubricant for work on rigid composite disks, which shall work “dry” to secure that the specimen is in direct contact with the disk surface. An alcohol-based lubricant should be used for materials that are sensitive to water. Alcohol 共ethanol兲 is considered dangerous to health by inhalation and ingestion and for this reason this lubricant should be avoided if possible.

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TABLE 6.1—Hardness of Abrasives and Materials.

6.5.3 Water-oil Based Lubricant This type of lubricant, water with an in-mixed oil forming an emulsion, will give a less aggressive action between cloth/abrasive and specimen surface than the water- and alcohol-based types. An oil film will act as a membrane between the polishing cloth and specimen. The lubricant is used for polishing of soft, ductile materials. Because of the oil, which might cause skin problems, the use should be as limited as possible.

6.5.4 Oil-Based Lubricant This lubricant is a “lapping oil” based on mineral oil 共heavy petroleum distillate兲. Like with the water-oil based lubricant mentioned above, it is used for soft, ductile materials

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Fig. 6.10—Grinding stone for plane grinding, the grinding takes place on the top surface of the stone.

to reduce the formation of deformations. Mineral oil may cause irritation by repeated skin contact and by inhalation of vapors or aerosols, or both. For these reasons the use should be limited or avoided, if possible.

6.6 Traditional Grinding The expression “traditional grinding” covers the grinding methods used for a very long time in metallographic/materialographic preparation: Grinding stones/disks with ceramic or bakelite bonds and silicon carbide 共SiC兲, alumina 共Al2O3兲, and zirconiumalumina wet grinding paper.

6.6.1 Grinding Stones/Disks Grinding Stones for Plane Grinding of Metals Grinding stones with aluminum oxide as abrasive and a ceramic bond are used mainly for plane grinding when a relatively large amount of material shall be removed. The wheel normally is of the recessed type 共see Fig. 6.10兲, the specimen holder being pressed against the top surface of the stone. The grinding stones change during the process, the main problems being uneven wear and clogging of the surface. The stone has to be trued regularly to keep the surface plane and dressed to remove material clogging the surface 共see Section 2.3.6兲. This is usually done with a diamond truing device placed on the grinding machine.

Diamond Disks for Grinding of Very Hard Materials Ceramics and other very hard materials have to be ground with diamond. This can be grinding disks with a metal bond or a bakelite bond. The metal bond gives a relatively rough surface of the specimen and the wear is relatively low. Bakelite bond produces a specimen surface with less deformation but the wear is higher than by the metal bond. Both types of diamond grinding disks are very expensive and only used for grinding of sintered carbides, ceramics, and other very hard materials. In the past few years, a new type of diamond disk with resin bonded fixed grains has been developed. These disks are considerably less expensive and suited for a wide scale of materials 共see Section 6.7兲.

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TABLE 6.2—Comparison between Grit Numbers according to ANSI Standard B74.18 and FEPA “P” Standard 43-GB. FEPA “P” Standard 43-GB1984 R 1993 P60 P80 P100 P120 P150 P180 P220 P240 P280 P320 P360 P400 P500 P600 P800 P1000 P1200 P1500 P2000 P2500 (P2400) (P4000)

Approx. Average Grain Diameter FEPA P μm 269 201 162 125 100 82 68 59 52 46 41 35 30 26 22 18 15 13 10 8.4 5

ANSI μm 268 192 141 116 93 80 67

ANSI B74.182006 60 80 100 120 150 180 220

52

240

42 34

280 320

27 22 16 13

360 400 500 600

6.5 5

(800) (1200)

6.6.2 SiC Wet Grinding Paper—Table 6.2 SiC paper is the traditional grinding medium, used since the 1950s, both for plane grinding and fine grinding. SiC grinding paper is made of a waterproof paper backing with a layer of SiC abrasive grains. As shown in Fig. 6.11, an adhesive layer called the make coat is first applied to the backing before the abrasive grains are applied. As the backing material passes through a strong electrostatic field the particles are oriented with their longest dimension in the vertical direction. This provides good grain retention and also orients the particles with their sharpest edges upwards. A second layer of adhesive, called the size coat, is then applied over the entire assembly.

Fig. 6.11—Schematic drawing of cross section of SiC grinding paper.

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The paper backing can be of A-type, relatively thin, and C-type, which is somewhat thicker. Type C is normally used for metallographic/materialographic grinding. The paper is supplied as disks in the diameters 200 mm 共8 in兲, 230 mm 共9 in兲, 250 mm 共10 in兲, and 300 mm 共12 in兲. The SiC abrasive is classified according to standards established by ANSI 共American National Standard Institute兲 and FEPA 共Federation of European Abrasive Producers兲. The grit sizes are split into two categories: macrogrits and microgrits. Macrogrits ranging from grit 12 to grit 220 are determined by sieving, the grit number indicating the number of openings per square inch. Macrogrits are the same in the ANSI standard and the FEPA standard, the FEPA designation having a P before the number. Microgrits ranging from grit 240 to grit 4000 are determined by sedimentation, and the grit numbers covering a specific grain size are not the same in the two standards 共see Table 6.2兲.

Comparison Between Standard Grits—Table 6.2 In practical preparation a selection of grits is used. The suppliers of consumables for metallographic/materialographic preparation supply both according to the American and European Standards. In Table 6.2, the most commonly used grits are shown for comparison 共P2400 and P4000 are not FEPA designations, 800 and 1200 are not ANSI designations兲.

Plane Grinding For plane grinding the grits 120 共P120兲, 180 共P180兲, 220 共P220兲, or 240 共P280兲 normally are used. As mentioned above, the finest possible grit should be chosen to limit the deformation of specimen surface 共see below兲. When using SiC paper, the last planegrinding step should be grit 220 or 240 共P220 or P280兲 to be sure of the correct result 共reproducibility兲 of the following preparation method. Considering that each sheet of paper is only grinding efficiently in 20– 60 s, depending on the material to be ground, often several sheets must be used to secure a totally plane specimen surface co-planar to the grinding surface.

Fine Grinding For fine grinding, three to four steps based on the following grits are used typically: 280 共P320兲, 320 共P360兲, 360 共P500兲, 400 共P600兲, 500 共P1000兲, 600 共P1200兲, 800 共P2400/ P2500兲, 1200 共P4000兲. A normal fine grinding sequence could be 320–400–600 using ANSI-designated paper or P320, P500, P1200 using FEPA designated paper. In the case of soft ductile materials, one or two fine steps can be added, 800, 1200 共ANSI兲 or P2400/P2500, P4000 共FEPA兲.

Material Removal The material removal rate for SiC paper is relatively high as long as the paper is not worn down. This is due to the abrasive grains being rather exposed and having a good space in between, allowing for the chips to be produced and taken away by the water flow. This is opposite to dry grinding on emery paper, which will very soon have a clogged surface causing deformations and material flow in the specimen surface. Because of the brittleness of the SiC and the relatively high load on the grains, they break down caused by fractioning and wear. In Fig. 6.12 this is shown schematically, the SiC grains with different rake angles are broken and worn, creating new, negative

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Fig. 6.12—Schematic drawing of grains on a SiC paper with different rake angles, as new and after 30–60 s use, the gray parts are worn away or fractured.

rake angles resulting in a loss of cutting action.29 This develops in 20– 60 s or longer, depending on the material to be ground, hard materials strongly reducing the time. According to tests made by Samuels7 the removal rate when grinding some metals like copper and copper alloys, aluminum and aluminum alloys, silver and titanium stays constant over a long period of time, and for some metals like nickel-chromium austenitic steels, nickel and nickel alloys, titanium alloys, chromium and gold, a deterioration in removal rate occurs in the first minutes and is followed by a period of relatively high material removal. These tests were based on a single specimen at a time, whereas in modern preparation three to six specimens often are ground at the same time, consequently reducing the lifetime of the paper. In Fig. 6.13, an SEM micrograph shows the single grains of a 220 grit SiC paper with the different shapes and sizes. Also the large variation in contacting points and rake angles can be seen. At 220 grit, the median grain size is 63 ␮m and the largest allowed grain size is 74 ␮m. Because of this large variation in shape and size, only around 5–10 % of the many visible contacting points of the grinding paper actually get in contact with the specimen surface. Only a fraction of these points are able to remove material from the surface. Samuels7 estimates that less than 1 in 1000 of the grains visible can be expected to actually remove material. During the process when the SiC grains break down, the cutting effect will change into plowing, shown in Figs. 6.3 and 6.14. At certain soft, ductile materials, grains or parts of fractured grains can be embedded in the specimen surface 共see Fig. 2.1 and Section 13.6.4兲.

Deformation As shown in Section 6.3, a 220 grit SiC paper will induce a relatively strong deformation of the specimen surface. This is mostly because of the single large SiC grains being very aggressive in the first seconds of the grinding process. Figure 6.14 shows a comparison between an SiC grinding paper and a grinding disk with diamond abrasive grains in a resin bond. The situation after 2 – 5 s, 共a兲 Fig. 6.14 shows the introduction of

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Fig. 6.13—SEM micrograph of a P220 SiC paper. The irregular shapes of the grains and the variety in grain size can be seen.

the deep deformations by the paper, whereas the grinding disk with grains embedded in a bond gives more moderate deformation.

Edge Retention—Relief In Section 3.1.3 edge retention is discussed, concentrating on mounting. Another important aspect is the resilience of the substrate, the surface, used for the grinding/ polishing. To totally avoid a rounding of edges, a hard substrate without resilience must be used. SiC paper has some resilience because the paper backing has a certain flexibility, but in most cases a sufficient planeness can be obtained for most materials. In more extreme cases, however, where edge rounding or relief, or both, must be absolutely avoided, SiC paper might have too much resilience. In Figs. 6.15 and 6.16 grit 220 SiC paper is compared to a diamond grinding disk with the same grain size, having almost no resilience. In Fig. 6.15, two unmounted, similar specimens are compared. The specimen on the SiC paper was rounded due to resilience of the paper backing; the specimen on the diamond disk is not rounded due to the very low resilience of the disk. Even with mounted specimens, SiC paper in certain extreme cases will create a round-

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Fig. 6.14—Comparison of surface deformation using SiC paper and a resin bonded diamond disk. After 2 – 5 s 共a兲 single large grains of the SiC paper give deep deformations, after 30 s 共b兲 the SiC grains are wearing down, and after 60 s 共c兲 the SiC grains are worn down creating plowing, causing deformation, see Section 6.2.1. The diamond grinding disk gives less deformation and remains almost constant during the process.

ing of the specimen or a relief of the specimen surface. In Fig. 6.16 a drawing of a medium hard, nitrided steel, mounted in epoxy resin, is shown. When prepared on SiC paper, the SiC particles grind away the surface irregularly due to the high differences in hardness between the nitrided layer and the core steel. Because of the limited difference in hardness between the nitrided layer and the SiC particles and the resilience of

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Fig. 6.15—Comparison between SiC grinding paper and a resin bonded diamond disk. The SiC paper has a relatively high resilience, and an edge rounding is introduced on an unmounted specimen. The diamond disk has no resilience and gives no rounding.

the paper backing, the layer protrudes above the surface of the specimen due to the relatively low rate of material removal. The diamond disk cuts all parts of the surface uniformly due to the extreme hardness of the diamond particles and the lack of resilience.

Environment—Economy As mentioned above the efficient grinding time to a high degree depends on the specimen material and the number of specimens prepared at the same time. At soft and medium hard materials the total plane and fine grinding might be performed with only four sheets of paper, but at hard materials, especially with several specimens in a holder, several sheets of each grain size must be used. In case of a high production of specimens this is relatively costly and it will cause a relatively high amount of waste. As a waste substance, the SiC paper is neutral.

6.6.3 Alumina—Zirconia Alumina Wet Grinding Paper Using alumina or zirconia alumina instead of SiC as the abrasive, a longer efficient grinding time is obtained. The alumina grinding paper is available in grit 120 and the zirconia alumina papers are available in the grits 60 共P60兲, 80 共P80兲, 120 共P120兲, and 180 共P180兲, and consequently they are only for plane grinding. Due to the longer efficient grinding time they are especially suited for automatic preparation using specimen holders with many specimens. The influence on the specimen surface is as described under SiC paper.

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Fig. 6.16—Comparison of edge rounding and relief with a mounted specimen with a hard surface layer prepared on SiC paper and a resin bonded diamond disk. At the SiC paper a relief develops between the hard layer and the mounting material/basic material.

6.7 Contemporary Grinding “Traditional” grinding described in the previous section has a number of drawbacks, especially when used for semiautomatic and fully automatic preparation. For this reason “contemporary” grinding has been developed, in this way eliminating or reducing the drawbacks: • Quality of specimen surface: Better edge retention, less deformation. • Constant removal rate: Fewer steps and higher reproducibility. • Less handling: By using fewer steps, and using automatic preparation systems, handling is reduced to a minimum and operation time is saved. • Less waste: By using longer lasting consumables, the amount of waste is reduced. In short it can be said that with contemporary grinding it is possible to prepare specimens with extreme hardness differences as a routine process. These specimens could only be prepared with great difficulty using the traditional methods. The grinding media used for contemporary grinding are almost all based on diamond as the abrasive, either as fixed 共bonded兲 in the surface of a rigid grinding disk, or added during the process on a rigid composite grinding disk 共rigid composite disk 共RCD兲兲. The products are supplied as disks in the diameters 200 mm 共8 in兲, 250 mm 共10 in兲, 300 mm 共12 in兲, and 350 mm 共14 in兲.

6.7.1 Magnetic Fixation As part of the development of the products for advanced preparation, it was important also to avoid the relatively troublesome handling of grinding papers and polishing cloths with adhesive back. For this purpose magnetic systems were developed using a

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Fig. 6.17—Resin bonded diamond disk for magnetic fixation on a support disk with a permanent magnet.

supporting disk with a permanent magnet foil on which the substrate, a grinding disk or polishing cloth, made with a ferromagnetic backing, is fixed 共see Fig. 6.17兲. The holding power is very high in the direction parallel to the supporting disk, in this way keeping the substrate on the disk, but vertically the holding power is low enabling the operator to easily remove the substrate. A further advantage is the use of only one supporting disk for all grinding/polishing steps instead of changing the supporting disk for each step. Normally the magnetic supporting disk is made especially for that purpose, but it is possible to convert a normal metal grinding/polishing disk by placing a magnetic foil with adhesive back on the disk. The drawbacks are an increase in the disk thickness, and after some time, the foil might loosen due to attack from liquids during the preparation process.

6.7.2 Resin-Bonded Diamond Grinding Disks Section 6.6.1 describes conventional diamond disks. These have either a metal or bakelite bond and because of the high price and careful maintenance 共truing is important to keep the surface plane兲, they are only used for very hard materials, harder than 600 HV 共55 HRC兲, where SiC and Al2O3 are not hard enough. Diamond as an abrasive, however, would be ideal for grinding of softer materials. In the past five to ten years, a new type of diamond grinding disk has been developed, taking advantage of the hard diamond, but supplied at a reasonable price, which matches the SiC grinding paper. The disk is suitable for materials harder than HV 150. The cost is kept low because the diamonds are fixed only in a thin layer in a resin bond and placed in segments on the surface of the disk as shown in Fig. 6.17 The figure shows how the disk is fixed to the supporting disk by a permanent magnet, as described above, but the disk can also be fixed by a double adhesive foil placed on a normal grinding/polishing disk. The bond keeping the diamond grains, Fig. 6.18, is made so that it allows the grains to leave the surface when the grain is worn. The disk is used with water like SiC paper. Using only a thin layer of bond with diamonds, the disk needs not to be trued, when the layer is worn away at the center of the disk the disk is discarded, see Section 6.7.7 for a more extensive description of this wear. Only a dressing of the surface with a dressing stick is needed if the surface is clogged.

Plane Grinding The disks are used for plane grinding, using the same grain sizes as for SiC paper, grit 80 共P80兲 to 220 共P220兲. Because of the constant removal rate 共see below兲 the whole grinding sequence can take place in one operation, even when much material shall be removed and the material has a high hardness.

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Fig. 6.18—Resin bonded diamond disk. Diamond grains placed in a bond.

Fine Grinding The disks can also be used for fine grinding in the grit sizes 360 共P600兲 and 600 共P1200兲.

Material Removal The disks have a relatively high, constant removal rate securing that the grinding process can be finished without interruptions. This is due to the high hardness of the diamonds and the ability of the bond to break down, releasing fresh abrasive grains.

Deformation The diamond grains, being of a more regular shape and with a closer tolerance of the grain size than SiC grains, will produce less deformation than SiC paper, as shown in Fig. 6.14. Also the position of the grains, placed in a bond 共see Fig. 6.18兲 gives less impact when touching the specimen surface, creating less deformation. The segmented surface, with grooves to lead away the swarf, is important to avoid smearing of the specimen surface.

Edge Retention—Relief Edge retention, to a high degree depending on the resilience of the disk, is very good. The resin bond is relatively hard and unflexible 共see Figs. 6.15 and 6.16兲 and the very hard diamonds are able to remove material even from very hard phases in the specimen surface, avoiding relief

Environment—Economy The diamond disk as described above has very little environmental impact when discarded. It only consists of a thin, tinned steel plate 共as used for canned food兲 and a very thin layer of synthetic resin Depending on the material to be prepared, one disk is equivalent to 100 sheets of SiC paper or more, making the cost comparable to the cost of SiC paper.

6.7.3 Resin-Bonded SiC Grinding Disks The diamond disks described above are only suited for materials harder than HV 150. Therefore, disks have been developed with SiC as an abrasive suited for softer materials. In general, the above description of the diamond grinding disks also covers the SiC grinding disks.

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6.7.4 Metal-Bonded Diamond-Coated Disks These types of disks are different from the conventional metal-bonded disks. The diamond abrasive is placed in a very thin layer on a metal surface and bonded 共coated兲 with a layer of nickel. These disks can be used for the softest to the hardest materials, but they are not used much because the cost per prepared specimen is high.

6.7.5 Diamond Pads This product, originally developed for grinding/polishing of glass, uses the diamond in a metal or bakelite bond in a dot matrix covering the surface of the pad. The metal bond is only suited for plane grinding of ceramics, sintered carbides, and other very hard materials. The grain size varies from 250 ␮m in steps down to 20 ␮m. The bakelite bond can be used for fine grinding of hard materials, being available in grain sizes 30, 10, and 2 ␮m. Dressing: It is important that the diamond pads are dressed regularly with a dressing stick, normally Al2O3 or SiC in a ceramic bond. This is to open the surface of the disk when clogging has taken place 共see Section 2.3.6兲.

6.7.6 Diamond/CBN/Al2O3 / SiC Film In the case of preparation of microelectronic devices, wafers, optical fibers, and certain ceramics where extreme flatness and very low deformation is needed, films 共lapping films兲 coated with diamond, CBN, Al2O3, or SiC can be used. The very accurately graded abrasive is coated on a thin polyester film either for gluing 共PSA兲 or for adhering only using water 共plain back兲. The films are used wet or dry and they are available both with a continuous layer of abrasive and with the abrasive as dots allowing the swarf to flow away. The film with dots 共ceramic beads兲 gives a higher material removal, a longer life, and a coarser finish, compared to films with a continuous layer. The films are available in steps from 30 ␮m down to 0.05 ␮m.

6.7.7 Rigid Composite Disks Since the 1970s, the rigid composite disk 共RCD兲 has been available for materialographic preparation. The RCD has the advantage of making very flat specimens with a constant removal rate and relatively little deformation, and this makes the RCD very well suited for fine grinding of most materials. During the process on an RCD, a diamond suspension is continuously added. This is known from lapping, a very common abrasive machining process used in the industry to produce flat surfaces. Normal lapping takes place on cast iron disks and the surface obtained is not suited for metallography/materialography 共see below兲. The surface of an RCD consists of a resin with mixed-in metal powder in different grain sizes, and it seems to be the effect of this surface which changes the process taking place on an RCD, from lapping to grinding. To explain the mechanisms of an RCD, a comparison was made between lapping 共loose grains兲 on a glass disk, grinding on a diamond film 共fixed grains兲, and grinding on two RCDs of different hardness.30

Experiment: Lapping Versus Grinding The scratch pattern of the specimen surface created with an RCD is similar to a surface made with grinding paper, apparently ground, with grinding defined as a process with

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Fig. 6.19—Pattern of scratches and deformations after grinding on a diamond film. SEM.

fixed abrasive grains, each grain acting as a machine tool producing a chip. This seems strange because when using an RCD, the abrasive, mostly diamond with a grain size of 6 – 9 ␮m, is added during the process. Normally these loose grains should create a lapping, defined as a process with loose abrasive grains, rolling and flowing in nearly a single layer between specimen surface and disk, and not a grinding. At lapping, the corner of the rolling grain digs into the specimen surface, the grain tumbles onto an edge, and then another corner contacts the specimen, and so on. Lapping is considered less appropriate for metallographic/materialographic preparation because the removal rate is low, and the specimen surface is rather strongly deformed. A steel specimen with a high finish was used for all parts of the experiment. Grinding took place on a diamond film, 9 ␮m, to secure a perfect grinding. For the lapping a floated glass disk with an alcohol/water diamond suspension was used with 9 ␮m of the same type of diamonds used on the film, added during the process. The RCD process was performed on two RCDs, RCD 1 and 2, both of the disposable type 共see below兲 with the composite placed in segments on the disk surface 共see Fig. 6.27 below兲. RCD 1 was with metal powder composite 共relatively hard and aggressive兲, and RCD 2 was with a composite without metal powder, which is relatively soft and with less aggressive material removal. For both RCDs the diamond suspension mentioned above was used. All the resulting surfaces were analyzed in an SEM. The results showed that the specimen ground on the film showed a typical grinding pattern with scratches in all directions 共Fig. 6.19兲. To the naked eye the surface was relatively bright. The specimen lapped on the glass plate showed a typical lapping pattern with two distinct features 共Fig. 6.20兲. The freely moving 共rolling兲 diamond grains have made a relief with cavities in the surface, and a few very large scratches have been produced, probably due to single grains fixed in the surface of the glass disk. It can be seen that the lapped surface is considerably rougher than the ground surface 共Fig. 6.19兲. To the naked eye the surface was dull. The specimen prepared on RCD 1 共Fig. 6.21兲 has scratches very similar to the

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Fig. 6.20—Pattern of scratches and deformations after lapping on a glass plate. SEM.

scratches initiated by grinding 共Fig. 6.19兲, only a little larger. The surface is reasonably plane between the scratches. To the naked eye the surface was relatively bright. The specimen prepared on RCD 2 共Fig. 6.22兲 has almost the same scratch pattern as at grinding 共Fig. 6.19兲. It is finer than the RCD 1 pattern due to the fact that RCD 1 is a more aggressive RCD. This also can be seen from the removal rates 共see below and Fig. 6.23兲. To the naked eye the surface was relatively bright. The conclusion of the SEM analysis is that according to the scratch pattern, the same process takes place when grinding on a film with fixed diamond grains and on an RCD surface with loose grains added during the process. The removal rate was also measured, defined as material removal in ␮m per 300 m 共movement of specimen on the grinding/lapping surface兲共see Fig. 6.23兲. It can be seen that the diamond film is very active during the first approximately 50 m and wears out after approximately 250 m. The glass disk has a relatively constant removal rate during the whole distance and the same is the case with the two RCDs. This is because the abrasive is added during the whole process. The aggressive RCD 1 shows a higher removal rate than the other three surfaces. Based on the above experiment, a suggestion for the mechanisms taking place during the processes was made and a model proposed. Lapping on a hard, homogenous disk: It is beyond doubt that the process with rolling grains makes indentations in the specimen material, in this way breaking particles out of the surface 共Figs. 6.20 and 6.24兲. A fractured, indented, dull surface can be seen only with a few scratches. A few grains will penetrate into the surface of the disk and produce a scratch like grain 共b兲 in Fig. 6.24. Process on an RCD: On an RCD the surface is very much softer than the sample material. This means that the abrasive grain is pressed into the disk surface so that a rolling is prevented and a process, creating chips like at grinding, takes place. Only a very small number of grains are rolling 共see Fig. 6.25兲. According to Samuels7 it seems that the abrasive grains embed in the upper regions of the edge faces of the segments where they can contact the specimen surface.

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Fig. 6.21—Pattern of scratches and deformations after grinding on a hard rigid composite disk 共RCD兲. SEM.

At RCD 1, the surface consists to a high degree of metal powder 共Fig. 6.25兲. This gives a variation in surface hardness, and the abrasive will penetrate differently into the surface, less in the metal particles. This means that the grain is able to make a larger chip, counting for the higher removal rate of RCD 1. In the case of RCD 2 with a considerably softer surface, the abrasive grains penetrate deeper into the disk resulting in a smaller effective diamond size, and the abrasive is held more firmly, which is important when grinding ductile materials.

Rigid Composite Disks „RCD… for Longtime Use The original RCDs were made as solid disks with a thick layer of composite material, consisting of a synthetic resin with mixed-in metal powder 共iron, copper兲, or a mineral powder like Al2O3. The surface can be with segments of different composites and with grooves of different types to remove the swarf during the process. The disks can be used for plane grinding with 30– 45 ␮m, but they are mostly used for fine grinding with 6 to 9 ␮m diamond suspension added during the process. The process has to run relatively dry, with a minimum of lubricant added during the process. As the disk surface texture turns smooth during use, a dressing is necessary with intervals to regain a rough surface and thereby secure the removal rate. The disks are difficult to use for hand preparation and are normally used with a semiautomatic specimen mover 共see Section 6.8兲. Most specimen movers work with the specimen holder placed eccentrically on the grinding disk 共see Polishing Dynamics 共Section 7.9.2兲. This eccentricity causes a wear concentrated around the center of the disk, making it concave 共Fig. 6.26兲. This unevenness will, when exceeding 100– 200 ␮m, cause an unevenness of the specimens and the effect of the disk will be reduced. The concave surface must be trued to regain the planeness and this is mostly done with a truing tool using diamond. Due to this rather laborious truing, many RCDs were not used and the use of SiC paper was preferred. The development of the thin, disposable RCD changed this situation.

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Fig. 6.22—Pattern of scratches and deformations after grinding on a soft rigid composite disk 共RCD兲. SEM.

Rigid Composite Disk, Disposable Taking into consideration the advantages of the RCD, it was evident that an RCD without the drawbacks mentioned above, and even compatible with SiC paper, should be developed. This was done with the disposable RCD, consisting of a tinned steel foil or a steel plate with segments of composite material. This is fixed magnetically to a supporting disk with a permanent magnet 共Fig. 6.27兲. The disposable RCD is made in two versions, one relatively aggressive for materials harder than 150– 200 HV and a softer one for softer materials in the 40– 250 HV range and for composite materials.

Plane Grinding The disposable RCD is normally not suited for plane grinding because it should not be used with diamond grain sizes larger than 15 ␮m. In some cases, however, when work-

Fig. 6.23—Comparison of removal rates of specimens after grinding on a diamond film, lapping on a glass plate and grinding on a hard and a soft RCD.

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Fig. 6.24—Schematic drawing of a lapping process. The abrasive grains are loose and rolls between the specimen and the lapping disk. A corner of the grain digs into the specimen surface, and the grain tumbles onto an edge. A track of angular indentations 共cavities兲 is produced in the specimen surface.

ing with “single-specimen preparation,” 共see Section 7.9.1兲 the amount of material to remove at this stage is so low that grinding with a hard RCD using 9-␮m diamond suspension can be considered a “plane grinding.”

Fine Grinding The disposable RCD is made for fine grinding with diamond suspension 9, 6, or 3 ␮m. The total fine grinding stage can be performed usually in only one step in 2 – 4 min and the specimen is ready for the first polishing step.

Material Removal The removal rate is considerably higher than at a conventional RCD. This is mostly because the disposable RCD works at a higher specific pressure and the removed material 共swarf兲 is efficiently removed through the channels between the segments. Also, it

Fig. 6.25—Schematic drawing of a material removal process on a rigid composite disk 共RCD兲. The majority of the abrasive grains are fixed in the surface of the disk 共grinding兲; only a small amount is moving 共lapping兲.

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Fig. 6.26—Wear pattern of grinding/polishing disk. Due to the geometry of disk and specimen holder, the wear around the center of the disk is stronger than at the periphery, causing a concave disk surface, after a certain preparation time.

shall not be dressed during use, but keeps its surface texture during the whole lifetime, securing a constant removal rate. The material removal varies with material type and type of RCD. The hard, more aggressive type has the highest removal rate 共see Fig. 6.23兲.

Deformation Using diamonds 共9 – 6 ␮m兲 with a narrow tolerance on the relatively flexible RCD surface, the grain, momentarily fixed in the surface, will not have the same damaging impact on the specimen surface as with fixed grains 共SiC paper兲. Also, by varying the amount of metal in the composite, the aggressiveness of the surface can be minimized which is very important with soft materials.

Edge Retention—Relief The composite material, although “microflexible,” will be rigid and plane as a total surface. This, together with the high cutting capacity of the diamond grains, will give a very good edge retention and practically no relief.

Wear As described earlier, an RCD turns concave during use 共see Fig. 6.26兲. To avoid the troublesome truing of the surface, the disposable RCD is discarded when the segments around the center of the disk are worn away, showing the user that the difference in planeness between periphery and center is so high that uneven specimens will be produced.

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Fig. 6.27—Disposable rigid composite grinding disc 共RCD兲 magnetically fixed to a support disc with a permanent magnet.

Environment—Economy The disposable RCD can be compared with a piece of tin plate or a thin stainless steel plate with a layer of paint, and it can be disposed of like a normal tin can or metal piece. The price per specimen using the RCD depends on the material to be prepared, but at normal use more than 100 specimen holders can be prepared on one RCD.

6.7.8 Fine Grinding Cloths When using very hard cloths, absolutely without nap, like nonwoven chemo textiles and nylon, with diamond suspension or spray/paste of a grain size of 9 ␮m or larger, the process can be defined as “fine grinding” if the pressure on the specimen is high. Polishing can be defined as grinding producing very small chips and is explained further in Chapter 7. In the above-mentioned case, however, a material removal similar to grinding can be obtained. The materials used for the fine grinding cloths are stainless steel mesh, woven polyester, woven silk, woven nylon, and nonwoven synthetics. These are all without nap and used with 15, 9, 6, or 3 ␮m diamond suspension or spray 共see Section 7.4兲. With the introduction of rigid composite disks 共RCDs兲 for soft materials 共see Section 6.7.7兲, the use of these cloths has been reduced.

Material Removal The removal rate is not as high as with an RCD, but higher than at a normal polishing step.

Deformation The deformation is much lower than at grinding on a disk with fixed abrasives. It is comparable to the deformation created by an RCD 共see Section 6.7.7兲.

Edge Retention—Relief Due to the relatively high resilience of the cloths, except the steel mesh, a certain edge rounding and relief might develop.

Environment—Economy All materials mentioned above can be discarded as normal waste; the cost per specimen is comparable to SiC paper.

6.8 Grinding/Polishing Equipment Mechanical grinding and polishing are normally performed on the same type of machines.

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Fig. 6.28—Polisher/grinder with two disks 共200/ 250 mm 共4 / 6 in兲 diameter兲 and 300 rpm for manual preparation.20

Only in a few cases machines only for grinding 共mostly plane grinding兲 are supplied. For this reason only equipment that can be described as “grinders” are included in this section. The grinders/polishers are described in Sections 7.8 and 7.9.

6.8.1 Plane Grinding Manual Grinding Plane grinding using grit 220 共240兲 or coarser can be done by hand on a rotating disk of a 200- 250- 300 mm 共8 - 10- 12 in兲 diameter disk with a grinding paper. The paper can be placed with a plain back in a water-filled disk, and the paper is sucked to the disk when rotating due to the centrifugal force, which moves the water to the outside of the paper. The paper may also have a self-adhesive backing or a double-adhesive foil can be used. For the technique of manual 共hand兲 grinding see Section 13.2.4.

Fig. 6.29—Belt grinder with two workstations for coarse grinding. Adjustable water flow and sink.19

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Fig. 6.30—Semiautomatic grinding machine 共grinding stone兲 for plane grinding with specimen holders. Diameter of grinding stone 356 mm 共14 in兲, 1450 rpm.20

Machines with one or two disks are available and used for both grinding and polishing; two disks can be of advantage when using four steps for grinding with SiC paper. Figure 6.28 shows a two-disk grinder/polisher 共250 mm 共10 in兲 disk diameter兲 with a single speed, 300 rpm, for hand grinding on SiC grinding paper. For a more effective grinding by hand, a belt grinder can be used, built with one or two work stations. The belt grinder works with a belt moving on two rolls and with a flow of water; it can be used for both plane and fine grinding. Figure 6.29 shows a belt grinder with two work stations, water flow system and sink.

Automatic Grinding Plane grinding of specimen holders with six or more specimens can be done on most automatic systems, which are described in Section 7.9. At very large holders with large specimens, it can be an advantage to plane grind on

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Fig. 6.31—Four stage hand-grinder for wet grinding on four strips of grinding paper in rolls.19

a grinding stone with a relatively high speed 共1450 rpm兲 and a diameter of 356 mm 共14 in兲. The machine, shown in Fig. 6.30, is only for plane grinding and fine grinding/ polishing must take place on another automatic grinder/polisher.

6.8.2 Fine Grinding Manual Grinding Fine grinding by hand takes place on equipment spanning from simple apparatus with four strips of grinding paper 共Fig. 6.31兲, to rotating grinder/polisher as mentioned under plane grinding 共Fig. 6.28兲. Figure 6.31 shows a four stage hand-grinding apparatus with four strips of SiC grinding paper supplied from rolls for plane and fine grinding.

Automatic Grinding Fine grinding of specimen holders either with a number of fixed specimens 共central force兲 or individually loaded 共single force兲 takes place on semi- or full-automatic grinders/polishers described in Section 7.9 Automatic grinding/polishing systems have gained ground because they reduce the work load on the metallographer and produce an overall better specimen quality. Also, the reproducibility is improved, securing that if a certain method is followed, the result always is consistent.

7 Mechanical Surface Preparation—Polishing 7.1 Polishing: Producing the True Structure AFTER PLANE GRINDING AND FINE GRINDING THE SPECIMEN SURFACE must be polished to obtain the true microstructure or a structure, which is satisfactory for a given analysis. In principle, the surface always will have a certain deformation 共artifacts兲, but if not too deep this can often be removed through the etching of the surface 共see Chapter 9兲. For a thorough description of artifacts and how to avoid them, see Section 13.5/6. This chapter covers mechanical polishing and chemical mechanical polishing 共CMP兲. Electrolytical and chemical polishing are described in Chapter 8. Mechanical polishing is defined as a material removing process with loose abrasive grains placed on a substrate like a polishing cloth. The abrasive can be added before or during the process and normally lubricant is applied during the process for lubrication and cooling. CMP can be defined as a material removal process where the material removal takes place chemically and mechanically at the same time 共see Section 7.12兲. Mechanical polishing is by far the most used process, and depending on the type of material and the nature of the preceding fine grinding step, one or several polishing steps are needed 共see Fig. 1.7兲.

7.1.1 Rough Polishing This step immediately follows the last fine grinding step and is usually done on a hard, napless cloth with 9 or 6 ␮m diamond. This step can be compared to the last step of fine grinding done on a hard, napless cloth 共see Section 6.7.8兲. The rough polishing step is very important because most of the material, damaged by the grinding, is removed in this step 共see Table 7.1兲.

7.1.2 Polishing The polishing is done in one to three steps with hard, medium hard, or soft cloths with diamond 3 – 0.25 ␮m or finer polishing media, such as silica and alumina, 0.1– 0.05 ␮m 共see Section 7.5兲, depending on the material to be polished.

7.2 Material Removal The process of material removal during polishing, micromachining, is considered to be the same as it is during grinding 共see Section 6.2兲. According to Samuels7 it seems that another mechanism, delamination, takes place when polishing with diamond abrasives below 3 ␮m. Delamination does not produce the elongated chips that result from micromachining, but small, plate-shaped equiaxed particles are produced. No ex120

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Fig. 7.1—Schematic drawing of an abrasive grain fixed in a fiber of a polishing cloth.

planations have been advanced for the mechanism by which delamination occurs during the polishing with the smallest grain sizes. At micromachining, the abrasive grain is able to produce a chip, implying that the grain is, at least momentarily, fixed in the polishing cloth, as shown schematically in Fig. 7.1. The diamond grain wedges between the cloth fibers with a rake angle sufficient to be able to cut a chip from the specimen surface. To obtain a high removal rate at rough polishing, hard cloths are used, creating a higher load on the grain, giving a larger chip. Using softer, more resilient cloths for the final steps, the load on the grain is reduced, causing smaller scratches and less deformation of the specimen surface.

7.2.1 Influence of Polishing Abrasive on Removal Rate For grinding, the hardness of the abrasive is important. Therefore, diamond is used for both rough polishing and polishing. For final polishing, alumina 共Al2O3兲, colloidal silica 共SiO2兲, and magnesia 共MgO兲 are also used. Likewise, the shape of the grain plays a role. Polycrystalline diamonds give a higher removal rate than monocrystalline diamonds,7 probably because the individual polycrystalline grain contains more angular points of the size needed to provide cutting points than those of monocrystalline.

7.2.2 Force on Specimens In principle, the removal rate increases linearly with the increase in specific pressure between specimen surface and the polishing surface once a certain low threshold value has been exceeded. Using a high force causing a high specific pressure might create a rounding of the specimen, and often the lubrication will not be satisfactory and heat might develop. Also, an increased wear of the polishing cloth will take place. For napless, hard cloths the specific pressure should be in the range of 30 to 100 kPa 共4.35 to 14.5 psi兲; for softer cloths the pressure should be 15 to 50 kPa 共2.2 to 7.25

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psi兲. Experience has shown that in specimens from 40 mm 共1.5 in兲 diameter and up, the force per specimen should not exceed 50 N 共11.5 lbf兲 to avoid overheating of the cloth and excessive wear. To compensate, the polishing time may be extended 1 to 4 min.

7.3 Deformation Polishing, as mentioned earlier, in principle being the same process as grinding, will produce shallower deformed layers. With hard cloths with a low resilience, a stronger deformation will develop than with softer cloths. The depth of the deformed layers is an order of magnitude smaller than that on surfaces ground with SiC paper, as shown by Samuels7 共see Table 7.1兲. This shows the importance of the rough polishing step 共6 ␮m diamond兲. For explanations of Dsb, Ds, and Dd see Section 6.3.1. In theory, even the finest abrasive will create a deformed layer. It is, however, possible to obtain a surface very close to the true structure with the use of very fine abrasives like alumina 共Al2O3兲 and silica 共SiO2兲 for the final polishing step. Silica, having a carrier liquid with a pH in the range of 8.5 to 11 共see Section 7.5.5兲 and a grain size of a fraction of a micron, will create a combined mechanical and chemical material removal 共see Section 7.12兲. Deformation in the form of smearing can take place with soft metals, the material being smeared across the surface. For this and other types of deformation, see Section 13.6. In the literature, the very thin deformed layer left by the last polishing step is often called the Beilby Layer. The existence of such a layer is not supported by recent research and the use of this term should be avoided; however, to give an impression of the mechanisms taking place, a short description of the theories by Beilby31 and Samuels7 will be given in the following section.

7.3.1 The Beilby Layer At the beginning of the 20th century, Sir George Beilby established the theory of the so-called Beilby layer. This layer was proposed to be of an amorphous nature created by a smeared layer that had passed through the liquid state 共Fig. 7.2兲.31 The layer would fill out the existing scratches and give the surface its mirror-like character. The layer was thought to have developed due to the very high temperatures

TABLE 7.1—Depth of the Plastically Deformed Layer. Annealed Polycrystalline 30 % Zn Brass by Manual Grinding/Polishing. Abrasive SiC paper SiC paper SiC paper Diamond Diamond Alumina, ␣-type Alumina, ␥-type

Grade μm / Grit 220 400 600 6 1 0–1 0–0.1

Scratches/ Dsb, μm 2.0/1.5/0.8/0.08/ 0.17 0.05/ 0.1 ¯ 0.03/-

Ds, μm 7.5 6.5 5.0 ¯ ¯ ¯

Dd, μm 77 43 22 1.0 0.7 2.5 0.7

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Fig. 7.2—Beilby layer, diagrammatic section of a calcite plate across the line of flow. The flowed material has completely filled up even the deepest scratches.31

attained at the points where an abrasive grain touches the specimen surface. This high temperature, being close to the melting point, would cause the material to melt or become very plastic. According to Samuels7 the layer, which Beilby considered amorphous and could be removed by etching, a phenomenon known to most metallographers, is simply deformed material still remaining on the surface 共see Fig. 7.3兲. When the original scratch and most of the deformation below the scratch is removed, the polished surface looks perfect. After etching, the deformed material is etched preferentially and the original scratch seems to reappear. This was supposed by Beilby, but what reappears is not the scratch, but an artifact created by the scratch. It could be called a scratch trace.

7.3.2 Influence of Polishing Abrasive, Cloth, and Fluid on Deformation Deformation will decrease with a lower abrasive grain size as shown in Table 7.1. The type of abrasive will play a role, diamond grains, especially on soft materials, will give more scratches than ␥-type alumina and silica; therefore, the small grain sizes of diamond 共1, 0, 25 ␮m兲 are not used for the final polishing of softer materials. Hard polishing cloths, without nap, will normally create more deformation than napped cloths; however, napped cloths might create other artifacts like relief and rounding of phases and edges. The polishing fluid is very important for lubrication, cooling, and removal of swarf. The lubrication is necessary to obtain a reduced friction between the cloth and

Fig. 7.3—Schematic drawing of Beilby Theory and Local Deformation Theory.7

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the specimen surface. The type of lubricant gives different lubricating effects, the oilbased lubricants giving the strongest effect, recommended for softer materials. The water-based type gives a medium effect suited for general purpose use, and the alcohol type gives a low effect suited for brittle materials. The oil-based lubricants also give a thin surface film on the cloth that minimizes the damaging effect from the cloth, important for soft materials. The cooling effect of the lubricant is important when many specimens at a time under a relatively high pressure are polished. The alcohol- and water-based lubricants cool most efficiently; the water-based type is preferred. In extreme cases, with many specimens with high pressure and a large disk diameter, a special disk cooling, usually with water, might be necessary to keep the temperature low enough. When using rigid composite disks 共RCD兲 it is important to have an efficient removal of swarf to prevent it from damaging the specimen surface. To a lesser degree, this is the case with hard cloths and even less on soft cloths.

7.4 Polishing Cloths Polishing cloths can be defined as substrates upon which a polishing medium is applied to perform a polishing process. The polishing cloth is supported by a rigid polishing disk made of metal or a polymer. As described in Section 7.2, the abrasive grain should, at least momentarily, be fixed by the cloth, making material removal possible. The fixing of the abrasive can be done in several ways, depending on the structure of the cloth. For hard cloths, the abrasive grains will be placed on the surface of the cloth, placed in hard fibers, securing a more aggressive attack, whereas on a soft cloth, the grains will penetrate into the nap of the cloth, and a less aggressive material removal will take place. Consequently, the cloth is a very important factor regarding material removal, but also the deformation developed during the process and the edge retention and relief are strongly influenced by the cloth. The term pad is often used for certain polishing cloths made of nonwoven material 共see below兲, but in the following cloth is used as the general term. A polishing cloth can be characterized through the following: • Material: All kinds of flexible materials can be used. The most used are: Chemotextiles, nonwoven materials, woven nylon, woven acrylates 共satin兲, woven silk, woven wool, a backing 共often cotton兲 with synthetic flocked nap. • Surface Structure: The material can be smooth, porous, perforated, woven, or flocked 共nap兲. The flocked cloths always have a nap, but other types also might have a napped surface. The nap normally will give the cloth a high resilience 共see below兲, but with certain cloths a high nap will lay down during use and create a compact, smooth surface with a relatively low resilience. The surface structure might strongly influence the polished surface 共see below兲. • Resilience: The resilience, the elasticity of the cloth in the vertical direction, dictates whether a cloth is hard or soft. All cloths can be compressed when subject to pressure from the specimen. A cloth having a low resilience is hard and a cloth with a high resilience is soft. A hard cloth, which can only be slightly compressed, will usually give a high material removal and create deep scratches and more damage to the specimen than a soft cloth. Two cloths, however, with the same low resilience can perform differently caused by the surface structure of the cloth. Figure 7.4 shows an aluminum/silicon specimen polished on a very hard cloth with an unsmooth, woven surface, shown in Fig. 7.6; the deformations in the Al/ Si surface are

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Fig. 7.4—AlSi material after polishing with 3 ␮m diamond suspension on a very hard cloth with a very irregular surface structure. The surface has deep scratches and strong deformation. The cloth is shown in Fig. 7.6. BF.

strong. Figure 7.5 shows the same specimen polished on a cloth with the same resilience, but with a relatively smooth, woven surface, shown in Fig. 7.8, the deformations are considerably reduced. A soft cloth with nap will normally have a relatively low material removal and create little deformation and small scratches. The nap will make an edge rounding. Also, because of the brushing effect 共the fibers of the nap brushing the specimen surface兲, a relief might develop if the specimen surface has phases of different hardness; the softer phase being preferably removed. Polishing cloths are fixed to the supporting grinding/polishing disk with a selfadhesive backing 共PSA兲 or through magnetism established by a steel foil integrated in the cloth 共see Section 6.7.1兲. Cloths can also be fixed by using a retaining ring that stretches the cloth over the disk. This often causes wrinkles of the cloth and should be avoided. Polishing cloths are supplied in the following diameters: 73 mm 共2.9 in兲, 102 mm 共4 in兲, 200 mm 共8 in兲, 250 mm 共10 in兲, 300 mm 共12 in兲, 350 mm 共14 in兲, and 400 mm 共16 in兲. For a table of available polishing cloths, see Section 13.2.2, Table 13.1.

Fig. 7.5—The same material as in Fig. 7.4 after polishing with 3 ␮m diamond suspension on a hard cloth with a smooth surface structure. The surface has considerably less scratches and deformation although the abrasive is the same. The cloth is shown in Fig. 7.8. BF.

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Fig. 7.6—Napless, very hard, woven, coated polyester cloth for fine grinding/rough polishing. SEM.

7.4.1 Edge Retention—Relief As described in Section 3.1.3 and Sections 6.6.2/6.7.7, edge retention is often very important and development of a relief should be avoided. The sections mentioned earlier and Figs. 6.15 and 6.16 describe how the resilience, the vertical flexibility of the preparation substrate, is decisive for the development of edge rounding and relief. It is evident that when using a cloth with a relatively high resilience as substrate, the risk of edge rounding and relief will increase strongly. This means that a good fine grinding, either on SiC grinding paper or on rigid composite disks, might be spoiled if the polishing cloths used for the following steps have a too high resilience or the polishing times are too long, or both. It is important that cloths with the lowest possible resilience to obtain a satisfactory result are used and the times are kept at a minimum. The characteristics regarding edge retention and relief will be discussed further for the single cloths below.

7.4.2 Cloths for Fine Grinding and Rough Polishing These cloths are all hard with very low to medium resilience. Although primarily used for fine grinding and rough polishing, some of the cloths can also be used for final polishing of medium hard and hard materials. They are typically used with diamonds from 15– 1 ␮m.

Fig. 7.7—Napless, hard, non woven, synthetic cloth for fine grinding/rough polishing. SEM.

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Fig. 7.8—Napless, hard, woven nylon, silk or acetate cloth for fine grinding/polishing. SEM.

Edge Retention—Relief All cloths for fine grinding and rough polishing, except the woven steel cloth, will have a low, often very low, resilience, which theoretically will cause an edge rounding of the specimen. In practice, however, if the preparation time is kept inside reasonable limits, the edge retention is high with these hard cloths, which, used with diamond as an abrasive, give a good flatness without relief.

Cloths Woven Steel: This is a cloth made of stainless steel wire mesh. The resilience is close to zero and consequently the edge rounding is very low. The cloth is used for fine grinding with 15– 6 ␮m diamond for hard metals, ceramics, and composites. Woven Coated Polyester 共Fig. 7.6兲: A napless, very hard, coated polyester cloth for use with 15– 3 ␮m diamond for fine grinding/rough polishing of metals, composites, ceramics, and hard metals. The resilience is very low giving very little edge rounding. Nonwoven Textile 共Fig. 7.7兲: A napless perforated/not perforated nonwoven cloth for use with 15– 3 ␮m diamond for fine grinding/rough polishing of harder materials and softer materials depending on the resilience of the cloth. On cloths with a certain resilience, an edge rounding may take place after prolonged polishing. Woven Nylon 共Fig. 7.8兲: A napless cloth for use with 9 – 1 ␮m diamond. Medium hard and suited for rough polishing and polishing of ferrous materials and cast irons to retain inclusions/graphite and maximize flatness. The very low resilience gives very little edge rounding. Woven Silk 共Fig. 7.8兲: A napless cloth for use with 9 – 1 ␮m diamond. Hard and suited for fine grinding/rough polishing and polishing of most metals, coatings, and plastics. The low resilience gives good flatness and very little edge rounding. Woven Synthetic Silk 共Acetate兲共Fig. 7.8兲: A napless cloth for use with 3 – 1 ␮m diamond. Hard and suited for rough polishing of most metals to maximize flatness with very little edge rounding and retention of hard phases.

7.4.3 Cloths for Polishing These cloths have medium to high resilience and are used for one or more polishing steps, an intermediate step or a final step. They are used with diamond in the 6 – 0.25 ␮m, mostly from 3 – 1 ␮m. Also, some can be used for oxide polishing 共see Section 7.5兲 for the final step. Some of these cloths are napless; some have naps of different height and structure.

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Fig. 7.9—Napless, medium hard, woven wool cloth for polishing. SEM.

Edge Retention—Relief The polishing cloths, having medium to high resilience and often a nap, will cause an edge rounding of the specimen, depending on the preparation time and force on the specimen. As a rule the polishing time should be kept as short as possible, with most time used on a napless cloth, which gives less rounding, and less time used on a napped cloth, often only for a short final polishing. The force on the specimen should be kept as low as possible, especially on napped cloths. In general, the napless polishing cloths will not develop a relief, but the napped cloth might develop relief if phases of different hardness are present in the specimen surface.

Cloths Woven Wool 共Fig. 7.9兲: A napless, soft cloth with medium resilience for use with 6 – 1 ␮m diamond. It is suited for polishing and fine polishing of minerals, glass, metals, composites, coatings, and polymers. An edge rounding might develop, but it will usually be acceptable. No relief will develop except in extreme cases. Synthetic Nap on Woven Backing 共Fig. 7.10兲: A cloth with a medium nap of flocked fibers on a 共cotton兲 backing for use with 6 – 0.25 ␮m diamond, alumina, and silica 共see Section 7.5兲. This cloth is for general usage for final polishing. The nap and backing give a very high resilience that will cause rounding of the edges of the specimen surface and often create a relief because of the brushing effect 共see Section 7.4兲. For these rea-

Fig. 7.10—Medium napped, soft, with synthetic fibers flocked on a backing, cloth for polishing. SEM.

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Fig. 7.11—Napless, soft, porous synthetic cloth for polishing with silica and alumina and for chemical mechanical polishing. SEM.

sons the cloth should only be used for a short time to establish the final specimen surface. Synthetic Nap on Nonwoven Backing: A soft cloth with a dense nap with high resilience to be used with 3 – 1 ␮m diamond. It is suited for one-step or final polishing of soft to hard ferrous and nonferrous metals. The dense nap gives relatively good edge retention in spite of the high resilience and no relief. Synthetic Porous Material 共Fig. 7.11兲: A soft, napless cloth with high resilience. The synthetic material 共neoprene兲 is chemically resistant and will take up the very fine alumina and silica suspension in the pores, and it is used with oxide suspensions 0.02– 0.05 ␮m 共see Section 7.5兲. The cloth is suited for the final step for most materials. The time should be short to avoid edge rounding. The risk for a relief is very little, but a certain relief might develop because of a chemical mechanical attack from the polishing medium. Woven Felt: A soft, napless cloth with very high resilience used for 9 – 1 ␮m diamond, alumina, and silica 共see Section 7.5兲. It is suited for rough and final polishing of hard metals, cast iron, and mild steels, preserving inclusions. The high resilience will cause edge rounding and possibly relief.

7.5 Polishing Abrasives The polishing abrasives are used in connection with a polishing cloth for the steps from rough polishing 共fine grinding兲 to the final polishing step. In general, diamond is used for all steps except the last step 共final polishing step兲. In case of harder materials, diamonds, down to 0.1 ␮m also cover the final step, but often, especially with softer materials and composites, a final cleaning step is made with an oxide, normally silica 共SiO2兲 or alumina 共Al2O3兲.

7.5.1 Diamond Suspensions Diamond suspensions are described in Section 6.4.

7.5.2 Diamond Spray Diamond spray is described in Section 6.4.

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Fig. 7.12—Alumina, agglomerated, the large agglomerates can be seen.

7.5.3 Diamond Paste Diamond paste is described in Section 6.4.

7.5.4 Alumina Alumina 共Al2O3兲 has been the classic polishing medium in metallographic/materialographic preparation. Earlier it was used for all polishing steps, often causing bad results, because the removal rate is very low. In modern preparation, alumina should only be used for the final polishing steps in grain sizes 1 – 0.05 ␮m. Alumina is available as suspensions and powders with two crystal types, alpha and gamma. The alpha crystal has relatively sharp edges giving the highest removal rates, whereas gamma is more rounded, causing a very small removal rate suited for the last polishing step. Both powder and suspension can be supplied in agglomerated and deagglomerated condition. In agglomerated alumina the particles will form agglomerates 共Fig. 7.12兲 because of the electric forces between the particles. These agglomerates will give a higher removal rate and might cause scratches in the specimen surface, although they are normally broken down during the polishing. In the deagglomerated alumina the material is treated to avoid the agglomerates so that only the single particles will be active 共Fig. 7.13兲, ensuring an ultrafine specimen surface. Alumina is available in grain sizes from 5 – 0.05 ␮m.

Fig. 7.13—Alumina, deagglomerated.

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Fig. 7.14—AlSi surface after polish with 3 ␮m diamond suspension, strong deformations in both matrix and silicon phase. BF.

Suspensions These are ready for use either in diluted or undiluted condition. In some cases the suspension is stabilized so that the alumina does not come out of suspension when not used. This is an advantage if used in automatic dispensing systems 共see Section 7.9.3兲. Alumina can be mixed with silica 共see below兲 to form special polishing suspensions.

Powders Powders have to be mixed with distilled or demineralized water to form a suitable suspension. In special cases, if water is not allowed for the preparation, the powder can be mixed with other fluids like glycerine or alcohol.

7.5.5 Silica Originally developed for the preparation of silicon wafers, colloidal silica 共SiO2 in a suspension兲 has gained ground in metallographic/materialographic preparation. The grain size is very small, 0.1– 0.02 ␮m, and the grains are almost spherical and softer than alumina, causing a very low mechanical material removal making SiO2 very well suited for the final polishing step. By comparing the microstructures of an aluminumsilicon alloy 共Figs. 7.14 and 7.15兲, the effect of silica can be recognized. The strong deformations from the 3 ␮m diamond polishing as shown in Fig. 7.14 are removed and both matrix and silicon are perfectly polished, see Fig. 7.15. For wafers and many other materials, the colloidal silica suspension works according to a chemical mechanical polishing 共CMP兲 process. The suspension, having a pH between 8.5 and 11, plays an important role in the material removal mechanism in CMP.32 The CMP gives SiO2 suspensions and suspensions based on SiO2 and other oxides, like iron oxide, an increased removal rate on ceramic materials and metal/ceramic composites and a number of metals 共see Section 7.12兲. A CMP can be established also when mild chemicals like hydrogen peroxide 共H2O2兲 and an ammonia 共NH3兲 solution are mixed into the suspension; this will be described under each material in the Material/Preparation Tables, Section 13.2.3. In this way, very soft and ductile materials can be mechanically polished to a deformation-free

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Fig. 7.15—The same material as in Fig. 7.14 but polished with colloidal silica after 3 ␮m diamond. The deformations are removed and the true structure can be seen. BF.

finish, avoiding electropolishing. Colloidal silica is available only as suspensions with a pH 8.5–11 and grain sizes from 1 – 0.02 ␮m. Attention: A colloidal silica suspension should not be allowed to dry on the polishing cloth, because it will then be unusable. The polishing cloth shall be carefully cleaned after use to avoid dried-in crystals which will cause scratching of the specimen surface. It can be of advantage to finish the polishing process by running up to 10 s only with water to clean the cloth and the specimen; otherwise the chemical attack might continue, resulting in etching of the specimen surface.

7.5.6 Other Oxides Magnesium oxide 共MgO兲, iron oxide 共Fe2O3兲共jeweler’s rouge兲, chromium oxide 共CrO兲, and cerium oxide 共CeO兲 are all polishing media which now are used very seldom. Al2O3 and SiO2 will in most cases do the same job and are much easier to work with.

7.6 Polishing Lubricants Polishing lubricants are described in Section 6.5.

7.7 The Metallographic/Materialographic Preparation Methods—Method Parameters As described above under sectioning, grinding, and polishing, a deformed or otherwise damaged layer inevitably is formed during the machining processes. The depth of this layer decreases with decreasing grain size of the used abrasive, and for this reason the specimen, in the preparation process, goes through a number of steps with each step removing the deformations from the previous step. The diagram in Fig. 1.7 shows the processes of both mechanical preparation and electropolishing. Figure 13.18 shows a typical process consisting of three stages, sectioning 共cutting兲, grinding, and polishing. The grinding stage and polishing stage both have two steps, plane grinding/fine grinding and rough polishing 共Polishing 1兲 and fine polishing 共Polishing 2兲. It can be seen that the deformations from the previous step are removed and the last step ends with very little or no deformation. The most critical steps are between cutting and plane

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grinding and between the last grinding step and rough polishing; this is especially the case when using SiC grinding paper for the last fine grinding step. It is important that the method is adapted to the specific material being prepared. For an overview of available methods refer to the 67 Traditional and Contemporary Methods covering most materials that is stated in Section 13.2.3. The following contains a brief description of the basic methods for most metals 共methods used for ceramics and other very hard materials are described in Section 6.3.2兲. The grinding stage: As described in Sections 6.6 and 6.7 this book discriminates between “Traditional” grinding based on SiC grinding paper and “Contemporary” grinding based on rigid composite disks 共RCDs兲. This gives two types of preparation procedures: The Traditional Methods 共T-Methods兲 based on grit P220 SiC paper for plane grinding and grits P320, P500, 共P1000兲 for fine grinding, and the Contemporary Methods 共C-Methods兲 based on SiC paper grit P220 for plane grinding, and one or two RCDs with 9 or 6 ␮m diamond abrasive for fine grinding. The polishing stage: At the T-Method the rough polishing step normally is on a hard, napless cloth with 6 ␮m diamond, a very important step for removal of the scratches and deformations from the grinding. In the C-Method the rough polishing step is often on a hard, napless cloth with 3 ␮m diamond for removal of the scratches and deformations from the RCD. For the T-Method, the rough polishing step is followed by a 3 ␮m diamond step on a hard, napless cloth followed by a final step on a soft, napped cloth with 1 ␮m diamond or on a soft, napless, porous cloth with alumina or silica. In the C-Method, the rough polishing step is followed by a final polishing as mentioned for the T-Method. The end result is to a high degree influenced by the consumables used in the preparation, as described earlier in this chapter, but also the parameters of the process play an important role. In the case of automatic polishing with the use of a specimen mover on a grinding/ polishing machine, all parameters, not associated with consumables, are controlled by the machine 共see Section 7.9兲. For manual 共hand兲 polishing, only the rpm of the polishing disk is a machine parameter.

7.7.1 RPM of Grinding/Polishing Disk This is typically in the range of 50– 600 rpm, but for certain machines with continuously variable speed, the rpm can be varied from close to 0 up to 1200 rpm. The rpm of the disk will, to a high degree, influence the relative velocity between specimen and grinding/polishing substrate. In principle this should be high to secure a high removal rate, but experiments have shown 共see Section 7.9.2兲 that at polishing, certain limits shall be observed, and for automatic polishing, 150 rpm is recommended. At grinding, however, higher velocities can be allowed corresponding to 300 rpm or more.

7.7.2 RPM of Specimen Holder To obtain the best results, the rpm of the specimen holder should be approximately the same as the rpm of the disk 共see Section 7.9.2兲. The direction, whether it rotates complementary to or contra to the direction of the disk is important 共see below兲. Most machines have rpm in the range from 3 – 300 rpm.

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7.7.3 Direction of Specimen Holder Most modern grinder/polishers work with the specimen mover rotating in the same direction as the grinding/polishing disk, complementary 共comp兲. This makes synchronous polishing possible 共see Section 7.9.2兲 securing the best polishing action, avoiding certain artifacts. If contra rotation 共counter rotation兲 is used, the removal rate is higher, the specimen mover and the disk rotating in opposite directions, but this can only be recommended for grinding, not polishing. Contra rotation is also used to keep the oxide suspension on the polishing cloth because then the specimen mover pulls the suspension towards the center of the polishing cloth, but according to polishing dynamics, as described in Section 7.9.2, the contra rotation has certain drawbacks, as mentioned above.

7.7.4 Force on Specimens The force 共load兲 on the specimens is important to obtain a satisfactory removal rate. At grinding the specific pressure shall be relatively high, in the range of 3 to 10 N / cm2 共4.35 to 14.5 psi兲共30 to 100 kPa兲, corresponding to a force of 20 to 70 N 共4.5 to 15.8 lbf兲 for a 30-mm 共1.25-in兲 specimen. The pressure will in certain cases influence the degree of deformation, especially for soft, ductile materials. Therefore, the pressure on the specimens shall be lower at polishing than at grinding, in the range of 14 to 40 kPa, corresponding to a force of 10 to 30 N 共2.3 to 7 lbf兲 for a 30-mm 共1.25-in兲 specimen. In principle, the specific pressure shall be the same for large specimens, but experience has shown that a maximum force of 50 N should be established on specimens of 40 mm 共1.5 in兲 in diameter and larger. This is to avoid an overheating and excessive wear of the polishing cloth. To compensate for the loss of material removal, the time can be extended from 1 to 4 min.

7.7.5 Process Time The duration of each step basically depends on the amount of material removed from the specimen surface 共stock removal兲. This, however, cannot normally be measured on most machines, and therefore the process time is used as an indicator. When grinding, the amount of material removed is so high that measurement is possible 共see below兲, but the removal rate at polishing is so low that measurement on a polisher is not possible. Only by measuring the time can a reproducible process be established. It should, however, be recognized that a specific preparation time does not guarantee that the necessary material is removed from the surface; this is only the case if the consumables used react like the consumables when the process was established. Also, parameters such as force should be correct to ensure reproducibility.

7.7.6 Stock Removal The whole preparation process is based on removal of material from step to step. The ideal way of working would be to measure the material 共stock兲 removed and stop the process when the preselected amount, corresponding to the deformations from the previous step, is removed. This is possible at the grinding steps, removing stock from 40 to 50 ␮m to several hundred micrometres per step. Grinder/polishers with measurement of stock removal are available in the market. At polishing, the stock removal is so low 共for example, 3 to 6 ␮m per 5 min兲 that it cannot be measured without high precision instruments, which are not usually available on grinder/polishers.

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7.8 Grinding/Polishing Equipment—Manual Preparation The basic polishing machine has a rotating turntable on which an interchangeable disk, covered with a polishing cloth, is placed. Normally the polishing process will consist of two to four steps, including rough polishing, polishing, and final polishing. In some cases, when the fine grinding has been done with the contemporary method 共see Section 6.7兲 only one polishing step might be sufficient. As described in Section 6.8, plane grinding, fine grinding, and polishing can take place on the same grinder/polisher only by changing the disk/disk surface used for each step. See Section 13.2.4 for the technique of manual 共hand兲 polishing. The grinder/polisher is a standard piece of equipment that is available in many models and sizes. Most models have one turntable for 200 mm 共8 in兲, 230 mm 共9 in兲共for SiC paper兲, 250 mm 共10 in兲, or 300 mm 共12 in兲 disks, one/two speeds or continuously variable speed, a water supply and a drain Figure 7.16 shows a grinder/polisher with mineral casting base. It will work with 200 and 254 mm 共8 and 10 in兲 disks 共platens兲 and is available in different models with one or two wheels 共turntables兲. One model has 150 and 300 rpm; another model has 30 to 600 rpm. A grinder/polisher with two turntables is also shown in Fig. 6.28. Very often the grinder/polisher is prepared for retrofitting of a semiautomatic specimen mover.

7.9 Grinding/Polishing Equipment—Automatic Preparation If we look at the typical specimen mover system for “automatic polishing,” the correct term would be “automatic preparation” because polishing is only part of the process. Also the word “automatic” needs explanation, taking into consideration that in most cases it expresses semi- or part-automation, meaning that only the basic process in each step is mechanized, all handling of specimen holders, change of disk, cleaning, etc., is done by hand. In some cases, however, the whole process is automated 共“fully automatic”兲 as described below. In the following the word “automatic” refers only to the basic process involving manual work. If the system is “fully automatic,” this will be described. The reason for using automatic equipment is that hand grinding/polishing is hard and, in the long run, overloads the hand and arm of the metallographer. Automatic preparation also ensures a better quality of the specimen through a uniform process that is reproducible. The dependence on the skill of the operator is reduced as well.

7.9.1 Machine Design The Englishman I. E. Stead, who continued the work done by H. C. Sorby, already invented a rotating specimen holder in 1900 for four specimens mounted on a movable arm so that the holder would sweep the rotating polishing disk. Many other principles have been suggested over the years, but the “specimen mover” with a number of specimens placed eccentrically on the grinding/polishing disk is dominating today. A supplement is vibratory polishing 共see below兲. The standard specimen mover system is a grinding/polishing machine with a rotating disk and a rotating specimen holder placed eccentrically on the disk 共see Fig. 7.17兲. The specimen holder or the individual specimens are pressed against the disk surface to obtain a grinding/polishing action.

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Fig. 7.16—Grinder/polisher, with mineral casting base for manual preparation and, as shown, with a specimen mover for semiautomatic preparation, 200/ 250 mm 共8 / 10 in兲 disks, 150– 300 rpm or 30– 600 rpm.19

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Fig. 7.17—Specimen holder placed eccentrically on the grinding/polishing disk.

For a specimen holder with several fixed specimens, these are fixed in suitable holes 共see Fig. 7.18兲 and during the operation, a central force is established pressing all the fixed specimens against the disk surface. The advantage of this system is a good flatness of the specimens, with the whole holder acting as a large “specimen” that avoids the angling of the holder in comparison to the disk surface 共see below兲. The disadvantage is the work 共fixing兲 involved, and the need for at least three specimens in the holder to keep the balance. In the event that only one specimen is to be prepared, “blind specimens” must be used. Also, the plane grinding may be prolonged to obtain that all specimens are in the same plane. The microscopic inspection of the specimens during the preparation process is rather tedious, having to put the whole holder on the microscope. The alternative is that specimens are placed in a holder plate and individually loaded and called “single specimen preparation” 共Fig. 7.19兲. The advantage is easy handling and being able to take out a specimen after every step of the preparation for inspection. The disadvantage is a tendency to “angling,” the specimen being only attacked in one direction, or “penciling,” the specimen being attacked along the periphery, especially when grinding on SiC paper 共see Fig. 7.20兲. In the first moments of the grinding the SiC grains will create a very strong pull in the specimen surface caused by the grains removing very much material in the first seconds 共see Section 6.6兲. The tendency will be to remove most material at the edge where the grains move into the specimen. As soon as an unevenness has been made, the specimen might start rotating

Fig. 7.18—Specimen holder with fixed specimens and central load.

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Fig. 7.19—Specimen holder plate with specimens placed in holes without fixation and individually loaded 共single specimens兲.

around its own axis and penciling will take place, or it might stay without rotation creating angling. Penciling and angling can be suppressed by working with as low specimens as possible and establish the smallest possible distance, d in Fig. 7.20, between holder plate and disk surface. Also, an exact guidance of the specimen in the holder plate will suppress the angling. The force on the specimens can be established through compressed air or by mechanical means. With central pressure the force is transferred through the center of the specimen holder. By individual load, a pressure foot will be lowered against each specimen 共see Section 7.7.4兲. A number of parameters should be controlled during the process 共see Section 7.7兲. On simpler systems, the operator sets the rpm of the disk and the force. The rpm of the holder is mostly fixed, and in some cases the direction, complementary or contra, can be set. The operator will stop the machine after a certain period of time. On more advanced systems all parameters are controlled through a microprocessor and programmed before the start of the process. This makes storing of programs 共methods兲 possible so that a method, once developed, can be reused whenever necessary. The microprocessor also may control other parameters such as dosing of abrasive suspension and lubricant 共see Section 7.9.3兲. The fully automatic systems are based on the above; only several preparation steps including cleaning and drying are programmed as a process. This means either the disks are changed automatically during the process or a certain number of disks are available in the machine 共see Section 7.9.3兲.

Fig. 7.20—Schematic drawing of a single specimen placed in the holder plate on a grinding/ polishing disk. If the distance d is too long, angling or penciling will take place at grinding on surfaces with fixed abrasives.

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Fig. 7.21—Polishing dynamics for a specimen holder eccentrically placed on a grinding/ polishing disk. Velocity vectors for two specimen holders, 30 rpm and 149 rpm are shown.

7.9.2 Polishing Dynamics As described above, the most common way of automatic polishing is placing the specimens in a specimen holder which rotates eccentrically on a polishing disk 共Fig. 7.21兲. As the dynamics between grinding/polishing disk and specimen holder have a certain influence on the preparation result, these dynamics shall be briefly described. It is evident that the relative velocity between the surface of the polishing disk and the surface of the specimen will depend on three factors: rpm of the disk, rpm of the holder and direction of rotation. Two systems that are quite common can be compared. 共1兲 Polishing disk: Specimen holder: Complementary 共comp兲 rotation 共2兲 Polishing disk: Specimen holder: Complementary 共comp兲 rotation

150 rpm 30 rpm 150 rpm 149 rpm

Comparing the velocity vectors in Fig. 7.21, we see that for system 共1兲 the velocity vectors are one-sided, causing a nonuniform material removal. This phenomenon is even more pronounced during contrarotation. In system 共2兲 the vectors cover all directions causing a uniform removal. This means that certain conditions, the optimum dynamic conditions 共ODC兲 can be defined.33 ODC will be when the relative velocity is constant during a full revolution of the specimen holder 共synchronous polishing兲, as can be seen in 共2兲共Fig. 7.21兲. If the rpm of the grinding/polishing disk is higher than the specimen holder, ODC is not fulfilled and the preparation might result in having artifacts like comet tails 共see Section 13.6兲.

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Fig. 7.22—Automatic grinding/polishing system for one specimen at a time.19

7.9.3 Semiautomatic and Fully Automatic Systems Considering that automatic preparation is useful, even with an output of very few specimens, semiautomatic and fully automatic systems can be considered very important. They are supplied in different sizes, catering from one to six specimens or more at a time. The tendency is to include as many parameters as possible in the automatic process, still maintaining the manual change of the disk and handling 共cleaning兲 of the specimen holder with the semiautomatic systems. With the microprocessor a programming of all parameters is possible.

Small Semiautomatic Systems The small systems will handle one to three specimens at a time on a 200 or 150 mm 共8 or 10 in兲 disk. The load is mostly supplied by a spring or a weight. In some cases a timer controlling the process is available. Figure 7.22 shows a grinder/polisher for low volume semiautomatic preparation, preparing one specimen at a time. Figure 7.23 shows a specimen mover for low volume

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Fig. 7.23—Specimen mover for one to three specimens, 8 rpm and force 2 – 20 N.20

semiautomatic preparation mounted on a grinder/polisher, preparing up to three specimens at a time. Specimens with very low deformations especially suited for EBDS 共see Section 7.10兲 can be produced.

Medium to Large Semiautomatic Systems These systems carry the work load in most laboratories. They work with 250, 300, 350, 400 mm 共10, 12, 14, 16 in兲 disks and specimen holders for six specimens or more, and mostly rpm, force, and process time can be controlled and preset 共see Section 7.7兲. A dispensing system 共see below兲 may also be included in the controls so that the total preparation sequence including dosing of abrasive and lubricant can be programmed. The possibility of a permanent storage of programs for different materials might be included as well, and newer systems allow for connection to a local net 共LAN兲 and for establishment of databases with preparation methods. It is even possible to download preparation methods from the Internet and use them directly. Figure 7.24 shows a semiautomatic system consisting of a number of grinder/ polishers, specimen movers and a dosing unit. The system is microprocessor controlled allowing for connection to a local network 共LAN兲, sharing preparation methods with other users.

Dispensing Apparatus Dispensing 共dosing兲 of abrasive and lubricant is part of the preparation process. Basically, the operator can perform this before and during the process, but especially adding lubricant during the process that ties the metallographer to the machine is against the idea of automatic preparation. Therefore, most semiautomatic systems have a lubricant-dispensing 共dosing兲 unit connected to the system, in this way adding small amounts 共adjustable兲 in regular intervals 共adjustable兲 to the disk surface during the process. To obtain a constant removal rate it is an advantage to apply the abrasive, preferably as a diamond suspension, during the process. This can be done with dispensing

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Fig. 7.24—Modular preparation system with single and central pressure, available in three different disk sizes, 200-, 250-, and 300- mm diameter. Equipped with an automatic dosing unit and programmable with preparation methods.20

共dosing兲 units available for one or several bottles of suspension/lubricants. An oxide polishing suspension can also be part of the suspensions to be applied, but this needs a water cleaning system as part of the dispensing unit. The more advanced semiautomatic preparation systems include the control of a dispensing unit.

Stock Removal Stock removal 共controlled material removal兲 is sometimes included in the control systems covering the grinding steps 共see Section 7.7兲.

Fully Automatic Systems These systems include all tasks of the preparation process. All parameters for the process are programmed and stored permanently before the start, and the automatic process includes: grinding, dispensing of abrasive and lubricant, cleaning and drying of specimen holder after every step, change of grinding/polishing surface, and polishing in several steps. In some cases stock removal can also be programmed. The goal is to supply a specimen ready for the microscope. In some cases the specimen holder with specimens is plane ground on another machine before going into the automatic system. In other systems, the plane grinding is part of the automated process. Figure 7.25 shows a fully automatic system that combines the function of a semi-

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automatic grinder/polisher, a dispensing system, an ultrasonic cleaner, and specimen dryer in one compact unit to be placed on a tabletop. It has single and central pressure, and it is programmable with permanent storage of methods.

Vibratory Polishing Systems Vibratory polishing is an alternative to the specimen mover described previously. It was originally developed for use in the hot cells preparing radioactive materials. The reason was the very simple design without rotating parts, cutting maintenance down to a minimum. Vibratory polishing is based on the principle of a vibrating plate in the shape of a bowl. A number of specimens, typically up to twelve, are mounted in weights and placed face down on the polishing cloth, covering the plate. The bowl shape takes care that a suspension, mostly Al2O3 or SiO2, stays on the cloth. The vibration has both a vertical and horizontal movement, normally established with an electromagnet. This means that the single specimen, caused by the inertia, moves slowly along the periphery of the bowl, in this way being polished through the movement between cloth and specimen. By adjusting the amplitude of the vibratory movement, the speed around the bowl can be controlled and set according to sample size and weight. The polishing action is very low, suited for sensitive materials making a scratch-free surface possible with very low deformation. Due to the low removal rate, a normal final polishing step will take several hours in which the apparatus can be left unattended. Figure 7.26 shows a heavy duty vibratory polisher with variable settings.

7.10 Special Preparation Techniques 7.10.1 PCB Coupons Printed circuit boards 共PCB兲 are often metallographically/materialographically inspected to ensure the quality of the metal layer in the holes of the board. For this purpose a so-called coupon is made 共see Fig. 3.17兲. PCB coupons to be tested according to the American standard IPC-TM-650 should be prepared so that the prepared surface is exactly through the middle 共diameter兲 of the holes to be inspected. This is usually done by mounting several coupons on two precision pins using two reference holes 共see Section 3.11.5 and Fig. 3.17兲. The two precision pins can be used as contact surface in a special specimen holder so that the coupons are placed exactly in relation to the holder. In this way the target 共the middle of the inspection holes兲 can be reached by using a number of adjustable stops on the holder. The stops are calibrated according to the surface on which the pins are resting, in this way securing that the process stops before the target is reached. Normally a rough SiC grinding paper is used for the first step, the grinding being stopped 100 to 200 ␮m from the target. By readjusting the holder the next step with a finer SiC paper will stop very close to the target. According to the type of PCB, the grinding steps shall be followed by one or more polishing steps. These steps are made without stops because the material removal at polishing is very low, minimizing the risk of removing too much material from the PCB. For a preparation process, see Method T-27 in Section 13.2.3.

7.10.2 Microelectronic Materials—Nonencapsulated Cross Sections Microelectronic materials are cross-sectioned to a specific point 共target兲 for both light microscopy and scanning electron microscope 共SEM兲 examination.

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Fig. 7.25—Fully-automatic, microprocessor controlled grinding/polishing system, with built-in dispenser, ultrasonic cleaner, and specimen dryer. Programmable, with permanent storage of methods.19

Cross sections serve two main functions:34 Cuts through representative structures within an IC show relationships of layers and features, such as step coverage, interfaces between layers, and possibly embedded defects or voids. • Precision cross sections through specific defects often lead to the process step or mechanism that produced the defect. When applicable, nonencapsulated cross-sectioning is simpler and faster than the classical encapsulated method. Results of nonencapsulated cross-sectioning are more suitable for viewing in a scanning electron microscope. The passivation layer of the IC provides sufficient encapsulation of malleable metallization to prevent smearing. Rounding of the front edge is avoided by using hard, flat grinding and polishing surfaces. •

Tripod Fixture—The Process Cross sections can be prepared with the relatively simple tripod fixture where the specimen is the third leg on a fixture 共see Fig. 7.27兲. Cross sections can also be prepared on

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Fig. 7.26—Heavy duty vibratory polisher, horizontal vibratory movement, with variable settings.19

semiautomatic systems and fully automatic systems; both are commercially available. In the following only the use of the tripod fixture will be described 共see also Material/Preparation Tables 22, Section 13.2.3兲. SiC paper 共600 grit兲 was used originally to grind to within 20 to 30 ␮m of the target. Polishing from that point was accomplished solely and slowly on a glass disk.34,35 However, the need for faster throughput and the introduction of hard tungsten plugs necessitated new polishing media and techniques. The procedure described below using a hand-held tripod fixture is basic, simple, and fast. It produces excellent results that can be imaged on either standard or field emission SEMs. The grinding procedure described involves several short steps with Al2O3 and diamond lapping film starting with relatively coarse grits. Satisfactory results can be obtained by grinding longer with fewer steps, but the procedure will be tedious if the overall grinding time is increased by using fine grain sizes to remove material slowly. Additionally, if the grinding time is excessive, the material removal rate may decrease as grinding/polishing media wear and it is difficult to judge whether enough material has been removed. Cross sections wider than the 5 by 5 mm 共0.20 by 0.20 in兲 in width will require significantly longer grinding and polishing times. The use of worn out grinding media should be avoided; fresh, finer grain size grinding/polishing media may have a faster removal rate than coarser, worn media. Even if a cleaved edge is close to the desired final line such that no grinding is required, a brief grinding on grit P4000 共US grit 1200兲 is recommended to make a flat surface. Grind only as necessary to create a flat surface, even if a part of the surface remains untouched. Jagged edges on a cleaved sample, if not removed, will scratch away the Al2O3 or diamond from the film.

Equipment and Consumables A tripod fixture with the specimen mounted on a sample mount 共paddle兲共see Fig. 7.27兲 is used by hand on the rotating grinding/polishing disk of a grinder/polisher with a 200 mm 共8 in兲 disk and variable speed, preferably 10 to 150 rpm 共see Section 7.9兲.

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Fig. 7.27—Tripod fixture, the specimen is placed as one of three “legs” of the hand held-holder.

A stereomicroscope and a metallurgical microscope with measuring abilities are required to check the progress of the preparation process. Sample mounts are used for carrying the sample 共specimen兲 during the preparation steps and for the analysis in SEM. The process involves grinding paper and lapping films, Al2O3 and diamond, and for polishing diamond suspension and a polishing cloth. Dry nitrogen 共or a supply of aerosol cans兲 is required to blow the specimens dry.

Preparation, See also Method C-22, Section 13.2.3 Sectioning can be done on a precision cut-off machine with a diamond wheel 共see Section 2.5兲. The desired cross section target should be within 50 ␮m of one edge. The silicon piece is then attached to a sample mount such that the edge containing the target is parallel to and extending over the edge of the sample mount 共cantilever fashion兲, placing the specimen on a hot sample mount 共125° C 共250° F兲兲 using wax, as shown in Fig. 7.28. Grinding takes place in three to four steps. The purpose of grinding is to rapidly achieve a surface, 1 ␮m away from and parallel to the desired cross section line 共target兲. The surface left by grinding, later to be polished, should be flat and scratches should be no greater than those caused by 1 ␮m Al2O3 or diamond particles on Al2O3/diamond films. The grinding procedure typically requires less than 15 min including inspection time. In Method C-22 the total preparation process is described. It is important that the specimen is adjusted so that the ground surface is parallel to the cross section line 共target兲. The time in minutes is not stated at the grinding steps, but the distance remaining to the target. This is to ensure that all deformation from the previous step is removed and to ensure that the target is not reached in a too early step. Polishing is used when a very fine finish is wanted. Microelectronics with metal systems of Al 共no tungsten兲 or gold 共no tungsten兲 are polished using a 0.05 ␮m Al2O3 lapping film or a soft, napped or napless, porous cloth using colloidal silica as the abrasive. In case of metal systems with Al/ W and Au/ W, polishing is done with a napless, hard, woven synthetic cloth and 0.1 ␮m diamond suspension or a napless, soft, porous cloth with 0.1 ␮m diamond suspension mixed in a 50:50 solution with colloidal silica.

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Fig. 7.28—Microelectronic specimen mounted on a sample mount for a tripod fixture.

7.10.3 Microelectronic Packages—Table 7.2—Target Preparation Electronic and microelectronic assemblies are complex material composites. The materials used are dissimilar in their chemical composition, their crystal structure, and their microstructure. Of technical importance for the qualification of the components are interfaces, grain boundaries and phase boundaries as well as heterogeneous precipitations. Imaging and analysis of the microstructure is a prerequisite for estimating the quality of a component. Further criteria for qualification, from the materialographic point of view, are inclusions, contaminations, pores, cracks, holes, as well as the evaluation of contours, e.g., the wetting angle of a soft solder connection.36 Due to the close packaging of electronic and microelectronic devices with many various materials within a small volume, microstructural examination is faced with the problem of simultaneously imaging different materials that have very different properties. Specimen preparation therefore involves the simultaneous processing of hard, often brittle materials and soft materials exhibiting plastic deformation. The materials most used in advanced integrated circuit packaging and interconnection technology, their use and hardness 共HU, see Section 21.5兲 are listed in Table 7.2.37 Each of the materials stated in Table 7.2 has its specific properties and, as can be seen, the hardness is very different and often the materials are brittle. This must be taken into consideration during the materialographic preparation; each individual step from cutting through grinding to the final polishing step is of significance. Mistakes made in the first stages of preparation can only be corrected during the subsequent steps with considerable difficulty or not at all. For each step the rate of material removal and the deformation layer which remains are important factors. The preparation parameters used 共grinding surface, type of abrasive, grain size, lubricant兲 must be carefully selected on the basis of the physical properties. The general rules for the preparation of solid materials are that soft and medium-hard materials should be plane ground using SiC grinding papers, whereas hard materials require resin-bonded

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TABLE 7.2—Materials Used in Electronic and Microelectronic Devices and Interconnections.

Material Al2O3 ceramic Silicon Nickel-phosphorus (NiP) Kovar (FeNiCo) Invar (FeNi) Aluminum (Al) Copper-silver (CuAg) solder Gold (Au)

Tin-silver (SnAg) solder Copper (Cu) Epoxy-fiberglass sheet Tin-lead (SnPb) solder

Common Applications in Mounting and Connection Technology Carriers (hybrid technology), body of components Semiconductors, transistors, ICs Resist layer, metallization Lead frames, circuit board core Lead frames, lead wires Housing, heat sinks, capacitor foils Solder (brazing) Surface finishing layers, (connectors, solder, adhesive and wire bond contacts) Soft solder Metallization on circuit boards, lead frames Circuit board material Soft solder

Universal Hardness (HU) 17000 9300 4000 1900 1800 1300 1100 500

300 300 280 230

disks with fixed diamond grains or rigid composite disks 共RCDs兲 with added diamonds. Very often for the devices described herein, both extremely hard and very soft materials must be prepared at the same time, and in such cases the preparation must be based on a compromise. The goal of the preparation is to obtain a flat specimen without relief between the different constituents and good edge retention, while at the same time avoiding deformation and other artifacts of the soft and brittle constituents. If only SiC grinding papers are used for grinding of hard materials, then edge rounding and relief will set in at an early stage. Plane grinding and the first steps of fine grinding should be done with the hardest possible abrasive suited for the hardest materials in the specimen and always using the finest grain size possible. Often SiC paper should not be used with a grit coarser than P500 to avoid damage to the brittle materials in the specimen, and during both grinding and polishing the pressure should be kept low to avoid damage.36 In the Material/Preparation Tables 19–26, Section 13.2.3, eight methods are indicated covering the preparation of different electronic components. To be able to select the method best suited for a given component, it shall be analyzed before the preparation starts to be able to decide on the best method and how the preparation shall be performed.

Inspection and Location of Fail Site—Target Preparation Before the preparation starts, the structure of the assembly should be studied by visual macroscopic methods to decide on the materials involved and to locate critical sites and the locations of both obvious and possible defects to be marked. Typical fail sites 共targets兲 include: poor solder joints, cracks in components, or defects in the circuit board material. These faults are then investigated more closely using other techniques

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like radiography, ultrasonic imaging, fine and gross leak testing, and die penetration. The orientation of the plane of preparation will depend upon the orientation or the features to be imaged and is often marked on the assembly plan. If the fail site 共target兲 has been located then this will determine the plane of preparation, often starting with the sectioning close to this plane. Special apparatus for target preparation is available in the market.

Sectioning and Mounting „Encapsulation… Sectioning must be done so that the site of interest is not damaged by deformation or input of heat. Therefore, very often the device is mounted 共encapsulated兲 before the sectioning takes place. Encapsulation shall be accomplished with only a low development of heat and the resin shall be able to fill out all cavities without shrinkage. This means that an epoxy with a low viscosity should be used, preferably under vacuum so that an impregnation takes place 共see Section 3.10兲. It is very important that the specimen is cleaned very effectively in acetone, preferably using ultrasonics before the encapsulation. After cleaning, the specimen should only be handled with a pair of tweezers and dried with N2 or absolutely clean air, not normal compressed air. Sectioning and mounting are described in detail in the Material/Preparation Tables 19 to 26.

7.10.4 EBSD Electron backscatter diffraction 共EBSD兲 has gained ground in recent years as an accessory to a scanning electron microscope 共SEM兲. The main advantage of EBSD is the possibility to link morphology 共grain size and shape兲 with crystallographic features 共phase, orientation, disorientation兲 on the microscopic scale, but still in a representative specimen area.38 The preparation is much simpler than for thin foils for TEM 共see Section 8.6兲, but more demanding than that for normal SEM. The information depth of EBSD is very low, in the range of 20– 370 nm depending on material, SEM, etc. This means that the surface of the specimen shall be without the thin distorted layer that normally exists after a mechanical polishing 共see Section 7.3兲. This can be obtained by etching, but etching should often be avoided for EBSD. For certain materials electrolytic polishing can give a deformation-free surface, but for many materials like ceramics, heterogeneous materials, etc., mechanical preparation is the only possibility to obtain a flat and distortion-free surface. For this reason the standard grinding/polishing process shall be adjusted, especially with regard to the last polishing step. In principle, the normal method used for a specific material can be used with special attention to the last polishing step using silica, which often is prolonged. A long preparation time using silica as an abrasive might give an unwanted relief, and therefore polishing cloths must be chosen very carefully.

Specimen Mover Systems The most used specimen mover 共standard system兲 for normal metallographic/materialographic preparation has a specimen holder rotating eccentrically on the grinding/ polishing disk 共see Section 7.9兲. The preparation methods described in Section 13.2.3 are based on the use of this standard specimen mover, normally operating with 150 rpm 共grinding/polishing disk and specimen holder兲 and a force per specimen not lower than 5 N 共1.1 lbf兲. This system will give acceptable results for EBSD for very hard materials like ceramics, possi-

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bly using chemical mechanical polishing 共CMP兲共see Section 7.12兲. For most materials, however, it is not possible to obtain a distortion-free surface after the last step, and this step either has to be prepared on a special slow moving specimen mover or by vibratory polishing. Specimen movers with very low rotation and force per specimen are commercially available. The rpm of both the disk and specimen holder can be adjusted to a relative velocity close to zero 共see Section 7.9.2兲 and the force on the specimen down to close to zero. This means that all metals can be prepared for EBSD in a reasonable time, often using CMP, see under the specific materials in Section 13.2.3. CMP is also needed for hard materials like certain ceramics. For specific preparation data for a high number of materials see Ref. 38.

Vibratory Systems Vibratory polishing normally gives good results for EBSD; the main drawback being the very long preparation times, although the vibratory polisher can work unattended. If vibratory polishing is used for all steps including grinding, a high surface waviness can be observed and due to the long polishing times a relief can develop. Therefore, vibratory polishing should be limited to the last step, having done the previous steps on the standard specimen mover or the slow specimen mover described above.38

7.11 Field Metallography/Materialography—Nondestructive Mechanical Preparation Field metallography is, as the term indicates, used in the field, often called in situ or on the spot. It is based on the grinding and polishing processes described above; portable apparatus is available that is able to prepare a small area nondestructively. Field metallography is used on large parts, steam pipes, etc., to be able to check the microstructure without destructing the work piece. Very often it is not possible to analyze the prepared spot and a replica is taken 共see below兲. The preparation methods and etching procedures to be used can be seen from Table 11.1 and Section 13.2.3. Many materials like steel, aluminum, and titanium are very well suited for electrolytic polishing using a portable electropolisher 共see Section 8.5兲.

7.11.1 Portable Grinder/Polishers These are available with a hand piece with a flexible rotating disk upon which a small piece of grinding paper or polishing cloth is placed. This apparatus can be supplied from the mains or battery operated. The normal preparation process in a number of steps is employed and normally, after etching, the prepared spot is analyzed with a portable microscope to ensure that the microstructure is acceptable for further examination. Following this, a replica is made. This replica is taken to the laboratory for examination. Often the grinder/polisher is used for the preparation of a spot that is finally electropolished/etched to obtain the microstructure 共see Section 8.5兲.

7.11.2 Replication Replication is a very important part of nondestructive preparation. Replication is a nondestructive procedure that records and preserves the topography of a materialographically prepared surface as a negative relief on a plastic film or other medium 共rep-

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lica兲. See also the ASTM Standard Practice for Production and Evaluation of Field Metallographic Replicas 共E 1351兲共Section 12.4兲. The replica material shall have a number of characteristics: • All features present on the surface that was replicated shall be accurately reproduced. • Simple and reproducible handling. • High stability and strength. • Flexibility so that replica can be made on curved surfaces. Replicas should be made either using a piece of plastic 共acetate兲 film or a fast curing silicone rubber-based material.

Plastic Film The film or foil is 12 by 18 mm 共0.5 by 0.75 in兲 in size. Two methods can be followed which are described in Section 13.4.3.

Silicone Rubber The silicone rubber-based material used is a two-component silicone rubber that is available in different types according to the specific purpose. The compound is supplied in cartridges that are mixed and dispensed on the prepared surface using a special hand-operated gun. The silicone rubber is very flexible, suited for curved surfaces, inside tubes, etc. The material is also very suitable for engineering inspection applications like microcracks, wear marks, corrosion marks, etc. For use of silicon rubber, see Section 13.4.3.

7.12 Chemical Mechanical Polishing Chemical mechanical polishing 共CMP兲 has been highly developed for the preparation of silicon wafers, but CMP is also used with advantage for other materials. In CMP, also called etch polishing or attack polishing, the specimen surface is attacked both mechanically 共by an abrasive兲 and chemically at the same time.32 Normally an abrasive suspension with an in-mixed chemical substance is used. Material removal occurs as a consequence of a combination of the chemical reaction of the chemical with the specimen surface material and the continuous removal of the reaction materials by the abrasive. Because of the removal of the reaction products, even chemical solutions that typically would not attack a given material will have an effect because the passivating layer is constantly removed. CMP is established either by using suspensions of silica 共SiO2兲 often with a pH between 8.5 and 11 or alumina 共Al2O3兲, with a pH between 3 and 7, or by mixing a chemical solution, often an etchant, with the oxide suspension. CMP, using a very fine abrasive like silica with a grain size of 0.02/ 0.05 ␮m, and a relatively weak chemical attack, will create surfaces almost without deformation and scratches. This means that CMP is very well suited for the final polishing step for most materials, creating a clean surface. Especially in soft and ductile materials this is an advantage. The polishing will take place on a relatively soft, porous polishing cloth, and therefore the time shall be limited to 0.5 to 1.5 min. Aluminum, refractory metals, Ti, and other metals can be polished with silica with or without an added chemical. Also, ceramics and other materials with high abrasion

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resistance are suited for CMP; both acidic alumina suspensions and basic silica can be used. For some materials like Ti and most Cu alloys, the final polishing step can be made using a silica suspension with the addition of hydrogen peroxide and ammonia solution. Ferrous metals and Ni-based alloys can be polished with acidic alumina. If the pH should be lowered, oxalic acid can be added, and if the pH shall be raised a chemical like potassium hydroxide can be added. For solutions used for the specific materials, see the Material/Preparation Tables, Section 13.2.3. With the modern advanced methods of preparation, CMP is mostly limited to the suspensions and solutions mentioned earlier. CMP, however, can be performed with a very high number of chemical solutions, mostly etchants.2,9

7.12.1 Protection—Corrosion at CMP When using the chemical solutions recommended in this book 共see Section 13.2.3兲 the corrosive attack on equipment and accessories is minimal. In the case of suspensions mixed with stronger chemicals 共acids兲, care should be taken to protect equipment and persons working with the mixture. Also, only synthetic polishing cloths made for CMP should be used.

7.13 Thin Sections For certain materials such as minerals, ores, ceramics, and plastics, the use of reflected light for microscopic examination is not always satisfactory. By using thin sections with a thickness of 20– 35 ␮m 共down to 7 – 10 ␮m at plastics and polymers兲 it is possible to examine the specimen in transmitted light, and if the thin section is polished, also in reflected light. To make a thin section a high amount of material must be removed by cutting, lapping/grinding, and polishing. The process is time consuming and extreme care should be taken not to make changes in the material of the thin section. Below follows a short description of thin section preparation for petrographic/ ceramic materials and for plastics/polymers.

7.13.1 Thin Sections of Petrographic/Ceramic Materials The preparation of thin sections can be done on machines and consumables available in the market. In the following a method as shown in Fig. 7.29 is described. Often impregnation of the material is needed before the cutting or the preparation, or both, can take place. For this and for a further description of the cutting, lapping, and polishing see Material/Preparation Tables 共M/P T兲 39 and 40 for petrographic/mineralogical materials and M/P T 02–06 for ceramics. 1. The specimen to be sectioned is selected often from a larger piece. 2. The specimen is sectioned normally with wet abrasive cutting using a diamond metal bond cut-off wheel. The size of the specimen depends on the size of the glass slide used 共see below兲. 3. For minerals, one side of the specimen is lapped in two steps with SiC powder, grit P220 and P1000, on a cast iron disk to obtain a plane surface; normally this is done in a special specimen holder plate on a semiautomatic grinder/polisher. For ceramics, grinding and polishing of one side are made as described in M/P T 02–06.

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4/5.

A glass slide 27 by 46 mm, 28 by 48 mm or 30 by 45 mm is ground to a given thickness, e.g., 1.164 mm on a special machine with a diamond grinding wheel or lapped in a holder as described in No. 9 below. 6. The specimen, with the prepared side towards the glass, is glued to the glass slide under vacuum using epoxy. 7. The surplus material of the specimen is removed by cutting with a diamond cut-off wheel to a thickness of about 0.5 mm 共0.02 in兲. 8. The mineralogical thin section is ground down to 80– 100 ␮m on a special machine with a diamond grinding wheel, or only lapped as described under No. 9. Ceramics are ground according to M/P T 02–06 to a thickness of approximately 80 ␮m. 9. Mineralogical materials are lapped with SiC powder on a cast iron disk in a special holder on a semiautomatic grinder/polisher so that the finished section has a thickness, including the resin layer, of e.g., 30 ␮m. The holder has built-in sticks of boron carbide or diamond so that the process stops when the section has the thickness that is wanted. If the thin section has been ground down to 80– 100 ␮m on a special machine, lapping only with grit P1000 SiC powder is needed. If all material shall be removed by lapping, two steps are used, grit P220 and grit P1000. Ceramics are fine ground and polished down to 5 – 30 ␮m depending on the ceramic. The preparation procedure follows M/P T 02–06. 10. If the thin section is to be polished, this is done in a special holder so that the final thickness is in the range of 20– 25 ␮m. The finished thin section can now be examined in reflected light. For examination in transmitted light, a cover glass shall be placed on the polished surface.

7.13.2 Thin Sections of Plastics/Polymers Thin sections are made when plastics and polymers are required to be examined by transmitted light or contain hard inclusions. Most often unfilled plastics and polymers can be examined in the form of thin microtome slices 共see below兲. If carefully prepared, the thin sections made by grounding/polishing will be less damaged than a thin microtome section so it is to a high degree the purpose of the examination that decides which method to use. In the following a method for preparing thin sections39–41 is described that is based on the methods stated in Material/Preparation Tables 64 and 65, Section 13.2.3. 1. A specimen with good edge retention is made. 2. A thin slice is cut from the prepared side of the specimen. See Material/ Preparation Tables 64 and 65. 3. The prepared side of the slice is glued to a glass slide with an adhesive while not disturbing the specimen material and without air bubbles. 4. Grind down manually or in a holder to about 20 ␮m from the required thickness. 5. Fine grind to about 5 ␮m from the required thickness. 6. Polish with 3 ␮m diamond and finish with alumina, step P 3 in Method C-64 to a thickness of 10– 15 ␮m. For examination in transmitted light, a cover glass is placed on the polished surface; this is not needed for reflected light. As mentioned above, thin sliced specimens of plastic and polymers can be made with a microtome, where the slice is cut in a thickness of 3 – 30 ␮m, generally around 10 ␮m. For further information, see Refs. 40, 41 and Section 7.14.

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Fig. 7.29—Method for preparation of petrographic/ceramic thin sections. 1. Sampling. 2. Cutting of a specimen. 3. Lapping of the specimen. 4./5. Grinding/lapping of glass slide. 6. Cementing of specimen to glass slide using epoxy under vacuum. 7. Cutting of surplus material. 8. Grinding on a special machine of thin section, or lapping as shown in 9 down to 80 ␮m 9. Lapping of thin section in a special holder down to e.g., 30 ␮m 共section and resin layer兲. 10. Polishing in a special holder down to approximately 25 ␮m. 11. The finished thin section.

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7.14 Microtomy—Ultramilling Both microtomy and ultramilling are mechanical preparation processes comparable to grinding and polishing, and made on relatively sophisticated equipment. In most cases the specimen, soft metal, or other soft materials can be examined without further preparation. Microtomy is developed for preparation of biological specimens for transmitted light. In this case the thin section is made by moving the specimen with a controlled feed into a fixed tool 共knife兲. In this way a section of a thickness of 0.5 to 60 ␮m can be made, suited for examination in transmitted light. This method can be used for preparation of plastics as described in Section 7.13.2 and for preparation of bone, teeth, and other organic materials. When used for metals the microtome produces a surface comparable to a plane grinding or polishing for examination in reflected light. To justify the use of a microtome and ultramilling 共see below兲 the finished surface should be of a high quality, ready for the microscope. Soft, nonferrous metals up to a hardness of 150 HV can be prepared on very stable microtomes using special knives with hard metal or diamond edge. Microtomes are commercially available. In ultramilling the specimen surface is prepared not with a knife but with a rotating milling tool. The specimen is placed on a sledge traveling underneath the milling head consisting of a vertical, rotating spindle equipped with a diamond cutting tool. The rotational speed of the spindle is adjustable between 500 and 3000 rpm. The feed between specimen and milling tool can be adjusted in steps from 1 ␮m, securing a very fine surface. Also the speed of the sledge can be adjusted according to the properties of the specimen material. The process is done in two steps, pre-milling with a special cutter, where the deformations from sectioning, etc., are removed, and the finishing step using a milling tool which leaves a very smooth surface ready for investigation. Ultramilling equipment is commercially available.

8 Electrolytic Polishing/Etching ELECTROLYTIC POLISHING OR ELECTROPOLISHING „ANODIC POLISHING… is a polishing method whereby the specimen is placed as an anode in an electrolytic cell and the electrolysis establishes a surface suitable for metallographic analysis. In principle, electropolishing is the ideal polishing method because no deformations are added to the surface during the process, and most or all deformations introduced before the polishing are removed. Also, the process is done in a very short time, usually in 5 to 20 s. The electrolysis has some effects that unfortunately limit the use. Most pure metals and a vast number of alloys can be electropolished, with special advantage to metals that are relatively difficult to polish mechanically, such as aluminum/aluminum alloys and copper/copper alloys. But as soon as the material has several phases with a certain difference in potential, the results are not satisfying. To limit the negative influence of the electrolysis by shortening the process time, the specimen is usually mechanically ground and sometimes polished before the electropolishing. An advantage with electropolishing is the possibility of electrolytic etching of the specimen as part of the process.

8.1 The Electrolytic Polishing/Etching Process Electrolytic polishing is the anodic dissolution of the specimen surface in an electrolytic cell 共see Fig. 8.1兲.42 An electrolytic cell is used very often for depositing a coating on a work piece, the cathode, removing the material from the anode; in this case a polishing of the anode barely takes place. It is, however, possible to control the conditions in the cell so that a “smoothing”, removal of all large-scale irregularities 共above 1 ␮m兲, takes place. This is followed by a “brightening” which is a removal of all submicroscopic irregularities down to approximately 0.01 ␮m, establishing a surface of the anode without irregularities that is suited for microscopical examination. The amount of

Fig. 8.1—Schematic drawing of an electrolytic cell, showing the anode, cathode and electrolyte.

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material removed is so small that the metal ions stay in the electrolyte without being deposited on the cathode. A number of factors play a role for obtaining the right conditions for polishing: • Shape of polishing chamber, position of anode and cathode. • Voltage. • Anode current density. • Electrolyte composition and temperature. • Flow of electrolyte. • Condition and area of the specimen surface. • Polishing time. The process, especially the brightening, is not fully understood, but the supposed process is described in the following.

8.1.1 The Polishing Cell The specimen surface normally has been ground on SiC grinding paper or on a diamond disk, 共grit P500 or finer兲, before electropolishing 共see Chapter 6兲. In some cases, however, it is possible to go straight to electropolishing from the cut-off, but in most cases a fine grinding, as mentioned, and even a rough polishing is needed. The surface before electropolishing will in all cases have “hills” and “valleys” as shown in Fig. 8.2. This figure shows the development of the process from the rough ground surface to the finished surface 共see further explanation below兲. The specimen is placed in an electrolytic cell 共Fig. 8.3兲 shown schematically with the specimen as anode, a thermometer for temperature control, a stirrer to obtain an electrolyte flow, and a cooling vessel around the cell to keep the temperature constant. The dc voltage is controlled by a potentiometer, the voltage and amperage can be measured on meters, and a timer will control the process time.

8.1.2 Smoothing and Brightening To explain the theory behind the process, an ideal polishing sequence based on an electrolytic cell using a potentiostat is used. The resulting current-density curve is shown in Fig. 8.4 with the developments on the specimen surface as shown in Fig. 8.2. When starting the process in the cell shown in Fig. 8.3, by increasing the voltage from 0 V towards Point B 共Fig. 8.4兲, at first a direct anodic dissolution takes place. At Point B, a viscous film is developed and an electroetching of the specimen surface takes place, removing very little material 共see Section 9.5兲. When the voltage/current density reaches the level of Point B an unstable condition develops until Point C, where a stable plateau is established with increasing voltage. At this plateau the previously developed viscous film, having a passivating effect, reaches equilibrium, enabling a smoothing of the specimen surface 共see Fig. 8.2兲. The material removal by diffusion through the viscous layer will be higher at the tops of the hills, the current being higher, because the diffusion path is shorter than at the valleys. This creates a smoothing of the surface. The best polishing takes place between C and D on the curve. With increasing current density, D towards E, oxygen bubbles develop and make openings in the viscous layer, creating pitting in the specimen surface. Close to D the gas development is still relatively low and polishing may take place, but at E the amount of bubbles will totally destroy the film and polishing is not possible. The presence of the viscous layer, however, cannot explain the brightening of the submicroscopic irregularities. On many examinations it has been proven that a thin solid film will arise on the surface of the anode, which will play an important part dur-

158


Fig. 8.2—Schematic drawing showing the surface of the specimen during the different steps developed during the electrolytic polishing and etching. The letters A to E refer to the curve in Fig. 8.4.

ing the polishing. This film is considered to have a thickness of a few atom layers and is very difficult to identify with regard to its composition. Some scientists think the film consists of metal oxide, but a final proof of that has not been obtained. The presence of the film, however, must be taken for granted. The very thin film follows very exactly the surface of the anode 共specimen兲 and the decrease of metal ions will be the same everywhere. This will cause a removal of the quite small irregularities.43 The voltage/current density curve at a cell without potentiostat will not show the same distinct plateau. Figure 8.5 shows a curve taken from polishing of mild steel on a commercial electropolisher.

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Fig. 8.3—Schematic drawing of an apparatus for electrolytic polishing/etching.

8.1.3 Electrolytic Etching For many materials, the etching process can take place as a continuation of the polishing but at a lower voltage. The low voltage, usually around one-tenth of the polishing voltage between A and B on the curve 共Fig. 8.4兲 creates a weak attack on the specimen

Fig. 8.4—Theoretical curve showing current density versus voltage during the process of electrolytic polishing/etching.

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Fig. 8.5—Current density/voltage curve at electropolishing of mild steel.

surface, preferably attacking the grain boundaries 共see Fig. 8.2兲. In some cases, like with stainless steel, the polishing electrolyte cannot be used for etching, and etching must be performed with another electrolyte outside the polishing chamber 共see Section 9.5兲.

8.1.4 Advantages and Disadvantages At the time when specimen preparation to a high degree was based on manual polishing with alumina, with long polishing times, the quality of the achieved preparation result was relatively low. Therefore, when electrolytic polishing was commercially developed around 1950, it gained ground for many years because the quality was higher than with alumina polishing. A number of artifacts developed during electropolishing, problems with edge retention, etc., were accepted as “necessary evils.” With the development of diamond polishing, rigid composite grinding disks and better polishing cloths, the quality of mechanical polishing has increased considerably, and the weak points of electropolishing can hardly be accepted for a number of materials, even when mechanical polishing normally takes more time than electrolytic polishing. With softer materials, relatively difficult to polish mechanically, the electropolishing still has an advantage. Electropolishing should be performed on commercially available polishers, specifically developed for that purpose. In principle, electropolishing can be performed in any electrolytic cell, but because of the risk of fire, explosion, spill, etc., the commercially developed apparatus provides better safety and good, reproducible results 共see Section 8.4兲. The following descriptions relate to the use of a commercial electropolisher.

Advantages • •

•

•

Etching included: For most materials it is possible to include the etching as the last step in the process. No deformation: The process leaves a clean, undistorted surface, not adding deformation to the specimen surface. This is an important feature when doing research work which is surface-related, or for preparing surfaces for micro hardness testing, X-ray studies and electron microscopy. Fast: The method is very fast. The polishing, which takes place after mechanical grinding and in some cases rough polishing, only takes 5 to 15 s for the polishing and 2 to 10 s for etching 共if possible兲. This can be very important in quality control. Reproducible: When all parameters of a procedure are established, the process can be exactly repeated giving reproducible results.

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Fig. 8.6—Mild steel mechanically polished with the inclusions clearly visible 共a兲, and electrolytically polished with the inclusions partly removed by the polishing process 共b兲.

•

Automatic: The modern electropolishers are totally automated so that all parameters are programmed before the process starts. This secures that the operation is totally independent of the operator. Also, a number of different methods can be saved in the database of the apparatus.

Disadvantages •

Nonuniform material removal: The different phases in the specimen surface will have a different electrochemical potential. This means that the material removal will be different from phase to phase 共preferential attack兲, the more anodic phase having the biggest removal rate. An example is gray cast iron, where the graphite will stand in relief relative to the matrix. Also, at inclusions a problem exists. See Fig. 8.6 showing mild steel polished mechanically 共a兲 with visible inclusions, and electropolished 共b兲 with inclusions partly removed. This takes place because the

162


Fig. 8.7—Surface with deformations from grinding still visible after electrolytic polishing.

•

• •

current density will increase around the inclusion so that material from the matrix is preferably removed which causes a relief or even a dropout of the inclusion 共see also Fig. 1.6兲. Low removal rate: The removal rate is relatively low, so in case of deep deformation in the specimen surface, the polishing time must be long, causing different artifacts to develop 共see below兲. Caused by the low removal rate, the deformations from the grinding scratches are not removed and they are visible in the surface, as shown in Fig. 8.7. This can be avoided if the grinding is done with a finer grit up to P4000, or even a rough polishing with 9 or 6 ␮m is performed. Bad edge retention: Even when the edge of the specimen is protected with a lacquer or mounted, the edge will be preferentially attacked and rounded 共see Fig. 8.8兲. Limited polished area: Depending on the available amperage restricting the current density, the polished area is limited. Short time polishing performed on com-

Fig. 8.8—Edge rounding after electrolytic polishing.

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mercial electropolishers takes place at 1 to 2 A / cm2 共0.16 A / in2兲. In most cases a polisher is made for a maximum amperage of 10 A 共see below兲. Artifacts—Unplane Surface: Due to the different potentials mentioned above, all variations in the specimen material tend to cause artifacts like increasing the size of pores, preferential attack of differently oriented grains and pitting 共see Fig. 1.6兲. The surface is often not plane but wavy, which causes problems at high magnifications. See also Sections 13.5.4 and 13.6.5.

8.2 Electrolytes The electrolyte is an important factor in the electropolishing process. A good electrolyte should have a number of characteristics to support a good polishing and etching. When choosing an electrolyte for polishing a metal, certain basic principles must be taken into consideration. The electrolyte must have a low viscosity since the viscosity determines the quality of the viscous layer that forms on the specimen surface. It must be a good solvent for the anodic material under the prevailing electrolytic conditions. The formation of any insoluble reaction products that deposits on the specimen surface interferes with the polishing operation. The electrolyte should, preferably, not attack the metal in the absence of the current, but it is not always possible. Similarly, preference will be given to an electrolyte that can be used at room temperature, and is little affected by changes in temperature, because in practice it is difficult to control and maintain an exact electrolyte temperature during the polishing operation. Lastly, the electrolyte must be stable and safe to handle. The most used electrolytes are based on perchloric, phosphoric, hydrochloric, or sulfuric acids mixed with ionizing solutions like acetic acid, alcohol, or water. Perchloric acid 共HClO4兲 is by far the most universal acid suited for polishing of a great number of metals. Unfortunately HClO4 is a very dangerous substance that can cause explosions, especially when mixed with acetic anhydride 共共CH3CO兲2O兲. It is safe, however, to use perchloric acid if the correct recommended recipes are used and the necessary precautions are taken 共see Section 13.3.2, Table 13.2兲. Nevertheless, use of perchloric acid is not permitted in some laboratories. If possible, an electrolyte that is mixed with perchloric acid and acetic acid 共glacial兲 should be avoided. The temperature of a perchloric acid electrolyte should not exceed 30 to 35° C 共90 to 100° F兲. It is practical to limit the number of electrolytes used in a laboratory from one to three, covering most materials. With a general purpose electrolyte based on perchloric acid covering aluminum/Al alloys, steel, stainless steel, zinc, lead, magnesium, titanium, and other metals, supplemented with an electrolyte based on phosphoric acid covering copper and copper alloys, most needs should be covered. These two electrolytes are: No. 1-1 共Table 13.2兲 78 mL perchloric acid 共60 %兲, 90 mL distilled water, 730 mL ethanol 共96 %兲, 100 mL butylcellosolve 共ethylene glycol monobutyl ether兲. The perchoric acid which must be shipped and stored separately, should be added to the mixture of ethanol, butylcellosolve, and water immediately before use. This electrolyte has a lifetime of around two months according to use. Attention: With this and other perchloric acid electrolytes, they should never be allowed to become more concentrated by evaporation of one or more of the components 共water/ethanol兲 during storage or use. No. 3-2 共Table 13.2兲 250 mL phosphoric acid, 500 mL distilled water, 250 mL etha-

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nol 共96 %兲, 50 mL propanol 共n-propanol, 100 %兲, 5 g urea 共carbamide兲. Water, ethanol, and propanol are mixed and the acid is added under constant stirring. For more electrolytes see Table 13.2, ASTM Standard Guide for Electrolytic Polishing of Metallographic Specimens 共E 1558兲 and Refs. 2,4, and 9. For Safety Precautions, see Section 26.2.

8.3 Electropolishing in Practice As already mentioned above electrolytic polishing has some limitations, but also has a number of advantages. Before deciding on the use of electropolishing for a given material a number of factors should be evaluated that are given below. See also Section 13.5.4 and 13.6.5.

8.3.1 Factors Influencing Electrolytic Polishing Material The material must be electrically conductive and, if mounted, a good electrical connection should be secured. At the same time, the mounting material around the specimen should not be conductive 共see Section 3.2.2兲.

Electrolyte The right electrolyte composition for a given material should be selected.

The Area to be Polished When using a commercially available electropolisher 共see below兲, the specimen is placed on a mask, defining the area to be polished. The area should be in relation to the voltage/amperage 共current兲 available. The smaller the area, the better, giving the best polishing conditions and the lowest development of heat. Typically an area of 1 to 2 cm2 共0.16 to 0.32 in2兲 is polished.

Voltage/Current The voltage depends on the type of material and electrolyte. Usually the voltage creating the necessary amperage 共current兲 to establish the correct current density is set.

The Flow of the Electrolyte It is important that the reaction products established on the specimen surface during the process are removed continuously and the temperature in the polishing chamber is kept low. This is done by circulating the electrolyte through the chamber. At the same time it is important not to create any air bubbles that are caused by a flow rate that is too high.

The Temperature of the Electrolyte The temperature should be kept as close to room temperature as possible. This gives the best polish with high reproducibility. If the electrolyte is heated to temperatures above 30 to 35° C 共90 to 100° F兲, the process deteriorates and with electrolytes with perchloric acid and ethanol, the risk of fire and explosion will increase. Therefore, if

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Fig. 8.9—Schematic drawing of a polishing table for electrolytic polishing.

more than a few polishings are done in a short period of time, the electrolyte must be cooled.

Time The polishing time should be as short as possible to avoid the negative effects of the electrolysis. For this reason it is important to prepare the specimen before the electropolishing.

8.3.2 Example of Electrolytic Polishing/Etching See Method E 1-01, Section 13.3.6 stating a much used method for steel.

8.4 Electrolytic Polishing Equipment Electropolishers have been commercially available for many years, both for normal polishing in the laboratory and as portable polishers for polishing on the spot. Also, apparatus for electrolytic thinning of specimens for TEM is available 共see Section 8.6兲. Only electropolishers for normal polishing for laboratory use will be described below.

8.4.1 Electropolishers for Laboratory Use These are usually built in two parts: a polishing table, the cell where the actual polishing is done, and an operating unit containing electronics and software.

The Polishing Table The main components 共see Fig. 8.9兲 are: the polishing chamber with cathode and mask upon which the specimen is placed, the electrolyte container with a pump circulating the electrolyte, driven from outside the electrolyte container with a magnet, cooling coil, and a contact beam making anodic contact to the specimen. The specimen is placed with the surface to be polished against the exchangeable mask. The mask has a hole of 0.5 to 5.0 cm2 共0.08 to 0.8 in2兲, allowing contact between the electrolyte and the specimen. The cathode of stainless steel is placed in the bottom of the polishing chamber and during the polishing/etching the pump circulates the

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Fig. 8.10—Electrolytic polisher/etcher with electrolyte temperature control and a load simulation mode for pre-selection of polishing/etching voltages. Input to power source is 1 kVA.19

electrolyte through the chamber in a laminar flow. This flow can be adjusted. Often the pump is driven magnetically as shown to avoid corrosion of metal parts. A cooling coil of stainless, acid resistant steel is placed around the pump, through which cooling water can be circulated to keep the electrolyte temperature constant, normally between 20 to 30° C 共70 to 90° F兲. In certain cases a cooled liquid is circulated making polishing at sub 0 ° C 共32° F兲 temperatures possible. The container is exchangeable, and in this way the electrolyte can be stored covered with a lid when not in use. This allows for the least possible handling of the electrolytes.

The Operating Unit The operating unit has controls for all process parameters and a power supply. Using a microprocessor, storing of polishing methods is possible that saves time when different materials are to be polished.

Electropolishers Electropolishers are only made by a few suppliers; an example is shown in Fig. 8.10. It has electrolyte temperature control and a load simulation mode for preselection of polishing/etching voltages. Input to power source is 1 kVA.

8.5 Field Metallography—Nondestructive Electropolishing One of the very first commercially available electropolishers in the 1940s was made for nondestructive polishing. Only a spot of 1 mm 共0.04 in兲 in diameter was made, allowing the tested product to be sold as “new.” This was done in the laboratory or at the manufacturer, but today nondestructive polishing is mostly “in the field,” “on the spot” 共in situ兲, used for inspection of work pieces such as steam pipes still in function. For the right type of materials 共see earlier in this chapter兲 electropolishing is well suited for nondestructive on the spot polishing because the polishing time is short. Normally the same electrolytes and data are used as for normal electrolytic polishing depending on the type of polisher used 共see Section 13.3.6兲. In most cases the spot to be examined is first treated mechanically 共see Section 7.11兲 to secure a deformation-free

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Fig. 8.11—Specimen of bronze for TEM. Electropolished with jets from two sides, 87 mA, 7.4 V, 5 min and 50 sec, electrolyte No. 3-2 共Table 13.2兲, electrolyte temperature 5 ° C 共41° F兲.

surface after electropolishing/etching. Often a replica is taken after polishing and etching 共see Sections 7.11.2 and 13.4兲. Portable polishers consisting of a “pencil” with a polishing chamber to be pressed against the work piece and a unit supplying electrolyte and an electric current are commercially available.

8.6 Electrolytic Thinning for TEM In a transmission electron microscope 共TEM兲, normally a 3-mm 共0.118 in兲 diameter specimen is used. This specimen must be very thin to allow for the TEM analysis, and electropolishing is suited for thinning of conductive metal specimens. By electrolytic thinning a hole is made in the specimen, and the edge of this normally is very thin, as shown in Fig. 8.11. The specimen is normally thinned first by grinding so that a 3-mm 共0.118-in兲 diameter disk with a thickness of 0.5 to 0.1 mm 共0.02 to 0.004 in兲 can be thinned. The thinning is a normal electrolytic polishing as described above, except the thinning, in most cases, takes place on both sides at the same time. This can actually be done in a glass beaker, positioning the specimen as anode, with a lacquer to cover the edges so that only the center is polished. This “window” technique is stopped when a hole is established in the specimen, and it is quickly taken under water to avoid further attack. This method is relatively laborious, giving less reproducible results; therefore, the commercial jet thinners have been developed. See Fig. 8.12 which shows a cross section of the polishing chamber. The specimen is placed in the middle in a movable holder. On each side of the specimen holder a nozzle holder is placed with a nozzle leading the electrolyte flow toward the sides of the specimen. A cathode is placed at each nozzle. The process is observed from one side either by watching or with a photocell reacting to the light which breaks through the hole in the specimen created by the polishing process. The light comes from a light source placed behind the specimen, and when the photocell is “hit” the process stops automatically, ensuring a very small hole in the specimen. Electrolytes and data from normal electrolytic polishing can often be used, but in

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Fig. 8.12—Schematic drawing of a polishing cell for electrolytic jet polishing for TEM. The specimen placed in a holder for quick removal, is attacked from both sides simultaneously, having two cathodes and the electrolyte in two jets conducted towards the specimen. Using a photocell instead of an eye, the process can be switched-off immediately when the light breaks through the specimen, assuring a very small hole in the specimen.

certain cases special electrolytes and temperatures, considerably below room temperature, are needed to be able to effectively control the process. See the literature on electrolytic thinning.44

8.7 Chemical Polishing Chemical polishing is a relatively simple method, comparable to electrolytic polishing, only without an electric current. It is a process based on the electrolytic action that takes place when a chemical solution gets into contact with the metal surface 共see also Section 9.4.1兲. The chemical polishing solutions are developed so that material is removed from the surface of the specimen in much the same way as in electrolytic polishing. This means that chemical polishing has the same disadvantages as mentioned above under electropolishing. The polishing is made by immersing the specimen into the polishing solution often combined with a rubbing to remove reaction products. Due to the disadvantages of the method and the trouble/danger with handling of chemicals, chemical polishing is not used much. With certain sensitive materials, however, like cadmium, lead, zinc, tin, and zirconium, chemical polishing might be useful when mechanical polishing or electropolishing are unsuccessful. See the literature, Refs. 2 and 9 for further information and for chemical polishing solutions.

9 Etching 9.1 Microetching—Contrast MICROETCHING IS ETCHING OF MICROSTRUCTURES TO BE OBSERVED BY magnification higher than 25⫻ 共50⫻ in Europe兲. For macroetching, see Section 9.7. In the bright field illumination 共BF兲 of the light microscope, a prepared metallographic/materialographic specimen will only show certain features like inclusions, nonmetallic phases 共graphite兲, pores, cracks, etc. It is usually not possible to see the microstructure because the light is reflected equally from the bright surface. Figure 9.1 shows a steel specimen, unetched 共a兲, and chemically etched 共b兲, the etched surface revealing the grains of the microstructure 共see also Fig. 1.10兲. To obtain an image with the structure details, a contrast between the elements in the microstructure has to be established. The contrast can be caused by a number of methods 共see the diagram Fig. 9.2兲. The most important of these methods will be further discussed in the following sections. Chemical microetching of metals is covered by ASTM Standard Practice for Microetching Metals and Alloys 共E 407兲, see also Section 12.5. For further study see the literature, Refs. 2, 4, 9, 21, 26, 27, 45–49.

9.2 Contrast Without Surface Modifications—Microscope Techniques In the bright field illumination 共BF兲 of the light microscope only structure details that differ in reflectivity from one another can be distinguished from each other. For this reason special microscope techniques have been developed, making it possible to observe certain details that cannot be observed in BF. See also Part III of this book.

9.2.1 Dark-Field Illumination „DF… In dark-field illumination, the light beam is angled to the specimen surface, making it possible to observe details like inclusions and scratches that stand in relief to the surrounding structure. This can be of advantage when observing some features, such as lightly etched grain boundaries and light scratches 共see Fig. 15.10兲.

9.2.2 Differential Interference Contrast „DIC… This illumination technique uses a beam splitter to direct two beams towards the specimen surface. This makes even very small differences in height 共relief兲 visible, and DIC can be used with great advantage using relief polishing 共see below兲, in this way avoiding an additional “etching” process 共see Fig. 15.14兲.

9.2.3 Polarized Light „POL… Using polarized light the microstructure of anisotropic metals such as zirconium and titanium can be observed without any treatment of the prepared surface. For isotropic 共cubic兲 metals, polarized light can be used when an anisotropic surface film is estab169

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Fig. 9.1—Unetched steel specimen. 共a兲 Only the inclusions can be seen. 共b兲 Etched in 3 % Nital 共100 mL ethanol 96 %, 3 mL nitric acid 65 %兲 revealing the grains.

lished on the specimen surface. In some cases a chemically etched surface can also be observed on an anisotropic material 共see Fig. 15.12兲.

9.2.4 Fluorescence Some materials emit radiation when illuminated by certain types of light. Fluorescence can be used to distinguish pores and other surface details 共see Section 3.10 and Fig. 3.14兲.

9.3 Contrast with Surface Modification—Etching To obtain the necessary contrast so that a surface can be observed in bright field in a reflected light microscope, a treatment, often called “etching” must take place. The most used method is “chemical etching” based on an electrochemical attack of the surface, but “electrolytic etching” and other methods such as “physical etching” are also used 共see Fig. 9.2兲.

9.3.1 Grain Contrast Etching To obtain grain contrast etching, certain grains in the specimen surface are influenced. Figure 9.318 shows 共1兲 a grain in relief caused by relief polishing 共which could also be established by ion etching 共see below兲; 共2兲 grains which are differently attacked by the

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171

Fig. 9.2—Diagram showing the methods to create surface contrast.

etchant; 共3兲 a grain covered by an interference layer 共film兲 that is selectively deposited; 共4兲 a layer deposited independently of the grains; and 共5兲 the film deposited according to the orientation of the grains.

9.3.2 Grain Boundary Etching In this type of etching the grain boundaries only are attacked 共see Fig. 9.3兲. Figure 9.3 shows: 共6兲 a grain boundary attacked by chemical etching; and 共7兲 a grain boundary after treatment under heat and vacuum.

9.3.3 Reproducibility During the preparation of the specimen, the process of making a contrast shall be reproducible. It is important that the “etching process” does not introduce artifacts, but

Fig. 9.3—Schematic drawing of grain contrast “etching.” 共1兲 Relief polishing, 共2兲 grains differently attacked, 共3兲 grain covered with interference layer, 共4兲 layer deposited independently of the grains, 共5兲 film deposited according to the orientation of the grains, 共6兲 grain boundary etch, 共7兲 grain boundary treated under vacuum and heat.

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ensures that the true structure is revealed. This is particularly important when image analysis is to be performed on the specimen in question 共see Part IV兲. Typical artifacts developed during etching are stains if the specimen surface was not properly cleaned after the last polishing step. Also pitting and other artifacts can be developed at over-etching.

9.3.4 Safety Precautions Especially in chemical etching it is important to take necessary safety precations. Before using or mixing any chemical, all product labels and pertinent Material Safety Data Sheets 共MSDS兲 should be read and undertood concerning all of the hazards and safey precautions to be observed 共see Section 26.2兲.

9.4 Classical Etching 9.4.1 Chemical Etching The most commonly used method for creating the necessary contrast in the specimen surface is chemical etching, also called dissolution etching.2,4,9,21,26,45–47 Chemical etching is a process based on the electrolytic action that takes place when a chemical solution 共etchant兲 is in contact with a metal surface. The etchant, normally having a “reduction” component that is usually an acid, an “oxidizer” component, and a “modifier” component, causes an electric potential between differently oriented grains, different phases, grains and boundaries, inclusions, and matrix, etc. The difference in attack, which is the amount of material removed from the single details, reveals the structure. For electrolytic etching, where the specimen is placed as an anode in an electrolytic cell, the applied current acts as the oxide component. A number of etchants for chemical etching are stated in Table 12.2.

9.4.2 Precipitation „Color… Etching This etching method, also called color etching or tint etching, uses a chemical etchant that reacts with the specimen surface and deposits a very thin insoluble film. The film acts as an interference layer producing colors in bright field illumination and polarized light. Variations in the grains influence the observed colors. Precipitation etching requires a high quality of the prepared specimen; even small scratches or deformations will be visible when the film is established.46,47

9.4.3 Heat Tinting Oxidizing will take place on the surface of metal specimens that are heated to temperatures in the range 250 to 700° C 共500 to 1300° F兲 in air. The oxidized film will vary in thickness according to the variations in the specimen material. If the layer is thicker than 30 nm, interference colors can be seen in the bright field of the microscope. Heat tinting is not suited for carbon steels and low-alloy steels, but works well with highalloy steels, tool steels, stainless steels, titanium, and other metals.

9.5 Electrolytic Etching 9.5.1 Anodic Etching Anodic etching, also known as electrolytic etching, is in principle the same as chemical etching, except in this case the specimen is placed as an anode in a galvanic cell. This

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173

means that material is removed from the specimen surface, causing an etching and not a polishing as with electrolytic polishing 共see Fig. 8.1兲. The etching takes place because the voltage and current density are low 共see Fig. 8.4兲. Frequently, electrolytic etching can be performed as the second step of the polishing-etching process, using a voltage of approximately 1 / 10 that used as the polishing voltage. In many cases, however, the electrolyte suited for polishing cannot be used for etching. In this case, electrolytic etching often takes place using a stainless steel vessel connected as a cathode containing the etchant. The specimen is handled with a pair of tongs, connected as an anode, and a suitable low direct current is established between the cathode and anode. An example is etching of stainless steel that can be electrolytically etched in an electrolyte 共etchant兲 of 10 g oxalic acid in 100 mL water, using a voltage of 6 V in 10 to 15 s. A number of etchants for electrolytic etching are stated in Table 12.2.

9.5.2 Anodizing During this process that is closely related to electrolytic etching/polishing, a layer, often an oxide film, is established on the surface of the specimen 共see Fig. 9.3共3–5兲兲. This interference layer will produce a colored image in bright field illumination and with polarized light. The layers can be related to the layers created at precipitation etching, heat tinting, and vapor deposition.

9.5.3 Potentiostatic Etching A reproducible, selectively working electrolytic etching is made with an electronic potentiostat and a reference electrode. With the potentionstat it is possible to establish a constant potential at the specimen surface 共anode兲. Because of the controlled etching process, potentiostatic etching is very well suited for selective etching of desired microstructural constituents with high reproducibility.

9.6 Physical Etching 9.6.1 Relief Polishing In some cases it is possible to establish a contrast by relief polishing that creates a small relief between the grains or the grain boundaries, or both 共see 1兲 in Fig. 9.3兲. Relief polishing is often done with a relatively resilient cloth 共see Section 7.4兲 and a very fine polishing medium like colloidal silica or alumina 共see Section 7.5兲. Relief can also be established through chemical mechanical polishing 共see Section 7.12兲. Relief polishing should only establish a very small relief between the single grains or other constituents, not to disturb the microstructure; therefore, often DIC is used when examining relief polished surfaces 共see Section 9.2.2兲.

9.6.2 Ion Etching This method, also called ion beam etching, uses an ion bombardment of the specimen to remove material from the single grains, depending on orientation and phase composition. Ion beam etching can be used for thinning of specimens for transmission electron microscopy 共TEM兲 as an alternative to electropolishing 共see Section 8.6兲. It is, however, also suited for etching microstructures, especially of nonconductive materials for materialographic examination.48 The ions, often argon, are supplied in a strong

174


vacuum 共10– 4 mbar兲 by an ion gun towards the specimen which is often placed so that the surface is bombarded under an angle.

9.6.3 Thermal Etching Thermal etching takes place at high temperatures in an oven with an inert atmosphere or vacuum. Both metals and ceramics can be thermally etched. During the process grooves are formed in the grain boundaries/phase boundaries and grain surfaces are curved. The method can be used at high-temperature microscopy for metals, but thermal etching is mostly used for etching of ceramics taking place at temperatures between 1000 and 1400° C 共1800 and 2500° F兲.26

9.6.4 Vapor Deposition Interference films can be established on the specimen surface by vacuum deposition of a suitable material. This method 共Pepperhof兲 will enhance the irregularities in the polished surface and the structure will be visible through the interference between the light reflected from the top of the film and the specimen surface. The film materials shall have a high refractive index; ZnS, ZnTe, ZnSe, and TiO2 are often used. The process takes place in a chamber with a vacuum of about 10– 5 mbar.49

9.6.5 Sputtering Sputtering—Cathodic Discharge Interference layers 共films兲 can be produced by sputtering. In sputtering, materials like carbon, gold, or gold-palladium alloys are atomized by bombarding a surface 共target兲 with high energy particles. Positively charged gas ions produced by electrical discharge 共1 to 5kV dc兲 are accelerated by a potential difference between the anode 共specimen兲 and cathode 共target兲 so that they bombard the cathode, thereby dislodging atoms that leave the surface in all directions. These atoms settle on the specimen surface where they form the desired layer. If undesirable reactions with the target material shall be avoided, the process shall take place at 0.03 to 0.05 mbar in an inert gas like argon.49

Reactive Sputtering At reactive sputtering, not an inert gas, but an atmosphere of oxygen is used. This means that the atomized target material is oxidized, forming oxidic layers on the specimen.49

9.7 Macroetching Macroetching can be defined as revealing the macrostructure for examination with the naked eye or at a magnifications up to 10⫻, either direct or by using sulfur prints 共Baumann prints兲. Macroetching is considered outside the scope of this book. Macroetching is described in great detail in the three following ASTM standards 共see also Section 12.4兲. Standard Test Method for Macroetching Metals and Alloys 共E 340兲. This standard is very comprehensive covering a wide range of materials. Standard Methods for Macrotech Testing Steel Bars, Billets, Blooms, and Forging 共E 381兲

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175

Standard Practice for Preparing Sulfur Prints for Macrostructural Examination 共E 1180兲

References „Part I… 关1兴

Crowther, D. S. and Spanholtz, R. B., “A New Name for Metallography? Try ‘Materialography’,” Metal Progress, September 1968, p. 21.

关2兴关3兴

Petzow, G., Metallographic Etching, ASM International, Materials Park, Ohio, USA, 1999. Petzow, G. and Mücklich, F., “Microstructure-Fascinating Variety in Stringent Rules,” Practical Metallography, Vol. 33, 1996, pp. 64–82. ASM Handbook, Metallography and Microstructures, Volume 9, ASM International, Materials Park, Ohio, USA, 2004. Edyvean, R. G. I. and Hammond, C., Journal of Historical Metallurgy, October 1998. Vilella, J. R., Metallographic Technique for Steel, American Society for Metals, Cleveland, Ohio, USA, 1938. Samuels, L. E., Metallographic Polishing by Mechanical Methods, ASM International, Materials Park, Ohio, USA, 2003. Bjerregaard, L., Geels, K., Ottesen, B., and Rückert, M., Metalog Guide, Struers A/S, Copenhagen, Denmark, 2000. Vander Voort, G. V., Metallography Principles and Practice, ASM International, Materials Park, Ohio, USA, 1999. Malkin, S., Grinding Technology, Ellis Horwood Ltd., Chichester, UK, 1989. Shaw, M. C., Principles of Abrasive Processing, Clarendon Press, UK, 1996. Shaw, M. C., Farmer, D. A., and Nakayama, K., “Mechanics of the Abrasive Cut-Off Operation,” Journal of Engineering for Industry, August 1967. Nelson, J. A. and Westricht, R. M., “Abrasive Cutting in Metallography,” Metallographic Specimen Preparation, Plenum Press, Plenum Publishing. Wellner, P., “Investigations on the Effect of the Cutting Operation on the Surface Deformation of Different Materials,” Practical Metallography, Vol. 17, 1980, p. 525. Geels, K., Andersen, A. T., and Damgaard, M., “An Analysis of Two Principles of Abrasive Cutting in Materialographic Cut-Off Machines,” Proceedings, MC95 International Metallography Conference, ASM International, Materials Park, Ohio, 1996, p. 251. Cloeren, H. H., “Thermische und mechanische Probenentnahme und deren Einfluss auf das wahre Gefüge,” Fortschritte in der Metallographie, Vol. 33, WerkstoffInformationsgesellschaft mbH, Frankfurt, Germany, 2002, p. 309. Geels, K., Müller, G., and Sorensen, J. I., “Oberflächenphenomene beim materialographischen Nasstrennschleifen,” Fortschritte in der Metallographie, Vol. 34, WerkstoffInformationsgesellschaft mbH, Frankfurt, Germany, 2003, p. 93. Waschull, H., Präparative Metallographie, Wiley-VCH Verlag, Weinheim, Germany, 1993. Courtesy of Buehler, Ltd. Courtesy of Struers A/S. Bramfitt, B. L. and Benscoter, A. O., Metallographer’s Guide, Practices and Procedures for Iron and Steels, ASM International, Materials Park, Ohio, USA, 2002. Barrett, J., “Electric Discharge Machining,” Metallographic Specimen Preparation, Plenum Press, Plenum Publishing Corporation, New York, USA, 1974, p. 69. Technical documents from DoALL Company, Des Plains, Illinois, USA, 2004.

关4兴关5兴关6兴关7兴关8兴关9兴关10兴关11兴关12兴关13兴关14兴关15兴

关16兴

关17兴

关18兴关19兴关20兴关21兴关22兴关23兴

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关24兴 Nelson, J. A. and Slepian, R. M., Practical Metallography, Vol. 7, 1970, p. 510. 关25兴 Glancy, S., Structure, Vol. 22, 1990, p. 14. 关26兴 Carle, V., Schäfer, U., Täffner, U., Predel, F., Telle, R., and Petzow, G., “Ceramography of High

Performance Ceramics: Description of the Materials, Preparation, Etching Techniques, and Description of the Microstructure,” Practical Metallography, Part I, Ceramographic Etch-

关27兴关28兴关29兴关30兴关31兴关32兴

关33兴关34兴关35兴关36兴关37兴关38兴关39兴关40兴关41兴关42兴关43兴关44兴

关45兴关46兴关47兴

关48兴关49兴

ing, Vol. 28, 1991, pp. 359–377; Part II, Silicon Carbide, Vol. 28, 1991, pp. 420–434; Part III, Zirconium Oxide, Vol. 28, 1991, pp. 468–483; Part IV, Aluminum Nitride, Vol. 28, 1991, pp. 542–552; Part V, Silicon Nitride, Vol. 28, 1991, pp. 592–610; Part VI, High-Temperature Superconductor YBa2Cu3O7, Vol. 28, 1991, pp. 633–648; Part VII, Boron Carbide, Vol. 31, 1994, pp. 218–233; Part VIII, Aluminum Oxide, Vol. 32, 1995, pp. 54–76. Elssner, G., Hoven, H., Kiessler, G., and Wellner, P., Ceramics and Ceramic Composites: Materialographic Preparation, Elsevier Science Inc., New York, USA, 1999. Exner, E. and Kuhn, K., Practical Metallography, Vol. 8, 1972, pp. 453–469. Bousfield, B., Surface Preparation and Microscopy of Materials, John Wiley & Sons, Chichester, UK, 1992. Damgaard, M. J., Bjerregaard, L., and Geels, K., Practical Metallography, Vol. 8, 2001, pp. 466–476. Beilby, G., Aggregation and Flow of Solids, MacMillan and Co. Ltd., London, UK, 1921. Luo, J. and Dornfeld, D. A., “Material Removal Mechanism in Chemical Mechanical Polishing: Theory and Modeling,” IEEE Transactions on Semiconductor Manufacturing, 2000. Geels, K. and Gillesberg, B., Practical Metallography, Vol. 37, 2000, pp. 150–159. Burgess, D. and Blanchard, R. A., Wafer Failure Analysis for Yield Enhancement, Accelerated Analysis, Half Moon Bay, California, USA, 2001. Ross, Boit, and Staab, Eds., Microelectronics Failure Analysis, ASM International, Materials Park, Ohio, USA, 1999. Wulff, F. W. and Arens, T., Structure, Vol. 32, 1998, p. 9. Reiter, K., Reiter, M., and Arens, T., Structure, Vol. 34, 1999, p. 12. Katrakova, D., Damgaard, M., and Mücklich, F., Structure, Vol. 38, 2002, p. 19. Kopp, W.-U. and Linke, U., Practical Metallography, Vol. 17, 1980. Trempler, J., Practical Metallography, Vol. 5, 2001, pp. 231–269. Trempler, J., Practical Metallography, Vol. 10, 2003, pp. 481–531. McG. Tegart, W. J., The Electrolytic and Chemical Polishing of Metals in Research and Industry, Pergamon Press Ltd., London, 1956. Knuth-Winterfeld, E., Korttidsmetoder til metallografisk elektropolering ved stuetemperatur, C. A. Reitzel, Copenhagen, Denmark, 1952. Thompson-Russell, K. C., and Edington, J. W., Monograph Five, Electron Microscope Specimen Preparation Techniques in Materials Science, N. V. Philip’s Gloeilampenfabrieken, Eindhoven, Holland, 1977. Beckert, M. and Klemm, H., Handbuch der metallographischen Âtzverfahren, Deutscher Verlag für Grundstoffindustrie, Leipzig, Germany, 1984. Beraha, E. and Shipgler, B., Color Metallography, American Society for Materials, Materials Park, Ohio, USA, 1977. Weck, E. and Leistner, E., “Metallographic Instructions for Colour Etching by Immersion, Part I 共1982兲, II 共1983兲 and II 共1986兲,” Deutscher Verlag für Schweisstechnik GmbH, Düsseldorf, Germany. Gräff, I., Practical Metallography, Vol. 36, 1999, pp. 669–684. Bühler, H. E. and Hougardy, H. P., Atlas of Interference Layer Metallography, Deutsche Gesellschaft für Materialkunde, Oberursel, Germany, 1980.

Part II: Metallographic/Materialographic Specimen Preparation—A Hands-On Manual

10 Introduction THE GOAL FOR ANY METALLOGRAPHIC/MATERIALOGRAPHIC PREPARAtion is a true microstructure, or at least a structure that makes a correct analysis of a structure detail possible. It should be stressed that an examination with a subsequent interpretation, using a light microscope or other method, is of no use if the prepared microstructure is not correct. This part of the book is made to guide the reader directly towards the correct preparation of the microstructure for most materials and material groups. To obtain more information on the true structure, a more detailed description of the total preparation process and the theories behind it, see Part I of this book. Before starting a preparation process, two facts must be considered: Specimen Material and Purpose of Examination.

10.1 Specimen Material The specimen material, in the following material, is decisive for the choice of a preparation process. It is evident that soft, hard, ductile, brittle, homogenous, heterogeneous, etc., materials cannot be treated the same way to obtain a correct result. To find the correct preparation method for a given material, the reader shall review Table 11.1 and find the material or group of materials corresponding to the given material 共see below兲.

10.2 Purpose of Examination Before a preparation method is selected, the purpose of examination, in the following the purpose, should be considered. A given material can be prepared often electrolytically in a relatively short time for one purpose, and for another purpose, a longer mechanical preparation sequence should be performed. An example is medium carbon steel. If the purpose of examination is the study of grain size, the electrolytic polishing method El-01, Section 13.3.6, can be used, having a total preparation time of approximately 3 min, including grinding 共less than 3 min兲 and polishing/etching 共10– 12 s兲. If the purpose is examination of inclusions, the mechanical methods, C-28 and T-28, Section 13.2.3, are recommended with a total preparation time of 10– 12 min. Based on the purpose, the user will select the correct process/method stated in the Material/Preparation Tables. Other information connected to the purpose, such as etchants, will be stated also.

10.3 Specimen Preparation Modern specimen preparation is based on a systematic approach, and in this way securing the reproducibility that is a must in both research and quality control. In the Material/Preparation Tables, Section 13.2.3, the total preparation process is stated, in179

180


cluding sectioning, mounting, grinding/polishing methods 共mechanical and electrolytical兲, and etching. Mechanical polishing can be done by hand and is also described in this part of the book, but for the indicated methods, a semiautomatic grinder/polisher is recommended. A section covering “trouble shooting” of all stages of the preparation process, and how to analyze the used preparation method to avoid or overcome artifacts is also included in Part II.

11 Specimen Material—Table 11.1 THE SPECIMEN MATERIAL, COMBINED WITH THE PURPOSE OF EXAMINAtion, is decisive for the choice of preparation process/method. Two physical properties, hardness and ductility, are important in selecting a specific preparation method, but conditions such as coatings or composites also play an important role. In Table 11.1, Section 11.3, most materials and the most common material combinations are indicated to guide the reader to a preparation process/method best suited for a specific material stated in the Material/Preparation Tables, Section 13.2.3.

11.1 Classification of Materials A classification of all available materials is needed to guide the reader to a specific material in an efficient way. This is done by defining twelve main groups partly based on material composition, such as “ceramics,” “ferrous metals,” etc., and on other important features like “coatings,” “electronic components,” etc. The twelve main groups are stated alphabetically 共see below兲. The main groups are split into a number of subgroups. An example is the main group Ceramics, which has five subgroups: Carbides, Nitrides, Oxides, Traditional Ceramics, and Other Ceramics. These subgroups lead to the specific material or material group, e.g., under Ceramics, Oxides: Al2O3, BaTiO3, CaO, CeO2, Cr2O3, MgO, SiO, ZnO, ZrO2, and Other Oxides. The twelve main groups 共alphabetic兲: • Ceramics • Coatings • Composites and Reinforced Materials • Electronic Components • Ferrous Metals • Mineralogical Materials • Nonferrous Metals • Organic Materials • Polymers • Powder Metals • Sintered Carbides

11.2 How to Use Table 11.1 When a given material or material group should be found in the table, the main group most likely will be evident such as Ceramics, Coatings, Ferrous Metals, Polymers, etc. If in doubt, a look at the subgroups will often lead the way to the material or material group. In the case of an alloy, the material should be found according to the component with the highest content. Example: The superalloy: 48 % Ni, 25 % Co, 19 % Cr, 7.5 % Fe, 0.5 % Ti, is classified under the main group Nonferrous Metals, subgroup Nickel and Nickel Alloys. 181

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When the material 共material group兲 is found, two or more Methods with Method Numbers are indicated in the same row. Now go to Section 13.2.3 and find the Material/ Preparation Tables with the same number. A number of purposes with corresponding preparation methods are indicated here 共see Chapter 12兲, and the method corresponding to the correct purpose is selected.

11.3 Table 11.1—Materials/Methods TABLE 11.1—Materials/Methods. Material Group/Material (Alphabetical) Ceramics Bioceramics Carbides

Nitrides

Other Ceramics Oxides

Borides Traditional Ceramics

Coatings

Electrolytically Deposited Other Coatings

Hydroxyapatite Coating Bioceramics, Others B 4C CrC SiC TaC TiC WC CBN Si3N4 TiN Al2O3 BaTiO3 CaO CeO2 Cr2O3 MgO SiO UO2 ZnO ZrO2 Oxides, Others Glasses, Optical Fibers Porcelain Slag Tile Other Traditional Ceramics Anodized Coatings Galvanization—Plated Coatings Other Electrolytically Deposited CVD Diffusion Coatings Hot Dip Zn-Coating Other Zn-based Coatings PVD

Method (See Section 13.2.3/3.6) T-01, C-01 T-05, C-05, T-06, C-06 T-02, C-02 T-03, C-03 T-02, C-02 T-03, C-03 T-03, C-03 T-03, C-03 T-03, C-03 T-04, C-04 T-03, C-03 T-03, C-03 T-05, C-05 T-06, C-06 T-06, C-06 T-06, C-06 T-05, C-05 T-06, C-06 T-06, C-06 T-68, C-68 T-06, C-06 T-06, C-06 T-05, C-05, T-06, C-06 T-06, C-06 T-07, C-07 T-06, C-06 T-06, C-06 T-06, C-06 T-06, C-06 T-08, C-08 T-09, C-09 T-09, C-09 T-08, C-08 T-09, C-09 T-10, C-10 T-10, C-10 T-08, C-08

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TABLE 11.1—(Continued.) Material Group/Material (Alphabetical)

Thermal Spray Coatings

Composites and Reinforced Electronic Components

Ceramic Components

Metallic Components

Polymer Components

Ferrous Metals

Carbon Steels

Cast Irons

Heat Treated

Paint Layers Other Coatings Flame HVOF (High Velocity Oxygen Fuel) Plasma Spray Coatings— Metallic Layers Plasma Spray Coatings— Ceramic Layers Plasma Spray Coatings— Composite Layers Other Thermal Spray Coatings SiC Fibers in Ti Matrix Glassfiber Reinforced Plastic Other Composite Materials Capacitors Resistors Diodes YBCO Ceramic Super Conductors Germanium, Silicon, Si Wafers Microelectronic Material (Semiconductor Device) Resistors Solderballs Other Metal Components Capacitors, Other Electronic Components Microelectronic Packages, Integrated Circuits, Transistors PCB Coupon Other Microelectronic Devices High Carbon Steels Low Carbon Steels Medium Carbon Steels Gray Cast Iron, Lamellar Cast Iron, Malleable Cast Iron, Nodular Cast Iron, White Cast Iron, others Heat Treated, High-Alloy Steels

Method (See Section 13.2.3/3.6) T-11, C-11 T-09, C-09 T-12, C-12 T-12, C-12 T-13, C-13 T-14, C-14 T-15, C15 T-12, C-12 T-16, C-16 T-17, C-17 T-18, C-18 T-19, C-19 T-19, C-19 T-19, C-19 T-20, C-20 T-21, C-21 C-22 T-23, C-23 T-24, C-24 T-23, C-23 T-25, C-25 T-24, C-24 T-26, C-26 T-27, C-27 T-26, C-26 T-28, C-28, E1-01 T-29, C-29, El-02 T-28, C-28, El-01 T-30, C-30, El-03 T-30, C-30, El-03 T-31, C-31, El-03 T-32, C-32, E1-03 T-28, C-28, El-03 T-33, C-33, El-04

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TABLE 11.1—(Continued.) Material Group/Material (Alphabetical) Steels High-Alloy Steels Low-Alloy Steels Other Ferrous Metals Pure Iron Surface Treated Steels

Tool Steels

Mineralogical

Constructed

Materials

Materials Natural

Nonferrous Metals

Aluminum and Al Alloys

Heat Treated, Low-Alloy Steels Stainless Steels Super Alloys, Fe-Based Other High-Alloy Steels High Strength Low-Alloy Steels Other Low-Alloy Steels

Carbonitrided Steels Carburized Steels Nitrided Steels Other Surface Treated Steels High Speed Steels Low-Alloyed Tool Steels Tool Steels, Others Portland Cement Clinker, Concrete Minerals Ores Pure Aluminum Cast Aluminum Alloys Wrought Aluminum Alloys Other Aluminum Alloys

Americium

Antimony and Sb Alloys

Pure Antimony Antimony Bearing Alloys Other Sb Alloys

Beryllium and Be Alloys Bismuth and Bi Alloys Cadmium

Chromium and Cr Alloys Cobalt and Co Alloys Copper and Cu Alloys

Method (See Section 13.2.3/3.6) T-33, C-33, El-04 T-34, C-34, El-05 T-35, C-35, El-06 T-33, C-33, El-05 T-36, C-36, El-04 T-34, C-34, E1-04 T-33, C-33, E1-02 T-34, C-34, El-07 T-37, C-37 T-37, C-37 T-37, C-37 T-37, C-37 T-38, C-38, El-08 T-38, C-38, El-09 T-38, C-38, El-09 T-39, C-39

T-40, C-40 T-40, C-40 T-41, C-41, El-10 T-41, C-41 T-43, C-43, El-10 T-42, C-42, El-10 See Material/ Preparation Tables 68 T-44, C-44, El-10 T–44, C-44, El-10 T-44, C-44, El-10 T-45, C-45, El-10 T-44, C-44, El-10 See Material/ Preparation Tables 68 T-46, C-46, E1-11

Pure Cobalt, Cobalt Alloys Super Alloys, Cobalt-Based Pure Copper Brass Bronze

T-47, C-47, El-12 T-48, C-48, El-12 T-50, C-50, El-13 T-49, C-49, El-13 T-49, C-49, El-14

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TABLE 11.1—(Continued.) Material Group/Material (Alphabetical) Copper Bearings Alloys Other Copper Alloys Germanium Gold and Au Alloys Hafnium and Hf Alloys Indium

Iridium and Ir Alloys Lead and Pb Alloys Magnesium and Mg Alloys Manganese and Mn Alloys Mercury and Amalgams Molybdenum and Mo Alloys Neptunium

Nickel, Ni Alloys and NiBased Super Alloys Niobium and Nb Alloys Osmium and Os Alloys Palladium and Pd Alloys Platinum and Pt Alloys Plutonium

Rare Earth Metals Rhenium and

Method (See Section 13.2.3/3.6) T-50, C-50, El-14 T-49, C-49, E1-13 T-21, C-21 T-51, C-51 T-62, C-62, El-11 See Material/ Preparation Tables 68 T-57, C-57 T-52, C-52, E1-15 T-53, C-53, E-16

T-54, C-54, El-01 See Material/ Preparation Tables 68 T-55, C-55, E1-01 See Material/ Preparation Tables 68 T-56, C-56, El-17

T-55, C-55 T-57, C-57 T-57, C-57 T-57, C-57 See Material/ Preparation Tables 68 See Material/ Preparation Tables 68 T-55, C-55

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TABLE 11.1—(Continued.) Material Group/Material (Alphabetical) Re Alloys Rhodium and Rh Alloys Ruthenium and Ru Alloys Selenium

Silicon Silver and Ag Alloys Tantalum and Ta Alloys Tellurium

Thallium

Thorium

Organic Materials

Tin, Sn Bearing Alloys and Other Sn Alloys Titanium and Ti Alloys Tungsten and W Alloys Uranium and Uranium Dioxide Vanadium and V Alloys Zinc and Zn Alloys Zirconium and Zr Alloys Zircalloy Biological Materials Bone Teeth Tissue

Method (See Section 13.2.3/3.6) T-57, C-57 T-57, C-57 See Material/ Preparation Tables 68 T-21, C-21 T-58, C-58, E1-18 T-55, C-55 See Material/ Preparation Tables 68 See Material/ Preparation Tables 68 See Material/ Preparation Tables 68 T-59, C-59, E1-19

T-60, C-60, E1-20 T-55, C-55, E1-21 T-68, C-68

T-55, C-55, E1-22 T-61, C-61, E1-23 T-62, C-62, E1-24

T-63, C-63

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TABLE 11.1—(Continued.) Material Group/Material (Alphabetical) Carbon, Coal, Graphite Paper, Wood Other Organic Materials Polymers Elastomers

Thermoplastics

Thermosetting Plastics

Powder Metals

Sintered Carbides (Cemented Carbides)

Ferrous Powder Metals Nonferrous Powder Metals Cemented Carbides, (Hard metals), Coated Sintered Carbides and Other Sintered Carbides

Method (See Section 13.2.3/3.6) T-63, C-63 T-63, C-63 T-63, C-63 Elastomers, Others EPDM Polymers Silicone Acrylic (CS) Acrylonitril Butadicne Styrene (ABS) Polyamid (PA) Polycarbonate (PC) Polyester, Saturated Polyethylene (PE) Polymethylmethacrylate (PMMA) Polyoxymethylene (POM) Polypropylene (PP) Polystyrene (PS) Polyvinylchloride (PVC) Thermoplastics, Others Epoxy Phenolic Resins (PF) Polyester, Unsaturated Polyurethane (PUR) Other Thermosetting Plastics

T-64, C-64 T-64, C-64 T-64, C-64 T-64, C-64 T-65, C-65 T-64, C-64 T-65, C-65 T-65, C-65 T-64, C-64 T-65, C-65 T-65, C-65 T-64, C-64 T-64, C-64 T-64, C-64 T-64, C-64 T-65, C-65 T-65, C-65 T-65, C-65 T-65, C-65 T-65, C-65

T-66, C-66 T-67, C-67, E1-25

12 Purpose of Examination 12.1 Purpose in General FOR A GIVEN MATERIAL SEVERAL PREPARATION METHODS WILL USUally be available, however, the correct method should be chosen based on the purpose of examination. For this reason, a number of relevant purposes are stated with each material/method in the Material/Preparation Tables, 共see Section 13.2.3兲. Table 12.1 shows a number of the most common “purposes of examination.” It is expressed in the following text and in the table as “purpose.” Most of these purposes are covered by one or more ASTM standards and, in this case, the standard共s兲 is indicated. For a given material also microetching is performed in accordance with the purpose of the examination, and therefore also chemical microetching with a list of etchants 共Table 12.2兲 is stated in this chapter.

12.2 Purpose: ASTM Standards A preparation is made very often to be able to make an examination according to an ASTM standard. Section 12.4 lists all ASTM standards commonly used in metallography and materialography and a Document Summary of each standard is indicated in a CD-ROM included with this manual. Other relevant standards 共ISO, BSI, DIN, etc.兲 are stated in Appendixes I and II. In Table 12.1, the ASTM standards are shown relating to purpose.

12.3 Table 12.1: Purpose/ASTM Standards Table 12.1indicates a number of common purposes of examination with the most important ASTM standards, if any. Not all applicable standards are listed in this table, only some of the more pertinent ones. As part of each Material/Preparation Tables 共Section 13.2.3兲, a similar table will be stated, but only the purposes and the ASTM standards, relevant for the material described in the Material/Preparation Tables, will be indicated.

12.4 ASTM Standards—Metallography 12.4.1 Introduction The metallographic field is covered by ASTM with a number of documents of the following types: Guide—a compendium of information or series of options that doesn’t recommend a specific course of action. Practice—a definitive set of instructions for performing one or more specific operations or functions that does not produce a test result. 188

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189

TABLE 12.1—Purpose/ASTM Standards. Purpose (alphabetic): Case or coating thickness/hardness Surface layers Perfect edge retention Graphite in cast iron Grain size, grain boundaries Heat-influenced zone Heat treatment Image analysis, rating of inclusion content High planeness Inclusions in steel Microhardness, hardness Microstructure

Phase identification Porosity Structure changes (forging) Thermal sprayed coatings: Distribution, porosity, unmelted particles

ASTM Standard (See Section 12.4) B 487, B 578, B 748, B 931, B 933, B 934, C 664, E 1077 A 247 B 390, E 112, E 930, E 1181, E 1382 E 1077 E 45, E 562, E 768, E 1077, E 1181, E 1245, E 1268, E 1382, E 2109 B 796, E 45, E 768, E 1245 B 578, C 730, C 849, C 1326, C 1327, E 10, E 18, E 92, E 103, E 110, E 140, E 384, E 448 A 247, A 892, B 657, B 665, E 3, E 45, E 112, E 407, E 562, E 768, E 883, E 930, E 1077, E 1122, E 1181, E 1245, E 1268, E 1351, E 1382, E 1558, E 1920, E 2015, E 2109, E 2283 A 247, B 657 B 276, E 2109, F 1854 E 1920, E 2109

Specification—an explicit set of requirements to be satisfied by a material, product, system, or service. Terminology—a document comprising definitions of terms—explanation of symbols, abbreviations, or acronyms. Test Method—a definitive procedure that produces a test result. Most of the standards covering metallography and materialography are published in the Annual Book of ASTM Standards, Volume 03.01, Metals—Mechanical Testing; Elevated and Low-Temperature Tests; Metallography 共ASTM Stock Number: S030100兲. The standards covering metallography, including Microindentation Hardness Testing, are under the jurisdiction of ASTM Committee E4. Those covering other types of hardness testing are under ASTM Committee E28.

Designation Each standard has a serial designation prefixed to the following title, the number following the dash indicates the year of original adoption as a standard or, in the case of revision, the year of the last revision. Thus, standards adopted or revised during the year 2003 have as their final number, 03. A letter following this number indicates more than one revision during that year, that is, 03a indicates the second revision in 2003, 03b, the third revision, etc. Standards that have been reapproved without change are indicated by the year of last reapproval in parentheses as part of the designation number, for example, 共2003兲. A superscript epsilon indicates an editorial change since the last revision or reapproval-␧1 for the first change, ␧2 for the second change, etc.

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In this manual, only the serial designations are indicated because the following numbers are continuously changed.

12.4.2 ASTM Standards in this Book All ASTM standards mentioned under METALLOGRAPHY in Volume 03.01 and others, relating to the subjects covered by this book, are listed below. Most of these will be stated as DOCUMENT SUMMARY in Section 12.4.3. The listed standards should not be considered as a complete list of standards covering the subject of metallography/ materialography and related subjects. Also, a few specifications covering materials are shown as examples. The standards listed are based on the situation as per October 2006, and this situation will change due to the development of new standards and the revision or deletion of old standards.

ASTM Standards Listed by Subject „Alphabetically… Coatings Test Methods for: B 487 Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of a Cross Section B 578 Microhardness of Electroplated Coatings B 588 Measurement of Thickness of Transparent or Opaque Coatings by DoubleBeam Interference Microscope Technique B 748 Measurement of the Thickness of Metallic Coatings by Measurement of Cross Section with a Scanning Electron Microscope C 664 Thickness of Diffusion Coating

Criteria for Metallographic Laboratory Evaluation, Safety, and Management Guide for: E 1578 Laboratory Information Management Systems 共LIMS兲 E 2014 Metallographic Laboratory Safety

Grain Size Test Methods for: E 1181 Characterizing Duplex Grain Sizes E 112 Determining Average Grain Size E 930 Estimating the Largest Grain Observed in a Metallographic Section 共ALA Grain Size兲 Practice for: B 390 Evaluating Apparent Grain Size and Distribution of Cemented Tungsten Carbides Guides for: E 1951 Calibrating Reticles and Light Microscope Magnifications

Inclusions Test Methods for: B 795 Determining the Percentage of Alloyed or Unalloyed Iron Contamination Present in Powder Forges 共P/F兲 Steel Parts

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B 796 Nonmetallic Inclusion Content of Powders Intended for Powder Forging 共P/F兲 Applications E 45 Determining the Inclusion Content of Steel

Indentation Hardness Testing Specifications for: E 140 Hardness Conversion Tables for Metals. Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness, Superficial Hardness, Knoop Hardness, and Scleroscope Hardness. Please refer to ASTM E 140 in the CD-ROM included with this manual. Test Methods for: C 730 Knoop Indentation Hardness of Glass C 849 Knoop Indentation Hardness of Ceramic Whitewares C 1326 Knoop Indentation Hardness of Advanced Ceramics C 1327 Vickers Indentation Hardness of Advanced Ceramics D 785 Rockwell Hardness of Plastics and Electrical Insulating Materials D 1415 Rubber Property-International Hardness D 2240 Rubber Property-Durometer Hardness E 10 Brinell Hardness of Metallic Materials E 110 Indentation Hardness of Metallic Materials by Portable Hardness Testers E 103 Rapid Indentation Hardness Testing of Metallic Materials E 18 Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials E 92 Vickers Hardness of Metallic Materials Practice for: E 448 Scleroscope Hardness Testing of Metallic Materials

Microindentation Hardness Testing Test Methods for: B 578 Microhardness of Electroplated Coatings B 931 Metallographically Estimating the Observed Case Depth of Ferrons Powder Metallurgy 共P/M兲 Parts B 933 Microindentation Hardness of Poweder Metallurgy 共P/M兲 Materials B 934 Effective Case Depth of Ferrous Poweder Metallurgy 共P/M兲 Parts Using Microindentation Hardness Measurements E 384 Microindentation Hardness of Materials Practice for: WK 382 Instrumented Indentation Testing

Porosity Test Method for: B 276 Apparent Porosity in Cemented Carbides See also under Quantitative Metallography

Quantitative Metallography Test Methods for: D 629 Quantitative Analysis of Textiles D 1030 Fiber Analysis of Paper and Paperboard

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D 2798 Microscopical Determination of the Reflectance of Vitrinite in a Polished Specimen of Coal E 562 Determining Volume Fraction by Systematic Manual Point Count E 1382 Determining the Average Grain Size Using Semiautomatic and Automatic Image Analysis E 1077 Estimating the Depth of Decarburization of Steel Specimens E 2109 Determining Area Percentage Porosity in Thermal Sprayed Coatings F 1854 Stereological Evaluation of Porous Coatings on Medical Implants Practices for: C-856 Petrographic Examination of Hardened Concrete E 1268 Assessing the Degree of Banding or Orientation of Microstructures E 1245 Determining the Inclusion or Second-Phase Constituent Content of Metals by Automatic Image Analysis E 2283 Extreme Value Analysis of Nonmetallic Inclusions in Steel and Other Microstructural Features

Sampling, Specimen Preparation and Photography Test Methods for: A 247 Evaluating the Microstructure of Graphite in Iron Castings B 328 Density, Oil Content, and Interconnected Porosity of Sintered Metal Structural Parts and Oil-Impregnated Bearings B 657 Metallographic Determination of Microstructure in Cemented Tungsten Carbides E 381 Macroetch Testing Steel Bars, Billets, Blooms, and Forgings E 340 Macroetching Metals and Alloys E 3 Preparation of Metallographic Specimens Practices for: B 665 Metallographic Sample Preparation of Cemented Tungsten Carbides E 122 Calculating Sample Size to Estimate, with a Specified Tolerable Error, the Average for Characteristic of a Lot or Process E 178 Dealing with Outlying Observations E 407 Microtching Metals and Alloys E 1180 Preparing Sulfur Prints for Macrostructural Examination E 768 Preparing and Evaluating Specimens for Automatic Inclusion Assessment of Steel E 1351 Production and Evaluation of Field Metallographic Replicas Guides for: A 892 Defining and Rating the Microstructure of High Carbon Bearing Steels E 1558 Electrolytic Polishing of Metallographic Specimens E 1920 Metallographic Preparation of Thermal Sprayed Coatings E 2015 Preparation of Plastics and Polymeric Specimens for Microstructural Examination E 883 Reflected-Light Photomicrography

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Terminology Terminology for: E 7 Metallography

X-Ray and Electron Metallography „This subject is not included in this Book.… Test Methods for: E 82 Determining the Orientation of a Metal Crystal E 2142 Rating and Classifying Inclusions in Steel Using the Scanning Electron Microscope Practices for: E 766 Calibrating the Magnification of a Scanning Electron Microscope E 963 Electrolytic Extraction of Phases from Ni and Ni-Fe Base Superalloys Using a Hydrochloric-Methanol Electrolyte E 81 Preparing Quantitative Pole Figures E 986 Scanning Electron Microscope Beam Size Characterization Performance Characterization E 975 X-Ray Determination of Retained Austenite in Steel with Near Random Crystallographic Orientation Guides for: E 1508 Quantitative Analysis by Energy-Dispersive Spectroscopy

ASTM Specifications—Examples Standard Specification for: A 1 Carbon Steel Tee Rails A 3 Steel Joint Bars, Low, Medium, and High Carbon 共Non-Heat-Treated兲 A 36 Carbon Structural Steel A 47 Ferritic Malleable Iron Castings A 48 Gray Iron Castings A 126 Gray Iron Castings for Valves, Flanges, and Pipe Fittings A 159 Automotive Gray Iron Castings A 197 Cupola Malleable Iron A 220 Pearlitic Malleable Iron A 242 High-Strength Low-Alloy Structural Steel A 338 Malleable Iron Flanges, Pipe Fittings, and Valve Parts for Railroad, Marine, and Other Heavy Duty Service at Temperatures Up to 650° F 共345° C兲 A 377 Ductile-Iron Pressure Pipe A 439 Austenitic Ductile Iron Castings A 532 Abrasion-Resistant Cast Irons A 536 Ductile Iron Castings A 572 High-Strength Low-Alloy Colombium-Vanadium Structural Steel A 602 Automotive Malleable Iron Castings A 656 Hot-Rolled Structural Steel, High-Strength Low-Alloy Plate with Improved Formability

12.4.3 ASTM Standards—Document Summaries For Document Summaries on the above mentioned standards please refer to the CDROM included with this manual.

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12.5 Chemical Microetching—Table 12.2—Table 12.3 The prepared specimen surface typically must be etched to reveal the microstructure depending on the purpose of examination. Mostly this is done with chemical solutions, etchants, developed for a specific material and often for a specific purpose. In ASTM Practice for Microetching Metals and Alloys 共E 407兲共see Section 12.4.3兲 a large number of etchants for metals are stated with the purposes 共uses兲. Based on Table 1 of the newest version of this practice 共ASTM E 407–99兲 and other sources, Refs. 2, 4, and 9, Part I, etchants are stated according to their purpose on each Material/ Preparation Tables, Section 13.2.3. The etchant is identified with a number. This number is taken to Table 12.2, which states the composition and procedure for the etching process. Table 12.2 is based on Table 2 of ASTM E 407–99 covering metals 共etchants 1–226兲 with additions 共etchants 901–950兲, mainly covering ceramics and plastics, taken from Petzow, Ref. 2, 共Part I兲, ASM Handbook, Vol. 9, Ref. 4, 共Part I兲, and Vander Voort, Ref. 9, 共Part I兲. Attention: The ASTM Practice E 407 mentioned above is updated at different time intervals and the reader should consult with the latest published version of the standard which can be found in Annual Book of Standards, Volume 03.01 共see Section 12.4.1兲. For etchants not mentioned in this book, see references in Section 9.1, and Literature, Chapter 27. Etchant Names: Some etchants have special names, like “Beraha.” These names are stated in Table 12.3, indicating the etchant number so that the composition can be found in Table 12.2. Table 12.3 is based on Table 3 of ASTM E 407. Theory of Microetching: For chemical etching theory, different types of etching and literature on etching see Chapter 9.

12.5.1 Etching Practice Chemical etching is a straightforward, reasonably simple process. In most cases a relative small quantity of the etchant is placed in a shallow beaker, and the carefully cleaned and dried specimen is immersed into the reagent. The specimen should always be held with a pair of tongs, and preferably with the surface turning upwards to be able to see the progress of the process. The specimen is moved gently to remove reaction products on the surface. In some cases a swabbing with a saturated piece of cotton can be recommended, but the cotton might scratch the surface and care should be taken that the cotton is regularly recharged with reagent. Safety Precautions: See Sections 9.3.4 and 26.2 and ASTM Guide for Metallographic Laboratory Safety 共E 2014兲. Please refer to E 2014 in the CD-ROM included with this manual.

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12.5.2 Table 12.2—Numerical List of Etchants TABLE 12.2—Numerical list of etchants. (This table contains etchants mentioned in the Material/ Preparation Tables and other etchants, seeASTM E 407.) Etchant 1

Composition 1 mL HF 200 mL water

2

3 mL HF 100 mL water

3

2 mL HF 3 mL HCl 5 mL HNO3 190 mL water 24 mL H3PO4 50 mL Carbitol (diethylene glycol monoethyl ether) 4 g boric acid 2 g oxalic acid 10 mL HF 32 mL water 5 g HBF4 200 mL water

4

5

6 7 8 9

10 11 12 13

25 mL HNO3 75 mL water 10– 20 mL H2SO4 80 mL water 10 mL H3PO4 90 mL water 3–4 9 sulfamic acid 5 drops HF 100 mL water 10 mL HF 90 mL methanol (90 %) 2 mL HF 100 mL water 20 mL HNO3 60 mL HCl 10 g oxalic acid 100 mL water

Procedure (a) Swab with cotton for 15 s. (b) Alternately immerse and polish several minutes. (c) Immerse 3 – 5 s. (d) Immerse 10– 120 s. (a) Swab 10 s to reveal general structure. (b) Immerse 15 min, wash 10 min in water to form film with hatching which varies with grain orientation. (a) Immerse 10– 20 s. Wash in stream of warm water. Reveals general structure. (b) Dilute with 4 parts water-colors constituents— mix fresh. Electrolytic: Use carbon cathode raising d-c voltage from 0 – 30 V in 30 s. Total etching time 3 min with agitation. Wash and cool. Repeat if necessary.

Electrolytic: Use Al, Pb, or stainless steel cathode. Anodize 1 – 3 min, 20– 45 V d-c. At 30 V, etch for 1 min. Immerse 40 s at 70° C 共160° F兲. Rinse in cold water. Immerse 30 s at 70° C 共160° F兲. Rinse in cold water. (a) Immerse 1 – 3 min at 50° C 共120° F兲. (b) Electrolytic at 1 – 8 V for 5 – 10 s. Use just prior to the last polishing operation. It is not intended as a final etchant. The specimen is examined as polished even under polarized light. Immerse 10– 30 s. Immerse or swab few seconds to a minute. Use hood. Do not store. Immerse or swab 5 – 60 s. Electrolytic at 6 V: (a) 10– 15 s. (b) 1 min. (c) 2 – 3 s. Use stainless steel cathode and platinum or Nichrome connection to specimen.

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TABLE 12.2—Numerical list of etchants. (This table contains etchants mentioned in the Material/ Preparation Tables and other etchants, seeASTM E 407.)(Continued.) Etchant 14 15

16 17

18 19

20 21 22

23

24

25

26

27

28

Composition 10 mL HNO3 90 mL methanol (95 %) 15 mL HNO3 15 mL acetic acid 60 mL HCl 15 mL water 5 – 10 mL HCl 100 mL water 5 mL HCl 10 g FeCl3 100 mL water 2 – 10 g CrO3 100 mL water A 8 g NaOH 100 mL water B Saturated aqueous solution of KMnO4 5 mL H2O2 (30 %) 100 mL HCl 1 g CrO3 140 mL HCl 100 mL HCl 0.5 mL H2O2 (30 %)

5 mL HCl 95 mL ethanol (95 %) or methanol (95 %) 5 mL HNO3 200 mL HCl 65 g FeCl3 10 g CuSO4 50 mL HCl 50 mL water 5 g FeCl3 10 mL HCl 50 mL glycerol 30 mL water 1 g KOH 20 mL H2O2 (3 %) 50 mL NH4OH 30 mL water 1 g FeNO3 100 mL water

Procedure Immerse few seconds to a minute. Age before use. Immerse 5 – 30 s. May be used electrolytically.

Electrolytic at 3 V for 2 – 10 s. Electrolytic at 6 V for few seconds.

Electrolytic at 3 V for 2 – 10 s. Immerse in freshly mixed Solutions A + B (1:1) for 5 – 10 s. If surface activation is necessary, first use Etch #18, then rinse in water. While still wet, immerse in Solutions A + B (1:1). Mixture of solutions A + B has 15 min useful life. Use hood. Mix fresh. Immerse polished face up for few seconds. Use hood. To mix, add the HCl to CrO3. Electrolytic at 3 V for 2 – 10 s. Use hood. Do not store. (a) Immerse or swab 1 / 2 – 3 min. Add H2O2 dropwise to maintain action. (b) Electrolytic, 4 V, 3 – 5 s. Electrolytic at 6 V for 10– 20 s.

Use hood. Immerse few seconds.

Immerse or swab 5 – 60 s. Made more active by adding few drops of H2SO4 just before use. Swab 16– 60 s. Activity may be decreased by substituting glycerol for water.

Dissolve KOH in water, then slowly add NH4OH to solution. Add 3 % H2O2 last. Use fresh—immerse few seconds to a minute. Swab or immerse few seconds to a minute.

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TABLE 12.2—Numerical list of etchants. (This table contains etchants mentioned in the Material/ Preparation Tables and other etchants, seeASTM E 407.)(Continued.) Etchant 29

30

31

32 33

34

35

36

37

38

39

40

41

Composition 1 g K2Cr2O7 4 mL H2SO4 50 mL water 25 mL NH4OH 25 mL water 50 mL H2O2 (3 %) 10 g ammonium persulfate 100 mL water

60 g CrO3 100 mL water 10 g CrO3 2–4 drops HCl 100 mL water 5 g FeCl3 50 mL HCl 100 mL water

20 g FeCl3 5 mL HCl 1 g CrO3 100 mL water 25 g FeCl3 25 mL HCl 100 mL water 1 g FeCl3 10 mL HCl 100 mL water 8 g FeCl3 25 mL HCl 100 mL water 5 g FeCl3 10 mL HCl 1 g CuCl2 0.1 g SnCl2 100 mL water 5 gFeCl3 16 ML HCl 60 mL ethanol (95 %) or methanol (95 %) 2 g K2Cr2O7 8 mL H2SO4 4 drops HCl 100 mL water

Procedure Add 2 drops of HCl just before using. Swab few seconds to a minute. Mix NH4OH and water before adding H2O2. Must be used fresh. Swab 5 – 45 s. (a) Swab or immerse to 5 s. (b) Immerse to 2 min to darken matrix to reveal carbides and phosphides. (c) Electrolytic at 6 V for few seconds to a minute. (d) Immerse 3 – 60 s. Can be heated to increase activity. Saturated solution. Immerse or swab 5 – 30 s. Add HCl just before use. Immerse 3 – 30 s. Phases can be colored by Nos. 35, 36, 37. (a) Immerse or swab few seconds to few minutes. Small additions of HNO3 activate solution and minimize pitting. (b) Immerse or swab few seconds at a time. Repeat as necessary. Immerse or swab few seconds at a time until desired results are obtained.

Immerse or swab few seconds at a time until desired results are obtained. Immerse or swab few seconds at a time until desired results are obtained Swab 5 – 30 s.

Immerse or swab few seconds at a time until desired results are obtained.

Immerse or swab few seconds to few minutes.

Add the HCl just before using. Immerse 3 – 60 s.

198



43 44

45 46

47

Composition 10 g cupric ammonium chloride 100 mL water NH4OH 20 mL NH4OH 1 g ammonium persulfate 50 mL NH4OH 20– 50 mL H2O2 (3 %) 0 – 50 mL water 1 g CrO3 100 mL water 15 mL NH4OH 15 mL H2O2 (3 %) 15 mL water 4 pellets NaOH 5 g NaCN or KCN 5 g 共NH4兲2S2O2 100 mL water

48

10 g NaCN 100 mL water

49

3 g FeSO4 0.4 g NaOH 10 mL H2SO4 190 mL water 5 mL acetic acid 10 mL HNO3 85 mL water 2 g FeCl3 5 mL HCl 30 mL water 60 mL ethanol or methanol 1 g sodium dichromate 1 g NaCl 4 mL H2SO4 250 mL water 1 – 5 mL NH4OH 100 mL water 1 g ammonium acetate 3 g sodium thiosulfate 7 mL NH4OH 1300 mL water

50

51

52

53 54

Procedure Add NH4OH to solution until neutral or slightly alkaline. Immerse 5 – 60 s. Immerse 5 – 30 s. Use fresh. Peroxide content varies directly with copper content of alloy to be etched. Immerse or swab to 1 min. Film on etched aluminum bronze removed by No. 82. Electrolytic at 6 V for 3 – 6 s. Use aluminum cathode. When mixing, add NaOH pellets last. For best results use before pellets have dissolved.

Use hood—Can give off extremely poisonous hydrogen cyanide. Precaution—Also poisonous by ingestion as well as contact. Use hood—Can give off extremely poisonous hydrogen cyanide. Precaution—Also poisonous by ingestion as well as contact. Electrolytic at 6 V: (a) 5 s for sigma. (b) 30 s for ferrite and general structure. (c) to 5 min for carbides. Electrolytic at 8 – 10 V 共0.1 A兲 for 5 – 15 s.

Use hood. Do not store. Electrolytic at 1.5 V for 20 to 60 s. Use platinum wires. Immerse few minutes.

Swab few seconds.

Immerse 5 – 60 s. Electrolytic at 0.3 A / cm2 for 5 – 30 s.

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56

57 58

59

60

61 62

63

64

Composition 1 mL H2SO4 15 mL HNO3 10 mL acetic acid 5 mL H3PO4 20 mL lactic acid 30 mL HNO3 10 mL H3PO4 20 mL acetic acid 10 mL lactic acid 75 mL acetic acid 25 mL H2O2 (30 %) 25 mL HF 25 mL HNO3 5 mL water 2 g AgNO3 40 mL water 40 mL HF 20 mL HNO3 25 mL HNO3 15 mL acetic acid 15 mL HF 5–7 drops bromine 60 mL HCl 40 mL HNO3 1 – 5 g CrO3 100 mL HCl 0.1 g CrO3 10 mL HNO3 100 mL HCl 5 mL HNO3 25 mL HCl 30 mL water

65

A 10 g ammonium persulfate 100 mL water B 10 g KCN 100 mL water

66

30 mL HF 15 mL HNO3 30 mL HCl 10 mL perchloric acid 10 mL 2-butoxyethanol 70 mL ethanol (95 %) 10 mL water

67

Procedure Swab gently 10– 15 s. Rinse with methanol and blow dry. Helps to chemically polish. If final etch is too even mild, follow with No. 98.

Swab gently 5 – 15 s. Rinse with ethanol or methanol and blow dry.

Immerse 6 – 15 s. Swab 3 – 20 s.

Mix AgNO3 and water, then add HF and HNO3. Swab 1 / 2 – 2 min.

Use hood. Let stand 1 / 2 h before using. Swab 3 – 20 s.

Use hood. Immerse few seconds to a minute. Vary composition of reagent and aging of reagent after mixing to suit alloy. Swab or immerse few seconds to a minute. Swab few seconds to a minute.

(a) Immerse 1 – 5 min. (b) Use hot. Will form chloride film on gold alloys if much silver is present. Ammonia will remove film. Use hood—Can give off extremely poisonous hydrogen cyanide. Precaution—Also poisonous by ingestion as well as contact. Mix 1 + 1 mixture of Solutions A and B just before use. (A mixture of 5 drops of each will cover the surface of a 1 in. dia. mount.) Immerse 1 / 2 – 2 min. Swab 3 – 10 s or immerse to 2 min.

Precaution—Keep cool when mixing and use. Electrolytic at 30– 65 V for 10– 60 s.

200



69 70

71

72

73

74

Composition 3 mL perchloric acid 35 mL 2-butoxyethanol 60 mL methanol (absolute) 5 mL perchloric acid 80 mL acetic acid 5 mL HF 2 mL AgNO3 (5 %) 200 mL water 5 mL HF 95 mL water

10 mL HF 45 mL HNO3 45 mL water 20 mL HCl 25 g NaCl 65 mL water

1 – 5 mL HNO3 100 mL ethanol (95 %) or methanol (95 %)

Procedure Precaution—Keep cool when mixing and use. Electrolytic at 60– 150 V for 5 – 30 s. Precaution—Keep cool when mixing and use. Electrolytic at 20– 60 V for 1 – 5 min. Swab for 5 – 60 s.

Add 5–10 drops of this solution on the final polishing wheel which has been charged with the polishing solution. The specimen is polished on this wheel until the surface turns black. Distilled water is then slowly added to the wheel and polishing continued until the surface is bright. At this time the specimen should be ready for examination via polarized light. Note—Use inert substance between cloth and wheel to prevent attack of the wheel. Wear gloves. Swab for 5 – 20 s.

Electrolytic etch—use carbon cathode and platinum wire connection to specimen. (a) 6 V ac for 1 min. (b) 5 V – 20 V ac for 1 – 2 min. (c) 20 V ac for 1 – 2 min. For etch-polishing, use shorter times. After etching, water rinse, alcohol rinse, and dry. Etching rate is increased, sensitivity decreased with increased percentage of HNO3. (a) Immerse few seconds to a minute. (b) Immerse 5 – 40 s in 5 % HNO3 solution. To remove stain, immerse 25 s in 10 % HCl-methanol solution. (c) For Inconels and Nimonics, use 5 mL HNO3 solution—electrolytic at 5 – 10 V for 5– 20 s. (d) Swab or immerse several minutes. (e) Swab 5 – 60 s. HNO3 may be increased to 30 mL in methanol only depending on alloy. (Ethanol is unstable with over 5 % HNO3). Do not store.

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76

77

78

79

80

Composition 5 g picric acid 8 g CuCl2 20 mL HCl 200 mL ethanol (95 %) or methanol (95 %) 4 g picric acid 100 mL ethanol (95 %) or methanol (95 %) 10 g picric acid 5 drops HCl 100 mL ethanol (95 %) or methanol (95 %) 10 g potassium metabisulfite 100 mL water 40 mL HCl 5 g CuCl2 30 mL water 25 mL ethanol (95 %) or methanol (95 %) 5 mL HCl 1 g picric acid 100 mL ethanol (95 %) or methanol (95 %)

81

2 g picric acid 1 g sodium tridecylbenzene sulfonate 100 mL water

82

5 g FeCl3 5 drops HCl 100 mL water 10 g CrO3 100 mL water

83

84

10 mL H2SO4 10 mL HNO3 80 mL water

85

2 g picric acid 25 g NaOH 100 mL water

Procedure Immerse 1 – 2 s at a time and immediately rinse with methanol. Repeat as often as necessary. (Long immersion times will result in copper deposition on surface.) Composition given will saturate with picric acid. Immerse few seconds to a minute or more. Adding a wetting agent such as zepherin chloride will increase response. Composition given will saturate the solution with picric acid. Immerse few seconds to a minute or more. Immerse 1 – 15 s. Better results are sometimes obtained by first etching lightly with No. 76 or 74. Swab few seconds to a minute.

Immerse or swab few seconds to 15 min. Reaction may be accelerated by adding a few drops of 3 % H2O2. Optional (for prior austenite grain boundaries)—temper specimen at 600– 900° F prior to preparation. Composition given will saturate the should with picric acid. (a) Immerse few seconds to a minute. (b) Immerse to 15 min with occasional swabbing for heavy grain boundary attack. Immerse 5 – 10 s.

(a) Electrolytic at 6 V for 5 – 60 s. Attacks carbides. (b) Electrolytic at 6 V for 3 – 5 s. Precaution—Add H2SO4 slowly to water and cool, then add HNO3. Immerse 30 s. Swab in running water. Repeat three times and repolish lightly. Immerse in boiling solution for 5 min. Precaution— Do not boil dry—anhydrous picric acid is unstable and highly explosive. Alternative: Electrolytic at 6 V for 40 s (room temperature). Use stainless steel cathode.

202



Composition 3 g oxalic acid 4 mL H2O2 (30 %) 100 mL water

87

10 mL HNO3 20– 50 mL HCl 30 mL glycerol

88

10 mL HNO3 20 mL HCl 30 mL water

89

10 mL HNO3 10 mL acetic acid 15 mL HCl 2–5 drops glycerol 10 mL HNO3 20 mL HF 20– 40 mL glycerol 5 mL HNO3 5 mL HCl 1 g picric acid 200 mL ethanol (95 %) or methanol (95 %) 10 mL HCl 100 mL ethanol (95 %) or methanol (95 %) concentrated HNO3

90

91

92

93 94

95

96

2 g CuCl2 40 mL HCl 40– 80 mL ethanol (95 %) or methanol (95 %) 2 g CuCl2 40 mL HCl 40– 80 mL ethanol (95 %) or methanol (95 %) 40 mL water 85 g NaOH 50 mL water

Procedure Solution should be freshly prepared. Immerse 15– 25 min when specimens or parts cannot be given usual metallographic polish. Multiple etching may be required. Use hood—Can give off nitrogen dioxide gas. Precaution—Mix HCl and glycerol thoroughly before adding HNO3. Do not store. Discard before solution attains a dark orange color. Immerse or swab few seconds to few minutes. Higher percentage of HCl minimizes pitting. A hot water rinse just prior to etching may be used to activate the reaction. Sometimes a few passes on the final polishing wheel is also necessary to remove a passive surface. Use hood—Can give off nitrogen dioxide gas. Precaution—Discard before solution attains a dark orange color. Immerse few seconds to a minute. Much stronger reaction than No. 87. Use hood. Do not store. Immerse or swab few seconds to few minutes.

Immerse 2 – 10 s.

This etchant is equivalent to a 1 + 1 mixture of No. 80 and No. 74 (5 % HNO3). Swab for 30 s or longer.

Immerse 5 – 30 min or electrolytic at 6 V for 3 – 5 s. Use hood. Electrolytic at 0.2 A / cm2 for few seconds. Submerged swabbing for few seconds to several minutes. Attacks ferrite more readily than austenite. Immerse or swab few seconds to few minutes.

Electrolytic at 6 V for 5 – 10 s.

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Composition 45 g KOH 60 mL water

98

10 g Fe共CN兲4 10 g KOH or NaOH 100 mL water

99

25 mL HCl 3 g ammonium bifluoride 125 mL water few grains potassium metabisulfite 10 g FeCl3 90 mL water 2 g CrO3 20 mL HCl 80 mL water concentrated NH4OH

100 101

102 103

104

105

106

20 mL HNO3 4 mL HCl 20 mL methanol (99 %) 5 mL HNO3 45 mL HCl 50 mL water 5 mL H2SO4 3 mL HNO3 90 mL HCl 7 mL HNO3 25 mL HCl 10 mL methanol (99 %)

Procedure Composition of solution is approximately 10 N. Electrolytic at 2.5 V for few seconds. Stains sigma and chi yellow to red brown, ferrite gray to blue gray, carbides barely touched, austenite not touched. Use hood—Can give off extremely poisonous hydrogen cyanide. Precaution—Also poisonous by ingestion as well as contact. Use fresh. (a) Immerse or swab 15– 60 s. Stains carbides and sigma. (To differentiate, No. 31 electrolytic at 4 V will attack sigma, but not carbides. If pitting occurs, reduce voltage.) (b) Immerse in fresh, hot solution 2 – 20 min. Stains carbides dark, ferrite yellow, sigma blue. Austenite turns brown on overetching. (c) Swab 5 – 60 s. (Immersion will produce a stain etch.) Follow with water rinse, alcohol rinse, dry. Mix fresh. (For stock solution, mix first three items. Add potassium metabisulfite just before use.) Immerse few seconds to a few minutes. Immerse few seconds. Immerse 5 – 60 s. (CrO3 may be increased up to 20 g for difficult alloys. Staining and pitting increase as CrO3 increased.) Use hood. Electrolytic at 6 V for 30– 60 s. Attacks carbides only. Immerse 10– 60 s.

Immerse 10 min or longer.

Use hood. Precaution—add H2SO4 slowly to HCl with stirring, cool; then add HNO3. Discard when dark orange color. Swab 10– 30 s. Use fresh to avoid pitting. Immerse or swab 10– 60 s.

204



Composition 10 mL H3PO4 50 mL H2SO4 40 mL HNO3

108

3 – 10 mL H2SO4 100 mL water 50 mL HCl 25 mL HNO3 1 g CuCl2 150 mL water 10 mL HCl 5 mL HNO3 85 mL ethanol (95 %) or methanol (95 %) 5 mL H2SO4 8 g CrO3 85 mL H3PO4 60 mL acetic acid 30 mL H2O2 (30 %) 15 mL acetic acid 15 mL HNO3 60 mL glycerol 15 mL acetic acid 20 mL HNO3 80 mL water

109

110

111

112 113

114

115

100 mL acetic acid 10 mL H2O2 (30 %)

116 117

5 – 10 g AgNO3 90 mL water 10 mL HCl 90 mL water

118

1 mL HNO3 75 mL diethylene glycol 25 mL water 1 mL HNO3 20 mL acetic acid 60 mL diethylene glycol 20 mL water

119

Procedure Use hood. Precaution—Mix H3PO4 and HNO3 thoroughly, then add H2SO4 slowly with stirring. Use fresh, but allow to cool. Electrolytic at 6 V for few seconds. Brown discoloration will form at edges of specimen. To slow reaction, add water (to 100 mL) very carefully with stirring. Attacks bakelite mounts. Electyrolytic at 6 V for 5 – 10 s. Tends to pit with longer times. Make fresh but allow to stand 30 min to avoid plating out copper. Immerse few seconds to a few minutes. Immerse to several minutes until deeply etched. Follow with light repolish.

Electrolytic at 10 V 共0.2 A / cm2兲 for 5 – 30 s. Reveals Ti- and Cb-rich areas at a faster rate than grain boundaries. Immerse 8 – 15 s. Do not store. Use fresh solution at 80° C 共176° F兲.

Use fresh solution at 40– 42° C 共104– 108° F兲. Immerse 4 – 30 min depending on depth of worked metal layer. Clean with cotton in running water. Immerse 10– 30 min depending on depth of worked metal layer. Clean in HNO3 if necessary. Swab. (a) Immerse for 1 / 2 – 5 min. Follow with electrolytic etch at low current density in same solution. If specimen has considerable surface flow, immerse in concentrated HCl for a few seconds, then follow above procedure. (b) Immerse for 1 / 2 – 2 min. Swab 3 – 5 s for F and T6, 1 – 2 min for T4 and O temper. Swab 1 – 3 s for F and T6, 10 s for T4 and O temper.

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TABLE 12.2—Numerical list of etchants. (This table contains etchants mentioned in the Material/ Preparation Tables and other etchants, seeASTM E 407.)(Continued.) Etchant 120 121

122 123

124

125

126

127

128

129

130 131

132

Composition 10 mL HF 90 mL water 0.7 mL H3PO4 4 g picric acid 100 mL ethanol (95 %) or methanol (95 %) 2 g oxalic acid 100 mL water 60 mL H3PO4 100 mL ethanol (95 %) 5 mL acetic acid 10 mL water 6 g picric acid 100 mL ethanol (95 %) or methanol (95 %) 10 mL acetic acid 6 g picric acid 100 mL ethanol (95 %) or methanol (95 %) 30 mL acetic acid 15 mL water 6 g picric acid 100 mL ethanol (95 %) or methanol (95 %) 20 mL acetic acid 20 mL water 3 g picric acid 50 mL ethanol (95 %) or methanol (95 %) 8 mL HF 5 mL HNO3 200 mL water 10 mL HF 30 mL HNO3 60 mL lactic acid 25 mL HCl 75 mL methanol 5 mL H2SO4 1 mL HF 100 mL methanol (95 %) 5 mL HF 10 mL HNO3 50 mL lactic acid

Procedure Immerse with gentle agitation 3 – 30 s. Composition critical. (a) Immerse with gentle agitation 10– 30 s. (b) To increase staining immerse and withdraw with a meniscus layer. Lightly apply etchant over surface until dark stain develops. Swab. Electrolytic: Use stainless steel cathode. Space electrodes 2 cm apart. Start at 3 V dc. After 30 s maintain at 11 / 2 V. Immerse with gentle agitation 10– 60 s.

Immerse with gentle agitation 15– 30 s.

Immerse with gentle agitation 1 – 30 s.



Swab 10– 20 s. Vary HF to increase or decrease activity. Caution—Keep below 24° C 共75° F兲. Electrolytic at 30 V for 30 s. Electrolytic at 50– 60 V for 10– 20 s.

Use fresh. (a) Swab with heavy pressure for 5 – 10 s. Water rinse, alcohol rinse, dry, then etch with No. 98c. (b) Swab for 5 – 30 s.

206



Composition 50 mL HNO3 50 mL acetic acid

134

70 mL H3PO4 30 mL water 80 mL HNO3 3 mL HF 20 mL H3PO4 80 mL water 10 g NaNO3 100 mL water 5 g FeCl3 2 mL HCl 100 mL ethanol (95 %) or methanol (95 %) 5 g (95 %) KCN 100 mL water 0.5 mL H2O2 (3 %)

135 136 137 138

139

140

141

142

144

145

146 147 148 149

50 mL acetic acid 50 mL HNO3 50 mL acetone 3 g NH4Cl 3 g CrO3 10 mL HNO3 90 mL water 5 mL HF 10 mL glycerol 85 mL water A 10 g sodium thiosulfate 100 mL water B 10 mL HCl 90 mL water 2 mL H2SO4 100 mL water 10 mL HF 100 mL HNO3 20 mL HNO3 80 mL HCl 5 mL HNO3 100 mL water 50 mL HCl 2 mL H2O2 (30 %) 50 mL water

Procedure Use hood. Do not store. Mix fresh. Immerse or swab 5 to 30 s. Will chemically polish with longer times. Sulfidized grain boundaries etched before normal grain boundaries. Electrolytic 5 – 10 V for 5 – 60 s. (Polishes at high currents.) Use hood. Warm specimen in boiling water prior to immersion for 10 to 120 s. Electrolytic at 10– 20 V for 10– 15 s. Electrolytic, 0.2 A / cm2, 1 min. Swab 10– 60 s.

Use hood—Can give off extremely poisonous hydrogen cyanide. Precaution—Also poisonous by ingestion as well as contact. Immerse 10– 100 s. Use hood. Do not store. Decomposes with possible explosion on standing. Immerse 10– 30 s. Swab 5 – 30 s. Do not store.

Electrolytic at 2 – 3 V for 2 – 10 s.

Electrolytic in Solution A: specimen is cathode, 10 V, 5 – 10 s. Then electrolytic in Solution B: specimen is anode, 10 V, 5 – 10 s.

Electrolytic at 3 – 10 V for 5 – 15 s. Use platinum wires. H2SO4 may be increased to 20 mL for deeper attack. Immerse 30 s - 3 min. Immerse 5 – 30 s. Immerse 10– 30 s. Immerse 10– 30 s. Do not store.

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151

152 153

154

155

158

157

158

159

160

161 162

Composition 60 mL HCl 20 mL HNO3 40 mL glycerol 10 mL HF 25 mL HNO3 150 mL water 85 mL NH4OH 15 mL H2O2 (30 %) 10 mL HNO3 50 mL HCl 60 mL glycerol 50 mL HCl 50 mL ethanol (95 %) or methanol (95 %) 3 mL selenic acid 10 mL HCl 100 mL ethanol (95 %)or methanol (95 %) 1 g thiourea 1 mL H3PO4 1000 mL water 25 g CrO3 150 mL HCl 50 mL water 10 mL HF 10 mL HNO3 20 mL glycerol 5 mL HF 20 mL HNO3 50 mL acetic acid 20 mL HF 15 mL H2SO4 5 mL HNO3 50 mL water 25 mL HNO3 5 mL HF A 50 mL lactic acid 30 mL HNO3 2 mL HF B 30 mL lactic acid 10 mL HNO3 10 mL HF

Procedure Use hood. Do not store. Swab few seconds to a minute. Discard when solution turns dark yellow. Swab 5 – 30 s.

Immerse 5 – 15 s. Do not store—Decomposes. Use hood. Do not store. Add HNO3 last. Discard when dark yellow. Immerse 10– 60 s. Preheating specimen in boiling water hastens reaction. Immerse 10– 100 s.

Immerse 1 – 15 min. (Up to 30 mL of HCl may be used for more vigorous action.) Stable for 3 – 90 days, depending on HCl concentrations. Electrolytic, 0.005– 0.01 A / cm2, 1 – 2 min.

Immerse 5 – 20 s.

Swab 5 – 15 s.

Swab 10– 30 s.

Immerse to 5 min.

Immerse 5 – 120 s. Swab 1 – 3 min in Solution A (acts as etch polish). To etch, swab with Solution B for 5 s. Repeat if necessary. The HF may be varied to give more or less etching.

208



164

165

Composition 30 mL H2SO4 30 mL HF 3–5 drop H2O2 (30 %) 30 mL water 50 mL HNO3 30 g ammonium bifluoride 20 mL water 10 mL HCl 90 mL ethanol

166


167

5 g NaCN 100 mL water

168

20 mL HCl 35 g NaCl 80 mL water 5 mL HNO3 50 mL ethylene glycol 20 mL ethanol (95 %) or methanol (95 %) 1 mL HF 30 mL HNO3 30 mL lactic acid

169

170

171

concentrated HCl

172


173

50 mL NH4OH 10– 30 mL H2O2 (50 %)

Procedure Immerse 5 – 60 s. Use this solution for alternate etch and polishing.

Use hood. Swab 3 – 10 s.

(a) Electrolytic at 10 V for 30 s. Use carbon cathode and platinum wire connection to specimen. For etch-polishing, use shorter time. (b) Electrolytic at 6 V for 10 s. Use stainless steel cathode and platinum or Nichrome wire contact to specimen. Use hood—Can give off extremely poisonous hydrogen cyanide. Precaution—Also poisonous by ingestion as well as contact. Mix 1 + 1 ratio of Solution A and B just before use. (A mixture of 5 drops of each will cover the surface of the 1 in. dia mount.) Immerse to several minutes. Use hood—Can give of extremely poisonous hydrogen cyanide. Precaution—Also poisonous by ingestion as well as contact. Electrolytic at 1 – 5 V ac for 1 – 2 min. Use platinum cathode. Composition given will saturate the solution with NaCl. Electrolytic at 11/2 V ac for 1 min. Electrolytic at 0.05 A / cm2 for 2 min. Use stainless steel cathode.

(a) Swab 5 – 30 s. Follow with water rinse, alcohol rinse, dry. (b) Swab for 10 s intervals. Increase HF to exaggerate grain boundaries. Use hood. Electrolytic at 5 V ac for 1 – 2 min. For etch-polishing, use shorter times. Follow with water rinse, alcohol rinse, and dry. Use hood—Can give off extremely poisonous hydrogen cyanide. Precaution—Also poisonous by ingestion as well as contact. Prepare 1 + 1 mixture of Solutions A and B just before use. (A mixture of 5 drops of each will cover the surface of a 1 in. dia mount.) Immerse 1 – 2 min. Immerse few seconds to a minute.

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Composition A 25 mL HNO3 1 g K2Cr2O7 1000 mL water B

175

176 177 178

179

180

181

182

183

184

185 186

40 g CrO3 3 g Na2SO4 200 mL water 1 g CrO3 1 mL H2SO4 100 mL water 2 g FeCl3 100 mL water 10 g NaOH 100 mL water 20 mL HF 20 mL HNO3 60 mL lactic acid A 10 mL HF 10 mL HNO3 30 mL lactic acid B 10 mL HF 10 mL HF 90 mL H2SO4 10 mL HNO3 30 mL acetic acid 50 mL glycerol 2 mL HCl 100 mL ethanol (95 %) or methanol (95 %) 10 mL HNO3 10 mL acetic acid 80 mL glycerol 2 drops HF 1 drop HNO3 25 mL glycerol 10 g FeCl3 2 mL HCl 100 mL water 10 mL HF 10 mL HNO3 10 mL HF 5 mL HNO3 85 mL water

Procedure Prepare 1 + 1 mixture of Solutions A and B. Apply with camel’s hair brush. Nonadherent film of silver chromate should form. If film adheres, add more of solution A, if none forms, add Solution B.

Immerse to 1 min.

Immerse 5 – 30 s. Swab or immerse 5 – 15 s. Swab for 5 – 20 s.

Use hood—Mix Solution B very slowly. Solution A is used as a chemical polish, though some etching will occur. Swab 2 or more minutes for desired surface. If surface is insufficiently etched use Solution B electrolytically at 1 / 2 – 1 V / in.2 of specimen. Use carbon cathode and platinum wire connection to specimen. Discard Solution B after 1 h. Immerse for 1 / 2 – 10 min at 38 to 42° C 共100– 108° F兲. Swab for 1 – 3 min.

Immerse for 1 / 2 – 10 min at 38 to 42° C 共100– 108° F兲 Immerse for 1 min.

Immerse for

1 – 5 min. 2

Swab for few seconds. Swab 3 – 2 s.

210



188

189

190

191

192

193

194

195

196

197 198

199

Composition 10 mL HF 30 mL HNO3 50 mL water 1 mL HF 50 mL HNO3 50 mL H2O2 (30 %) 50 mL water 10 mL HF 25 mL HNO3 45 mL glycerol 20 mL water 8 g KOH 10 mL H2O2 (30 %) 60 mL water 25 mL HF 18 g benzalkonium chloride 35 mL methanol (95 %) 40 mL glycerol 1 – 3 mL HF 2 – 6 mL HNO3 100 mL water 2 drops HF 1 drop HNO3 3 mL HCl 25 glycerol 20 mL HF 20 mL HNO3 60 mL glycerol 30 mL H3PO4 30 mL ethylene glycol 50 mL ethanol (95 %) 18 g CrO3 75 mL acetic acid 20 mL water 5 g oxalic acid 100 mL water 30 mL HF 30 mL HNO3 30 mL glycerol 2 mL HF 5 g AgNO3 100 mL water

Procedure Swab 3 – 20 s.

Swab until stain is removed.

Swab 3 – 20 s.

Swab 3 – 20 s.

Swab 3 – 20 s.

Swab 3 – 10 s or immerse 10– 30 s. (HF attacks and HNO3 brightens the surface of titanium. Make concentration changes on this basis.) Swab 3 – 20 s.

Immerse 5 – 30 s.

Electrolytic at 18– 20 V 共0.03 A / cm2兲 for 5 – 15 min. Dissolve CrO3 in hot water and cool before adding acetic acid. Keep solution below 2 ° C 共35° F兲 during use. Electrolytic at 80 V for 5 – 30 min. Do not store. Electrolytic at 6 V for 5 – 20 s. Swab for 60 s.

Swab for 5 s

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Composition A 40 g CrO3 3 g Na2SO4 200 mL water

Procedure Immerse in Solution A with gentle agitation for several seconds. Rinse in Solution B.

B 40 g CrO3 200 mL water 201

A 40 g CrO3 1.5 g Na2SO4 200 mL water

Immerse in Solution A with gentle agitation for several seconds. Rinse in Solution B.

B

202

203 204

205

206

207

208

209

40 g CrO3 200 mL water A 10 g CrO3 1 g Na2SO4 200 mL water B 40 g CrO3 200 mL water 20 g CrO3 100 mL water 10 mL perchloric acid 10 mL glycerol 70 mL ethanol (95 %) 10 mL water 5 mL HF 2 mL AgNO3 (5 %) 100 mL water 5 mL HF 10 mL HNO3 10 mL glycerol 30 mL HNO3 30 mL acetic acid 30 mL water 1 mL NH4OH 3 g ammonium persulfate 10 mL water 15 mL HNO3 3 mL HF 80 mL water

Immerse in Solution A for 2 – 5 s. Rinse in Solution B.

Electrolytic at 0.2 A / cm2 for 5 s. Precaution—Keep cool when mixing and use. Electrolytic at 15– 50 V for 15– 60 s.

Swab vigorously for 10– 60 s. Wet cotton frequently. Precaution—Discard after use. Solution decomposes on standing. Electrolytic at 9–12 V for 1 – 10 min. Swab for 5 – 30 s.

Immerse or swab few seconds to a minute.

Immerse 5 – 60 s.

212



Composition 50 mL water (cold) saturated with sodium thiosulfate 1 g potassium metabisulfite

211

3 g potassium metabisulfite 10 g sodium thiosulfate 100 mL water

212

10–50 % HCl in water 0.5– 1.0 g potassium metabisulfite per 100 mL of aqueous HCl solution Optional: 1 g CuCl2 1 – 3 g FeCl3 2 – 10 g ammonium bifluoride 2 – 10 mL HCl 0.5– 3 mL selenic acid 100 mL ethyl alcohol (95 %)

213

214

1 g sodium molybdate 100 mL water

215

240 g sodium thiosulfate 30 g citric acid 24 g lead acetate 1000 mL water

216

8 – 15 g sodium metabisulfite 100 mL water

217

5 g ammonium bifluoride 100 mL water

218

3 g ammonium bifluoride 4 mL HCl 100 mL water

Procedure First ingredient in stock solution. Add potassium metabisulfite before use. Solution good for several days, or longer. Immerse face up, gently agitate until coloration begins, allow to settle. Stop etch when surface is red-violet. Etch time varies with material. Colors matrix phases. Use fresh solution. Immerse specimen face up, gently agitate solution until coloration begins, allow to settle. Stop etch when surface is red-violet. Etch time varies with material. Colors matrix phases. For more corrosion resistant alloys. Increase the HCl and potassium metabisulfite contents. Use optional ingredients to improve coloration, if needed. Colors matrix phases. Use by immersion only. For more corrosion resistant alloys, increase the HCl and selenic acid content. For highly corrosion-resistant alloy, use 20– 30 mL HCl. Colors second phase constituents. Use by immersion only. Add nitric acid to lower the pH to 2.5–3. Add 0.1– 0.5 g ammonium bifluoride for carton steels. Use by immersion only. Colors carbides. Immerse about 15 s. Mix in order given. Store in a dark bottle at least 24 h before use at 20° C. Lightly preetch specimen before use. Use small portion of stock solution for 4 h max. Pre-etch steel specimens with nital before tinting the MnS (add 0.2 g sodium nitrite to 100 mL of etch) white. Colors phosphides in cast iron. Colors matrix of Cu alloys. Do not store. Mix fresh. Immerse specimen face up. Agitate solution gently until coloration begins, allow to settle. Stop when surface is dark. use crossed polarized light and sensitive tint to improve coloration. Mix fresh, use plastic coated tongs and polyethylene beaker. Immerse until surface is colored. Mix fresh, use plastic coated tongs and polyethylene beaker. Immerse until surface is colored. Works best with attack-polished specimens.

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Composition 60 mL HNO3 40 mL water

220

20 g NaOH 100 mL water

221

50 mL water 50 mL ethyl alcohol 50 mL methyl alcohol 50 mL HCl 1 g CuCl2 2.5 g FeCl3 2.5 mL HNO3 8 g Na2SO4 100 mL water A 8 g oxalic acid 5 mL H2SO4 100 mL water B H2O2 (30 %) 10 mL H2O2 (30 %) 20 mL 10 % aqueous NaOH 4 g NaOH 100 mL saturated aqueous KMnO4 15 mL HCl 10 mL acetic acid 5 mL HNO3 2 drops glycerol

222 223

224 225 226

901 902 903 904

1 g KOH 100 mL water Plasma etching with CF4 gas and O2 gas (1:1) See etchant 98 (Murakami’s reagent) 30 g K3Fe共CN兲6 3 g NaOH 60 mL water

Procedure Electrolytic etch, does not reveal twins in ␥ stainless steel. Excellent grain boundary etch for ferritic stainless steels. Use at 1 V dc, 120 s, with stainless cathode; 0.6 V dc with platinum cathode. Electrolytic etch, colors ␦-ferrite in stainless steel. Use at 2 – 20 V dc, 5 – 20 s, stainless steel cathode. If ␦ is not colored, increase NaOH to 40 g. Use by immersion. Will not attack sulfides in stainless steels.

(a) Few seconds to 1 minute. (b) Pre-etch 2 s in No. 74, rinse, and etch 20 s. Mix equal volumes of Solutions A and B just before use. Etch 2 – 3 s; 3 s pre-etch in No. 74 may be needed.

Immerse 10 s at 20° C 共68° F兲. Immerse 10 s at 20° C 共68° F兲. Use hood—Can give off nitrogen dioxide gas. Precaution—Mix HCl and glycerol thoroughly before adding HNO3. Do not store. Discard before solution attains a dark orange color. Use fresh or age up to 1 min. Immerse or swab few seconds to few minutes. Can increase HNO3 to increase strength. Sometimes a few passes on the final polishing wheel is also necessary to remove a passive surface. Electrolytic: Use stainless steel cathode. 40 V DC at 3 A / cm2 in 30– 60 s 3 – 5 min, 60– 80 W Use hot, 30– 40 min for SiC with 1 % B4C or boiling for B-doped SiC Immerse 5 – 30 min at 110° C 共230° F兲

214



906

907

908

909

910

911 912 913 914 915 916

917

918 919 920 921

922

923 924

Composition 10 g K3Fe共CN兲6 10 g NaOH 20 mL water 10 g K3Fe共CN兲6 10 g NaOH 80 mL water 10 mL HNO3 (65 %) 10 g K3Fe共CN兲6 100 mL water 30 g K3Fe共CN兲6 3 g NaOH 60 mL water 10 mL HNO3 (65 %) 10 mL HF (40 %) 10 mL water 10 mL HF (40 %) 50 mL lactic acid 30 mL HNO3 (65 %) 10 mL HF (40 %) 30 mL HNO3 (65 %) 10 mL HCl (32 %) 10 mL H2O2 (30 %) Plasma etching CF4 gas and O2 gas (2:1) H3PO4 (85 %) Molten NaOH (free of water) 10 mL 10 % aqueous NaH solution 10 mL 10 % aqeous potassium ferricyanide solution 50 mL water (Modified Murakami, see etchant 98) Thermal etch in air 1100– 1500° C

H3PO4 (85 %) HCl (32 %) Sat. aq. Na2S 20 mL HNO3 (65 %) 10 mL HF (40 %) 20 mL water 45 mL HNO3 (65 %) 5 mL HF (40 %) 50 mL water KHSO4, molten 15 mL HNO3 (65 %) 100 mL water

Procedure Immerse 5 – 10 min

Immerse 10– 20 min

Immerse 30– 40 min at 60° C 共140° F兲

Immerse 8 – 15 min. Use boiling

Immerse seconds to min

Immerse 2 min Immerse seconds to min 1 – 5 min, 60– 80 W Use boiling up to 15 min 20 s to 3 min at 300– 350° C 共570– 660° F兲, 2–3 samples per melt Immerse 30 min at 100° C 共212° F兲)

15– 20 min at 1300– 1400° C 共2370– 2550° F兲 (Etch temperature is approximately 150° C 共300° F兲 below sintering temperature 5 s to 3 min at 250° C 共480° F兲 Immerse 3 – 6 min Immerse up to 1 min Immerse up to 15 min

Immerse up to 15 min agitate

Immerse 15– 20 s at 300° C Immerse 3 – 5 min at 25– 60° C 共77– 140° F兲

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926 927 928 929

930 931

932 933 934

935

936 937

938

939

940 941

942

Composition 10 g NaOH 10 g K3Fe共CN兲6 100 mL water Thermal etch in air H3PO4 (85 %) Thermal etch in air 3 mL HCl (32 %) 2 mL HF (40 %) 95 mL water 2 mL HF (32 %) 98 mL water 5 mL HNO3 (65 %) 5 mL HF (40 %) 90 mL water 10 mL HNO3 (65 %) 10 mL HF (40 %) 50– 100 g NaOH 100 mL water 15 mL HCl (32 %) 10 mL HF (40 %) 90 mL water 30 mL HCl (32 %) 5 mL H2O2 (32 %) 70 mL water 30 mL CH3COOH (glacial acetic acid) 10 mL H2O2 (30 %) 30 mL HCl (32 %) 2 g FeCl3 100 mL water 25 mL HCl (32 %) 8 g FeCl3 100 mL water 15 mL HCl (32 %) 50 mL aq. sodium thiosulfate (16 %) 3 mL aq. CrO3 (10 %) 30 mL water 50 mL HCl (32 %) 50 mL water 25 down to 9 mL HNO3 (65 %) 25 down to 9 mL CH3COOH (glacial acetic acid) 100 mL glycerol (87%) 200 mL acetyl acetone 1 – 2 mL nitric acid (65 %)

Procedure Immerse seconds to minutes

Minutes to 1 h at 1300– 1400° C 共2370– 2550° F兲 (according to sintering temperature) Immerse 3 s to 2 min at 250° C 共480° F兲 30– 60 min at 1200° C 共2190° F兲 5 s to 2 min Immerse 5 s to 2 min

Immerse 10– 15 min Immerse, up to 20 s

Immerse up to a few min Immerse up to a few min Immerse up to a few min

Immerse up to a few min

Immerse up to a few min Immerse up to a few min

Add CrO3 just before use

Immerse 1 – 10 min Immerse s to min

Immerse 2 – 18 min in ultrasonic bath to break up the oxide layer

216



945

Composition 100 mL HNO3 (65 %) 100 mL H2SO4 + CrO3 (chromosulfuric acid) (Variable concentration) 60 g CrO3 (chromium (VI)oxide) 100 mL water HNO3 (65 %)

946

C6H4共CH3兲2 (xylol) (99.8 %)

947 948

C6H15N (triethylamine (99 %) 30 mL HCl (32 %) 100 mL distilled water A: Freshly prepared mixture of equal quantities of 10 % (mass/mass) aqueous solutions of K3Fe 共CN兲6 (III) (potassium ferricyanide and potassium or sodium hydroxide)

944

949 ASTM Standard B 657, Etching Technique 1 950 ASTM Standard B 657, Etching Technique 2 951 ASTM Standard B 657, Etching Technique 3

Procedure Immerse in 2 min at 70° C, time varies

Immerse several hours at 70° C Polyethylene (PE): Immerse in seconds to minutes Polyoxymethylene (POM) and polypropylene (PP): Immerse in 10 min Polyethylene, polypropylene: Immerse 3 days at 70° C Polyamid, polyethylene: 70° C for 60 s. Nylon 6: 65– 70° C for 2 – 3 min. Nylon 6,6: 75° C for 3 – 4 min Immerse seconds to minutes Immerse 20 s Etch in mixture A at approx. 20° C for 2 – 10 s. Flush the test-piece section with water immediately, without removing the oxide layer. Dry the surface carefully with acetone or alcohol without wiping

A: same as A (949) B: A mixture of equal volumes of concentrated hydrochloric acid and water

Etch at approx. 20° C in mixture A for 3 – 4 min.. then wash in water and etch in mixture B for approx. 10 s. Next wash in water, then in alcohol and dry the test-piece section. Finally, etch in mixture A for approx. 20 s

A: same as A (949)

Etch in mixture A at approx. 20° C for 3 – 6 min

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12.5.3 Table 12.3—Etchant Names TABLE 12.3—Etchant names. (This table was taken fromASTM E 407.) Common Name Acetic glyceregia Alkaline Sodium Picrate Aqua regia Barker’s Beraha’s Carapella Chrome regia Contrast CP 4 El-1R Flat Flouregia Frank’s Fry’s G Glyceregia Gorsuch Grard’s No. Green contrast

No. 89, 226 85 12 5 99, 155, 211–215 138 101 141 60 107 133 90, 158 104 79 107 87 75 135 94

Common Name Groesbeck’s Hatch Howarth’s Kalling’s 1 Kalling’s 2 Keller’s Klemm’s Kroll’s Marble’s Marshall’s Murakami’s Nital Palmerton Phoschromic Picral Ralph’s Super Picral Vilella’s 92-5-3

No. 19 2 84 95 94 3 210 192, 187 25 223 98 74 200 111 76 221 77 80 105

13 Specimen Preparation 13.1 Introduction THIS CHAPTER COVERS THE PRACTICAL PREPARATION OF THE MATERials stated in Table 11.1 for each material two different methods of the mechanical preparation process are stated in 68 Material/Preparation Tables. These tables also contain specific information on ASTM standards and etching described in Chapter 12. Electropolishing is covered by 25 methods. At the end of the chapter, Section 13.5 covers Trouble Shooting regarding the process and the results. The background for the preparation process, including general advice and hints for wet abrasive cutting and mounting can be found in Part I. Advice and hints for the total preparation process covering specific materials will be stated on each Material/ Preparation Table and in Section 13.5.

13.2 Mechanical Preparation—The “Traditional” and “Contemporary” Methods As described in Part I, two basic methods are available for the metallographer, one is based on SiC grinding paper or other “traditional” grinding media, referred to as the “traditional” method with a T-number, and another method, based on rigid composite disks 共RCDs兲, referred to as the “contemporary” method, with a C-number. Both methods will be stated side-by-side in the Material/Preparation Tables, Section 13.2.3.

13.2.1 Material/Preparation Tables Each sheet of Material/Preparation Tables has a number starting with 1–68. The two Method Tables, one for the C-Method and one for the T-Method are part of the Material/ Preparation Tables and have the same number as the sheet, for example, C-01 and T-01. Each sheet with tables can be from three to six pages, depending on the amount of text. The tables include as far as possible all relevant information for the preparation process of the given material or material group. The text is in the following order: Material or Material Group, see Section 11.2 and Table 11.1. Material Properties: For most materials, four basic properties are stated: Crystal Structure, Density in g / cm3, Melting Point in °C 共°F兲, and Hardness, 共for nonferrous metals the figures for hardness are taken from ASM Handbook, Vol. 02, Properties and Selection: Nonferrous Alloys and Special-Purpose Materials, ASM International, Materials Park, Ohio, USA, 1990. The hardness can be in HB, HK, HRC, HV, and Moh 共in some cases, no hardness is indicated兲. Comments on Material: Basic information on the material and the preparation of the material. General Comments on: 218

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219

Sectioning Mounting Grinding Polishing Etching Purpose: A table indicating relevant methods relating to the purpose of examination and ASTM standards 共see Section 12 and Table 12.1兲. Preparation Process: Sectioning: Specific indications. Mounting: Specific indications. Attention: In most cases several types of mounting materials can be used. In these cases only examples, “bakelite” 共hot mounting兲 and “acrylics” 共cold mounting兲 are stated. Grinding: Specific indications. Polishing: Specific indications. Contemporary Method: Method Table. Traditional Method: Method Table. Etchants: Table with relevant etchants.

13.2.2 Method Tables—Generic Methods—Parameters/Consumables— Table 13.1 Generic Methods The Method Tables covering the C- and T-methods contain a number of parameters and consumables. The methods should be considered “generic,” and state a basic procedure for a given material, using a standard semiautomatic grinder/polisher with exchangeable grinding/polishing disks. The specimens are either “single specimens” or “fixed specimens” in a holder on a 300 mm 共12 in兲 grinding/polishing disk. If material or equipment/consumables vary, the data must be changed accordingly 共see below under “Force per Specimen” and “Time”兲. The time stated for each step can in some cases be shortened with the stated times being to the “safe side.” This is because the preparation time normally is the only indication we have of “material removal.” During the preparation a certain amount of material should be removed. The best would be a direct measurement, but in normal practice only the process time can be measured, giving an indication of material removal based on experience. Variation in polishing cloths, abrasives, etc., justifies the relatively long times indicated to secure a sufficient material removal, but often the metallographer with experience will be able to shorten these times.

Steps The method is divided into a number of steps: PG 共plane grinding兲. This is the first step and is usually performed with one or several sheets of 220 grit SiC grinding paper. In the row, Time 共see below兲 normally “Until plane” is stated, indicating that a sufficiently prepared surface, coplanar to the surface of the paper and with a regular “220” scratch pattern covering the whole specimen surface is obtained. In some cases a coarser grain like grit 180 can be used before grit 220, but 220 should always be used as the last paper for PG. This ensures the reproducibility of the method. For some materials 共very hard or soft兲, grit 220 grinding paper is not stated for PG;

220


TABLE 13.1—Comparison Between Surfaces for Grinding and Polishing from a Number of Suppliers with Abbreviations Used in Method Tables.

Suppliers Abbreviations in Method Tables Dia, pad, bak or met

Buehler

Struers

Leco

Ultra-Prep

Diamond Pad

Diamond Spot Pattern Cameo Platinum Cameo Silver Cameo Gold

Allied High Tech

Mark V

Bonded Diamond Disk

Flex Diamond Disk

Lapmaster

Dia, disk, fixed, res RCD, hard

Apex DGD

MD-Piano

ApexHerculesH

RCD, soft

ApexHercules S

MDAllegro MD-Largo

Cloth, napless, v. hard, wov, syn Cloth, napless, hard, nonwov syn Cloth, napless, hard, wov, silk Cloth, napless, hard, wov, syn

Ultra-Pad

DP/MDPlan

Texmet 2000 Texmet 1000

DP/MDPan

Leco Pol Pan-W

Kempad Pan-B

Met-X

Pan-W

Ultra-Pol

DP/MDDur DP/MDDac

Silk

Silk

Silk

Silk

Gold Technotron Nylon

Gold Label Nylon

RAM Nylon

ASR Nylon

Broad cloth

Micro LP

Alpha A

NTR

Cloth, napless, med hard, wov, wool Cloth, med nap, soft, syn Cloth, napless, soft, porous, syn

Trident Nylon

Plan Cloth

DP/MDMol Microcloth Chemomet

DP/MDNap OP/MDChem

Lecloth Black Technotron

SpecCloth Chem-Pol

Supreme

in these cases, PG, possibly made in several steps, shall end with the Disk/Cloth stated in the Method Table. See also Time below. FG 共fine grinding兲. This can be in several steps indicated with a number, e.g., FG 1. P 共polishing兲. This can be in several steps, indicated with a number, e.g., P 1. In most methods, the last step indicated is with silica/alumina. Often this step can be omitted, depending on the purpose of the preparation.

Parameters Each step contains a number of parameters: Disk/Cloth: The surface covering the rotating disk of the grinding/polishing machine. Abrasive Type: The abrasive used for grinding and polishing. Grit/Grain Size: Grit, indicated with a P- number corresponding to the FEPA stan-

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dard 共see Table 6.2 for comparison to American standard兲. In case of diamond or another abrasive, the grain size is indicated in ␮m. Lubricant Type: The type of medium used for lubrication during the process. Rotation Disk/Holder, Comp/Contra: rpm of grinding/polishing disk and specimen holder. “Comp” means complementary: The disk and holder rotates in the same direction. “Contra” means counter rotation: The disk and the holder rotates in opposite directions. Force per Specimen: The force in N and lb per specimen. Attention: The force is based on a 30 mm 共1.25 in兲 mounted specimen with the specimen totaling approximately 50 % of the mount. At 25 mm 共1 in兲 specimens the force should be reduced with the factor 0.7. At 40 mm 共1.50 in兲 only increase the force up to a maximum of 50 N 共11 lb兲 and as compensation, to obtain the necessary material removal, extend the preparation time with 1 – 4 min. This is to avoid a possible overheating of the polishing cloth that can take place at a force on each specimen of more than 50 N 共11 lb兲. With SiC grinding paper, a very high force might create heavy damage to the specimen 共see Section 6.6兲 and the paper, if not glued to the disk, might be torn away. Be aware that the values indicated are for a single specimen. When using a holder with say six fixed specimens, the value should be increased with a factor 6. Time: The number of minutes the specimens are in contact with the disk. Attention: For specimens larger than 30 mm 共1.25 in兲 the time should be extended 共see Force per Specimen above兲. Also, if the grinding/polishing disk is smaller than 300 mm 共12 in兲, the time should be extended. At PG, until plane indicates that the specimen surface should be uniformly covered with a regular scratch pattern. The time used depends on the quality of the sectioning and the alignment of the specimens if a specimen holder with several fixed specimens is used.

Consumables—Abbreviations—Table 13.1 The methods are based on the use of a number of consumables which are described in the Method Tables with abbreviations. These consumables have different names from the different suppliers. For this reason a description is given below for each type of consumable. Based on this, the user should be able to choose the correct consumable from any supplier. The surfaces used for grinding and polishing can be difficult to describe. For this reason, a list of surfaces from a number of suppliers is stated in Table 13.1. The descriptions are given according to the abbreviations used in the Method Tables, stated alphabetically. For a more detailed description of consumables see Part I.

Abbreviations Used in Method Tables—Description of Consumables Alco: Alcohol-based lubricant. This lubricant should be phased out if possible and replaced with water-based lubricant because ethyl alcohol 共ethanol兲 is considered a danger to health in certain countries. Alumina: Al2O3 suspension as abrasive. Bak: The abrasive is fixed in a bakelite bond. Cloth: A surface made of a textile or other flexible material fixed to the polishing disk with adhesive backing or magnetically. Disk: A surface for grinding/polishing made of a material with a “rigid” surface normally fixed to the polishing disk like a cloth, or in some cases a solid disk taking the place of the polishing disk.

222


Dia: Diamond as abrasive. This is followed by spr or susp, or both 共see below兲. Diamond: Diamond as abrasive. Fixed: The abrasive is fixed in the surface of the disk. Hard: A hard rigid composite disk 共RCD兲 or polishing cloth with a relatively hard, aggressive surface. A hard cloth could be satin woven, very thin or compact 共see “V. hard”兲 without nap and with a very low resilience. Low nap: Polishing cloth with a very short nap could be synthetic material. Low resilience. Med„ium… hard: Polishing cloth, napless, with a low resilience. Med„ium… nap: Polishing cloth with a medium nap could be a flocked cloth with relatively high resilience. Met: The abrasive is fixed in a metal bond. Napless: Polishing cloth without nap 共see Hard above兲. Nonwov: Polishing cloth made of a nonwoven material. Oil: Oil-based suspension or lubricant. This type should be avoided because oilbased products are considered dangerous to health in certain countries. Oil-based diamond suspensions are only stated in the T-methods. Lubricants based on oil emulgated with water 共see below兲. Pad: Diamond pad 共disk兲 with either metal or bakelite bond. Porous: Polishing cloth with a porous surface mostly used for oxide polishing. RCD: Rigid Composite Disk. Res: The abrasive is fixed in a resin bond like epoxy, different from bakelite. SiC paper: SiC wet grinding paper, normally with a C weight backing, and normally used with plain backing 共see Section 13.2.4兲. In certain cases it is an advantage to use paper with an adhesive back for “heavy” automatic grinding. Silica: Colloidal silica 共SiO2兲 as abrasive. Silk: Polishing cloth made of silk. Soft: A soft RCD or cloth with a relatively soft, less aggressive surface. For a cloth, soft indicates a certain relative resilience, and can be with “Nap” or “Napless.” Spr: Diamond spray. Susp: Diamond suspension. Syn: Polishing cloth made of synthetic material. V.hard: A very hard cloth with an aggressive surface mostly used for “fine grinding” 共see “Hard” above兲. Wat: Water-based suspension or lubricant. This type should be preferred because alcohol- and oil-based products are considered dangerous to health in certain countries. Water: Normal tap water or recirculated water, with or without an additive. Wat-oil: Lubricant based on water with an in-mixed oil forming an emulsion. Wool: Polishing cloth made of wool. Wov: Polishing cloth made of a woven material.

13.2.3 Material/Preparation Tables—Methods C-01/T-01 to C-68/T-68 This section contains 68 numbered sheets with Material/Preparation Tables 共M/PT兲 that include material/process information and two Method Tables. To find the correct M/PT use Table 11.1 Using these tables should guide the user to obtaining a satisfactory preparation result based on the material and the examination purpose. The data stated in the Method Tables are based on a specimen of 30 mm 共1.25 in兲

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diameter, clamped in a specimen holder on a 300 mm 共12 in兲 grinding/polishing disk. Using a smaller disk diameter might prolong the preparation time. The specimen area should be approximately 50 % of the mount. The force indicated is per specimen and should be multiplied with the number of fixed specimens in the holder. The dosing levels for lubricant and abrasives are to be adjusted individually because temperature, humidity, etc., has a significant influence on the preparation process. Take care that the surface of the polishing cloth/RCD is just “moist” when touched with a fingertip, not “wet.” For manual preparation see Section 13.2.4; often the data indicated in the T-methods and some of the C-methods are suited for preparation by hand. For electrolytic polishing see Section 13.4.2.

Material/Preparation Tables 01 Material: Hydroxyapatite „HA… coating Material Properties: HA: Ca10共PO4兲6共OH兲2 Comments on Material: Ceramic materials that are specially developed for use as medical and dental implants are called bioceramics. They include alumina and zirconia, bioactive glasses, glass-ceramics, coatings and composites, hydroxyapatite 共HA兲, tricalcium phosphate 共TCP兲 and other calcium phosphates and radiotherapy glasses. The most used bioceramics are calcium phosphate compounds, especially HA and TCP. This is because they have almost the same compositions as the skeleton 共69 % of bone is HA兲 and they have excellent biocompatibility. When these ceramics are implanted into the living body 共in vivo兲 for a range of time, it is found that they have a strong chemical bond with bone tissue and finally become a firm attachment. Ceramics are brittle and they are less suited for load-bearing applications. Therefore, a calcium phosphate like HA is used as a coating on materials such as titanium alloys or stainless steel where it can contribute its bioactive properties, while the metallic component bears the load. Also the coating gives a relatively rough surface that increases the mechanical fixation of the component. The accepted method of applying HA coatings to metallic implants is plasma spraying. The coatings with HA and TCP are made with a controlled porosity. This porosity and other features like the contact between base material 共substrate兲 and coating should be materialographically examined. For preparation of other bioceramics see Material/Preparation Tables 共M/PT兲 05 and 06, and for other ceramic coatings see M/PT 14.

224


Sectioning: HA/TCP are very sensitive materials and should be kept free of contamination during the cutting. This can be done by masking the areas of concern using plastic film and tape. It is important that the specimen is mounted and vacuum impregnated before sectioning takes place to avoid damaging the brittle ceramic layer 共see below兲. The sectioning should be done on a precision cutter with a cut-off wheel suited for the base material 共substrate兲. The specimen should be oriented so that the coating is compressed into the substrate during the cutting 共see also M/PT 08兲. The thinnest possible cut-off wheel should be used and the feed speed should be low. Mounting: Before sectioning a careful vacuum infiltration of the specimen should take place 共see M/PT 02 and Section 3.10兲. It is important that all open pores are filled with epoxy so that the coating cannot be contaminated or damaged during the following preparation. The sectioned specimen should possibly be vacuum impregnated after the sectioning and carefully mounted in epoxy to secure a good edge retention. Grinding: In Methods C-01 and T-01 it is an assumption that the base material can be ground with SiC grinding paper. For grinding surfaces for the harder ceramics see M/PT 02–06. Grinding times should be kept at a minimum. Polishing: Also, polishing times should be as short as possible to secure a good edge retention. Etching: Normally the HA/TCP layer is not etched, but relief polishing, creating a “physical etching” can be used 共see Section 9.6兲. For other ceramics see M/PT 02 to 06. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure Phase identification Porosity Thermal spray coatings: Distribution, porosity, unmelted particles

ASTM Standard 共See Section 12.4兲 Method C-01

E E E E

562, E 1245, 1268, E 1382 562, E 1245, 1268, E 1382

C 730, C 849, C 1326, C 1327, E 384 E 3, E 562, E 883, E 1245, E 1268, E 1382

C-01 C-01

C-01, T-01 C-01, T-01 C-01, T-01 C-01 C-01

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Preparation Process 01 Sectioning Cut-Off Wheel

Al2O3 or SiC, backlite bond or diamond, metal bond

Mounting Hot Compression Mounting

Resin Time Minutes

Cold Mounting

Resin Time Minutes/Hours

Epoxy 6 – 12 h

Grinding Attention: In C-methods when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-01: In some cases a step with a napless, hard, wov, silk cloth and 1 ␮m diamond, other parameters like step P 2 in method T-01, can be added as P 1, making the shown P 1 to P 2. Contemporary Method C-01 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 Polishing Disk/Cloth SiC paper SiC paper RCD, Cloth, napless soft soft, porous, syn Abrasive Type SiC SiC Dia, spr Silica or susp Grit of Grain 320 500 9 0.04 Size ␮m Lubricant Type Water Water Alco/wat Rotation 300/ 150 300/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp Comp Comp Contra Force per 30 共7兲 30 共7兲 40 共9兲 15 共3.3兲 Specimen N 共lb兲 Time Until plane 1 5–6 2–4 Minutes

226


Traditional Method T-01 共For definitions of parameters and consumbles Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 Polishing Cloth, Disk/Cloth SiC SiC SiC SiC Cloth, napless, Paper Paper Paper Paper napless, hard, wov, hard, wov, silk syn Abrasive SiC SiC SiC SiC Dia, spr or Dia, spr Type susp or susp Grit or P220 P320 P500 P1000 6 3 Grain Size 共␮m兲 Lubricant Water Water Water Water Alco or Alco or Type wat wat Rotation 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/ Comp or Comp or Comp Comp Comp Comp Contra contra contra or or contra contra Force per 20 共4.5兲 20 共4.5兲 20 共4.5兲 20 共4.5兲 20 共4.5兲 20 共4.5兲 Specimen N 共lb兲 Time Until 0.5–1 0.5–1 0.5–1 6 3 Minutes plane

see P3 Cloth, napless, soft, porous, syn Silica 0.04/ 0.05

150/ 150

Contra

10 共2.2兲

1–2

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Material/Preparation Tables 02 Material: Boron carbide, B4C. Silicon carbide, SiC. Other carbides Material Properties: B4C: Rhombohedral, 2.52 g / cm3, 2450° C 共4442° F兲, HV 3400–3800 SiC: Hexagonal/cubic, 3.21 g / cm3, 2300° C 共4172° F兲, HV 2800–3600 Comments on Material: High-performance ceramics can roughly be characterized by structure and function. They can be divided roughly into two categories, structural and functional ceramics. For those structural ceramics like silicon nitride, silicon carbide, some types of zirconium dioxide, and a number of mixed ceramics based on Al2O3, the properties are directed towards mechanical strength and other mechanical properties. For those functional ceramics like barium titanate, zinc oxide, and titanate the properties are directed towards electric, magnetic, dielectric, and optical properties. Some ceramics like aluminum oxide 共the most important high-performance ceramic兲 and zirconium dioxide can be optimized towards either structural or functional properties. For in-depth information on ceramics and preparation of ceramics see Carle et al. Ref. 26, 共Part I兲 and Elsner et al. Ref. 27, 共Part I兲. In contrast to metals, the evaluation of ceramic materials with light microscopy can be carried out both by reflected light and 共with some exceptions兲 on thin sections by transmitted light. For economic reasons, however, the more simple preparation of specimens for reflected light is preferred for routine examination. For preparation of thin sections see Section 7.13.1. Compared to metals, ceramics have a high to very high hardness, a low ductility, and a high brittleness. The high hardness influences the preparation to a high degree, but other factors like porosity and brittleness also makes the preparation difficult. Brittleness: This might cause pull-outs during cutting and grinding, the ceramic grains being removed by the abrasive. Pull-outs are especially critical in materials with a vitreous 共amorphous兲 phase between the grains. Also cracks and surface stress can develop during sectioning and grinding 共see Sections 6.3.2 and 13.6兲. Porosity: Often the following should be determined: Total porosity, pore type, shape, size, and pore size distribution. Pull-outs are often made during the first stages of the preparation. These pull-outs can be observed as pores and often will disturb the analysis of grains, etc. Also, the edges of the original pores will be damaged and rounded after grinding and fine grinding. In case of differences in hardness between phases, material can be smeared into the original pores 共see also Section 13.6兲. Preparation methods: Due to the large variations in ceramic materials, five Material/ Preparation Tables, 02–06, with ten methods, are stated in the following. Preparation times: A wide variation in time is provided in the method tables. This is due to the large variations in ceramic materials which in some cases call for long times, especially in the case of a high porosity.

228


Sectioning: The bond of the diamond cut-off wheel, its thickness and also the type, size, and concentration of the abrasive grains are mainly responsible for the quality of the cut surface. Both metal bond 共bronze兲 and bakelite bond can be used. Bakelite bond will give the least damage to the surface and should be used on brittle/porous materials. Depending on the material properties, feed rate and rotational speed of the cut-off wheel should be adjusted. The higher porosity and risk of pull-outs of a material, the slower the feed rate. The rotational speed should not exceed 2000 rpm and often a lower speed should be used. The surface quality can normally be improved by using a cut-off wheel with small grain size, giving a drawback when cutting large specimens as the cutting time is prolonged. The concentration of diamonds in the bond should not be too high, causing the wheel to “press” and “pinch,” which will create pull-outs and micro and macrocracks 共see Section 2.4.2兲. The same types of material damage develop with a very hard bond. As a rule the cutting should be made with a thinnest possible wheel with a grain size around 94 ␮m. Special care should be taken when clamping specimens. Pressure spots induce high stress which might fracture the material prior to cutting. In case of very brittle and porous materials, an impregnation before cutting can be necessary 共see below and also Section 13.6兲. Mounting: Vacuum impregnation: If the porosity is higher than 5 % it is advisable to impregnate under vacuum in a special apparatus using epoxy of low viscosity and possibly a dye 共see Section 3.10兲. Impregnation should often be repeated after grinding to close pores that have been opened. Mounting: Dense ceramic specimens with porosity under 5 % can be prepared unmounted, clamped in a holder, if the shape permits. Ceramics with a porosity over 5 % should be impregnated as described above and mounted in a cold mounting material, preferably epoxy having an addition of hard filler to increase the hardness of the mounting material. For very stable ceramics that will not be damaged by the pressure, hot compression mounting in a mineral filled epoxy is preferred because it provides a mount with a hardness matching the ceramic. In certain cases hot mounting can be made with acrylic that can be used virtually without pressure 共see Section 3.4兲. Grinding: Plane grinding 共PG兲 is normally done with grinding disks with diamond 共see Sections 6.6.1 and 6.7.2兲. PG is causing relatively heavy damage to the specimen surface; for this reason the finest possible grain size should be chosen. If using diamond pads, the metallic bond will be the most aggressive, giving short times but with strong damage. For sensitive ceramics the less aggressive bakelite bond should be used. If the ceramic is not too hard 共functional ceramics兲, SiC grinding paper might be used. Fine grinding 共FG兲 normally takes place using diamond but in relatively soft, brittle materials, sensitive to pull-outs, SiC paper can be used down to P4000. Fine grinding 共FG兲 can be done on different surfaces stated in the Method Tables. In case of brittle materials the pressure when using RCDs should be kept at 25 N 共5.7 lb兲. On materials with many pores the swarf from the RCD might be forced into the pores, making examination very difficult. In this case a napless very hard, woven, synthetic cloth is used for FG.

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229

Polishing: The 6 ␮m and 3 ␮m diamond steps are very important for most ceramics, removing the heavy deformations from grinding. In the case of pores a 1 ␮m diamond step can be useful to establish the edges of the pores. Oxide polishing gives chemical mechanical action on ceramics. The effect can often be increased by adding small quantities of H2O2 共32 %兲 and ammonia solution 共25 %兲 to the colloidal silica. This polishing can be used for relief polishing 共see Section 9.6兲. Etching: Ceramic materials may often be difficult to examine under the microscope since reflection differences in the structure are very slight. Various etching and contrast methods can be used. Oxide materials are often contrasted by thermal etching in air, vacuum, or various gases. The temperature range is usually between 1200 and 1650° C 共2200 and 3000° F兲共Approximately 150° C 共300° F兲 below sintering temperature in air.兲 Etching time can be from 15 minutes to several hours. Chemical etching mostly takes place only with hot 共boiling兲 acid mixtures or molten metal salts. All etching shall take place under a fume hood with extreme care. Often optical etching like dark field and DIC can be used on the specimen surface taken directly from the preparation 共relief polishing兲. Also plasma etching and ion etching are used 共see Chapter 9兲. Purpose ASTM Standard 共See Section 12.4兲 Methods Case or coating thickness/hardness, C-02 surface layers Perfect edge retention Grain size, grain boundaries E 112, E 930, C-02, T-02 E 1181, E 1382 Image analysis, rating of inclusion E 562, E 1245, C-02 content E 1268, E 1382 High planeness Microhardness, hardness C 730, C 849, C 1326, C-02, T-02 C 1327, E 384 Microstructure E 3, E 562, E 883, E 1245, C-02, T-02 E 1268, E 1382 Phase identification C-02, T-02 Porosity C-02


Diamond, metal bond, or bakelite bond

230


Mounting Hot Compression Resin Epoxy with Cold Mounting Resin Epoxy Mounting Mineral Filler Time Minutes 9 Time 6–8 h Minutes/ Hours Grinding C-02: Often the FG2 step can be omitted. T-02: Often the PG step can be omitted. T-02: PG and FG1: Often both steps or only FG1 should be changed to bakelite bond. Also, conventional diamond disks, preferably with bakelite bond can be used 共see Section 6.6.1兲. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-02: Often P 2 can be changed to a napless, hard, silk cloth or be omitted. C-02, T-02: Final polishing step: Chemical mechanical polishing can be used by adding small quantities of H2O2 共32 %兲 and ammonia solution 共25 %兲 to the colloidal silica. Etching Etchants for oxides see Material/Preparation Tables 05/06.

Contemporary Method C-02 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 P2 P3 Polishing Cloth, med Cloth, Disk/Cloth Dia. disk, Dia. disk RCD, Cloth, napless, fixed, res fixed, res soft napless, nap, syn soft, hard, porous wov, syn Abrasive Type Diamond Diamond Dia.spr Dia.spr Dia.spr Silica or susp or susp or susp Grit or Grain P220 P1200 9 3 1 0.04/ 0.05 Size ␮m Lubricant Type Water Water Alco or Alco or Alco or wat wat wat

Chapter 13

Rotation Disk/Holder rpm/rpm Comp/Contra Force per Specimen N 共lb兲 Time Minutes


231

300/ 150

300/ 150

150/ 150 150/ 150

150/ 150

150/ 150

Comp or contra 25 共6兲

Comp

Comp

Comp

Comp

Contra

25 共6兲

30 共7兲

30 共7兲

25 共6兲

15 共3.4兲

Until plane

2

8–15

10–120

2–10

1–6

Traditional Method T-02 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 P3 Polishing Cloth, Cloth, Cloth, Cloth, Disk/Cloth Dia Dia Cloth, pad, pad, napless, napless, napless, napless, napless, soft, hard met met v. hard, v. hard, hard, porous wov, non nonwov/ non silk wov, wov/ wov, syn wov, syn syn Abrasive Diamond Diamond Dia, Dia, Dia, Dia, Silica Type spr or spr or spr spr susp susp or susp or susp Grit or 125 40 15 9 6 3 0.04/ 0.05 Grain Size ␮m Lubricant Water Water Alco/wat Alco/wat Alco/wat Alco/wat Type 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Rotation Disk/ Holder rpm/rpm Comp/ Comp Comp Comp Comp Comp Comp Contra Contra Force per 30 共7兲 30 共7兲 30 共7兲 30 共7兲 30 共7兲 20 共4.5兲 10 共2.2兲 Specimen N 共lb兲 Time Until 2–10 6–15 6–15 5–30 10–60 1–10 Minutes plane

232


Etchants Material B 4C SiC with 5–15 % oxide additions SiC with 1 % B4C SSiC

SSiC doped with B SSiC doped with Al SiC with B4C SiSiC

Etchants 共see Table 12.2兲 901 902

905

Uses General structure Secondary phase remain Grain boundaries Alpha/alpha 共␣ / ␣兲 grain boundaries Alpha/beta 共␣ / ␤兲 phase boundaries Grain boundaries

906

Grain boundaries

907 908

Grain boundaries Grain boundaries

903 904

Material/Preparation Tables 03 Material: Chromium carbide, CrC. Titanium carbide, TiC. Titanium nitride, Tin Cubic boron nitride, CBN. Tungsten carbide, WC. Other ceramics Material Properties: TiC: Face-centered cubic, 4.93 g / cm3, 3140° C 共5684° F兲, HV 2800–3500 TiN: Face-centered cubic, 5.4 g / cm3, 2950° C 共5342° F兲, HV 2450 CBN: Face-centered cubic, 3.48 g / cm3, 1700° C 共3092° F兲, HV 4500 WC: Hexagonal, 15.7 g / cm3, 2780° C 共5036° F兲, HV 2400 Comments on Material: See Material/Preparation Tables 02. Preparation times: A wide variation in time is provided in the Method Tables. This is due to the large variations in ceramic materials which in some cases call for long times, especially in the case of high porosity. Sectioning: See Material/Preparation Tables 02. Mounting: See Material/Preparation Tables 02. Grinding: See Material/Preparation Tables 02, and directions for specific materials below. Polishing: See Material/Preparation Tables 02, and directions for specific materials below. Etching: See below and Material/Preparation Tables 02. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention

ASTM Standard 共See Section 12.4兲

Methods C-03

Chapter 13

Grain size, grain boundaries

E E E E

Image analysis, rating of inclusion content High planeness Microhardness, hardness


112, E 930, 1181, E 1382 562, E 1245, 1268, E 1382

C 730, C 849, C 1326, C 1327, E 384 E 3, E 562, E 883, E 1245, E 1268, E 1382

Microstructure Phase identification Porosity

233

C-03, T-03 C-03

C-03, T-03 C-03, T-03 C-03, T-03 C-03


Diamond, metal bond, or bakelite bond

Mounting Hot Compression Resin Epoxy with Cold Mounting Resin Epoxy Mounting Mineral Filler Time 9 Time 6–8 h Minutes Minutes/Hours Grinding C-03: PG: If the surface is very rough, start with Dia, disk, fixed res, P120. T-03: The PG step can often be omitted. T-03: PG and FG 1: Often both steps or only FG 1 should be changed to bakelite bond. Also conventional diamond disks, preferably with bakelite bond can be used 共see Section 6.6.1兲. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing Tungsten carbide: C-03: FG 2 can be omitted, P 1 can be changed to a napless, hard, wov silk cloth and a P 2 step from Method C-02 can be included before the final step 共see also Method C-67兲.

234


Contemporary Method C-03 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 P2 Polishing Cloth, Disk/Cloth Dia, disk, RCD, hard RCD, Cloth, napless, fixed, res soft napless, soft, hard, porous, wov, syn syn Abrasive Type Diamond Dia, spr or Dia, spr or Dia, spr or Silica susp susp susp Grit or Grain P220 9 3 3 0.04/ 0.05 Size ␮m Lubricant Type Water Alco or wat Alco or wat Alco or wat Rotation 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp Comp Comp Contra contra Force per 35 共8兲 35 共8兲 35 共8兲 25 共5.5兲 10 共2.2兲 Specimen N 共lb兲 Time Until plane 5–6 10–15 8–10 2 Minutes

Traditional Method T-03 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ FG 3 P1 P2 P3 Polishing PG FG 1 FG 2 Cloth, Cloth, Cloth, Cloth, Cloth, Dia, Disk/Cloth Dia, napless, napless, napless, napless, napless, pad, pad, soft, hard, v. hard, v. hard, hard, met met porous, wov, non wov, wov, syn silk wov, syn syn syn Dia, Dia, Dia, Silica Abrasive Diamond Diamond Dia, spr/ spr/ spr/ Type spr/ susp susp susp susp Grit or 125 40 15 9 6 3 0.04/ 0.05 Grain Size ␮m Lubricant Water Water Alco Alco Alco Alco Type Rotation 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm

Chapter 13

Comp/ Contra Force per Specimen N 共lb兲 Time Minutes


235

Comp or Comp or Comp contra contra 30 共7兲 30 共7兲 40 共9兲

Comp

Comp

Comp

Contra

40 共9兲

40 共9兲

25 共5.5兲

10 共2.2兲

Until plane

6–8

5–6

5–6

2

2

Etchants Material CrC, HfC, TiC, VC TaC WC

6–8

Etchants 共see Table 12.2兲 909 910, 911 912

Uses General structure General structure General structure

Material/Preparation Tables 04 Material: Silicon nitride, Si3N4 Material Properties: Si3N4: Hexagonal, 3.18 g / cm3, 1900° C 共3452° F兲, HV 800– 1900 Comments on Material: See Material/Preparation Tables 02. Preparation times: A wide variation in time is provided in the Method Tables. This is due to the large variations in ceramic materials which in some cases call for long times, especially in the case of high porosity. Sectioning: See Material/Preparation Tables 02. Mounting: See Material/Preparation Tables 02. Grinding: See Material/Preparation Tables 02. Polishing: See Material/Preparation Tables 02. Etching: See below and Material/Preparation Tables 02. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure Phase identification


Methods C-04

E E E E

C-04, T-04

112, E 930, 1181, E 1382 562, E 1245, 1268, E 1382

C 730, C 849, C 1326, C 1327, E 384 E 3, E 562, E 883, E 1245, E 1268, E 1382

C-04

C-04, T-04 C-04, T-04 C-04, T-04

236


Porosity

C-04


Diamond, metal bond

Mounting Hot Compression Resin Epoxy Cold Mounting Resin Epoxy Mounting with Filler Time 9 Time 6–8 h Minutes Minutes/Hours Grinding C-04: PG: If the surface is very rough, start with Dia, disk, fixed, res, P120. T-04: PG with 125 ␮m diamond can often be omitted. T-04: PG and FG 1: Often both steps or only FG 1 should be changed to bakelite bond. Also conventional diamond disks, preferably with bakelite bond can be used 共see Section 6.6.1兲. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-04: P 1 can often be omitted so that FG 3 is the last step. In some cases also FG 3 can be omitted. Contemporary Method C-04 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 Polishing Disk/Cloth Dia, disk, RCD, soft RCD, soft RCD, soft Cloth, fixed, res napless, soft, porous, syn Abrasive Type Diamond Dia, spr or Dia, spr or Dia, spr or Silica susp susp susp Grit/Grain P220 9 3 0.25 0.04/ 0.05 Size ␮m Lubricant Type

Water

Alco or wat

Alco or wat

Alco or wat

Chapter 13



300/ 150

150/ 150

150/ 150

150/ 150

150/ 150


Comp

Comp

Comp

Contra

50 共11兲

40 共9兲

25 共5.5兲

10 共2.2兲

Until plane

7–8

7–8

6–8

1

Traditional Method T-04 共For definitions of parameters and Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 Polishing Cloth, Disk/Cloth Dia, pad, Dia, pad, Cloth, napless, met met napless, hard, v. hard, non non wov, wov, syn syn Abrasive Type Diamond Diamond Dia, spr or Dia, spr or susp susp Grit or 125 30 9 6 Grain Size ␮m Lubricant Water Water Alco or Alco or wat Type wat Rotation 300/ 150 300/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp Comp Comp contra 30 共7兲 30 共7兲 40 共9兲 40 共9兲 Force per Specimen N 共lb兲 Time Until 4 8–10 5–6 Minutes plane Etchants Material Si3N4 Si3N4 Si3N4 AlN-Al2O3

Etchants 共see Table 12.2兲 913 914 915 916

237

consumables see P2

P3

Cloth, napless, hard, wov, silk

Cloth, napless. soft, porous, syn

Dia, spr or Silica susp 3 0.04/ 0.05

Alco or wat 150/ 150

150/ 150

Comp

Contra

30 共7兲

15 共3.4兲

5–6

2

Uses General structure Grain boundaries Grain boundaries Grain boundaries

238


Material/Preparation Tables 05 Material: Aluminum oxide, Al2O3. Chromium oxide, Cr2O3 Material Properties: Al2O3: Trigonal 共rhombohedral兲, 4.0 g / cm3, 2050° C 共3722° F兲, HV 2500–2800 Cr2O3: Hexagonal, 5.12 g / cm3, 2340° C 共4244° F兲, HV 2900 Comments on Material: See Material/Preparation Tables 02. Preparation times: A wide variation in time is provided in the Method Tables. This is due to the large variations in ceramic materials which in some cases call for long times, especially in the case of high porosity. Sectioning: See Material/Preparation Tables 02. Mounting: See Material/Preparation Tables 02. Grinding: See Material/Preparation Tables 02 and directions for specific materials below. Polishing: See Material/Preparation Tables 02 and directions for specific materials below. Etching: See below and Material/Preparation Tables 02. Purpose ASTM Standard 共See Section 12.4兲 Methods Case or coating thickness/hardness, C-05 surface layers Perfect edge retention Grain size, grain boundaries E 112, E 930, C-05, T-05 E 1181, E 1382 Image analysis, rating of E 562, E 1245, C-05 inclusion content E 1268, E 1382 High planeness Microhardness, hardness C 730, C 849, C 1326, C-05, T-05 C 1327, E 384 Microstructure E 3, E 562, E 883, C-05, T-05 E 1245, E 1268, E 1382 Phase identification C-05, T-05 Porosity C-05


Diamond, metal bond

Chapter 13


239

Mounting Hot Compression Resin Epoxy with Filler Cold Mounting Resin Epoxy Mounting 6–8 h Time 9 Time Minutes Minutes/ Hours Grinding T-05: The PG step with 125 ␮m diamond and FG 2 can often be omitted. T-05: PG and FG 1: Often both steps or only FG 1 should be changed to bakelite bond. Also conventional diamond disks, preferably with bakelite bond can be used 共see Section 6.6.1兲. Very hard oxides: Use C-03. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-05: Cr2O3: The steps FG 1 and P 2 can be omitted. Contemporary Method C-05 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 P2 P3 Polishing Cloth, med Cloth, Disk/Cloth Dia, disk, Dia, disk, RCD, Cloth, napless, fixed, res fixed, res soft napless, nap, soft, soft, hard, porous, syn wov, syn syn Abrasive Type Diamond Diamond Dia, spr Dia, spr Dia, spr Silica or susp or susp or sup Grit or P220 P1200 9 6 1 0.04/ 0.05 Grain Size ␮m Lubricant Type Water Water Alco Alco Alco or wat or wat or wat Rotation 150/ 150 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp or Comp Comp Comp Contra contra contra 35 共8兲 35 共8兲 35 共8兲 30 共6.6兲 25 共5.5兲 25 共5.5兲 Force per Specimen N 共lb兲

240


Time Minutes

Until plane

1

9–10

8

2–3

1–2

Traditional Method T-05 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 P3 Polishing Cloth, Cloth, Cloth, Cloth, Cloth, Dia Disk/Cloth Dia napless, napless, napless, napless, nappad, pad, soft, hard, hard, less, v. hard met met porous, wov, v. hard, non wov, syn silk wov, syn wov, syn syn Abrasive Diamond Diamond Dia, spr/ Dia, spr Dia, spr Dia, spr Silica Type susp or or susp or susp susp Grit or 125 40 15 9 6 3 0.04/ 0.05 Grain Size ␮m Lubricant Water Water Alco or Alco or Alco or Alco or Type wat wat wat wat Rotation 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/ Comp or Comp or Comp Comp Comp Comp Contra Contra contra contra Force per 30 共7兲 30 共7兲 40 共9兲 40 共9兲 40 共9兲 20 共4.7兲 15 共3.4兲 Specimen N 共lb兲 Time Until 2 6–7 6–7 5–6 5–6 2 Minutes plane Etchants Material Al2O3

Etchants 共see Tables 12.2兲 917

Al2O3 Cr2O3

918 923

Uses Grain boundaries and small grains Grain boundaries General structure

Chapter 13


241

Material/Preparation Tables 06 Material: Barium titanate, BaTiO3. Calcium oxide, CaO. Cerium oxide, CeO2. Magnesium oxide, MgO. Silicon oxide, SiO2. Zirconium dioxide, ZrO2. Zinc oxide, ZnO. Other oxides. Borides. Porcelain Tile. Slag. Other traditional ceramics Material Properties: CeO2: Cubic, 7.28 g / cm3 MgO: Cubic, 3.5 g / cm3, 2800° C 共5072° F兲, HV 1130 SiO2: Hexagonal, 2,2-2,65 g / cm3, 1710°C 共3100°F兲, HV 1000—1250 ZrO2: Monoclinic, 5.7– 6 g / cm3, 2690° C 共4874 °F兲, HV 1500–1900 Comments on Material: See Material/Preparation Tables 02. Preparation times: A wide variation in time is provided in the Method Tables. This is due to the large variations in ceramic materials which in some cases call for long times, especially in the case of high porosity. Sectioning: See Material/Preparation Tables 02. Mounting: See Material/Preparation Tables 02. Grinding: See Material/Preparation Tables 02 and directions for the specific materials below. Polishing: See below and Material/Preparation Tables 02 and directions for the specific materials below. Etching: See below and Material/Preparation Tables 02. Purpose ASTM Standard 共See Section 12.4兲 Methods C-06 Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries E 112, E 930, C-06, T-06 E 1181, E 1382 E 562, E 1245, Image analysis, rating of C-06 inclusion content E 1268, E 1382 High planeness Microhardness, hardness C 730, C 849, C 1326, C-06, T-06 C 1327, E 384 Microstructure E 3, E 562, E 883, C-06, T-06 E 1245, E 1268, E 1382 Phase identification C-06, T-06 Porosity C-06


Diamond, metal bond or SiC, bakelite bond

242


Mounting Hot Compression Resin Epoxy with Filler Cold Mounting Resin Epoxy Mounting 6–8 h Time 9 Time Minutes Minutes/ Hours Grinding Borides: T-06: FG 4 can be changed to grit 4000 SiC paper and P 1 can be changed to FG 3 in C-06. Calcium oxide: C-06: PG can be done with SiC paper grit 500, FG 1 and FG 3 can be omitted by changing FG 2 to 9 ␮m diamond. Zirconium dioxide: The methods C-02 and C-05 can also be used. Often the step P 3 in C-05 can be omitted. Porcelain and traditional ceramics: The step FG 2 can be omitted and FG 3 can be prolonged to 10 min Tile, slag: Method C-02 can be used with SiC paper grit 220 for PG and FG 1 and P 3 omitted. T-06: FG 3 and FG 4 can be omitted if a 6 ␮m step is performed 共see below兲. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing T-06: In some cases a P 1 step with 6 ␮m diamond and a napless, hard, wov, silk cloth should be added with further data like P 1 indicated below. In this case FG 3 and FG 4 may be omitted. T-06: Often the step P 2 can be omitted. Contemporary Method C-06 共For definitions of parameters Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 Polishing Disk/Cloth Dia, disk, RCD, RCD, RCD, soft fixed, res hard soft

Abrasive Type Grit or Grain size ␮m

Diamond P220

Dia, spr or Dia, spr or Dia, spr susp susp or susp 9 6 3

and consumables see P1

P2

Cloth, Cloth, napless, napless, soft, hard, porous, wov, syn syn Dia, spr or Alumina susp 3 0.02/ 0.05

Chapter 13

Lubricant Type Rotation Disk/ Holder rpm/rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

Water


243




Oil-wat 150/ 150

150/ 150


Comp

Comp

Comp

Comp

Contra

40 共9兲

35 共8兲

35 共8兲

20 共4.4兲

15 共3.4兲

Until plane

5–6

5–6

5–6

5–6

3–5

150/ 150

Traditional Method T-06 共For definitions of parameters and consumables Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 FG 4 P1 P2 Polishing Cloth, Disk/ SiC SiC SiC SiC SiC Cloth, Cloth paper paper paper paper paper napless, napless, hard, hard, wov, wov, silk syn Dia, Abrasive SiC SiC SiC SiC SiC Dia, spr Type spr or or susp susp Grit or P220 P320 P500 P1200 P2400 3 1 Grain Size ␮m Lubricant Water Water Water Water Water Alco Alco Type or wat or wat Rotation 100/150 300/150 300/150 150/150 150/150 150/150 150/150 Disk/ Holder rpm/rpm Comp Comp Comp Comp Comp Comp Comp/ Comp or or Contra or contra contra contra Force per 30 共7兲 30 共7兲 30 共7兲 30 共7兲 20 共4.5兲 25 共5.5兲 25 共5.5兲 Specimen N 共lb兲 Time Until 0.5–1 0.5–1 0.5–1 0.5–1 5–8 5–15 Minutes plane

see P3 Cloth, napless, soft, porous, syn Silica

0.04 / 0.05

150/150

Contra

15 共3.4兲

3–5

244


Etchants Material CaO MgO Porcelain ZnO ZrO2 Ba TiO3

Etchants 共see Table 12.2兲 919, 920, 921, 922, 923 919, 924 930 925 926, 927 928, 929

Uses General structure General structure General structure Grain boundaries Grain boundaries Grain boundaries

Material/Preparation Tables 07 Material: Glasses. Optical fibers Comments on Material: There are many different types of glass with different chemical and physical properties. Glass can be defined as an amorphous solid. A material is amorphous when it has no long-range order, that is, when there in no regularity in the arrangement of its molecular constituents on a scale larger than a few times the size of these groups. For example, the average distance between silicon atoms in vitreous silica 共SiO2兲 is about 3.6 Å, and there is no order between these atoms at distances above about 10 Å. A solid is a rigid material that does not flow when it is subjected to moderate forces. This definition is not totally agreed upon. In the ASTM standard for glass, the material is described as “glass is an inorganic product of fusion which has been cooled to a rigid condition without crystallization.” This description is based on the fact that most glass is made by cooling a liquid in such a way that it does not crystallize. The difficulty with this view is that glasses can be prepared without cooling from the liquid state. Glass coatings are deposited from the vapor or liquid solution, sometimes with chemical reactions. Sodium-silicate glass made by evaporation and baking is indistinguishable from sodium-silicate glass made by cooling from the liquid. The main types of glass and their used are: Soda lime 共containers, windows, lamp bulbs兲, pyrex borosilicate 共headlamps, cookware, laboratory ware兲 vitreous silica 共semiconductor crucibles, lamps, optical components, optical fibers兲, alkali lead 共lamp tubing, sealing兲, “E” lime aluminosilicate 共fibers兲, lime magnesia aluminosilicate 共high temperatures, cookware兲. Optical fibers are coated strands of optically pure glass with a thickness of 9 – 62.5 ␮m that carry digital information over long distances. They are also used in medical imaging and mechanical engineering inspection. Preparation of glass is not difficult; if planeness is important, the use of Method C-07 should be preferred. Glass being a very brittle material can be prepared by lapping 共see Section 6.7.7兲 and Method T-39. As the surface of glass is softened by water, this liquid should be used to carry the lapping abrasive to obtain the highest removal rate. Also at polishing a hydrated layer is formed by chemical reaction and the process can be described as chemical mechanical polishing 共CMP兲, the polishing abrasive only removing the soft reaction layer 共see Section 7.12兲.

Chapter 13


245

Sectioning: Wet abrasive cutting with a diamond metal bond cut-off wheel preferably on a precision cut-off machine. Because of the brittleness of the glass, the feed rate should be low and the use of a thin cut-off wheel should be preferred. In the case of examination of a coating, the area to be examined should be under compression when the cut-off wheel enters the work piece 共see also Material/Preparation Tables 08–10兲. Mounting: In general, hot compression mounting cannot be recommended due to the risk of cracking because of the pressure and thermal cycle in the mounting press. If considered possible, the hot compression mounting should be with epoxy with a filler to obtain a high hardness of the mounting material. Cold mounting can be with acrylics 共with a filler兲, epoxy, and polyester. Grinding: Most glasses can be ground with SiC grinding paper. As an alternative, diamond disks with fixed abrasives in a resin bond should be used combined with an RCD 共see Method C-07兲 if a very plane surface is needed. Also lapping 共see Method T-39兲 and diamond lapping film can be used 共see Section 6.7.6兲. Polishing: Polishing can be done with diamond, silica, and alumina. The methods mentioned below may be extended as indicated. To increase the CMP, an acidic suspension can be used for the final polishing step by adding a few drops of nitric acid. Etching: Normally glasses are not etched.

Purpose 共alphabetic兲: Case or coating thickness/hardness, surface layers Perfect edge retention Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure Phase identification Porosity


Methods C-07

C-07

C 730

C-07, T-07 C-07, T-07 C-07, T-07 C-07


Diamond, metal bond


Resin Time Minutes

Cold Mounting


Acrylics/Epoxy 6 – 10 min/ 6 – 8 h

246


Grinding C-07: FG 1 can be omitted and FG 2 changed to 9 ␮m diamond. In this case two polishing steps are added 共see below兲. Medium hard materials: C-07: PG can be changed to SiC paper grit 500 followed by the three steps mentioned above and below. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-07: A polishing step like P 1 in Method T-07 can be added. If FG 1 is omitted and FG 2 is changed as mentioned above, two polishing steps, P 1 from C-06 and P 1 from T-07 are added. T-07: A step like P 2 in Method T-06 can be used between FG 4 and P 1 to secure a good edge retention. A few drops of HNO3 can be added to the final polishing step 共see above兲. Contemporary Method C-07 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 Polishing Disk/Cloth Dia, disk, Dia, disk RCD, soft fixed, res fixed, res Abrasive Type Diamond Diamond Dia, spr, or susp Grit or Grain size ␮m P220 P1200 1 Lubricant Type Water Water Wat Rotation Disk/Holder 150/ 150 150/ 150 150/ 150 rpm/rpm Comp/Contra Comp Comp Comp Force per Specimen N 共lb兲 30 共7兲 30 共7兲 35 共8兲 Time Until plane 3–5 7 Minutes Traditional Method T-07 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 FG 4 P1 Polishing Disk/Cloth SiC paper SiC paper SiC paper SiC paper SiC paper Cloth, napless, soft, porous syn Abrasive Type SiC SiC SiC SiC SiC Silica

Chapter 13

Grit or Grain Size ␮m Lubricant Type Rotation Disk/Holder rpm/rpm Comp/Contra Force per Specimen N 共lb兲 Time Minutes


247

P320

P400

P800

P1000

P4000

0.04/ 0.05

Water

Water

Water

Water

Water

300/ 150

300/ 150

300/ 150

300/ 150

300/ 150

150/ 150

Comp 20 共4.5兲

Comp 20 共4.5兲

Comp 20 共4.5兲

Comp 20 共4.5兲

Comp 20 共4.5兲

Contra 15 共3.4兲

Until plane

0.5–1

0.5–1

0.5–1

0.5–1

2

Material/Preparation Tables 08 Material: Anodized coatings. CVD coatings. PVD Coatings Material Properties: See below. Comments on Material: Anodizing is used for surface treatment of aluminum products. The work piece is placed as an anode in an electrolytic bath, and an aluminum oxide layer is developed. It consists of a solid layer of typically 0.005– 0.04 ␮m towards the work piece and further a layer with pores 5 – 25 ␮m thick. Solid aluminum oxide has a hardness in the range of 2000 HV, the hardness of the porous layer is normally higher than 1000 HV. Hard anodizing is performed at low temperatures around 5 ° C 共41° F兲 and gives a coating with few small pores and thickness up to 50– 100 ␮m. Anodizing is mainly used for decorative finishing and protection against wear and corrosion. Metallographic/materialographic examination is mainly made for measurement of the thickness, microhardness, and the quality of the coating. Chemical vapor deposition 共CVD兲 is a method of forming dense structural parts or coatings using the decomposition of relatively high vapor pressure gases. Coatings, which are the most common application of CVD, generally fall into one of two categories, electronic materials or protective coatings, and are applied either as conversion coatings or as deposited coatings. Conversion coatings involve the surface formation of a compound where one of the elemental components is already present on the surface. At deposited coatings all the elemental constituents of the coating comes from the vapor phase Protective coatings are deposited onto a work piece 共substrate兲 to provide wear, corrosion or erosion protection, or both. A high number of materials, metals, and ceramics can be used for coatings. Metallographic/materialographic examination includes the purposes mentioned above and the adhesion between coating and work piece 共substrate兲.

248


Physical vapor deposition 共PVD兲 is a method of depositing a coating using a vacuum chamber and an electric current between the material source and the work piece. The material source can consist of any electrically conductive metal. The coating has a thickness of 3 – 5 ␮m and the hardness can go up to 5000 HV using AlTiN as the coating material. Used coating materials are Cr, CrN, Ni, Ag, Ti, TiAlCN, TiCN, AlTiN, TiO, TiN, and ZrN. The coatings are made for corrosive protection, decoration, high hardness, improved wear resistance, and reduced friction. The metallographic/materialographic examination includes the purposes mentioned above. Sectioning: It is important that the cutting takes place perpendicular to the surface to be prepared. If the plane of the cross section is not perpendicular to the plane of the coating, the measured thickness will be greater than the true thickness. For example, an inclination of 10° will contribute a 1.5 % error. The cutting should preferably take place on a precision cut-off machine using the thinnest possible cut-off wheel with a bakelite bond, the wheel suited for the work piece material, not the coating material. The wheel speed should be in the range of 25 m / s 共82 ft/ s兲. Diamond cut-off wheels should only be used for very hard work piece materials like ceramics. It is very important that the cut-off wheel is entering the work piece through the coating at the area later to be examined so that the coating is compressed into the work piece. This reduces the risk that the true condition of the coating 共adherence to substrate material兲 is disturbed. For this reason also the feed speed should be low. If shearing is used for sectioning of plate material, the grinding time should be prolonged to remove damaged material and possible cracks between base material and coating caused by the shearing 共see Section 2.7.3兲 Mounting: It is very important that edge rounding and gaps between sample and mounting material are avoided. Therefore, a mounting material without shrinkage should be used, preferably epoxy. On very hard coatings hot mounting with epoxy with a filler should be preferred if heat and pressure can be tolerated. Also a phenolic resin with carbon fibers can be of advantage. In hot mounting a special application can be made to secure the edge: Tightly wrap up the specimen in Al-foil 共household type兲. This gives a good separation between mounting material and coating. Choose a mounting material with hardness as close as possible to the hardness of the coating. As an alternative cold mounting with epoxy can be used, and in case of porosity, vacuum impregnation can be an advantage 共see Section 3.10兲. Grinding: The preparation process should secure the highest possible edge retention. This means that all grinding, either on SiC grinding paper or rigid composite disks 共RCDs兲, should be as short as possible. Polishing: Also the polishing steps should be kept as short as possible. Etching: For most examinations no etching is needed.

Chapter 13

Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Heat influenced zone Image analysis, rating of inclusion content High planeness Microhardness, hardness


ASTM Standard 共See Section 12.4兲 B 487, B 578, B 681, B 748

Method C-08

B 390, E 112, E 930, E 1181, E 1382

C-08, T-08

E 562 E 1245, E 1268, E 1382

B 578, C 730, C 849, C 1326, C 1327, E 10, E 18, E 92, E 103, E 110, E 140, E 384, E 448 E 3, E 407, E 883


249

C-08, T-08 C-08

C-08, T-08

C-08, T-08 C-08, T-08 C-08, T-08


Bakelite, Al2O3 or SiC depending on the work piece 共substrate兲 material 0.5 mm 共0.019 in兲 thickness

Mounting Hot Compression Resin Epoxy with Filler Cold Mounting Resin Epoxy Mounting Time 9 Time 6–8 h Minutes Minutes/ Hours Grinding C-08, T-08: If possible make PG step with SiC paper grit 500. C-08: FG 1 and FG 3: Often these two steps can be omitted. C-08: For CVD coating and PVD coatings on a hard substrate change PG and FG 1 to PG from Method C-09. C-08: For preparation of CVD and PVD coatings, use shortest times stated. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued.

250


Polishing C-08: For preparation of anodized coatings, the P 1 step can be changed to a napless, hard, wov, silk cloth. Contemporary Method C-08 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 Polishing Cloth, Disk/Cloth SiC paper Sic paper RCD, soft RCD, soft Cloth, napless, napless, soft, hard, wov, syn porous, syn Abrasive Type SiC SiC Dia, spr or Dia, spr Dia, spr Silica susp or susp or susp Grit/Grain P320 P500 9 3 3 0.04/ 0.05 Size ␮m Lubricant Type Water Water Alco or Alco or Wat-oil wat wat Rotation 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp Comp Comp Comp Contra contra Force per 30 共7兲 30 共7兲 30 共7兲 25 共4.5兲 20 共4.5兲 10 共2.3兲 Specimen N 共lb兲 Time Until 0.5–1 3–8 3–7 1.5–5 0.5–1 Minutes plane Traditional Method T-08 共For Section 13.2.2.兲 Grinding/ PG FG 1 Polishing Disk/Cloth SiC SiC paper paper

Abrasive Type

SiC

SiC

definitions of parameters and consumables see FG 2

FG 3

P1

P2

P3

SiC paper

SiC paper

Cloth, napless, hard, wov, syn

Cloth, napless, soft, porous, syn

SiC

SiC

Cloth, napless, hard, non wov, syn Dia, spr or susp

Dia, spr or susp

Silica

Chapter 13

Grit or Grain Size ␮m Lubricant Type Rotation Disk/ Holder r/min/r/min Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

P220

P320

P500

1200

Water

Water

Water

Water


6

Alco or wat 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150

251

3

0.04/ 0.05


150/ 150

Comp or contra 25 共5.7兲



Comp

Comp

Comp

Contra

25 共5.7兲

20 共4.3兲

20 共4.3兲

10 共2.3兲

Until plane

0.5–1

0.5–1

0.5–1

3–5

2–5

0.5–1

Material/Preparation Tables 09 Material: Electrolytically deposited coatings: Galvanization, plated coatings, other coatings. Diffusion coatings. Other coatings Material Properties: See below. Comments on Material: Electrolytically deposited coatings are produced by electrolysis, the work piece 共substrate兲 placed as a cathode in an electrolyte with an anode of the coating material. In galvanization, zinc is used as the coating material and in electroplating 共plating兲 other metals like chrome may be used. For Zn coatings also see Material/Preparation Tables 10. Diffusion coating is a process in which the work piece is either coated with another material and heated to a sufficient temperature in a suitable environment or exposed to a gaseous or liquid medium containing the other material, causing diffusion of the coating material into the work piece surface resulting in a change of the composition and properties of the surface 共see also Material/Preparation Tables 37兲. An example of other coatings is electroless plating in which metal ions in a dilute aqueous solution are plated out on the work piece by means of an autocatalytic chemical reduction. Typical examples of metallographic/materialographic examination of coatings are the layer thickness, porosity of coating, cracks, adherence to base material, and the diffusion zone between substrate 共work piece兲 and coating. Sectioning: See Material/Preparation Tables 08. Mounting: See Material/Preparation Tables 08. As an alternative to epoxy for cold mounting, acrylics with a filler can be used. Grinding: See Material/Preparation Tables 08.

252


Polishing: See Material/Preparation Tables 08. For zinc coatings, see Material/ Preparation Tables 10. Etching: For most examinations, etching is not needed, but an etchant for Sn coating on steel is stated below and etchants for Zn coatings are stated in Material/ Preparation Tables 10. ASTM Standard 共See Section 12.4兲 Method B 487, B 587, B 748, B 931, B 933, B 934 C-09

Purpose Case or coating thickness/hardness surface layers Perfect edge retention Grain size, grain boundaries Heat influenced zone Image analysis, rating of inclusion content High planeness Micohardness, hardness

B 390, E 112, E 930, E 1181, E 1382 E 562, E 1245, E 1268, E 1382



C-09, T-09 C-09, T-09 C-09

C-09, T-09

C-09, T-09 C-09, T-09 C-09, T-09


Al2O3 or SiC according to base material, bakelite bond, 0.5 mm 共0.019 in兲 thickness


Resin Time Minutes

Epoxy 8–10

Cold Mounting


Epoxy 6–8 h

Grinding Plated coatings: C-09: Use SiC paper grit 500 for PG. Diffusion coatings: C-09: FG 1: RCD, soft can be changed to a napless v. hard, wov, syn cloth. C-09: PG: SiC paper grit 220 or grit 320 can be used instead of a diamond disk. C-09: For some Zn coatings where water sensitivity is suspected, diamond spray and alcohol-based lubricants are preferred at the step FG 1 and P 1. If silica in P 2 is too alkaline use alumina, pH 7-7.5.

Chapter 13


253

C-09: P 2: For sensitive layers this step can be changed to a napless, hard, wov, silk cloth with 1 ␮m diamond spray and alcohol-based lubricant. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-09: A step like P 3 in Method T-17 can be added before the final step. Contemporary Method C-09 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 Polishing Cloth, Disk/Cloth Dia, disk, RCD, Cloth, napless, fixed, res soft napless, soft, hard, porous, wov, syn syn Abrasive Type Diamond Dia, spr Dia, spr Silica or susp or susp Grit/Grain Size ␮m P220 9 3 0.04/ 0.05 Lubricant Type Water Alco or wat Alco or wat Rotation Disk/Holder 300/ 150 150/ 150 150/ 150 150/ 150 rpm/rpm Comp/Contra Comp or Comp Comp Contra contra Force per Specimen N 共lb兲 25 共5.7兲 25 共5.7兲 25 共5.7兲 15 共3.4兲 Time Until plane 3–5 3–5 0.5–1 Minutes Traditional Method T-09 共For definitions Section 13.2.2.兲 Grinding/ PG FG 1 Polishing Disk/Cloth SiC SiC paper paper

of parameters and consumables see Fg 2

FG 3

P1

P2

SiC paper

SiC paper

Cloth, napless, hard, wov, syn Dia, spr or susp 3 Wat-oil

Cloth, napless, soft, porous, syn Silica

Abrasive Type

SiC

SiC

SiC

SiC

Grit or Grain Size ␮m Lubricant Type

P220 Water

P320 Water

P500 Water

P1200 Water

0.04/ 0.05

254


Rotation Disk/Holder rpm/rpm Comp/Contra

Force per Specimen N 共lb兲 Time Minutes Etchants Material Sn coating on steel Zn coatings, see M/PT-10

300/ 150 300/ 150 300/ 150 150/ 150 150/ 150

150/ 150




Comp

Comp

Contra

30 共7兲

30 共7兲

15 共3.4兲

Until plane

0.5–1

0.5–1

0.5–1

2–3

1

Etchants 共see Table 12.2兲 183

Uses General structure

Material/Preparation Tables 10 Material: Hot dip zinc coatings. Other Zn coatings Material Properties: See below. Comments on Material: In hot dipped zinc coating the work piece is dipped into molten zinc. This is a very efficient way to apply a sufficient thickness of zinc to obtain a very good corrosion protection. Other Zn coatings include electrolytically deposited coatings mentioned in Material/ Preparation Tables 09, and the below stated methods should be seen as alternatives to Methods C/T-09. The metallographic/materialographic examination of Zn coatings includes thickness measurement of the coating, adhesion of coating to base material, microstructure of base material, and coating and failure analysis like cracks in the coating. Sectioning: See Material/Preparation Tables 08. Mounting: See Material/Preparation Tables 08. It is very important that mounting is done without gaps between sample and mounting material because the water sensitive zinc is strongly influenced by water bleeding from the gap. Degrease the specimen in acetone before mounting. Place the specimen in clips to keep it upright. Use epoxy for cold mounting or bakelite with a carbon filler for hot mounting. In case of having many pieces of coated sheets in the same mount, gluing the sheets together with instant glue and hot mounting give good results without bleeding of liquid from the gaps between the sheets.

Chapter 13


255

Grinding: Pure zinc is very soft and sensitive to water. The purer the zinc of the coating is, the softer and the more water-sensitive it becomes. Therefore, plain, hot dipped, and electrolytically deposited coatings are soft and prone to mechanical deformation and they cannot be cleaned with water. Ethanol or isopropanol should be used for cleaning. It is important that the grinding steps are properly performed to avoid excessive damage that is very difficult to remove during the polishing. Polishing: Water-free suspensions and lubricants should be used for polishing of zinc coatings. The polishing can be finished with a cleaning step 共see below兲. Etching: Etching times should be short and concentration of etchant low to avoid over-etching 共see below兲. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Heat influenced zone Image analysis, rating of inclusion content High planeness Microhardness, hardness


ASTM Standard 共See Section 12.4兲 Method B 487, B 578, B 748 C-10

E 112, E 930, E 1181, E 1382 E 562, E 1245, E 1268, E 1382

C-10, T-10 C-10, T-10 C-10

C-10, T-10


C-10, T-10 C-10, T-10 C-10, T-10


Al2O3 or SiC according to base material, bakelite bond, 0.5 mm 共0.019 in兲 thickness


Resin Time Minutes

Bakelite with Carbon Filler 8–10

Cold Mounting

Resin

Epoxy

Time Minutes/ Hours

6–8 h

256


Grinding Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-10: P 1 can be changed to a hard silk cloth as used in P 2 and P 3 can be omitted. C-10 and T-10: The polishing can be finished with a cleaning step 共see P 3 in Method C-10兲. This is to avoid contact with water to the finished surface. For all other cleaning alcohol should be used. In the case of very sensitive Zn coatings, water free suspensions and lubricants should be used with Method C-10. Contemporary Method C-10 共For definitions of parameters Section 13.2.2.兲 Grinding/ PG FG 1 P1 Polishing Disk/Cloth SiC paper RCD, soft Cloth napless, hard, wov, syn Abrasive Type

SiC

Grit/Grain Size ␮m Rotation Disk/Holder rpm/rpm Comp/Contra

P320 300/ 150

Force per Specimen N 共lb兲 Time Minutes


P3 Cloth, napless, soft, porous, syn See above

Dia, spr or susp 9 150/ 150

Dia, spr or susp 3 150/ 150

Cloth, napless, hard, wov, silk Dia, spr or susp 1 150/ 150

150/ 150


Comp

Comp

Comp

Comp

30 共7兲

25 共5.7兲

20 共4.5兲

10 共2.2兲

Until plane

4

4–6

4–6

15– 20 s

Chapter 13

Traditional Method T-10 Section 13.2.2.兲 Grinding/ PG Polishing Disk/Cloth SiC paper


257

共For definitions of parameters and consumables see FG 1

Fg 2

FG 3

P1

P2

SiC paper

SiC paper

SiC paper


Abrasive Type

SiC

SiC

SiC

SiC

Dia, spr or susp

Grit or Grain Size ␮m Lubricant Type Rotation Disk/Holder rpm/rpm Comp/Contra

P220

P320

P500

P1200

3

Cloth, napless, med hard, wov, wool Dia, spr or susp 1

Water

Water

Water

Water

Alco

Wat-oil

300/ 150

300/ 150

300/ 150

150/ 150

150/ 150

150/ 150




Comp

Comp

Comp

20 共4.3兲

20 共4.3兲

15 共3.4兲

Until plane

0.5–1

0.5–1

0.5–1

4–6

1–2

Force per Specimen N 共lb兲 Time Minutes Etchants Material Zn-Fe

Etchants 共see Tables 12.2兲 74a

Uses Structure of galvanized sheet

Material/Preparation Tables 11 Material: Paint layers Comments on Material: Paint layers can be very different, either charged directly on the base material of the work piece or on a coating. The metallographic/materialographic examination includes measurement of layer thickness, adhesion to work piece surface, and failures in the paint. Sectioning: Sectioning shall take place as mentioned for coatings, see Material/ Preparation Tables 08. Mounting: See Material/Preparation Tables 08. Grinding: See Material/Preparationn Tables 08.

258


Polishing: See Material/Preparation Tables 08. The paint coat normally is very soft compared to the base material. This increases the risk of edge rounding and the polishing times should be kept to a minimum, depending on the base material. Etching: For etching, an etchant suited for the base material should be used. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Heat influenced zone Image analysis, rating of inclusion content High planeness Microhardness, hardness

ASTM Standard 共See Section 12.4兲 B 487, B 578, B 748

Method C-11

E 112, E 930, E 1181, E 1382

C-11, T-11

E 562, E 1245, E 1268, E 1382 B 578, C 730, C 849, C 1326, C1327, E 10, E 18, E 92, E 103, E 110, E 140, E 384, E 448 E 3, E 407, E 883


C-11, T-11 C-11

C-11, T-11

C-11, T-11 C-11, T-11 C-11, T-11


Al2O3 or SiC, bakelite bond, 0.5 mm 共0.019 in兲 thickness

Mounting Hot Compression Resin Bakelite or Epoxy Cold Mounting Resin Epoxy Mounting with Filler 6–8 h Time 8–10 Time Minutes Minutes/ Hours Grinding T-11: FG 1: This step with grit 320 is only needed at hand preparation. Attention: In C-methods, when using RCD: The disk concave during use. When the diffenence is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued.

Chapter 13


259

Polishing C-11: P 2 can changed to step P 2 in Method T-11. T-11: P 2 can be changed to P 2 in Method C-11. Contemporary Method C-11 共For definitions of parameters and consumable see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 P2 Polishing Cloth, Disk/Cloth SiC paper SiC paper RCD, soft Cloth, napless, napless, soft, porous, hard, syn wov, silk Abrasive Type SiC SiC Dia, spr Dia, spr Silica or susp or susp Grit or Grain 220 500 9 3 0.04/ 0.05 Size ␮m Lubricant Type Water Water Alco or Alco or wat wat Rotation 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp Comp Comp Contra contra Force per 35 共8兲 35 共8兲 20 共4.5兲 20 共4.5兲 10 共2.2兲 Specimen N 共lb兲 Time Until 0.5–1 4–6 2–6 1 Minutes plane Traditional Method T-11 共For definition of parameters and consumables Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 Polishing Disk/Cloth SiC SiC SiC SiC Cloth, paper paper paper paper napless, hard, wov, syn Abrisive Type

SiC

SiC

SiC

SiC

see P2 Cloth, napless, med hard, wov, wool Dia, spr or susp 1 Wat-oil

Dia, spr or susp Grit or Grain Size ␮m P320 P500 P1200 P4000 3 Lubricant Water Water Water Water Alco or Type Wat Rotation Disk/Holder 300/ 150 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150

260


rpm/rpm Comp/Contra



Comp

Comp

Comp

Comp

Comp

20 共4.5兲

20 共4.5兲

20 共4.5兲

20 共4.5兲

15 共3.4兲

Until plane

0.5–1

0.5–1

0.5–1

2–5

1–3

Material/Preparation Tables 12 Material: Thermal spray coatings: Flame, HVOF „High Velocity Oxygen Fuel… and other coatings Material Properties: See below. Comments on Material: Thermal spraying is a group of processes in which finely divided metallic or nonmetallic surface materials are deposited in a molten or semimolten condition on a substrate to form a spray deposit. The surfacing material may be in the form of powder, rod, cord, or wire. A common feature of all thermal spray coatings is their lenticular grain structure resulting from the rapid solidification of small globules, flattened from striking a cold surface at high velocities. Flame spraying or the combustion wire thermal spray process is basically the spraying of molten metal 共ceramics and cements can be used in rod or composite form兲 onto a surface to provide a coating. Material in wire form is melted in a flame and atomized using compressed air to form a fine spray. This flame spray process is called a “cold process” 共relative to the work piece material being coated兲, as the substrate 共work piece兲 temperature can be kept low during the processing, avoiding damage, metallurgical changes, and distortion to the substrate material. Flame spraying is used for improvement of wear resistance, etc., at machine elements and for anticorrosion coatings. HVOF/HVAF 共high velocity oxygen fuel/high velocity air fuel兲 and LVOF 共low velocity oxygen fuel兲 are spraying processes using material in powder form which is melted in a flame to form a fine spray. In HVOF the spray velocity is extremely high and the coatings are very dense, strong, and show low residual tensile stress or in some cases compressive stress. This enables very much thicker coatings to be applied than possible with other spray processes. Metallography/materialography is used for examination of a number of features, decisive for the quality of the coating, described below. Bond: The bonding at the thermal spray coating/substrate interface and between the particles in the spray coating should be such that both mechanical interlocking and diffusion bonding occur. A number of factors like cleanliness, temperature, time, velocity, and physical/chemical properties influence the bonding.

Chapter 13


261

Microstructure: The coatings show lamellar or flattened grains appearing to flow parallel to the substrate. The structure is heterogeneous that is due to the variations in the condition of the individual particle on impact. An important feature is the presence of unmelted particles and also whether the coating contains some porosity. Porosity: This is present in most thermally sprayed coatings due to a lack of fusion between sprayed particles or the expansion of gases generated during the spraying process. A porosity of 1 to 25 % is normal but can be influenced by changes in process and materials. Linear detachment: Cooling and solidification of most materials is accompanied by contraction or shrinkage. This generates a tensile stress within the particle and a compressive stress within the surface of the substrate. As the coating is built up, so are the tensile stresses in the coating. At a certain point the thickness will be reached while the tensile stresses will exceed that of the bond strength or cohesive strength and linear detachment will occur. Oxides: Most metallic coatings suffer oxidation during normal thermal spraying in air. The products of oxidation are usually included in the coating. Oxides are generally much harder than the coating metal. Oxides in coatings can be detrimental towards corrosion, strength, and machinability. During metallographic/ materialographic examination it is important to be able to discriminate between oxides and pores 共voids兲. Other features to be examined are coating thickness, hardness, and microhardness. Metallographic/materialographic preparation: Preparation of thermal spray coatings is more difficult than the average specimen. This is due to the difference in coating material and substrate 共work piece兲 material, the complicated nature of the coating, etc. All stages in the preparation process should be carefully executed to obtain a sufficient result; a special problem is to reveal the true porosity 共see Section 13.6.4, “Pull-Outs—False Porosity”兲. As the preparation process has this very important influence on the microstructure, it is important that a systematic and reproducible process is maintained. The preparation process is described below, and two ASTM standards cover specifically the preparation and examination of thermal sprayed coatings: Standard Guide for Metallographic Preparation of Thermal Sprayed Coatings 共E 1920兲 and Test Method for Determining Area Percentage Porosity in Thermal Sprayed Coatings 共E 2109兲.

262


Sectioning: Care must be exercised to avoid affecting the soundness of the coating and the interface between the coating and the substrate. Friable, porous, or brittle coatings may be vacuum impregnated with epoxy before sectioning to protect the specimen 共see Section 3.10兲. Specimens should always be sectioned such that the coating is compressed into the substrate. If the coating or interface is placed under tension, it may cause the coating to be pulled away from the substrate or result in delamination of the coating. If a part of the specimen has been under stress, this part should not be included in the examination of the specimen. Sectioning methods creating strong damage to the specimen, even wet cutting with a normal cut-off wheel, should be avoided. Preferably precision cutting should be used with the thinnest possible cut-off wheel, using Al2O3 or SiC in a bakelite bond according to the substrate material. Only in case of very thick ceramic layers a diamond wheel should be used. The cut-off wheel speed should be in the range of 25 m / s 共82 ft/ s兲 and the feed speed should be low to minimize the damage. Mounting: It is very important that edge rounding and gaps between sample and mounting material are avoided. Therefore, a mounting material without shrinkage should be used, preferably epoxy. At very hard coatings hot mounting with epoxy with a filler should be preferred if heat and pressure can be tolerated. Also, a phenolic resin with carbon fibers can be an advantage. However, only cold mounting with epoxy should be used in the initial determination of the true characteristics of a coating before considering the use of any other mounting material because hot mounting might influence the microstructure. As a rule hot mounting should only be used for mounting of dense, nonfriable coatings with substrates a minimum of 1.5 mm 共0.06 in兲 thick. Choose a mounting material with hardness as close as possible to the hardness of the coating. In case of porosity, vacuum impregnation can be required 共see Section 3.10兲 and often the use of a dye can be of advantage 共see Section 3.10.1兲. Grinding: Grinding may have a strong influence on the edge retention and a number of artifacts like false porosity and smearing 共see below兲. Due to the many different types of thermal coatings and substrate materials, the grinding sequence will vary, but it should be possible to find a useable method among the methods described in the Material/Preparation Tables 12–15. Polishing: It is very important to evaluate the type of coating and substrate before the start of the preparation because of the high variety of coatings and substrate materials. Two important features are whether one or more of the components in the microstructure are brittle or ductile. In case of a brittle component, often pull-outs will take place during the grinding, causing a “false porosity” that can only be removed with a prolonged polishing. In case of a ductile component this might be smeared into the existing pores 共voids兲 and a too dense microstructure might appear. To avoid this the use of SiC grinding paper should be reduced and grinding on rigid composite disks 共RCDs兲 or very hard cloths followed by at least two polishing steps should be used. See Section 13.6.4, “Pull-Outs—False Porosity,” where a number of thermal spray coatings are shown. Etching: The thermally sprayed coating is usually not etched, but etchants for the substrate material can be used, mentioned under this material.

Chapter 13

Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Heat influenced zone Image analysis, rating of inclusion content High planeness Microhardness, hardness


ASTM Standard 共See Section 12.4兲 B 487, B 748

Method C-12

E 112, E 930, E 1181

C-12, T-12

E 45, E 562, E 768, E 1245, E 1382, E 2109

B 578, C 730, C 849, C 1326, C 1327, E 10, E 18, E 92, E 103, E 110, E 140, E 384, B 448 E 3, E 45, E 407, E 562, E 768, E 883, E 1245, E1920

Microstructure

Phase identification Porosity Thermal spray coatings: Distribution, porosity, unmelted particles

263

E 2109 E 1920, E 2109

C-12, T-12 C-12

C-12, T-12

C-12, T-12

C-12, T-12 C-12 C-12, T-12



Mounting Hot Compression Resin Epoxy or Bakelite Cold Mounting Resin Epoxy Mounting with Filler Time 8–10 Time 6–8 h Minutes Minutes/ Hours Grinding Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued.

264


Polishing C-12: At certain thermal spray coatings where longer polishing times are needed, the P 1 step can be changed to diamond with grain size 6 ␮m and the P 1 and P 2 steps shown will be “P 2” and “P 3.” Contemporary Method C-12 共For Section 13.2.2.兲 Grinding/ PG Polishing Disk/Cloth Dia, disk, fixed, res

Abrasive Type

Diamond

Grit/Grain Size ␮m Lubricant Type Rotation Disk/Holder rpm/rpm Comp/Contra

P220 Water 300/ 150




FG 2

P1

P2

Dia, disk fixed, res

RCD, soft


Cloth, napless, soft, porous, syn Alumina

Diamond Dia, spr or susp P1200 9 Water Alco or wat 300/ 150 150/ 150

Dia, spr or susp 3 0.02/ 0.05 Alco or wat 150/ 150 150/ 150

Comp

Comp

Comp

Contra

30 共7兲

30 共7兲

25 共5.7兲

10 共2.2兲

5–7

4–6

1

Until plane 2

Traditional Method T-12 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 FG 4 P1 P2 Polishing Cloth, Disk/Cloth SiC SiC SiC SiC SiC Cloth, paper paper paper paper paper napless, med. nap, hard, wov, syn soft, syn Abrasive SiC SiC SiC SiC SiC Dia, spr Dia, spr Type or susp or susp Grit or P220 P320 P500 P1200 P2400 3 1 Grain Size ␮m Lubricant Water Water Water Water Water Alco or Alco or Type wat wat Rotation 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder

Chapter 13

rpm/rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes


265




Comp

Comp

Comp

Contra

25 共5.7兲

25 共5.7兲

20 共4.5兲

20 共4.5兲

Until plane

0.5–1

0.5–1

0.5–1

0.5–1

3

0.5–1

Material/Preparation Tables 13 Material: Plasma spray coatings: Metallic layers Material Properties: See below. Comments on Material: Plasma spraying is a thermal spraying process in which a nontransferred arc is utilized as the source of heat that ionizes a gas that melts and propels the coating material to the work piece 共substrate兲. Compared to combustion 共flame兲 spraying the plasma spraying provides rapid heating, low particle flight time, more inert flame and higher velocity, resulting in a finer, denser microstructure with less oxide inclusions. For further information see Material/Preparation Tables 12. Sectioning: See Material/Preparation Tables 12. Mounting: See Material/Preparation Tables 12. Grinding: See Material/Preparation Tables 12. Polishing: See Material/Preparation Tables 12. Etching: See Material/Preparation Tables 12. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Heat influenced zone Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure

Phase identification Porosity


Method C-13

E 112, E 930, E 1181

C-13, T-13 C-13, T-13 C-13

E 45, E 562, E 768, E 1245, E 1382, E 2109

B 578, C 730, C 849, C 1326, C 1327, E 10, E 18, E 92, E 103, E 110, E 140, E 384, E 448 E 3, E 45, E 407, E 562, E 768, E 883, E 1245, E 1920 E 2109

C-13, T-13

C-13, T-13

C-13, T-13 C-13

266


Thermal spray coatings: Distribution, porosity, unmelted particles

E 1920, E 2109

C-13, T-13



Mounting Hot Compression Resin Epoxy or Bakelite Cold Mounting Resin Epoxy Mounting with Filler Time 8–10 Time 6–8 h Minutes Minutes/ Hours Grinding C-13: PG: Grit 320 should be used if possible. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-13: P 2: Can be changed to P 2 from Method T-12. Contemporary Method C-13 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 P2 Polishing Cloth, Disk/Cloth SiC paper RCD, soft RCD, Cloth, napless, soft napless, soft, hard, porous, wov, syn silk Abrasive Type SiC Dia, Dia, Dia, Silica spr or spr or spr or susp susp susp Grit/Grain P220 9 3 3 0.04/ 0.05 Size ␮m Lubricant Water Alco or wat Alco or wat Alco or wat Type

Chapter 13



267

300/ 150

150/ 150

150/ 150

150/ 150

150/ 150


Comp

Comp

Comp

Contra

25 共5.5兲

25 共5.5兲

25 共5.5兲

10 共2.3兲

Until plane

4–6

5–7

3–4

0.5–1

Traditional Method T-13 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 FG 4 P1 P2 Polishing Cloth, Disk/Cloth SiC SiC SiC SiC SiC Cloth, paper paper paper paper paper napless, napless, soft, hard, porous, wov, syn silk Abrasive SiC SiC SiC SiC SiC Dia, spr Alumina Type or susp Grit or P220 P320 P550 P1200 P4000 3 0.02/ 0.05 Grain Size ␮m Lubricant Water Water Water Water Water Alco or Type wat Rotation 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp or Comp or Comp Comp Comp Contra contra contra contra Force per 25 共5.7兲 25 共5.7兲 25 共5.7兲 25 共5.7兲 25 共5.7兲 15 共3.4兲 10 共2.2兲 Specimen N 共lb兲 Time Until 0.5–1 0.5–1 0.5–1 0.5–1 3–4 0.5–1 Minutes plane

268


Material/Preparation Tables 14 Material: Plasma spray coatings: Ceramic layers Material Properties: See below. Comments on Material: See Material/Preparation Tables 12 and 13. Sectioning: Depending on the substrate an Al2O3 or SiC, bakelite bond, or diamond metal bond, 0.5 mm 共0.019 in兲 thickness cut-off wheel should be used. In case of very brittle coatings a diamond wheel with bakelite bond should be used, see Material/Preparation Tables 12. Mounting: See Material/Preparation Tables 12. Grinding: Remove at least 500 ␮m during the PG step to ensure that all damage from the cutting is removed. Pull-outs will be developed during the grinding, resembling pores 共see below兲. See also Material/Preparation Tables 12. Polishing: Polishing must be performed until the pull-outs made during the grinding are removed. Check the porosity and go on polishing with the P 1 step until the porosity level is constant. See also Material/Preparation Tables 12. Etching: See Material/Preparation Tables 12. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Heat influenced zone Image analysis, rating of inclusion content High planeness Microhardness, hardness

Microstructure



Method C-14

E 112, E 930, E 1181

C-14, T-14 C-14, T-14 C-14

E 45, E 562, E 768, E 1245, E 1382, E 2109

B 578, C 730, C 849, C 1326, C 1327, E 10, E 18, E 92, E 103, E 110, E 140, E 384, E 448 E 3, E 45, E 407, E 562, E 768, E 883, E 1245, E 1920 E 2109 E 1920, E 2109

C-14, T-14

C-14, T-14

C-14, T-14 C-14 C-14, T-14

Chapter 13


269


Al2O3 or SiC, bakelite bond, or diamond metal or bakelite bond, 0.5 mm 共0.019 in兲 thickness

Mounting Epoxy or Cold Mounting Resin Epoxy 共vacuum Bakelite impregnation兲 with Filler Time 8–10 Time 6–8 h Minutes Minutes/ Hours

Hot Compression Resin Mounting

Grinding The PG step is very important 共see above兲. C-14, T-14: PG: At thin or brittle layers, or both, change to PG from Methods T-13. C-14: FG 1: For very hard ceramic layers, the disk should be changed to RCD, hard. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-14, T-14: The time for the step, P 1 depends on the porosity level 共see M/PT 12兲. Contemporary Method C-14 共For definitions Section 13.2.2.兲 Grinding/ PG FG 1 Polishing Disk/Cloth Dia, disk, RCD, fixed, res soft

of parameters and consumables see

Abrasive Type

Diamond

Grit/Grain Size ␮m Lubricant Type Rotation Disk/Holder

P220 Water 300/ 150

Dia, spr or susp 9 Alco or wat 150/ 150

FG 2

P1

P2

RCD, soft


Dia, spr or susp 3 Alco or wat 150/ 150


Dia, spr or susp 3 0.04/ 0.05 Alco or wat 150/ 150 150/ 150

270


rpm/rpm Comp/Contra Force per Specimen N 共lb兲 Time Minutes


Comp

Comp

Comp

Contra

40 共9兲

35 共8兲

35 共8兲

15 共3.4兲

Until plane

4–5

3

3–4

1

Traditional Method T-14 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P3 Polishing Disk/Cloth Dia, pad, met Cloth, napless, Cloth, napless, Cloth, napless, v. hard, non hard, soft, wov/wov, syn non-wov, syn porous, syn Abrasive Type Diamond Dia, spr or susp Dia, spr or susp Alumina Grit or Grain Size ␮m 40 9 3 0.02/ 0.05 Lubricant Type Water Alco or wat Alco or wat Rotation Disk/Holder 300/ 150 150/ 150 150/ 150 150/ 150 rpm/rpm Comp/Contra Comp or Comp Comp Contra contra Force per 25 共5.7兲 25 共5.7兲 25 共5.7兲 20 共4.5兲 Specimen N 共lb兲 Time Until plane 6–7 3–4 1–2 Minutes

Material/Preparation Tables 15 Material: Plasma spray coatings: Composite layers Material Properties: See Material/Preparation Tables 12 and 13. Comments on Material: See Material/Preparation Tables 12 and 13. Sectioning: See Material/Preparation Tables 12 and 14. Mounting: See Material/Preparation Tables 12. Grinding: See Material/Preparation Tables 12 and 14. Polishing: See Material/Preparation Tables 12 and 14. Etching: See Material/Preparation Tables 12. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention


Method C-15

Chapter 13


Grain size, grain boundaries Heat influenced zone

E 112, E 930, E 1181


E 45, E 562, E 768, E 1245, E 1382, E 2109

B 578, C 730, C 849, C 1326, C 1327, E 10 E 18, E 92, E 103, E 110, E 140, E 384, E 448 E 3, E 45, E 407, E 562, E 768, E 883, E 1245, E 1920

Microstructure


E 2109 E 1920, E 2109

271

C-15, T-15 C-15, T-15 C-15

C-15, T-15

C-15, T-15 C-15, T-15 C-15 C-15, T-15


Al2O3 or SiC, bakelite bond, or diamond metal bond, 0.5 mm 共0.019 in兲 thickness

Mounting Hot Compression Resin Epoxy or Bakelite Cold Mounting Resin Epoxy Mounting with Filler 6–8 h Time 8–10 Time Minutes Minutes/ Hours Grinding C-15: PG: For softer composites this can be changed to PG or FG 1 in Method T-15 C-15: FG 2 and FG 3: It is important that the true level of pores is obtained at these steps.

272


C-15: FG 1: If the composite layer is very hard 共ceramic兲, the disk can be changed to RCD, hard. During the FG 2 step the level of porosities should be evaluated, and FG 2 shall go on until the level stays constant. T-15: If the composite layer contains hard ceramics 共⬎800 HV兲, SiC paper should be changed to diamond pads. PG: 40 ␮m, met, FG 1: Diamond pad 10 ␮m, bak. See also Method T-14. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-15 and T-15: The last step can be changed to P 2 from Method T-12. T-15: P 1 and P 2: It is important that the true level of pores is obtained at these steps. During the P 2 step the level porosities should be evaluated, and P 2 shall go on until the level stays constant. Contemporary Method C-15 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 P2 Polishing Cloth, Disk/Cloth Dia, disk RCD, soft RCD, Cloth, napless, fixed, res soft napless, soft, porous, hard, wov, syn silk Abrasive Type Diamond Dia, spr or Dia, spr or Dia, spr or Silica susp susp susp Grit/Grain P220 9 3 3 0.04/ 0.05 Size ␮m Lubricant Type Water Alco or wat Alco or wat Alco or wat Rotation 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp Comp Comp Contra contra Force per 30 共7兲 35 共8兲 35 共8兲 25 共5.7兲 10 共2.3兲 Specimen N 共lb兲 Time Until plane 5–6 5–7 3–4 1 Minutes Traditional Method T-15 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 P3 Polishing

Chapter 13


Cloth, napless, v. hard, nonwov/ wov, syn Dia, spr, or susp 6



Dia, spr or susp 3

Silica



150/ 150

Comp

Comp

Comp

Contra

25 共4.5兲

25 共4.5兲

20 共4.5兲

20 共4.5兲

10 共2.2兲

0.5–1

0.5–1

15–20

10

0.5–1

Disk/ Cloth

SiC paper

SiC paper

SiC paper

SiC paper

Abrasive Type

SiC

SiC

SiC

SiC


P220

P320

P500

P1000

Water

Water

Water

Water

Rotation Disk/Holder rpm/rpm Comp/ Contra

300/ 150

300/150

300/150

150/150


Comp

Comp

25 共4.5兲

Until plane

0.5–1


273

0.04/ 0.05

Material/Preparation Tables 16 Material: Composites: SiC fibers in Ti matrix Material Properties: See below. Comments on Material: A composite material is characterized as consisting of two or more different components. Depending on the bonding component used, a distinction is made between metal matrix composites, ceramic matrix composites, and plastic matrix composites. The intention behind a composite material is to combine the favorable properties of various materials and, at the same time, compensate for less favorable properties. The required combination of properties determines the choice of materials. Another vital factor in achieving a material with favorable properties is whether the various components “work together.” For example, good bonding between the components is important and no unintentional component alterations may occur during the production process. In the area of metal matrix composites, cermets, the high hardness of ceramic particles or the extreme strength of ceramic fibers, will typically be combined with the toughness of the metal.

274


Metallographic/materialographic examination includes separation between components, porosity, and transitions between components. Due to the very wide variety of composite materials it is only possible to indicate six basic methods in the Material/Preparation Tables 16 to 18, and these should be changed according to the given material following the comments stated for each stage/step in the preparation process. The most common problems with the preparation of composites are related to relief and unplaneness between the different components, often combined with smearing of material from a soft component covering pores, etc., of the other components. Sectioning: Depending on the hardness of the components of the composite, sectioning should be made as wet abrasive cutting with an Al2O3 / SiC, bakelite bond cut-off wheel or a diamond wheel. If the bond between the components in the composite is sufficiently high, a diamond wheel with metal bond can be used. If the bond is not adequate or one of the components is very hard and brittle, or both, bakelite bond should be used. The sectioning should be performed with great care, and often it is an advantage to use a precision cutting machine for the cutting using thin wheels 共see Material/Preparation Tables 12兲. A band saw should only be used for cutting of a large piece, later to be cut with a cut-off wheel. Mounting: As composite materials often have very high differences in hardness, mounting in a relatively hard mounting material is of advantage. In the case of porosity in one or more of the components, vacuum impregnation may be needed 共see Section 3.10兲. Grinding: In case of very high differences in hardness, SiC grinding paper may be less suited for grinding, removing too much material from the soft component creating relief. In case of ceramic components, diamond disks should be used for grinding. Polishing: As a general rule, both grinding and polishing times should be kept as short as possible to secure the planeness. It is important, however, that the hardest component is correctly ground/polished at each step before going on to the next finer step. Etching: Etching is performed according to the components of the composite. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness


Method C-16

E 112, E 930, E 1181 E 562, E 1245, E 1382

C-16, T-16 C-16

B 578, C 730, C 849, C 1326, C 1327, E 10, E 18, E 92, E 103, E 110, E 140, E 384, E 448

C-16, T-16

Chapter 13

Microstructure


E 3, E 407, E 562, E 883, E 1245, E 1382


275

C-16, T-16 C-16, T-16 C-16


Diamond, metal bond

Mounting Hot Compression Resin Epoxy or Bakelite Cold Mounting Resin Epoxy Mounting with Filler Time 8–10 Time 6–8 h Minutes Minutes/ Hours Grinding The material is relatively difficult to prepare because of the very hard SiC and the relatively soft and tough Ti. It is important that the SiC phase is “finished” in each step, before going to the next finer step. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing Ti may be chemically-mechanically polished: C-16: P 2 and T-16: P 3: Use the solution: 96 mL silica, 2 mL H2O2 共30 %兲, 2 mL NH3 solution 共25 %兲. Contemporary Method C-16 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 Polishing Cloth, Disk/Cloth Dia, disk Dia, disk RCD, RCD, Cloth, napless, fixed, res fixed, res soft soft napless, hard, wov, soft, porous, silk syn Abrasive Type Diamond Diamond Dia, spr Dia, spr Dia, spr Silica orsusp or susp orsusp See note Grit/Grain P220 P600 9 3 1 0.04/ 0.05 Size ␮m

276


Lubricant Type Rotation Disk/Holder rpm/rpm Comp/Contra Force per Specimen N 共lb兲 Time Minutes

Water

Water 150/ 150




300/ 150

150/ 150


Comp

Comp

Comp

Comp

Contra

30 共7兲

30 共7兲

20 共4.5兲

20 共4.5兲

10 共2.3兲

Until plane

2

4

5

3

1

Traditional Method T-16 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 P3 Polishing Cloth, Cloth, Disk/Cloth Dia, Dia, Cloth, napless, napless, pad, pad, napless, soft, hard, met bak v. hard, porous, wov, nonwov/ syn silk wov, syn Abrasive Type Diamon Diamond Dia, spr or Dia, spr or Silica susp susp See note Grit or Grain 40 10 6 1 0.04/ 0.05 Size ␮m Lubricant Type Water Water Alco or wat Alco or wat Rotation 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp Comp Comp Contra contra Force per 30 共7兲 25 共4.5兲 20 共4.5兲 20 共4.5兲 10 共2.2兲 Specimen N 共lb兲 Time Until plane 3 5 3 1–2 Minutes

Material/Preparation Tables 17 Material: Composites: Glass fiber reinforced plastic Material Properties: See below. Comments of Material: See Material/Preparation Tables 16. No “contemporary” method is developed for this kind of material, instead, Method C-17 describes a method using SiC grinding paper. See also the Material/Preparation Tables 64 and 65 covering polymers.

Chapter 13


277

Sectioning: See Material/Preparation Tables 16. Mounting: See Material/Preparation Tables 16. Grinding: See Material/Preparation Tables 16. Polishing: See Material/Preparation Tables 16. Etching: See Material/Preparation Tables 16. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness

Microstructure


Method C-17, T-17

E 112, E 930, E 1181 E 45, E 562, E 768, E 1245, E 1382

C-17, T-17 C-17, T-17

B 578, C 730, C849, C 1326, C 1327, E 10, E 18, E 92, E 103, E 110, E 140, E 384, E 448 E 3, E 45, E 407, E 562, E 768, E 883, E 1245

C-17, T-17


C-17, T-17 C-17, T-17 C-17, T-17


Al2O3 or SiC, bakelite bond or diamond, metal bond or bakelite bond


Resin Time Minutes

Cold Mounting


Epoxy 6–8 h

Contemporary Method C-17 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 P3 Polishing

278



Disk/Cloth

SiC paper

SiC paper


Abrasive Type

SiC

SiC


P220

P1200

Dia, spr orsusp 3

Cloth, napless, medium hard, wov, wool Dia, spr orsusp 1

Water

Water

300/ 150

150/ 150



150/ 150


Comp

Comp

Comp

Contra

30 共7兲

20 共4.5兲

20 共4.5兲

10 共2.2兲

Until plane

0.5–1

3–5

3

1


0.04/ 0.05

Traditional Method T-17 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 P2 P3 P4 Polishing Cloth, Cloth, Cloth, Disk/Cloth SiC SiC SiC Cloth, paper paper paper napless, napless, napless, napless, soft, hard, hard, hard, porous, wov, silk wov, silk wov, syn silk Abrasive Type SiC SiC SiC Dia, spr Dia, spr Dia, spr Silica or susp or susp or susp Grit or P220 P320 P500 9 3 1 0.04/ 0.05 Grain Size ␮m Lubricant Water Water Water Alco or Alco or Alco or Type wat wat wat Rotation 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp Comp Comp Comp Comp Contra contra Force per 30 共7兲 25 共4.5兲 25 共4.5兲 20 共4.5兲 20 共4.5兲 20 共4.5兲 10 共2.2兲 Specimen N 共lb兲

Chapter 13

Time Minutes

Until plane

0.5–1

0.5–1


4

4

4

279

2–3

Material/Preparation Tables 18 Material: Composites. Other composite materials Comments on Material: See Material/Preparation Tables 16. Sectioning: See Material/Preparation Tables 16. Mounting: See Material/Preparation Tables 16. Grinding: See Material/Preparation Tables 16. Polishing: See Material/Preparation Tables 16. Etching: See Material/Preparation Tables 16. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness



Method C-18

E 112, E 930, E 1181

C-18, T-18

E 45, E 562, E 768, E 1245, E 1382

C-18

B 578, C 730, C 849, C 1326, C 1327, E 10, E 18, E 92, E 103, E 110, E 140, E 384, E 448 E 3, E 45, E 407, E 562, E 768, E 883, E 1245

C-18, T-18

C-18, T-18 C-18, T-18 C-18


Al2O3 or SiC, bakelite bond or diamond, metal bond or bakelite bond

280


Mounting Hot Compression Resin Epoxy or Bakelite Cold Mounting Resin Epoxy Mounting with Filler Time 8–10 Time 6–8 h Minutes Minutes/ Hours Grinding T-18: At composites with ceramics, SiC grinding paper may not be used; use diamond for grinding 共see Method T-16 or use Method C-18兲. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C/T-18: Polishing step with silica: Depending on the matrix of the material, alumina is used instead of silica. See under the actual material. Also the silica step can be changed to P 2 from Method T-12. T-18: P 2: Can be changed to step P 2 from Method T-12 as final step. Contemporary Method C-18 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 Polishing Disk/Cloth Dia, disk, RCD, Cloth, Cloth, fixed, res soft napless, hard, napless, wov, syn soft, porous, syn Abrasive Type Diamond Dia, spr or Dia, spr or Silica susp susp Grit/Grain Size ␮m P220 9 3 0.04/ 0.05 Lubricant Type Water Alco or wat Alco or wat Rotation 300/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp or Comp Comp Contra Comp/Contra contra Force per Specimen N 共lb兲 30 共7兲 40 共9兲 40 共9兲 10 共2.2兲 Time Until plane 4–6 3–5 1 Minutes Traditional Method T-18 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 P3

Chapter 13

Polishing Disk/Cloth



Cloth, napless, hard, wov, silk Dia, spr or susp 3


150/ 150


Alco or wat 150/ 150 150/ 150

SiC paper

SiC paper

SiC paper

SiC paper

Abrasive Type

SiC

SiC

SiC

SiC


P220

P320

P500

P1200

Water

Water

Water

Water


300/ 150 300/ 150

300/ 150


281

0.04/ 0.05


Comp

Comp

Comp

Comp

Comp

Contra

25 共5.5兲

25 共5.5兲

25 共5.5兲

20 共4.5兲

20 共4.5兲

10 共2.3兲

Until plane

0.5–1

0.5–1

0.5–1

4–5

3

0.5–1

Material/Preparation Tables 19 Material: Ceramic capacitors. Ceramic resistors. Diodes Comments on Material: In ceramic capacitors, ceramic resistors, and diodes we have the hard, brittle ceramic or glass phases combined with softer materials like silicon and metals. Delamination, voidage, and cracks are typical processing defects which can be assessed by materialography/metallography. Also materialography/metallography can be used for dimension analysis. The monolithic ceramic capacitor consists of ceramic plates, often barium titanate, coated with layers of a silver-palladium alloy and with terminations in silver. The barium titanate being very brittle and sensitive to mechanical stress must be prepared very carefully with Method T-19 below; only the two grinding steps PG and FG 1 should be omitted so that the preparation starts with grit P500 grinding paper. Ceramic resistors are normally made with a less brittle and harder ceramic 共alumina兲 and Method C-19 can be recommended. Glass and silicon of the diodes are very brittle materials and very careful preparation is necessary. Method T-19 is considered the most suitable.

282


A number of artifacts can be developed during the preparation, like pull-outs, cracks, delaminations, and relief 共see Section 13.5兲. The correct mounting 共encapsulation兲 is important; uncorrect mounting may create voids and gaps between mounting material and the single constituents, leaving the constituent unsupported causing rounding and possibly cracking. Methods C-19 and T-19 may also be used for preparation of other electronic/ microelectronic devices like integrated circuits 共see also Material/Preparation Tables 26兲. Sectioning: Wet abrasive cutting with a diamond metal bond cut-off wheel as thin as possible. This should preferably take place on a precision cut-off machine, both to obtain the smallest possible stress to the specimen and to be able to cut reasonably precise in the correct distance from the site 共target兲 to be investigated. This distance should be so that neither the damages from the cutting and from the rough grinding steps will influence the surface at the site of interest 共target兲. In case the part 共capacitor兲 is relatively small, the part can be encapsulated 共mounted兲共see below兲 and a sectioning is not necessary; the inspection plane 共target兲 can be reached by grinding. Mounting: The lowest possible heating of the specimen should take place during mounting, so hot mounting should be avoided. Cold mounting in epoxy is recommended because of the low viscosity, the low peak temperature, and the possibility of vacuum impregnation 共see Section 3.10兲. Grinding: It is important that the very brittle materials are not damaged too much by the rough grinding papers and often, as mentioned above, the grinding should start with the grits P320 or P500. If a relief between areas with a high difference in hardness should be avoided, Method C-19 should be used if possible. Polishing: Polishing times should be kept as short as possible to avoid relief, but often long times are needed to remove deformation and other artifacts developed during the grinding. Often a water-oil based lubricant should be used for the final diamond steps. Etching: Normally no chemical etching takes place, but physical etching, like relief polishing can be used 共see Section 9.6兲. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure Phase identification Porosity


E 112, E 1382 E 562, E 1245, E 1382

C-19, T-19 C-19, T-19

E 92, E 384 E 3, E 407, E 562, E 883, 1245, E 1382

C-19, T-19 C-19, T-19 C-19, T-19 C-19, T-19

Chapter 13


283

Preparation Process 19 Sectioning Cut-Off wheel

Diamond, metal bond, 0.5 mm 共0.019 in兲 thickness

Mounting Hot Compression Mounting Resin Cold Mounting Resin Epoxy Time Time 12– 24 h Minutes Minutes/Hours Grinding C-19 and T-19: For very sensitive materials it is recommended not to use the PG step with grit P220 grinding paper, but start with grit P320 or P500. Diodes: C-19: It is recommended to use SiC paper grit P220 for PG and grit P500 for FG 1 so that FG 1 共RCD, soft兲 is changed to FG 2. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-19: P 2: At materials with less tendency for relief, the cloth can be changed to med nap, soft, syn. Diodes: C-19: The cloth for the step P 1 is changed to napless, hard, wov, syn, and the cloth for P 2 is changed to med nap, soft, syn. C-19: In case of sensitive materials like constituents of soft metals 共diodes兲, the lubricant for 3 ␮m and 1 ␮m diamond-polishing steps should be water-oil based. T-19: Often the step P 1 can be omitted. Contemporary Method C-19 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 P3 Polishing Cloth, Cloth, Disk/Cloth Dia, disk, RCD, Cloth, napless, napless, res soft napless, soft, hard, hard, porous, wov, silk wov, silk syn Abrasive Type Diamond Dia, Dia, Dia, Silica spr or spr or spr or susp susp susp Grit/Grain P220 9 3 1 0.04/ 0.05 Size ␮m

284


Lubricant Type

Water



300/ 150

Alco or wat Alco or wat 150/ 150

150/ 150

150/ 150


Comp

Comp

Comp

Contra

30 共7兲

20 共4.5兲

20 共4.5兲

10 共2.2兲

Until plane

4–6

1–2

1–2

0.5–1

Traditional Method T-19 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 P3 P4 Polishing Disk/ SiC SiC SiC SiC Cloth, Cloth, Cloth, Cloth, napnapnapCloth paper paper paper paper napless, less, less, less, soft, hard, hard, hard, porous wov, wov, wov, silk silk silk Silica Dia, Dia, Abrasive SiC SiC SiC SiC Dia, spr spr Type spr or or or susp susp susp Grit or P220 P320 P500 P1200 9 6 1 0.04/ 0.05 Grain size ␮m Lubricant Water Water Water Water Alco Wat-oil Wat-oil Type or wat Rotation 300/ 150 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/ Holder rpm/rpm Comp/ Comp Comp Comp Comp Comp Comp Comp Contra Contra 15 共3.4兲 20 共4.5兲 20 共4.5兲 20 共4.5兲 20 共4.5兲 20 共4.5兲 20 共4.5兲 10 共2.2兲 Force per Specimen N 共lb兲 Time Until 0.5–1 0.5–1 0.5–1 10–15 5–10 2 0.5–1 Minutes plane

Chapter 13


285

Material/Preparation Tables 20 Material: YBCO ceramic super conductors Comments on Material: A superconductor is an element, intermetallic, or compound that will conduct electricity without resistance below a certain temperature, Tc. However, this applies only to direct current 共dc兲 electricity and to finite amounts of current. All known superconductors are solids, and all require extreme cold to enter a superconductive state. Once set in motion, current will flow forever in a closed loop of superconducting material—making it the closest thing to perpetual motion in nature. Tc is the critical transition temperature below which a material begins to superconduct, and research is going on to find the material with the highest Tc. Superconductors are categorized in Type 1 and Type 2. Type 1 category is mainly comprised of metals and metalloids that require extremely low temperatures, Tc, up to a few K, to become superconductive. The Type 2 category is comprised of metallic compounds and alloys, of which the “perovskites,” metal-oxide ceramics like the so-called YBCO compounds composed of yttrium, barium, copper, and oxygen, are important because they have a Tc higher than 90 K. In general, YBCO materials are very brittle and porous, so pull-outs and microcracks can be introduced during the sectioning and grinding stages. The Method T-20 is developed for YBa2Cu3O7+, and in case of materials too hard for SiC grinding paper, or an extremely plane specimen is wanted, Method C-20 can be used. Sectioning: Sectioning should take place with utmost care because of the brittle and porous material. Wet abrasive cutting can be done with a thin diamond cut-off wheel, metal bond, or, if damage should be reduced, with bakelite bond on a precision cut-off machine. The cut-off wheel should be as thin as possible and for some softer materials, a thin SiC bakelite bond wheel, 0.5 mm 共0.02 in兲 can be used. The feed rate should be low and the wheel speed in the range of 1000 rpm. If the porosity is high, it can be recommended to vacuum impregnate the specimen before cutting 共see below兲. The clamping of the specimen during cutting should be so that pressure spots are avoided, as these can cause fractures in the material. Very sensitive materials can be glued to a piece of nonmetallic base material which is then clamped in the machine. When water is used for cutting, place the cut specimen in alcohol for one hour if the material is water sensitive. Mounting: If the porosity is above 5 % it is advisable to vacuum impregnate the sectioned specimen with epoxy possibly using a dye 共see Section 3.10兲. The material should not be hot mounted, but mounting after impregnation should be with a slow curing epoxy. To balance the hardness of the epoxy a filler can be added 共see Section 3.11.2兲. Grinding: As grinding with rough grinding papers causes pull-outs and microcracks, the PG step with grit P220 grinding paper may be changed to grit P320 if the surface after cutting seems relatively little damaged. Water should be avoided for water sensitive materials 共see below兲. Polishing: To remove pull-outs and microcracks polishing may be carried out at low pressure over relatively long times 共see methods below兲.

286


Etching: No etchants are stated below, but contrast can be developed as indicated.

Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure


Methods C-20

E 112, E 930, E 1181, E 1382 E 562, E 1245, E 1268, E 1382

C-20, T-20 C-20

E 384 E 3, E 562, E 883, E 1245, E 1268, E 1382

C-20, T-20 C-20, T-20


C-20, T-20 C-20, T-20


Diamond, metal bond 共bakelite bond兲, or SiC bakelite bond, 0.5 mm 共0.019 in兲 thickness

Mounting Hot Compression Resin Cold Mounting Resin Epoxy 共with filler兲 Mounting Time Time 12– 24 h Minutes Minutes/Hours Grinding C-20: FG 1 and FG 2: If material is highly sensitive to water use a water-free diamond suspension. T-20: If the material is not water sensitive, water should be used as a cooling fluid for the steps PG and FG 1 to FG 4. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-20: P 1: If the material is water sensitive, use P 1 and P 2 from T-20.

Chapter 13


287

T-21: If material is water sensitive, use water-free diamond suspension or spray for P 1 and P 2 as indicated. Contemporary Method C-20 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 Polishing Disk/Cloth SiC paper RCD, soft RCD, soft Cloth, napless, soft, porous, syn Abrasive Type SiC Dia, spr Dia, spr Silica or susp or susp Grit or Grain Size ␮m P220 9 3 0.04/ 0.05 Lubricant Type Water/dry Alco, water-free Alco, water-free Rotation Disk/Holder 150/ 150 150/ 150 150/ 150 150/ 150 rpm/rpm Comp/Contra Comp Comp Comp Contra Force per Specimen N 共lb兲 15 共3.4兲 25 共5.7兲 25 共5.7兲 20 共4.5兲 Time Until plane 3 3–10 1–2 Minutes Traditional Method T-20 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 FG 4 P1 P2 Polishing Cloth, Disk/Cloth SiC SiC SiC SiC SiC Cloth, paper paper paper paper paper napless, napless, hard, hard, wov, silk wov, silk Abrasive Type SiC SiC SiC SiC SiC Dia, spr Dia, spr or susp or susp Grit and P220 P500 P1200 P2400 P4000 1 0.25 Grain Size ␮m Alco, Lubricant Type Dry Dry Dry Dry Dry Alco, waterwater free free Rotation 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp Comp Comp Comp Comp Comp Comp Force per 15 共3.4兲 15 共3.4兲 15 共3.4兲 15 共3.4兲 15 共3.4兲 10–15 10–15 Specimen 共2.–3.4兲共2.3–3.4兲 N 共lb兲

288


Time Minutes Etchant Material YiBa2Ca3O7+

Until plane

0.5–1

0.5–1

0.5–1

0.5–1

4–20

5–15

Etchants 共see Table 3.2兲 Uses Contrast can be made by: a兲 vapor depositing of interference layer 共e.g., iron oxide兲 b兲 Observation of the polished specimen in polarized light

Material/Preparation Tables 21 Material: Germanium. Silicon. Si wafers. Other semiconductors Material Properties: Germanium: Face-centered cubic, 5.3 g / cm3, 937.4° C 共1719° F兲. Silicon: Face-centered cubic, 2.42 g / cm3, 1420° C 共2588° F兲. Comments on Material: Germanium and silicon are metalloids and belong to the group of materials, semiconductors. Silicon is the most commonly used material and is often prepared as a chip 共see Material/Preparation Tables 22 and 26兲 or as a wafer/solid piece, which is discussed here. It is, however, only the preparation for metallographic/materialographic examination, the polishing 共thinning兲, which is part of the production process, is outside the scope of this book. The semiconductors are brittle materials that fracture easily, and especially as thin wafers, the specimens should be handled with great care. Sectioning: Wet abrasive cutting with a diamond metal bond cut-off wheel, 0.5 mm 共0.02 in兲 thick or thinner. The cutting should be done on a precision cut-off machine to obtain the most controlled cutting with a low feed speed. The clamping should not be directly on the specimen, but with elastic material as spacers. Often it can be of advantage to encapsulate the specimen before cutting. Sectioning for production of wafers is outside the scope of this book. Mounting: For preparation of the flat side of a wafer, the wafer or a piece of the wafer is temporarily glued with wax to a support disk which can be placed in the specimen holder. In the case of a cross section of the wafer, the specimen is cold mounted and placed in the mounting mold supported by clips to hold it in an upright position 共see Section 3.9兲. Due to the brittle nature of the semiconductors these should not be hot mounted, but cold mounted, preferably with epoxy. Grinding: The rough grits of SiC grinding papers will damage silicon and other semiconductors rather strongly, and therefore the grits P220 and P320 should only be used if relatively much material should be removed. If the cut surface is of a good quality, the plane grinding should be done with a grit P500 grinding paper if possible. To avoid SiC grinding paper for fine grinding, use Method C-21. As an alternative to SiC grinding papers, Al2O3/diamond lapping films can be used 共see Section 6.7.6 and Material/Preparation Tables 22兲. Polishing: Polishing times should be as short as possible to avoid edge rounding. The semiconductor materials respond very well to chemical mechanical polishing with colloidal silica, but also here the time should be as short as possible. Etching: See Etchants below.

Chapter 13



289

ASTM Standard 共See Section 12.4兲 Methods C-21

E 112, E 930, E 1382

C-21, T-21

E 562, E 1245, E 1382

C-21

E 384 E 3, E 562, E 883, E 1245, E 1382

C-21, T-21 C-21, T-21


C-21, T-21 C-21, T-21


Diamond, metal bond, 0.5 mm 共0.02 in兲 or thinner


Resin Time Minutes

Cold Mounting


Epoxy 12– 24 h

Grinding C-21 and T-21: Plane grinding with grit P220 or P320, or both, should be avoided if possible. C-21: PG: Grit P500 SiC paper can be used. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-21 and T-21: Polishing times should be kept as short as possible. C-21 and T-21: P 1: This step can be changed to step P 2 in Method T-21. Contemporary Method C-21 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 P2 Polishing

290



Disk/Cloth

Dia, disk, fixed, res

RCD, soft

RCD, soft

Abrasive Type Grit or Grain Size ␮m Lubricant Type Rotation Disk/ Holder rpm/rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

Diamond P500

Dia, spr or susp 9

Dia, spr or susp 3

Cloth, napless, hard, wov, syn Dia, spr or susp 3

Water

Alco or wat

Alco or wat

Alco or wat

300/ 150

150/ 150

150/ 150

150/ 150

150/ 150

Comp

Comp

Comp

Comp

Contra

15 共3.4兲

20 共4.5兲

20 共4.5兲

20 共4.5兲

10 共2.3兲

Until plane

4

3

3

1–2

Silica 0.04/ 0.05


共For definitions of parameters and consumables see

Abrasive Type

SiC

Grit or Grain P500 Size ␮m Lubricant Type Water Rotation Disk/Holder rpm/rpm Comp/Contra Force per Specimen N 共lb兲

300/150

FG 1

FG 2

FG 3

P1

P2

P3

SiC paper

SiC paper

SiC paper


Cloth, napless, soft, porous

SiC

SiC

SiC

P1000

P2400

P4000

Dia, spr or susp 3


Water

Water

Water

Alco or wat 300/150 300/150 300/150 150/150

Comp Comp Comp Comp Comp 15–25 20 共4.5兲 20 共4.5兲 20 共4.5兲 20 共4.5兲共3.4–5.7兲

Silica 0.04/ 0.05

Alco or wat 150/150 150/150

Comp Contra 20 共4.5兲 10–15 共2.2–3.4兲

Chapter 13

Time Minutes Etchants Material Si, Si alloys Si, Si alloys Si Si

Until plane

1.5–2

1.5–2

1.5–2

Etchants 共see Table 12.2兲 931 932 933 934


4

3

291

1–3

Uses General structure General structure General structure To reveal SiO2

Material/Preparation Tables 22 Material: Microelectronic material „semiconductor device… Preparation of cross section of a semiconductor device using a tripod fixture for hand preparation on a grinder/polisher with a 200 mm 共8 in兲 polishing disk and variable speed 0 – 150 r / min. Comments on Material: Nonencapsulated cross sections through microelectronic material 共semiconductor devices兲 serve two main functions. Cuts through representative structures within an IC show relationships of layers and features, such as step coverage, interfaces between layers, and possibly embedded defects or voids. Precision cross sections through specific defects often lead to the process step or mechanism which produced the defect 共see Section 7.10.2兲. The preparation of a nonencapsulated cross section of microelectronic material is described below. The method is considered a “C-Method,” using a combination of SiC grinding papers and Al2O3/diamond lapping films 共see Section 6.7.6兲, and no “T-Method” is stated. Sectioning: The specimen should be a piece of silicon roughly 5 mm 共0.20 in兲 square. The desired cross section target should be within 50 ␮m from the edge. The specimen can be cut out with a thin diamond cut-off wheel on a precision cut-off machine medium speed or cleaved. Determine the desired cross section line 共target兲. If suitable landmarks do not exist, create visible marks with a laser or mechanical probe. Mounting: Heat up a sample mount to approximately 125° C 共250° F兲. Apply a dot of wax and mount the specimen in cantilever fashion on the sample mount. The target cross section line must extend beyond the end of the sample mount 共see Section 7.10.2兲. Place the sample mount with specimen in the tripod fixture. Grinding: The purpose of grinding is to rapidly achieve a surface 1 ␮m away from and parallel to the desired cross section line. If more than 40 ␮m of material should be removed to reach the final cross section line, begin grinding with SiC paper grit P1200 共see step PG below兲. If the distance to line is 20 ␮m or less, start with step FG 1 below. FG 3 and FG 4 uses Al2O3 and diamond lapping film plane back, placed with water as a “glue” on a plane, smooth surface 共glass/metal plate兲 on the polishing disk.

292


Diamond lapping film can be used as an alternative to SiC paper, and Al2O3 lapping film in the steps PG and FG 1, 2, 3, and 4; this is stated in the Method Table below. Step FG 5 shall always be with diamond lapping film. Attention: Always let the grinding/polishing disk rotate into the edge containing the target, except at the last polishing step 共reverse position兲. Polishing: The completed cross section should be exactly centered on the contact, via, or other feature in the target. Polishing will only remove very little material 共 2 ␮m or less兲 and cannot remove deep scratches or damage created by grinding too close to the desired finish with coarse abrasives. Polishing is most important when the cross section is to be viewed in a high-resolution field emission SEM. Type of “polishing” depends on the composition of the specimen: Si, SiO2, and Al with/without thin barrier layers: Repeat step FG 4 after step FG 5, only with 0.05 ␮m Al2O3 lapping film in 0.5 min or longer until the diamond scratches are removed. Finish with 0.5 min holding the fixture in reverse position 共see Section 7.10.2兲. Si, SiO2, and metallization including tungsten plugs or layers: Use step P 1 below, holding the fixture in reverse position 共see Section 7.10.2兲. Etching: Normally no etching is used.


Diamond wheel metal bond 0.5 mm 共0.019 in兲 thickness or by cleaving

Mounting Hot Compression Resin See above Cold Mounting Resin See above Mounting Time Time Minutes Minutes/Hours Contemporary Method C-22 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 FG 4 FG 5 P1 Polishing Al2O3 SiC SiC Disk/Cloth SiC Al2O3 Diamond Cloth, paper paper paper lapping napless, or or or or or hard, diamond diamond film diamond diamond diamond lapping lapping wov, syn lapping lapping lapping film film film film film Abrasive SiC or SiC or SiC or AlAl-oxide Diamond Dia, susp Type diamond diamond diamond oxide Grit/Grain P1200 P2400 or P4000 or 1 0.3 0.1 0.1 Size ␮m or 15 8 3

Chapter 13

Lubricant Type Rotation Disk/ Holder rpm/ rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes


293

Water

Water

Water

Water

Water

Water

Alco

60/ 100

60/ 100

60/ 100

60/ 100

30

30

70/ 100

Weight of fixture Until within 22 ␮m from target line





Weight Weight of fixture of fixture Until 0.5–1, within 1- until 1.5 ␮m target from target line

Material/Preparation Tables 23 Material: Resistors. Other electronic metal components Comments on Material: Metal film resistors and other metal-based electronic components often consist of several very different types of material that range from a very soft metal to a very hard ceramic. The methods stated below should be considered as supplement to the methods stated in Material/Preparation Tables 19 and 26. Sectioning: See Material/Preparation Tables 19 and 26. Mounting: See Material/Preparation Tables 19 and 26. Grinding: See Material/Preparation Tables 19 and 26. Polishing: See Material/Preparation Tables 19 and 26. Etching: See Material/Preparation Tables 19. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness


E 112, E 1382 E 562, E 1382

C-23, T-23 C-23, T-23

E 92, E 384

C-23, T-23

294


Microstructure

E 3, E 407, E 562, E 883, E 1245, E 1382


C-23, T-23 C-23, T-23 C-23, T-23


Diamond wheel metal bond or SiC bakelite bond, 0.5 mm 共0.019 in兲 thickness.

Mounting Hot Compression Resin Cold Mounting Resin Acrylics with a Mounting Filler/Epoxy Time Time 6 – 15 min/ 12– 24 h Minutes Minutes/Hours Grinding C-23: In the case of a high amount of ceramics in the specimen, PG may be changed to a diamond pad, 30 ␮m, bakelite bond. See also Methods C/T-19. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing T-23: The step P 1 can be followed by a step like P 1 in Method C-23. Contemporary Method C-23 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 Polishing Disk/Cloth SiC paper RCD, soft RCD, soft Cloth, napless, soft, porous, syn Abrasive Type SiC Dia, spr Dia, spr Silica or susp or susp Grit or Grain Size ␮m 320 9 3 0.04/ 0.05 Lubricant Type Water Alco or wat Alco or wat Rotation Disk/Holder 300/ 150 150/ 150 150/ 150 150/ 150 rpm/rpm Comp/Contra Comp or Comp Comp Contra contra Force per Specimen N 共lb兲 35 共8兲 35 共8兲 35 共8兲 20 共4.5兲

Chapter 13

Time Minutes

Until plane

3–4


3

295

0.5–1

Traditional Method T-23 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 Polishing Disk/Cloth SiC paper SiC paper SiC paper SiC paper Cloth, napless, hard, wov, syn Abrasive Type SiC SiC SiC SiC Dia, spr or susp Grit or Grain P220 P320 P500 P1200 3 Size ␮m Lubricant Type Water Water Water Water Alco or wat Rotation 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp or Comp or Comp Comp Contra Contra Contra Force per 30 共7兲 30 共7兲 30 共7兲 30 共7兲 30 共7兲 Specimen N 共lb兲 Time Until plane 0.5–1 0.5–1 0.5–1 3 Minutes

Material/Preparation Tables 24 Material: Solder balls. Microelectronic packages Comments on Material: The tin-lead solders used for solder balls often have to be prepared together with other components like printed circuit boards 共PCBs兲, ceramics, plastics, etc. 共see Section 7.10.3兲. This means that the ideal preparation of the soft solder is not possible if the other components also should be prepared in an acceptable way. For soft solders the main problem is embedding of abrasive grains and particles from the preparation process 共see below and Section 13.5/6兲. In case of soldered joints, cracks may develop after the preparation due to stress, and for this reason the specimen should be examined and documented immediately after preparation. For preparation of PCBs see Material/Preparation Tables 27. For microelectronic packages see also Material/Preparation Tables 19 and 26.

296


Sectioning: Sectioning often involves cutting through components of very different hardness. Wet abrasive cutting should be done with a diamond metal bond cut-off wheel if the sectioning involves ceramics, and a SiC bakelite wheel if cutting involves only softer materials 共see also Material/Preparation Tables 26兲. Cutting should be done on a precision cut-off machine to secure a precise cut and make the use of a thin wheel, 0.5 mm 共0.02 in兲 or thinner, possible. In case of component-mounted boards, take care that all specimens are properly identified before they are sectioned from the PCB. The cut should be in a certain distance from the level of investigation so that damage from the cutting can be removed at grinding and polishing. Often the section to be investigated should be encapsulated 共mounted兲 in epoxy prior to cutting to ensure the integrity of delicate joints/components. Mounting: The specimen should be carefully cleaned in acetone and preferably ultrasonics before mounting. Hot mounting cannot be recommended. Cold mounting with epoxy and vacuum impregnation is recommended so that all voids are filled with epoxy 共see Section 3.10兲. Grinding: For specimens containing ceramics the Method C-24 should be used with Method C-19 as an alternative. Polishing: In case of embedded abrasive grains, the use of diamond paste can be tried out for the 3 and 1 ␮m steps; also the use of only small amounts of lubricant may prevent embedding of particles. Etching: Normally no etching is made, but in case of etching, see Material/ Preparation Tables 52. ASTM Standard 共See Section 12.4兲

Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure Phase identification

Method C-24

C-24, T-24 C-24, T-24

E 92, E 384 E 3, E 407, E 883

C-24, T-24 C-23, T-23 C-23, T-23


Diamond, metal bond or SiC, bakelite bond, thinnest possible

Chapter 13


297

Mounting Hot Compression Mounting Resin Cold Mounting Resin Epoxy Time Time 12– 24 h Minutes Minutes/Hours Grinding C-24: FG 1 and T-24: FG 3: Grind until solder balls are visible, being close to target. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-24, T-24: In case of embedded diamonds, diamond paste may be used instead of spray/suspension for the 3 ␮m and 1 ␮m steps. Contemporary Method C-24 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 P2 Polishing Cloth, Disk/Cloth SiC paper SiC paper RCD, soft Cloth, napless, medium napless, soft, hard, porous, wov, wool syn Abrasive Type SiC SiC Dia, spr or Dia, spr or Silica susp susp Grit or Grain 220 320 9 3 0.04/ 0.05 Size ␮m Lubricant Type Water Water Alco or wat Wat-oil Rotation Disk/Holder 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 rpm/rpm Comp/Contra Comp or Comp or Comp Comp Contra contra contra Force per Specimen 20 共4.5兲 15 共3.4兲 20 共4.5兲 20 共4.5兲 15 共3.4兲 N 共lb兲 Time Until plane To target 2 1–2 1 Minutes

298


Traditional Method T-24 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 P3 Polishing Cloth, Cloth, Disk/Cloth SiC SiC SiC SiC Cloth, nappaper paper paper paper napless, napless, less, soft hard, hard, nonwov, wov, silk porous, syn syn Abrasive SiC SiC SiC SiC Dia, spr Dia, spr Silica Type or susp or susp Grit or Grain P220 P320 P500 P1200 3 1 0.04/ 0.05 Size ␮m Lubricant Water Water Water Water Wat-oil Wat-oil Type Rotation 300/ 150 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp or Comp or Comp Comp Comp Contra contra contra contra Force per 30 共7兲 30 共7兲 30 共7兲 30 共7兲 20 共4.5兲 20 共4.5兲 15 共3.4兲 Specimen N 共lb兲 Time Until 0.5–1 0.5–1 0.5–1 4 2 0.5–1 Minutes plane

Material/Preparation Tables 25 Material: Capacitors. Other polymer electronic components Comments on Material: Film capacitors often incorporate two layers of dielectric film that have each been metallized on one side; these strips are stacked and rolled. The assembly may be packaged in a polymeric conformal coating or in a molded polymeric housing. Sectioning: See Material/Preparation Tables 19. Mounting: See Material/Preparation Tables 19. Grinding: If the specimen contains phases of very different hardness, Method C-25 should be preferred. Polishing: Polishing times should be kept as short as possible to avoid relief. Etching: Normally no etching is done. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention


Method C-25

Chapter 13



E 112, E 1382


E 562, E 1245, E 1382

Microstructure

E 3, E 407, E 562, E 883, E 1245, E 1382


E 92, E 384

299

C-25, T-25 C-25, T-25 C-25, T-25 C-25, T-25 C-25, T-25 C-25, T-25


Diamond, metal bond or SiC, bakelite bond, 0.5 mm 共0.02 in兲 thick

Mounting Hot Compression Resin Cold Mounting Resin Acrylics/Epoxy Mounting Time Time 6 – 10 min/ 8 – 12 h Minutes Minutes/Hours Grinding C-25: PG step: In the case of little or no ceramic material, SiC paper can be used. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Contemporary Method C-25 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 P3 Polishing Cloth, Disk/Cloth Dia, disk, RCD, soft Cloth, napCloth, napless, res less, hard, napless, soft, wov, silk hard, wov, porous, silk syn Abrasive Type Diamond Dia, spr or Dia, spr or Dia, spr or Silica susp susp susp

300



P220

9

6

1

0.04/ 0.05

Water

Alco or wat

Wat-oil

Wat-oil

300/ 150

150/ 150

150/ 150

150/ 150


Comp

Comp

Comp

25 共5.7兲

20 共4.5兲

20 共4.5兲

15 共3.4兲

Until plane

5

1–2

0.5–1

0.5

150/ 150

Traditional Method T-25 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 P3 Polishing Cloth, Cloth, Disk/Cloth SiC SiC SiC SiC Cloth, paper paper paper paper napless, napless, napless, soft v. hard, hard, wov, syn wov, silk porous, syn Abrasive Type SiC SiC SiC SiC Dia, spr Dia, spr Silica or susp or susp Grit or Grain P320 P500 P800 P1200 6 3 0.04/ 0.05 Size ␮m Lubricant Water Water Water Water Alco or Alco or Type wat wat Rotation 300/ 150 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp Comp Comp Comp Contra contra 30 共7兲 30 共7兲 30 共7兲 30 共7兲 30 共7兲 20 共4.5兲 15 共3.4兲 Force per Specimen N 共lb兲 Time Until 0.5–1 0.5–1 0.5–1 3 2 0.5–1 Minutes plane

Chapter 13


301

Material/Preparation Table 26 Material: Microelectronic packages. Integrated circuits. Transistors. Other microelectronic devices Comments on Material: As an introduction to preparation of microelectronic packages Section 7.10.3 should be studied to get an impression of the problems involved. Electronic and microelectronic devices and packages are complex material composites. Imaging and analysis of the various material microstructures, layered structures, and interfaces are necessary for a number of reasons, including package qualification, monitoring of the manufacturing process, incoming quality control, and failure analysis. The dimensions of the individual features range from fractions of a micron to several cm 共fraction of an in兲. Due to the close packing of the various materials within a small volume, all materials having very different properties; materialographic preparation faces the problem of making all the materials suited for proper analysis. It is essential to have a general understanding of the physical properties of all materials used in the construction of the package 共see Table 7.1兲. As a rule the preparation is tailored to the predominant component material to be analyzed, but often all materials must be considered to obtain a satisfactory result. Ignoring the unique interfaces that are present in a microelectronic package will likely result in artifacts induced during the preparation process. Such artifacts may be edge rounding, relief, embedding of abrasive grains, smearing and fracturing, and introduction of microcracks. Several of these artifacts could be misinterpreted as defects in the package developed during the production or in other ways. Making a cross section of a microelectronic package is a destructive test; it is important that as much information as possible about the device is gathered before the preparation starts. Such information is important to decide on the target of the preparation and may be important to be able to decide whether a defect was pre-existing or induced during the preparation. Also, this information is important in case of failure analysis. The information can be obtained through a number of analysis techniques like radiography, ultrasonic imaging, and macrophotography. Based on the available information, the preparation process is decided upon as either one of the two methods indicated below or other methods stated in Material/Preparation Tables 19, 22, 23, and 25, with the Methods C-19 and T-19 as the first choice. Sectioning: Wet abrasive cutting with a diamond metal bond cut-off wheel, 0.5 to 1 mm 共0.02 to 0.04 in兲 thick on a precision cut-off machine with 1500 to 2000 rpm. Often an electroplated diamond wheel can be used with advantage, and in the case of very hard components a diamond wheel with bakelite bond should be used. In certain cases depending on the materials, SiC bakelite bond cut-off wheel can be used. Cutting before encapsulation: In some cases the package should be opened to be able to make the encapsulation 共mounting兲. This can be done with wet abrasive cutting as mentioned or with grinding away the material or by other means. It is important that this process takes place at a safe distance to the site to be investigated.

302


Cutting after encapsulation: Wet abrasive cutting as stated above is recommended. It is important that the specimen is oriented, with respect to wheel rotation, such that the brittle material in the specimen, like silicon, is cut in compression. Doing this will minimize delamination or fracturing, or both, of the brittle component material. Also the specimen should be positioned so that the wheel cuts into the smallest dimension of the critical parts in the package. To shorten the following preparation process, the cutting should be done in a plane relatively close to the site of investigation with this under the condition that the damage caused by the cutting is “under control.” Mounting: Microelectronic packages cannot be subjected to pressure and heat, so only cold mounting, most often as an encapsulation in epoxy under vacuum, is recommended. Encapsulation: It is very important that the package is carefully cleaned to secure a complete adhesion by the epoxy during the encapsulation. This can be done in acetone, preferably in a beaker in an ultrasonic bath. Drying should be done with N2 gas or absolutely pure compressed air; normal compressed air should be avoided. The cleaned part should be handled with a pair of tweezers and dried in an oven at 50° C 共122° F兲. The package is placed in the mounting mold so that the plane of interest will ultimately be parallel to the cutting wheel. If needed, the specimen is supported with clips or by other means. It is important that the mounting material adheres to all constituents and that all topographical features of the package is filled with mounting material. This can best be provided with an epoxy with a low viscosity and impregnation under vacuum 共see Section 3.10兲. Also a pressure vessel can be used for securing a good encapsulation 共see Section 3.7兲. Grinding: Considering the often very brittle materials in the specimen, plane grinding with rough SiC grinding papers should be avoided. In the methods stated below plane grinding is with grit P320 grinding paper, but this paper should only be used if the plane grinding is in a plane relatively far from the site of interest 共target兲. If possible, depending on the surface established by the sectioning, the plane grinding should be done with an RCD stated in Method C-26, step FG 2, below. In case of packages with many soft, ductile materials, Method T-26 below may have the best grinding steps. Polishing: It is very important that the deformation and other damage developed during the grinding is removed during the rough polishing step. Often step P 2 in Method T-26 can be omitted. For packages containing predominantly soft materials 共plastics兲, it can be of advantage to use a mixture of 50 % colloidal silica and 50 % deagglomerated alumina 共0.05 ␮m兲 for the final polishing step. Etching: Normally no chemical etching takes place, but physical etching, like relief polishing and methods like deposition of layers can be used 共see Section 9.6兲.

Chapter 13

Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure Phase identification Porosity


303


E 112, E 1382 E 562, E 1245, E 1382

C-26, T-26 C-26, T-26

E 92, E 384 E 3, E 407, E 562, E 883, E 1245, E 1382

C-26, T-26 C-26, T-26 C-26, T-26 C-26, T-26


Diamond, metal bond or SiC, bakelite bond, 0 to 1 mm 共0.02 to 0.04 in兲 thick, see also above.

Mounting Hot Compression Mounting Resin Cold Mounting Resin Epoxy Time Time 12– 24 h Minutes Minutes/Hours Grinding C-26, T-26: Only use rough grits of SiC grinding paper, when not close to target. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing T-26: Often the step P 2 can be omitted. C-26: P 2: Often the cloth can be changed to a med nap, soft, syn, if the difference in hardness of the components materials is not high. C-26 and T-26: For predominantly soft materials use a mixture of 50 % colloidal silica and 50 % deagglomerated alumina 共0.05 ␮m兲 for the final polishing step. C-26 and T-26: For the steps with 6, 3, and 1 ␮m diamond, colloidal silica can be used as lubricant.

304


Contemporary Method C-26 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 P2 P3 Polishing Cloth, Disk/Cloth SiC paper SiC paper RCD, soft Cloth, nap- Cloth, napless, less, hard, napless, wov, syn hard, wov, soft, porous, silk syn Abrasive SiC SiC Dia, spr or Dia, spr or Dia, spr or Silica Type susp susp susp Grit or Grain 220 320 9 3 1 0.04/ 0.05 Size ␮m Lubricant Water Water Alco or Wat-oil Wat-oil Type wat Rotation 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp or Comp Comp Comp Contra contra contra Force per 25 共5.7兲 25 共5.7兲 20 共4.5兲 20 共4.5兲 20 共4.5兲 10–15 Specimen 共2.2–3.4兲 N 共lb兲 Time Until 0.5–1 2–15 1–5 1–4 0.5–1 Minutes plane 共Close to target兲 Traditional Method T-26 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ FG 3 P1 P2 P3 P4 Polishing PG FG 1 FG 2 Cloth, Cloth, Cloth, Disk/ SiC SiC SiC SiC Cloth, napnapnapCloth paper paper paper paper napless, less, less, less, soft, hard, hard, hard, porwov, wov, wov, ous, silk syn silk syn Silica Dia, Dia, Abrasive SiC SiC SiC SiC Dia, spr spr Type spr or or or susp susp susp Grit or P320 P500 P800 P1200 6 3 1 0.04/ Grain 0.05 Size ␮m Lubricant Water Water Water Water Wat-oil Wat-oil Wat-oil Type

Chapter 13

Rotation Disk/ Holder rpm/ rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes


305

300/ 150 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150


Comp

Comp

Comp

Comp

Comp

Comp

Contra

30 共7兲

30 共7兲

30 共7兲

20 共4.5兲

20 共4.5兲

20 共4.5兲

Until plane

0.5–1

0.5–1

0.5 –1 共Close to target兲

5–15

1–2

1–4

10–15 共2.2– 3.4兲 0.5–1

Material/Preparation Tables 27 Material: PCB coupon Comments on Material: For a description of PCB coupons with reference holes and their preparation, see Section 7.10.1. A “contemporary” method is not developed for this type of preparation; therefore, Method C-27 is a “traditional” method using SiC grinding paper. Sectioning: The coupon is normally cut out with a router or punched out. A precision cut-off machine with a diamond cut-off wheel, metal bond, can also be used. Mounting: Two to six coupons are mounted with a cold mounting material like acrylics in a special mounting mold to be placed in a special holder, with reference pins, to obtain a controlled material removal. Grinding: Grinding is done in two steps against adjustable stops mounted on the specimen holder to stop material removal before the center of the holes to be inspected. Polishing: The polishing steps P 3 and even P 2 in Methods C-27 and T-27 may be omitted according to the type of PCB and the purpose of examination. Etching: If an etching is wanted this can be done in the polishing step P 3: Use 96 mL colloidal silica, 2 mL H2O2 共30 %兲 and 2 mL ammonia solution 共25 %兲.


Diamond, metal bond, if not routed or punched, see above.

306


Mounting Hot Compression Mounting Resin Cold Mounting Resin Acrylics Time Time 8 – 10 min Minutes Minutes/Hours Grinding C-27, T-27: Grinding is performed against adjustable stops 共see above兲. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-27, T-27: Etching can be done through chemical mechanical polishing with 96 mL colloidal silica, 2 mL H2O2 共30 %兲 and 2 mL ammonia solution 共25 %兲. Contemporary Method C-27 共For definitions of parameters Section 13.2.2.兲 Grinding/ PG FG 1 P1 Polishing Disk/Cloth SiC paper SiC paper Cloth, napless, hard, wov, syn Abrasive Type

SiC

SiC


P220 Water 300/ 150

P1200 Water 150/ 150


P3

Cloth, napless, soft, porous, syn Dia, spr or Dia, spr or Silica susp susp 3 1 0.04/ 0.05 Water Water 150/ 150 150/ 150 150/ 150

Comp or Comp Comp contra Force per Specimen N 共lb兲 20 共4.5兲 20 共4.5兲 20 共4.5兲 Time See above See above 2 Minutes

Cloth, napless, hard, wov, wool

Comp

Contra

15 共3.4兲 2

10 共2.2兲 0.5

Traditional Method T-27 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 P3 Polishing

Chapter 13


307

Disk/Cloth

SiC paper SiC paper Cloth, napless, hard, wov, syn

Abrasive Type

SiC

SiC


P220

P1200

Cloth, napless, soft, porous, syn Dia, spr or Dia, spr or Silica susp susp 6 1 0.04/ 0.05

Water 300/ 150

Water 300/ 150

Water 150/ 150

Water 150/ 150

150/ 150


Comp

Comp

Comp

Contra

20 共4.5兲

20 共4.5兲

15 共3.4兲

10 共2.2兲

2

0.5


See above See above 2


Material/Preparation Tables 28 Material: High carbon steels. Medium carbon steels Material Properties: Alpha iron 共ferrite兲: Body-centered cubic, gamma iron 共austenite兲: Face-centered cubic, 7.85 g / cm3, 1528° C 共2782° F兲, HV 70 共ferrite兲. Low carbon steel: ⬍0.2 % C, medium carbon steel: 0.2–0.5 % C, high carbon steel: ⬎0.5 % C 共weight %兲. Comments on Material: The plain carbon steels are characterized by their composition, having only carbon as the important alloying element. A typical medium carbon steel 共SAE-AESI 1042兲 has the composition: 0.4–0.47 % carbon, 0.60–0.90 % manganese, maximum 0.040 % phosphorus, maximum 0.05 % sulfur. The plain carbon steels and other steels are classified according to their composition by the American Iron and Steel Institute 共AISI兲 and the Society of Automotive Engineers 共SAE兲. ASTM also has a classification system built on the steel product and its application. The ASTM standards are specifications for specific products; a few examples are: A 1, A 3, A 36 共see Section 12.4.2兲. The microstructure of plain carbon steels is a mixture of ferrite and pearlite, with an increase in pearlite corresponding to the increase in carbon content. At 0.8 % carbon, only pearlite is present and above 0.8 % carbon, cementite will develop. Medium and high carbon steels are relatively easy to prepare. The problem is to obtain a true ferrite without deformation. At higher carbon contents with small amounts of ferrite, the preparation can be cut down to three or four steps for routine examination 共see below兲. These materials are well suited for electrolytic polishing.

308


Sectioning: The correct selection of the specimen is important, especially on rolled material 共see Section 2.1兲. In wet abrasive cutting an Al2O3 cut-off wheel should be used. Overheating should be avoided because martensite can be developed. Cutting pressure should be moderate and cooling should be efficient on both sides of the cut-off wheel. If shearing or band sawing is used, the increase in deformation should be taken into consideration, prolonging the plane grinding step, or possibly use of a rougher grinding paper before grit 220. Mounting: For routine examination bakelite as powder or tablets is sufficient. In the case of examination of coatings, other mounting materials should be used 共see Material/Preparation Tables 08–15兲. For mounting for electrolytic polishing, see Section 3.11.6. Grinding: Grinding normally will give no problems with these materials. Care should be taken that the deformations from plane grinding are effectively removed before the polishing. If not, the deformed ferrite can be seen after etching, and the process must be repeated from FG 1. In the case of water sensitive inclusions, mineral spirits or kerosene can be used for grinding with SiC grinding paper 共see also Material/Preparation Tables 36兲. Polishing: The problem can be to obtain a perfect ferrite phase as mentioned above. In the case of only small deformations, prolong the 3 ␮m step for 1 – 2 min. For medium carbon steels the final step could be with diamond 共see below兲. A common test on steels is nonmetallic inclusion identification; often SEM and EDAX analysis is used. As Si may be contained in the indigenous inclusions, silica 共SiO2兲 should be avoided for the last polishing step. Therefore this step should be changed to diamond 共see below兲. Electrolytic polishing can be recommended. Etching: A high number of etchants are available for steels. In most cases a relative small selection will cover the need in a given laboratory 共see below兲. Electrolytic etching is possible.

Purpose Case or coating thickness/hardness surface layers Perfect edge retention Grain size, grain boundaries

ASTM Standard 共See Section 12.4兲 B 487, E 1077

Method C-28

E 112, E 930, E 1181, E 1382

Heat influenced zone Heat treatment

E 1077

Image analysis, rating of inclusion content High planeness Inclusions in steel Microhardness, hardness

E 45, E 562, E 768, E 1077, E 1245, E 1268, E 1382, E 2283

C-28, T-28, El-01 C-28 C-28, T-28, El-01 C-28

E 45, E 768, E 1245 E 10, E 18, E 92, E 103, E 110, E 140, E 384, E 448

C-28, T-28 C-28, T-28

Chapter 13

Microstructure


A 892, E 3, E 45, E 407, E 562, E 768, E 883, E 1077, E 1181, E 1245, E 1268, E 1351, E 1382, E 1558

Phase identification

309

C-28, T-28, El-01

C-28, T-28, El-01 C-28, T-28, El-01

Structure changes 共forging兲


Al2O3, bakelite bond

Mounting Hot Compression Resin Bakelite Cold Mounting Resin Acrylics Mounting Time 8–9 Time 6 – 10 min Minutes Minutes/Hours Grinding T-28: In some cases, at high C content, FG 1 can be omitted. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-28 and T-28: In case of SEM and EDAX analysis of inclusions, the final polishing step is changed to diamond 1 ␮m, see step P 2 in Method C-29. Also, 0.25 ␮m diamond can be used as a step after 1 ␮m diamond, using the same cloth and same data. C-28: P 1: The cloth can be changed to napless, hard, wov, silk. C-28: P 2: This step can be changed to diamond 1 ␮m, see P 2 in C-29, and the silica step will be P 3 or it may be omitted. T-28: P 3: Often the alumina suspension can be diluted with water 1:1. In some cases this step can be omitted.

310


Contemporary Method C-28 共For definitions of parameters and Section 13.2.2.兲 Grinding/ PG FG 1 P1 Polishing Disk/Cloth Dia, disk, RCD, hard Cloth, fixed, res napless, hard, wov, syn Abrasive Type Diamond Dia, spr Dia, spr or susp or susp Grit or Grain Size ␮m P220 9 3 Lubricant Type Water Alco or wat Alco or wat Rotation 300/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp Comp contra Force per 30 共7兲 25 共5.5兲 20 共4.5兲 Specimen N 共lb兲 Time Until plane 4–6 3 Minutes

consumables see P2 Cloth, napless, soft, porous, syn Silica 0.02/ 0.05 150/ 150

Contra 10 共2.2兲 1–4



Abrasive Type Grit or Grain Size ␮m Lubricant Type Rotation Disk/Holder rpm/rpm Comp/Contra Force per Specimen N 共lb兲

FG 1

FG 2

P1

P2

P3

SiC paper

SiC paper

SiC

SiC

SiC

P320

P500


Cloth, napless, porous, syn Alumina

P220


Water

Water

Water

Alco or wat

300/ 150

300/ 150

300/ 150

150/ 150


150/ 150


Comp

Comp

Comp

Comp

Contra

40 共9兲

40 共9兲

30 共7兲

20 共4.5兲

10 共2.2兲

0.02/ 0.05

Chapter 13

Time Minutes

Until plane

Etchants Material Fe+ C and Fe+ ⬍ 1 C + ⬍ 4% additions

0.5–1

0.5–1


3

3

311

1–4

Etchants 共see Table 12.2兲 Uses 76, 74a, 77, 78, 79 General structure 74a, 77, 31a, 223 Ferrite grain boundaries 80, 81, 82 Prior austenitic grain boundaries in martensitic and bainitic steels 78, 222a Untempered martensite 31b, 78 Carbides and phosphides 共matrix darkened carbides and phosphides remain bright兲 83 Cementite attacked rapidly, sustenite less, ferrite and iron phosphide least 84 Overheating and burning stains carbides 85 Stains carbides 86 Chemical polish-etch 210, 211 Colors ferrite 213, 214 Colors carbides 216 Color latch martensite in low carbon 222b high-alloy grades for dual phase steels; reveals pearlite, darkens martensite and outlines austenite

Material/Preparation Tables 29 Material: Low carbon steels Material Properties: Alpha iron 共ferrite兲: Body-centered cubic, gamma iron 共austenite兲: Face-centered cubic, 7.85 g / cm3, 1528° C 共2782° F兲, HV 70 共ferrite兲. Low carbon steel: ⬍0.2% C, medium carbon steel: 0.2– 0.5 % C, high carbon steel: ⬎0.5% C 共weight %兲 Comments on Material: Low carbon steels are relatively easy to prepare. The problem is to obtain a true ferrite without deformation. This depends on the carbon content and often, at higher carbon contents, a fine grinding step can be omitted for routine examination 共see Material/Process Tables 28兲. Sectioning: See Material/Preparation Tables 28. Mounting: See Material/Preparation Tables 28. Grinding: See Material/Preparation Tables 28. Polishing: See Material/Preparation Tables 28. Etching: See Material/Preparation Tables 28.

312


Purpose Case or coating thickness/hardness surface layers Perfect edge retention Grain size, grain boundaries Heat influenced zone Heat treatment Image analysis, rating of inclusion content High planeness Inclusions in steel Microhardness, hardness Microstructure


Method C-29

E 112, E 930, E 1181, E 1382

C-29, T-29, El-02 C-29

E 1077

E 45, E 562, E 768, E 1077, E 1245, E 1268, E 1382, E 2283 E 45, E 768, E 1245 E 10, E 18, E 92, E 103, E 110, E 140, E 384, E 448 A 892, E 3, E 45, E 407, E 768, E 883, E 1077, E 1181, E 1245, E 1268, E 1351, E 1382, E 1558


C-29, T-29, El-02 C-29

C-29, T-29 C-29, T-29 C-29, T-29, El-02 C-29, T-29, El-02 C-29, T-29, El-02




Mounting

Cold Mounting

Resin Time Minutes

Bakelite 8–9


Acrylics 8 – 10 min

Grinding C-29: P 2: This step can be changed to SiC paper grit P220/320. T-29: In some cases, at a relatively high carbon content, FG 1 can be omitted. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued.

Chapter 13


313

Polishing C-29 and T-29: In case of SEM and EDAX analysis of inclusions, the final polishing step is changed to diamond 1 ␮m, see step P 2 in Method C-29 and step P 3 in T-29. Also 0.25 ␮m diamond can be used as a step after 1 ␮m diamond, using the same cloth and same data. C-29: P 2: For certain materials 共cast iron兲 this step can be omitted or P 3 can be omitted. C-29 and T-29: Silica can be used instead of alumina. T-29: A fine polishing step, P 3, from C-29 can be added. Contemporary Method C-29 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 P3 Polishing Cloth, nap Cloth, Disk/Cloth Dia, disk RCD, soft Cloth, med. nap, soft, less, soft, fixed, res napless, porous, syn hard, wov, syn syn Dia, spr Alumina Dia, spr Abrasive Diamond Dia, or or Type spr or susp susp susp Grit or Grain P220 9 3 1 0.02/ 0.05 Size ␮m Lubricant Water Alco Alco Alco Type or wat or wat or wat Rotation 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp Comp Comp Contra contra Force per 25 共5.5兲 30 共6.6兲 25 共5.5兲 25 共5.5兲 10 共2.2兲 Specimen N 共lb兲 Time Until plane 4–6 4–5 1 1 Minutes

314


Traditional Method T-29 共For definitions of parameters and consumables Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 Polishing Cloth, Disk/Cloth SiC SiC SiC SiC Cloth, paper paper paper paper napless, napless, hard, hard, wov, silk wov, syn Abrasive Type Grit or Grain Size ␮m Lubricant Type Rotation Disk/Holder rpm/rpm Comp/Contra Force per Specimen N 共lb兲 Time Minutes

Dia, spr or susp 3

P3 Cloth, med nap, soft, syn Dia, spr or susp 1

SiC

SiC

SiC

SiC

P220

P320

P500

P1200

Water

Water

Water

Water

Comp or Comp contra 40 共9兲 40 共9兲

Comp

Comp

Comp

Comp

Comp

40 共9兲

40 共9兲

40 共9兲

35 共8兲

35 共8兲

Unit plane

0.5–1

0.5–1

3–4

3–4

1

300/ 150

Dia, spr or susp 6

see

Alco or Alco or Alco or wat wat wat 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150

0.5–1

Etchants See Material/Preparation Tables 28.

Chapter 13


315

Material/Preparation Tables 30 Material: Gray cast iron, lamellar. Malleable cast iron Material Properties: Alpha iron 共ferrite兲: Body-centered cubic, gamma iron 共austenite兲: Face-centered cubic, 7.85 g / cm3, 1528° C 共2782° F兲, HV 70 共ferrite兲. Gray cast iron: Carbon 2.5–4.0 %, silicon: 0.5–3.5 %, manganese: 0.2–1.3 %, phosphorus 0.002–1.0 %, sulfur: 0.2–0.15 % 共weight %兲. Comments on Material: Gray cast iron is by far the most used cast iron. The microstructure consists of ferrite or pearlite with graphite in flakes 共lamellar兲, or both, or in other shapes. The name refers to the color of a fresh fractured surface, which is grayish because of the graphite. Gray cast iron has a relatively high silicon content because silicon promotes the formation of graphite during solidifidation. The microstructure of lamellar cast iron contains 5–10 volume % of graphite, and the lamellar size and distribution are important for the strength of the cast iron, but in general lamellar cast iron has a relatively low strength because of the graphite. The type, size, and distribution are standardized in the ASTM Standard Test Method for Evaluating the Microstructure of Graphite in Iron Castings 共A 247兲. Also, a number of other specifications are described in ASTM standards; some examples covering gray cast iron and malleable cast iron are: A 47, A 48, A 126, A 159, A 197, A 220, A 338, and A 602 共see Sections 12.4.2兲. Malleable cast iron, also called TG 共temper graphite兲 iron, is made by heat treatment of white cast iron. During this treatment, up to 20 h, the carbides of the white cast iron are changed into graphite which will be separated into irregularly shaped nodules in a ferritic or ferritic/pearlitic matrix. This condition makes malleable cast iron comparable to steel regarding strength, but the importance of this material has been reduced because of the development of nodular cast iron 共ductile cast iron兲共see Material/Preparation Tables 31兲. As the microstructure strongly influences the mechanical properties of cast iron, metallographic/materialographic examination is important. The examination is supported by standard reference comparison charts or image analysis techniques, or both, to determine the morphology, size, and distribution of the graphite on an unetched specimen. During the metallographic/materialographic preparation, the retention of the free graphite in a ferrite/pearlite matrix causes a problem. The difference in hardness between the two phases and the relative brittleness of the graphite may cause pull-outs of the graphite and development of a relief between the phases. To obtain a correct result of a running analysis, it is important that the same high number of graphite lamellars/nodules are satisfactorily present in the structure without missing parts of the graphite. The pull-outs to a high degree take place during the rougher steps of the grinding and therefore it is important that the graphite is re-established during the fine grinding and polishing steps. SiC paper may cause a pull-out of graphite even at the fine grain sizes. In that case Method C-30 should be used. In the case of a matrix containing much ferrite this may cause problems with deformations 共see Material/Preparation Tables 28兲. For certain cast irons, electrolytic polishing can be used. Method C-29 and T-29 can also be used for cast iron.

316


Sectioning: These materials are normally sectioned with wet abrasive cutting without problems using an Al2O3, bakelite bond cut-off wheel. If band sawing is used, the increase in deformation should be taken into consideration, prolonging the plane grinding step, or possibly use of a rougher grinding paper before grit 220. Standards test bars are to be preferred, reducing the amount of sectioning, only it should be considered, whether the microstructures of the test bar truly represent the structure of the casting. Mounting: Normally a mounting is not needed except for establishing a suitable shape for automatic preparation. Often the preparation and examination shall take place as part of a production process and the time for preparation is very short. In that case the shape of the test bar coming from the production should be so that it fits into a specimen holder or specimen holder plate without mounting. If graphite close to the edge shall be examined, mounting in a suitable mounting material with a hardness corresponding to the cast iron is recommended. Grinding: In Method T-30 the high number of grinding papers is due to the development of the correct graphite at the finest papers. In case of problems with retaining of graphite, the steps FG 3 and FG 4 may be used without water. Often the number of steps can be reduced 共see also Method T-31兲. Always use fresh paper, as worn down paper may create pull-out of the graphite. Polishing: In case of routine examination without image analysis, polishing may stop after the P 1 step for Method C-30 and after the P 2 step in Method T-30. Electrolytic polishing cannot be recommended, but it may be used for routine examination of certain materials. Etching: See Material/Preparation Tables 28. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Graphite in cast iron Grain size, grain boundaries Heat treatment Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure


Method C-30

A 247 E 112, E 930, E 1181, E 1382

C-30, T-30 C-30, T-30, El-03 C-30, T-30 C-30

E 562, E 1077, E 1245, E 1382

E 10, E 18, E 92, E 103, E 110, E 140, E 384, E 448 A 247, E 3, E 407, E 562, E 883, E 1245, E 1351, E 1382, E 1558

C-30 C-30, T-30, El-03

Chapter 13


317




Resin Time Minutes

Bakelite 8–9

Cold Mounting

Resin Time Minutes/ Hours


Grinding Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-30: A P 3 step from T-30 can be added. Contemporary Method C-30 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 Polishing Disk/Cloth SiC paper RCD, soft Cloth, Cloth, short napless, nap, hard, wov, syn soft, syn Abrasive Type SiC Dia, spr or susp Dia, spr or Dia, spr or susp susp Grit or Grain P220 9 3 1 Size ␮m Lubricant Type Water Alco or wat Alco or wat Alco or wat Rotation 300/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp Comp Comp contra Force per 30 共7兲 30 共7兲 30 共7兲 25 共5.7兲 Specimen N 共lb兲 Time Until plane 5–7 4–6 2–3 Minutes

318


Traditional Method T-30 共For definitions of parameters Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 FG 4 Polishing Disk/ SiC SiC SiC SiC SiC Cloth paper paper paper paper paper

Abrasive Type

SiC

P1

P2

P3

Cloth, napless, hard, wov, silk or nonwov, syn Dia, spr or susp 6



Dia, spr or susp 1

Silica

SiC

SiC

SiC

SiC

P320

P500

P1200

P2400

Water

Water

Water

Water


Comp

Comp

Comp

Comp

Comp

Contra

30 共7兲

30 共7兲

30 共7兲

30 共7兲

25 共5.7兲

10 共2.2兲

Until plane

0.5–1

0.5–1

0.5–1

4–5

2–3

1

Grit or P220 Grain Size ␮m Lubricant Water Type Rotation Disk/ Holder rpm/ rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

and consumables see

300/150

Alco or wat 100/150 300/150 300/150 300/150 150/150

0.5–1


0.04/ 0.05

Alco or wat 150/150 150/150

Chapter 13


319

Material/Preparation Tables 31 Material: Nodular cast iron „ductile iron… Material Properties: Alpha iron 共ferrite兲: Body-centered cubic, gamma iron 共austenite兲: Face-centered cubic, 7.85 g / cm3, 1528° C 共2782° F兲, HV 70 共ferrite兲. Nodular cast iron: Carbon 3.0–4.0 %, silicon: 1.8–2.8 %, manganese: 0.1–1.0 %, phosphorus: 0.01–0.1 %, sulfur: 0.01–0.03 % 共weight %兲. Comments on Material: Nodular cast iron, also called ductile iron and spheroidal graphite 共SG兲 cast iron, is a cast iron with the graphite in the form of nodules or spheres. Unlike malleable cast iron 共see Material/Preparation Tables 30兲, the nodules are developed during the solidification due to small additions of magnesium and cerium. The advantage of nodular cast iron is the considerable increase in toughness, caused by the spheroidal graphite, which makes it comparable to steel for many purposes. The type, size, and distribution are standardized in the ASTM Standard Test Method for Evaluating the Microstructure of Graphite in Iron Castings 共A 247兲. Also a number of other specifications are described in ASTM standards; some examples are: A 377, A 439, A 536, and A 439 共see Sections 12.4.2兲. The metallographic/materialographic examination of the microstructure is as described in the Material/Preparation Tables 30. Also Methods C-30 and T-30 can be used for nodular cast iron. Sectioning: See Material/Preparation Tables 30. Mounting: See Material/Preparation Tables 30. Grinding: Fine grinding with the finer grades of SiC paper in Method T-31 is important to re-establish the graphite after pull-outs with the coarser grades. Polishing: At routine examinations, not using image analysis, the specimen surface after the 3 ␮m polishing step might be satisfactory. Electrolytic polishing cannot be recommended, but it may be used for routine examination of certain materials. Etching: See Material/Preparation Tables 28. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Graphite in cast iron Grain size, grain boundaries Heat treatment Image analysis, rating of inclusion content High planeness Microhardness, hardness


Method C-31

A 247 E 112, E 930, E 1181, E 1382

C-31, T-31 C-31, T-31 C-31, T-31 C-31

E 562, E 768, E 1245, E 1382

E 10, E 18, E 92, E 103, E 110, E 140, E 384, E 448

C-31, T-31

320


Microstructure

A 247, E 3, E 407, E 562, E 883, E 1245, E 1351, E 1382, E 1558

C-31, T-31, El-03

Hot Compression Resin Bakelite Cold Mounting Resin Acrylics Mounting Time 8–10 Time 8 – 10 min Minutes Minutes/Hours




Resin Time Minutes

Bakelite 8–9

Cold Mounting



Grinding C-31: SiC grinding paper P220 can be used for PG. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-31 and T-31 Both methods can be finished with a fine polishing step with silica 共see Method T-30 step P 3兲. Contemporary Method C-31 共For definitions Section 13.2.2.兲 Grinding/ PG FG 1 Polishing Disk/Cloth Dia, disk, RCD, soft fixed, res Abrasive Type

Diamond

Dia, spr or susp

of parameters and consumables see FG 2

P1

Cloth, napless, hard, nonwov, syn Dia, spr or susp

Cloth, napless, hard, wov, syn Dia, spr or susp

Chapter 13



P220

9

3

1

Water 300/ 150





Comp

Comp

Comp

25 共5.7兲

25 共5.7兲

20 共4.5兲

3–4

3–4

3–4

Force per Specimen N 共lb兲 Time Until plane Minutes

Traditional Method T-31 共For definitions of parameters and consumables Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 Polishing Cloth, Disk/Cloth SiC SiC SiC SiC Cloth, paper paper paper paper napless, napless, hard, hard, wov, silk wov, silk Abrasive Type

SiC

SiC

SiC

SiC

Dia, spr or susp


P220

P320

P500

P1000

6

Water

Water

Water

Water

300/ 150

300/ 150

300/ 150


321

see P3

Cloth, napless, med hard, wov, wool Dia, spr Dia, or susp spr or susp 3 1

Alco or Alco or Wat-oil wat wat 150/ 150 150/ 150 150/ 150 150/ 150

Comp or Comp or Comp or Comp contra contra contra 30 共7兲 30 共7兲 30 共7兲 30 共7兲

Comp

Comp

Comp

30 共7兲

25 共5.7兲

20 共4.5兲

Until plane

5

3–4

3–4

0.5–1

0.5–1


0.5–1

322


Material/Preparation Tables 32 Material: White cast iron Material Properties: Alpha iron 共ferrite兲: Body-centered cubic, gamma iron 共austenite兲: Face-centered cubic, 7.85 g / cm3, 1528° C 共2782° F兲, HV 70 共ferrite兲. White cast iron: Carbon 1.8–3.6 %, silicon: 0.5–1.9 %, manganese: 0.25–0.8 %, phosphorus: 0.006–0.2 %, sulfur: 0.06–0.2 % 共weight %兲. Comments on Material: If the liquid iron-carbon is solidified relatively fast, the carbide is not formed as graphite like in gray cast iron, but as cementite in a network. This makes the white cast iron very hard and wear resistant, and the cementite gives the fractured surface the white appearance. If white cast iron is heated over a period of time, the cementite will break down to form graphite 共see Material/Preparation Tables 30兲. White cast iron is often alloyed with nickel, chromium, or molybdenum or combinations thereof, to improve the wear resistance. The different types of white cast irons are standardized in the ASTM Specification for Abrasion-Resistant Cast Irons 共A 532兲共see Sections 12.4.2兲. Materialographic preparation of white cast iron is relatively easy because of the very hard cementite. Sectioning: Wet abrasive cut-off should be done with a soft Al2O3, bakelite bond cut-off wheel. White cast iron may be difficult to cut because of internal stresses and the feed speed should be low. For very hard materials a CBN wheel resin bond may be needed 共see Section 2.4.2兲. Mounting: Normally mounting is not needed except in the case of examination of surface layers 共see Material/Preparation Tables 08–15兲, or in the case of obtaining a shape of the specimen suited for automatic preparation. If possible, the specimen should be sectioned so that it can be placed in a specimen holder without mounting. Grinding: Because of the high hardness, the SiC grinding papers will be worn very fast, and especially at the PG step several sheets may be needed. Polishing: The polishing step with silica may be omitted for routine examinations 共see below兲. Etching: See below and Material/Preparation Tables 28, 33, and, 34.

Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness


Method C-32

E 112, E 930, E 1181, E 1382 E 562, E 768, E 1245, E 1382

C-32, T-32 C-32

Chapter 13

Microhardness, hardness Microstructure

E E E E


10, E 18, E 92, E 103, E 110, 140, E 384, E 448 3, E 407, E 562, E 883, E 1245, 1351, E 1382, E 1558

323

C-32, T-32 C-32, T-32


Al2O3, bakelite bond. For very hard materials 共⬎HV 500–700兲 a CBN wheel resin bond may be needed 共see Section 2.4.2.兲.

Mounting Hot Compression Resin Epoxy with Filler Cold Resin Acrylics Mounting Mounting with Filler 6 – 15 min Time 8–10 Time Minutes Minutes/ Hours Grinding C-32 and T-32: The PG step may start with SiC grinding paper grit P120 or P180, if a high material removal is needed. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-32: P 3. This step can often be omitted. T-32: A step like P 2 in Method C-32 can be added. Contemporary Method C-32 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 P3 Polishing Cloth, Cloth, med Disk/Cloth Dia, disk RCD, hard Cloth, nap, soft, napless, fixed, res napless, syn soft, hard, wov, porous, silk syn Abrasive Type Diamond Dia, spr or Dia, spr or Dia, spr or Silica susp susp susp Grit or Grain P220 9 3 1 0.04/ 0.05 Size ␮m

324


Lubricant Type Water Rotation 300/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or contra 30 共7兲 Force per Specimen N 共lb兲 Time Until Minutes plane




150/ 150

Comp

Comp

Comp

Contra

30 共7兲

30 共7兲

25 共5.7兲

15 共3.4兲

4

4

3

1

Traditional Method T-32 共For definitions of parameters and Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 Polishing Disk/Cloth SiC SiC SiC Cloth, paper paper paper v. hard, wov, syn

consumables see P2

P3

Cloth, napless, hard nonwov, syn Dia, spr or Dia, spr or susp susp


Abrasive Type

SiC

SiC

SiC


P220

P320

P500

9

6

Dia, spr or susp 3

Water

Water

Water


300/ 150

300/ 150

300/ 150




Comp

Comp

35 共8兲

30 共7兲

4

3

Comp or Comp or Comp or Comp contra contra contra 40 共9兲 40 共9兲 40 共9兲 40 共9兲

Force per Specimen N 共lb兲 Time Until Minutes plane

0.5

0.5

4

Etchants Material White cast iron

Etchants 共see Table 12.2兲 210 See also Material/Preparation Tables 28, 33, and 34


Chapter 13


325

Material/Preparation Tables 33 Material: High-alloy steels. Heat-treated, low-alloy steels. Heattreated, High-alloy steels. Other ferrous metals Material Properties: Alpha iron 共ferrite兲: Body-centered cubic, gamma iron 共austenite兲 face-centered cubic, 7.85 g / cm3, 1528° C 共2782° F兲, HV 70 共ferrite兲. High-alloy steels: ⬎8 % total alloying elements 共weight %兲. Comments on Material: High-alloy steels have been developed to obtain special characteristics like resistance to corrosion, heat, and wear. The corrosion resistant steels, stainless steels, are described in Material/Preparation Tables 34. The heat resistant steels can be low- or high-alloyed depending on the temperature range. The high-alloyed steels may contain chromium, molybdenum, nickel, cobalt, and titanium to obtain highest heat resistance. For iron-based super alloys, see Material/Preparation Tables 35. The wear resistant high-alloy steels, tools steels, may contain a high percentage of chromium and manganese, molybdenum, and vanadium 共see Material/Preparation Tables 38兲. High-alloy steels can be difficult to prepare because of the often relatively soft matrix. It can be difficult to conserve all inclusions and carbides, especially if the specimen should be examined by image analysis. Also hardened alloy steels can be difficult to prepare; they often have different hardness within the microstructure and contain a high amount of very hard and brittle carbides. For problems with smearing, loss of inclusions, etc., see Section 13.6. Often electrolytic polishing can be used. Sectioning: Wet abrasive cutting with an alumina, bakelite bond cut-off wheel with an effective cooling should be without problems. For very hard materials a CBN wheel resin bond may be needed 共see Section 2.4.2兲. Cutting with a band saw may give deformations and possible work hardening in steels with an austenitic structure that should be removed at a prolonged plane grinding, or only used for initial cutting followed by wet abrasive cutting. Mounting: Normally mounting is not needed except in case of examination of surface layers 共see Material/Preparation Tables 08–15兲 or in case of obtaining a shape of the specimen suited for automatic preparation. If possible the specimen should be sectioned so that it can be placed in a specimen holder without mounting. Grinding: In case of water-sensitive inclusions or carbides Method C-33 should be preferred without the final polishing step. Polishing: Electrolytic polishing can be recommended for steels not having a too heterogenous microstructure. Etching: For observation of certain phases, like carbides, in the microstructure, a minimal relief can be developed during the last polishing step so that these can be seen in the microscope without chemical etching 共see Section 9.6兲. A number of etchants are stated below 共see also Material/Preparation Tables 34兲. Purpose Case of coating thickness/ hardness, surface layers Perfect edge retention

ASTM Standard 共See Section 12.4兲 E 1077

Method C-33

326



E 112, E 930, E 1181, E 2283


E 1077

Image analysis, rating of inclusion content

E 45, E 562, E 768, E 1077, E 1122, E 1245, E 1268, E 1382, E 2283

High planeness Inclusion in steel

E 45, E 768, E 1122, E 1245

Microhardness, hardness

E 10, E 18, E 92, E 103, E 110, E 140, E 384, E 448 A 892, E 3, E 45, E 407, E 562, E 768, E 883, E 1077, E 1181, E 1245, E 1268, E 1351, E 1382, E 1558

Microstructure


C-33, T–33, El-04 C-33 C-33, T-33 C-33




Al2O3, bakelite bond. For very hard materials 共⬎HV 500–700兲 a CBN wheel resin bond may be needed 共see Section 2.4.2.兲.


Resin Time Minutes

Bakelite 8–10

Cold Mounting


Grinding C-33: PG: For low-alloyed steels SiC paper grit P220 should be used. C-33: FG 1: For low-alloyed steels an RCD soft can be used.

Acrylics 6–10

Chapter 13


327

Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Contemporary Method C-33 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 Polishing Cloth, med. Disk/Cloth Dia, disk, RCD, hard Cloth, nap, soft, syn fixed, res napless, hard, wov, silk Abrasive Type Diamond Dia, spr or Dia, spr or Dia, spr or susp susp susp Grit/Grain Size ␮m P220 9 6 1 Lubricant Type Water Alco or wat Alco or Alco or wat susp Rotation Disk/Holder 300/ 150 150/ 150 150/ 150 150/ 150 rpm/rpm Comp/Contra Comp or Comp Comp Comp contra Force per 30 共7兲 30 共7兲 35 共8兲 25 共5.7兲 Specimen N 共lb兲 Time Until plane 4–5 4–5 2–3 1 Minutes Traditional Method T-33 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 P3 Polishing Cloth, Cloth, Disk/Cloth SiC SiC SiC SiC Cloth, napnappaper paper paper paper napless, less, less, soft, hard, hard, wov, silk wov, syn porous, syn Abrasive Type SiC SiC SiC SiC Dia, spr Dia, spr Alumina or susp or susp Grit or P220 P320 P500 P1200 6 3 0.02/ 0.05 Grain Size ␮m Lubricant Type Water Water Water Water Alco or Alco or wat wat Rotation Disk/ 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Holder

328


rpm/ rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes




Comp

Comp

Comp

Contra

30 共7兲

30 共7兲

25 共5.7兲

10 共2.2兲

Until plane

0.5

0.5

0.5

3–4

3

1

Etchants Material Fe+ 4 − 12 Cr Fe+ 12− 30 Cr+ ⬍ 6Ni 共400 Series兲

High temperature

Nonstainless maraging steels Nonstainless maraging steels

Etchants 共see Table 12.2兲 80, 87, 88, 89, 90, 91, 79, 210 80, 87, 88, 89, 34, 40, 92, 93, 94, 95, 91, 226 96, 97, 98 31c 86 219 220 89, 25, 105, 106, 97, 212, 221 107, 108, 213, 86 109, 89, 99, 100, 221 83b, 86

Uses General structure General structure Sigma phase Carbides Chemical polish etch Grain boundary Darkens delta ferrite General structure ␤ precipipate chemical polish etch General structure Grain boundaries, chemical polish etch

Material/Preparation Tables 34 Material: Stainless steels. Pure iron Material Properties: Alpha iron 共ferrite兲: Body-centered cubic, gamma iron 共austenite兲: Face-centered cubic, 7.85 g / cm3, 1528° C 共2782° F兲, HV 70 共ferrite兲. Austenitic stainless steels: 15–24 % chromium, 3–22 % nickel. Ferritic stainless steels: 10.5–27 % chromium. Martensitic stainless steels: 11.5–18 % chromium. Duplex stainless steels: 23–28 % chromium, 2.5–5.0 % nickel, 1.0–2.0 % molybdenum. Precipitation-hardening stainless steels: 12.25–18 % chromium, 7.5–8.5 % nickel 共weight %兲.

Chapter 13


329

Comments on Material: The stainless steels are corrosion resistant steels classified according to the type of microstructure, austenitic, ferritic, austenitic-ferritic, martensitic, duplex, and precipitation-hardening. The austenitic stainless steels have a microstructure of austenite at room temperature because of a high nickel content, and they are nonmagnetic. The steels are chromium-nickel steels, and a typical alloy is the steel 18 % chromium, 8 % nickel. The ferritic stainless steels are basically chromium steels without nickel, therefore, the ferritic microstructure. Martensitic stainless steels are chromium steels with a higher carbon content than other stainless steels making hardening possible. Duplex stainless steels have a mixed microstructure of ferrite and austenite. Precipitation-hardening stainless steels are alloyed with elements as copper and aluminum to establish the precipitation hardening. They can have either a ferritic or martensitic microstructure. Pure iron 共Fe兲 has a ferritic microstructure. Most stainless steels having an austenitic or ferritic microstructure give difficulties in metallographic/materialographic preparation because these structures are relatively soft and ductile. Austenite may work harden during cutting and grinding. It can be difficult to remove all deformation and scratches and obtain a true structure preserving all inclusions, often brittle carbides and oxides. The martensitic microstructure is easier to prepare, but in case of brittle carbides, these can easily be damaged. For advice on smearing, inclusions, etc., see Section 13.6. The ferrite of pure iron may give problems with deformations 共see Material/ Preparation Tables 28兲. Sectioning: Wet cut-off cutting with a correct Al2O3, bakelite bond cut-off wheel will be without problems. Cutting with a band saw and shearing may give deformations and cold work that should be removed at a prolonged plane grinding. For deformation sensitive austenitic steels these methods should be avoided. Mounting: Normally mounting is not needed except in the case of examination of surface layers 共see Material/Preparation Tables 08 to 15兲 or in case of obtaining a shape of the specimen suited for automatic preparation. If possible, the specimen should be sectioned so that it can be placed in a specimen holder without mounting. Grinding: Due to deep deformations and possible cold work in the austenite, it is important that the fine grinding steps are carefully performed to secure that all deformations and cold work from the sectioning and plane grinding are removed. Using new SiC grinding paper there is a risk that retained austenite is transformed into martensite due to mechanical deformation. Also very rough papers and high grinding forces should be avoided, as deep deformation, introduced in the first grinding steps may not be removed by the fine grinding. Polishing: It can be a problem to obtain a perfect ferrite phase as mentioned above. In the case of only small deformations, prolong the 3 ␮m step for 1 – 2 min. Often electrolytic polishing can give very good results 共see Section 13.3兲.

330


Etching: For stainless steels, observation of inclusions can normally be done without etching. Chemical etching is relatively difficult, often electrolytic etching gives good results. A much used electrolytic etching is with 10 g oxalic acid, 100 mL water, using 6 – 8 volts for 20– 30 s, in a stainless steel beaker, using the beaker as cathode 共see Section 9.5兲. For etchants, see below and Material/ Preparation Tables 33. Etchants for pure iron, see Material/Preparation Tables 28. Purpose Case or coating thickness/hardness surface layers Perfect edge retention Grain size, grain boundaries

ASTM Standard 共See Section 12.4兲 E 1077

Method C-34

E 112, E 930, E 1181, E 1382

Heat influenced zone Heat treatment Image analysis, rating of inclusion content High planeness Inclusions in steel Microhardness, hardness

E 1077

C-34, T-34 El-05 C-34 C-34, T-34 C-34

E 45, E 562, E 768, E 1077 E 1245, E 1268, E 1382, E 2283 E 45, E 768, E 1245 E 10, E 18, E 92, E 103, E 110, E 140, E 384, E 448 A 892, E 3, E 45, E 407, E 562, E 768, E 883, E 1077, E 1181, E 1245, E 1268, E 1351, E 1382, E 1558

Microstructure


C-34, T-34 C-34, T-34 C-34, T-34, El-05

C-34, T-34, El-05 C-34, T-34, El-05




Mounting Hot Compression Resin Bakelite Cold Mounting Resin Acrylics Mounting Time 8–10 Time 6 – 10 min Minutes Minutes/Hours

Chapter 13


331

Grinding C-34: PG: Use SiC paper grit P320 for pure iron. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing T-34: P 1: This step can be changed to an FG 4 step with SiC paper grit P4000, same data as FG 3. C-34 and T-34: The final step can be done with alumina 0.02/ 0.05 ␮m. Contemporary Method C-34 共For definitions of parameters and Section 13.2.2.兲 Grinding/ PG FG 1 P1 Polishing Disk/Cloth SiC paper RCD, soft Cloth, napless, hard, wov, syn Abrasive Type SiC Dia, spr or susp Dia, spr or susp Grit/Grain P220 9 3 Size ␮m Lubricant Type Water Alco or wat Alco or wat Rotation 300/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp Comp contra Force per 25 共5.5兲 30 共7兲 25 共5.5兲 Specimen N 共lb兲 Time Until plane 5–7 5–6 Minutes Traditional Method Section 13.2.2.兲 Grinding/ PG Polishing Disk/ SiC Cloth paper

consumables see P2 Cloth, napless, soft, porous, syn Silica 0.04/ 0.05

150/ 150

Contra 15 共3.3兲 1–2

T-34 共For definitions of parameters and consumable see FG 1

FG 2

FG 3

P1

P2

P3

SiC paper

SiC paper

SiC paper


Cloth, napless, med hard, wov, wool

Cloth, napless, soft, porous

332


Abrasive Type Grit or Grain Size ␮m Lubricant Type Rotation Disk/ Holder rpm/ rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

SiC

SiC

SiC

SiC

Dia, spr or susp 6

Dia, spr or susp 3

P220

P320

P500

P1200

Water

Water

Water

Water

Alco or wat 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150


150/ 150




Comp

Comp

Comp

Contra

20 共4.4兲

30 共7兲

25 共5.5兲

15 共3.4兲

Until plane

0.5–1

0.5–1

0.5–1

4

3–5

1–2

Etchants Material Fe+ 12− 20 Cr+ 4 − 10 Ni+ ⬍ 7 % other elements 共controlled transformation, precipitation hardening, stainless maraging alloys兲

Fe+ 16- 25 Cr+ 3 − 6 Ni+ 5 − 10

0.04/ 0.05

Etchants 共see Table 3.2兲 80, 31c, 89, 99, 100, 91


31c 86

Carbides Chemical polishetch Darkness delta ferrite General structure

220 Fe+ 15− 30 Cr+ 6 − 40 Ni+ ⬍ 5% other elements 共300 series兲

Silica

13b, 89, 87, 88, 83a, 80, 94, 95, 91, 101, 212, 221, 226 13 a, 102, 31 c, 48 c, 213 48, 96, 97, 98

Carbides and sensitization Stains sigma phase

Chapter 13

Mn 共200 series兲


103, 104, 98

86 219

220 Pure iron

74a 75 210

333

Delineates sigma phase and welds of dissimilar metals Chemical polish-etch Grain boundary etch 共no twins兲 Darkens delta ferrite Grain boundaries Substructure Colors ferrite grains

Material/Preparation Tables 35 Material: Super alloys, iron based Material Properties: Alpha iron 共ferrite兲: Body-centered cubic, gamma iron 共austenite兲: Face-centered cubic, 7.85 g / cm3, 1528° C 共2782° F兲, HV 70 共ferrite兲. Super alloys 共Fe based兲: 26 to 55 % nickel, 13 to 23 % chromium, 1 to 2.5 % titanium, 1 to 9 % molybdenum 共weight %兲. Comments on Material: The Fe based super alloys are closely related to the high alloy steels described in Material/Preparation Tables 33. Sectioning: See Material/Preparation Tables 33. Mounting: See Material/Preparation Tables 33. Grinding: See Material/Preparation Tables 33. Polishing: See Material/Preparation Tables 33. Etching: See below and Material/Preparation Tables 33 and 34. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size. grain boundaries Heat influences zone Heat treatment Image analysis, rating of inclusion content High planeness


Method C-35

E 112, E 930, E 1382

C-35, T-35, E1-06 C-35 C-35, T-35 C-35

E 45, E 562, E 768, E 1245, E 1382, E 2283

334


Inclusions in steel Microhardness, hardness Microstructure

E 45, E 768, E 1245 E 10, E 18, E 92, E 103, E 110, E 140, E 384 E 448 A 892, E 3, E 45, E 407, E 562, E 768, E 883 E 1245, E 1351, E 1382, E 1558

C-35, T-35 C-35, T-35

C-35, T-35, E1-06


C-35, T-35, E1-06

Preparation Process 35 Sectioning Cut-off Wheel


Mounting Hot Compression Resin Bakelite Cold Mounting Resin Acrylics Mounting Time 8–10 Time 6 – 10 min Minutes Minutes/Hours Grinding C-35: PG: SiC paper grit P220 can be used. C-35: FG 1: Very often this step can be omitted. In that case the step FG 2 共RCD, soft兲 is prolonged to seven minutes. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100— 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-35: P 2: Often this step can be omitted. C-35: P 3: Alumina 共0.02/ 0.05兲 can be used. Contemporary Method C-35 Section 13.2.2.兲 Grinding/ PG Polishing Disk/Cloth Dia, disk, fixed, res

Abrasive Type

Diamond


FG 2

P1

P2

P3

RCD, hard

RCD, soft

Cloth, short nap, soft, syn

Dia, spr or susp

Dia, spr or susp

Cloth, napless, hard, wov, silk Dia, spr or susp


Dia, spr or susp

Chapter 13

Grit/Grain size ␮m Lubricant Type Rotation Disk/ Holder rpm/rpm Comp/Contra Force per Specimen N 共lb兲 Time Minutes

335

220

9

9

6

1

0.04/ 0.05

Water





150/ 150


Comp

Comp

Comp

Comp

Contra

30 共7兲

30 共7兲

30 共7兲

25 共5.7兲

15 共3.4兲

Until plane

3

3

4

3

1–2

300/ 150


Abrasive Type


SiC

共For definitions of parameters and consumable see FG 1

FG 2

FG 3

SiC paper

SiC paper

SiC paper

SiC

SiC

SiC

P1

P2

Cloth, Cloth, napless, napless, hard, hard, wov, silk wov, syn Dia, spr or susp 6

Dia, spr or susp 3

P3 Cloth, med. nap, soft, syn Dia, spr or susp 1

Grit or Grain P220 P320 P500 P1000 Size ␮m Lubricant Water Water Water Water Alco or Alco or Alco or Type wat wat wat Rotation 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp or Comp or Comp Comp Comp Comp contra contra contra 30 共7兲 30 共7兲 30 共7兲 30 共7兲 30 共7兲 30 共7兲 20 共4.5兲 Force per Specimen N 共lb兲 Time Until 0.5–1 0.5–1 0.5–1 4–5 4 1–2 Minutes plane Etchants Material Super alloys 共Fe based兲

Etchants 共see Table 12.2兲 86, 87, 94, 221, 226

Uses General etch

336


111 111

General structure ␥⬘ depletion

Material/Preparation Tables 36 Material: High strength low-alloy steels Material Properties: Alpha iron 共ferrite兲: Body-centered cubic, gamma iron 共austenite兲: Face-centered cubic, 7.85 g / cm3, 1528° C 共2782° F兲, HV 70 共ferrite兲. High strength low-alloy steels: Low and medium carbon steels with small amounts of alloying elements, vanadium, niobium, titanium. Comments on Material: High strength low-alloy 共HSLA兲 steels are a group of lowand medium-carbon steels with small amounts of alloying elements to improve the yield strength. The steels are classified by SAE according to yield strength and by ASTM according to composition, mechanical property requirements, and application. Examples of the ASTM specifications are: A 242, A 572, and A 656 共see Section 12.4.2兲. The microstructure of HSLA steels is a mixture of ferrite, pearlite, bainite, and martensite, and the problems regarding preparation are the same as with mediumand low-carbon steels 共see Material/Preparation Methods 28 and 29兲. In some cases, water sensitive inclusions should be examined; for this reason the polishing steps in Methods C-36 and T-36 are stated with water-free lubricants. Sectioning: At wet abrasive cutting with an Al2O3 cut-off wheel, overheating should be avoided because martensite can be developed. Cutting pressure should be moderate and cooling should be efficient on both sides of the cut-off wheel. If shearing or band sawing is used, the plane grinding should be prolonged to remove possible deformation or a rougher grinding paper should be used before grit P220. Mounting: For routine examination bakelite as powder or tablets is sufficient. In the case of examination of coatings, other mounting materials should be used 共see Material/Preparation Tables 08–15兲. For mounting for electrolytic polishing, see Section 3.11.6. Grinding: Grinding normally will give no problems with these materials. Care should be taken that the deformations from plane grinding are effectively removed before the polishing. If not, the deformed ferrite can be seen after etching and the process must be repeated from FG 1. Polishing: The problem can be to obtain a perfect ferrite phase as mentioned above. In the case of only small deformations, prolong the 3 ␮m step for 1 – 2 min. Electrolytic polishing can be recommended for certain alloys. Etching: A high number of etchants are available for steels. In most cases a relative small selection will cover the need in a given laboratory 共see Material/ Preparation Tables 28 and 33兲. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention


Method C-36

Chapter 13



E 112, E 930, E 1181, E 1382


E 1077

Image analysis, rating of inclusion content High planeness Inclusion in steel

E E E E

Microhardness, hardness

E 10, E 18, E 92, E 103, E 110, E 110, E 140, E 384, E 448 A 892, E 3, E 45, E 407, E 562, E 768, E 883, E 1077, E 1122, E 1181, E 1245, E 1268, E 1351, E 1382, E 1558

Microstructure

45, E 562, E 768, 1077, E 1245, 1268, E 1382, E 2283 45, E 768, E 1245


337

E-36, T-36 El-04 C-36 C-36, T-36, El-04 C-36



Preparation Process 36 Sectioning Cut-Off-Wheel


Mounting Hot Compression Resin Bakelite Cold Mounting Resin Acrylics Mounting Time 8–10 Time 6 – 10 min Minutes Minutes/Hours Grinding C-36: PG: SiC paper grit P220 can be used. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued.

338


Polishing C-36 and T-36: Steps P 1 and P 2 are stated with water-free diamond suspensions. These can be changed to normal water-based suspensions. C-36: P 2: This step can be followed by a final step with silica like step P 3 in Method C-35. Contemporary Method C-36 Section 13.2.2.兲 Grinding/ PG Polishing Disk/Cloth Dia, disk, fixed, res Abrasive Type Diamond



P220

9

Water

Alco or wat


300/ 150

150/ 150

Alco or oil, water-free 150/ 150


Comp

Comp

30 共6.6兲

25 共5.7兲

Until plane

5–6

4–5

Force per pecimen N 共lb兲 Time Minutes

Traditional Method Section 13.2.2.兲 Grinding/ PG Polishing Disk/ SiC Cloth paper

FG 1

P1

RCD, soft

Cloth, napless, hard, wov, syn Dia, spr or susp, water-free 3

Dia, spr or susp

P2 Cloth, med. nap, soft, syn Dia, spr or susp, water-free 1 Alco or oil, water-free 150/ 150

Comp 15 共3.4兲 2–3

T-36 共For definitions parameters and consumables see FG 1

FG 2

FG 3

P1

P2

P3

SiC paper

SiC paper

SiC paper


Cloth, naplesss, hard, wov, syn Dia, spr or susp 3


Abrasive Type

SiC

SiC

SiC

SiC

Grit or Grain Size ␮m

P220

P320

P500

P1200

0.02/ 0.05

Chapter 13

Lubricant Type

Rotation Disk/ Holder rpm/rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes


339

Alco or oil, waterfree 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150

Alco or oil, waterfree 150/ 150

150/ 150




Comp

Comp

Comp

Contra

25 共5.7兲

25 共5.7兲

25 共5.7兲

10 共2.2兲

Until plane

0.5–1

0.5–1

0.5–1

3

3

1–2

Water

Water

Water

Water

Etchants See Material/Preparation Tables 28 and 33.

Material/Preparation Tables 37 Material: Carbonitrided steels. Carburized steels. Nitrided steels. Other surface treated steels Material Properties: Alpha iron 共ferrite兲: Body-centered cubic, gamma iron 共austenite兲: Face-centered cubic, 7.85 g / cm3, 1528° C 共2782° F兲, HV 70 共ferrite兲. Comments on Material: Case hardening is a term that covers the process of changing the surface layer of steel by absorption of carbon or nitrogen, or both. The process can be done in different ways as carbonitriding, carburizing, cyaniding, nitriding, and nitrocarburizing. With or without further heat treatment a hard surface layer is created. Mostly low carbon steels are used for carburization, often a case with a carbon content of 0.7–1 %, and a hardness of approximately 60 HRC 共HV 700兲. The case depth varies from 0.3 to 3 mm depending on processing time and temperature. For nitriding low carbon steels and steels alloyed with Al, Cr, and V are used. The hardness of the diffusion layer may be up to 70 HRC 共HV 1000兲 and the thickness 0.01– 0.5 mm depending on process time and temperature. The metallographic/materialographic examination normally covers layer thickness, diffusion zone, and defects in the layer. For this reason it is very important to obtain the highest degree of edge retention 共see also the Material/Preparation Tables 08–15兲.

340


Sectioning: Cutting, often of a test piece treated along with the work piece, should be wet abrasive cutting with an Al2O3, bakelite bond cut-off wheel. It is important that excessive heat and deformation is avoided. When cutting nitrided layers that are very hard, a relatively soft wheel is used and cooling should be very effective. If shearing or band sawing is used, the plane-grinding step should be prolonged to remove possible deep deformation. It is important that the cutting takes place perpendicular to the surface to be prepared. If the plane of the cross section is not perpendicular to the plane of the surface layer, the measured thickness will be greater than the true thickness. For example, an inclination of 10° will contribute a 1.5 % error. Mounting: It is very important that edge rounding and gaps between sample and mounting material are avoided. Therefore, a mounting material without shrinkage should be used, preferably epoxy. For very hard coatings hot mounting with epoxy with a filler should be preferred. Also, a phenolic resin with carbon fibers can be of advantage. For hot mounting a special application can be made to secure the edge: Tightly wrap up the specimen in Al foil 共household type兲. This gives a good separation between mounting material and surface layer. Also, a copper foil can be used on nitrided and carburized layers giving an excellent edge definition and contrast. Choose a mounting material with hardness as close as possible to the hardness of the coating. As a less ideal alternative, cold mounting with epoxy or an acrylic material with filler can be used. Grinding: The preparation process should secure the highest possible edge retention. This means that all grinding, either on SiC grinding paper, diamond pads, or rigid composite disks 共RCDs兲, should be as short as possible. In Method T-37 the grinding is suggested with diamond pads, considered for very hard surface layers. In case of softer layers these pads can be changed to SiC grinding paper, as stated in Method T-32 共see below兲. It has been found that the use of fixed diamonds for plane grinding of certain nitrided and carburized layers may introduce fine cracks in the hard layer, therefore, SiC paper should be used 共see below兲. Polishing: Also the polishing steps should be kept as short as possible. Etching: See Material/Preparation Tables 28, 33, and 34. Purpose Case or coating thickness/hardness, surface layers Prefect edge retention Grain size, grain boundaries Heat influenced zone Heat treatment Image analysis, rating of inclusion content High planeness Inclusions in steel Microhardness, hardness


Method C-37, T-37

E 112, E 1382

C-37, C-37, C-37, C-37,

E E E E E E

45, E 562, E 768, E 1077 1245, E 1268, 1382, E 2283 45, E 768, E 1245 10, E 18, E 92, E 103, 140, E 684, E 448

T-37 T-37 T-37 T-37

C-37, T-37 C-37, T-37

Chapter 13

Microstructure


341

A 892, E 3, E 45, E 407, E 562, E 768, E 883, E 1077, E 1245, E 1268, E 1351, E 1382, E 1558


C-37, T-37




Resin Time Minutes

Expoxy with Filler 9

Cold Mounting


Epoxy with filler 6–8 h

Grinding C-37 and T-37: PG: For certain nitrocarburized/nitrided layers, disks/pads with fixed diamonds should be avoided 共see above兲. SiC paper grit P220 should be used. Also FG 1 in Method T-37 shall be changed to SiC paper grit P320/P500 共see Method T-32兲. C-37: Very often FG 1 can be changed to RCD, soft and FG 2 can be omitted. T-37: In case of relatively soft surface layers, the diamond pads in PG and FG 1 can be changed to SiC grinding paper 共see Method T-32兲. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing T-37: To improve edge retention, the step P 2 can be changed to P 2 from Method C-37. Contemporary Method C-37 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding PG FG 1 FG 2 P1 P2 Polishing Cloth, med Disk/Cloth Dia, disk RCD, hard RCD, soft Cloth, nap, soft, syn fixed, res napless, hard, wov, syn

342


Abrasive Type Grit or Grain Size ␮m Lubricant Type Rotation Disk/Holder rpm/rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

Diamond 220

Dia, spr or susp 9

Dia, spr or susp 3

Water

Alco or wat

Alco or wat Alco or wat

Alco or wat

300/ 150

150/ 150

150/ 150

150/ 150

150/ 150


Comp

Comp

Comp

Comp

25 共5.5兲

25 共5.5兲

40 共9兲

25 共5.5兲

Until plane

5

4–5

4–5

1–2

Traditional Method T-37 共For definitions of Section 13.2.2.兲 Grinding/ PG FG 1 Polishing Disk/Cloth Dia, pad Dia, pad met met

Dia, spr or susp 3

Dia, spr or susp 1

parameters and consumables see FG 2

P1

P2



Abrasive Type

Diamond

Diamond


125

40

Cloth napless, v. hard nonwov or wov, syn Dia, spr or susp 9

Water 300/ 150

Water 300/ 150

Alco or wat Alco or wat Alco or wat 150/ 150 150/ 150 150/ 150



Comp

Comp

Contra

40 共9兲

40 共9兲

15 共3.4兲

4–5

4–6

1

Force per Specimen N 共lb兲 Time Until plane 2 Minutes

Etchants See Material/Preparation Tables 28, 33, and 34.

0.04/ 0.05

Chapter 13


343

Material/Preparation Tables 38 Material: High-speed steels. Low-alloyed tool steels. Other tool steels Material Properties: Alpha iron 共ferrite兲: Body-centered cubic, gamma iron 共austenite兲: Face-centered cubic, 7.85 g / cm3, 1528° C 共2782° F兲, HV 70 共ferrite兲. Comments on Material: The tool steels cover a wide range from the highly alloyed high-speed steels to low-alloy steels with small amounts of a few alloying elements. Most tool steels contain molybdenum or tungsten, or both. Often other elements like vanadium, cobalt, nickel, and chrome are added. The tool steels are classified by the American Iron and Steel Institute 共AISI兲 using a letter to represent each class of steel. Tool steels are metallographically/materialographically examined for inclusion content, decarburization, degree of spheroidization, grain size, hardness, etc., and they are often difficult to prepare because of the hardness and the brittle carbides. For advice on artifacts developed during the preparation, see Section 13.6. Sectioning: In the case of nontempered tool steels, it is important that the sectioning takes place without excessive heat because this will introduce localized tempering effects. Cutting should take place as wet, abrasive cutting with an efficient cooling, preferably using a thin cut-off wheel, or a relatively soft wheel, or both. The feed speed should be low with a low force in the cut. For high-hardness, high-alloy steels, precision cutting with a thin CBN cut-off wheel may be of advantage, producing a cut surface with very little damage. Steels with a hardness below 35 HRC may be cut using a band saw, but in this case, because of the considerable deformation, the plane grinding should start with SiC grinding paper rougher than grit 220. In case of as-quenched high-alloy steels, the specimen may be sectioned by fracture. Mounting: For routine examination bakelite as powder or tablets is sufficient if heat degredation is not anticipated. In the case of examination of coatings, other mounting materials should be used 共see Material/Preparation Table 08–15兲. For mounting for electrolytic polishing, see Section 3.11.6. Grinding: The often very hard material will wear out the SiC grinding papers in a very short time, and often several sheets of each grain size should be used. In case of pull-outs of carbides at high-alloy steels, Method C-38 should be preferred. Polishing: For routine examination, the number of steps may be reduced 共see below兲. Etching: A number of etchants are stated below. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Heat influenced zone Heat treatment

ASTM Standard 共See Section 12.4兲 B 748, C 664

Method C-38

E 112, E 1382

C-38, T-38 C-38, T-38 C-38, T-38

344


Image analysis, rating of inclusion content High planeness Inclusions in steel Microhardness, hardness Microstructure

E 45, E 562, E 768, E 1077 E 1245, E 1268, E 1382, E 2283

C-38, T-38

E 45, E 768, E 1245 E 10, E 18, E 92, E 103, E 110, E 140, E 384, E 448 A 892, E 3, E 45, E 407, E 562, E 768, E 883, E 1077, E 1245, E 1268, E 1351, E 1382, E 1558

C-38 C-38, T-38


C-38, T-38



Mounting Hot Compression Resin Bakelite Cold Mounting Resin Acrylics Mounting Time 8–10 Time 6 – 10 min Minutes Minutes/Hours Grinding C-38: For certain tool steels, the step P 1 can be changed to an RCD, soft. T-38: For routine examination the step FG 3 may be omitted. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-38: For certain tool steels, the step P 2 can be changed to P 3 from Method T-38 or P 3 共Method T-38兲 can be added. T-38: In case of routine examinations, the step P 2 can be changed to step P 1 from Method C-38, as the last step. Contemporary Method C-38 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG P1 P2 Polishing

Chapter 13

Disk/Cloth

Dia, disk, fixed, res

RCD, hard

Abrasive Type

Diamond

Grit or Grain Size ␮m Lubricant Type Rotation Disk/ Holder rpm/rpm Comp/Contra


345

Cloth, med. nap, soft, syn

P220

Dia, spr or susp 9


Dia, spr or susp 1

Water 300/ 150




Comp

Comp

Comp

35 共8兲

35 共8兲

40 共9兲

6–8

6–8

1–2

Comp or contra Force per Specimen 35 共8兲 N 共lb兲 Time Until plane Minutes

Traditional Method T-38 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 P3 Polishing Cloth, Cloth, Disk/Cloth SiC SiC SiC SiC Cloth, paper paper paper paper napless, napless, napless soft hard, hard, porous, wov, silk wov, syn syn Abrasive Type SiC SiC SiC SiC Dia, spr Dia, spr Alumina or susp or susp Grit or Grain P220 P320 P550 P1200 6 3 0.02/ 0.05 Size ␮m Lubricant Water Water Water Water Alco or Alco or Type wat wat Rotation 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp or Comp or Comp Comp Comp Comp contra contra contra Force per 40 共9兲 40 共9兲 40 共9兲 40 共9兲 40 共9兲 30 共7兲 15 共3.4兲 Specimen N 共lb兲 Time Until 0.5–1 0.5–1 0.5–1 5 4 1–2 Minutes plane

346


Etchants Material Tool steels

Etchants 共see Table 12.2兲 74a, 80, 14 110 210, 211 214 224, 225

Uses General structure Grain boundaries in tempered tool steel Colors ferrite, lower alloy grades Colors cementite Carbides attacked and colored

Material/Preparation Tables 39 Material: Cement clinker. Concrete Material Properties: Portland cement clinker, mineralogical composition: Alite 共C3S兲 35–75 %, Belite 共C2S兲 0–40 %, Aluminate 共C3A兲 1–10 %, Ferrite 共C4AF兲 2–15 %, Periclase 共MgO兲 0–3 %, Free lime 共CaO兲 0–5 %, Arcanite 共K2SO4兲 0–3 %, Ca-Langbeinite 共2CaSO4兲 0–3 %. Comments on Material: Portland cement clinker is a raw material for cement production consisting of several mineral phases with different physical properties, as mentioned above. Hardened concrete consists of cement paste mixed with aggregates like sand and stone. Cement clinker and concrete can be examined in reflected light and in transmitted light. The preparation of cross sections for reflected light is stated below. Thin sections for transmitted light is described in Section 7.13. Both cement clinker and concrete often are very sensitive to water used during the preparation and, consequently, this should be avoided, especially during the last steps of the preparation. Sectioning: The material being brittle should be treated carefully to avoid damage. Often it can be of advantage to impregnate the specimen before cutting 共see below兲. Cutting is preferably done with a precision cut-off machine with a thin cut-off wheel, diamond, metal bond or SiC, bakelite bond and with a water-free coolant. Mounting: Very often the specimen is porous so that impregnation with epoxy is needed to stabilize the material. Also, often the examination, especially at concrete, is done to determine pores 共air voids兲 and microcracks, and therefore it can be recommended to add fluorescent dye to the epoxy 共see Section 3.10兲. Grinding: The traditional method, T-39, stated below is based on lapping on cast iron disks, as known from preparation of mineralogical materials. Often the lapping can be changed to the use of SiC grinding paper, as indicated under Preparation Process 39 below. Polishing: The two methods stated below have a 3 ␮m step as the last polishing step. If needed, this step can be followed by finer steps, as indicated under Preparation Process 39 below. Etching: Normally these materials are not etched.

Chapter 13

Purpose Case or coating thickness/hardness, surface layer Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure Phase identification Porosity


ASTM Standard 共See Section 12.4兲 Cement clinkers and concrete are covered by a number of ASTM standards. These are not stated here, as it is considered outside the scope of this book.

347

Method C-39

C-39, T-39 C-39

C-39, T-39 C-39, T-39 C-39, T-39 C-39


Diamond, metal bond or SiC, bakelite bond, 0.5 mm 共0.019 in兲 thickness


Resin Time Minutes

Cold Mounting


Epoxy 8 – 12 h

Grinding C-39: PG, if material is very water sensitive use alcohol or glycerol instead of water. C-39: PG and FG: For clinker, lower force on specimens to 15 N. C-39: In some cases 共clinker兲 FG 1 can be omitted. T-39: In some cases the lapping on cast iron disks can be changed to SiC paper, P220, P320, P500 and P1000 using glycerol as cooling fluid. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued.

348


Polishing C-39: P 1: For clinker, lower force per specimen to 10 N. C-39 and T-39: If needed, P 1 can be followed with one or two steps, see P 2 in Method C-38 with water-free lubricant, followed by P 2 in Method T-37. Contemporary Method C-39 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 Polishing Disk/Cloth Dia, disk, fixed, Dia, disk, fixed, RCD, soft Cloth, napless, res res hard, wov, syn Abrasive Type Diamond Diamond Dia, spr or susp, Dia, spr or water-free susp, water-free Grit or Grain P220 P1200 9 3 Size ␮m Lubricant Type Water/ Water/glycerol Alco, Alco, waterglycerol water-free free Rotation 300/ 150 300/ 150 300/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or contra Comp Comp Comp Force per 35 共8兲 35 共8兲 35 共8兲 20 共4.5兲 Specimen N /lb Time Until plane 5 5 5 Minutes Traditional Method T-39 共For definitions of parameters Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 Polishing Disk/Cloth Cast iron Cast iron Cast iron disk disk disk

Abrasive Type

FG 3

P1

Cloth, napless, hard, wov, syn SiC powder SiC powder SiC powder SiC powder Dia, spr or susp, waterfree P220 P400 P800 P1200 3

Grit or Grain Size ␮m Lubricant Type Glycerol Rotation Disk/Holder rpm/rpm

and consumables see

150/ 150

Cast iron disk

Glycerol

Glycerol

Glyecerol

150/ 150

150/ 150

150/ 150

Alco or oil, water-free 150/ 150

Chapter 13

Comp/Contra Force per Specimen N 共lb兲 Time Minutes


Contra 5 共1.1兲

Contra 5 共1.1兲

Contra 5 共1.1兲

Contra 5 共1.1兲

Comp 20 共4.5兲

2–3

2–3

2–3

2–3

5

349

Material/Preparation Tables 40 Material: Minerals. Ores Comments on Material: Minerals, ores, and rocks cover a wide field of materials with a high variety of phases. Most often minerals are brittle and hard, but often with a very different hardness of the different phases. This makes preparation of minerals relatively difficult, both because of the risk of deformation, the brittleness, pores, and cracks, creating the risk of pull-outs, and the tendency for relief between the phases. Minerals are prepared as polished sections for reflected light examination and as thin sections for transmitted light examination. Below the preparation of polished sections is described; thin sections are described in detail in Section 7.13 共see also Material/Preparation Tables 39兲. Sectioning: It is important that the often very hard and brittle material is not damaged too much during the sectioning. Often the cutting of an intermediate piece is cut with a large machine specially built for cutting of minerals, using a diamond cut-off wheel, metal bond. For the actual specimen, wet abrasive cutting is often done with a thin diamond, metal bond cut-off wheel on a precision cut-off machine to ensure a good surface. In case of very brittle materials, with pores and cracks, an impregnation before the cutting is recommended 共see below兲. For softer minerals an SiC bakelite bond cut-off wheel can be used. Mounting: Often the specimen, being brittle and with pores and cracks, should be impregnated under vacuum with an epoxy 共see Section 3.10兲. To easily distinguish pores and cracks, the epoxy resin can be added as a dye 共see Section 3.10兲. Also, an impregnetion with a dye makes it possible to distinguish between original pores and “pores,” pull-outs, caused by the preparation process 共see Section 13.6兲. Grinding: The “traditional” grinding of minerals is made as a lapping with loose grains 共see Section 6.7.7兲. This method is stated in Method T-39, however, below, the two methods stated are with fixed grains considered the most useful for polished sections. Some phases in minerals are very sensitive to deformation like certain soft and ductile metals. For this reason the fine grinding step with 9 ␮m diamond in Method C-40 and the steps with 9 ␮m and 6 ␮m in Method T-40 are very important to create a deformation free surface, and these steps should be prolonged if the deformation is not reduced to a satisfactory level that can be removed by the 3 ␮m step. Polishing: In the case of phases with very different hardness, the polishing time should be kept as short as possible and the force as low as possible to reduce relief.

350


Etching: Etching of minerals can be done for identification of the single phases in a mineral based on the reaction of a specimen material to a standard set of reagents. Another approach is to use the reagents for revealing the microstructural details, as it is known from etching of metals. Both approaches are relatively complicated and fall outside the scope of this book. ASTM Standard 共See Section 12.4兲 Method C-40 ASTM standards covering minerals and ores are not stated here, as it is considered outside the scope of this book. Grain size, grain boundaries C-40, T-40 Image analysis, rating of inclusion C-40 content High planeness Microhardness, hardness C-40, T-40 Microstructure C-40, T-40 Phase identification C-40, T-40 Porosity C-40 Purpose Case or coating thickness/hardness, surface layers Perfect edge retention


Diamond, metal bond or SiC, bakelite bond, 0.05 mm 共0.019 in兲 thickness


Resin Time Minutes

Cold Mounting


Epoxy 8 – 12 h

Grinding C-40: For soft/brittle materials, SiC paper grit P320 can be used. C-40: FG: For hard materials a step like FG 1 in Method C-39 can be added. Attention: In C-methods, when using RCD: the disk turns concave during use. When the difference is more than 100– 50 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-40: P 1 and P 2: For hard materials a step like P 2 in Method C-38 can be used between the steps P 1 and P 2.

Chapter 13


351

T-40: P 1 can be followed by a P 2 step like in Method C-40 Contemporary Method C-40 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 Polishing Cloth Disk/Cloth Dia, disk RCD, soft Cloth, napless, fixed, res napless, soft, hard, porous, syn wov, syn Abrasive Type Diamond Dia, spr, or susp Dia, spr or Silica susp Grit or Grain P220 9 3 0.04/ 0.05 Size ␮m Lubricant Type Water Alco or wat Alco or wat Rotation 300/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp Comp Comp contra Force per 20 共4.5兲 20 共4.5兲 20 共4.5兲 10 共2.2兲 Specimen N 共lb兲 Time Until plane 3–6 3–5 1 Minutes Traditional Method T-40 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ FG 3 P1 Polishing PG FG 1 FG 2 Cloth, Cloth, napless, Cloth, Disk/Cloth Dia, pad Cloth, napless, napless, bak napless, v. hard hard, v. hard v. hard, nonwov/ wov, silk nonwov/ nonwov/ wov wov wov Abrasive Type Diamond Dia, spr Dia, spr Dia, spr Dia, spr or susp or susp or susp or susp Grit or Grain 30 9 6 3 1 Size ␮m Lubricant Type Water Alco Alco Alco Alco or wat or wat or wat or wat Rotation 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp Comp Comp Comp Comp Force per 25 共5.7兲 30 共7兲 30–40 共7–9兲 30–40 共7–9兲 10–30 共2.3–7兲 Specimen N 共lb兲

352

Time Minutes


Until plane

5

5

5

2

Material/Preparation Tables 41 Material: Pure aluminum. Cast aluminum alloys Material Properties: Aluminum: Face-centered cubic, 2.699 g / cm3, 660.2° C 共1220° F兲, HV 150. Cast alloy: Aluminum-silicon: 12.5 % Si 共eutectic composition兲. Other cast alloys: Aluminum-silicon-magnesium, aluminum-silicon copper, aluminum silicon-copper-magnesium, aluminum-magnesium, aluminum-zinc-magnesium, aluminum-copper-titanium-magnesium 共weight %兲. Comments on Material: Commercially pure aluminum has an aluminum content higher than 99 % for wrought alloys and 99.5 % for cast alloys. Cast alloys can be alloyed with a number of elements as mentioned above. Aluminum and its alloys are classified through a number of systems, the most important is the system established by the Aluminum Association 共see below兲. Another important system uses the chemical symbols of the most important alloying elements combined with a number stating the content in weight %. AlMg3MnCr describes an alloy with 3 % magnesium and amounts of manganese and chromium, normally 共but not always兲 below 1 % each. Less important alloying elements are not mentioned. Aluminum Association has developed a system for wrought and cast alloys consisting of four numbers followed by a — with a letter and a number. For wrought alloys the four numbers are like: nnnn, at cast alloys the numbers have a dot: nnn.n. For wrought alloys the first number expresses: 1nnn Commercially pure aluminum 共⬎99 % 兲 2nnn Copper as most important alloying element 3nnn Manganese 4nnn Silicon 5nnn Magnesium 6nnn Magnesium and silicon. 7nnn Zinc 8nnn Other alloying elements 9nnn Is not used For cast alloys the first number expresses: 1nn.n Commercially pure aluminum 共⬎99.5% 兲 2nn.n Copper 3nn.n Silicon with copper or magnesium 4nn.n Silicon 5nn.n Magnesium 6nn.n Is not used 7nn.n Zinc 8nn.n Tin 9nn.n Other alloying elements

Chapter 13


353

The letter following the — expresses heat treatment and the number will express further specification of the alloy. ASTM has specified a high number of aluminum alloys and a number of test methods for aluminum. Pure aluminum is a very soft and ductile metal that can be difficult to prepare mechanically. It is important that deformations developed during sectioning and grinding are removed through the polishing steps. Also, there is a risk of embedded grains 共see Section 13.6.4兲. Electrolytic polishing can be done with a perchloric acid electrolyte and often gives very good results. Cast aluminum alloys and wrought alloys are easier to polish mechanically and they are normally not suited for electropolishing. Sectioning: Wet abrasive cutting with an SiC bakelite bond cut-off wheel should be recommended. To avoid solid state transformation in certain materials, an efficient cooling is important. If shearing or band sawing are used, it is important that the induced heavy deformation is removed during the plane grinding step. Mounting: Both hot and cold mounting materials can be used. In the case of heat-sensitive alloys cold mounting is recommended. For examination of pores 共castings兲, vacuum impregnation may be of advantage 共see Section 3.10兲. Preferably the mounting material should be a little harder than the hardest constituent in the specimen material. In the case of examination of thin layers it can be recommended that the specimen is tightly wrapped in thin metal foil 共e.g., household aluminum foil or nickel foil兲 and then hot mounted. In this way the surface layer can be easily distinguished from the mounting material. Grinding: It is important that the deformation from sectioning and the rough grinding steps are removed. If the grinding steps give too high deformation, the force per specimen should be reduced. Polishing: The rough polishing steps with 6 and 3 ␮m are important. If strong deformation can be seen after 3 ␮m, the process should be repeated from FG 1. With only small deformation the time can be prolonged or the force increased, or both. If relief develops between matrix and a second phase, Method C-41 should be used. Electrolytic polishing can be used for pure aluminum and for not too heterogenous alloys. Etching: It can be difficult to etch the surface of aluminum due to a thin oxide film. Also, it is difficult to etch the matrix and several intermetallic phases and precipitates with the same etchant, making the use of several ecthants necessary. It is, however, possible to avoid this for a number of alloys by using a color etchant based on potassium permanganate 共Weck, see Ref. 47, Part I兲: 100 mL distilled water +4 g potassium permanganate, after dissolving: +1 g sodium hydroxide. Immersion in 15 s at room temperature with a freshly prepared solution. The drawback with this etchant is that the specimen surface must be absolutely free from deformation. This can be obtained by pre-etching the surface with 100 mL distilled water +2 g sodium hydroxide. Immersion in 30 to 60 s at room temperature. For other etchants, see below, and Material/Preparation Tables 42/43.

354


Purpose Case or coating thickness/ hardness, surface layers Perfect edge retention Grain size, grain boundaries Heat treatment Image analysis, rating of inclusion content High planeness Microhardness, hardness

ASTM Standard 共See Section 12.4兲 B 487

Method C-41

E 112, E 930, E 1181, E 1382

C-41, T-41 El-10 共pure Al兲 C-41, T-41 C-41, T-41

E 562, E 1245, E 1382

E 10, E 18, E 92, E 103, E 110, E 140, E 384, E 448 E 3, E 407, E 562, E 883, E 1181, E 1245, E 1351, E 1382, E 1558

Microstructure


C-41, T-41

C-41, T-41, El-10 共pure Al兲 C-41, T-41


SiC, bakelite bond

Mounting Hot Compression Resin Bakelite Cold Mounting Resin Acrylics Mounting Time 8–9 Time 6 – 10 min Minutes Minutes/Hours Grinding C-41: PG: If possible use SiC paper grit P320. T-41: Very often FG 4 can be omitted. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-41: P 2: This step can often be omitted. Pure Al: Electrolytic polishing will give good results.

Chapter 13


355

Contemporary Method C-41 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 P3 Polishing Cloth, med Cloth, Disk/Cloth SiC paper RCD, soft Cloth, nap, soft, syn napless, napless, soft, porous, med hard, syn wov, wool Abrasive Type SiC Dia, spr or Dia, spr or Dia, spr or Silica susp susp susp Grit or Grain P220 9 3 1 0.04/ 0.05 Size ␮m Lubricant Type Water Water Wat-oil Wat-oil Rotation 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp Comp Comp Comp Contra Force per 25 共5.7兲 30 共7兲 25 共5.7兲 20 共4.5兲 15 共3.3兲 Specimen N 共lb兲 Time Until plane 5 5 1–2 1–2 Minutes Traditional Method T-41 共For definitions of parameters Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 FG 4 Polishing Disk/Cloth SiC SiC SiC SiC SiC paper paper paper paper paper

and consumables see

Abrasive Type

Dia, spr or susp 6

SiC

SiC

SiC

SiC

SiC

P1

P2

P3




Grit or P220 P320 P500 P1200 P2400 0.04/ Grain 0.05 Size ␮m Lubricant Water Water Water Water Water Alco or WatType wat oil Rotation 300/150 300/150 300/150 300/150 150/150 150/150 150/150 150/150 Disk/ Holder rpm/ rpm

356


Comp/ Contra





Comp Comp Comp Comp Contra or contra 25 共5.7兲 25 共5.7兲 25 共5.7兲 20 共4.5兲 15 共3.4兲

0.5–1

0.5–1

0.5–1

0.5–1

4

3–4

1–2

Etchants Material Pure aluminum Cast aluminum 共2000 series兲 Cast aluminum 共4000 series兲

Etchants see 共Table 12.2兲 1a, 2, 3 3, 2, 1a 8a, 6, 7 3, 1a

Uses General structure General structure Phase identifications General structure

Material/Preparation Tables 42 Material: Other aluminum alloys Material Properties: Aluminum: Face-centered cubic, 2.699 g / cm3, 660.2 °C 共500° F兲, HV 150. Comments on Material: See Material/Preparation Tables 41. Sectioning: See Material/Preparation Tables 41. Mounting: See Material/Preparation Tables 41. Grinding: See Material/Preparation Tables 41. Polishing: See Material/Preparation Tables 41. Etching: See Material/Preparation Tables 41/43 and below. Purpose ASTM Standard 共See Section 12.4兲 Method Case or coating thickness/hardness, B 487 C-42 surface layers Perfect edge retention Grain size, grain boundaries E 112, E 930, E 1181, E 1382 C-42, T-42 El-10 Heat treatment C-42, T-42 Image analysis, rating of inclusion E 562, E 1245, E 1382 C-42, T-42 content High planeness Microhardness, hardness E 10, E 18, E 92, E 103, C-42, T-42 E 110, E 140, E 384, E 448 Microstructure E 3, E 407, E 562, E 883, C-42, T-42, E 1181, E 1245, E 1351, El-10 E 1382, E 1558 Phase identification C-42, T-42

Chapter 13


357


SiC, bakelite bond

Mounting Hot Compression Resin Bakelite Cold Mounting Resin Acrylics Mounting Time 8–9 Time 6 – 10 min Minutes Minutes/Hours Grinding C-42: PG: If possible use SiC paper grit P320. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-42: P 1: For harder alloys this step can be changed to a napless, hard, wov, silk cloth. C-42: For softer alloys the step P 1 from Method T-42 can be added, between FG 1 and P 1. T-42: P 3 can be followed by a step with silica, see C-42. Also at harder alloys the step P 3 can be omitted. Often electrolytic polishing can be recommended for the examination of the microstructure. Contemporary Method C-42 共For definitions of parameters and Section 13.2.2.兲 Grinding/ PG FG 1 P1 Polishing Disk/Cloth SiC paper RCD, soft Cloth, napless, med hard, wov, wool Abrasive Type SiC Dia, spr or susp Dia, spr or susp Grit or Grain P220 9 3 Size ␮m Lubricant Type Water Water Wat-oil Rotation 300/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm

consumables see P2 Cloth, napless, soft, porous, syn

Silica 0.04/ 0.05

150/ 150

358


Comp/Contra



Comp

Comp

Contra

30 共7兲

25 共5.7兲

15 共3.3兲

5

3

1–2

Traditional Method T-42 共For definitions of parameters and consumables Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 Polishing Cloth, Disk/Cloth SiC SiC SiC SiC Cloth, paper paper paper paper napless, napless, hard, hard, wov, silk wov, syn Abrasive Type Grit or Grain Size ␮m Lubricant Type Rotation Disk/Holder rpm/rpm Comp/Contra Force per Specimen N 共lb兲 Time Minutes Etchants Material Al alloys 共7000 series兲

SiC

SiC

SiC

SiC

P220

P320

P500

P1200

Water

Water

Water

Water

300/ 150

300/ 150

300/ 150

Dia, spr or susp 6

see P3

Cloth, med. nap, soft, syn Dia, spr Dia, spr or susp or susp 3 1

Alco or Alco or Wat-oil wat wat 150/ 150 150/ 150 150/ 150 150/ 150

Comp or Comp or Comp or Comp contra contra contra 25 共5.7兲 25 共5.7兲 25 共5.7兲 25 共5.7兲

Comp

Comp

Comp

25 共5.7兲

25 共5.7兲

15 共3.4兲

Until plane

4

4

1

0.5–1

0.5–1

Etchants 共see Table 12.2兲 3, 1a, 2 4, 5 3b, 6

0.5–1

Uses General structure Grain structure under polarized light Phase identification

Chapter 13


359

Material/Preparation Tables 43 Material: Wrought aluminum alloys Material Properties: Aluminum: Face-centered cubic, 2.699 g / cm3, 660.2° C 共500° F兲, HV 150. Wrought aluminum alloys: Manganese. Magnesium. Magnesium-manganese-chrome. Magnesium-silicon. Copper. Copper-manganese and copper-silicon-manganese. Zinc-magnesium. Zinc-magnesium-copper. Lithium-copper-magnesium. Comments on Material: See Material/Preparation Tables 41. Sectioning: See Material/Preparation Tables 41. Mounting: See Material/Preparation Tables 41. Grinding: See Material/Preparation Tables 41. Polishing: Alloys containing magnesium may be sensitive to water and should be polished with water-free lubricants 共see also Material/Preparation Tables 41兲. Etching: See Material/Preparation Tables 41/42 and below. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Heat treatment Image analysis, rating of inclusion content High planeness Microhardness, hardness


Method C-43

E 112, E 930, E 1181, E 1382

C-43, T-43, El-10 C-43, T-43 C-43, T-43

E 562, E 1245, E 1382

E E E E

Microstructure

10, E 18, E 92, E 103, E 110, 140, E 384, E 448 3, E 407, E 562, E 883, E 1181, 1245, E 1351, E 1382, E 1558


C-43, T-43 C-43, T-43, El-10 C-43, T-43


SiC, bakelite bond

Mounting Hot Compression Resin Bakelite Cold Mounting Resin Acrylics Mounting Time 8–9 Time 6 – 10 min Minutes Minutes/Hours

360


Grinding C-43: PG: If possible use SiC paper grit P320. C-43: FG 2: Very often this step can be omitted. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Contemporary Method C-43 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 P2 Polishing Cloth, napDisk/Cloth SiC paper RCD, soft RCD, soft Cloth, less, soft, napless, med hard, porous, syn wov, wool Abrasive Type SiC Dia, spr or Dia, spr or Dia, spr or Silica susp susp susp Grit or Grain P220 9 3 3 0.04/ 0.05 ize ␮m Lubricant Type Water Alco or wat Alco or wat Wat-oil Rotation 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp Comp Comp Comp Contra Force per 20 共4.4兲 30 共6.6兲 25 共5.7兲 15 共3.4兲 15 共3.4兲 Specimen N 共lb兲 Time Until plane 5–7 5 5 1 Minutes Traditional Method T-43 共For definitions Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 Polishing Disk/Cloth SiC SiC SiC paper paper paper

Abrasive Type Grit or Grain Size ␮m


FG 4

P1

P2

SiC paper

SiC paper



SiC

SiC

SiC

SiC

SiC

P220

P320

P500

P1200

P2400

Alumina 0.02/ 0.05

Chapter 13

Lubricant Type Rotation Disk/Holder rpm/rpm Comp/Contra

Force per Specimen N 共lb兲 Time Minutes Etchants Material 1000 series

Water

Water

Water

Water

Water

361

Wat-oil

300/ 150 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150

150/ 150





Comp

Comp

Contra

25 共5.7兲

20 共4.5兲

15 共3, 4兲

Unit plane

0.5–1

0.5–1

0.5–1

0.05–1

3–4

1–2

Etchants 共see Table 12.2兲 1a, 2, 3, 4, 5

3000 series

6, 7 3, 1a 4, 5

5000 series

8a, 6, 7 3, 1a, 2, 6, 8a 4, 5

6000 series


3, 1a, 2, 6, 8a, 222 4, 5 1a, 2, 7, 6, 8a

Uses General structure Grain structure under polarized light Phase identifications General structure Grain structure under polarized light Phase identifications General structure Grain structure under polarized light General structure Grain structure under polarized light Phase identifications

Material/Preparation Tables 44 Material: Pure antimony. Sb alloys, and Sb bearing alloys. Pure bismuth. Bi alloys Material Properties: Antimony: Hexagonal, 6.691 g / cm3, 630.5° C 共1167° F兲. Bismuth: Hexagonal, 9.78 g / cm3, 271.3° C 共520° F兲, HB 70. Comments on Material: Both antimony and bismuth are seldomly used as pure metals, but mostly used as alloying elements. Antimony is used for bearing alloys. Pure antimony is relatively hard and pure bismuth is soft. Both metals are very brittle. Sectioning: Care should be taken that the brittle materials are not damaged too much during the cutting. At wet abrasive cutting, a thin SiC cut-off wheel bakelite bond should be used. To avoid cracking during cutting it may be useful to mount the specimen in epoxy before cutting.

362


Mounting: Both hot and cold mounting can be used. Be careful that the high pressure during hot mounting doesn’t damage the brittle specimen. Grinding: During grinding with SiC grinding paper, the paper may be loaded with the material because this is not taken away by the water flow. A loaded paper should not be used as it will give stronger damage to the specimen. The water flow should be strong and the aggressiveness of the paper can be dampened by adding a small amount of hard wax to the paper surface before use, or the new paper can be “run-in” with a hard material in a few seconds. Polishing: It is important that all deformations from the grinding are removed after the rough polishing step P 1. For polishing of pure antimony and pure bismuth, a solution of 3 % nitric acid in glycerol can be added to the silica used for the last step. At polishing of Sb alloys containing lead, the last polishing step can be with a 0.3 alumina suspension with added ammonium tartrate, 1 g per 1 L distilled water. At polishing of Bi, the 6 ␮m step can be omitted 共see below兲. Both pure antimony and bismuth are well suited for electrolytic polishing. Etching: See below. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure


Method C-44

E 112, E 930, E 1181, E 1382

C-44, T-44 El-10 C-44, T-44

E 562, E 1245, E 1382

E E E E

10, E 18, E 92, E 103, E 110, 140, E 384, E 448 3, E 407, E 562, E 883, E 1181, 1245, E 1351, E 1382, E 1558


C-44, T-44 C-44, T-44, El-10 C-44, T-44


SiC, bakelite bond

Mounting Hot Compression Resin Bakelite Cold Mounting Resin Acrylics/Epoxy Mounting 6 – 10 min/ 6 – 8 h Time 8–9 Time Minutes Minutes/ Hours

Chapter 13


363

Grinding T-44: For harder alloys, FG 4 can be omitted. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-44 and T-44: P 1: At polishing of bismuth and Bi alloys this step can be omitted. C-44: P 3: At polishing of bismuth and Bi alloys the time may be increased to several minutes. For the final step chemical mechanical polishing can be recommended 共see above兲. Contemporary Method C-44 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 P2 P3 Polishing Cloth, Cloth, Disk/Cloth SiC paper SiC paper RCD, soft Cloth, napless, napless, napless, med hard, soft, wov, silk hard, porous, wov, syn wool Abrasive Type SiC SiC Dia, spr Dia, spr Dia, spr Silica or susp or susp or susp Grit or Grain P220 P320 9 6 3 0.04/ 0.05 Size ␮m Lubricant Type Water Water Water Alco or Wat-oil wat Rotation 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/ Holder rpm/ rpm Comp/ Comp or Comp Comp Comp Comp Contra Contra contra Force per 25 共5.7兲 25 共5.7兲 30 共7兲 25 共5.5兲 25 共5.7兲 15 共3.3兲 Specimen N 共lb兲 Time Until 0.5–1 5 4 3 1 Minutes plane

364


Traditional Method T-44 共For definitions of parameters and consumables Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 FG 4 P1 P2 Polishing Cloth, Disk/ SiC SiC SiC SiC SiC Cloth, napCloth paper paper paper paper paper napless, less, med. hard, hard, wov, wov, silk wool Abrasive SiC SiC SiC SiC SiC Dia, spr Dia, spr Type or susp or susp Grit or P220 P320 P500 P1200 P2400 6 3 Grain Size ␮m Lubricant Water Water Water Water Water Wat-oil Wat-oil Type Rotation 300/150 300/150 300/150 150/150 150/150 150/150 150/150 Disk/ Holder rpm/ rpm Comp/ Comp Comp Comp Comp Comp Comp Comp Contra or or or contra contra contra Force per 20 共4.5兲 20 共4.5兲 20 共4.5兲 20 共4.5兲 20 共4.5兲 20 共4.5兲 15 共3.4兲 Specimen N 共lb兲 Time Until 0.5–1 0.5–1 0.5–1 0.5–1 4–5 3 Minutes plane Etchants Material Sb, lean, Sb alloys Sb Sb, Sb alloys Sb-Pb alloys Bi, Bi alloys Bi-Sn alloys, Bi-Ca alloys

see P3 Cloth, napless, soft, porous, syn Silica 0.04/ 0.05

150/150

Contra

15 共3.4兲

1



938 936, 937, 940 938, 941 937, 940 938

Grain contrast General structure General structure General structure General structure

Chapter 13


365

Material/Preparation Tables 45 Material: Pure beryllium. Be alloys Material Properties: Beryllium: Hexagonal close-packed, 1.8 g / cm3, 1350° C 共2462° F兲, HRB 80. Comments on Material: Beryllium is a light metal which is mostly used as an alloying element, improving the strength of the alloy. Pure beryllium is toxic to inhale which means that the preparation process, when dust is developed, must take place in a glove box or under an efficient fume hood, or both. Pure beryllium resembles magnesium 共see Material/Preparation Tables 53兲 it deforms and fractures easily and preparation must be done with great care. Sectioning: For wet abrasive cutting a thin SiC bakelite bond cut-off wheel should be used. For alloys based on copper, a medium hard wheel is recommended. For nickel-based alloys a softer wheel should be used. The cooling should be efficient to avoid thermal damage. When cutting pure beryllium and alloys with a high Be content, it is important that the sludge, metal dust, and particles from the wheel are correctly disposed of because of the toxicity. Mounting: Both hot mounting and cold mounting can be used. Grinding: When wet grinding pure beryllium and alloys with a high Be content the dust is bound by the water, but care must be taken to have the correct disposal of the sludge. For pure beryllium the force on the specimen should be reduced and often it can be of advantage to make the grinding on a stationary paper in one direction. Polishing: For pure beryllium and certain alloys electrolytic polishing is recommended. Also a chemical mechanical polishing can be used 共see below兲. Etching: Pure beryllium can be examined in polarized light. For etchants, see below. Purpose ASTM Standard 共See Section 12.4.兲 Case or coating B 487 thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries E 112, E 930, E 1181, E 1382 Image analysis, rating of inclusion content High planeness Microhardness, hardness

Microstructure Phase identification

E 562, E 1245, E 1382

E E E E E

Method C-45

C-45, T-45, El-10 C-45, T-45

C-45, T-45 10, E 18, E 92, E 103, 110, E 140, E 384, 448 3, E 407, E 562, E 883, E 1181, E 1245, C-45, T-45, 1351, E 1382, E 1558 El-10 C-45, T-45

366



SiC, bakelite bond

Mounting Hot Compression Resin Bakelite Cold Mounting Resin Acrylics Mounting Time 8–9 Time 6 – 10 min Minutes Minutes/Hours Grinding C-45: PG: If possible use SiC paper grit P320. T-45: Pure Be is relatively brittle and grinding should be performed with Method T-45, but with lower force than indicated. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-45, T-45: For the last step with silica, one part of hydrogen peroxide 共30 %兲 can be added to five parts of silica suspension. Contemporary Method C-45 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding PG FG 1 P1 P2 Polishing Cloth, Disk/Cloth Dia, disk, RCD, soft Cloth, napless, fixed, res napless, soft, hard, porous, syn wov, silk Abrasive Type Diamond Dia, spr Dia, spr or Silica or susp susp Grit or Grain P220 9 3 0.04/ 0.05 Size ␮m Lubricant Type Water Water Water Rotation Disk/Holder 300/ 150 150/ 150 150/ 150 150/ 150 rpm/rpm Comp/Contra Comp or contra Comp Comp Contra Force per Specimen 20 共4.4兲 30 共6.6兲 25 共5.5兲 15 共3.4兲 N 共lb兲 Time Until plane 5 4–5 1–2 Minutes

Chapter 13

Traditional Method see Section 13.2.2.兲 Grinding/ PG Polishing Disk/Cloth SiC paper

Abrasive Type Grit or Grain Size ␮m Lubricant Type Rotation Disk/ Holder rpm/ rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes Etchants Material Pure Be Be alloys


367

T-45 共For definitions of parameters and consumables FG 1

FG 2

FG 3

P1

P2

P3

SiC paper

SiC paper

SiC paper

SiC

SiC

SiC

SiC

P320

P500

P1200



P220


Water

Water

Water

Water

Alco-wat Wat-oil

300/ 150

300/ 150

300/ 150

150/ 150 150/ 150

0.04/ 0.05

150/ 150 150/ 150

Comp or Comp or Comp or Comp contra contra contra 25 共5.7兲 25 共5.7兲 25 共5.7兲 20 共4.5兲

Comp

Comp

Contra

20 共4.5兲

20 共4.5兲

15 共3.4兲

Until plane

4–5

3–4

1–2

0.5–1

0.5–1

0.5–1

Etchants 共see Table 12.2兲 9, 10 11

Uses General structure via polarized light General structure

Material/Preparation Tables 46 Material: Pure chromium. Cr alloys Material Properties: Chromium: Body-centred cubic, 7.17 g / cm3, 1875° C 共3407° F兲, HB 125. Comments on Material: Chromium belongs to the refractory metals and pure chromium is soft and ductile. The alloys, which are commercially available, often used for plating, are hard and relatively brittle. The machinability of chromium is low and cold working is easy which makes chromium relatively difficult to prepare mechanically.

368


Sectioning: Wet abrasive cutting can be made with an SiC bakelite bond cut-off wheel. Due to the poor machinability a relatively soft wheel, as thin as possible, should be used. Mounting: Both hot and cold mounting can be used. Grinding: Because of the poor machinability the grinding papers should only be used as long as they are cutting efficiently, if not, cold work and deformation will develop. Polishing: It is important that the deformations from grinding are removed during the rough polishing step. It can be difficult to remove all deformation by mechanical polishing and often chemical mechanical polishing can be an advantage 共see below兲. Also electrolytic polishing can be recommended. Etching: Chromium is difficult to etch, two etchants are stated below. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure


E 112, E 930, E 1181, E 1382 E 562, E 1245, E 1382

E E E E

10, E 18, E 92, E 103, E 110, E 140, 384, E 448 3, E 407, E 562, E 883, E 1181, E 1245, 1351, E 1382, E 1558


Method C-46

C-46, T-46, El-11 C-46, T-46

C-46, T-46, El-11 C-46, T-46, El-11 C-46, T-46


SiC, bakelite bond

Mounting Hot Compression Resin Bakelite Cold Mounting Resin Acrylics Mounting Time 8–9 Time 6 – 10 min Minutes Minutes/Hours Grinding T-46: Very often FG 3 can be omitted. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued.

Chapter 13


369

Polishing C-46 and T-46: The last polishing step can be with alumina 共0.02– 0.05 ␮m兲 in distilled water 共100 mL兲 with sodium hydroxide 共5 g兲, or alumina 共300 mL兲 with hydrogen peroxide 共H2O2兲共20 mL兲共30 %兲. C-46: If needed the step P 1 from T-46 can be used between FG 1 and P 1 expanding the method with one step. C-46: P 2: This step can often be omitted. Contemporary Method C-46 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 P3 Polishing Cloth, med. Cloth, napDisk/Cloth Dia, disk, RCD, soft Cloth, nap, soft, syn less, soft, fixed, res napless, porous, syn hard, wov, silk Abrasive Diamond Dia, spr or Dia, spr or Dia, spr or Silica Type susp susp susp Grit or Grain P220 9 3 1 0.04/ 0.05 Size ␮m Lubricant Type Water Alco or wat Alco or wat Alco or wat Rotation 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/ Holder rpm/ rpm Comp/Contra Comp Comp Comp Comp Contra Force per 30 共7兲 30 共7兲 30 共7兲 25 共5.7兲 15 共3.39兲 Specimen N 共lb兲 Time Until plane 4 4 3 1–2 Minutes Traditional Method T-46 共For Section 13.2.2.兲 Grinding/ PG FG 1 Polishing Disk/Cloth SiC SiC paper paper


FG 3

P1

P2

P3

SiC paper

SiC paper




370


Abrasive Type

SiC

SiC

SiC

SiC

Grit or Grain Size ␮m Lubricant Type Rotation Disk/ Holder rpm/ rpm Comp/ Contra Force per Specimen N共lb兲 Time Minutes

P220

P320

P500

P1200

Water

Water

Water

Water

Etchants Material Cr

Dia, spr or susp 6

Dia, spr or susp 3

Alumina

0.02/ 0.05

Alco or wat 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150

150/ 150

150/ 150

Comp

Comp

Comp

Comp

Comp

Comp

Contra

15 共3.4兲

15 共3.4兲

15 共3.4兲

15 共3.4兲

30 共7兲

20 共4.5兲

10 共2.3兲

Until plane

0.5–1

0.5–1

0.5–1

4–5

3

1

Etchants 共see Table 12.2兲 12, 13c

Wat-oil


Material/Preparation Tables 47 Material: Pure Cobalt. Co Alloys Material Properties: Cobalt: Above 417° C 共783° F兲: Face-centred cubic. Below 417° C 共783° F兲: Hexagonal close packed, 8.8 g / cm3, 1495° C 共2723° F兲. Comments on Material: Cobalt is a metal with characteristics close to iron and nickel; it is tough and the machinability is relatively low. Cobalt is very magnetic and used for magnets and for alloying element to improve strength. For super alloys based on cobalt, see Material/Preparation Tables 48. For cobalt in cemented carbides, see Material/Preparation Tables 67. Pure cobalt being tough and with a tendency to cold work and deformation is relatively difficult to prepare. Cobalt alloys are less difficult. Preparation is similar to the refractory metals 共see Material/Preparation Tables 55兲. Sectioning: Wet abrasive cutting is done with an SiC bakelite bond cut-off wheel. A thin and relatively soft wheel is recommended to secure a cut with the lowest deformation possible. Mounting: Hot mounting and cold mounting can be used. Grinding: Due to the toughness of cobalt the SiC grinding papers shall not be used for too long of a time to avoid smeared layers.

Chapter 13


371

Polishing: It is important that the rough polishing step has removed the deformation from the grinding. If this cannot be obtained with the 3 ␮m step, a 6 ␮m step is used 共see below兲. Electrolytic polishing can be recommended. Etching: See below. Purpose Case or coating thickness/ hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness


Method C-47

E 112, E 930, E 1181, E 1382

C-47, T-47, El-12 C-47, T-47

E 562, E 1245, E 1382

E E E E E E

Microstructure

10, E 18, E 92, E 103, 110, E 140, E 384, 448 3, E 407, E 562, E 883, 1181, E 1245, E 1351, 1382, E 1558


C-47, T-47, El-12 C-47, T-47, El-12 C-47, T-47


SiC, bakelite bond

Mounting Hot Compression Resin Bakelite Cold Mounting Resin Acrylics Mounting Time 8–9 Time 6 – 10 min Minutes Minutes/Hours Grinding Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-47: The step P 1 from Method T-47 can be used between the FG 1 step and the P 1 step 共see above兲. C-47: P 2: Often this step can be omitted. T-47: The method can be expanded with P 3 from C-47.

372


Contemporary Method C-47 共For definitions Section 13.2.2.兲 Grinding/ PG FG 1 Polishing Disk/Cloth Dia, disk RCD, hard fixed, res

Abrasive Type Grit or Grain Size ␮m Lubricant Type Rotation Disk/Holder rpm/rpm Comp/Contra Force per Specimen N 共lb兲 Time Minutes

Diamond Dia, spr or susp P220 9 Water

of parameters and consumables see P1

P2

P3


Cloth, med nap, soft, syn


Dia, spr or susp 1

0.02/ 0.05


Alco or wat

150/ 150


150/ 150

150/ 150

Comp 25 共5.7兲

Comp 30 共7兲

Comp 30 共7兲

Comp 30 共7兲

Contra 10 共2.2兲

Until plane

5–6

4

2

Traditional Method T-47 共For definitions of parameters and consumables Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 Polishing Cloth, Disk/Cloth SiC SiC SiC SiC Cloth, paper paper paper paper napless, napless, hard, hard, wov, wov, silk silk Abrasive SiC SiC SiC SiC Dia, spr Dia, spr Type or susp or susp Grit or Grain P220 P320 P500 P1200 6 3 Size ␮m Lubricant Water Water Water Water Alco Alco Type or or wat wat Rotation 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/ rpm Comp/ Comp or Comp or Comp or Comp Comp Comp Contra contra contra contra

see P3 Cloth med. nap, soft, syn Dia, spr or susp 1 Alco or wat 150/ 150

Comp

Chapter 13



373

20 共4.5兲

20 共4.5兲

20 共4.5兲

15 共3.4兲

25 共5.7兲

30 共7兲

30 共7兲

Until plane

0.5–1

0.5–1

0.5–1

4–5

4

2

Etchants Material Pure Co Hard-facing and tool metals High temperature alloys

Etchants 共see Tables 12.2兲 14, 15, 17 18, 19, 20 20, 18, 16, 21, 22b, 24, 25 19

Uses General structure General structure General structure Phase identification

Material/Preparation Tables 48 Material: Cobalt-based super alloys Material Properties: Cobalt: Above 417° C 共783° F兲: Face-centered cubic. Below 417° C 共783° F兲: Hexagonal close packed, 8.8 g / cm3, 1495° C 共2723° F兲. Super alloys 共Co based兲: Heat-resistant casting alloys: 20–32 % chromium, 7–13 % tungsten, 1–11 % nickel and molybdenum, niobium, zirconium, titanium, aluminum, tantalum, boron, silicon and manganese. Wrought heat-resistant alloys: 1–15 % iron, 3–35 % nickel, 20–30 % chrome, 7–10 % molybdenum, carbon, manganese, tungsten, niobium 共weight %兲. Comments on Material: The cobalt-based super alloys are high-temperature resistant materials. They are hard and tough, relatively easy to prepare. Stellite is a special cobalt-based alloy with 45–65 % Co, 25–35 % Cr, and 5–20 % W. This alloy is very wear resistant used only as casting alloy. It is hard and brittle. Cobalt is also used in cemented carbides 共see Material/Preparation Tables 67兲. Sectioning: Wet abrasive cutting is done with an SiC bakelite bond cut-off wheel. Very often shearing or other more rough sectioning methods should be avoided, as serious distortions and cold work could be introduced. Use only these methods for sectioning of large pieces, later to be sectioned by wet cutting. Mounting: Both hot mounting and cold mounting can be used. In case of edge retention a hot mounting material like bakelite or epoxy with a filler should be used. Grinding: For the harder alloys, like stellite, Method C-48 should be preferred. Polishing: For the final step with alumina, the pH should be lowered to around 4. Electrolytic polishing is recommended. Etching: See Material/Preparation Tables 47. Purpose Case or coating thickness/hardness surface layers Perfect edge retention


Method C-48

374



E 112, E 930, E 1181, E 1382


E 562, E 1245, E 1382

Microstructure

E 3, E 407, E 562, E 883, E 1181, E 1245, E 1351, E 1382, E 1558

E 10, E 18, E 92, E 103, E 110, E 140, E 384, E 448


C-48, T-48 E-12 C-48, T-48

C-48, T-48 El-12 C-48, T-48 El-12 C-48, T-48


SiC, bakelite bond

Mounting Hot Compression Resin Bakelite/ Cold Mounting Resin Acrylics Mounting Epoxy Time 8–9 Time 6 – 10 min Minutes Minutes/Hours Grinding C-48: FG: Very often FG 1 can be changed to RCD, soft, and FG 2 and FG 3 can be omitted. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-48 and T-48: The P 3 step: Use alumina with a pH around 4.

Chapter 13


Contemporary Method C-48 共for definitions of parameters Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 Polishing Disk/Cloth Dia, disk RCD, hard RCD, soft RCD, soft fixed, res

Abrashive Type Grit or Grain Size ␮m Lubricant Type Rotation Disk/Holder rpm/rpm Comp/ Contra Force per Specimen N共lb兲 Time Minutes

375


P3

Diamond Dia, spr or susp P220 9

Dia, spr or susp 6

Dia, spr or susp 3

Cloth, nap- Cloth, less, hard, napless, wov, syn soft, porous, syn Dia, spr Alumina or susp 3 0.02/ 0.05

Water





150/ 150

Comp

Comp

Comp

Comp

Contra

30 共7兲

30 共7兲

25 共5.7兲

30 共7兲

15 共3.4兲

4–5

4

5

2–4

1–2

300/ 150


Until plane

Traditional Method T-48 共For definitions parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 P3 Polishing Cloth Cloth Disk/Cloth SiC SiC SiC SiC Cloth paper paper paper paper napless, napless, napless, soft, hard, hard, porous, wov, silk wov, syn syn Abrasive SiC SiC SiC SiC Dia, spr Dia, spr Alumina Type or susp or susp Grit or Grain P220 P320 P500 P1200 6 3 0.02/ Size ␮m 0.05 Lubricant Water Water Water Water Alco or Alco or Type wat wat Rotation 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp or Comp or Comp Comp Comp Contra contra contra contra

376


Force per 30 共7兲 30 共7兲 30 共7兲 Specimen N 共lb兲 Time Until 0.5–1 0.5–1 Minutes plane Etchants See Material/Preparation Tables 47.

30 共7兲

30 共7兲

30 共7兲

10 共2.3兲

0.5–1

5

2–3

1

Material/Preparation Tables 49 Material: Copper and copper alloys. Brass. Bronze. Other copper alloys Material Properties: Copper: Face-centered cubic, 8.93 g / cm3, 1083° C 共1981° F兲, HRB 37. ␣-brass: Body-centered cubic, up to 38 % zinc. ␣-␤-brass: Body-centered cubic, 38 to 47 % zinc. Bronze: Up to 30 % tin Comments on Material: Copper makes alloys with a high number of other metals. In alloys improving the characteristics of pure copper, small amounts of alloying elements like silver, cadmium, sulfur, tellurium, chromium, beryllium, and cobalt are used. The alloys with zinc, brasses, are numerous, often with lead as a further alloying element. In special brasses further elements like aluminum, tin 共1–2 %兲 manganese nickel and iron are used. Brass can be obtained as wrought and cast alloys. The alloys with tin, bronzes are supplied as wrought bronzes with up to 6 % tin and cast bronzes with up to 30 % tin Often zinc is added up to 2 % and other elements like phosphorous and lead. Aluminum bronze is a group of bronzes with 5–11 % aluminum, up to 6 % nickel, 6 % iron, and 2 % manganese. Manganese bronze contains 5–15 % manganese. Copper-nickel alloys have a nickel content of 4.5–45 % nickel with small amounts of iron and manganese. Copper and copper alloys are specified in a number of systems by a number of organizations. The most important are: UNS System, Standard Designations for Copper and Copper Alloys, by Copper Development Association 共CDA兲. AMS System, Aerospace Material Specifications, by Society of Automotive Engineers 共SAE兲. ASME System, by American Society of Mechanical Engineers 共ASME兲. ASTM System by ASTM. AWS System by American Welding Society 共AWS兲. Ingot No System by Brass and Bronze Ingot Manufacturers. Federal System and Military System. SAE System by American Society of Mechanical Engineers 共ASME兲. Metallographic examination is often used for the determination of grain size, evaluation of the distribution of second phase, and control of heat treatment.

Chapter 13


377

Copper alloys are soft and ductile, making them difficult to prepare without deformation. Care should be taken to keep the deformation low at sectioning and grinding and to remove deformation from previous steps. See also the Material/ Preparation Tables 50 covering the preparation of pure copper and copper bearing alloys. Sectioning: Wet abrasive cutting with an SiC bakelite bond cut-off wheel. Use an efficient cooling to avoid recrystallization of cold-worked lean alloys. When using shearing or band sawing, care should be taken that the strong deformation developed is removed during the plane grinding. Mounting: Hot and cold mounting can be used. Grinding: Sectioning and the rough grinding steps introduce deep deformation so it is important to remove this during the finer grinding steps. Polishing: It can be very difficult to remove the last deformation and obtain a scratch-free surface with mechanical polishing. Using chemical mechanical polishing at the last polishing step is an efficient way to obtain a correct surface 共see below兲. Electrolytic polishing gives very good results with a number of brasses and bronzes. Etching: See below. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries

Heat treatment Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure



Method C-49

E 112, E 930, E 1181, E 1382

C-49, T 49, El-13 共Brass兲, El14 共Bronze兲 C-49, T-49 C-49, T-49

E 562, E 1245, E 1382

E E E E

10, E 18, E 92, E 103, E 110, E 140, 384, E 448 3, E 407, E 562, E 883, E 1181, E 1245, 1351, E 1382, E 1558

C-49, T-49 C-49, T-49, El-13 共Brass兲, El 14 共Bronze兲 C-49, T-49

378



SiC, bakelite bond

Mounting Hot Compression Resin Bakelite Cold Mounting Resin Acrylics Mounting Time 8–9 Time 6 – 10 min Minutes Minutes/Hours Grinding Attention: In C-method, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-49 and T-49: For Cu and Cu-alloys a chemical mechanical polishing can be obtained in the last polishing step by mixing 98 共96兲 mL colloidal silica with 1 mL 共2 mL兲 H2O2 共30 %兲 and 1 mL 共2 mL兲 ammonia solution 共25 %兲. Electrolytic polishing: Brass: El-13. Bronze: El-14 Contemporary Method C-49 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 Polishing Cloth, Disk/Cloth SiC paper RCD, soft Cloth, napless, napless, soft, hard, wov, porous, syn syn Abrasive Type SiC Dia, spr Dia, spr Silica or susp or susp See note Grit or Grain P220 9 3 0.04/ 0.05 Size ␮m Lubricant Type Water Alco or wat Wat-oil Rotation 300/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Contra Comp Comp Contra Force per 25 共5.7兲 30 共7兲 25 共5.5兲 15 共3.3兲 Specimen N 共lb兲

Chapter 13

Time Minutes

Until plane


4

4

379

2–3

Traditional Method T-49 共For definitions of parameters Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 FG 4 Polishing Disk/ SiC SiC SiC SiC SiC Cloth paper paper paper paper paper

and consumables see

Abrasive Type

SiC

SiC

SiC

SiC

SiC

SiC

Grit or Grain Size ␮m Lubricant Type Rotation Disk/ Holder rpm/ rpm Comp/ Contra

P220

P320

P500

P1200

P2400

Water

Water

Water

Water

300 / 150

300 / 150

300 / 150

150 / 150


Comp Comp Comp Comp Comp or contra 25 共5.7兲 25 共5.7兲 25 共5.7兲 20 共4.5兲 25 共55.7兲

Contra

0.5–1

0.5–1

1

Comp or contra Force per 25 共5.7兲 Specimen N 共lb兲 Time Until Minutes plane

Etchants Material Cu-Al 共aluminum, bronze兲 Cu-Be Cu-Cr Cu-Mn Cu-Ni Cu-Si

0.5–1

FG 5

P1

P3

SiC paper

Cloth napless, soft, porous, syn Silica See note

P4000


Water

Water

Wat-oil

150 / 150

150 / 150

150 / 150

0.5–1

Etchants 共see Table 12.2兲 44, 31d, 34 b, 35, 36, 37, 38, 39, 40, 45, 215 46, 41, 45 41 41 34, 47, 48, 40, 49, 50 41

0.5–1

3

0.04 / 0.05

150 / 150

10 共2.2兲

Uses General structure General General General General General

structure structure structure structure structure

380


Cu-Sn 共tin bronze兲 Admirality metal Gilding metal, cartridge metal, free cutting brass, nickel silver Cu alloys

51, 52

General structure

8b 31d, 32, 33, 41, 42, 49

General structure General structure

26, 41, 33, 39, 53,

General structure

27, 28, 29, 30, 44, 31d, 32, 34b, 35, 36, 37, 38, 210, 215 43, 28, 49

42, 49, 210 54

Chemical polish and etch Darkens beta in alpha-beta brass Etching of cold worked brass

Material/Preparation Tables 50 Material: Pure copper. Copper-bearing alloys Material Properties: Copper: Face-centered cubic, 8.93 g / cm3, 1083° C 共1981° F兲, HRB 37. Copper bearing alloys: 3.5–25 % lead, 3.5–11 % tin, 0.5–4 % zinc, small additions of antimony, nickel and iron 共weight %兲. Comments on Material: Commercially pure copper, 99.9–99.99 %, can be obtained as oxygen-free electronic copper and as tough pitch copper containing very small amounts of oxide. Copper bearing alloys have high contents of lead and tin, as mentioned above. Pure copper is very ductile and soft making the preparation difficult. Copper bearing materials, having the very soft phases of lead and tin is difficult to prepare without smearing of these phases. The methods described in Material/Preparation Tables 49 can also be used for pure copper. For further information see Material/ Preparation Tables 49. Sectioning: Wet abrasive cutting with an SiC bakelite bond cut-off wheel. When using shearing or band sawing, care should be taken that the strong deformation developed is removed during the plane grinding. Mounting: Hot and cold mounting can be used. Grinding: Sectioning and the rough grinding steps introduce deep deformation so it is important to remove this during the finer grinding steps.

Chapter 13


381

Polishing: It is important that the deformation developed during the grinding is removed after the step with 9 ␮m or 6 ␮m. For pure copper it can be very difficult to remove the last deformation and obtain a scratch- free surface with mechanical polishing. Using chemical mechanical polishing at the last polishing step is an efficient way to obtain a correct surface 共see below兲. Electrolytic polishing gives good results with pure copper using Method El-13. Electrolytic polishing of bearing alloys can be done with Method El-14 if the amount of phases is not too high. Etching: Etching can take place between preparation steps to remove deformation 共see below兲. See etchants below. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries

Heat treatment Image analysis, rating of inclusion content High planeness Microhardness, hardness


Method C-50

E 112, E 930, E 1181, E 1382

C-50, T-50, El-13 共Pure copper兲, El-14 共Bearing alloys兲 C-50, T-50 C-50, T-50

E 562, E 1245, E 1382

E E E E

Microstructure

10, E 18, E 92, E 103, E 110, 140, E 384, E 448 3, E 407, E 562, E 883, E 1181, 1245, E 1351, E 1382, E 1558


SiC, bakelite bond

C-50, T-50 C-50, T-50, El-13 共Pure copper兲, El-14 共Bearing alloys兲

382


Mounting Hot Compression Resin Bakelite Cold Mounting Resin Acrylics Mounting Time 8–9 Time 6 – 10 min Minutes Minutes/Hours Grinding T-50: FG 4: This step can often be omitted. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-50 and T-50: To remove deformation after the last FG step etch with 100 mL water mixed with 100 mL ethanol and 10 g iron 共III兲 nitrate before the P 1 step. C-50 and T-50: For Cu and Cu alloys a chemical mechanical polishing can be obtained in the last polishing step by mixing 98 共96兲 mL colloidal silica with 1 mL 共2 mL兲 H2O2 共30 %兲 and 1 mL 共2 mL兲 ammonia solution 共25 %兲. An alternative is adding a few drops of the nitrate etchant mentioned above to the colloidal silica during the polishing. Electrolytic polishing: Pure copper: El-13. Copper bearing alloys: El-14. Contemporary Method C-50 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 P2 Polishing Cloth, napDisk/Cloth SiC paper SiC paper RCD, soft Cloth, less, soft, napless, med hard, porous, wov, wool syn Abrasive Type SiC SiC Dia, spr or Dia, spr or Silica susp susp See note Grit or Grain P220 P320 9 3 0.04/ 0.05 Size ␮m Lubricant Type Water Water Alco or wat Wat-oil Rotation 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp Comp Comp Contra contra Force per Specimen 20 共4.4兲 20 共4.4兲 30 共7兲 2.5 共5.7兲 15 共3.3兲 N 共lb兲 Time Until plane 0.5–1 3–4 5 1–2 Minutes

Chapter 13


Traditional Method T-50 共For definitions of parameters and consumables Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 FG 4 P1 P2 Polishing Cloth, Disk/ SiC SiC SiC SiC SiC Cloth, napCloth paper paper paper paper paper napless, less, med hard, hard, wov, wov, silk wool Abrasive SiC SiC SiC SiC SiC Dia, spr Dia, spr Type or susp or susp Grit or Grain Size ␮m Lubricant Type Rotation Disk/ Holder rpm/ rpm Comp/ Contra

P220

P320

P500

P1200

P2400

6

3

Water

Water

Water

Water

Water

Wat-oil

Wat-oil

Pure Cu

共see P3 Cloth, napless, soft, porous, syn Silica See note 0.04/ 0.05

300/150 300/150 300/150 150/150 150/150 150/150 150/150 150/150

Comp or contra Force per 20 Specimen 共4.5兲 N 共lb兲 Time Until Minutes plane Etchants Material

383



Comp

Comp

Comp

Comp

Contra

20 共4.5兲

20 共4.5兲

25 共5.7兲

25 共5.7兲

15 共3.3兲

0.5–1

0.5–1

0.5–1

0.5–1

3–4

3–4

1

Etchants 共see Table 12.2兲 26, 27, 28, 29, 30, 31d, 32, 33, 34b, 35, 36, 37, 38, 39, 40, 41, 42, 8b, 210, 215 43, 28


Chemical polish and etch

384


Material/Preparation Tables 51 Material: Pure gold. Au alloys Material Properties: Body-centered cubic, 19.3 g / cm3, 1063° C 共1945° F兲 Comments on Material: Gold belongs to the precious metals which include the platinum-group metals 共see Material/Preparation Tables 57兲, gold and silver, Pure gold, 99.99 % is seldomly used, most often gold is alloyed with silver, copper, nickel, or the platin-metals. Gold is the most ductile metal; it can be rolled to a thickness of 1 / 12 000 mm. Gold is used for jewelry and has a number of industrial applications. Often gold is used as a coating on other materials, and for electronic parts gold is used as coatings for certain components 共see Section 7.10.3 and Material/Preparation Tables 22 and 26兲. Pure gold, being very soft and ductile, is very difficult to prepare; deformation and smearing are difficult to avoid. Also, there is a risk of embedded abrasive grains in the specimen surface. Some alloys are harder and therefore easier to prepare. Sectioning: Because of the high price of gold, the wet abrasive cutting should be with a thin cut-off wheel to reduce the kerf loss. Cutting is best done on a precision cut-off machine using SiC bakelite bond cut-off wheels 0.5 mm 共0.02 in兲 thick and with an efficient cooling. In the case of examinations of coatings, the cutting should be done correctly 共see Material/Preparation Tables 08–10兲. Also, it can be of advantage to mount the specimen in epoxy before cutting to stabilize the coating 共see below兲. If using shearing, the strong deformation of the edge should be taken care of when plane grinding the specimen. Mounting: Hot and cold mounting can be used. Very often coatings should be examined and the correct hot mounting material, with a filler, should be used. Also, cold mounting with epoxy may be satisfactory 共see Sections 3.1.3 and 3.11兲. Grinding: If following a proper cutting, grit P220 grinding paper should be avoided, starting with grit P320. To reduce the induction of deformation in the material, the grinding paper can be covered with a thin layer of wax, or the paper can be “worn-in” with a hard specimen for a few seconds. It is important that all deformation from the previous step is removed. In the case of embedded SiC grains in the specimen surface, use Method C-51. To avoid embedded abrasive grains 共see Section 13.6.4兲, a softer grinding/polishing surface should be used. In the case of embedded grains the FG 2 step of Method C-51 can be changed to a hard, nonwoven, synthetic cloth. Also diamond paste, fixing the grains in the cloth, can be used. As an alternative to C-51, Method C-58 for silver can be used. For the softest materials, Method C-51 should be used. Polishing: For pure gold and alloys with a high gold content chemical mechanical polishing can be used for the last polishing step 共see below兲. Etching: See etchants below. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention


Method C51

Chapter 13

Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure


E 112, E 930, E 1181, E 1382 E 562, E 1245, E 1382

E E E E

10, E 18, E 92, E 103, E 110, 140, E 384, E 448 3, E 407, E 562, E 883, E 1181, 1245, E 1351, E 1382, E 1558


385

C-51, T-51 C-51, T-51

C-51, T-51 C-51, T-51 C-51, T-51


SiC, bakelite bond, 0.5 mm 共0.02 in兲 thick

Mounting Hot Compression Resin Bakelite/Bakelite Cold Resin Mounting with a Filler Mounting Time 8–9 Time Minutes Minutes/ Hours

Acrylics/ Epoxy 6 – 10 min/ 6–8 h

Grinding C-51: The step FG 2 can be changed to a hard, nonwoven, synthetic cloth if embedded abrasive grains are a problem using the RCD. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-51 and T-51: Both methods can be finished with chemical mechanical polishing: Step P 3 in C-51 with alumina 共0.05 ␮m兲 added a few drops of etchant 62: 1 – 5 g CrO3, 100 mL HCl 共see Etchants below兲. C-51: For certain alloys the step P 1 can be changed to 3 ␮m diamond, followed by P 2 from Method T- 51 for 2 – 8 min so that P 2 and P 3 are omitted. T-51: Can be finished with P 3 from C-51. T-51: Steps FG 3 and FG 4 can be changed to P 1 from C-51. In some cases P 1 can be omitted, and P 2 changed to 1 ␮m diamond.

386


Contemporary Method C-51 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 P2 P3 Polishing Cloth, nap- Cloth, Disk/Cloth SiC paper SiC paper RCD, Cloth, napless, soft napless, less, med soft, soft, hard, porous, wov, silk wov, wool syn Abrasive SiC SiC Dia, Dia, Dia, Alumina Type spr or spr or spr or 共see note兲 susp susp susp Grit or Grain P220 P320 9 6 3 0.02/ 0.05 Size ␮m Lubricant Water Water Alco or Wat-oil Wat-oil Type wat Rotation 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp Comp Comp Comp Comp Contra Force per 20 共4.5兲 20 共4.5兲 25 共5.7兲 20 共4.5兲 20 共4.5兲 10 共2.3兲 Specimen N 共lb兲 Time Until 0.5–1 5 5 3 1 Minutes plane

Traditional Method T-51 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 FG 4 P1 P2 Polishing Cloth, Disk/Cloth SiC SiC SiC SiC SiC Cloth, med paper paper paper paper paper napless, nap, med soft, hard, syn wov, wool Dia, Abrasive SiC SiC SiC SiC SiC Dia, spr Type spr or or susp susp Grit or Grain 320 500 1000 2400 4000 3 0.25 Size ␮m Lubricant Water Water Water Water Water WatWatType oil oil

Chapter 13




300/ 150 300/ 150 300/ 150 300/ 150 300/ 150 150/ 150

387

150/ 150


Comp

Comp

Comp

Comp

Comp

Comp

20 共4.5兲

20 共4.5兲

20 共4.5兲

20 共4.5兲

20 共4.5兲

15 共3.4兲

Until plane

0.5–1

0.5–1

0.5–1

1

4

2–8

Etchants Material Pure Au Au alloys ⬎90 % noble metals ⬍90 % noble metals

Etchants 共see Table 12.2兲 61, 62 63 64b, 62 63 61 65

Uses General structure Chemical polish and etch General structure Chemical polish and etch General structure General structure

Material/Preparation Tables 52 Material: Pure lead. Pb alloys. Pb bearing alloys Material Properties: Lead: Face-centered cubic, 11.34 g / cm3, 327° C 共621° F兲, HV 25–40. Lead bearing alloys: 0.9–11.0 % tin, 3–16 % antimony, 0.1–0.7 % copper, arsenic, bismuth, zinc, aluminum, cadmium 共weight %兲. Comments on Material: Lead is a very soft and ductile metal with a low melting point and a recrystallization temperature around 20° C 共68° F兲. Lead and most lead alloys are toxic both when inhaled and ingested. Pure lead is difficult to prepare, whereas bearing alloys are less difficult. After cold working lead rapidly recrystallizes. The cold work developed during sectioning and grinding should be kept at a minimum to avoid development of a pseudostructure through recrystallization. Also, abrasive grains are easily embedded in the specimen surface. No “contemporary” 共C兲-method for lead is available. C-52 describes a method based on etching between steps. T-52 is a “normal” “traditional” method. Method C-52 with etching between steps is recommended for pure lead. Sectioning: Abrasive wet cutting of pure lead and lead alloys can be done with a thin SiC bakelite cut-off wheel, preferably on a precision cutting machine. Also, a toothed cut-off wheel can be used. Pure lead also can be cut by using a sharp knife or a band saw or hand saw with fine teeth. If a microtome is available, very good surfaces can be obtained so that grinding is not needed 共see Section 2.7.6兲. In the case of examination of corrosion products 共batteries兲, the specimen should be impregnated before sectioning 共see Section 3.10兲.

388


Mounting: As a rule pure lead and lead alloys should not be hot compression mounted, both because of the low recrystallization temperature and because of voids and pores in the alloys that possibly may collapse under the high pressure of hot mounting. To obtain the lowest possible temperature during cold mounting, epoxy should be used 共see Section 3.8.3兲. Grinding: To minimize the risk of embedded SiC grains in the specimen surface, the grinding paper can be treated with wax and a low pressure is used. Also paraffin can be used instead of water. In both cases an abundant flow of liquid should be used to secure the removal of loose grains. In Method C-52 the specimen is etched after the last grinding step 共FG 2兲 to remove deformation from grinding 共see below兲. Polishing: It is important that the deformation from the grinding is removed during the rough polishing step. For pure lead chemical mechanical polishing is recommended for the last polishing step 共see Method C-52 below兲. Lead and some lead alloys are suited for electrolytical polishing. Etching: See below. ASTM Standard 共See Section 12.4兲 Method B 487 C-52, T-52


E 112, E 930, E 1181, E 1382 E 562, E 1245, E 1382

C-52, T-52, El-15 C-52, T-52

E E E E

C-52, T-52

10, E 18, E 92, E 103, E 110, 140, E 384, E 448 3, E 407, E 562, E 883, E 1181, 1245, E 1351, E 1382, E 1558

C-52, T-52, El-15 C-52, T-52


SiC bakelite bond cut-off wheel, 0.5 mm 共0.02 in兲 thick, low speed, very careful, see also above.

Chapter 13


389

Mounting Hot Compression Resin Mounting

Cold Mounting Resin

Time Minutes

Time Minutes/Hours

Acrylics/epoxy w. lowest possible peak temp. 6 – 8 min/ 12– 24 h

Grinding T-52: PG, FG 1 and FG 2: Charge SiC papers with wax or use paraffin instead of water. C-52: Instead of water, paraffin is used for SiC steps. C-52: After FG 2 the specimen is etched in Solution 1: 15 mL acetic acid, 15 mL nitric acid 共65 %兲, 60 mL glycerol. Do not store, use fresh solution at 80° C 共176° F兲. The solution is etchant 113 below. See also alternative below. C-52: As an alternative to Solution 1, Solution 2 can be used: 100 mL hydrogen peroxide 共30 %兲 mixed with 139 mL ammonia 共25 %兲. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-52 and T-52: For pure lead use chemical mechanical polishing with last step, P 3: Solution 3: 84 mL glycerol, 8 mL acetic acid 共96 %兲, 8 mL ammonia 共25 %兲. 10 mL of Solution 3 is added to 90 mL colloidal silica. Also a mixture of 90 mL silica and 10 mL hydrogen peroxide 共30 %兲 can be used. A third possibility is adding a few drops of ammonium tartrate to the silica. T-52: P 2: This step can often be omitted. Contemporary Method Section 13.2.2.兲 Grinding/ PG Polishing Disk/Cloth SiC paper

C-52 共For definitions of parameters and consumables see

Abrasive Type Grit or Grain Size ␮m

FG 1

FG 2

FG 3

P1

P2

P3

SiC paper

SiC paper

SiC paper

Cloth, med. nap, soft, syn


SiC

SiC

SiC

SiC

P320

P500

P1200

P2400


Dia, spr or susp 1

Silica, see note 0.04/ 0.05

390


Lubricant Type Rotation Disk/Holder rpm/rpm Comp/Contra Force per Specimen N共lb兲 Time Minutes

Paraffin Paraffin Paraffin Paraffin Wat-oil

Wat-oil

300/ 150 300/ 150 300/ 150 300/ 150 150/ 150

150/ 150

150/ 150

Comp 15 共3.4兲

Comp 15 共3.4兲

Comp 15 共3.4兲

Comp 15 共3.4兲

Comp 20 共4.5兲

Comp 15 共3.4兲

Contra 10 共2.2兲

0.5–1

0.5–1

0.5–1

0.5–1

3–4

3

1–2



Abrasive Type


FG 1

FG 2

P1

P2

P3

SiC paper

SiC paper



SiC

SiC

SiC

320

500

1200

Dia, spr or susp 9

Dia, spr or susp 3


Water

Water

Water

Alco or wat

Wat-oil

150/ 150

150/ 150

150/ 150

150/ 150

150/ 150

150/ 150

Comp 10–20 共2.2–4.5兲

Comp 10–20 共2.2–4.5兲

Comp 10–20 共2.2–4.5兲

Comp 15–20 共3.4–4.5兲

Comp 15–20 共3.4–4.5兲

Contra 10 共2.2兲

Until plane

0.5–1

0.5–1

4–5

3

2

Etchants Material Pure Pb Pure Pb, Pb+ ⬍ 2Sb, Pb+ ⬎ 2Sb, Pb+ Ca Pb+ ⬍ 2Sb Pb+ ⬎ 2Sb

Etchants 共see Table 12.2兲 57, 112 113 114, 115, 57, 74b 114, 57, 74b

0.04/ 0.05

Uses General structure For alternate polishing and etching General structure General structure

Chapter 13

Pb+ Ca Pb alloys Babbitt


112 116, 117b 74b

391

General structure General structure General structure

Material/Preparation Tables 53 Material: Pure magnesium and Mg alloys Material Properties: Magnesium: Hexagonal close-packed, 1.74 g / cm3, 650° C 共1202° F兲, HB共B兲 35. Magnesium alloys: 1.2–10 % aluminum, 0.15–1.5 % manganese, 0.2–3.0 % rare earths, 1.8–3.0 % thorium, 0.5–5.7 % zinc, 0.6–0.7 % zirconium 共weight %兲. Comments on Material: Magnesium is the light metal with the lowest specific gravity in practical use. Pure magnesium is rarely used because of the low strength, but in form of alloys based on the five alloying elements mentioned above. Magnesium alloys are normally available as low-pressure casting alloys, high-pressure casting alloys, and wrought alloys. Magnesium alloys are not universally classified, but in ASTM “Practice for Temper Designation of Magnesium Alloys, Cast and Wrought” 共B 296兲 a designation is stated. Magnesium is soft and will easily cold-work making it difficult to prepare. As the dust from grinding may ignite, all sectioning and grinding should be with a cooling fluid. Pure magnesium and many alloys are sensitive to water. The preparation of Mg cast and wrought alloys vary considerably, and therefore a number of suggestions are stated below. For harder alloys use Method C-53. Sectioning: At examination of die castings it should be recognized that the microstructure varies strongly through the casting. This should be considered when selecting the sample. Wet abrasive cutting with an SiC cut-off wheel. Care should be taken to avoid excessive deformation of the cut surface and the fixing of the work piece should be as gentle as possible. As mentioned above the magnesium swarf/dust may ignite and even development of hydrogen may take place at the contact with water, and special precautions should be made. If cutting with a shear or a band saw, at least 1 mm of the cut surface should be removed during the plane-grinding step. Mounting: The pressure that is needed for hot mounting may cause cold-work in the specimen, and cold mounting should be preferred. In case of heat-sensitive alloys only epoxy should be used for cold mounting, keeping the peak temperature low 共see Section 3.8.3兲. Grinding: The plane grinding should be performed with the finest possible grit. If the sectioned surface is not very rough, the first grinding step can be with grit P320 or P500 as deep deformations are very difficult to remove at the later steps. For water-sensitive materials use a mixture of glycerol and ethanol, 1:3, instead of water, or pure ethanol for the finer grits. In case of embedded SiC particles in the specimen surface, charge the surface of the grinding paper with wax.

392


Polishing: For most materials water should be totally avoided for polishing. Ultrasonic cleaning in ethanol between polishing steps is recommended. During the polishing a relief may develop between the matrix and hard particles; to avoid this use Method C-53. Also this method should give the smallest amount of embedded abrasive grains in the specimen surface. By the final cleaning, water should be avoided for most alloys. Use soap and ethanol, and avoid using cotton after the last polishing step because new scratches may be introduced. Pure magnesium and most alloys can be electrolytically polished. Etching: Magnesium having a hexagonal close-packed crystal structure can be examined in polarized light. For enchants, see below. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure


Method C-53

E 112, E 930, E 1181, E 1382

C-53, T-53, El-16 C-53, T-53

E 562, E 1245, E 1382

E E E E


10, E 18, E 92, E 103, E 110, C-53, T-53 140, E 384, E 448 3, E 407, E 562, E 883, E 1181, E 1245, C-53, T-53, 1351, E 1382, E 1558 El-16 C-53, T-53


SiC, bakelite bond


Resin Time Minutes

Cold Mounting


Acrylics 6 / 10 min

Grinding C-53 and T-53: If the material is very water sensitive use ethanol or a mixture 1:3 of glycerol and ethanol instead of water. C-53: FG 1: For water-sensitive materials use water-free lubricant.

Chapter 13


393

Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing Cleaning: For most alloys cleaning between polishing steps should be done without water. C-53 and T-53: If the specimen material is sensitive to water use water-free polishing media and lubricants. C-53 and T-53: The final cleaning can be done on a rotating polishing cloth, med nap, soft, syn, only with ethanol. C-53: P 3: This step can be changed to step P 2 in Method T-53, only with 1 ␮m diamond in 2 min. C-53: Polishing step, P 3: Mix silica 1:1 with ethanol. T-53: P 1: This step can be changed to a step like FG 3 with SiC paper grit 2400. T-53: P 2: The cloth can be changed to napless, med hard, wov, wool. T-53: P 3: For pure Mg: Use same data as P 2 except grain size: 1 ␮m. Contemporary Method C-53 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 P3 Polishing Cloth, Cloth, Disk/Cloth SiC RCD, Cloth, napless, soft, napless, paper soft napless, med hard, porous, syn hard, wov, wov, wool silk Abrasive SiC Dia, spr or Dia, spr or Dia, spr or Silica, see Type susp susp susp above Grit or Grain P500 9 6 3 0.04/ 0.05 Size ␮m Lubricant Water Alco or wat Alco or wat Wat-oil Type Rotation 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp Comp Comp Comp Contra Force per 20–30 共4.5–7兲 20–30 30 共7兲 15 共3.3兲 10 共2.2兲 Specimen 共4.5– 7兲 N 共lb兲 Time Until plane 5–8 4 3–5 1–2 Minutes

394


Traditional Method T-53 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 P3 Polishing Cloth, Cloth, Disk/Cloth SiC SiC SiC SiC Cloth, napless, paper paper paper paper napless, med. soft, nap hard, wov, silk soft, syn porous, syn Abrasive Type SiC SiC SiC SiC Dia, spr Dia, spr Silica or susp or susp Grit or 220 320 500 1200 15 3 0.04/ 0.05 Grain Size Lubricant Water Water Water Water Alco or Alco or Type oil oil Rotation 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp Comp Comp Comp Comp Comp Contra Force per 20–30 20–30 20–30 10–20 30 共7兲 25 共5.7兲 15 共3.4兲 Specimen 共4.5–7兲共4.5–7兲共4.5–7兲共2.3–4.5兲 N 共lb兲 Time Until 0.5–1 0.5–1 1–2 3–4 3–4 0.5–1 Minutes plane Etchants Material Pure Mg

Mg-Mn Mg-Al, Mg-Al-Zn 共Al+ Zn⬍ 5 % 兲

Mg-Al, Mg-Al-Zn 共Al+ Zn⬎ 5 % 兲 Mg-Zn-Zr and Mg-Zn-Th-Zr

Mg-Th-Zr Mg-rare earth-Zr

Etchants 共see Table 12.2兲 118, 119, 74a, 120, 121, 122 123 119, 74a, 124, 122 118, 119, 74a, 125, 124, 123, 122 120, 125, 126, 127 124, 126, 127 118, 119, 74a, 125, 124, 121, 122 120, 125, 126, 127 118, 119, 74a, 1d, 128, 124, 126, 127, 121, 122 120, 121 118, 119, 74a, 1d, 124, 127, 121, 122 120, 121

Uses General structure Stainfree polish-etch General structure General structure Phase identification Grain structure General structure Phase identification General structure Phase identification General structure Phase identification

Chapter 13


395

Material/Preparation Tables 54 Material: Pure manganese. Mn alloys Material Properties: Manganese: Body-centered cubic or body-centered tetragonal, 7.2 g / cm3, 1260° C 共2300° F兲, HRC 35. Comments on Material: Manganese is a metal resembling iron, but it is harder and very brittle. It is primarily used as an alloying element, examples are with steel, where 0.2–2 % manganese is used, brass with up to 3 % and bronze with 5 – 15 % Mn. Pure manganese and alloys with high manganese content are not difficult to prepare. In the case of most alloys, the Material/Preparation Tables covering the base metal should be followed. Sectioning: Wet abrasive cutting with an Al2O3 bakelite bond cut-off wheel. Mounting: Hot and cold mounting can be used. Grinding: No special precautions are needed. Polishing: Pure manganese and some alloys can be electrolytically polished. Etching: See below. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure


Method C-54

E 112, E 930, E 1181, E 1382

C-54, T-54, El-01 C-54, T-54

E 562, E 1245, E 1382

E 10, E 18, E 92, E 103, E 110, E 140, E 384, E 448 E 3, E 407, E 562, E 883, E 1181, E 1245, E 1351, 1382, E 1558


C-54, T-54, El-01 C-54, T-54


C-54, T-54


396


Mounting Hot Compression Resin Bakelite Cold Mounting Resin Acrylics Mounting Time 8–10 Time 6 – 10 min Minutes Minutes/Hours Grinding C-54: PG: For pure Mn use SiC paper grit P220. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Contemporary Method C-54 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 Polishing Disk/Cloth Dia, disk, RCD, hard Cloth, napless, Cloth, napless, fixed, res hard, wov, syn soft, porous, syn Abrasive Type Diamond Dia, spr or susp Dia, spr or Alumina susp Grit or Grain P220 6 3 0.02/ 0.05 Size ␮m Lubricant Type Water Alco or wat Alco or wat Rotation 300/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or contra Comp Comp Contra Force per 30 共7兲 40 共9兲 30 共7兲 15 共3.4兲 Specimen N 共lb兲 Time Until plane 4 4 2 Minutes

Chapter 13


397

Traditional Method T-54 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 Polishing Cloth, Disk/Cloth SiC paper SiC paper SiC paper SiC paper Cloth, napless, napless, soft, hard, porous, wov, syn syn Abrasive Type SiC SiC SiC SiC Dia, spr or Alumina susp Grit or Grain P220 P320 P500 P1200 3 0.02/ 0.05 Size ␮m Lubricant Type Water Water Water Water Alco or wat Rotation 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp or Comp or Comp Comp Contra contra contra contra Force per 35 共8兲 35 共8兲 35 共8兲 35 共8兲 35 共8兲 15 共3.7兲 Specimen N共lb兲 Time Until 0.5–1 0.5–1 0.5–1 4 1–2 Minutes plane Etchants Material Mn-Fe, Mn-Ni, Mn Cu, Mn alloys Pure Mn, Mn-Cu, and small additions of Ni, Cu, Fe, Ge



942

General structure

398


Material/Preparation Tables 55 Material: Pure molybdenum. Mo alloys. Pure niobium„Columbium…. Nb „Cb… alloys. Pure rhenium. Re alloys. Pure tantalum. Ta alloys. Pure tungsten. W alloys. Pure vanadium. V alloys Material Properties: Molybdenum: Body-centered cubic, 10.2 g / cm3, 2620° C 共4748° F兲, HV 200. Niobium 共Columbium兲: Rhombohedral, 8.4 g / cm3, 1950° C 共3542° F兲. Rhenium: Hexagonal close packed, 20.53 g / cm3, 3000 °C 共5432° F兲, HK 200. Tantalum: Body-centered cubic, 16.6 g / cm3, 2996° C 共5425° F兲, HV 110. Tungsten: Body-centered cubic, 19.3 g / cm3, 3410° C 共6170° F兲, HV 350. Vanadium: Body-centered cubic, 5.96 g / cm3, 1710 °C 共3110° F兲, HB 72. Comments on Material: Molybdenum, niobium, rhenium, tantalum, tungsten, and vanadium all having high melting points belong to the refractory metals. They are seldomly used pure but mostly as alloying elements. Pure niobium, rhenium, tantalum, and vanadium are soft and ductile, difficult to prepare. Pure molybdenum and tungsten are harder and more brittle. All metals have a low machinability and this combined with development of deformation and cold-work makes it difficult to obtain a true microstructure by mechanical polishing; often it must be combined with chemical mechanical polishing. Sectioning: Wet abrasive cutting can be made with a SiC bakelite bond cut-off wheel. Due to the poor machinability and to minimize the deformation, a relatively soft wheel, as thin as possible, should be used. Mounting: Both hot and cold mounting can be used. In case of examination of porosity, a vacuum impregnation with epoxy may be useful 共see Section 3.10兲. For mounting of wires, see Section 3.12. Foils and wire samples should preferably be cold mounted to avoid induction of deformation at hot compression mounting. Grinding: Because of the poor machinability the SiC grinding papers should only be used as long they are cutting efficiently; if not, cold work and deformation will develop. In case of alloys with hard nonmetallic precipitates, it may be of advantage to use Method C-55 to avoid relief and pull-outs. Variation regarding specific materials, see below. Polishing: It is important that the deformations from grinding are removed during the rough polishing step, and if needed this step must be prolonged. It can be difficult to remove all deformation by mechanical polishing and often chemical mechanical polishing can be an advantage 共see below兲. Also electrolytic polishing can be recommended 共see below for methods covering the different metals兲. Etching: See etchants below. Molybdenum may be electrolytically etched 共see Method El-01兲.

Chapter 13


399

Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries


Method C-55

E 112, E 930, E 1181, E 1382


E 562, E 1245, E 1382

C-55, T-55, Elmethods, see below C-55, T-55

E E E E E E

Microstructure

10, E 18, E 92, E 103, 110, E 140, E 384, 448 3, E 407, E 562, E 883, 1181, E 1245, E 1351, 1382, E 1558


C-55, T-55

C-55, T-55 Elmethods, see below C-55, T-55


SiC, bakelite bond, a thin wheel

Mounting Hot Compression Resin Bakelite Cold Mounting Resin Acrylics Mounting Time 8–9 Time 6 – 10 min Minutes Minutes/Hours Grinding Niobium: T-55: An extra step with P4000 SiC paper can be added after FG 4. Rhenium: Method C-55 can be recommended. Tantalum and other very soft metals: C-55: A grinding step with P320 SiC paper can be used between PG and FG 1 steps. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued.

400


Polishing Tungsten: C-55, T-55: The polishing step P 1 may be prolonged. Molybdenum: C-55 and T-55: To remove deformed layers, the P 2 step can be used with 0.05 ␮m alumina dispersed in a small amount of a 30 % K3Fe 共CN兲6 aqueous solution. Molybdenum, niobium, tantalum, tungsten: C-55, T-55: To remove deformed layers, the P 2 step can be used with colloidal silica 共95 mL兲 added 5 mL of a 20 % aqueous solution of chromium 共VI兲 oxide 共20 g CrO3 in 100 mL distilled water兲. Molybdenum: C-55 and T-55: For last step mix 96 mL of colloidal silica with 2 mL of ammonia 共25 %兲 and 2 mL of hydrogen peroxide 共30 %兲. Niobium, pure vanadium: C-55, T-55: The last polishing step can be done as chemical mechanical polishing: Mix 80 mL of colloidal silica with 20 mL of hydrogen peroxide 共30 %兲. Tungsten, vanadium: C-55 and T-55: For last step mix 95 mL of colloidal silica with 5 mL of hydrogen peroxide 共30 %兲. Rhenium: C-55, T-55: The last polishing step can be done as chemical mechanical polishing: 15 g potassium ferricyanide 共K3Fe共CN兲6, 2 g sodium hydroxide 共NaOH兲, 100 mL distilled water and equal part of silica. Electropolishing: Molybdenum: El-01, Vanadium: El-22, Tungsten: El-21 Contemporary Method C-55 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 Polishing Cloth, napDisk/Cloth Dia, disk, RCD, soft Cloth, less, soft, fixed, res napless, porous, syn hard, wov, silk Abrasive Type Diamond Dia, spr Dia, spr Silica, or susp or susp see above Grit or Grain P220 9 3 0.04/ 0.05 Size ␮m Lubricant Type Water Alco or wat Alco or wat Rotation 300/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp Comp Contra Contra Force per 20–30 20–30 30 共7兲 10–15 Specimen 共4.5–7兲共4.5–7兲共2.3–3.4兲 N 共lb兲 Time Until plane 3–5 3–4 2–5 Minutes

Chapter 13


401

Traditional Method T-55 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 FG 4 P1 P2 Polishing Cloth, Disk/Cloth SiC SiC SiC SiC SiC Cloth, paper paper paper paper paper napless, napless, soft, hard, wov, syn porous, syn Abrasive SiC SiC SiC SiC SiC Dia, spr Silica, Type or susp see above Grit or Grain P220 P320 P500 P1200 P2400 3 0.04/ 0.05 Size ␮m Lubricant Water Water Water Water Water Alco or Type wat Rotation 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/contra Comp or Comp or Comp or Comp Comp Comp Contra contra contra contra 20–30 20–30 20–30 20–30 20–30 20 共4.5兲 20 共4.5兲 Force per 共4.5–7兲共4.5–7兲共4.5–7兲共4.5–7兲共4.5–7兲 Specimen N 共lb兲 Time Until 0.5–1 0.5–1 0.5–1 0.5–1 3–5 2–5 Minutes plane Etchants Material Mo base As cast Nb and Nb alloys Re base Pure Ta Ta alloys

Pure W As cast W-Th Pure V V alloys

Etchants 共see Table 12.2兲 98c, 129, 130, 131 132 a 129, 66, 158, 159, 160, 161, 162, 163 164, 129, 160 13b, 98c, 132b, 170a 177 159, 66, 178, 163, 161, 179 164 158 98c, 131 132a 209 170b, 165b 197, 198 199, 198

Uses General structure Chemical polish prior to etching General structure Grain boundaries General structure General structure General structure Grain boundaries and inclusions Grain boundaries—retains carbide precipitate General structure Chemical polish prior to etching General structure General structure Grain boundaries General structure

402


Material/Preparation Tables 56 Material: Pure nickel. Ni alloys. Ni Based super-alloys Material Properties: Nickel: Face-centered cubic, 8.89 g / cm3, 1452° C 共2646° F兲. Nickel-copper alloys: 28–34 % copper, 1 % manganese, 1 % iron, carbon, aluminum. Nickel-iron alloys: 0.1 % carbon, 0.2 % manganese, 0.2 % iron. Super alloys 共nickel based兲: Heat resistant casting alloys: 8–15 % chromium, 2–28 % molybdenum 0.5–2 % niobium, 0.8–4.7 % titanium, 0.5–6 % aluminum, 1–18.5 % iron, 0.1–10 % tungsten, 0.3–1 % tantalum, 2.5–18.5 % cobalt, carbon, zirconium, boron. Wrought heat resistant alloys: 1–8 % iron, 2–19 % cobalt, 5–50 % chromium, 0.4–5 % titanium, 3–25 % molybdenum, carbon, tungsten, niobium, aluminum, zirconium, boron, tantalum 共weight %兲. Comments on Material: Pure nickel and nickel-copper alloys are mostly used for the good resistance to corrosion, also for this purpose nickel is used for coatings. Nickel being somewhat magnetic, it makes special magnetic alloys with iron. The superalloys are very heat resistant. Nickel is a metal with characteristics close to iron and cobalt; it is tough and the machinability is relatively low. Pure nickel being tough and with a tendency to cold-work and deformation is relatively difficult to prepare. Nickel alloys are less difficult. Sectioning: Wet abrasive cutting is done with an SiC bakelite bond cut-off wheel with an efficient cooling. A thin and relatively soft wheel is recommended to secure a cut with the lowest deformation possible. Very often shearing or other more rough sectioning methods should be avoided, as serious distortions and cold-work could be introduced. Use only these methods for sectioning of large pieces later to be sectioned by wet cutting. Mounting: Hot mounting and cold mounting can be used. In the case of examination of nickel coatings, see Material/Preparation Tables 08–10. Grinding: Due to the toughness of nickel the SiC grinding papers shall not be used for a too long time, to avoid smeared layers. Polishing: It is important that the rough polishing step has removed the deformation from the grinding. In case of pure nickel and soft alloys, it may be necessary to add a silica step to the methods 共see below兲. Electrolytic polishing can be recommended. Often a very short electrolytic polishing after mechanical polishing will remove smeared material 共see Method El-17兲. Etching: Nickel is relatively difficult to attack, strong solutions are needed 共see etchants below兲. Purpose Case of coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries


Method C-56

E 112, E 930, E 1181, E 1382

C-56, T-56, El-17

Chapter 13

Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure


403

E 562, E 1245, E 1382

C-56, T-56

E E E E E

C-56, T-56, El-17 C-56, T-56, El-17

10, E 18, E 92, E 103, E 110, 140, E 384, E 448 3, E 407, E 562, E 883, 1181, E 1245, E 1351, E 1382, 1558


C-56, T-56


SiC, bakelite bond

Mounting Hot Compression Resin Bakelite Cold Mounting Resin Acrylics Mounting Time 8–9 Time 6 – 10 min Minutes Minutes/Hours Grinding C-56: PG: For pure nickel and the most ductile alloys SiC paper grit P220/ 320 should be used. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing Pure Ni and Ni-Cu alloys: T-56: P 3 can be followed by or replaced by a step with silica, see P 2 in Method C-56. C-56: P 2: Alumina 0.02/ 0.05 ␮m can be used instead of silica. T-56: In some cases FG 3 can be omitted. Contemporary Method C-56 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 Polishing Cloth, Disk/Cloth Dia, disk, RCD, soft Cloth, napless, soft, fixed, res napless, porous, hard, wov, syn syn

404


Abrasive Type

Diamond

Grit or Grain Size ␮m Lubricant Type Rotation Disk/Holder rpm/rpm Comp/Contra Force per Specimen N共lb兲 Time Minutes

P220

Dia, spr or susp 9

Dia, spr or susp 3

Silica 0.04/ 0.05

Water 300/ 300



150/ 150


Comp

Comp

Contra

30 共7兲

30 共7兲

15 共3.3兲

Until plane

4–6

4–5

2

Traditional Method T-56 共For definitions of parameters and consumables Section 13.2.2.兲 Grinding/ PG FG1 FG 2 FG 3 FG 4 P1 P2 Polishing Cloth, Disk/ SiC SiC SiC SiC SiC Cloth, napCloth paper paper paper paper paper napless, less, hard, hard, wov, wov, silk silk Abrasive SiC SiC SiC SiC SiC Dia, Dia, Type spr or spr or susp susp Grit or Grain Size ␮m Lubricant Type Rotation Disk/ Holder rpm/ rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

P220

P320

P500

P1000

P1200

Water

Water

Water

Water

Water

Comp

Comp

Comp

Comp

Comp

6

3

see P3 Cloth, med nap, soft, syn Dia, spr or susp 1

Alco Alco Alco or wat or wat or wat 300/150 300/150 300/150 150/150 150/150 150/150 150/150 150/150

Comp

Comp

Comp

25 共5.7兲 25 共5.7兲 25 共5.7兲 25 共5.7兲 25 共5.7兲 30 共7兲

30 共7兲

20 共4.5兲

Until plane

3

1–2

0.5–1

0.5–1

0.5–1

0.5–1

4

Chapter 13

Etchants Material Etchants 共see Table 12.2兲 Pure Ni and 133, 134, 47, 135, 136, 25, 108, 31c high Ni alloys 137 Ni-Ag 38, 138, 50, 139 Ni-Al 50, 140, 141, 142, 89, 143 Ni-Cr 144, 50, 83, 134, 145, 98, 146, 147, 13a Ni-Cu 38, 138, 50, 133, 140, 25, 134, 47, 48b, 94, 108, 34 Ni-Fe 50, 140, 141, 83, 134, 148, 40, 107, 149 74e, 25, 150 Ni-Mn 74e Ni-Mo 143 Ni-Ti 143, 151, 50, 133 Ni-Zn 152 Superalloys 94, 105, 138, 153, 12, 87, 89, 212, 226, 25, 94 107, 111, 13a 133 154 19b, 155, 156 22a 157 107

154 18 213


405

Uses General structure Grain boundary sulfidation General structure General structure General structure General structure General structure Orientation pitting General structure General structure General structure General structure General structure Grain size Reveals microstructural inhomogneity Grain boundary sulfidation Fine precipitation structure Differential matrix and nonmetallic staining For passive alloys 共for example, UNS Alloy N06625兲 Specific for UNS Alloys N10004 Submicroscopic structure in aged super alloys particularly for electron microscopy Stains the matrix when ␥⬘ precipitates are present ␥⬘ banding Pre-etch activation for passive specimens 共electrolytic etchant兲 Colors carbide and ␥⬘

406


Material/Preparation Tables 57 Material: Pure palladium. Pd alloys. Pure platinum. Pt alloys. Pure iridium. Ir alloys. Pure osmium. Os alloys. Pure rhodium. Rh alloys. Pure ruthenium. Ru alloys Material Properties: Palladium: Face-centered cubic, 12.16 g / cm3, 1553° C 共2827° F兲. Platinum: Face-centered cubic, 21.37 g / cm3, 1773.5° C 共3224° F兲. Iridium: Face-centered cubic, 22.42 g / cm3, 2350° C 共4262° F兲, HV 220. Osmium: Hexagonal, 22.48 g / cm3; 2700° C 共4892° F兲. Rhodium: Face-centered cubic, 12.5 g / cm3, 1985° C 共3605 °F兲, HV 122. Ruthenium: Hexagonal, 12.2 g / cm3, 2450° C 共4442° F兲. Comments on Material: The above-mentioned metals belong to the so-called platinum metals that belong to the precious metals with gold and silver. Platinum is used as base metal in a number of alloys used for jewelry and technical purposes. The other metals are to a high degree used as pure or as alloying elements in materials for the electronics, medical, and other industries. Palladium and platinum are soft ductile metals, difficult to prepare because of deformation and smearing. Iridium and rhodium, and especially the hexagonal close-packed ruthenium and osmium are harder and less difficult to prepare. Because of the high ductility, embedded abrasive grains in the specimen surface is a risk 共see below兲. No “contemporary” method is available for these metals, and C-57 is a variation of T-57. In case of harder alloys the C-methods, C-51 共se also Grinding below兲 and C-58 may be used. Sectioning: Because of the high price of the platinum metals, the wet abrasive cutting should be with a thin cut-off wheel to reduce the kerf loss. Cutting is best done on a precision cut-off machine using SiC bakelite bond cut-off wheels 0.5 mm 共0.02 in兲 thick with efficient cooling. In the case of examinations of coatings, the cutting should be done correctly 共see Material/Preparation Tables 08–10兲. Also, it can be of advantage to mount the specimen in epoxy before cutting to stabilize the coating 共see below兲. If using shearing, the strong deformation of the edge should be taken care of when plane grinding the specimen. Mounting: Hot and cold mounting can be used. If coatings should be examined the correct hot mounting material, with a filler, should be used. Also cold mounting with epoxy may be satisfactory 共see Sections 3.1.3 and 3.11兲. Grinding: If following a proper cutting, grit P220 grinding paper should be avoided, starting with grit P320. It is important that all deformation from the previous step is removed. Wax can be used to reduce the aggressiveness of the SiC paper, or the paper can be “dulled” by grinding a hard material in 1 – 5 s before use. In the case of embedded SiC grains in the specimen surface, use Method C-51 or C-58 to reduce the use of SiC grinding paper. To avoid embedded abrasive grains 共see Section 13.6.4兲, a softer grinding/polishing surface should be used. In the case of embedded grains the FG 2 step of Method C-51 or the FG 3 step of C-58 can be changed to a hard, nonwoven, synthetic cloth. Also diamond paste can be used to improve the fixation of the diamond grains.

Chapter 13


407

Polishing: Methods C-57 and T-57 both use diamond for the last polishing step. For use of silica for the last step see Methods C-51 and C-58. For chemical mechanical polishing 共etch-polishing兲 of ruthenium and osmium alloys see Etchants below. Etching: See below. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure


Method C-57

E 112, E 930, E 1181, E 1382

C-57, T-57

E 562, E 1245, E 1382

C-57, T-57

E E E E

C-57, T-57

10, E 18, E 92, E 103, E 110, 140, E 384, E 448 3, E 407, E 562, E 883, E 1181, 1245, E 1351, E 1382, E 1558


C-57, T-57 C-57, T-57


SiC, bakelite bond, 0.5 mm 共0.02 in兲 thick

Mounting Hot Compression Resin Bakelite Cold Resin Acrylics/epoxy Mounting Mounting Time Time 8–9 6 – 10 min/ 6 – 8 h Minutes Minutes/Hours Grinding See above. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-57: For pure metals use wat-oil lubricant in P 1 and P 2. T-57: P 2: This step can be changed to P 3 in C-57.

408


Contemporary Method C-57 Section 13.2.2.兲 Grinding/ PG FG 1 Polishing Disk/ SiC SiC Cloth paper paper


FG 3

SiC paper

Abrasive Type

SiC

SiC

SiC

Grit or Grain Size ␮m Lubricant Type Rotation Disk/ Holder rpm/rpm Comp/ Contra

P220

P320

P500

Water

Water

Water

300/ 150

300/ 150

300/ 150

Comp or contra Force per 15–20 Specimen 共3.4–4.5兲 N 共lb兲 Time Until Minutes plane

FG 4

P1

P2

P3

SiC SiC Cloth, paper paper napless, hard, wov, silk SiC SiC Dia, spr or susp P1200 P2400 6



Water Water Alco or wat 150/ 150/ 150/ 150 150 150


150/ 150

Comp

Contra

Comp Comp Comp Conmp Comp or contra 15–20 15–20 15–20 15–20 15–20 共3.4–4.5兲共3.4–4.5兲共3.4– 共3.4– 共3.4–4.5兲 4.5兲 4.5兲 0.5–1 0.5–1 0.5–1 0.5–1 4

Traditional Method T-57 共For definitions Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 Polishing Disk/Cloth SiC SiC SiC paper paper paper

Dia, spr or susp 0.25

Wat-oil

15 共3.4– 10–15 4.5兲共2.3– 3.4兲 2 1–2


FG 4

P1

P2

SiC paper

SiC paper

Cloth, med nap, soft, syn Dia, spr or susp 1 Wat-oil

Abrasive Type

SiC

SiC

SiC

SiC

SiC


P320

P500

P1000

P2400

P4000


Water

Water

Water

Water

Water

Wat-oil

Chapter 13



300/ 150 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150

Comp or contra 15–20 共3.4– 4.5兲 Until plane

Etchants Material Pure Pd Pd alloys ⬎90% noble metals ⬍90 % noble metals Pure Pt Pt alloys ⬎90 % noble metals ⬍90 % noble metals Pt-10 % Rh Os base

Rh base Ru base


409

150/ 150

Comp

Comp

Comp

Comp

Comp

Comp

15–20 共3.4– 4.5兲 0.5–1

15–20 共3.4– 4.5兲 0.5–1

15–20 共3.4– 4.5兲 0.5–1

15–20 共3.4– 4.5兲 0.5–1

15–20 共3.4–4.5兲

10–15 共2.3–3.4兲

4

2

Etchants 共see Table 12.2兲 61, 166, 62, 165a 166, 64a, 62, 165a 61 65 64a, 73a 167 64b, 73a 61 65 168 165a 165a 171 73b 73b

Uses General structure General structure General structure General structure General structure Electrolytic polish and etch General structure General structure General structure General structure General structure Etch-polish for viewing grains for polarized light General structure General structure Etch-polish for viewing grains for polarized light

Material/Preparation Tables 58 Material: Silver. Ag alloys Material Properties: Silver: Face-centered cubic, 10.5 g / cm3, 961° C 共1762° F兲, HV 25. Comments on Material: Silver is used for jewelry and in the electronics and chemical industries. Pure silver, like the other precious metals 共see Material/ Preparation Tables 51 and 52兲, is soft and ductile and therefore has a strong tendency to deformation and smearing during the preparation. Also, abrasive grains can be embedded in the specimen surface 共see Section 13.6.4兲. Silver alloys, like Ag-Cu, Ag-Pd, and Ag solders are harder and therefore easier to prepare. Often silver is used as a coating and if this coating should be examined the methods stated in Material/Preparation Tables 08–10 may be used.

410


Sectioning: Because of the relatively high price of silver, the wet abrasive cutting should be with a thin cut-off wheel to reduce the kerf loss. Cutting is best done on a precision cut-off machine using SiC bakelite bond cut-off wheels 0.5 mm 共0.02 in兲 thick with an effective cooling. In the case of examination of coatings, the cutting should be done correctly 共see Material/Preparation Tables 08–10兲. Also, it can be of advantage to mount the specimen in epoxy before cutting to stabilize the coating 共see below兲. If using shearing, the strong deformation of the edge should be taken care of when plane grinding the specimen. Mounting: Hot and cold mounting can be used. If coatings should be examined, the correct hot mounting material,with a filler, should be used. Also, cold mounting with epoxy may be satisfactory 共see Sections 3.1.3 and 3.11兲. Grinding: If following a proper cutting, grit P220 grinding paper should be avoided, starting with grit P320. Wax can be used to reduce the aggressiveness of the SiC paper, or the paper can be “dulled” by grinding a hard material in 1–5 s before use. It is important that all deformation from the previous step is removed. In the case of embedded SiC grains in the specimen surface, use Method C-58. To avoid embedded abrasive grains 共see Section 13.6.4兲, a softer grinding/ polishing-surface should be used. For this reason the FG 3 step of Method C-58 can be changed to a hard, nonwoven, synthetic cloth and possibly the FG 2 step can be omitted. Also diamond paste, fixing the grains in the cloth, can be used. As an alternative to C-58, Method C-51 for gold can be used. Polishing: For pure silver and alloys with a high content of silver, chemical mechanical polishing can be used for the last polishing step 共see below兲. Electrolytic polishing can be used for pure silver and certain alloys. Etching: See Etchants below. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure Phase identification


Method C-58

E 112, E 930, E 1181, E 1382

C-58, T-58, El-18 C-58, T-58

E 562, E 1245, E 1382

E E E E

10, E 18, E 92, E 103, E 110, 140, E 384, E 448 3, E 407, E 562, E 883, 1181, E 1245, E 1351, E 1382, E 1558

C-58, T-58 C-58, T-58, El-18 C-58, T-58, El-18

Chapter 13


411

Preparation Process 58 Sectioning SiC, bakelite bond, 0.5 mm 共0.02 in兲 thick

Cut-Off Wheel Mounting Hot Compression Mounting

Resin Time Minutes

Bakelite or bakelite w. filler 8–9

Cold Mounting


Acrylics/ Epoxy 6 – 10 min/ 6–8 h

Grinding See above. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-58: P 2: Chemical mechanical polishing of silver alloys can be done by adding a solution of 25 mL distilled water, 25 mL ammonia solution 共32 %兲 and 10– 20 mL hydrogen peroxide 共30 %兲 to 1000 mL of colloidal silica. C-58: P 2: This step can be changed to P 2 from Method T-58. Contemporary Method C-58 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 Polishing Disk/Cloth

SiC paper

SiC paper

SiC paper

Abrasive Type

SiC

SiC

SiC

Grit/Grain Size ␮m Lubricant Type

P220

P320

P500

Water

Water

Water

RCD, soft

Cloth, napless, hard, wov, silk Dia, spr Dia, spr or susp or susp 9 3

Alco or Wat-oil wat Rotation Disk/Holder 300/ 150 300/ 150 150/150 150/150 150/150 rpm/ rpm

Cloth, napless, soft, porous, syn Silica, see note above 0.04/ 0.05

150/150

412



Comp Comp Comp Comp Comp or contra 20 共4.5兲 20 共4.5兲 20 共4.5兲 25 共5.7兲 20 共4.5兲

Contra

Until plane

1

0.5–1

0.5–1

5

5

10 共2.2兲

Traditional Method Section 13.2.2.兲 Grinding/ PG Polishing Disk/Cloth SiC paper

T-58 共For definitions of parameters and consumables see

Abrasive Type

Grit or Grain Size ␮m Lubricant Type Rotation Disk/ Holder rpm/ rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

FG 1

FG 2

SiC paper

SiC

FG 3

FG 4

P1

P2

SiC paper SiC paper

SiC paper

SiC

SiC

SiC

SiC

Cloth, napless, med hard, wov, wool Dia, spr or susp

320

500

1000

2400

4000

3

Cloth, med nap, soft, syn Dia, spr or susp 0.25

Water

Water

Water

Water

Water

Wat-oil

300/ 150 300/ 150 300/ 150

300/ 150 300/ 150 150/ 150

Watoil 150/ 150

Comp Comp Comp or contra 15–20 15–20 15–20 共3.4–4.5兲共3.4–4.5兲共3.4–4.5兲

Comp

Comp

15–20 15–20 15–20 共3.4–4.5兲共3.4–4.5兲共3.4–4.5兲

10–15 共2.3–3.4兲

Until plane

0.5

2

Etchants Material Pure Ag Ag alloys Ag-Cu alloys Ag-Pd alloys

0.5

0.5

Etchants 共see Table 12.2兲 172 173, 62 65, 61, 174, 175, 62 130 173

Comp

1

Comp

4

Uses General General General General

structure structure structure structure

Chapter 13

Ag solders

173, 176


413

General structure

Material/Preparation Tables 59 Material: Tin, Sn bearing alloys and other Sn alloys Material Properties: Body-centered tetragonal 共⬎13.2° C 共56° F兲兲, 7.29 g / cm3, 232° C 共450° F兲, ⬍HV 25. Tin bearing alloys: 7 to 8 % antimony, 0.5 % lead, 3 to 4 % copper, iron, arsenic, bismuth, zinc, aluminum. Other tin alloys: Tin-lead, tin-copper, tin-zinc 共weight %兲. Comments on Material: Pure tin is a soft metal, with a recrystallization temperature close to room temperature. Pure tin is often used for coating to obtain a reduced corrosion 共tinned steel plate兲 and on electric parts to make soldering easier. Tin-lead alloys are used for solders and tin-antimony alloys for bearing materials. Tin and tin alloys being soft and having a low recrystallization temperature makes the preparation very difficult, and all steps in the preparation process must be performed with great care. For the softest alloys use Method T-59. Sectioning: Abrasive wet cutting of pure tin and tin alloys can be done with a thin SiC bakelite cut-off wheel, preferably on a precision cutting machine with an efficient cooling. Pure tin also can be cut by using a sharp knife or with a band saw or hand saw with fine teeth. In the case of sawing the very deformed zone must be carefully removed during grinding. For cutting of tinned steel plate, see Material/Preparation Tables 08. Mounting: As a rule pure tin and tin alloys should not be hot mounted, both because of the low recrystallization temperature and because of voids and pores in the alloys which possibly may collapse under the high pressure of hot mounting. To obtain the lowest possible temperature during cold mounting, epoxy with a low peak temperature should be used 共see Section 3.8.3兲. In the case of examination of thin coatings see Material/Preparation Tables 08–10. Grinding: To minimize the risk of embedded SiC grains in the specimen surface, the grinding paper can be treated with wax and a low pressure is used. For water sensitive alloys paraffin 共kerosene兲 can be used instead of water. Polishing: It is important that the deformation from the grinding is removed during the rough polishing step. Chemical mechanical polishing can be used at the last step 共see below兲. For pure tin and certain alloys, the specimen surface can be “cleaned” by electrolytic “shock-polishing,” using Method El-19 in only 1 – 2 s. Tin and some tin alloys are suited for electrolytical polishing. Water sensitive alloys: use water-free lubricants and clean between steps without water 共see below兲. Etching: See Etchants below.

414



ASTM Standard 共See Section 12.4兲 Method B 487 C-59

E 112, E 930, E 1181, E 1382

C-59, T-59, El-19 C-59, T-59

E 562, E 1245, E 1382

E E E E

10, E 18, E 92, E 103, E 110, 140, E 384, E 448 3, E 407, E 562, E 883, E 1181, 1245, E 1351, E 1382, E 1558


C-59, T-59 C-59, T-59, El-19 C-59, T-59, El-19

Preparation Process 59 Sectioning SiC bakelite bond cut-off wheel, 0.5 mm 共0.02 in兲 thick, low speed, very careful 共see also above兲

Cut-Off Wheel


Resin

Time Minutes

Cold Mounting

Resin

Time Minutes/Hours

Epoxy, lowest possible peak temp. 12– 24 h

Grinding T-59: The cutting action of SiC papers P1000 and P1200 can be reduced by using wax before grinding, or making the paper “dull” by first grinding a hard material in 10 s. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-59 and T-59: P 3: Mix 96 mL of colloidal silica with 2 mL ammonia 共25 %兲 and 2 mL of hydrogen peroxide 共30 %兲.

Chapter 13


415

T-59: P 1: This step can be changed to a step like FG 4, only with SiC paper grit P4000. C-59 and T-59: To remove deformed layers and scratches, electrolytic polishing in a short time, 1 – 2 s 共shock-polishing兲, can be recommended to follow the P 3 step 共see Method El-19兲. Water sensitive alloys: C-59: The step P 1 can be omitted and the step P 3 is changed to a diamond step like P 2 in Method T-57 using a water-free lubricant. Contemporary Method C-59 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 P3 Polishing Cloth, nap- Cloth, napless, Disk/Cloth SiC RCD, Cloth, soft, porous, less, med paper soft napless, hard, wov, hard, wov, syn wool silk Abrasive SiC Dia, spr Dia, spr Dia, spr Silica Type or susp or susp or susp Grit or Grain 320 9 6 3 0.04/ 0.05 Size ␮m Lubricant Water Alco or wat Alco or Wat-oil Type wat Rotation 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp Comp Comp Comp Contra Force per 20 共4.5兲 25 共5.5兲 25 共5.5兲 25 共5.5兲 10–15 Specimen 共2.3–3.3兲 N 共lb兲 Time Until plane 5 5 4 1–2 Minutes Traditional Method Section 13.2.2.兲 Grinding/ PG Polishing Disk/Cloth SiC paper

Abrasive Type

SiC

T-59 共For definitions of parameters and consumables see FG 1

FG 2

FG 3

FG 4

P1

P2

P3

SiC paper

SiC paper

SiC paper

SiC paper



SiC

SiC

SiC

SiC

Dia, spr or susp

Cloth, napless, med hard, wov, wool Dia, spr or susp

Silica

416


Grit or Grain Size ␮m Lubricant Type Rotation Disk/ Holder rpm/ rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

P220

P320

P500

P1000

P1200

6

3

0.04/ 0.05

Water

Water

Water

Water

Water

Comp

Comp

Comp

Comp

Comp

Comp

Comp

Contra

20 共4.5兲

20 共4.5兲

20 共4.5兲

20 共4.5兲

20 共4.5兲

20 共4.5兲

25 共5.5兲

Until plane

0.5–1

0.5–1

0.5–1

0.5–1

5

5

15–20 共3.3– 4.4兲 1–2

Alco Wat-oil or wat 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150

Etchants Material Pure Sn Sn-Cd Sn-Fe Sn-Pb

Sn coatings on steel Babbitts Sn-Sb-Cu

Etchants 共see Table 12.2兲 74d, 180, 151 181 74d 74d, 177a 182, 183, 74b 116 183 184 74b

Uses General structure Grain boundaries General structure General structure General structure Darkens Pb in Sn Pb eutectic General structure General structure General structure

Material/Preparation Tables 60 Material: Titanium and Ti alloys Material Properties: Titanium: 共allotropic: more than one crystallographic form兲: ␣-titanium: Close-packed hexagonal, ␤-titanium: Body-centered cubic, 4.5 g / cm3, 1670° C 共3038° F兲, HB 70. Titanium alloys: ␣ alloys: Alloying elements: Aluminum, gallium, germanium, carbon, oxygen, and nitrogen. ␤ alloys: Alloying elements: 共Isomorphous group兲: Molybdenum, vanadium, tantalum, and niobium. 共Group forming eutectoid systems兲: Manganese, iron, chromium, cobalt, nickel, copper, and silicon.

Chapter 13


417

Comments on Material: Titanium is a relatively new metal that is expensive to produce, but nevertheless is gaining ground for applications in the aerospace chemical, and medico-technical industries. Titanium has a high strength to weight ratio, and it has a self-healing oxide layer that provides an effective barrier against incipient corrosion. Commercial titanium grades and alloys are divided into four groups: 1兲 commercially pure titanium, 2兲 ␣ and near ␣ alloys such as Ti-6Al-2Sn-4Zr-2Mo, 3兲 ␣-␤ alloys like Ti-6Al-4V, and 4兲 ␤ alloys that have a high content of vanadium, chromium, and molybdenum. Commercially pure titanium and most of the alloys are soft and ductile with a low machinability, difficult to prepare because of development of a deformed layer. Also, titanium can be sensitive to hydrogen and high temperatures during the preparation. Heat-treated alloys are harder and consequently easier to prepare. Sectioning: Due to the high ductility and toughness of titanium it has low machinability. Consequently it can be very difficult to cut with wet abrasive cutting using the standard cut-off wheels because the edge will clog-up with abraded material. Titanium should be cut with a special SiC, bakelite bond wheel with a strong flow of cooling fluid to obtain a cool and burr-free cut. Sectioning with a shear or with a band saw cannot be recommended, but if they are used, care should be taken with prolonged plane grinding to remove the heavy deformation 共cold work兲 developed during cutting. Mounting: Generally hot and cold mounting can be used. Because of the low machinability of titanium a mounting material with a high wear resistance should be used 共see Section 3.1.3兲. Still it can be experienced that the mounting material is removed at a much higher rate than the sample. This can be dampened by placing two or more samples in the same mount, not only one in the center of the mount. If the specimen should be etched with a strong etchant, a mounting material with a high chemical resistance should be used. In the case of examination of surface layers, special mounting materials should be used 共see Material/Preparation Tables 08–10兲. If the examination involves the hydride phase, it may be of advantage to leave the specimen unmounted or use an epoxy which cures slowly at a temperature not much above room temperature. Grinding: As rough SiC papers will leave deep deformation in the specimen, the plane grinding should be performed with the finest grinding paper possible. Plenty of water should be used. In the two methods below grit 220 is stated for plane grinding, but if the sectioned surface is not very rough, grit 320 should be preferred. New papers should be used. Often the paper can only be used in 20– 25 s to avoid smearing and development of cold work. Polishing: Using finer and finer diamond grades as is normally done develops deformed layers in titanium, very difficult to remove. Therefore, the deformation from the grinding is removed by chemical mechanical polishing 共see below兲. Both pure titanium and a number of alloys can be electrolytically polished. Etching: A microstructure of titanium can be examined in polarized light without etching. For Etchants, see below.

418


Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Heat treatment Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure


Method C-60

E 112, E 930, E 1181, E 1382

C-60, T-60, El-20 C-60, T-60 C-60

E 562, E 1245, E 1382

E E E E


10, E 18, E 92, E 103, E 110, 140, E 384, E 448 3, E 407, E 562, E 883, E 1181, 1245, E 1351, E 1382, E 1558

C-60, T-60 C-60, T-60, El-20 C-60, T-60, El-20


SiC, bakelite bond, specially developed for titanium

Mounting Hot Compression Resin Bakelite/Epoxy Cold Resin Epoxy Mounting with Filler Mounting Time 8–9 Time 8 – 24 h Minutes Minutes/Hours Grinding C-60 and T-60: Use a grit 320 grinding paper for the PG step if possible, for pure titanium and soft alloys. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-60: For the step P 1 use one of the following solutions: 90 mL silica with 10 mL hydrogen peroxide 共30 %兲 or 96 mL silica, 2 mL hydrogen peroxide 共30 %兲 and 2 mL ammonia solution 共25 %兲.

Chapter 13


419

T-60: For the steps P 1, P 2, and P 3 use the solution: 260 mL silica, 40 mL hydrogen peroxide 共30 %兲, 1 mL nitric acid 共65 %兲 and 0.5 mL hydrofluoric acid 共40 %兲. Contemporary Method C-60 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 Polishing Disk/Cloth SiC paper RCD, soft Cloth, napless, soft, porous, syn Abrasive Type SiC Dia, spr or susp Silica, see note above Grit or Grain 220 9 0.04/ 0.05 Size ␮m Lubricant Type Water Alco or wat Rotation 300/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Contra Comp Contra Force per 25 共5.7兲 30 共7兲 20–30 共5.7–6.6兲 Specimen N 共lb兲 Time Until plane 5 8–10 Minutes

Traditional Method T-60 共For definitions of parameters and Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 Polishing Disk/Cloth SiC SiC SiC SiC Cloth, paper paper paper paper napless, soft, porous, syn Abrasive SiC SiC SiC SiC Silica, Type see note above Grit or Grain P220 P320 P500 P1200 0.04/ 0.05 Size ␮m Lubricant Water Water Water Water Type

consumables see P2

P3



420



Force per Specimen N 共lb兲 Time Minutes Etchants Material Pure Ti

Ti-5Al-2.5Sn Ti-6Al-6V-2Sn

300/ 150 300/ 150 300/ 150 150/ 150 150/ 150

150/ 150

150/ 150




Comp

Contra

Contra

Contra

20 共4.5兲

35 共8兲

20 共4.5兲

10 共2.2兲

Until plane

0.25–1

0.25–1

0.25–1

10

2

2

Etchants 共see Table 12.2兲 186, 187, 67, 68, 69, 217 188 72 189 190

Uses General structure Removes stain Chemical polish and etch Reveals hydrides Stains alpha and transformed beta, retained beta remains white General structure General structure General structure General structure General structure

Ti-Al-Zr 191 Ti-8Mn 192 Ti-13V-11Cr-3Al 共aged兲 192 Ti Si 193 Ti alloys 186, 187, 192, 194, 158, 132b, 1c, 67, 68, 69, 3a, 218 11, 1c Reveals alpha case 72, 192, 178 Chemical polish and etch 170a Outlines and darkens hydrides in some alloys 188 Removes stain

Material/Preparation Tables 61 Material: Zinc and Zn alloys Material Properties: Zinc: Close-packed hexagonal, 7.14 g / cm3, 419° C 共786° F兲. Zinc alloys: Zn is mainly alloyed with aluminum, 1 to 15 % and copper up to 4 %. Other alloying elements are lead, cadmium, iron, titanium, magnesium, and tin 共weight %兲. Comments on Material: Zinc is to a high degree used for die-casting and for coating of steel sheet 共see Material/Preparation Tables 08–10兲. Zinc is very difficult to prepare because of the tendency to form layers of plastic deformation with smearing and twins when being ground and polished. Also, embedding of abrasive grains during grinding and polishing is a risk.

Chapter 13


421

Sectioning: Abrasive wet cutting of pure zinc and zinc alloys can be done with a thin SiC bakelite cut-off wheel, preferably on a precision cutting machine with an efficient cooling. Zinc also can be cut by shearing or with a band saw or hand saw with fine teeth. In the case of shearing and sawing the very deformed zone must be carefully removed during grinding. For cutting of zinc coated steel sheet, see Material/Preparation Tables 08–10. Mounting: Cold mounting should be preferred because hot compression mounting may cause deformation and recrystallization in the material. In the case of mounting of zinc coated steel sheet, see Material/Preparation Tables 08–10. Grinding: If the sectioned surface is not very rough, plane grinding should be done with grit 320 SiC grinding paper. To minimize the risk of embedded SiC grains in the specimen surface, the grinding paper can be treated with wax and a low pressure is used. Also, paraffin can be used instead of water. For pure zinc it can be of advantage to extend the time for the last FG steps to ensure that deformation from earlier steps is removed. Polishing: Only use a polishing cloth for zinc, do not mix with copper or lead. It is important that the deformation from the grinding is removed during the P 1 polishing step. Pure zinc and some zinc alloys are suited for electrolytic polishing. Cleaning: Avoid water for cleaning between the polishing steps; use alcohol for cleaning and finish the polishing with a very brief polish with pure alcohol followed by rinsing and drying. Etching: A microstructure of zinc can be examined in polarized light without etching. For Etchants, see below. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Heat treatment Image analysis, rating of inclusion content High planeness Microhardness, hardness

Microstructure



Method C-61

E 112, E 930, E 1181, E 1382

C-61, T-61, El-23 C-61, T-61 C-61

E 562, E 1245, E 1382

E 10, E 18, E 92, E 103, E 110, E 140, E 384, E 448 E 3, E 407, E 562, E 883, E 1183, E 1245, E 1351, E 1382, E 1558

C-61, T-61

C-61, T-61, El-23 C-61, T-61, El-23

422



SiC bakelite bond, thin wheel

Mounting Hot Compression Resin Bakelite Cold Mounting Resin Acrylics Mounting Time 8–9 Time 6 – 10 min Minutes Minutes/Hours Grinding T-61: Cutting action of SiC papers can be dampened with wax. If possible, use grit P320 for the PG step. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-61: In some cases P 2 can be omitted. Also, the cloth in P 2 can be changed to a medium nap, soft, synthetic. T-61: A step like P 2 in Method T-57 can be added between steps P 1 and P 2. Cleaning: Avoid water for cleaning between polishing steps, use alcohol for cleaning and finish the polishing with a very brief polish with pure alcohol followed by rinsing and drying. Contemporary Method C-61 Section 13.2.2.兲 Grinding/ PG Polishing Disk/Cloth SiC paper


Abrasive Type

SiC


FG 1

P1

P2

P3

RCD, soft



P320

Dia, spr or susp 9


Water 300/ 150


Wat-oil 150/ 150


150/ 150

Comp

Comp

Comp

Comp

Contra

Dia, spr or susp 1

0.04/ 0.05

Chapter 13



423

25 共5.7兲

30 共7兲

25 共5.7兲

20 共4.5兲

10–15 共2.2–3.3兲

Until plane

4

4–6

3–5

1–2

Traditional Method T-61 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 Polishing Disk/Cloth

SiC paper

SiC paper

SiC paper

SiC paper

Abrasive Type

SiC

SiC

SiC

SiC


P220

P320

P500

Water 300/ 150

Water 300/ 150


Until plane

Force per Specimen N 共lb兲 Time Minutes Etchants Material Pure Zn Zn-Co Zn-Cu

Zn-Fe Die castings

P1200

0.04/ 0.05

Water 300/ 150

Water 150/ 150

Wat-oil 150/ 150

150/ 150



Comp

Comp

Contra

20 共4.3兲

20 共4.3兲

10 共2.2兲

0.5–1

1–2

1–2

4–6

1–2

Etchants 共see Table 12.2兲 200a 177 201 203 74a 202



Uses General structure General structure General structure Distinguishes gamma 共␥兲 and epsilon 共␧兲 Structure of galvanized sheet General structure

424


Material/Preparation Tables 62 Material: Zirconium. Zr alloys. Zircalloy. Hafnium. Hf alloys Material Properties: Zirconium: Close-packed hexagonal, 7.14 g / cm3, 1490° C 共2714° F兲. Hafnium: Close-packed hexagonal, 13.3 g / cm3, 1700° C 共3092° F兲. Zircalloy: Zirconium with tin, oxide, iron, chromium, and nickel. Comments on Material: Pure zirconium and zircalloy are mainly used for cladding of uranium fuel elements for nuclear power plants. Hafnium also is used in the nuclear reactors. Both pure zirconium and hafnium are soft and ductile, difficult to prepare, they deform easily and mechanical twinning may develop. Also the machineability is low. Sectioning: Sectioning should take place with great care to avoid excessive deformation. Wet abrasive cutting can be done with an SiC bakelite bond cut-off wheel. Preferably the cutting should take place with a precision cut-off machine using a thin wheel 共0.5 mm 共0.02 in兲兲. It is important that the cooling is very efficient so that over-heating is avoided. If shearing or band sawing is used, plane grinding should be extended to remove the strong deformation caused by these cutting methods. Mounting: Hot mounting and cold mounting can be used. If the specimen is to be studied for hydrogen content, or in the case of a risk for mechanical twinning by the pressure at hot mounting, cold mounting should be preferred. As the specimen may be attacked by rather strong acids for chemical mechanical polishing and etching, a mounting material with good chemical resistance, like epoxy, should be used 共see Sections 3.6.1 and 3.13.1兲. Grinding: To avoid excessive deformation, the plane grinding should preferably be done with a grit P320 grinding paper. The grinding should always be wet because Zr and Hf dust may generate fire. The cutting action of the finer grinding papers may be dampened with wax. Polishing: To obtain a surface free from deformation, the final mechanical polishing step can be turned into chemical mechanical polishing. The chemical solutions contain strong acids and precautions should be taken to avoid attack of the grinding/polishing disk and the machine 共see below兲. In the case of hard particles in the specimen surface, use Method C-62 to avoid relief. For pure metals use Method T-62 because SiC paper has a better cutting action than diamond. Etching: Both zirconium and hafnium can be examined in polarized light. For Etchants, see below.

Chapter 13

Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries

Heat treatment Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure


425


Method C-62

E 112, E 930, E 1181, E 1382

C-62, T-62, El-24 共Zirconium兲, El-11 共Hafnium兲 C-62, T-62

E 562, E 1245, E 1382

C-62

E 10, E 18, E 92, E 103, E 110, E 140, E 384, E 448

C-62, T-62

E E E E

C-62, T-62, El-24 共Zirconium兲, El-11 共Hafnium兲 C-62, T-62, El-24 共Zirconium兲 El-11 共Hafnium兲

3, E 407, 562, E 883, 1181, E 1245, E 1351, 1382, E 1558


Preparation Process Sectioning Cut-Off Wheel

SiC bakelite bond, a thin wheel

Mounting Hot Compression Resin Bakelite/Epoxy Cold Resin Mounting Mounting Time 8–9 Time Minutes Minutes/Hours

Acrylics/ Epoxy 6 – 10 min /6–8 h

426


Grinding C-62 and T-62: Avoid grit P220 if possible for PG. T-62: The cutting action of the SiC papers can be damped with wax. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-62 and T-62: The step P 2: A chemical mechanical polishing can be obtained by using 96 mL colloidal silica with 2 mL hydrogen peroxide 共30 %兲 and 2 mL ammonia solution 共25 %兲 or 95 mL colloidal silica with 5 mL chromium trioxide solution 共20 g CrO3 to 100 mL distilled water兲. Another solution is 75 mL distilled water, 10 g oxalic acid, 5 mL acetic acid 共glacial兲, 6 mL nitric acid 共70 %兲 and 2 mL hydrofluoric acid 共48–52 %兲共Caution!兲. One part of the solution is mixed with four parts of silica for the purer zirconium materials and 1 to 1 for zircalloys and hafnium materials. Also, a mixture of 90 mL colloidal silica and 10 mL of hydrogen peroxide 共30 %兲 can be used. Zirconium can be electropolished with Method El-24 and hafnium with El-11. Contemporary Method C-62 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 Polishing Disk/Cloth SiC paper RCD, Cloth, napless, Cloth, napless soft hard, wov, syn soft, porous, syn Abrasive SiC Dia, spr or susp Dia, spr or Silica, see note Type susp above Grit/Grain P320 9 3 0.04/ 0.05 Size ␮m Lubricant Type Water Alco or wat Alco or wat Rotation 300/ 150 150/ 150 150/ 150 150/ 150 Disk/ Holder rpm/rpm Comp/ Comp or contra Comp Comp Contra Contra 20 共4.5兲 30 共7兲 25 共5.5兲 15 共3.3兲 Force per Specimen N 共lb兲 Time Until plane 4–5 4–5 4–8 Minutes

Chapter 13


427

Traditional Method T-62 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 FG 4 P1 P2 Polishing Cloth, Disk/ SiC SiC SiC SiC SiC paper Cloth, Cloth paper paper paper paper napless, napless, soft, hard, wov, silk porous, syn Abrasive SiC SiC SiC SiC SiC Dia, spr Silica Type or susp see note above Grit or P320 P500 P1200 P2400 P4000 3 0.04/ 0.05 Grain Size ␮m Lubricant Water Water Water Water Water Wat-oil Type Rotation 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/ Comp or Comp Comp Comp Comp Comp Contra Contra contra Force per 20 共4.3兲 20 共4.3兲 20 共4.3兲 20 共4.3兲 20 共4.3兲 20 共4.3兲 10 共2.2兲 Specimen N 共lb兲 Time Until 0.5–1 0.5–1 0.5–1 0.5–1 4–6 3–10 Minutes plane Etchants Material Zr base

Etchants 共see Table 12.2兲 66, 67, 204, 68, 69, 205 206 71 72

Uses General structure Electrolytic polish and etch Grain structure under polarized light Chemical polish and etch

Material/Preparation Tables 63 Material: Bones. Carbon. Coal. Graphite. Paper. Teeth. Tissue. Wood. Other organic materials Comments on Material: Common to the preparation of organic materials is the grinding steps on SiC grinding paper to the finest grit. For this reason no “contemporary” method is developed, and both Methods C-63 and T-63 stated below are “ traditional” methods. Often organic materials, having pores, cracks, and voids should be impregnated to obtain a surface that can be satisfactorily prepared 共see below兲.

428


Sectioning: Many organic materials like paper and wood can be cut with a scissor or a fine toothed saw. Other materials like teeth, bones, and coal should be cut on a precision cut-off machine with a thin cut-off wheel, either with SiC bakelite bond, diamond in a metal bond, or with fine teeth. In some cases the material should be impregnated before cutting 共see below兲. For some materials like coal, the selected sample is crushed and the particles are mounted in a transparent mounting material 共see Section 3.11.4兲. Mounting: Often the material contains pores, cracks, and cavities, or it is very brittle. In this case a vacuum impregnation with epoxy should be done 共see Section 3.10兲. An example of an organic material, difficult to prepare without impregnation is paper. It is important that the paper fibers are totally wetted. This is done with an epoxy with a low viscosity, which, to obtain the best wetting, is thinned with acetone or another thinner. A method is to briefly soak the paper specimen in acetone to wet it, soak the specimen in a 50 % acetone/epoxy mixture for several minutes with abundant stirring. Then transfer the specimen to a 10 % acetone/90 % epoxy mixture for several minutes, followed by transfer to a bath with 100 % epoxy for several minutes and finally transfer to a second bath of 100 % epoxy in the mounting cup in which the specimen should be hardened. Several specimens can be mounted in the same mounting cup, using clips to keep the specimens upright and separated. Grinding: In the two methods stated below grinding to P4000 is stated. For some materials the steps FG 3 and FG 4 can be omitted. Polishing: Diamond polishing generally is not suited for organic materials; therefore, diamond is only used for one polishing step in Method T-63. The polishing step, with silica in Method C-63 can vary considerably in time, depending on the material being prepared. Etching: Normally no etching is done. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure Phase identification


Method C-63, T-63

C-63, T-63 C-63, T-63

E 384 E 883

C-63, T-63 C-63, T-63 C-63, T-63

Chapter 13


429


Thin wheel, SiC bakelite bond or diamond with metal bond or with fine teeth

Mounting Hot Compression Resin Cold Mounting Resin Epoxy/Acrylics Mounting Time Time 6 – 12 h / 6 – 10 min Minutes Minutes/Hours Grinding C-63, T-63: Carbon and similar materials: Step FG 3 and FG 4 can be omitted, when followed by a step with 3 ␮m diamond 共see below兲. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded trued. Polishing Carbon and similar materials and paper: C-63 and T-63: Establish a P 1 step with a napless, hard cloth with 3 ␮m diamond, see step P 1 in Method C-62, followed by P 1 in C-63 or T-63. To improve planeness a napless, hard, wov, silk cloth can be used in P 1 of T-63, possibly followed by P 1 in C-63. Bones and teeth: T-63: The step P 1 from Method C-64 can be added as final step. Paper: C-63: The step FG 4 can be changed to the step P 1 in Method C-62 using wat-oil lubricant. Contemporary Method C-63 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 FG 4 P1 Polishing Disk/Cloth SiC SiC SiC SiC SiC Cloth, paper paper paper paper paper napless, soft, porous, syn Abrasive Type SiC SiC SiC SiC SiC Silica Grit or Grain P320 P500 P1200 P2400 P4000 0.04/ 0.05 Size ␮m Lubricant Type Water Water Water Water Water Rotation 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder

430


rpm/rpm Comp/Contra Force per Specimen N 共lb兲 Time Minutes


Comp

Comp

Comp

Comp

Contra

30 共7兲

30 共7兲

20 共4.3兲

20 共4.3兲

10 共2.2兲

Until plane

2

2

2

1–2

1–10

Traditional Method T-63 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 FG 4 P1 Polishing Disk/Cloth SiC paper SiC paper SiC paper SiC paper SiC paper Cloth, med nap, soft, syn Abrasive Type SiC SiC SiC SiC SiC Dia, spr or susp Grit or Grain P320 P500 P1200 P2400 P4000 1 Size ␮m Lubricant Type Water Water Water Water Water Wat-oil Rotational 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp Comp Comp Comp Comp contra Force per 30 共7兲 30 共7兲 30 共7兲 20 共4.3兲 20 共4.3兲 15 共3.4兲 Specimen N 共lb兲 Time Until 2 2 2 1–2 1–6 Minutes plane

Material/Preparation Tables 64 Material: EPDM polymers. Silicone. Other elastomers. Polypropylene „PP…. Polystyrene „PS…. Polyvinylchloride „PVC…. Other thermoplastics Comments on Material: Plastics and polymers cover a very wide range of materials with different characteristics, rigid, semi-rigid, and nonrigid. The plastics and polymers are classified in ASTM Classification System for Specifying Plastic Materials 共D 4000兲.

Chapter 13


431

A basic reason for making materialographic examinations of plastics and polymers is to gain a more complete understanding of the relationships between the manufacturing processes, the microstructure and texture of the material, and the product’s performance. The microstructures of plastics and polymers visible in the light microscope are affected to a considerably greater extent by their chemical composition and method of production than is the case with metals. Plastics and polymers can be examined in different ways, as cross sections 共polished兲 in reflected light, or as thin sections and microtome sections in transmitted light 共see Section 7.13兲. The cross sections can be prepared by grinding and polishing and by ultramilling; only the preparation by grinding and polishing is described below. Plastics and polymers are normally soft and very often the material is sensitive to heat and possibly also to the type of cooling fluid used during the preparation. It is important that the correct fluid is used in sufficient amounts both at sectioning, grinding, and polishing to avoid thermal damage. Heat developed may cause a softening of the material resulting in embedding of abrasive grains in the specimen surface. It can be advised to test the cooling fluids 共water, alcohol, etc.兲 and mounting material 共acrylics, etc.兲 on the specimen material before the preparation to check the resistance of the material. The preparation of plastics and polymers is described in the ASTM Standard Guide for Preparation of Plastics and Polymeric Specimens for Microstructural Examination 共E 2015兲. No “contemporary method” is developed for these materials, so Method C-64 below is a variant of the “traditional method,” T-64 by Trempler, Ref. 40, 共Part I兲. Also, Methods C-65 and T-65 can be used for these materials. For further information on preparation of plastics and polymers see Refs. 40 and 41, 共Part I兲. Sectioning: Selection: The selection of the test specimen is extremely important and dependent upon the purpose of the examination, the material, and the microscopical technique to be used. It should be decided whether the specimen should be taken as a cross section, longitudinal, or inclined. The selection criteria must include the following considerations: The size and scale of homogeneity/ heterogeneity of all structures, textures, and other features within the work piece being studied, the size or scale and distribution of the structures to be studied, and the need for control/reference specimens. In general, sectioning should produce a flat, relatively damage-free surface near to the region of interest. Depending on the type of material, the sectioning can be made by cutting with a sharp knife, a pair of scissors or a scalpel. This technique will introduce a strain 共typically dominated by ductile deformation兲 in the region near the cut face. The width of the strain region can be minimized by properly securing the specimen during cutting, using a sharp instrument, making the cut with uniform speed and force, and making the cut at the appropriate temperature 共often below room temperature兲. The cut face from a 共cryogenically兲 microtomed specimen is often ready for microstructural examination with minimal final polishing or without additional preparation. Sawing either manually or by precision cut-off machine can be done with a sharp, fine short-toothed saw blade with an efficient cooling. The surface after sawing is rather rough and the region with nonuniform strain must be removed by the following grinding and polishing. Also, wet abrasive cutting with a precision cut-off machine using a wheel with electroplated

432


diamonds or an abrasive wheel with SiC in a bakelite bond may be used. Abrasive wheels tend to clog when cutting certain materials and a diamond wheel should be preferred, using a low feed rate. The cutting should take place with an efficient cooling using a cooling fluid which is nonreactive with the specimen material. Often small specimens or parts, or both, with the plane of interest not parallel to a flat surface may require mounting prior to sectioning to facilitate sectioning of the specimen parallel to the desired plane to be polished. Also, laminated, friable, or very ductile materials may be mounted prior to sectioning to minimize damage during the process. Mounting: The specimen can be clamped between plates of the same or similar type of material as the specimen. Also, the specimen can be cold mounted using a mounting material that does not react with the specimen material, and generally with a peak temperature sufficiently below the softening temperature of the specimen material. The softening temperature being in the range from 70 to 125° C 共158 to 257° F兲 for most plastics and polymers limits the use of cold mounting materials to acrylics having a peak temperature of 90° C 共194° F兲 and slow curing epoxy with a peak temperature of 30 to 60° C 共86 to 140° F兲. It can be recommended to work with a temperature not above 40° C 共104° F兲. This limits the cold mounting material to a slow curing epoxy that also can be used for vacuum impregnation in case of porous or cracked specimen materials 共see Section 3.10兲. To discriminate between the mounting material and the specimen material, the epoxy should be added to a dye. To slow down the curing to keep the temperature low, the smallest amount of mounting material should be used, and curing can take place in a refrigerator. Also, cooling can be obtained by placing metal heat sinks into or around the mount. In the case of the mounting of small parts, powder or particles, see Section 3.11. In the case of a very sensitive specimen material, the specimen can be sputter coated with a 20 to 60 nm thick metal film of gold or gold/palladium to form a barrier towards the mounting material. Also, a ⬎100 nm film will make a good contrast between the specimen-mounting material. In the case of examination of materials with hard fibers an acrylic mounting material with a filler should be used. Hot mounting cannot be recommended for plastics and polymers because of the high temperatures and high pressure. Grinding: In Methods C-64 and T-64 four grinding steps are indicated, but often the step FG 4 and in fewer cases both FG 3 and FG 4 can be omitted. The force on the specimens should be low and the rotational speed of the grinding/polishing wheel should not be higher than indicated in the methods. The specimen surface should be inspected after every 15 to 30 s of grinding to ensure that material removal does not go beyond the area of interest; this is especially important at mounted and impregnated specimens. Water is normally used as cooling fluid and the cooling must be effective. In case the specimen material reacts with water, another fluid must be chosen. Perfluorinated liquids, such as those used as diffusion pump oil or as cooling liquids for active electronic circuits, are often appropriate for use with water-soluble plastics and polymers. In the case of embedded SiC grains, use more cooling fluid, lower the force on the specimen and briefly move a blind specimen across the new grinding paper before it is used for the specimens.

Chapter 13


433

Polishing: When using the grinding papers grit P2400 and P4000 as indicated in Methods C-64 and T-64, the rough polishing, step P 1, can be done with 3 ␮m diamond. It is important to ensure a good cooling during the polishing. Use water, or in special cases glycerol, as lubricant. Care must be taken not to embed the abrasive in the specimen which can easily occur with softer plastics and polymers. The use of a lubricant that contains a surfactant or wetting agent can minimize the embedding of the abrasive. Also, a polish only with distilled water in a few minutes may remove embedded grains. If after the step P 1, only a few fine scratches are visible, then proceeding to the final polish, as indicated in Method T-64, is appropriate. If numerous scratches are visible, then repeat the step P 1 or follow Method C-64, going to a step with 1 ␮m diamond. Cleaning: Cleaning is very important when preparing plastics and polymers. The specimen should be cleaned between each step in an aqueous solution of dish soap if the material is not water sensitive. The use of ultrasonic baths cleaning is usually an acceptable practice. However, materials such as partially cured resins may be damaged by excessive cavitation in ultrasonic cleaning. When drying, avoid hot air. Etching: Relief polishing may be sufficient to establish a good examination of the specimen in dark field illumination 共DF兲 or in differential interference contrast 共DIC兲共see Section 9.2兲. For Etchants, see below. ASTM Standard 共See Section 12.4兲


Method C-64, T-64

C-64, T-64 C-64, T64

D 785, D 1415, D 2240, E 384 E 3, E 2015, E 883

C-64, T-64 C-64, T-64 C-64, T-64


SiC bakelite bond, thin, a thin electroplated diamond wheel or a fine toothed saw blade

434


Mounting Hot Compression Resin Cold Mounting Resin Acrylics/Epoxy Mounting Time Time 6 – 15 min/ 12– 24 h Minutes Minutes/Hours Grinding C-64, T-64: For some materials the steps FG 4 and even FG 3 can be omitted. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-64, T-64: Check that the specimen material is not damaged by the lubricant. For water sensitive materials use glycerol. Clean in distilled water. C-64 and T-64: Colloidal silica can be used instead of alumina. T-64: Often the step P 1 can be omitted. Contemporary Method C-64 共For definitions Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 Polishing Disk/ SiC SiC SiC SiC Cloth paper paper paper paper

Abrasive Type

SiC

SiC

SiC

SiC


P1

P2

P3

SiC paper




Dia, spr or susp 1

Alumina

SiC

Grit or P320 P500 P1200 P2400 P4000 0.02/ Grain 0.05 Size ␮m Lubricant Water Water Water Water Water Wat-oil Wat-oil Type Rotation 150/150 150/150 150/150 150/150 150/150 150/150 150/150 150/150 Disk/ Holder rpm/ rpm

Chapter 13



Comp

Comp

Comp

Comp

Comp

Comp

10–20 共2.2– 4.5兲 Until plane

10–20 共2.2– 4.5兲 0.5–1

10–20 共2.2– 4.5兲 0.5–1

10–15 共2.2– 3.4兲 0.5–1

10–15 共2.2– 3.4兲 0.5–1

20 共4.5兲 20 共4.5兲 10 共2.2兲

4–5

Comp

435

3

Contra

Up to 10

Traditional Method T-64 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 FG 4 P1 P2 Polishing Cloth, Disk/Cloth SiC SiC SiC SiC SiC Cloth, paper paper paper paper paper napless, napless, soft, hard, wov, syn porous, syn Alumina Abrasive Type SiC SiC SiC SiC SiC Dia, spr or susp Grain or P320 P500 P1200 P2400 P4000 3 0.02/ 0.05 Grain Size ␮m Lubricant Water Water Water Water Water Wat-oil Type Rotation 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp Comp Comp Comp Comp Comp Contra Force per 10–20 10–20 10–20 10–15 10–15 20 共4.5兲 10 共2.2兲共2.2–4.5兲共2.2–4.5兲共2.2–4.5兲共2.2–3.4兲共2.2–3.4兲 Specimen N 共lb兲 Time Until 0.5–1 0.5–1 0.5–1 0.5–1 5 Up to 10 Minutes plane

436


Etchants Material Polypropylene 共PP兲 Polyethylene 共PE兲 Polyamid 共PA兲

Etchants 共see Table 12.2兲 943, 942, 945, 946 945 946 946, 947

Uses General structure Reveals lamellar structure Reveals spherolites General structure

Material/Preparation Tables 65 Material: Acrylics. Acrylonitrile butadiene styrene „ABS…. Polyamid „PA…. Polycarbonate „PC…. Polyethylene „PE…. Polymethyl methacrylate „PMMA…. Polyester „saturated…. Polyoxymethylene „POM…. Epoxy „EP…. Phenolics. Polyester „un saturated…. Polyurethane „PUR…. Other thermosetting plastics Comments on Material: See Material/Preparation Tables 64. Also Methods C-64 and T-64 can be used for these materials. Sectioning: See Material/Preparation Tables 64. Mounting: ASTM E 2015 recommends: For polyurethanes 共PUR兲: Sputter coat with 40 nm of gold, and encapsulate in a moderately soft epoxy 共70 to 75 Shore D hardness兲 under vacuum and cure at room temperature for 24 h. For polycarbonates: Sputter as for PUR and encapsulate in acrylic or hard epoxy 共80 Shore D hardness or greater兲 under vacuum; cure acrylic at less than room temperature; cure epoxy at room temperature for 24 h. For polymethyl methacrylate 共PMMA兲 the same procedure as for polycarbonates is recommended only a hard setting epoxy resin should be used since PMMA may react with acrylic mounting resin For polyester thick films and sheets: Sputter as for PUR and encapsulate in moderately hard 共75 to 80 Shore D hardness兲 epoxy under vacuum 共for contrast兲, and cure epoxy at room temperature for 24 h. Grinding: ASTM E 2015 recommends: For grinding of PMMA and polycarbonates: The FG 3 step in Methods C-65 and T-65 are changed to a rough polishing step with 6 ␮m diamond or to 9 ␮m diamond for polyester thick films and sheets 共see below兲. For preparation of soft and ductile materials, use T-65. Polishing: ASTM E 2015 recommends: For final polishing of urethanes, PMMA and polycarbonates: The P 3 step in Methods C-65 and T-65 are changed to 0.05 ␮m gamma alumina 共see below兲. Etching: See etchants below and Material/Preparation Tables 64. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries


Method C-65, T-65

C-65, T-65

Chapter 13

Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure Phase identification


437

C-65, T-65

D 785, D 1415, D 2240, E 384 E 3, E 2015

C-65, T-65 C-65, T-65 C-65, T65


SiC bakelite bond, thin wheel or wheel with fine teeth or a thin electroplated diamond wheel

Mounting Hot Compression Resin Cold Mounting Resin Acrylics/Epoxy Mounting Time Time 6 – 15 min/ 12– 24 h Minutes Minutes/Hours Grinding C-65 and T-65: For PMMA and polycarbonates: Change the step FG 3 to a rough polishing step with a soft napless nonwoven synthetic cloth, 6 ␮m diamond, lapping oil, 150/ 150 r / min, Comp, 18–27 共4–6兲 N 共lb兲, 30 s, repeat as needed. For polyester thick film and sheets: Change the step FG 3 to a rough polishing step with a perforated hard nonwoven chemitextile pad, 9 ␮m diamond, distilled water, 120/ 120 r / min, Comp, 13 共3兲 N 共lb兲, 30 s, repeat as needed. C-65: Often a step with SiC paper grit P2400 should be added between FG 2 and FG 3. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-65 and T-65: For urethanes, PMMA and polycarbonates: Use 0.05 ␮m alumina for final polishing, step P 3, instead of the stated silica. For polyester thick film and sheets: Use 0.05 ␮m alumina mixed with colloidal silica in high pH aqueous suspension for step P 3. C-65: Often the steps P 1 and P 2 can be omitted.

438


Contemporary Method C-65 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 P3 Polishing Cloth, Cloth, Disk/Cloth SiC SiC SiC SiC Cloth, paper paper paper paper napless, med nap, napless, soft, syn soft, hard, porous, wov, silk syn Silica Dia, Abrasive Type SiC SiC SiC SiC Dia, spr spr or or susp susp Grit or P320 P500 P1200 P4000 3 1 0.04/ 0.05 Grian Size ␮m Lubricant Water Water Water Water Wat-oil Wat-oil Type Rotation 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp Comp Comp Comp Comp Comp Contra or Contra 20–30 20–30 20–30 20–30 30 共7兲 20–30 10–20 Force per 共4.5–7兲共4.5–7兲共4.5–7兲共4.5–7兲共4.5–7兲共2.2–4.5兲 Specimen N 共lb兲 Time Until 0.5–1 0.5–1 0.5–1 3–4 2–3 0.5–1 Minutes plane Traditional Method T-65 共For definitions Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 Polishing Disk/Cloth SiC SiC SiC paper paper paper


P1

P2

P3

SiC paper



Dia, spr or susp 1

Silica

Wat-oil

Abrasive Type

SiC

SiC

SiC

SiC


P320

P500

P1200

P2400


Water

Water

Water

Water

Wat-oil

0.04/ 0.05

Chapter 13




300/ 150 150/ 150 150/ 150 150/ 150 150/ 150

Comp or contra 20–30 共4.5– 7兲 Until plane

Etchants Material

439

150/ 150

150/ 150

Comp

Comp

Comp

Comp

Comp

Contra

20–30 共4.5– 7兲 0.5–1

20–30 共4.5– 7兲 0.5–1

20–30 共4.5– 7兲 0.5–1

30 共7兲

20–30 共4.5–7兲

10–20 共2.2–4.5兲

3–4

2–3

0.5–1

Polyoxymethylene 共POM兲


Polycarbonate of styrene

948 947

Uses Reveals spherolite spherolite cores and growth direction General structure General structure

Material/Preparation Tables 66 Material: Powder Metals. Ferrous. Nonferrous Material Properties: Iron-graphite mixtures: Up to 0.8 % carbon. Iron-copper: 2 to 20 % copper. Iron- copper-carbon: 2.0 to 5.0 % copper, 0.8 % carbon. Iron-phosphorous: Phosphorous less than 1 %. Iron- nickel: 2 to 4 % nickel, 0.4 to 0.8 % carbon, up to 2.0 % copper. Stainless steels: Compositions that approximate AISI designations 303, 304, 316, for austenitic stainless steels and 410 for martensitic stainless steels. Copper-base: Bronzes with 10.0 % tin Brasses with 10, 20, and 30 % zinc. Nickel silver with 18 % zinc and 18 % nickel. Some alloys may contain 2.0 % lead. Titanium-based: 6.0 % aluminum, 4.0 % vanadium. Aluminum-based: 0.25 to 4.4 % copper, 0.6 to 0.8 % silicon, 0.4 to 1.0 % magnesium 共weight %兲. Comments on Material: Powder metal is one of the four major methods of forming metals 共casting, machining, and plastic forming兲. It is the process of producing metal shapes from metallic powders. The metal powder is blended, pressed 共compacted兲 into shape, and sintered to temperatures just below the melting point. The process offers a wide variety of alloys and material properties. The main production of powder metal parts is small to medium sized parts for the auto and manufacturing industry. The advantage is that the parts have a good surface finish with close dimensional tolerances so that machining is reduced or avoided. Other alloys are made for cutting tools with tungsten carbide and other carbides 共see Material/Preparation Tables 67兲. Powder metals are classified with a prefix and a code, an example is: CNZ—1816–13, where C means copper 共base

440


element兲, N means nickel 共minor element #1兲, Z means zinc 共minor element #2兲, 18 means percentage of minor element #1, 16 means percentage of minor element #2, and 13 means minimum yield strength. During the sintering, recrystallization and grain growth occur between the particles in a contact area, and a grain and lattice structure such as known from solid metals is developed. Voids and pores between the particles are still present, depending on the amount of compression and the time of sintering. When doing metallographic/materialographic examination, the major difference between solid metals and powder metals is the amount of porosity. Sintered materials generally exhibit 0 to 50 % porosity which affects mechanical properties and strongly interferes with the preparation and interpretation of the microstructure. Careful preparation is important because the shape of the porosity is as important as the amount in judging sintered strength and the degree of sintering. The main problem during the preparation is the smearing of the pores during grinding and rough polishing that may occur even when the pores are filled with a resin 共see below兲. For mounting of uncompacted powder, see Section 3.12.4. Preparation of mounted specimens with uncompacted powder is in principle done as for the base material, but often the preparation times should be reduced to avoid over-polishing of the powder particles embedded in the epoxy. Sectioning: Selection: As the density and other features can vary considerably, it is important that the specimens are selected from the surface and interior of the part and from top and bottom. Wet abrasive cutting with an SiC or Al2O3 bakelite bond cut-off wheel, depending on the base material of the powder metal. Preferably a precision cut-off machine with an effective cooling and a thin wheel 共0.5 mm 共0.02 in兲兲 should be used to reduce material damage. In the case of band sawing, the relatively large deformed layer of the cut surface should be removed through a careful plane grinding. Mounting: Before mounting it may be necessary to remove fluids absorbed in the pores of the material during the manufacture and cutting. If the specimen can be heated, the fluids 共water and oil兲 can be removed by heating the specimen in a short time on a hot plate under a fume hood. If the specimen material cannot be heated an extractor-condenser like the Soxhlet apparatus may be used. The apparatus consists of a flask, a siphon cup, and a condensing-coil unit that fits on the top of the flask. A solvent, such as toluene or acetone, is placed in the flask, and the specimen to be cleaned is placed in the siphon cup. Six cycles, requiring a total of 1 h, will usually ensure removal of the oil. The method is described in ASTM Standard Test Method for Density, Oil Content, and Interconnected Porosity of Sintered Metal Structure Parts and Oil-Impregnated Bearings 共B 328兲. Also, ultrasonic cleaning under a fume hood for one h in 1-1-1 trichloroethane and a hot ultrasonic bath has been recommended. The residual entrapped solvent should be evaporated from the specimen. Mounting of specimens, which should be examined for porosity, should be done with a low viscosity epoxy, ensuring an effective vacuum impregnation 共see Section 3.10兲. If edge retention is important, the epoxy should be mixed with a filler 共see Section 3.11.2兲. Other specimens can be hot mounted or cold mounted with acrylics.

Chapter 13


441

Grinding: For materials with high porosity and which are relatively soft and ductile it may be of advantage to extend Method T-66 with a step using grit 2400 grinding paper 共see below兲. Polishing: It is important that the porosity is “clean,” all pores must be opened, after the 3 ␮m diamond step. If this is not the case, the step should be prolonged. For the final polishing step a chemical mechanical polishing may be of advantage 共see under the Material/Preparation Tables covering the base material兲. Etching: Often the specimen is examined in unetched condition to evaluate the number and distribution of the particle boundaries. Etchants used for the base metal may be used; these can be found under the relevant Material/Preparation Tables. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness

Microstructure


Method C-66

E 112, E 930, E 1181, E 1382

C-66, T-66

E 562, E 1245, E 1382

C-66, T-66

B E E B E

C-66, T-66

931, B 932, B 933, 10, E 18, E 92, E 103, E 110, 140, E 384, E 448 328, E 3, E 407, E 562, E 883, E 1181, 1245, E 1382, E 1558


C-66, T-66 C-66, T-66


SiC or Al2O3, bakelite bond, thin wheel

Mounting Hot Compression Resin Bakelite Cold Resin Epoxy/Acrylics Mounting Mounting Time Time 8–10 6 – 12 h / 6 – 10 min Minutes Minutes/Hours

442


Grinding T-66: In case of soft, ductile materials a grinding step, FG 4, with grit P2400 grinding paper can be added. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-66 and T-66: For final polishing chemical mechanical polishing may be used 共see the relevant Material/Preparation Tables for the base material兲. C-66: Often the step P 2 can be omitted. Contemporary Method Section 13.2.2.兲 Grinding/ PG Polishing Disk/Cloth SiC paper

C-66 共For definitions of parameters and consumables see FG 1

FG 2

P1

P2

P2

SiC paper

RCD, soft


Cloth, med nap, soft, syn Dia, spr or susp 1


Abrasive Type

SiC

SiC

Grit/Grain Size ␮m Lubricant Type Rotation Disk/Holder rpm/ rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

P220

P500

Dia, spr or susp 9

Water

Water

Alco or wat Alco or wat Alco or wat

300/ 150

300/ 150 150/ 150

150/ 150

150/ 150

150/ 150

Comp or contra 20–30 共4.5–7兲

Comp

Comp

Comp

Comp

Contra

20–30 共4.5–7兲

20–30 共4.5–7兲

20–30 共4.5–7兲

20–30 共4.5–7兲

10–15 共2.2–3.4兲

5

4

3

1

Until plane 1

0.02/ 0.05

Chapter 13


443

Traditional Method T-66 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 FG 3 P1 P2 P3 Polishing Cloth, Cloth, Disk/Cloth SiC SiC SiC SiC Cloth, paper paper paper paper napless, napless, napless, soft, hard, hard, porous, wov, silk wov, syn silk Abrasive SiC SiC SiC SiC Dia, spr Dia, spr Alumina Type or susp or susp Grit or Grain P220 P320 P500 P1200 6 3 0.02/ 0.05 Size ␮m Lubricant Water Water Water Water Alco or Alco or Type wat wat Rotation 300/ 150 300/ 150 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp or Comp or Comp Comp Comp Contra contra contra contra Force per 20–30 20–30 20–30 20–30 20–30 20–30 10–15 共4.5–7兲共4.5–7兲共4.5–7兲共4.5–7兲共4.5–7兲共4.5–7兲共2.2–3.4兲 Specimen N 共lb兲 Time Until 0.5–1 0.5–1 0.5–1 4 3 1–2 Minutes plane Etchants See under the relevant Material/Preparation Tables covering the base material of the powder metal.

Material/Preparation Tables 67 Material: Sintered „cemented… tungsten carbides. Hard metals. Other coated sintered carbides Comments on Material: Cemented carbides 共sintered carbides, hard metals兲 are sintered materials consisting of tungsten carbide or a mixture of tungsten carbide, titanium, or tantalum carbide in powder form, sintered in a matrix of cobalt or nickel. Cemented carbides, being very hard and tough with a high wear resistance, are suited for cutting tools, metal forming tools, rock drilling, and other purposes where a high wear resistance is needed. To improve the wear resistance of the cutting tool, often the cemented carbide insert is coated by chemical vapor deposition 共CVD兲 with one or more hard materials like titanium carbide, titanium nitride, titanium carbonitride, and aluminum oxide, the coating being 0.2 to 10 ␮m thick.

444


Cemented carbides are covered by a number of ASTM standards regarding specimen preparation 共B 665兲, determination of microstructure 共B 657兲, apparent grain size 共B 390兲, and apparent porosity 共B 276兲共see below and Section 12.4兲. The high hardness of cemented carbides makes only metallographic/ materialographic preparation with diamond possible. The relatively soft cobalt can be smeared over the carbides and lack of adequate pressure on the specimen during polishing may result in pull-outs 共material being torn from the surface of the specimen兲. This condition may erroneously be interpreted as porosity 共see Section 13.6.4兲. Sectioning: The carbides, being very hard, the wet abrasive cutting should be done with a diamond metal bond cut-off wheel preferably on a precision cut-off machine so that a thin wheel can be used, reducing the damage to the cut surface. The cutting, with an efficient cooling, should be performed with a suitable low feed speed to avoid fracturing of the relatively brittle material, especially at the end of the cut. Mounting: Due to the high hardness, cemented carbides should always be mounted in a mounting material with a filler. For hot mounting, epoxy with a filler is recommended and for cold mounting acrylics with a filler or epoxy with an in-mixed filler may be used 共see Sections 3.1.3 and 3.11.2兲. In the case of examination of coatings, an epoxy mounting material should be used 共see also Material/Preparation Tables 08–15兲. Grinding: If the sectioning has been without excessive deformation, the PG step in Method T-67 can be omitted. Polishing: It is important that all deformation from the previous steps are removed after the 3 ␮m diamond step, P 1 in Method C-67 and P 2 in T-67. Often the surface after this step is satisfactory for routine examination. Alumina should not be used for cemented carbides with cobalt matrix because the surface may corrode. Also, the cleaning should be with alcohol only because water may corrode the cobalt matrix. Etching: See etchants below. A physical etching by relief polishing can be made if a napped cloth is used for the final polishing step, a relief between carbides and matrix will develop 共see below兲 Also, vapor deposition of interference layers may give good results 共see Section 9.6兲. Purpose Case of coating thickness/ hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure Phase identification


Method C-67

B 390, E 1382 E 562, E 1245

C-67, T-67 C-67, T-67

E 10, E 18, E 92, E 140, E 384 B 657, B 665, E 3, E 562, E 1245

C-67, T-67 C-67, T-67 C-67, T-67

Chapter 13

Porosity

B 276


445

C-67, T-67


Diamond, metal bond

Mounting Hot Compression Resin Epoxy Cold Resin Epoxy with Filler/ Mounting with Filler Mounting Acrylics with Filler Time Time 6 – 12 h / 6 – 10 min Minutes Minutes/ Hours Grinding C-67: Very often the FG 2 step can be omitted. T-67: Very often the PG step can be omitted. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-67: In case of pull-outs developed during the grinding, the time of step P 1 should be prolonged. T-67: In case of pull-outs developed during the grinding, the time of step P 2 should be prolonged. C-67 and T-67: The final polishing step can be changed to 1 ␮m diamond on a medium napped cloth 共see Method T-65, step P 2兲. Contemporary Method C-67 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 P2 Polishing Cloth, Disk/Cloth Dia, disk, RCD, hard RCD, Cloth, napless, fixed, res soft napless, soft, porous, hard, wov, syn syn Abrasive Type Diamond Dia, spr or Dia, spr or Dia, spr or Silica susp susp susp Grit or Grain P120 9 3 3 0.04/ 0.05 Size ␮m

446


Lubricant Type Rotation Disk/Holder rpm/rpm Comp/Contra Force per Specimen N 共lb兲 Time Minutes

Water

Alco or wat Alco or wat Alco or wat

150/ 150

150/ 150

150/ 150

150/ 150

150/ 150


Comp

Comp

Comp

Contra

35 共8兲

35 共8兲

30 共6.6兲

15 共3.4兲

Until plane

5

5–10

5–8

1–2

Traditional Method T-67 共For definitions of parameters and Section 13.2.2.兲 Grinding/ PG FG 1 FG 2 P1 Polishing Cloth, Disk/Cloth Dia Dia pad, Cloth, napless, pad, met bak napless, hard, v. hard nonwov, syn wov, syn Abrasive Type Diamond Diamond Dia, spr or Dia, spr or susp susp Grit or Grain 125 30 15 6 Size ␮m Lubricant Water Water Alco or Alco or wat Type wat Rotation 300/ 150 300/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp or Comp Comp contra contra 30 共7兲 30 共7兲 40 共9兲 40 共9兲 Force per Specimen N 共lb兲 Time Until 3–5 6 5 Minutes plane Etchants Material Cemented tungsten carbides according to ASTM Standard B 657 共Etching Technique 1兲


consumables see P2

P3

Cloth, Cloth, napless, napless, soft, hard, porous, wov, syn syn Dia, spr or Silica susp 3 0.04/ 0.05 Alco or wat 150/ 150

150/ 150

Comp

Contra

30 共7兲

15 共3.4兲

5

2

Uses Identification of ␩ phase

Chapter 13

Cemented tungsten carbides according to ASTM Standard B 657 共Etching Technique 2兲 Cemented tungsten carbides according to ASTM Standard B 657 共Etching Technique 3兲


447

949 in combination with 950

Identification of ␥ phase

951

Identification of ␣ phase

Material/Preparation Tables 68 Material: Uranium and Uranium dioxide. Americium. Cadmium. Indium. Mercury and amalgams. Neptunium. Plutonium. Rare earth metals. Selenium. Tellurium. Thallium. Thorium Material Properties: Uranium: Body-centered cubic, 238.07 g / cm3, 1689° C 共3010° F兲, HV 190. For all other materials mentioned above, see below. Comments on Uranium: Uranium 共U兲 belongs to the rare earth metals radioactive group. It is the most important of the rare earth metals 共see below兲 because it has been used as a metallic fuel in producing atomic energy. The metallic fuels have been superceded by oxide fuels, and the information below covers preparation of uranium dioxide 共UO2兲. Uranium dioxide is normally used in the form of pellets that are made through a process where the raw material in powder form is sintered at a high temperature. In this state the uranium dioxide can be considered a ceramic material of cubic crystal structure with a very high melting point. U and UO2 are radioactive materials and a health hazard so that all handling shall take place in hot cells or glove boxes through manipulators so that human contact with the radioactive material is avoided. The metallographic/materialographic preparation process follows the same lines as normal preparation, only as mentioned in a shielded environment and with special precautions regarding the disposal of the used consumables. The preparation process stated below is for uranium dioxide, and two methods, a “C-method” and a “T-method” are indicated. Comments on Other Materials: Americium 共Am兲, neptunium 共Np兲, plutonium 共Pu兲, and thorium 共Th兲 are radioactive metals and will not be discussed further. Cadmium 共Cd兲, indium 共In兲, and thallium 共Tl兲 are very soft metals that are seldom used. Cd and Tl are toxic. These metals will not be discussed further. Mercury 共Hg兲 and amalgams: Amalgams are mercury alloys consisting of Hg mixed with powders of silver, tin, copper, and zinc. Only amalgams can be metallographically prepared, and these alloys will not be discussed further. Rare earth metals: This group of 15 metals are very rarely prepared and will not be discussed further. For yttrium 共Y兲 see Material/Preparation Table 20. Selenium 共Se兲 and tellurium 共Te兲 are semiconductors and very toxic and will not be discussed further. For preparation of the semiconductors silicon and germanium see Material/Preparation Tables 21.

448


Sectioning: The uranium dioxide, in pellet form, is normally encapsulated in epoxy 共mounted兲 prior to cutting. This is to minimize fragmentation of the material and thereby reduce the waste and contamination issues. The cutting is done on a special cutting machine made for the special conditions in a hot cell/glove box, using a diamond wheel with resin or metal bond. A wheel with electroplated diamonds may also be used, especially when cutting encapsulated material. When working with radioactive material the volume of liquid in any hot cell/glove box is strictly controlled to a minimum. Consequently, cutting is carried out with a low rotational wheel speed, controllable feed rate, and wheel cooling by dip transfer of the coolant to the wheel so that splashing is avoided and the consumption of coolant is kept very low. Mounting: Cold mounting with epoxy is used. Vacuum impregnation is used on some applications 共see Section 3.10兲. Grinding: Grinding and polishing are carried out on special semiautomatic machines, often with modifications of standard machines so that all handling can take place through manipulators. When using SiC grinding paper, as indicated in Method T-68 below, a large amount of low level contaminated waste is generated which involves costly disposal. Polishing: For the final step both alumina and colloidal silica can be used, often with addition of hydrogen peroxide 共see below兲. Etching: See below. Purpose Case or coating thickness/hardness, surface layers Perfect edge retention Grain size, grain boundaries Image analysis, rating of inclusion content High planeness Microhardness, hardness Microstructure


Methods C-68

E 112, E 930, E 1181, E 1382

C-68, T-68

E 562, E 1245, E 1268, E 1382

C-68

C 730, C 849, C 1326, C 1327, E 384 E 3, E 562, E 883, E 1245, E 1268, E 1382

C-68, T-68


C-68, T-68 C-68


C-68, T-68

Diamond, metal/resin or electroplated, see above.

Chapter 13


449


Resin Time Minutes

Cold Mounting


Epoxy 6–8 h

Grinding C-68 and T-68: When using water for cooling this shall be only as drops to reduce contaminated waste 共see above兲. Attention: In C-methods, when using RCD: The disk turns concave during use. When the difference is more than 100– 150 ␮m between the center and the periphery, the disk is either discarded or trued. Polishing C-68 and T-68: P 3: Mix 90 mL of alumina or colloidal silica with 10 mL of hydrogen peroxide 共30 %兲. Contemporary Method C-68 共For definitions of parameters and consumables see Section 13.2.2.兲 Grinding/ PG FG 1 P1 P2 P3 Polishing Cloth, Cloth, Disk/Cloth Dia, disk, RCD, Cloth, napless, fixed, res hard napless, napless, hard, wov, soft, hard, porous, nonwov, syn syn syn Abrasive Diamond Dia, Dia, Dia, Silica Type spr or spr or spr or 共see susp susp susp note兲 Grit/Grain P220 6 6 3 0.04/ 0.05 Size ␮m Lubricant Water Wat Wat Alco Type 共drip兲共drip兲共drip兲 or wat Rotation 300/ 150 150/ 150 150/ 150 150/ 150 150/ 150 Disk/Holder rpm/rpm Comp/Contra Comp or Comp Comp Comp Contra contra Force per Specimen N 共lb兲 30 共6.6兲 30 共6.6兲 35 共8兲 30 共6.6兲 30 共6.6兲 Time 2 5 5 4 1.5 Minutes

450


Traditional Method Section 13.2.2.兲 Grinding/ PG Polishing Disk/ SiC Cloth paper

T-68 共For definitions of parameters and consumables see

Abrasive Type Grit or Grain Size ␮m Lubricant Type Rotation Disk/ Holder rpm/ rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes Etchants Material UO2

FG 1

FG 2

FG 3

P1

P2

P3

SiC paper

SiC paper

SiC paper

SiC

SiC

SiC

SiC

Cloth, napless, hard, nonwov, syn Dia, spr or susp

Cloth, med. nap, soft, syn Dia, spr or susp

P220

P320

P500

P1000

6

3

Cloth, napless, soft, porous, syn Alumina 共see note兲 0.02/ 0.05

Water 共drip兲 150/ 150




Alco

Alco

150/ 150 150/ 150 150/ 150

Comp

Comp

Comp

Comp

Comp

25 共5.5兲

25 共5.5兲

25 共5.5兲

25 共5.5兲

20 共4.4兲 20 共4.4兲 20 共4.4兲

3 ⫻ 1 min 4 ⫻ 1 min 6 ⫻ 1 min 10⫻ 1 min 8


Comp

6

Contra

5


13.2.4 Manual Preparation The methods stated in Section 13.2.3 are based on semiautomatic preparation. It is possible, however, to use the data stated in the Method Tables for manual 共hand兲 preparation also. The T-methods are most suited for preparation by hand, both the methods based on SiC grinding paper, and the methods based on diamond disks/pads, but also the C-methods, often using resin bonded diamond disks and rigid composite disks 共RCDs兲 for grinding, can in some cases be transferred to manual 共hand兲 preparation 共see below兲. As manual 共hand兲 preparation is less uniform, to a high degree depending on the operator, the times indicated in the Method Tables should only be taken as guidelines 共see below兲.

Chapter 13


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Manual grinding/polishing should preferably be done on two machines, a grinder with one or two disks especially designed for SiC paper 共see below兲, rotating with 300 rpm, and a polisher 共150 and 300 rpm兲 with one or two interchangeable disks for mounting of several polishing cloths or one magnetic disk 共see Section 6.7.1兲. For manual grinding and polishing, disks for 230 mm 共9 in兲 grinding paper and for 200 mm 共8 in兲 polishing cloths should be preferred. Separating the grinding and polishing on two machines reduces the risk of contamination, but both processes can also be done on the same machine. Before starting on manual preparation, it is recommended to read relevant sections in Chapters 6 and 7.

Grinding SiC Grinding Paper In the Method Tables, P220 grit is usually stated as the first step. If the original surface of the specimen is very rough it might be necessary to start with P120 or P180 grit before grinding with a P220 grit. In general, paper with plain back should be used, the paper being fixed by a thin layer of water between the paper and the disk. For this purpose the disk has a raised edge, allowing water to stay on the disk when not rotating, and water is added to the disk before the sheet of paper is placed. A ring is often used to keep down the edge of the paper, but this ring is not fixing the paper, the fixation takes place through the suction between disk surface and sheet, because most of the water is slung away by the centrifugal force when the disk starts rotating. The paper should not be stored in water between uses because this weakens the bond of the paper. Paper with adhesive back can also be used, but generally the force on the paper at manual grinding is so low that a plain backed paper can be used. Also, paper with adhesive back is considerably more expensive than plain backed paper. As a “middle solution” a double adhesive foil can be placed between disk and paper and the foil can be used for many sheets. Water should be supplied in a constant flow to the center of the rotating disk securing that all debris is washed away. When grinding, hold the specimen in a firm grip, with a relatively strong pressure, both hands can be used, and move it from periphery to center of the paper surface and back in a slow movement. Be careful that the specimen is held so that the scratches are in the same direction on a given paper. Also, be careful that the specimen is not tilting, making facets on the surface. When going to next finer grit paper, turn the specimen 90° so that the new scratch pattern can be seen perpendicular to the scratches from the previous step. Continue grinding until all scratches from the previous step are removed, and as a rule go on for at least the same period of time to remove possible deformation. This rule covers harder materials with limited deformations introduced, but for softer, more sensitive materials grinding shall go on for a longer period of time. In some cases it might be necessary to use several sheets of the same grit. Do not use the paper for too long, depending on the hardness of the material, the paper is worn after 20– 120 s. If the paper is worn out it is not removing material but creating deformation in the specimen surface 共see Chapter 6兲. The specimen surface ground correctly is dull with parallel scratches. If the surface is bright, the paper has been worn and new paper should be used. All grinding steps can be done without cleaning in between, but after the last 共finest兲 step the specimen should be cleaned and dried 共see below兲.

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Diamond Disks—Diamond Pads Diamond disks with fixed diamond grains are in the form of diamond in a metal/ bakelite bond on a solid disk, as diamond pads or as resin 共epoxy兲 bonded diamonds, both on a thin backing, to be fixed by adhesion or magnetically to a grinding/polishing disk. They are all used with a flow of water and in the same way as SiC paper.

Rigid Composite Disks „RCD… A disposable RCD is placed on a disk magnetically as described for polishing cloths below, or a solid disk is used 共see Section 6.7.7兲. Also, the diamond is charged as stated below, only spray and suspension can be used. The disk shall rotate with 150 rpm. It can be difficult to use an RCD for hand preparation because the RCD normally works with relatively little lubrication to avoid “aqua planing.” This process drags strongly in the specimen and it might be difficult to hold it by hand. The effect is not very strong on less aggressive 共soft兲 RCDs, and hand preparation can easily be performed. The specimen is rotated around the disk, as described below under polishing; take care that the whole surface of the disk is used to avoid an unplane surface. A firm pressure is applied during grinding with RCD; both hands are often used, like for SiC paper. The disk should be cleaned regularly to avoid swarf closing the openings between the segments on the surface.

Diamond Polishing If using polishing cloths with adhesive back, take care that a number of disks, corresponding to the number of polishing steps, including the step with silica or alumina, is available. In this way, the cloths charged with different grain sizes can easily be changed during the process and should only be removed from the disk when worn out, securing the highest degree of cleanliness and avoiding contamination from disk to disk. If cloths with magnetic backing are used, the cloth can be removed easily from the magnetic disk which can stay in the machine, and only one disk is needed. In the case of a new cloth, charge the cloth with a reasonable amount of diamond, at paste, use approximately 1 g for a 200 mm disk and recharge regularly with 0.5 g. At diamond spray, spray one round on the cloth for a start and respray every 2 – 3 min during the process. At suspension, charge the new cloth with a reasonable amount and recharge during the process every 2 – 3 min from a spray bottle. If a product with “diamond and lubricant in one” is used, it is added as stated below for lubricant. According to Samuels Ref. 7, 共Part I兲, diamond paste should give the highest removal rate at manual polishing. In the case of a used cloth, take care that the cloth can be used for the material in question. Normally a cloth should only be used for the same group of materials; this gives three sets of disks with cloths in an all-round laboratory: for ferrous metals, nonferrous metals, and for ceramics. Starting with a dry cloth, the cloth is wetted with a reasonable amount of lubricant so that the total surface is moist, but not “swimming,” 共see below兲. It is preferable to use a water-based lubricant because alcohol- and oil-based lubricants may be dangerous to health. The polishing disk should rotate with 150 r / min and the specimen is rotated slowly in a circle against the direction of the disk. The specimen is moved slowly from the periphery to the center of the disk and back to secure a uniform wear of the polishing cloth. By rotating the specimen, all phases in the specimen surface are uniformly

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treated, ensuring a minimum of artifacts in the surface. Charge the cloth 共RCD兲 with small amounts of lubricant at the center of the disk in short intervals so that the surface is just “moist” when touched with a fingertip, not “wet.” The pressure during polishing is firm at the rough steps and lower at the final steps. Also, at all steps, the pressure is reduced during the last approximately 30 s. Important: The times indicated in the Method Tables are based on semiautomatic preparation, therefore the times for manual preparation could be longer. Until experience with a given material is developed, take care that deformations and scratches from the previous step are removed by looking at the specimen surface in the microscope 共see the “Metallographer’s Rule of Thumb” and Trouble Shooting 共Section 13.5兲兲.

Silica and Alumina Polishing Be careful, especially with silica 共SiO2兲 polishing, that the cloth is absolutely clean before starting the process, not having dried-in particles from previous polishing; these particles might scratch the specimen surface. Circulate the specimen as described above, adding the polishing medium to the center of the cloth from a spray bottle in small amounts at short intervals. When finished, clean the specimen and the cloth by further “polishing” in approximately 10 s with plenty of water added to the center of the cloth. Silica can be especially difficult to remove and at certain, not too sensitive materials, the specimen surface can be rubbed with a wad of cotton. To clean a porous cloth use the edge of a piece of plastic as a scraper on the rotating cloth to remove remaining polishing media to avoid particles that will later dry-in on the cloth.

Cleanliness and Cleaning It is important that a step is not contaminated with abrasive grains from the previous step. The specimen should be washed and cleaned with cotton in lukewarm water and finally rinsed with ethanol and dried in a stream of warm air or cleaned 共dry兲 compressed air 共see also Chapter 5兲. The hands of the operator should also be washed.

13.3 Electrolytic Polishing and Etching In electrolytic polishing, or electropolishing, the specimen is placed as an anode in an electrolytic cell. Material is removed from the specimen surface through the electrolysis, and because of this, the prepared surface often has a number of artifacts 共see Chapter 8兲. If the specimen has two or more phases, with different potential, like cast iron and contains nonmetallic 共nonconductive兲 inclusions, or both, the prepared surface will not usually show a true or acceptable microstructure. Electropolishing has, however, a number of advantages. The surface created is usually scratch-free and without deformation, an advantage for soft metals, difficult to polish mechanically. Also electropolishing is very effective for routine polishing, the polishing time is very short, and often the etching can take place as part of the process. In certain cases like in stainless steel, the etching cannot be done with the electrolyte used for polishing, and “external etching” can take place using a low voltage and a special electrolyte 共see Section 9.5兲. Trial and Error: To develop a new method, start with a relatively low voltage and increase with 5 V for each trial until the correct voltage 共current density兲 is found. Grind with relatively fine SiC paper between trials to remove traces from the previous

454


electropolishing. Newer electropolishers 共see below兲 have a built-in scan function that indicates the correct voltage/current level for a given material. Trouble Shooting: See Section 13.6.5. Electrolytic polishing is described in the ASTM Guide for Electrolytic Polishing of Metallographic Specimens 共E 1558兲共see Section 12.4兲.

13.3.1 Electropolishers The methods stated in this book are based on the use of an apparatus in which the specimen is placed as an anode on top of a polishing chamber with a mask defining a specific area to be polished, the chamber containing a cathode and a flow of electrolyte. The area is usually from 0.5– 5 cm2 共0.08– 0.8 in2兲. A number of parameters, voltage, polishing/etching current 共amperage兲, flow rate of electrolyte, polishing/etching time, and electrolyte temperature, are controlled by the apparatus 共see Chapter 8兲.

13.3.2 Electrolytes—Methods for Electropolishing—Table 13.2 A number of electrolytes have been developed for most metals, mainly based on perchloric, perchloric/acetic, phosphoric, and sulfuric acids. The composition of a number of electrolytes covering most materials is stated in Table 13.2. To obtain the formulas of a very high number of electrolytes, see Table 2 in the ASTM Standard E 1558 共see Section 12.4兲. To find the correct electrolyte for a specific material, go to Table 11.1 and find the Electropolishing Method 共El-Method兲 number. These methods are stated in Section 13.3.5. The El-Method numbers are also stated in the Material/Preparation Table, Section 13.2.3. In the El-Method, the Electrolyte number is stated. This number is taken to Table 13.2, and the composition is found. When mixed, the electrolytes often have a relatively short shelf life, around two months for the most used perchloric acid type. Life also depends on the number of polishings performed. Often an electrolyte only works best after a few polishings when a number of metal ions are established. Attention: Perchloric acid is very dangerous 共explosion兲 when in contact with organic material at high concentrations. For this reason, only “authorized” electrolytes containing perchloric acid should be used, and care should be taken that the concentration of perchloric acid is not increased by evaporation of other ingredients in the electrolyte, like ethanol. General Safety Precautions: Work with acids and other chemicals is potentially dangerous. Before using or mixing any chemicals, all product labels and pertinent Material Safety Data Sheets 共MSDS兲 should be read and understood. All general precautions should be taken regarding protection of persons. For specific information on handling electrolytes, see Chapter 26.

13.3.3 Table 13.2—Electrolytes for Electropolishing/Etching Comments to Table 13.2: The electrolytes are split into five groups. The group number is the first digit in the Electrolyte Number. Group 1: Perchloric Acid and Alcohol With and Without Organic Additions Group 2: Perchloric Acid and Glacial Acetic Acid in Varying Proportions Group 3: Phosphoric Acid in Water or Organic Solvent Group 4: Mixed Acids or Salts in Water or Organic Solvent Group 5: Alkaline Solutions

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TABLE 13.2—Electrolytes for Electropolishing/Etching. Electrolyte Number Use 1-1 Steel, cast iron, Al, Al alloys, Ni, Sn, Ag, Be, Ti, Zr, U, heat resisting alloys 1–2

1–3

1–4

2-1

Iron and steel in general, stainless steel, Al, Al alloys, Ni, Sn, Ag, Mo, Ti, Zr, Pb, PbSa, Zn, Zn-Al-Cn, Mg and high Mg alloys Carbon, steels, alloyed steels, stainless, steels, martensite, high temp. alloys, Pb, Al-Cu alloys, Mn, Mo, Sn, Ti, Ti-alloys, Zr, V Cast iron, low alloyed C-steels, stainless steels, Be, Mg, Ni

3-1

Austenitic steels, Cr, Hf, Ni, Pb, Th, Ti Alpha, alpha+beta brass, Cu-Fe, Cu-Co, Co, Cd

3-2

Cu, brass, Au

4-1

Cd, Mg, Zn, Pb

4-2

Bronzes, brasses, examination of inclusions, materials with strongly varying structural elements, steels with inclusions

5-1

W

Formula Ethanol (95 %) 700 mL 2-butoxy ethanol 100 mL Perchloric acid (30 %) 200 mL

Ethanol (95 %) 730 mL Distilled water 90 mL Butylcellosolve 100 mL Perchloric acid (60 %) 78 mL

Methanol (100 %) 600 mL Perchloric acid (60 %) 60 mL Butylcellosolve 360 mL Vogel’s Sparbeize 2 mL

Ethanol (95 %) 800 mL Propanol (100 %) 100 mL Perchloric acid (60 %) 15 mL Sodium thiocyanate dihydrate 60 g Citric acid 75 g Hydroxychinolin ortho 10 g

Acetic acid (glacial) 950 mL Perchloric acid (60 %) 50 mL Distilled water 600 mL Ortho phosphoric acid (84 %) 400 mL Distilled water Ethanol (95 %) 250 mL Propanol (100 %) 50 mL Ortho phosphoric acid (84 %) 250 mL Urea 5 g Vogel’s Sparbeize 2 mL Ethanol (95 %) 800 mL Butylcellosolve 80 mL Distilled water 20 mL Sodium thiocyanate dihydrate 160 g Methanol (100 %) 900 mL Propanol (10 %) 140 mL Butylcellosolve 200 mL Acetic acid (glacial) 120 mL Cobalt nitrate (II) 400 g Iron (III) nitrate 40 g Tartaric acid 140 g Urea 4 g Distilled water 1000 mL Sodium hydroxide 20 g

Remarks One of the best formulas for universal use. Add the perchloric acid to the mixture of the other two components. Universal use. Add the perchloric acid to the mixture of the other three components. Shelf life around two months. Vogel’s Sparbeize is an inhibitor used in industrial electrolytic polishing. The electrolyte can be used without this. Attention: Methanol is a poison, use fume hood. Mix in the following way: Propanol and ethanol are mixed and hydroxychinolin is dissolved. After dissolution the sodium thiocyanate is added and after dissolution the citric acid. When the citric acid is added, the liquid turns muddy, but turns clear when all is dissolved and the perchloric acid is added. Alternative to Group 1 electrolytes for certain materials. Alternative to electrolyte No. 3-2 for Cu alloys.

Vogel’s Sparbeize is an inhibitor used in industrial electrolytic baths; this or another similar inhibitor improves the electrolyte, but can be omitted.

The sodium thiocyanate is dissolved in the mixture of water and ethanol. When in solution the butylcellosolve is added. Methanol and propanol are mixed and tartaric acid is dissolved in the mixture, then the cobalt nitrate, the iron nitrate and the urea is dissolved. At last the acetic acid and butylcellosolve are added. Attention Methanol is a poison, use fume hood. The NaOH content can be increased to 100 g

456


13.3.4 Mechanical Preparation for Electropolishing To shorten the polishing time and thereby improve the quality of the electropolished surface, the specimen is normally ground on a number of SiC grinding papers before polishing. In the Method Tables 共Section 13.3.6兲 only three grinding steps are stated. If only fine grinding 共FG兲 is indicated, often a plane-grinding step should be performed before the FG steps. If the polishing time should be reduced, it is recommended to use finer grits of SiC paper, a rigid composite disk, or a hard polishing cloth both with diamond for fine grinding and rough polishing 共see the Method Tables for the given material in Section 13.2.3兲.

Short Time „Shock… Polishing In case of materials difficult to electropolish, the polishing time can be reduced to 1 – 2 s, in some cases repeated two to three times, when a mechanical preparation, including the 3 ␮m and even 1 ␮m diamond steps are performed. In this way only an electrolytical “cleaning” of the surface takes place.

13.3.5 Electropolishing—Method Tables In Section 13.3.6 a number of Method Tables are stated, containing the parameters for electropolishing of a number of metals. The methods are called El-01 to El-25. The user will find the method for a specific material by using Table 11.1. The methods are also stated in the Material/Preparation Tables 共Section 13.2.3兲.

Parameters Preparation before the electrolytic polishing is stated with a number of parameters 共abbreviations兲 similar to the Method Tables of mechanical preparation 共see Section 13.2.2兲. The electrolytic polishing and etching is stated with the following parameters: Electrolyte. An “electrolyte number” will be stated. This number is taken to Table 13.2, which indicates the formula of the electrolyte. Area. The polished area in cm2, always 1 cm2 共0.16 in2兲. The current stated corresponds to this area. Temp. The electrolyte temperature during the process in °C 共°F兲. The temperature should not increase more than 10° C above room temperature during the polishing process. If polishing large areas or many specimens with short intervals, the electrolyte must be cooled 共see Chapter 8兲. Voltage. Voltage between specimen 共anode兲 and cathode in V 共see Area above兲. Two values are indicated: polishing and etching. Current. Current 共amperage兲 in A passing between the cathode and the specimen. The process depends on the correct “current density,” A per cm2共in2兲. Flow Rate. The flow of electrolyte through the polishing chamber. The rate is indicated as low, medium, and high. Time. Polishing and etching time in seconds, indicating the period of time the voltage is on.

13.3.6 Electropolishing—Methods El-01 To El-25 This section contains 25 Method Tables for electrolytic preparation. The tables include the data regarding preparation before the electropolishing, and the data for electropolishing and etching.

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457

The data for electropolishing are based on the use of a commercial available electropolisher 共see Section 8.6兲 that is able to control the stated data. The values indicated refer to an area of 1 cm2 共0.16 in2兲. In the case of mounted specimens, the mounting resin in the surface of the mount should not be conductive 共see Section 3.11.6兲. Attention: A mixed electrolyte will often have a limited shelf life, the most used perchloric acid based electrolyte 共No. 1–2兲 only approximately two months. Trouble Shooting: See Section 13.6.5.

Method Table—Electrolytic Polishing Method El-01 Material: High carbon steels. Medium carbon steels. Manganese and Mn alloys. Molybdenum and Mo alloys Method El-01 Grinding/ Polishing Disk/Cloth Abrasive Type Grit/Grain Size ␮m Lubricant Type Rotation Disk/Holder rpm/rpm Comp/ Contra Force per Specimen N 共Ib兲 Time Minutes

FG 1

FG 2

FG 3

SiC paper SiC

Electropolishing/ Etching SiC SiC Electrolyte No. paper paper 共Table 13.2兲 SiC SiC Area cm2

P220

P320

P500

300/ 150

Electrolytic Electrolytic Polishing Etching 1–3 1–3 1

1

Temperature °C 共°F兲 Water Water Voltage V

20–30 共68–86兲 40

20–30 共68–86兲 2–3

300/ 150

1.8–2

0.2–0.3

Comp or Comp Comp contra 30 共7兲 30 共7兲 30 共7兲 Flow Rate

Medium

Medium/ high

0.5–1

6–8

2–5

Water 300/ 150

0.5–1

Current A

0.5–1

Time s

Comments Electrolytes: 1–2 or 1–1 can be used as alternatives. In case of inclusions, use electrolyte 4–2.

Method Table—Electrolytic Polishing Method El-02 Matherial: Low carbon steels Method El-02 Grinding/ FG 1 Polishing Disk/Cloth SiC paper

FG 2

FG 3

SiC paper

SiC paper

Electropolishing/ Etching Electrolyte No. 共Table 13.2兲

Electrolytic Polishing 1–2

Electrolytic Etching 1–2

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Abrasive Type Gri/Grain Size ␮m Lubricant Type Rotation Disk/ Holder rpm/rpm Comp/ Contra Force per Specimen N 共Ib兲 Time Minutes

SiC

SiC

SiC

Area cm2

1

1

P220

P320

P500

Water

Water

Water

Temperature °C 共°F兲 Voltage V

20–30 共68–86兲 35–40

20–30 共68–86兲 1,5

300/ 150

300/ 150

300/ 150

Current A

1.8–2

0.2–0.3

Comp Comp or contra 30 30 共7兲共7兲

Comp

30 共7兲

Flow Rate

Medium

Medium/ high

0.5–1

0.5–1

Time s

8

5

0.5–1

Comments Steels with very low carbon content could be fine ground with P1000 SiC paper. Electrolyte: In case of inclusions, use 4-2.

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Method Table—Electrolytic Polishing Method El-03 Material: Gray cast iron. Malleable cast iron. Nodular cast iron Method El-03 Grinding/ FG 1 Polishing

FG 2

Disk/Cloth

SiC paper

SiC paper

Abrasive Type

SiC

SiC

Grit/Grain Size ␮m Lubricant Type Rotation Disk/Holder rpm/rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

P500

P1200

Water

Water

300/ 150 150/ 150

FG 3

Electropolishing/ Etching Electrolyte No. Cloth, napless, 共Table 4.4兲 hard, wov, silk Dia, Area cm2 spr or susp 6 Temperature °C 共°F兲 Alco or Voltage V wat 150/ Current A 150


1

20–30 共68–86兲 80 1.8–2

Comp or Comp Comp contra 30 共7兲 20 共4.5兲 30 共7兲

Flow Rate

Low/medium

0.5–1

Time s

4–6

0.5–1

4–5

Electrolytic Etching

Comments In general, cast iron is not suited for electrolytic polishing. If performed, the process should be short and etching should be chemical with etchant No. 74 共Nital兲共Table 12.2兲. The result can be improved by introducing a polishing step before the electropolish, see step P 2 in Method T-30, and cut down the electrolytic polishing to 3 – 4 s.

Method Table—Electrolytic Polishing Method El-04 Material: Heat treated steels Method El-04 Grinding/ Polishing

FG 1

FG 2

FG 3

Disk/Cloth

SiC paper

SiC paper

SiC paper

Abrasive Type

SiC

SiC

SiC

Electropolishing/ Etching Electrolyte No. 共Table 13.2兲 Area cm2



1

1

460


Grit/Grain Size ␮m Lubricant Type

P220

P320

300/ 150

300/ 150

P500

Alco or water 300/ 150 150/ 150 150/ 150

Rotation Disk/Holder rpm/rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

Temperature °C 共°F兲

20–30 共68–86兲

20–30 共68–86兲

Voltage V

80

Current A

2

0.2–0.3


Comp or Contra 30 共7兲

Comp

30 共7兲

Flow Rate

Medium

Medium

0.5–1

0.5–1

0.5–1

Time s

10

2–10

Comments Electrolyte: 1-2 or 1-1 can be used as alternatives. Steels with a high Cr–Ni content might not be electrolytically etched as part of the process 共see Method El-05兲.

Method Table—Electrolytic Polishing Method El-05 Material: Stainless steels. High alloy steels Method El-05 Grinding/ FG 1 Polishing Disk/Cloth Abrasive Type Grit/Grain Size␮m Lubricant Type Rotation Disk/Holder rpm/rpm Comp/ Contra Force per Specimen N 共lb兲

FG 2

FG 3


SiC paper SiC

SiC paper SiC

SiC paper SiC

P320

P500

P1000

Water

Water

Water


Electrolytic Etching 1–2, see below

1


20–30 共68–86兲 40–50

20–30 共68–86兲 15–20

300/ 150 300/ 150 300/ 150 Current A

1.9

0.2–0.3


Low/medium High

Comp 30 共7兲

Flow Rate

Chapter 13

Time Minutes

0.5–1

0.5–1

0.5–1


Time s

12

461

up to 120

Comments Etching: For stainless steels external electrolytic etching in oxalic acid 共10 %兲 at 6 V in 10– 15 s, can be recommended. Electrolytes: 1–3 can be used as an alternative. 2-1 is suited for austenitic steels. In some cases FG can be reduced to grit P500 SiC paper.

Method Table—Electrolytic Polishing Method El-06 Material: Super alloys, Fe based Method El-06 Grinding/ FG 1 Polishing Disk/Cloth Abrasive Type Grit/Grain Size ␮m Lubricant Type Roation Disk/Holder rpm/rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

FG 2

FG 3

SiC paper SiC

SiC aper SiC

SiC paper SiC

P220

P320

P500

Water

Water

Water


Electrolytic Electrolytic Polishing Etching 1–1

1–1

1

1

20–30 共68–86兲 40–50

20–30 共68–86兲

300/ 150 300/ 150 300/ 150 Current A

1.5–2

0.2–0.3


Comp 30 共7兲

Flow Rate

Medium

High

0.5–1

0.5–1

Time s

10–12

5–10

0.5–1


Comments Electrolyte: 1–2 and 1–3 can be used as alternatives.

462


Method Table—Electrolytic Polishing Method El-07 Material: Iron, pure Method El-07 Grinding/ FG 1 Polishing Disk/Cloth Abrasive Type Grit/Grain Size Lubricant Type Rotation Disk/Holder rpm/rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

FG 2

FG 3




SiC paper SiC

SiC paper SiC

SiC paper SiC

1

1

P320

P500

P1000


20–30 共68–86兲 30–35

20–30 共68–86兲 1.5

Water

Water

Water

300/ 300

150/ 300

150/ 150 Current A

1.5–2

0.2

Comp or Comp or Comp contra contra 30 共7兲 30 共7兲 20 共4.5兲

Flow Rate

Medium

Medium/ high

0.5–1

Time s

8–10

5

0.5–1

0.5–1

Comments Electrolyte: 1–2 and 1–3 can be used as alternatives. In case of inclusions, use 4-2.

Method Table—Electrolytic Polishing Method El-08 Material: High-speed steels Method El-08 Grinding/ FG 1 Polishing

FG 2

FG 3

Disk/ Cloth

SiC paper

SiC paper

SiC paper

Abrasive Type Grit/Grain Size ␮m

SiC

SiC

SiC

P220

P320

P500

Lubricant Type

Water

Water

Water

Electropolishing/ Etching Electrolyte No. 共Table. 13.2兲 Area cm2 Temperature °C 共°F兲 Voltage V


1 20–30 共68–86兲 45–55

Electrolytic Etching See below

Chapter 13

Rotation Disk/ Holder rpm/rpm Comp/ Contra Force per Specimen N 共lb兲 Times inutes

300/ 150

300/ 150

150/ 150



Comp

0.5–1

0.5–1


Current A

2

30 共7兲

Flow Rate

Medium

0.5–1

Time s

6–10

463

Comments Etching: External electrolytic etching with oxalic acid 共10 %兲 at 5 – 10 V in 10– 15 s. Electrolytes: 1-1 and 1–3 can be used as alternatives.

Method Table—Electrolytic Polishing Method El-09 Material: Low-alloyed tool steels Method El-09 Grinding/ FG 1 Polishing Disk/Cloth

SiC paper Abrasive Type SiC Grit/Grain P220 Size ␮m Lubricant Water Type Rotation 300/ 150 Disk/ Holder rpm/rpm Comp/ Comp or Contra contra 30 共7兲 Force per Specimen N 共lb兲 Time 0.5–1 Minutes

FG 2

FG 3

Electropolishing/ Etching Electrolyte No. 共Table 13.2兲 Area cm2 Temperature °C 共°F兲 Voltage V

SiC paper SiC P320

SiC paper SiC P500

Water

Water

300/ 150

300/ 150 Current A



1 20–30 共68–86兲 30–40

1 20–30 共68–86兲 3

1.8–2

0.3


Flow Rate

Medium

Medium/ high

0.5–1

Time s

6–10

5–10

0.5–1

Comments Electrolytes: 1-1 and 1–3 can be used as alternatives.

464


Method Table—Electrolytic Polishing Method El-10 Material: Aluminum and Al alloys. Antimony and Sb alloys. Beryllium and Be aloys. Bismuth and Bi alloys Method El-10 Grinding/ FG 1 Polishing Disk/Cloth Abrasive Type Grit/Grain Size ␮m Lubricant Type Rotation Disk/Holder rpm/rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

FG 2

FG 3




SiC paper SiC

SiC paper SiC

SiC paper SiC

1

1

P500

P1200

P2400


20–30 共68–86兲

20–30 共68–86兲

Water

Water

Water

20–40

5

300/ 150

150/ 150 150/ 150 Current A

1.5–2

0.2–0.4

Comp or Comp contra 20 共4.5兲 20 共4.5兲

Comp 20 共4.5兲

Flow Rate

Low/medium High

0.5–1

0.5–1

Time s

5–15

0.5–1

10–20

Comments Cast Al with Si is not suited for electrolytic polishing. Al alloys with a low Si content can often be polished as Al alloys. Electrolytes: 1–1 and 1–3 can be used as alternatives. Al-Cu alloy should be polished with the electrolyte 1–3. Etching: Often electrolytic etching is not satisfactory, chemical etching is recommended 共see the Material/Preparation Tables, Section 13.2.3兲. Fine grinding: By introducing grit P4000 SiC paper before electropolishing the polishing time can be shortened and a possible relief reduced. Antimony: The electrolyte 2–1 can be an alternative. Beryllium: The electrolytes 1–1 and 1–4 can be alternatives.

Method Table—Electrolytic Polishing Method El-11 Material: Chromium and Cr alloys Method El-11 Grinding/ FG 1 Polishing

FG 2

FG 3

Electropolishing/ Etching


Electrolytic Etching

Chapter 13


2–1

Disk/ Cloth

SiC paper

SiC paper

SiC paper

Abrasive Type Grit/ Grain Size ␮m Lubricant Type Rotation Disk/ Holder rpm/rpm Comp/ Contra

SiC

SiC

SiC

P500

P1200

P2400

Temperature 20–30 °C 共°F兲共68–86兲

Water

Water

Water

Voltage V

35–45

Current A

1.8–2.2


300/ 150 150/ 150 150/ 150

Electrolyte No. 共Table. 13.2兲 Area cm2

465

1


Comp

20 共4.5兲

20 共4.5兲

Flow Rate

Medium

0.5– 1

0.5– 1

0.5–1

Time s

10–15

5–10

Comments Etching: Chemical etching is recommended 共see Material/Preparation Tables 46兲. Fine grinding: By introducing grit 4000 SiC paper and a rough polishing step 共see Method T-46, step P 1兲, the polishing time can be shortened or deformations in the electropolished surface can be avoided.

Method Table—Electrolytic Polishing Method El-12 Material: Cobalt and Co alloys Method El-12 Grinding/ FG 1 Polishing Disk/Cloth Abrasive Type Grit/Grain Size ␮m Lubricant Type

FG 2

FG 3

SiC paper SiC

SiC paper SiC

SiC paper SiC

P500

P1200

P2400

Water

Water

Water

Electropolishing/ Etching Electrolyte No. 共Table. 13.2兲 Area cm2



1

1


20–30 共68–86兲 15–30

20–30 共68–86兲 3–4

466


Rotation Disk/ Holder rpm/rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

150/ 150 150/ 150 150/ 150

Current A

1.8–2.5

0.1–0.2

Comp

Comp

Comp

15 共3.4兲

15 共3.4兲

15 共3.4兲

Flow Rate

Medium

Medium/ high

0.5–1

0.5–1

0.5–1

Time s

10–15

5–10

Comments Electrolyte: As an alternative use phosphoric acid 共85 %兲.

Method Table—Electrolytic Polishing Method El-13 Material: Brass. Copper alloys. Pure Cu Method El-13 Grinding/ Polishing Disk/Cloth Abrasive Type Grit/Grain Size ␮m Lubricant Type Rotation Disk/Holder rpm/rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

FG 1

FG 2

FG 3

SiC paper SiC

SiC paper SiC

SiC paper SiC

P500

P1200

P2400




1

1

Temperature °C 共°F兲 Water Water Water Voltage V 300/ 150 150/ 150 150/ 150 Current A

20–30 共68–86兲 15–30 1.8–2.5

20–30 共68–86兲 3–4 0.1–0.2


Comp

Comp

20 共4.5兲

20 共4.5兲

Flow Rate

Medium

Medium/ high

0.5–1

0.5–1

0.5–1

Time s

10–5

5–10

Comments ␤ brass: Having more than one phase, further fine grinding with SiC paper grit 4000 is recommended to shorten the electropolishing time. Also a mechanical polishing step with 3 ␮m diamond can be recommended 共see Method T-49兲. Copper alloys: See also El-14. Copper with oxides: See ␤ brass above.

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467

Method Table—Electrolytic Polishing Method El-14 Material: Bronze. Copper bearing alloys Method El-14 Grinding/ Polishing Disk/Cloth Abrasive Type Grit/Grain Size ␮m Lubricant Type Rotational Disk/Holder rpm/rpm Comp/Contra

FG 1

FG 2

FG 3

SiC paper SiC

SiC paper SiC

SiC paper SiC

P500

P1200

P2400

Water

Water

Water

300/ 150

150/ 150 150/ 150 Current A

Comp or Comp contra 20 共4.5兲 20 共4.5兲

Force per Specimen N 共lb兲 Time 0.5–1 Minutes

0.5–1




1

1


20–30 共68–86兲 40–60

20–80 共68–86兲 2

1.5–2

0.1–0.2

Comp 20 共4.5兲

Flow Rate

Medium

High

0.5–1

Time s

10–15

10–15

Comments Bronze and other alloys with several phases see Method El-13 regarding preparation before electropolishing.

Method Table–Electrolytic Polishing Method El-15 Material: Lead and Pb alloys Methods: El-15 Grinding/ FG 1 Polishing

FG 2

FG 3

Cloth, napless, hard wov, sil Dia spr or susp 6

Disk/Cloth

SiC paper

SiC paper

Abrasive Type

SiC

SiC

Grit/Grain Size ␮m

P500

P1200

Electropolishing Etching Electrolyte No. 共Table 13.2兲


Area cm2

1


20–30 共68–86兲

1–1

Electroytic Etching

468


Lubricant Type Rotation Disk/ Holder rpm/rpm Comp/ Contra Force per Specimen N 共lb兲 Time inutes

Water

Water

Wat-oil

150/ 150 150/ 150 150/ 150

Voltage V

40–60

Current A

1.5–2

Comp

Comp

Comp

20 共4.5兲

20 共4.5兲

20 共4.5兲

Flow Rate

Low

0.5–1

0.5–1

5

Time s

3–5

Comments Etching: Chemical etching 共see Material/Preparation Tables 52兲. Electrolytes: 1–2, 2–1, and 4–1 can be used as alternatives. Electrolytic polishing of Pb should only be last step in a mechanical preparation process 共see Method T-52兲.

Method Table–Electrolytic Polishing Method El-16 Material: Magnesium and Mg alloys Method El-16 Grinding/ FG 1 Polishing Disk/Cloth SiC paper Abrasive SiC Type Grit/Grain P500 Size ␮m Lubricant Water Type Rotation 150/ 150 Disk/ Holder rpm/rpm Comp/ Comp Contra Force per 20 共4.5兲 Specimen N 共lb兲 Time 0.5–1 Minutes Comments

FG 2

FG 3

SiC paper SiC

SiC paper SiC

P1200

P2400

Water

Water




20–30 共68–86兲 40–50

150/ 150 150/ 150 Current A

1

1.5–2

Comp

Comp

20 共4.5兲

20 共4.5兲

Flow Rate

Low

0.5–1

5

Time s

10–15

Chapter 13


469

Etching: Often the surface is etched by the electrolyte. Chemical etching is recommended 共see Material/Preparation Table 53兲. Electrolytes: 1–2 and 1–4 can be used as an alternative.

Method Table—Electrolytic Polishing Method El-17 Material: Nickel and Ni alloys. Ni-based super alloys Method El-17 Grinding/ FG 1 Polishing Disk/Cloth SiC paper Abrasive SiC Type Grit/Grain P500 Size ␮m Lubricant Water Type Rotation 150/ 150 Disk/ Holder rpm/ rpm Comp/ Comp Contra Force per 20 共4.5兲 Specimen N 共lb兲 Time 0.5–1 Minutes

FG 2

FG 3

SiC paper SiC

SiC paper SiC

P1000

P1200

Water

Water




20–30 共68–86兲 40–50

150/ 150 150/ 150 Current A

1

2–2.5

Comp

Comp

20 共4.5兲

20 共4.5兲

Flow Rate

Low

0.5–1

0.5–1

Time s

10

Comments Etching: Chemical etching is recommended 共see Material/Preparation Tables 56兲. Electrolyte: 2–1 can be used as an alternative. Preparation before electropolishing: See Method El-13 and T-56. Short time 共shock兲 polishing: Often a specimen, prepared according to M/PT 56 can be “cleaned” by electrolytic polishing in 1 – 2 s.

Method Table—Electrolytic Polishing Method El-18 Material: Silver and Ag alloys Method El-18 Grinding/ FG 1 FG 2 FG3 Polishing Disk/Cloth SiC SiC SiC paper paper paper

Electropolishing Electrolytic Electrolytic Etching Polishing Etching Electrolyte No. 1–2 1–2 共Table 13.2兲

470


Abrasive Type Grit/Grain Size ␮m Lubricant Type Rotation Disk/ Holder rpm/rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

SiC

SiC

SiC

Area cm2

1

1

P320

P500

P2100


20–30 共68–86兲 20

20–30 共68–86兲 15

Current A

1.7

Flow Rate

Medium

Medium

Time s

10

5–10

Water Water Water 300/ 150

150/ 150

150/150

Comp Comp Comp or contra 10 10 10 共2.3兲共2.3兲共2.3兲 0.5–1

0.5–1

0.5–1

Comments Electrolyte: 1–1 can be used an alternative.

Method Table—Electrolytic Polishing Method El-19 Material: Tin and Sn alloys Method El-19 Grinding/ FG 1 Polishing Disk/Cloth Abrasive Type Grit/ Grain Size ␮m Lubricant Type Rotation Disk/Holder rpm/rpm Comp/ Contra Force per Specimen N 共lb兲

FG 2

FG 3


Electrolytic Electrolytic Polishing Etching

SiC paper SiC

SiC paper SiC

SiC paper SiC

P500

P1000

P1200


20–30 共68–86兲

Water

Water

Water

Voltage V

60

1–2 1

300/ 150 150/ 150 150/ 150 Current A

1.5–2

Comp or Comp Comp contra 20 共4.5兲 20 共4.5兲 20 共4.5兲 Flow Rate

Medium

Chapter 13

Time Minutes

0.5–1

0.5–1

0.5–1


Time s

471

10

Comments Etching: Use chemical etching 共see Material/Preparation Tables 59兲. Electrolytes: 1–1 and 1–3 can be used as alternatives. Preparation before electropolishing: To avoid deformation, a rough polishing step can be performed before electropolishing 共see Method T-59兲. See also Method El-10 for antimony alloys.

Method Table—Electrolytic Polishing Method El-20 Material: Titanium and Ti alloys Method El-20 Grinding/ FG 1 Polishing Disk/Cloth Abrasive Type Grit/Grain Size ␮m Lubricant Type Rotation Disk/Holder rpm/ rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

FG 2

FG 3

SiC paper SiC

SiC paper SiC

SiC paper SiC

P500

P1200

P2400

Water

Water

Water



1


20–30 共68–86兲 35–40

1–2

300/ 150 150/ 150 150/ 150 Current A

2


Comp

Comp

25 共5.7兲

25 共5.7兲

Flow Rate

Medium

0.5–1

0.5–1

0.5–1

Time s

20–30

Comments Etching: Chemical etching is recommended 共see Material/Preparation Tables 60兲. Electrolytes: 1-1, 1–2, and 2–1 can be used as alternatives.

472


Method Table—Electrolytic Polishing Method El-21 Material: Tungsten and W alloys Method El-21 Grinding/ FG 1 Polishing Disk/Cloth Abrassive Type Grit/Grain Size ␮m Lubricant Type Rotation Disk/Holder rpm/rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

FG 2

FG 3

Electropolishing/ Etching Area cm2

SiC paper SiC

SiC paper SiC

SiC paper SiC

P1200

P2400

P4000

Water

Water

Water

Electrolytic Electrolytic Polishing Etching 1

Temperature 20–30 °C 共°F兲共68–86兲 Voltage V 50

150/ 150 150/ 150 150/ 150 Current A

2–2.5

Comp

Comp

Comp

20 共4.5兲

20 共4.5兲

20 共4.5兲

Flow Rate

Low

0.5–1

0.5–1

0.5–1

Time s

15–20

Comments Etching: Chemical etching is recommended 共see Material/Preparation Tables 55兲.

Method Table—Electrolytic Polishing Method El-22 Material: Vanadium and V Alloys Method El-22 Grinding/ FG 1 Polishing Disk/Cloth SiC paper Abrasive SiC Type Grit/Grain P500 Size ␮m Lubricant Water Type Rotation 150/150 Disk/Holder rpm/rpm

FG 2

FG 3

SiC paper SiC

SiC paper SiC

P1200

P2400

Water

Water

Electropolishing/ Etching Electrolyte No. 共Tables 13.2兲 Area cm2



20–30 共68–86兲 40–50

150/150 150/150 Current A

1

2–2.5

Chapter 13


Comp

Comp


Comp

15 共3.4兲 15 共3.4兲 15 共3.4兲 Flow Rate

Medium

0.5–1

10

0.5–1

473

0.5–1

Time s

Comments Etching: Chemical etching is recommended 共see Material/Preparation Tables 55兲. Fine grinding: See Method El-11.

Method Table—Electrolytic Polishing Method El-23 Material: Zinc and Zn alloys Method El-23 Grinding/ FG 1 Polishing Disk/Cloth Abrasive Type Grit/Grain Size ␮m Lubricant Type Rotation Disk/Holder rpm/rpm Comp/ Contra Force per Specimen N 共lb兲 Time minutes

FG 2

FG 3

SiC paper SiC

SiC paper SiC

SiC paper SiC

P500

P100

P1200

Water

Water

Water

Electropolishing/ Etching Electrolyte No. 共Table 13.2兲 Area cm2 Temperature °C 共°F兲 Voltage V

150/150 150/150 150/150 Current A

Comp

Comp

Electrolytic Electrolytic Polishing Etching 4–1 1 20–30 共68–86兲 40–45 2–2.5

Comp

15 共3.4兲 15 共3.4兲 15 共3.4兲 Flow Rate

Medium

0.5–1

20–25

0.5–1

0.5–1

Time s

Comments Etching: Chemical etching can be recommended 共see Material/Preparation Tables 61兲. Preparation before electropolishing: A rough polishing step can be performed to avoid deformation 共see Method T-61兲. Electrolytes: 1–2 can be used as alternative.

474


Method Table—Electrolytic Polishing Method El-24 Material: Zirconium and Zr alloys Method El-24 Grinding/ FG 1 Polishing Disk/Cloth Abrasive Type Grit/Grain Size ␮m Lubricant Type Rotation Disk/Holder rpm/rpm Comp/ Contra Force per Specimen N 共lb兲 Time Minutes

FG 2

FG 3

SiC paper SiC

SiC paper SiC

SiC paper SiC

P1200

P2400

P4000

Water

Water

Water



1


20–30 共68–86兲 40–50

1–3

150/ 150 150/ 150 150/ 150 Current A

Comp

Comp

Comp

15 共3.4兲

15 共3.4兲

15 共3.4兲

Flow Rate

Medium

0.5–1

0.5–1

0.5–1

Time s

10

Comments Etching: Chemical etching is recommended 共see Material/Preparation Tables 62兲. Electrolytes: 1–1 and 1–2 can be used as alternatives. For preparation before electropolishing: See Method T-62.

Method Table—Electrolytic Polishing Method El-25 Material: Hard metals. Sintered carbides Method El-25 Grinding/ Polishing Disk/Cloth

FG 1

FG 2

FG 3

Electropolishing/ Etching See See See Electrolyte No. below below below 共Table 13.2兲 Abrasive Type Area cm2 Grit/Grain Temperature Size ␮m °C 共°F兲 Lubricant Type Voltage V Rotation Disk/Holder rpm/rpm

Electrolytic Electrolytic Polishing Etching 5–1 1 20–30 共68–86兲 15–24

Chapter 13



Flow Rate

Medium

Time s

1

475

Comments Electropolishing can only be done as a shock polishing. The specimen is prepared according to Material/Preparation Tables 67 except for the last step, which is done as electropolishing, shown above.

13.4 Field Metallography/Materialography—Nondestructive Preparation Nondestructive preparation is used for metallographic/materialographic examination in the field on steam pipes, boilers, etc., and for inspection of large structures like drop forgings, weldings, etc. The preparation of the surface is along the same lines as for a normal specimen; both mechanical and electrolytic preparation can be used. Portable apparatus are available for mechanical grinding/polishing and electropolishing, either cable- or battery-driven. A portable microscope is needed to check the prepared surface before, in most cases, a replica is made so that the microstructure can be examined in the laboratory. The process, apparatus, and consumables are described in Part I.

13.4.1 Mechanical Preparation The same grinding and polishing media are used as stated in the T-methods 共see Section 13.2.3兲. A surface of approximately 25 mm 共1 in兲 diameter is prepared to be sure that a replica of 12 by 18 mm 共0.5 by 0.75 in兲 can be made. The prepared surface is normally chemically etched before the replica is made. The preparation should be done very carefully and the prepared area cleaned between polishing steps and before replication 共see also Manual Preparation, Section 13.2.4兲. Trouble Shooting: See Section 13.5/6.

13.4.2 Electrolytic Polishing Normally grinding before electropolishing is made mechanically by hand or with a portable grinder. Often also a rough mechanical polishing is performed to shorten down the electropolishing time and thereby improving the result. For electropolishing, the data stated in Section 13.3.6 are used only the polished area and corresponding voltage/current should be calculated. Etching can often be done electrolytically as part of the polishing process. Trouble Shooting: See Sections 13.5.4 and 13.6.5.

13.4.3 Replication The prepared surface is controlled with a portable microscope to ensure that the surface expresses a microstructure that can be accepted for further examination. The replica can be made either with a piece of plastic 共acetate兲 film or with an amount of silicon rubber-based material positioned on the prepared spot 共see Section 7.11.2兲.

476


Fig. 13.1—Part after torching, heavy thermal damage.

Plastic Film The plastic film, 12 by 18 mm 共0.5 by 0.75 in兲, normally made of methyl acetate, can be used in two ways. It can be wetted on one side with a suitable solvent such as mono methyl acetate and after a moment 共5 – 10 s兲 to dissolve the surface, pressed against the prepared spot, or the spot can be wetted with the solvent, and the film pressed against the spot. It should be held against the work piece with stable, high pressure with a finger, and it should be placed very carefully to avoid a movement parallel to the work piece surface. It is important that the film adheres to the work piece before it is removed; usually a time of 10– 20 s is needed. In case the plastic film is transparent, it may be difficult to distinguish the details of the microstructure. This can be improved by coating the backside with black paint or tape. Another more complicated, but better type of enhancement is to place the replica in a sputtering device producing an interference layer on the replica 共see Section 9.6.5兲.

Silicone Rubber The silicone rubber material is dispensed with a hand-operated dispensing gun directly on the prepared spot. The material will cure in 5 – 15 min and can be used at temperatures from −10° C 共15° F兲 to 180° C 共350° F兲. When the replica is made it is placed on a glass slide with double adhesive tape to improve the handling both for microscopy and for filing together with the report. See also Section 7.11 and ASTM Practice for Production and Evaluation of Field Metallographic Replicas 共E 1351兲 in Section 12.4.

13.5 Trouble Shooting—How to Improve Preparation Results The goal of metallographic/materialographic specimen preparation is to produce a specimen that gives a true picture of the microstructure, reflecting the influence of the previous manufacturing process or any other process intended to influence or change the properties of the material. If the material has in any way been treated with an influence on the microstructure as a result, either thermally, mechanically, or chemically, this change has to be visible so it may be classified or graded. In many cases the purpose of the metallographic/

Chapter 13


477

Fig. 13.2—Part after sawing, heavy mechanical damage.

materialographic examination is the validation of the quality of the involved process. Therefore, it is of utmost importance that the finished specimen, after metallographic/ materialographic preparation, displays the changes introduced during the manufacturing, no more and no less. The preparation must in no way change the structure which means it must not add any characteristics that have not been there before and, as important, it must not remove any of the characteristics that have been introduced during manufacturing. Otherwise the metallographer may misinterpret the result shown in the microscope that might result in either faulty parts being classified as being satisfactory, or good parts as being scrap. To illustrate the above here are a couple of examples: If a specimen is coated with a thin layer of a soft material this coating can be smeared over the base material, indicating a thicker layer than actually exists. Thus the layer can be measured and accepted even if the actual layer thickness is insufficient. More often it will happen that correctly manufactured parts are rejected because of incorrect specimen preparation. If hardened materials are cut using insufficient cooling the reached temperature might anneal the material, resulting in a lower hardness. Thus, a complete batch of correctly treated parts might be scrapped only because of faulty specimen preparation. The first case, accepting faulty parts as correct ones, might be the most critical, but the other, scrapping good parts, can also be very costly. Therefore it is essential that the prepared specimen shows what can be described as the “True Structure.” As shown previously, the entire preparation process can be divided into a series of preparation steps, from cutting over mounting to grinding and polishing. All these steps can introduce preparation artifacts if they are not carried out correctly. In the following the individual preparation steps are listed and possible failures that can occur during these steps are explained. Afterwards these preparation artifacts and how to avoid or overcome them are discussed in detail.

13.5.1 Sectioning There are several possible reasons for sectioning: • To reduce the size of the work piece and turn it into a manageable sample.

478


• •

To be able to measure or examine layers, coatings, hardened zones, or welds. To be able to examine a part in different orientations or angles. In all cases it is important to ensure that a representative part of the work piece is taken out for further examination. Especially important when sectioning a part with a surface treatment or some sort of layer is the correct angle of the cut. If the cut is not carried out in an angle of 90° to the surface, the layer, coating, or hardened zone will be enlarged, and the result is a kind of taper section, something used quite often on purpose when mounting samples for easier measurement of layer thickness 共see Section 3.11.1兲. Apart from that, the most important consideration to take when sectioning is to avoid any mechanical or thermal influence that could alter the structure. As previously described, wet abrasive cutting is the most appropriate way of sectioning when also time and economy are considered. Most of the other sectioning techniques introduce either heavy thermal damage such as after torching as shown in Fig. 13.1, or mechanical damage as is the case after hacksawing to be seen in Fig. 13.2. In case of bandsawing, however, an acceptable result often can be obtained when the correct machine, saw blade, speed, pressure, and cutting fluid are used. For this reason the following examples are concentrating on wet abrasive cutting and bandsawing. However, also with these two methods, thermal or mechanical, damage can occur if care is not taken.

Thermal Damage Thermal damage is a result of excessive heat generated in the cut. Either because of insufficient cooling due to an insufficient amount of cutting fluid in the actual cut or because the feed speed is too high and thus too much heat is introduced 共see Section 2.3兲. Thermal damage can change the structure of the material to be examined which especially is critical with heat treated parts where these structural changes can result in wrong readings in the following microhardness tests. To avoid thermal damage make sure that there always is plenty of cooling fluid in the cut and that the feed speed is set correctly, i.e., not too high 共see Figs. 13.7 and 13.8兲. In wet abrasive cutting, also the selection of cut-off wheels is important. Wheels with a hard bond release abrasive grains slower. That makes them more economical but also less suited for cutting of harder materials, as blunt abrasive particles will not cut properly, but instead introduce heat and result in thermal damage 共see also Section 2.3.5兲. At bandsawing, the type of saw blade is important 共see Section 2.7.4兲.

Mechanical Damage Wet Abrasive Cutting Mechanical damage mostly occurs when cutting brittle materials or materials with brittle or fragile coatings. In many cases damage first occurs when the cut-off wheel is exiting the part to be sectioned. If the force or the selected feed speed is too high, the sample fractures easily. If it is not possible to use a low pre-set constant feed-speed and thus avoid the damage, it usually helps to support the sample with some similar material or bond it onto another material using wax. When cutting coated materials it is very important to cut through the layer or coating into the base material as this then acts as a support. Otherwise the layer might be pushed away from the base material resulting in cracks or delamination. During the

Chapter 13


479

final examination in the microscope it can be impossible to tell if this kind of fault is a real fault from production or if it has been introduced during cutting. Cylindrical, coated samples can, if possible, be rotated during cutting, thus securing support of the coating over the entire circumference.

Bandsawing Bandsawing, as a rule, always leaves more mechanical damage than wet abrasive cutting. For most materials this damage, if all sawing parameters are correct, can be removed through an effective plane grinding, but in case of a too low band velocity or a too coarse pitch of the band, or both, an unacceptable mechanical damage can be developed. Also, feed speed that is too high or a cutting fluid that is not enough or is wrong may give a very rough surface with deep mechanical damage.

13.5.2 Mounting There are several reasons for mounting samples. The most common reason is simply to get specimens with uniform size and shape to facilitate future preparation. In this case, requirements to the mounting techniques are limited. However, a few matters should be considered. If the sample to be mounted is sensitive to heat, cold mounting should be preferred to hot mounting, because the temperature during hot mounting can get as high as 180– 200° C 共350– 400° F兲. Cold mounting is not really “cold” but temperatures seldom exceed 100° C 共210° F兲 for a normal-sized mount of 30 mm 共1.25 in兲 diameter. If the temperature is really critical then only slow curing epoxy resins can be used. To keep temperatures as low as possible epoxy resins can sometimes even be cured in a refrigerator. That takes a longer time but the temperature of the mount does not exceed room temperature. Some materials and fragile samples are sensitive to pressure. In this case, hot mounting cannot be used and cold mounting must be utilized instead.

Impregnation Porous materials are usually impregnated under vacuum and here epoxy resins are used; most of the other resins will start boiling when exposed to a pressure below the atmospheric pressure. Vacuum impregnation has several advantages: • Vacuum impregnation acts as a reinforcement of the sample because the resin works as a bonding agent in the pores. This facilitates the following specimen preparation as pull-out of material is eliminated or at least reduced. Pull-out of particles during the final polishing steps is very often the cause of deep scratches resulting in lengthy reruns of the preparation method. • Colored dyes can be added to the epoxy resin to help distinguish between porosity and pull-out. Very often fluorescent dyes are used as these show up more brightly than normal colors. This dye is added to the epoxy resin before impregnation. During impregnation all pores connected to the surface are filled with the dyed epoxy resin and after the preparation is finished all the filled pores can be identified easily. Areas that are not filled can then be either unfilled pores or pull-outs. The trained metallographer can often determine pull-outs from pores by looking at the circumference of the “hole.” Pull-outs leave a more jagged edge than real pores 共see also Section 3.10兲.

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Fig. 13.3—Deformation after grinding on SiC grinding stone, grit 150.

Shrinkage A general rule when cold mounting is that the faster a resin cures or the higher the caring temperature gets, the higher the shrinkage. Shrinkage of the resin can result in a variety of preparation artifacts 共see also Section 3.1兲.

Staining Water, cleaning agents, alcohol, and etchants are trapped in the gap between specimen and resin Cleaning is almost impossible and the different liquids will continue seeping out of the gap and staining the specimen. This can produce problems both when examining the specimen, but also when etching the specimen, as some other liquid might cover part of the surface, which then will not be attacked correctly 共see Fig. 3.1兲. When hydrofluoric acid is used for etching, this can even ruin the objective of the microscope because the acid seeping out of the gap during examination of the specimen might etch the glass.

Fig. 13.4—Deformation after grinding on ZrO2 / Al2O3 paper, grit 120.

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Fig. 13.5—Deformation after grinding on SiC paper, grit P1000.

Scratching If the gap is large enough, coarse abrasive grains from an earlier preparation step can be transferred to one of the final steps, ruining the preparation result and contaminating the polishing cloth.

Edge Rounding Gaps can also result in edge rounding of the sample, as the resin cannot support the edge of the sample. However, when using modern preparation methods, this risk is quite limited since the consumables used today provide very good edge retention.

Delamination When resins with relatively high shrinkage are used for mounting of samples with porous coatings, the coating can be pulled away from the substrate during the polymerization of the resin This is quite rare and not explained in the section: How to Overcome Preparation Artifacts.

Fig. 13.6—Deformation after grinding on rigid composite disk 共RCD兲 using 6 ␮m diamonds.

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13.5.3 Mechanical Preparation As cutting or mounting, or both, not always are necessary operations the “real” specimen preparation process usually is defined as grinding and polishing. Preparation time should be kept as short as possible. In production control, time is important and the faster the specimens are finished the earlier production can continue. The second important point is that shorter preparation times usually also reduce costs for consumables and labor. The first preparation step is grinding.

Grinding There are two considerations when the grinding process is started. • How is the surface finish from the previous cutting? • Are the specimens prepared as single specimens or are they clamped in a specimen holder? If cutting has been carried out correctly the surface finish is in many cases sufficient for immediate fine grinding. However, if the specimens are clamped together in a holder, plane grinding has to be carried out first to level all specimens in the specimen holder at the same height. In this case the correct grit/grain size of abrasive has to be selected to have a removal rate high enough to achieve short grinding times, but on the other hand, not too coarse to avoid unnecessary deformation which then must be removed in the following steps. Figures 13.3 and 13.4 show the deformation after plane grinding with a grinding stone, 150 grit and a ZrO2 / Al2O3 grinding paper, grit 120, respectively, and the heavy deformation is evident. Figures 13.5 and 13.6 show the much smaller deformation at SiC grinding paper grit P1000 and a rigid composite disk 共RCD兲 using 6 ␮m diamonds. Especially with soft materials, very coarse grit sizes should be avoided. The deformation introduced can be very deep and might take a very long time to be removed in the following steps. It can even happen that fractured abrasive grains become embedded into the soft material during the preparation and may disturb future preparation. Like with cutting, sufficient cooling is required to avoid thermal damage of the specimens. Water is in most cases sufficient but for water-sensitive materials other fluids like water-free oil can be used to avoid attack of the sensitive phases. Recirculation cooling systems are advantageous in these cases because the fluid is reused continuously. However, in many cases even water-sensitive materials can be ground using water as a lubricant during the first step since plenty of material still is removed afterwards and material is removed beyond the damaged area.

Polishing After grinding to a sufficiently fine finish the preparation is continued with polishing. During polishing the last deformation is removed and a reflective surface is produced. A reflective surface is necessary for examination in an optical microscope. Additionally, the surface should be plane without height differences between different phases or rounded edges. Otherwise a correct evaluation of the specimen might be difficult or even impossible. Especially when working with very thin coatings, edge rounding cannot be tolerated. There are several ways to avoid edge rounding and unplaneness. Using the correct mounting technique was already mentioned, but also the choice of polishing cloths is

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very important for the result. Soft cloths usually give a better reflectivity but can easily generate unplane samples and rounded edges. During polishing, a lubricant must be used to avoid any thermal damage. Especially during the final stages of the preparation, water-free products must be used if the material to be prepared is water sensitive. Otherwise certain phases might be attacked or even dissolved and a correct assessment is no longer possible.

13.5.4 Electrolytic Polishing As described in Section 8.3, electrolytic polishing is well suited for the preparation of homogeneous materials whereas it is difficult, in most cases impossible, to get acceptable results with heterogeneous materials. The most common artifacts are relief, missing inclusions 共see Fig. 8.6兲 and edge rounding 共see Fig. 8.8兲. In any case, like with mechanical preparation, it is important that the consumables used are in perfect condition. Take care that the correct electrolyte for the given material is available 共see Section 13.3兲. The electrolyte must not be too old since impurities in the electrolyte may cause phenomena that might lead to a wrong interpretation of the prepared specimen. Used electrolytes may be heavily loaded with metal ions from the specimens. These ions can act as catalysts and reduce the lifetime of the electrolyte which in turn will have a negative influence on the following preparation. Therefore the electrolytes must be discarded in due time.

13.5.5 General Rules—“The Metallographer’s Rule of Thumb” Before the actual preparation process is started it is important to define the purpose of the specimen preparation: “Why am I going to prepare this specimen; what do I want to evaluate?” If you are working with the inspection of incoming materials and have to check a certain type of steel for a certain heat treatment, e.g., normalized, a short preparation of an unmounted sample will in most cases be sufficient. A slight rounding of the edge or a few scratches will not influence the examination. In this case it is important to get a result in a very short time and in many cases also at low cost. Therefore a short preparation method with few steps is selected. However, specimens with very specific characteristics, such as a very thin coating that has to be measured accurately, must be treated in a completely different way. Already during cutting great care has to be taken to avoid damage of the coating. The sample should be mounted in a resin with low shrinkage to prevent any edge rounding and also the preparation method has to be selected carefully with regards to planeness and edge retention. The entire preparation process will take longer, as in the previous example, and the cost will be higher, but it is the only way to ensure that the correct result is obtained. When the purpose is established, use the “Metallographer’s Rule of Thumb,” when a new preparation procedure shall be developed:

Put Up a Goal for Each Preparation Step When following this rule, the result of every step is checked in the microscope. This is to avoid that one of the early steps are not correctly made, a fact that often is not realized before the final polishing step, causing a repetition of the whole process. The above also means that you request as much information as possible if you are asked to prepare a new material or a different kind of sample. Without having sufficient information about the type of material, mechanical, chemical, or thermal treatment,

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service history and request to the final examination, it is very difficult to choose the correct preparation method and to put up acceptable goals for the preparation process.

13.6 Trouble Shooting—How to Overcome Preparation Artifacts In the following sections the most important preparation artifacts are described in some detail and solutions on how to avoid or overcome them are presented. • Whenever a new method is established for a specific material, the specimens should be checked under the microscope after every step to ensure that the scratches, deformation, and other possible damage from the previous step have been removed before continuing with the next step. • The preparation times should be kept as short as possible without sacrificing the quality of the preparation. This usually results in specimens with better planeness and edge retention and saves time and consumables. • When utilizing “fresh” consumables like RCDs or polishing cloths where abrasive has to be added, they have to be used for a while before they reach maximum performance. Allow for a slightly longer preparation time in the beginning. The first part of the preparation process, sectioning, does by and large not cause very high requirements to the equipment used. But generally it can be said that at wet abrasive cutting the more automatic cut-off machines can produce better or at least more repeatable results than manual equipment. Mounting depends much more on the correct choice of consumables than on the equipment used, especially with cold mounting where no equipment except maybe a vacuum chamber for the impregnation is employed. With the grinding and polishing procedures it is a completely different situation. To be able to achieve the best possible preparation results and to use the guidelines stated in the following sections, the specimen preparation has to be carried out on either semiautomatic or automatic equipment. Otherwise it is not possible to control force, time, dosing levels, polishing dynamics and other preparation parameters and consistent results can only be accomplished with great difficulty.

13.6.1 Preparation Artifacts—Flow Charts The following artifacts are described both in words and pictures, and a flow chart is used to show ways to improve the quality of the prepared specimen and avoid the artifacts.

Sectioning Thermal damage Mechanical damage Cracks Delamination

Mounting Staining Scratching Edge rounding

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Grinding and Polishing Scratching Lapping tracks Deformation Smearing Pull-outs—False porosity Embedded abrasive Destroyed inclusions—Pull-outs Edge rounding and relief Comet tails

Flow Chart Symbols The symbols used in the flow chart indicate the following:

13.6.2 Sectioning—General Problems—Flow Charts Wet Abrasive Cutting General Problems As an introduction to the flow charts for the specific artifacts connected to wet abrasive cutting, a number of general problems with suggested solutions are indicated in the table below. Problem

Cause

Solution

Wheel does not cut or stops cutting after some time

Incorrect wheel, the abrasive has become blunt, or the rim of the wheel has been clogged Arc of contact too large

Wheel wears very fast Wheel wobbles or vibrates

Wheel is too soft Wheel is not straight

Use a softer wheel, or in case of very hard material use diamond or CBN as abrasive Increase the force, if possible Use oscillating cutting Use a harder wheel Change wheel

Wheel is not clamped correctly Wheel is too hard

Wheel breaks

Bearings of machine are defect Feed speed too high

Clamp the wheel correctly Use a softer wheel or reduce the speed of the wheel Have machine repaired Reduce the feed speed

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Problem

Cause

Solution

Work piece has moved

Clamp the work piece correctly Did the wheel attack a tilting surface? Take care that a notch is made before the cutting starts Check fixation of work piece Internal stress in work piece, lower feed speed or preferable use oscillating/step cutting, clamp sample downwards on both sides Change wheel

Wheel bends while cutting

“Disk brake effect,” the wheel is pinched in cut

Wheel does not cut straight

Wheel bond varies Work piece not clamped correctly Attack of wheel not perpendicular

Signs of overheating of specimen surface

Feed speed too high Wheel is too hard or too thick Feed speed too low Wheel is clogged Feed speed too high Arc of contact too large

Cooling not efficient

Foam and smell from the cooling liquid, or both

Additive to cooling liquid is not active, bacteria might have developed

Realign and clamp work piece Change position of work piece or take care that the wheel makes a notch before the cutting starts Reduce feed speed Use a softer wheel or a thinner wheel Increase feed speed Used a softer wheel Reduce feed speed Change position of work piece or use a softer wheel Check the cooling system, the level of the cooling liquid and the positioning of the nozzles Check that the cooling liquid has the correct additive content or clean system using bacterial killer, or both.

Wet Abrasive Cutting—Flow Charts Thermal Damage There can be different reasons for thermal damage of the sample during cutting. Mostly thermal damage is directly visible as discoloration on the cut surface, as shown in Fig. 13.7. A cross section through the discolored area shows how deep the thermal damage extends, see Fig. 13.8. A correctly cut sample does not display any discoloration and is free from any thermal damage, as shown in Fig. 13.9. The most common reason is the lack of cooling fluid during cutting. A relatively large amount of cooling fluid is needed to remove the heat generated during cutting. Therefore the

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Fig. 13.7—Thermal damage after cutting with insufficient cooling.

recirculation-cooling unit has to be monitored and the level of cooling liquid checked regularly and refilled if necessary. Another reason might be the wrong selection of the cut-off wheel. As described in Section 2.6.1, different cut-off wheels are available for different materials. If a wheel is used which is too “hard” for the material to be cut, “free cutting” cannot be obtained, the specific pressure in the cut rises and overheating will take place. To avoid overheat-

Fig. 13.8—Cross section of part shown in Fig. 13.7, deep thermal damage can be seen.

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Fig. 13.9—No thermal damage after cutting.

ing a softer wheel must be used. A softer wheel will break down faster, releasing more abrasive grains and consequently cut more efficiently through hard materials. The same behavior can be achieved by reducing the speed of the cut-off wheel. If it is possible to adjust the spindle speed on the cut-off machine the “hardness” of the wheel can be modified. Lower speed makes the wheel act softer and higher speed produces harder wheels 共see Section 2.3.8兲. Instead of changing wheels when different materials have to be cut, an adjustment of the wheel speed can simply compensate for the variation in hardness of the different materials. The third reason for thermal damage is very often a too high feed speed. Material from the sample cannot be removed as fast as the wheel is moved into the cut. “Free cutting” is not achieved and overheating is taking place 共see Sections 2.3.5 and 2.3.8兲. Often the reason for using high feed speed is to save time. This is usually not a good idea, since the time saved during cutting has to be used again in the grinding process to remove the thermal damage. In many cases more time has to be spent than was saved in the first place. Therefore it cannot be recommended to go too fast during cutting; it usually prolongs the total preparation time instead of reducing it. Thermal damage during cutting can usually be avoided if these three guidelines are followed: • Check and maintain the correct cooling fluid in the recirculation-cooling unit. Direct the cooling fluid into the cut. • Select the correct cut-off wheel for the material to be cut. If a variable wheel speed is available it can be used instead of changing the cut-off wheel. • Adjust the feed speed depending on sample material and size.

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Abrasive Wet Cutting, Thermal Damage

Fig. 13.10—Plasma sprayed coating with crack.

Mechanical Damage When cutting correctly, the total amount of applied energy can be transformed into removal of material. If the feed speed is too high more energy is applied than can be transformed. The excess energy has to be consumed somehow, and where it often is transformed into heat resulting in thermal damage with metallic materials, it can result in the initiation of cracks in brittle materials as shown in Figs. 13.10 and 13.11.

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Fig. 13.11—Prior to grinding and polishing, the sample was vacuum impregnated using an epoxy resin with a fluorescent dye 共showing up green when examined using fluorescent light兲. As the crack is completely filled with resin it was there before the grinding and polishing were started. Whether it was there before cutting or created during cutting cannot be said.

With solid materials we very often get cracks extending from the surface into the material whereas we often see delamination, the separation of layers, with coated materials. Therefore special care has to be taken with ceramics and other brittle materials and with coated materials. In Fig. 13.12 a delamination is seen; the coating is not in contact with the base material. In many cases thermal damage is restricted to the area around the cut, whereas cracks propagate deep into the material. Often materials are examined to see whether cracks or delamination have been introduced during the manufacturing process. This means that cracks or delamination that have been introduced during cutting might cause the entire series to be scrapped or at least lead to a lot of extra work, because the production process will be suspected to be faulty. This can be avoided by impregnation of the specimen before cutting using an epoxy with a fluorescent dye. In Fig. 13.11 a specimen is shown that has been vacuum impregnated before grinding and polishing so when examined in the micro-

Fig. 13.12—Delamination between coating and base material.

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scope it can be seen whether a crack existed before the preparation. The same type of impregnation can be done before cutting. To reduce the risk of introducing cracks during cutting a few simple rules should be followed. • Always use moderate feed speed. • Use the correct cut-off wheel for the material to be cut. In the case of coatings the cut-off wheel should be selected to suit the majority of the material, e.g., a thin ceramic coating on a steel bar should be cut using an abrasive Al2O3 wheel suitable for the steel bar instead of using a diamond cut-off wheel that would suit the ceramic coating only. • Thin cut-off wheels should be preferred to thicker wheels because they remove less material and thus introduce less energy. • With very brittle and fragile materials, vacuum impregnation prior to the cut can reinforce the samples and prevent cracking. • With coatings: always cut through the coating into the base material. Thus the coating is supported all the time and the risk of cracking is reduced.

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Abrasive Wet Cutting, Mechanical Damage

Bandsawing General Problems When working with a vertical bandsaw a number of problems can be experienced, and below the most important of these are listed with suggested solutions 共see also Section 2.7.4兲.

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Problem Premature dulling of teeth

Band vibrating in the cut

Band teeth ripping out

Surface of finished cut too rough

Premature band breakage

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Solution Decrease band velocity. Use band with finer pitch. Apply proper cutting fluid when cutting ferrous and nonferrous materials. Keep teeth engaged. Do not allow the teeth to idle through cut. Increase feeding pressure. Apply cutting fluid at point of cut, saturating the teeth evenly when cutting ferrous and nonferrous alloys. Be sure that band is running with teeth pointing down. Increase or decrease band velocity. Increase band tension. Use band with finer pitch. Increase feeding pressure. Hold work piece firmly. Use fine-pitch bands on thin work piece sections. Eliminate vibration by holding work piece firmly while it is fed into the band. Use cutting fluid on ductile materials. If gullets are loading, use heavier duty cutting fluid. Reduce feed pressure. Increase band velocity. Use band with finer pitch. Use slower feeding rate. Apply correct amount of proper cutting fluid. Change to band with gage that is not too heavy for diameter of wheels and speed of the machine. Decrease band velocity. Check periphery of wheels for defects. Cracking at weld. Try longer annealing period, decrease unit load by using finer pitch. Decrease feeding pressure. Decrease band tension. Properly adjust band tool guides. Apply cutting fluid. Increase band tension. Adjust guides close to work piece. Use band with coarser pitch. Decrease feeding pressure.

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Gullets loading

Band not running true against saw guide backup bearing

Negative camber developing in band Cutting rate too slow

Band leading in cut

Premature loss of set

Positive camber developing in band

Band developing twist

Use band with coarser pitch. Apply cutting fluid. Lower band velocity. If clicking against saw guide backup bearing, remove burr on back of band where joined. If hunting back and forth against saw guide backup bearing, re-weld with back of band in true alignment. Check alignment of band carrier wheels. Check saw guide backup bearing, if worn or unbalanced, replace same. Band riding too heavy on saw guide backup bearing. Adjust band for alignment on top and bottom wheels. Increase band velocity. Use band with coarser pitch. Increase feeding pressure. Apply cutting fluid. Unbalanced set or partial dullness caused by striking hard inclusion in material being cut. Apply cutting fluid. Saw guides out of adjustment. Carefully readjust guide inserts or rollers. If worn, replace same. In the case of brush-equipped cut-off machines, make sure brushes are properly adjusted, if worn, replace with new. Reduce feeding pressure. Band too wide for radii being cut. Decrease band velocity. Apply cutting fluid. Reduce feeding pressure. Use band with coarser pitch to permit greater tooth penetration. Saw guides too far apart, adjust closer to work piece. Band binding in cut, decrease feeding pressure. Side inserts or rollers of saw guides adjusted too close to band. Wrong width of band for radii. Decrease band tension.

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13.6.3 Mounting—General Problems—Artifacts General Problems—Hot Mounting In the following overview some of the general problems that can arise during hot mounting are shown and both cause and the possible solution are described 共see also Section 3.6兲.

General Problems—Cold Mounting In the subsequent overview some of the problems that can arise during cold mounting are shown and both cause and the possible solution are described 共see also Section 3.13兲.

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Problem The surface of the mount is sticky after normal curing time.

The mount is brown after curing, too rapid curing.

It is very difficult to remove the mount from the mounting mold.

The mount is soft after curing, not cured completely.

Specimen moves, turns, falls or floats in the mounting mold.

Cause/Solution The components are not mixed in the correct quantities, the mixing has not been correct or the room temperature has been too low. Mix carefully with the exact portions of each component and check that the room temperature is approx. 20–22° C 共68– 72° F兲. Also cover the mounting cup so as to prevent any reaction between the surface of the mount and the air. The temperature during curing has been too high. Mix carefully with the exact portions of each component and check that the room temperature is approx. 20–22° C 共68– 72° F兲. When using large amounts of resin make sure that the mount is cooled during curing. Use either a stream of cool air, a water bath or a refrigerator. The mounting resin 共epoxy兲 has very little shrinkage and good adhesion to all materials. Use a more flexible mounting mold or coat the inner surface with a thin layer of silicone mold release agent. The components are not mixed in the correct quantities or one of the components is too old. Check the expiry date of the components and make sure to measure the correct quantities of each component. The mount can maybe be saved by placing it in an oven at 40–50° C 共100– 120° F兲. The specimen is very light. Coat the bottom of the mounting mold with spray lacquer and position the specimen before the lacquer is dry or use double adhesive tape to secure the specimen.

Staining Staining is the discoloration of the specimen surface through residues of liquids used during preparation, cleaning, or etching of the specimen. Sometimes staining is used to purposely contrast the specimen surface in order to identify different phases, but here we are only talking about unintended discoloration. Staining usually occurs when the sample is not mounted correctly and there is a gap between the sample and the mounting material. This gap is often filled with lubricant that is accumulated there during polishing or with cleaning liquid or etchant that has been used during the preparation process. Very often the gap is rather narrow, but the capillary action fills the gap easily with liquid. Figure 3.1 共Section 3.1.2兲 shows a

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specimen surface with staining caused by a gap, and in Fig. 3.2共b兲 a correct mount is seen without gap and consequently without staining. To avoid staining the subsequent rules can be followed: • Always clean and degrease the samples prior to mounting; this will provide a better adhesion of the resin to the sample. • Select a resin with very low shrinkage; these usually are hot mounting resins containing a filler material or epoxy resins for cold mounting. The epoxy resins provide the best result, especially with vacuum impregnation; however, the long curing time often prohibits their use. • Clean the specimen carefully after each step, possibly using ultrasonic cleaning. • Dry the specimen very thoroughly to avoid bleeding out of liquids during examination with the microscope. • Use a piece of soft tissue together with a hair dryer to make sure that all liquid is removed from the gap. 共Be careful with soft materials that the tissue does not scratch the material.兲 • After etching the specimen make sure that all etchant is removed from the specimen or the gap in the specimen, otherwise the specimen might start “bleeding” on the microscope. This can destroy the specimen, or, if hydrofluoric acid was used, even the objective of the microscope.

Scratching Scratching is usually not related to mounting; however, under certain circumstances a poor quality of the mount might result in scratching of the specimen surface. As with the previous example, incorrect mounting can result in a gap between the sample and the mounting material. During preparation some of the abrasive particles can be trapped in the gap and carried on to the following preparation stage, as shown in Fig. 13.13. If the particles are falling out of the gap and stay on the polishing cloth they will result in few but distinct scratches. To avoid scratching because of poor mounting quality, follow these rules:

Fig. 13.13—Abrasive grains in the gap between sample and mounting resin When these fall out during preparation they will result in scratching.

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•

Always clean and degrease the samples prior to mounting; this will provide a better adhesion of the resin to the sample. • Select a resin with very low shrinkage; these usually are hot mounting resins containing a filler material or epoxy resins for cold mounting. The epoxy resins provide the best result, especially with vacuum impregnation; however, the long curing time often prohibits their use. • Clean the specimen carefully after each step, possibly using ultrasonic cleaning. If abrasive particles are carried from one preparation step to a following step, it will not only damage the specimen and require at least part of the preparation method to be repeated, it will also require the contaminated polishing cloth to be exchanged. The result is both longer preparation time and increased cost 共see also Section 13.6.4兲.

Edge Rounding Mounting is often carried out to protect the edges of the sample, especially when the sample is coated with very thin layers of another material. To be able to measure the thickness of these layers accurately it is crucial that they are absolutely plane without any rounding. The same is valid when microhardness testing has to be carried out very close to the edge; also here perfect planeness of the sample is required. Today’s selection of consumables for grinding and polishing has made the preparation easier and faster as previously stated. Still, when the maximum edge retention is required it is usually not possible to avoid mounting the samples. The correct mounting resin has to be selected carefully to avoid a gap between sample and mounting material, and usually there are not so many choices. The best option when mounting samples with porous or fragile coatings is epoxy resin because this can be used under vacuum and will provide both a reinforcement of the coating and a mount without any gap. For mounting of samples with very hard coatings or the mounting of surface hardened materials it can be advantageous to use hot mounting. In this case resins with different filler materials are available. This makes it possible to select a mounting resin that has similar wear characteristics as the material to be prepared. Thus a uniform removal of material across the entire specimen surface is obtained and perfect planeness and edge retention will be the result 共see Section 3.1.3.兲 Figure 3.2共a兲 shows a mount with a mounting material not in contact with the sample, causing edge rounding. In Fig. 3.2共b兲 the correct mounting material adhering to the sample is used.

13.6.4 Grinding and Mechanical Polishing—Flow Charts Scratching The mechanical removal of material from the surface is carried out step-by-step using continuously finer grain sizes of abrasive. The abrasive particles act as machining tools, removing small chips of material. As a result, the surface is covered with unidirectional grinding scratches getting smaller after every step of the preparation, disappearing totally at the end, or at least being so small that they are no longer visible in an optical microscope. The unidirectional pattern is achieved when the specimen is prepared using some kind of automatic or semiautomatic preparation equipment as described in Section 7.9. To avoid scratches on the finished sample, the specimen has to be examined after every preparation step to ensure that all scratches from the previous step have been removed completely before continuing to the following step. Otherwise steps from one of the early grinding steps might still be visible after final polishing. It is crucial that the specimen is checked carefully after every step because the removal rate

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Fig. 13.14—Scratched and deformed surface after plane grinding.

of smaller abrasives is much less than that of larger abrasives causing the polishing times needed to be extremely long if a final polishing step should remove scratches from an initial grinding step. Figure 13.14 shows the very rough scratch pattern with heavy deformations after plane grinding, in contrast to the pattern developed during the fine grinding shown in Fig. 13.15. It is also very important to clean the specimens carefully after every step as contamination of a polishing cloth quite easily can occur. 共Scratching because of mounting gaps has been described in Section 13.6.3.兲

Fig. 13.15—Uniform scratching after fine grinding.

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Scratching

Lapping Tracks During mechanical preparation the abrasive particles should act as small cutting tools, machining chips from the surface of the specimen. This requires the abrasive grain to be held firmly on the polishing cloth while the specimen is passing over it as the abrasive grain otherwise will start rolling. Since we use loose abrasives that are added during preparation, this presents a challenge to the polishing cloth used. The polishing cloth must be selected carefully depending on the grain size of abrasive it is going to be used with and especially in relation to the hardness of the material to be prepared. If the polishing cloth is too soft the abrasive will disappear into the fabric and will not remove any material. If the pol-

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Fig. 13.16—Specimen with lapping tracks, BF.

ishing cloth is too hard the abrasive cannot be pressed deep enough into the cloth and the abrasive may start rolling, resulting in lapping tracks. If the cloth is even harder, or a rigid fine grinding disk with too high of a hardness is used, the abrasive might even be pressed into the sample material and become firmly embedded 共see the section below on embedded abrasives兲. Lapping on softer materials does not remove any material, it only introduces deep deformation. The lapping tracks are easy to identify, they follow a straight line, like a grinding scratch; however, it is interrupted as the abrasive grain is tumbling across the surface, as shown in Figs. 13.16 and 13.17 in bright field 共BF兲 and differential interference contrast 共DIC兲, respectively. For information on polishing cloths see Section 7.4.

Fig. 13.17—Specimen with lapping tracks, DIC.

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Lapping Tracks

Deformation The entire mechanical preparation process is based on the removal of material through grinding and polishing as described earlier. Any mechanical treatment will result in a certain amount of plastic deformation of the surface of the specimen. It is the purpose of metallographic/materialographic specimen preparation to remove the deformation from the surface to allow for the examination of the true structure. Therefore, metallographic/materialographic specimen preparation is carried out in steps to gradually remove the deformation from the previous steps; see Fig. 13.18 that shows the preparation process schematically from the surface left after cutting through plane grinding, fine grinding, and polishing to a surface to be examined on the microscope 共see also Section 7.7兲. However, very often some residual deformation is left after the preparation is finished and that can lead to wrong conclusions; see Fig. 13.19 that shows the remaining deformation from an earlier grinding step. Therefore, it is

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Fig. 13.18—The preparation process. Deformation is removed step-by-step.

Fig. 13.19—Remaining deformation from preparation, following early grinding scratches.

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Fig. 13.20—Color etched specimen, remaining deformation can clearly be seen.

important to follow certain preparation routines and to check the specimens frequently during preparation. Generally each step has to remove the material deformed during the previous step, while at the same time only introducing a limited amount of new deformation. With today’s modern consumables the preparation of most materials can be reduced to about four steps resulting in a deformation free sample surface. If these steps are not carried out correctly deformation may be visible after preparation. Very often the deformation is first visible after etching. Especially color etching will reveal even the smallest amount of remaining deformation as shown in Fig. 13.20.

Fig. 13.21—Smearing on a soft type of steel.

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Deformation

Smearing Smearing is not as common as many of the other artifacts; however, it is important to be aware of the possibility and the influence smearing can have on the final result. Smearing usually happens with very soft materials, as shown in Fig. 13.21, and often when soft materials are contained in layers. Instead of being cut cleanly the material is pushed across the surface. Especially when the thickness of layers has to be measured, e.g., copper and solder layers on a PCB, the correct thickness must be obtained, otherwise the part might be not acceptable. As can be seen in Fig. 13.22 the soft solder material has been deformed and dragged across the copper layer following a coarse grinding scratch. The exact measurement of the different layers in this case is not possible. Therefore, smearing is not acceptable and has to be avoided. Also, smeared material may hide the pores in the surface 共see Pull-Outs—False Porosity, below兲. Mostly the occurrence of smearing is due to one of the following reasons: • Wrong type of abrasive used. Abrasives that are too blunt cannot cut properly and may result in smearing. Therefore diamond is the best choice of abrasive for the first, relatively coarse polishing steps. Diamond is the hardest known abrasive and consequently will produce a clean cut over a long period of time. Polycrystalline diamonds are superior for specimen preparation.

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Fig. 13.22—Smearing on a PCB. The solder material is smeared over the copper layer, following a grinding scratch.

•

•

•

Insufficient lubricant level during polishing. When the amount of lubricant added to the polishing cloth is too low, the lubricant film between specimen and cloth can be imperfect and thus smearing can occur. The lubricant level should be maintained on a stable level throughout the entire preparation step in a way that the polishing cloth is moist but not wet. Polishing cloths that are too soft. With soft polishing cloths the abrasive can be pressed too deep into the textile and thus not create any cutting action. Change to a harder polishing cloth or increase the abrasive grain size 共see below兲. Abrasive grain size that is too small. This is similar to the above reason; small abrasive grains can also be pressed so deep into the fabric of the cloth that their cutting action is nonexistent. Either increase the size of the abrasive used or change to a harder polishing cloth to avoid the condition that the abrasive is pressed too deep into the fabric.

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Smearing

Pull-Outs—False Porosity As stated earlier, the goal of metallographic/materialographic preparation is to show the true structure. For most solid materials that is a relatively easy task, but porous materials quite often produce a challenge, even to experienced metallographers. Depending on the type of material, the preparation process can produce either a too high porosity level or a too low level. Porous, brittle materials usually display a higher porosity level than what is actually in the material due to fracturing of the material during cutting and plane grinding. This fracturing creates pull-outs, cavities in the surface, and cracks 共see Section 6.3.2, see also pull-outs in connection with inclusions in the following section兲.

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Ductile materials often display a too low porosity since the softer metallic material can be smeared into the pores during plane grinding, covering these up. The following examples are taken from the same type of application, thermal spray coatings, using two different types of materials where the above can be seen very clearly. To reach the correct result, displaying the accurate porosity level with the same routine can be used with both types of material. When preparing such a specimen for the first time it is important to monitor the porosity level throughout the entire preparation and first continue to the following preparation step when the porosity level stays constant. With brittle materials it will get smaller and smaller until it reaches the correct level as shown in Figs. 13.23–13.26. At ductile materials the porosity level will increase with finer and finer preparation steps until the final, correct level is reached, as shown in Figs. 13.27–13.32. In both sections on false porosity the use of an RCD is recommended. Experience shows that the constant supply of abrasive during preparation on an RCD gives the most constant removal of material and thus is best suited for fine grinding of both soft and hard porous materials when the correct porosity level has to be obtained. If the use of an RCD is not possible the correct type of abrasive for the material in question should be selected. On hard, brittle materials diamond grinding disks or diamond pads in successively finer grain sizes should be used to remove the damage from plane grinding. For soft materials fine grained SiC paper can be selected; however, it is important to change the paper frequently to allow fresh, still sharp grains to remove material and thus avoid smearing.

Fig. 13.23—Ceramic plasma sprayed coating after plane grinding, the porosity level is very high due to many pull-outs.

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Fig. 13.24—Same specimen as in Fig. 13.23 after fine grinding, pull-outs are reduced.

Fig. 13.25—Same specimen as in Fig. 13.23 after diamond polishing, pull-outs are further reduced.

Fig. 13.26—Same specimen as in Fig. 13.23 after final polishing, correct porosity level.

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Fig. 13.27—WC/Co plasma sprayed coating after plane grinding. The surface is completely smeared and the pores are not visible.

Fig. 13.28—Same specimen as Fig. 13.27 after fine grinding. Most of the pores are still smeared over.

Fig. 13.29—Same specimen as Fig. 13.27 after 6 ␮m polishing. Pores start to open up.

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Fig. 13.30—Same specimen as Fig. 13.27 after 3 ␮m polishing. More pores are opening up.

Fig. 13.31—Same specimen as Fig. 13.27 after 1 ␮m polishing.

Fig. 13.32—Same specimen as Fig. 13.27 after final polishing on colloidal silica. Correct porosity level.

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Pull-Outs, False Porosity, Hard, Brittle Materials

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False Porosity, Soft, Ductile Materials

Destroyed Inclusions Many materials contain different types of nonmetallic inclusions. They are naturally contained in the material or added to improve machinability. These inclusions have different mechanical behavior than the base material; they can be harder or softer and often they have other thermal expansion values resulting in relatively bad adhesion of the inclusions to the base material. During metallographic/materialographic preparation these inclusions can be crushed if they are very brittle 共see Fig. 13.33兲, or removed by a long napped polishing cloth if they are soft, but the result is the same, partly or completely missing inclusions in the base material. Apart from misleading results in the following microscopic examination, these inclusion particles, pulled out during the preparation can also result in other preparation artifacts such as scratching. There is, however, another important group of inclusions, the water-sensitive inclusions. If not treated correctly, the result after preparation will be the same with these inclusions as with those described above; they will simply be missing when examining the specimen 共see Fig. 13.34兲. This takes place if the polishing consumables used, especially during the last steps of the preparation, contain water.

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Fig. 13.33—Brittle inclusion, removed during polishing.

Fig. 13.34—Missing water-sensitive inclusions.

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Destroyed Inclusions

Embedded Abrasives Contrary to pull-outs, no material is removed from the specimen, but during preparation, abrasive grains are embedded into the specimen surface. Also, this is unwanted

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because the foreign matter will make interpretation much more difficult or even impossible. Embedded abrasives are only seen with relatively soft materials, and mostly because they are prepared on preparation disks that are quite hard; this can be rigid composite disks 共RCDs兲 or hard polishing cloths, but even from SiC grinding paper grains can be embedded in the specimen material. This can pose a problem with certain composite materials. If they consist of both hard and soft phases, RCDs and hard polishing cloths are recommended to keep the specimens plane and avoid edge rounding. Therefore, a way has to be found to fulfill both requirements at the same time, plane specimens without embedded abrasive grains. Figure 13.35 shows embedded abrasive particles after 3 ␮m diamond polishing in a PbSn solder, and Fig. 13.36 shows the same specimen in SEM. To resolve the problem with embedded abrasive it is essential to know when the abrasive particles became embedded. Therefore, the specimens have to be checked after every preparation step to be certain

Fig. 13.35—Embedded abrasive 共3 ␮m diamonds兲 in PbSn solder.

Fig. 13.36—Same specimen as Fig. 13.35, SEM image of diamonds in the solder phase.

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Embedded Abrasive

Edge Rounding and Relief The goal of specimen preparation is to produce specimens showing the true structure. This usually requires perfect edge retention and absolutely plane specimens. With composite materials containing phases of very different hardness or materials with thin, sometimes multiple coatings, this can present a serious challenge to the metallographer. Figures 13.37 and 13.38 show a composite material with relief and without relief, respectively. Figures 13.39 and 13.40 show a coated material with rounded edge and with perfect edge retention, respectively.

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Fig. 13.37—Composite material with relief between fibers and matrix.

Fig. 13.38—Same specimen as Fig. 13.37 after correct preparation, perfect planeness.

Fig. 13.39—Coated material with rounded edge.

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Fig. 13.40—Same specimen as Fig. 13.39 after correct preparation, perfect edge retention.

Edge rounding has already been touched upon in connection with mounting in Section 3.1.3; however, it is not always possible to mount the sample and in the following some tips are provided to get good edge retention without mounting. Basically the same rules are valid to avoid relief between the different phases in the specimen. • Use rigid composite disks 共RCDs兲 for fine grinding and relatively hard cloths for polishing to keep the specimen flat. • Use diamond as the abrasive because it can cut equally through all phases. • Use polishing times as short as possible. • Use as few polishing steps as necessary, e.g., go directly from 6 to 1 ␮m polishing, omit the 3 ␮m step. • Use a lubricant with higher viscosity for the finer polishing steps.

Fig. 13.41—Specimen after unidirectional polishing with comet tails around the inclusions.

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Edge Rounding and Relief

Comet Tails Comet tails owe their name to their characteristic shape. They are found adjacent to inclusions or pores and are the result of unidirectional polishing 共see Fig. 13.41兲. By adjusting the polishing dynamics, comet tails can be avoided easily 共see Section 7.9.2兲. As with the other artifacts we also assume here that the preparation process is carried out on some kind of semiautomatic or automatic equipment. To achieve an acceptable polishing result it is necessary that the specimen is moved across the entire surface of the polishing disk and that the specimen holder at the same time is rotated around its center. This is difficult to carry out manually, but most modern machines are designed

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to utilize the entire preparation surface and to rotate the specimens at the same time. One reason to move the specimen across the entire preparation surface is to wear the polishing cloth symmetrically, thus increase the lifetime and as result reduce the cost of specimen preparation. But more important is that the specimen is subjected to a unidirectional influence from the polishing cloth. This is important as different phases or constituents in the specimen react differently to metallographic/materialographic specimen preparation. If we are polishing a material with hard inclusions, the inclusions will be polished slower than the rest of the material, and after a while the inclusions will stick slightly out of the base material. As a result, less of the base material will be removed in the “shadow” of the inclusion. When examined in the microscope this characteristic feature will look like a comet tail. Apart from disturbing the examination it will also make, for instance, correct automatic inclusion rating using image analysis impossible, since the inclusions will seem larger than they actually are. To avoid comet tails it is important that the speed of the polishing disk and the speed of the specimen holder or specimen mover disk in which the specimens are located are almost the same. They must not be identical because the specimens otherwise would run in exactly the same track over and over again, but they should be similar. As a rule of thumb the speed of the specimen holder should not differ more than ±5 – 10 % from the speed of the preparation disk. This is only relevant during polishing where the removal rate is limited and the relative softness of the cloths contributes to uneven removal between softer and harder phases. Grinding is carried out on hard supporting disks and the removal rate is much higher. Here comet tails will not occur and therefore the speed of the grinding disk can be much higher than the speed of the specimen holder to achieve a higher removal rate and thus a shorter preparation time.

13.6.5 Electropolishing—General Problems—Artifacts In the following overview some of the problems and artifacts that can be observed during electrolytic preparation are indicated and both cause and the possible solution are displayed.

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General Problems and Artifacts Problem Surface not polished or only partly polished Spots that have not been polished

Cause Current density insufficient Electrolyte too old Insufficient quantity of electrolyte Gas bubbles

Etching of the polished surface

Chemical attack of grain boundaries after switching off the current

Phases in relief

Polishing film is inadequate

Pitting

Polishing time too long Polishing time too long

Voltage too high Insufficient anodic layer Attack at the edge of the specimen The center of the specimen is deeply attacked or not polished at all Deposits on the surface Wavy surface or residual deformation

Film too viscous or too thin Polishing film did not form in the center of the specimen Insoluble reaction products

Polishing time too short Flow rate too high or too low Rough surface after grinding Electrolyte too old Selective polishing because of potential differences in surface 共heterogeneous material兲

Solution Adjust the voltage Renew electrolyte Add electrolyte Reduce the flow rate Adjust flow rate Check the electrolyte temperature Decrease the voltage Remove the specimen immediately when the current is switched off Choose a less corrosive electrolyte Increase the voltage Improve the mechanical preparation of the specimen Reduce the polishing time Improve the mechanical preparation Decrease the time Lower the voltage Reduce flow rate Use a different electrolyte Decrease the voltage Increase flow rate Increase the voltage Reduce the flow rate Add more electrolyte Renew electrolyte or try a different one Increase the voltage Increase the time Change the flow rate Improve the preparation prior to electrolytic polishing Renew electrolyte Other electrolyte with other polishing data or use mechanical preparation instead

Part III: Light Microscopy

14 Introduction METALLOGRAPHY/MATERIALOGRAPHY COMPRISES THE OPTICAL EXAMInation of a material for the purpose of giving a qualitative and quantitative description of that material’s structure. The structure is characterized by size, shape, distribution, density, orientation, and type of phases, as well as microstructural defects 共see Fig. 1.2兲. In this context, the light microscope is an important tool. In the following chapter, the basic physical principles of reflected light microscopy and the most important methods of microscopic examination will be described in more detail. In Chapter 16 a short introduction to electron-microscopy and scanning probe microscopy is given. The optical effect of enlargement that occurs when one looks through the rounded glass of a convex lens 共magnifying lens or loupe兲 was known to the ancient Egyptians, Greeks, and Romans. Today, a convex lens still serves as a magnifying glass for observing small objects, the useful magnification is limited to 10– 15⫻. The first microscope, consisting of two lenses, was probably built by either Hans and Zacharias Jansen in about 1590 in the Netherlands or by Cornelius Drebbel around 1600. In connection with the growing significance of the natural sciences in the 19th century, microscopic observations in the fields of medicine, biology, and geology became ever more important. H. C. Sorby in England 共1864兲 and A. Martens in Germany 共1878兲 were the first to prepare metallographic polished sections of steel and cast iron, examine them by microscope, and sketch or photograph their visible structure. Microscopes used today are still built according to the old principle of a system of lenses placed together. Their essential elements are source of light, lens, eyepiece 共or ocular兲, prism, mirror, and shutter and filtering systems.

14.1 Visible Light–Table 14.1–Table 14.2 Light that can be seen by the human eye is an electromagnetic light wave with wavelengths of between 350 and 780 nm. Depending on the wavelength, the human eye sees different colors 共see Table 14.1兲. White light consists of a mixture of all the colors in the spectrum. Light of an even wavelength is monochromatic. When wavelengths of a particular range are missing from a beam of polychromatic light, we see a mixed color 共Table 14.2兲. TABLE 14.1—Range of Wavelength of Visible Light and Color. Range of Wavelength, nm 360–440 440–495 495–580 580–640 640–780

Color violet blue green yellow/orange red

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TABLE 14.2—Spectral Color Filtered Out and Visible Mixed Color. Spectral Color Filtered Out Violet Ice blue Yellow Red

Mixed Color Green-yellow Orange Ultramarine blue Blue-green

14.2 The Human Eye The construction of the human eye is similar to that of a camera 共Fig. 14.1兲. Thanks to the muscles in our eyes, the focal distance of their flexible lenses 共1兲 can be varied to enable us to focus on any object at a distance between approximately 20 cm and infinity. The inner diameter of the iris 共3兲 can be varied to change the amount of light falling into it. This variation produces a sharp image on the retina 共2兲, the gray values of which are received by receptor-rods, and the color values of which are received by the cones and transformed into electrical impulses. These impulses are in turn transmitted via the optical nerve 共4兲 to the brain where they are then processed. For example, let us look at a 160 m 共⬃490 ft兲 high tower from a distance of about 300 m 共⬃915 ft兲. If we imagine two lines that extend from the middle of our eye, one to the foot of the tower and one to the top, we get what is called the visual angle. In this example, the visual angle ␦ is about 30 degrees. We are not able to recognize the faces of people on the tower because the visual angle is too small for our eye to process. But if we go closer to the tower, then we can better recognize the details of the building and the people. This means that the closer we bring an object to our eye, however, thereby increasing the visual angle, the more details we are able to discern. Normally, we are able to read the text on a page of a book from a distance of 25 cm 共⬃10 in兲. This distance is called the conventional visual range, or visual range of reference. It enables us to compare the magnification data of different optical systems. To make out the details of the individual letters on that page of text, we must decrease the visual angle. If we bring the text closer to our eyes, in order to increase the

Fig. 14.1—Light path of the human eye, with lens, cornea 共1兲, retina 共2兲, iris 共3兲, optical nerve 共4兲.1

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visual angle further, the text begins to blur because the ability of our lenses to adjust to the visual angle is limited.

14.3 Magnifying Lens and Microscope Magnifying glasses and microscopes are optical devices that enable us to increase the visual angle between the eye and objects that are small and near so that details that cannot be seen with the unaided eye now become visible. If we place a convex lens 共magnifying glass兲 between our eyes and the page of text, the visual angle is increased and the details of individual letters as well as the surface structure of the paper become visible. A magnifying glass produces an enlargement by means of a single imaging step. The object lies in the center of focus and the eye is accommodated ad infinitum. The smaller the focal point of the magnifying lens, the greater the magnification. Practically speaking, a magnification of the object of 10 up to a maximum of 15 times its actual size remains in the useful range. By using several lenses arranged one after the other, the magnification effect can be increased considerably. The construction of the classical microscope consists of a two-lens system. The magnification takes place in two image-forming steps. First, an enlarged image of the object is projected by the objective in the intermediate image plane. This image is then magnified by the ocular, or eyepiece.

14.4 Magnification Magnification, M, as the function of an optical instrument is defined as:

M=

Visual angle with optical instrument ␦1 Visual angle without optical instrument ␦2

共1兲

or M = tan ␦1/tan ␦2

共2兲

Magnification by a compound microscope results as a product of the magnification of the objective and the magnification of the eyepiece M = Mobjective ⫻ Meyepiece

共3兲

15 The Optical Reflected Light Microscope 15.1 The Path of Light Rays FIGURE 15.1 SHOWS THE COURSE OF LIGHT RAYS IN A MODERN THREElens transmitted light microscope with “infinity optics” 共the ICS principle, which means “Infinity Color-corrected System”兲. Let us follow the light rays that emanate from an object 共1兲. From these rays the objective 共2兲 projects an image to infinity. The intermediate lens 共3兲 that also intervenes in the progress of the light rays creates a magnified intermediate image 共4兲 from the rays that are now running parallel. This intermediate image is further magnified by the eyepiece 共5兲. As the illustration shows, the visual angle ␦1 that results when this optical system is used is considerably greater than it is when the object is viewed by the naked eye at the same distance of 25 cm 共⬃10 in兲, visual angle ␦2.

15.2 The Objective The objective consists of a combination of lenses, both converging and diverging, that are precisely adjusted to one another. This makes a correction of any part of the imageforming process possible whereby something has been lost, e.g., missing color, and a flat intermediate image is projected. The angle of opening 2␣, the aperture of the objective lens system, is crucial for the quality of a microscopic system 共Fig. 15.2兲. An effective aperture is one that is as large as possible so that as many diffraction spectrum maxima as possible of the rays reflected by the object can be captured and an image rich in detail consequently rendered. If, with regard to the illumination, one uses a condenser lens system 共Fig. 15.2兲 that concentrates the initially parallel rays into a cone, the objective can then catch rays that are even more diffracted. This means a greater optical resolving power and, consequently, more detail. For technical reasons, the angle at which a ray of light can enter into the objective is maximally ␣ = 72°.

15.2.1 Numerical Aperture—Resolution-Magnification–Table 15.1–Table 15.2 The numerical aperture, by means of which a comparison can be made between two objectives, is defined as follows: NA = n ⫻ sin ␣

共1兲

In this equation, ␣ is half of the aperture angle of the objective. If air is present between the objective and the object, the refractive index, n ⬃ 1 共see Table 15.1兲. 528

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Fig. 15.1—Optical path A in a three-lens transmitted light microscope with infinity optics with the visual angle ␦1 compared to the visual angle ␦2, when the object is viewed by the naked eye in beam path B. With object A and B 共1兲, objective 共2兲, tube lens 共3兲, magnified intermediate image 共4兲, eyepiece 共5兲, eye 共6兲.1

Under comparable conditions, maximum achievable image brightness is proportional to NA2. The greater the aperture of the objective and the shorter the light wavelength 共␭兲 the better one can distinguish two adjacent image points from one another. The shortest distance 共do兲 is a measure of the resolving power of the microscope. This is shown schematically in Fig. 15.3. According to the laws of wave optics, one has achieved this distance 共do兲 when a maximum degree of refraction is emitted from each of two image points that are separated from one another by a minimum of refraction. Ernst Abbe has defined this relationship mathematically with the following equation:

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Fig. 15.2—Optical path of a condenser lens system with object in transmitted light 共1兲, light beam 共2兲, objective 共3兲, condenser 共4兲.1 TABLE 15.1—Immersions Agents, Their Refractive Index, and the Possible Numerical Aperture. Medium Air Water Immersion oil Monobromonaphtalene Methylene iodide

Refractive Index (n) 1 1.333 1.515 1.66 1.740

do =

Numerical Aperture NA to 0.95 to 1.4

␭ ␭ ⬇ NAObjective + NACondensor 2NA

共2兲

Example: If we assume that the aperture of the objective and the condenser is 1.25 and a wavelength 共␭兲 in the middle range of 0.5 ␮m, respectively, we receive, as the smallest distance possible between two object points that can just be distinguished, a do value of 0.2 ␮m.

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Fig. 15.3—The shortest distance 共d0兲 between two adjacent image points. The shortest distance is a measure of the resolving power of the microscope.

The resolving power can be improved by using light of shorter wavelength and a larger aperture in the objective. With the use of white light, if one takes a medium wavelength ␭ of 0 , 56 ␮m and an immersion objective with an aperture of 1.4 and with k = 0.61, a resolving power of 0.25 ␮m results. For blue light with a wavelength of ␭ = 0 , 49 ␮m, one gets a resolving power, under otherwise identical conditions, of about 0.2 ␮m. Table 15.2 shows some values of resolutions that are theoretically possible for various objectives and for a wavelength of 0 , 55 ␮m. Here, do is the distance between two points on the object and Do is the point distance on the intermediate image. In actual practice, the attainable resolution is usually less than the theoretical values stated in Table 15.2. It is dependent on the quality of the objective, the optimal setting of the aperture diaphragm, use of the right immersion oil and, naturally, the specimen. One gets the best results with dust-free microscope systems and clean objectives and well prepared specimens. The overall magnification of a microscope is the product of the scale magnification of the objective multiplied by the ocular magnification. The magnification number indicates how many times larger the intermediate image produced by the objective is than the object itself. M = Mobjective ⫻ Meyepiece

共3兲

With a 50⫻ objective and a 10⫻ eyepiece the overall magnification of the microscope is 500⫻. Commonly used are 5⫻, 10⫻, 20⫻, 50⫻, and 100⫻-objectives. Additional magnifications gained through the use of between-lenses or zoomdevices are to be borne in mind. M = Mobjective ⫻ Meyepiece ⫻ Mbetween-lens

or zoom-device

共4兲

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TABLE 15.2—Values of Resolutions that are Possible for Various Objectives and for a Wavelength of 0 , 55 μm. Objective 5⫻ 10⫻ 40⫻ 40⫻ 63⫻ 100⫻

NA 0.15 0.30 0.75 1.3 oil 1.4 oil 1.3 oil

do / μm 2.2 1.1 0.45 0.26 0.24 0.26

Do / μm 11.2 11.2 17.9 10.3 15.1 25.8

The magnifications achieved individually by the objective, the intermediate lens, and the eyepiece must be attuned to one another. One obtains optimal image quality with an objective of a high scale number in combination with an eyepiece of low magnification. For example, the combination 50⫻-objective and 5⫻-eyepiece is preferable to the combination 10⫻-objective with 25⫻-eyepiece. The total magnification of a microscope should be from 500 to a maximum of 1000 times the aperture of the objective. This is the maximum useful magnification that allows the objective to reproduce tiny details in which the intermediate image can then be magnified further by the eyepiece. The numerical aperture of an objective increases with the objective magnification, while the depth of field decreases. It is possible to increase the depth of focus, within limits, by lowering the aperture diaphragm. But this is done at the cost of resolution. Setting the aperture diaphragm too low results in empty enlargements and blurred images inasmuch as one thereby leaves the range of useful magnification. In the case of dry objectives, there is air between the front lens and the object. A maximum aperture of 0.95 is possible. In the case of immersion objectives, use of certain immersion agents with a higher refraction index between the front lens and the object makes possible an increase of the numerical aperture to 1.7. This is shown in Fig. 15.4. Table 15.1 shows some values of immersions agents, their refractive index and the possible numerical aperture. The numerical aperture 共NA兲 is of essential significance for: • Maximum image brightness • Resolving power • Useful total magnification • Depth of focus

15.2.2 Aberrations in Image-Formation Geometric and chromatic aberrations in image-formation are possible with uncorrected optical systems. Geometric aberrations in the imaging process can occur even with monochromatic light. These include: Aperture errors: With light beams on a plane parallel to the axis, the convergence on the image side occurs not in the ideal image plane but rather either in front of it 共in the case of converging lens兲 or behind it 共in the case of dispersing lens兲. Coma: Off-axis point objects appear as asymmetrical areas with a comet-like tail. Astigmatism: Point objects appear not as point images but rather as line images. Curvature of field: The image points of a larger object do not lie on a plane but

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Fig. 15.4—Improved resolution by use of an immersion liquid 共6兲 between object, over slip 共5兲 and objective 共3兲.1

instead on a curved surface. With uncorrected optical systems one can therefore focus sharply either on the center of the image or else on peripheral zones. Distortion: The image scale is dependent on the distance of the image point from the optical axis. Increasing that scale leads to a pillow-shaped distortion. Decreasing the scale results in barrel-shaped distortions. With the polychromatic light used in microscopy, chromatic aberration can also occur. Since the refractive index decreases with an increase in wavelength, the focal length of a lens for these light rays increases. The image of an object point, produced by short-wave light 共violet兲 lies in front of the image produced with long-wave light 共red兲. Undesirable color fringes are the result. The chromatic difference of spherical aberration manifests itself in blue and yellow fringes. With an appropriate combination of converging and dispersing lenses made of optical glass with varying dispersive and refractory properties, these aberrations can be corrected and objectives with varying optical properties can be produced.

15.2.3 Available Objectives Depending on the purpose for which they are used and the quality that is required of the microscopic image, various corrected objective lens systems are available for selection. The objectives most often used are achromats. They are inexpensive because they consist of relatively few lenses. Spherically they are corrected for one wavelength and chromatically for only two wavelengths, usually red and green. This may lead to red and blue color fringes around the object, but this can be avoided to a large extent through the use of a green filter. Because the flatness of field is limited, they are appropriate for visual fields of up to approximately 18 mm in diameter. These objectives can be used for routine tasks, including those as in polarized light. They are less useful for

534


microscopy in darkfield and for color photography, especially when there is a high degree of magnification. With fluorite or semiapochromatic objectives, spherical and chromatic aberration is more strongly corrected. Flatness of field is also improved. For these reasons such objectives can be used for fields of vision of up to 23 mm in diameter and are appropriate for color microphotography in reflected light and transmitted light as well as for dark field and DIC. With apochromats, spherical aberration is corrected for two colors and chromatic aberration for three colors. Because of their even further improved flatness of field, these objectives can be used for fields of vision of up to 25 mm in diameter. And because color fringes hardly ever occur, these high-quality objectives are well suited for color photography and for microscoping in dark field. Because of the better image correction, higher numerical apertures are possible and consequently a better resolution. These objectives are therefore appropriate for the upper range of magnification to differentiate the finest details 共precipitations, grain boundaries兲 and capture them in their true colors. This means, however, less depth of field and a smaller working distance between objective and object in comparison with achromats. Plan apochromats and epiplan apochromats exhibit an outstanding flatness of field and can therefore be used for large fields of view. Furthermore, since they possess color correction for four wavelengths, the color rendering is optimal. The high numerical aperture makes a maximum of resolution power possible. These objectives in the upper price range satisfy the highest demands in research and technology. Objectives are usually marked with color rings corresponding to their magnifications: red-5⫻, yellow-10⫻, green-20⫻, blue-50⫻, white-100⫻. The most important technical data are also inscribed on the barrel of the objective. For example, Epiplan-Neofluar 10⫻ / 0 , 30 HD DIC ⬁/0 provides the following information: “Epiplan” means that this is an objective for a reflected light microscope that renders a flattened intermediate image. “Fluar” refers to the fluorite glass with which the objective has been constructed. The indicated scale number “10⫻” means that the intermediate image is 10 times larger than the object. “0.30” is the numerical aperture of the objective. Using a light with an assumed wavelength of ␭ = 500 nm, a resolving power of 1 ␮m can be calculated. “HD DIC” means that this objective can be used for bright-field 共BF兲 illumination, dark-field illumination 共DF兲, and differential interference contrast 共DIC兲 illumination. On most microscopes, objectives of varying scale number are exchangeable with the rotatory nosepiece. To keep the focus essentially unchanged, the distance between the screw-on surface of the objective and the eyepiece head is an important mechanical dimension. It is called the mechanical tube length and is engraved on the objective. If “⬁” is indicated there, this means that the object is imaged to infinity by the objective and that an additional tube lens produces a real intermediate image. With a transmitted light microscope, objects are placed on a glass stage and protected by a cover glass. Consequently, transmitted light objectives are calculated and corrected for a cover glass thickness of 0.17 mm.

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Fig. 15.5—Schematic cross section of an eyepiece, with the position of the intermediate image plane 共1兲, the boundaries of the visible field of vision 共2兲, the eyepiece optical system 共3兲, the pupil of the observer’s eye 共4兲 and the focusing ring for the diopter adjustment 共5兲.1

In our example we are looking at an objective for reflected light microscopy. Because one usually examines uncovered specimens, the cover glass thickness is represented as a “ 0.”

15.3 Eyepieces The simplest eyepieces consist of a convergent lens that acts as a magnifying glass. Good eyepieces are equipped with a corrected lens system including an eye lens 共above兲 and a field lens 共below兲. Figure 15.5 shows a schematic cross section of an eyepiece with the position of the intermediate image plane 共1兲, the boundaries of the visible field of vision 共2兲, the eyepiece optical system 共3兲, the pupil of the observer’s eye 共4兲, and the focusing ring for the diopter adjustment 共5兲. Although eyepieces magnify the intermediate image that is produced by the objective, they do not bring about any further improvement in resolving power. But since the angle of vision is now larger, the human eye is able to discern more detail. If aberrations are still present in the intermediate image, they can be corrected with the appropriate eyepieces. Many eyepieces are designed for people who wear eyeglasses. They are usually equipped with eyecups. The eyecups can be attached or they can be folded up to get the right visual distance if the individual wants to use the microscope without eyeglasses. The area of the intermediate image that can be examined, the field of view, is restricted by the field lens and the aperture diaphragm. The value S is the measure of the field of vision and is indicated on every eyepiece. The diameter of the field of vision can be calculated from the field of vision value of the objective together with the objective’s scale number: Field of vision value S/M 共objective兲 An example: If M 共objective兲 = 40 and S 共eyepiece兲 = 18 mm, the result is a viewing field of 0.45-mm diameter. Wide-field eyepieces should be used only in combination with corrected plane objectives that produce a well flattened intermediate image. Micrometer eyepieces have a glass plate with a scale situated on the plane surface of the diaphragm. After the system has been calibrated, linear measurements as well as

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measurement of angles 共goniometric eyepiece兲 can be made. The corresponding standard guides for calibrating are cited. A tip: The eyepiece can also be used as a magnifying glass. Simply turn the eyepiece, train the eye lens on the object, and look through the field 共condensing兲 lens.

15.4 Illumination Illumination source and light path are important elements of a microscope. Halogen lamps are often used, as are xenon high-pressure lamps. Halogen lamps of between 25 and 100 watts emit light with a color temperature of about 3000 K. This must be kept in mind when colored photographs are being taken and conversion filters must be used for correction. Xenon high-pressure lamps that produce between 100 and 500 watts are available, and they produce a light that is more like natural light. Spectral response of the radiated light and color temperature are about 5000 K. A microscope’s illumination should • Be adapted to the illuminated object field. • Illuminate completely and evenly the object field to be observed. • Be such that the illuminated object field is adapted to the field of vision of the microscope. • Be adjustable according to the aperture angle.

15.4.1 Koehler’s Illumination System The illumination system proposed by August Koehler in 1893 is still used today with many optical systems using transmitted- and reflected-light microscopy. The Koehler’s illumination method produces images that are illuminated with evenly distributed light using three lenses placed between the light source 共1兲 in Fig. 15.6 and the reflector 共2兲. This type of illumination also contributes to the enhancement of the resolution power. On reflected-light microscopes used for metallography/ materialography the Koehler illumination system is adjusted by the microscope factory and should not be changed by the user, for transmitted light, the system shall be adjusted regularly. The three lenses of the Koehler system are part of the illumination elements 共A兲 in Fig. 15.6. As the first lens in front of the light source 共1兲, the collector lens forms an image of the light source at the second lens, the first condenser lens. The third lens, the second condenser lens, reproduces the image of the light source in the back focal plane of the objective 共3兲 after passing the reflector 共2兲. In this way the surface of the specimen is uniformly illuminated. In the path of the illuminating light rays there are two important diaphragms. The centering radiant field diaphragm makes it possible to adjust the illuminated object field to the microscope’s actual field of view. This diaphragm is correctly set when the image of the edges of the diaphragm disappear behind the border of the field of vision. Stray light is avoided and contrast is heightened. With reflected-light microscopes a one-time setting of the field diaphragm is sufficient; it does not have to be readjusted each time the objective is changed. By means of the aperture diaphragm, the cone of light is adjusted to the aperture of the objective. It has an optimal setting when that part of the light rays that is not diaphragmed out covers about two-thirds of the objective’s entrance pupil. This diaphragm must be reset whenever the objective is changed to meet the requirements of

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Fig. 15.6—Bright field 共BF兲 illumination in reflected light and components in the optical path for establishing contrast: Light source 共1兲, beamsplitter, color neutral 共2兲, objective 共3兲, object 共4兲, lens 共5兲 and contrast components on the side of the lamp 共A兲, on the side of the eyepiece 共B兲 and components for both light paths 共C兲.1

the desired image. This means that a compromise must be made between resolution, contrast, and depth of focal field.

15.5 Microscope Options The optical elements of a microscope, i.e., the objective, tube lens, eyepiece or projective, illuminators with light source, aperture and light field diaphragm—are assembled in a mechanical device, the microscope body. Depending on the expandability and capability of the built-in optical and mechanical assembly parts, one differentiates between student microscopes, laboratory microscopes, and research microscopes. Student microscopes are the most simply built and therefore the most limited in their uses. The interchangeability of the individual optical elements is limited. Because of their ease of use these microscopes are appropriate for the beginner or are used for the preselection of specimens. Laboratory 共or working兲 microscopes are equipped in such a way that they can be

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used without problem for many routine tasks. The stage can be rotated or can be adjusted in an x-y-direction, or both, and the focusing of the objective occurs through a coarse and fine focusing mechanism. As an illumination source, a halogen bulb is mostly used. Koehler illumination as well as interchangeable objectives and filters make it possible to perform all the usual examination procedures. Attachment possibilities for further fixtures, as for example analogue or digital cameras, are present. Research microscopes belong to the top class of instruments. With these microscopes all the essential parts, such as lamp-housing, condenser turret, object holding stage, objective rotator, and tubes are interchangeable and can be adapted to special tasks. Specimens can be viewed in either reflected or transmitted light. All known methods of microscopic examination are possible. The motorized variants are especially convenient because they make it possible for change of objective, focusing, and movement of the mechanical stage to occur automatically. Moreover, with the appropriate software all the important data such as objective, illumination, magnification, coordinates of the object, and the digital photographing of the image can be saved and later retrieved. In a metallographic/materialographic laboratory, reflected-light microscopes of either the upright or inverted type are used. If other materials are also examined, for example, ceramic, stone, glass, or synthetics, a microscope with reflected-light as well as transmitted-light beam projection is necessary.

15.6 The Reflected-Light Microscope In metallography/materialography, ground and polished surfaces of materials are the main objects that are examined with reflected 共incident兲 light. The essential parts of a reflected-light microscope are: light source, condenser, aperture- and radiant-field diaphragm, filter holder, reflector, rotating nosepiece with reflected-light objective, stage, intermediate optic, body tube, and eyepiece.

15.6.1 Upright Type of Reflected-Light Microscope With the reflected-light microscope of the upright type that is customarily used in materials research, the top surface of the specimen is illuminated from above through the objective. Here the light rays are reflected or scattered. These rays are collected by the objective. The tube lens projects an enlarged intermediate image that is caught by the eyepiece and further magnified. Figure 15.7 shows a modern upright type, reflected-light microscope, for routine purposes. The specimen lies on a movable stage. Direct observation of the fully lit position is possible. For the area being examined to be positioned absolutely perpendicular to the optical axis, the specimen must be correspondingly orientated with a leveling device. The thickness of the specimen is limited by the working distance between objective and stage.

15.6.2 Inverted Type of Reflected-Light Microscope In the field of metallography/materialography, reflected light microscopes of the inverted type are also used often. Following the suggestion of Le Chatellier, the specimen

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Fig. 15.7—Upright type reflected-light microscope.2

is placed on a movable specimen stage with a hole above the microscope column and the objective. Figure 15.8 shows a modern research microscope, inverted type, reflected-light. The inverted type has the following advantages: 共1兲 The specimen is simply placed with the prepared surface facing down on the stage and over the hole; 共2兲 There is no need for cumbersome manipulation of a leveling device in order to get the prepared surface of the specimen perpendicular to the light path; 共3兲 Larger, irregularly shaped specimens can be easily examined microscopically as well, inasmuch as the working distance object-objective is not affected by the size of the specimen. One disadvantage is that the prepared surface can become scratched when it is placed on the stage. Furthermore, one may not be able to see the illuminated area very clearly. The objective of a reflected-light microscope differs from that of a transmittedlight microscope. Optical calculations must take into account the fact that surfaces like polished specimens are examined without a cover glass. In addition, reflected-light objectives are especially well dereflected so that no disruptive “false flashes” are superimposed on the image of the specimen. With both systems, all the necessary construction elements are integrated in the microscope. With a rotating nosepiece, different objectives can be inserted into the beam path and the magnification thereby changed. Exchangeable slide-in components permit quick and simple change to other types of illumination or filters.

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Fig. 15.8—Inverted type reflected-light microscope for research.3

A camera connection makes documentation of the magnified image of the object possible.

15.7 Optical Examination Methods The prepared specimen normally has a plane surface. The ground and polished metallic surface reflects light very well, therefore, usually shine brightly. The surface is either silver or slightly colored, depending on the composition of the material. However, we can differentiate individual portions of structural constituents only when they show different contrast. If the reflection difference between two structural constituents is greater than 10 %, they can be distinguished from each other. If that difference is less than 10 %, contrast must be heightened using methods suited to that purpose. Before contrasting, either by chemical or physical means, can be undertaken on a ground and polished specimen, the specimen should first be observed in a polished condition. To this end it is advisable to begin with the lowest degree of magnification and then proceed to greater magnification. This enables one to check the quality of the specimen preparation. Moreover, fissures, shrinkage and pores, inclusions, impurities, corroded areas, thin oxide films, peripheral layers, and their adhesion to the base material can already be detected. If the contrast between individual structural constituents is sufficiently high, they can be distinguished as well. With most metallographically/materialographically prepared specimens, however, the reflection differences between the individual structural constituents or phases are so small that the contrast must be heightened by using carefully selected methods. One process used to effect a change in the specimen surface, and which is connected with contrast-heightening, is the electrochemical etching method. This process includes the classical chemical as well as electrolytic etching. In addition, physical contrasting methods, including thermal etching, ionic etching, and the application of interference coating are used to bring about a change in the

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surface of the specimen 共see Figs. 9.1 and 9.2兲. These methods are described in more detail in Chapter 9. Our task here is to consider in greater detail various optical methods of producing contrast that do not cause any change in the specimen surface. The four main optical contrast methods used for the purpose of examining the textures and structures of metallographically/materialographically prepared specimens with a microscope are the following: bright-field illumination, dark-field illumination, polarization contrast, and differential interference contrast.

15.7.1 Bright-Field „BF… Illumination Reflected light bright-field illumination is the most important method used in reflected-light microscopy. In this process, the light that is reflected into the light path of the microscope passes through the objective directly onto the specimen surface. Figure 15.6 shows the light path when bright-field illumination is used. An integrated vertical illuminator 共1兲 emits a light that travels through the reflected-light aperture diaphragm and the radiant-field diaphragm. The light beam is then reflected by a color neutral beam splitter 共2兲, which is set at 45° to the optic axis, and through the objective 共3兲 the beam strikes the surface of the specimen 共4兲. There, the reflected or scattered beams again pass through the objective 共3兲 and traverse the beam splitter 共2兲. The tube lens 共5兲 then projects the intermediate image. The image is further enlarged by the eyepiece. Half-translucent mirrors may be used as beam splitters, but a higher light yield is obtained by using prism illuminators. Figure 15.6 also shows the location of all possible contrasting components arranged in a small area above the objective with A: Contrasting element of the illumination side, B: Contrasting element of the observation side, and C: Space for components for both light paths. The reflecting capacity of the individual structural constituents depends on their refraction number n. More important, however, is the varying absorption power of individual phases and diffuse reflections. Differences in absorption of individual phases and the presence of diffuse reflections create contrasts. If this contrast is sufficient, the differences can be visible to the eye. Accordingly, the polished specimen of a single-phase gold alloy, as well as those of many multiphase metal alloys, show hardly any contrasts. If the material has constituent parts of widely varying reflection power, e.g., cast iron with laminated graphite, steel with slag inclusion or sulfides, those individual constituent parts are already microscopically detectable immediately after the material has been polished. Diffuse reflection occurs when there are rough surfaces, grain boundaries, and scratches. But the presence of these things may also give some indication, in individual cases, of the material’s structure. For microstructures in bright field 共BF兲, see Figs. 7.15 and 15.10共a兲. In other methods of achieving optical contrast, the light rays emanating from the light source are diverted or else altered. Various reflectors that are built into the reflector slide of the microscope are used for this purpose. To gain a particular kind of microscopic illumination or to observe the specimen in a particular way, one simply inserts the reflector in the corresponding position.

15.7.2 Dark-Field „DF… Illumination

In the case of reflected-light dark-field illumination 共Fig. 15.9兲, the light that is emitted by the reflected-light illuminator 共1兲 does not fall directly on the specimen surface. By

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Fig. 15.9—Dark field 共DF兲 illumination in reflected light, with light source 共1兲, mirror step assembly 共2兲, mirror with an oval hole 共3兲, light, directed in a second housing case towards the objective 共4兲, sample surface 共5兲.1

means of a reflector “staircase” 共2 and 3兲, the light is conducted around the actual objective and into a second housing case 共4兲 where it strikes a ring-shaped concave reflector. This device reflects the rays at a very flat angle of illumination onto the specimen surface 共5兲. Only scattered light returns for observation in the microscopic beam path. For this reason, the flat surface of a well-polished specimen appears dark. Reflected-light dark-field illumination is well suited to show the quality of a polished surface inasmuch as the oblique light rays allow lapping tracks, scratches, and fine cracks to show up bright. Unevenness and rough surfaces are easily detected as well. Hard phases that stand out, deeper-lying soft phases, as well as contraction cavities and pores display bright edge seams 共relief兲. Half-opaque phases may show their inherent color. Figure 15.10 shows a carbon steel in bright field 共a兲 and dark-field 共b兲. The structure and texture as well as surface details can be clearly seen with dark-field illumination.

15.7.3 Polarization Contrasting „POL…

When contrast is achieved using polarization, a polarizer 共P兲 is inserted into the illumination beam pathway and an analyzer 共A兲 into the observation beam pathway 共Fig.

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Fig. 15.10—Microstructure of carbon steel in bright field 共a兲 and dark field 共b兲.

15.11兲. The direction of transmission of the analyzer 共6, A兲 is at a right angle to the polarizer 共2, P兲. Only the depolarized portions of the rays can reach the tube lens 共7兲. In this polarized light a lambda plate 共6a, ␭兲 changes the gray contrast into color contrast. Interference reflection can be prevented by using a rotating ␭ / 4-plate 共antiflexplate兲 between the object and the objective. In the case of substances that are optically isotropic, e.g., cubic or amorphous, the specimen always appears dark because reflection from these materials does not lead to a change in the state of polarization. The polarized light is, consequently, not let through by the analyzer. Structural constituents that are optically anisotropic, as for example zinc, titanium, spheroidal graphite, some nonmetallic inclusions or minerals on the other hand, do change the polarization state of a ray of light when reflected. Then the depolarized portions of the light can penetrate the analyzer.

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Fig. 15.11—Polarization contrast 共POL兲 in reflected light, with polarizer 共2 P兲, analyzer 共6 A兲, lambda plate 共6a ␭兲.1

Observation of a metallographic/materialographic polished specimen in polarized light is therefore useful for differentiating between isotropic 共cubic兲 and anisotropic 共noncubic兲 phases. Ferromagnetic phases can be identified as well inasmuch as the plane of polarization, affected by the magnetization, is turned. For this reason, the domain boundaries of the magnetic zones appear in varying degrees of brightness. The gray contrasts that occur in anisotropic phases can be transformed into color contrasts through the use of a lambda plate 共6a兲 in the observation beam pathway. Isotropic phases can likewise be contrasted in polarized light by applying an optically anisotropic layer. For example, an oxide layer applied by anodization to aluminum produces color contrasts. With slag, minerals, ceramic, and glass that show half-opaque behavior, the use of polarized light results in less scattered light. This makes a better contrast possible and the structural constituents can be delineated better one from another. The microstructure in Fig. 15.12 shows titanium with deformed areas made visible with polarization contrast 共POL兲.

15.7.4 Differential Interference Contrasting „DIC… When Nomarski’s differential interference contrast method is used, the polarized ray of light is split into two beams of different oscillation directions 共Fig. 15.13兲 by a doubly

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Fig. 15.12—Microstructure of titanium in polarized light. Cold work is visible.

refracting prism 共4兲. These two rays are out of phase with each other when they strike the specimen 共6兲. If the specimen surface is not completely flat, path differences are the result. In a reverse direction, the reflected or scattered beams, or both, now traverse the DIC-prism 共4兲 and the analyzer 共7兲, thereby acquiring the same oscillation direction and now capable of interfering with the intermediate image. The path differences that are caused by the specimen surface are converted to gray values. Unevenness becomes visible as relief. With a lambda plate, color contrasts can be obtained. Figure 15.14 shows a microstructure of a soldering in bright field 共BF兲共a兲 and in differential interference contrast 共DIC兲共b兲. In BF the solder can only be seen as a gray phase in the lighter matrix, but in DIC the solder can be clearly discriminated from the matrix.

15.7.5 Fluorescence in Reflected Light Specific areas of a microstructure can be marked with a fluorescence dye 共see Section 3.10.1兲. These areas will absorb light of a specific wavelength in a short period of time, and then emit the light. The wavelength of the emitted light is always around 20– 50 nm longer than the incoming light. If blue light is absorbed, green light is emitted, from UV-light visible light is emitted. Especially at the examination of medical and biological samples, fluorescence is often used, as specific dyes are suited for specific phases in the sample. In this way an exact microscopic examination can be performed. In metallography/materialography the use of a dye can give important information on size and distribution of pores, cracks, gaps between basic material and surface layers, etc. 共see Section 3.10.1兲. At the reflected fluorescence microscopy 共Fig. 15.15兲 a short pass filter 共A兲 is placed in the light path, only allowing light of a narrow wavelength to pass to the specimen. In between is placed a beam splitter 共B兲, which reflects the short waved reflected light and only let through the long waved emitted light. The reflected light that is not absorbed by the specimen surface is stopped by a long pass filter 共C兲; this filter only lets the long waved fluorescence light pass. Lamps with a high degree of red or infrared light are less suited for fluorescence

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Fig. 15.13—Differential interference contrast 共DIC兲 in reflected light, with doubly refracting prism 共4兲, objective 共5兲, specimen 共6兲 and analyzer 共7兲.1

microscopy; mercury vapor lamps with a line type spectrum are to be preferred. For a microstructure impregnated with a dye and examined with fluorescence see Fig. 3.14.

15.8 Practical Use of the Microscope 15.8.1 Setting up the Microscope If possible, the microscope should be set up in a room of its own on a stable worktable. There should be sufficient space to the right and to the left of the apparatus for the depositing of specimens and supplemental equipment. If no separate room is available for microscopic or measurement work, the instrument should be located in a place removed from all sectioning, grinding, and polishing equipment to avoid any transference of vibrations or abrasion particles. Moisture, especially alkaline and acid vapors from electrolytic polishing or chemical etching, can also damage important parts of the microscope after just a short time. Such chemical procedures should be performed under a fume hood in a separate room.

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Fig. 15.14—Microstructure of a soldering in bright field 共BF兲共a兲 and differential interference contrast 共DIC兲共b兲.

15.8.2 Working with the Microscope In this section and the following two sections, a number of points are stated that should be followed when working with the microscope. • Adjust the height of your chair in such a way that you are sitting erect but comfortably as you look into the eyepiece and can reach all the operating parts of the instrument effortlessly. • Turn on the source of light. • Place a specimen on the microscope stage 共focus plane兲. • Look into the distance, then, without changing the focus of your eyes, look into the eyepiece. • Adjust the distance between the eyepieces according to the distance between your eyes. • If you do not wear glasses, put rubber eyecups on the eyepieces to get the right eye distance to the eyepiece.

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Fig. 15.15—Fluorescence: Short pass filter 共A兲, beamsplitter 共B兲 and long pass filter 共C兲.1

If you do wear glasses, check to see whether the eyepieces are designed accordingly. If you have done everything right you will have a clear view of everything in the whole field of vision.

15.8.3 Correct Adjustment of the Microscope •

Begin by using an objective of a low scale number and bring the specimen into focus. • Open the field diaphragm and center this and the condenser in such a way that the viewing field is illuminated evenly. • Close the field diaphragm and, through centering, bring the little fuzzy fleck of light that is still present into the middle of the viewing field. • This fleck of light can be brought into sharp focus by vertically adjusting the condenser. • Open the centered field diaphragm in such a way that the diaphragm leaves extend out over the field of vision. • Open the aperture diaphragm and close it again carefully until the image has become dark enough to show sufficient contrast. With transmitted-light microscopes, a change of objective requires each time a readjustment to accommodate the settings of the field and aperture diaphragms. Such readjustments are not necessary with reflected-light microscopes. With the latter it is sufficient to adjust the aperture diaphragm to the object and the objective.

15.8.4 Focusing and Practical Use •

The task of getting a sharp focus on shiny polished specimens of metal can be facilitated by partially closing the radiant-field diaphragm. After that, focus sharply on the image of the radiant-field diaphragm. Because this diaphragm is imaged in the

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object plane, it is easy to find the image of the specimen surface. As an alternative move the field of view to the edge of the sample. The contrast between the sample and the mounting material or air allows for a simple focus. • In focusing the microscope, use at first an objective of weak magnification and look for the area of interest. Then change to objectives with a higher magnification, as necessary. With unfamiliar specimens it is advisable to experiment with all the different illumination possibilities 共optical contrasting methods兲. Often structural details can be identified better in this way and distinguished from one another. If an oil immersion objective is used on an upright type microscope, the area of the object that is of interest is first of all located with an objective of a low magnification 共10 ⫻ 兲. Then one focuses with the oil immersion objective 共e.g., 100⫻兲. After that, using the objective revolver, this objective is turned to the side and the one with the lower magnification is again swung into position. Now one applies a drop of immersion oil to the illuminated area on the object, trains the objective with the higher magnification on the specimen, and refocuses with fine focusing. Proceeding in this way can avoid dampening other objectives with oil. In case of an inverted microscope, first focus with the oil immersion objective without oil. The specimen is removed then from the microscope, and a very small drop of immersion oil is placed on the center of the objective. Now the specimen is replaced and a fine focusing is done. After work with the microscope is finished, the oil on the objective and on the specimen is removed immediately and carefully with fine tissue paper and then cleaned with ethanol. •

15.8.5 Measurements of Length The microscopic image can be measured with eyepiece crosses on which there are scales, squared grids, or reference samples. This can be in the form of a reticle, which is a system of lines, circles, dots, cross hairs, or wires, or some other pattern, placed in the eyepiece or at an intermediate plane on the optic axis which is used as a measuring reference, focusing target, or to define a camera field of view. Also a graticule, which is a scale on glass or other transparent material placed in the eyepiece or at an intermediate plane on the optic axis can be used. The scale of the reticle or the graticule serves as a reference gage. The distance between gradation marks on this scale is very precise, e.g., 0.1 mm. Let us suppose that we want to measure the length of an integral part of a microstructure that we are examining with an objective with a scale number of 100. If its apparent length amounts to 1.2 mm in the intermediate image of the eyepiece, its true length can be determined by dividing by the scale number on the objective. The length is 1.2 mm divided by 100, i.e., 12 ␮m. It is not necessary to take the magnification of the eyepiece into consideration. A calculated magnification, using the manufacturer’s supplied ratings, as mentioned earlier, is only an approximation of the true magnification, since individual optical components may vary from their marked magnification. For a precise determination of the magnification 共calibration兲 observed through an eyepiece, a stage micrometre is used. This is a graduated scale, placed like a specimen on the stage of a microscope and used for calibration. It is very important that the measuring devices used are precise, and it is recommended that these should be traceable to the National Institute of Standards and Technology 共NIST兲 or a similar organization.

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Measurements should be performed according to ASTM Standard Guide for Calibrating Reticles and Light Microscope Magnifications 共E 1951兲. This guide covers methods for calculating and calibrating microscope magnifications, photographic magnifications, video monitor magnifications, grain size comparison reticles, and other measuring reticles.

15.8.6 Measurements of Height Differences Occasionally it is of interest to measure height differences of layers of differing hardness or the depth of scratches. To do this, an objective of a high numerical aperture is used because its depth of focus is very slight. One narrows the field diaphragm to a small circle and focuses on the highest plane. On the fine-focusing knob scale a value can be read. Then one focuses on the deepest place and again reads off the appropriate value. If one knows the level difference 共obtained from the instruction manual兲 that corresponds to the distance between two scale-marks on the fine focus mechanism, one can easily calculate the measurement. Use of a dial gage that is connected to the microscope stage or of an electric position encoder is more convenient.

15.8.7 Maintenance of the Microscope Microscopes are precision instruments that should serve their purpose for many years. For this reason they should be handled with care. Dust particles or smoke are especially a problem. Always cover your microscope with a protective dust cover after you have finished working and turned it off. The front lenses of the objective are especially sensitive. Avoid letting the objective come into contact with the specimen or the stage when you are focusing. The most minute scratches that can occur when these touch one another can cause blurred areas in the image. Etched specimens should be thoroughly cleaned and dried before they are used in the microscope. Acids and residual moisture can not only leave flecks on the specimen but also have an adverse effect chemically on the front lenses of the objective, as for example can happen with hydrofluoric acid. If you must remove dust from the objective, eyepiece, or filter, blow them off with a rubber dust blower. Fingerprints, traces of grease, and residues of immersion oil can be removed with a cotton ball dipped in grease-free benzene if necessary. It is a good idea to have the service department of the manufacturer check the device at least once a year and make any adjustments or calibrations that may be necessary. Leave repair work to the service department of the manufacturer also.

15.9 Documentation The documentation of microscopic images can be done in different ways. In the early days of microscopy, the viewer sketched the image details that interested him. Today either reflex cameras for photos in various formats or video or digital cameras, or both, are used. Modern microscopes are equipped accordingly. They have their own photograph/ television connection. One can change over to this connection from the ordinary binocular tube via a beam splitter. Figure 15.16 shows the light path. Through a photo-ocular 共3兲, the intermediate image 共2兲, coming from the tube lens 共1兲, is magnified and projected to infinity. The

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Fig. 15.16—Optical path for photomicrography, with tube lens 共1兲, intermediate image 共2兲, photo eyepiece 共3兲, central shutter 共4兲, camera lens 共5兲 and image in the film plane 共6兲.1

photo-objective produces from this an intermediate image on the film plane in the camera 共6兲 if the central shutter 共4兲 is opened for exposure. The size of this intermediate image must be adjusted to the format of the film. With microphotography film, for example, a magnification with the factor 2.5⫻ must be effected when the original intermediate image has a diameter of 20 mm. This means that the entire image cannot be captured on film of microphotography format. The housing of a reflex camera can be joined to the photo/TV connection by means of an adapter with a built-in objective. The reflex camera should be equipped with an electric motor for film transport and a remote control switch. One disadvantage is that the flipping up of the mirror at the moment of exposure may cause both the microscope and the camera to vibrate, resulting in blurred images. For professional documentation, microscope cameras are to be preferred. All the important camera settings can be regulated electronically from a control desk. The camera itself works with a vibration-free shutter. Depending on the model, the film cassette may be exchangeable. For several years now, video cameras and digital cameras have been increasingly used for image documentation. Because semiconductor sensors can be used with the modern CCD-cameras that have very small active surface areas, the enlarged intermediate image in the microscope must be reduced again. For this purpose, TV-adapters with special optics and a fixed reduction factor are necessary. With a TV-zoom-adapter, the reduction factor and consequently the area of image detail can be changed. In this way, the size of the image can be made to fit the format of the camera or video printer.

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This can be of advantage in connection with the required standard magnifications. Such linear standard magnifications are 25, 50, 75, 100, 200, 250, 400, 500, 750, 800, and 1000⫻. The picture taken by the camera can be shown on a monitor, printed out by a video printer, or processed and stored in digitalized form on a PC. In this process, the overall magnification, Mtotal, can be calculated from the optical magnification, Moptical, and the electronic magnification Melectronic. Moptical = Mobjective ⫻ Madapter

共5兲

where Mobjective is the magnification of the objective, and Madapter is the magnification of the adapter. Melectronic = Dmonitor/Dsensor

共6兲

where Dmonitor is the diagonal length of the image of the monitor and Dsensor is the diagonal of the active surface of the picture sensor. So the overall magnification is Mtotal = Moptical ⫻ Melectronic

共7兲

In addition to the conventional CCD-cameras that shoot from 25–30 images per minute, “Slow-Scan” CCD-cameras are also being used in even greater numbers. These cameras take fewer images per second but with higher resolution and with less noise. In combination with a PC, digitalized images can be processed and archived. Thanks to the many highly efficient software programs, they can also be qualitatively improved, marked, and labeled. Program modules that analyze structure make possible the quantitative measurement of the structural parameters and a description of the measurement results in the appropriate form, the numerical values in the form of tables or clarifying diagrams 共see Part IV of this book兲.

15.10 The Confocal Laser Scan Microscope Depth of focal field is a fundamental problem in light microscopy. It is also the reason why we produce surfaces that are as plane possible when preparing metallographic/ materialographic specimens and why we arrange them perpendicularly to the microscope’s light ray. This is the only way to achieve a sharp image over a larger area. The greater a microscope’s magnification, the smaller the field of view, and the shallower the depth of focal field. This system-determined limitation on the light microscope can be circumvented, and the possibilities for its use significantly broadened with the help of modern laser and computer technologies. The specimen surface can be scanned in a line-by-line manner with a focused laser ray. Confocal reproduction conditions, the recording, storage, and processing of the signals in a PC, make a three-dimensional representation of the specimen surface possible. The laser scan microscope 共LSM兲 thus combines the advantages of the light microscope with those of the scanning microscope and the profilometer.

15.10.1 Function of Confocal Laser Scan Microscope Figure 15.17 shows the path of light rays and the operational mechanism for the device. The laser ray is focused onto the specimen through the objective lens. Light that is

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Fig. 15.17—Path of light rays and the operational mechanism for a confocal laser scan microscope.1

reflected there is focused onto a variable pinhole aperture by an additional lens. Only light coming from the objective’s focal plane can reach the detector unimpeded. Light coming from other optical planes is suppressed by the confocal spatial filter that consists of lens and aperture. The specimen surface, with the light ray falling onto it, can be scanned point-by-point, line by line, by means of the dichroic mirror. The light signals received by the detector are converted into electronic impulses and digitally processed. We, therefore, obtain a reproduction of the level specimen surface on a monitor. Because of the low depth of focal field, we obtain an “optical section” in x, y coordinates when the surface is irregular. By successively changing the arrangement of the object along a series of defined steps in direction z, we can record several sections and compile these images into a three-dimensional stacked image, process them digitally and draw qualitative as well as quantitative conclusions about the topography of the specimen surface. Lasers with varying excitation wavelengths in the ultraviolet through infrared spectral range are used. As lasers of wavelengths 488 and 514 nm 共25 mW兲 and HeNe lasers of wavelengths 543 nm 共1 mW兲 and 633 nm 共5 mW兲 are usually used in metallography/materialography. At 0.2, the laser scan microscope’s lateral resolution capability is somewhat better than that of the conventional light microscope. Depth resolution depends on the wavelength of the laser light, the numerical aperture 共NA兲 of the objective and the diameter of the aperture, which is a determining factor for the quality of the confocal spatial filter. Assuming that the aperture’s diameter in front of the detector approaches zero, the following holds true for reflective surfaces:

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Fig. 15.18—Confocal laser scan microscope.1

dz = n ⫻ 0.89 ⫻ ␭/共NA兲2

共8兲

where dz is the axial half-width of an intensity curve of light reflected by the object, determined by the height of the object stage; ␭ is the laser's wavelength and n is the refraction index. In practice, values between 20 and 50 nm turn out to correlate with a useful depth of focal field, depending on objective type and the medium that is between the objective and the object.

15.10.2 Applications of Confocal Laser Scan Microscope Possible types of lighting for LSM are bright-field, differential interference contrast, and fluorescence. If lasers that emit polarized light are used, polarization microscopy can also be used. Figure 15.18 shows a confocal laser scan research microscope set up with a motorized fine focusing stage and monitor. In the area of material research and testing, confocal light microscopy is suitable for the investigation of the surfaces of metallic materials, ceramics, plastics, and replicas as well as of semitransparent and transparent layers such as glass, polymer foils, coatings, or varnishes. In addition to the representation of compounds, surface profiles can be recorded and the microroughness of very small areas such as tears, pores, and hollow spaces can

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Fig. 15.19—Confocal image of a fractured steel plate.4

be three-dimensionally ascertained. The arrangement and thickness of single and multiple layers can also be represented and quantitatively analyzed. Figure 15.19 shows a fractured steel plate, the single grains can be seen threedimensionally.

15.11 Stereo Microscopy For the purpose of a three-dimensional evaluation of fractured surfaces, the size and shape of those fractures, as well as the three-dimensional shape and configuration of constituent elements, it is advantageous to use a stereomicroscope. With a stereomicroscope the same spot on a specimen can be viewed from two places at a short distance from one another, similar to the distance between the two eyes of a human being. Modern stereomicroscopes may use two different principles for the light ray paths. Following the Greenough principle, two light ray systems are directed onto the specimen through two identical objectives that are tilted toward one another at the stereo angle. This yields two images that produce a single three-dimensional image when observed through the two eyepieces. Following the telescope principle, two parallel but not axially aligned light beams are directed through an objective. The beams are deflected by the objective and strike the specimen at the stereo angle. With this method of operation, an expansion of the operational possibilities becomes relatively easy because supplementary optical modules can be installed either above or below the body of the microscope. For stereomicroscopes, a number of exchangeable objectives are obtained with the magnifications from 5⫻ to 100⫻ and eyepieces from 5⫻ to 20⫻.

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Fig. 15.20—Stereo microscope with digital camera.3

Apochromatic objectives are well suited for three-dimensional observations. For flat objects like prepared specimens, wafers and foils, plan achromats are better suited. For the finest structures with very low contrast, the apochromats can be used with advantage. The magnification can be changed by zoom when a special system of lenses is used. According to design and manufacturer the variation in magnification may be between 3:1 or 12:1. The observation of details depends to a high degree on the illumination that shall be adapted to the object and the purpose of examination. Therefore, different illumination systems can be obtained like halogen-incandescent lamp for incident light or coaxial illumination, optical fiber for vertical illumination, and other light sources for highest light intensity and for homogeneous illumination. Metallographic/ materialographic specimens or other flat, strongly reflecting objects like LCDs, wafers, and integrated circuits may be examined most effectively with coaxial illumination. Three-dimensional objects may be illuminated from two sides or with ringillumination. Using illumination under an angle will give an improved observation of

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high differences in the surface. Vertical illumination is best suited for exposing of cavitations and open pores. Fluorescence modules make examination of fluorescence substances possible. The advantages of stereomicroscope systems are: Ample working distances, large object fields, and the three-dimensional viewing of nonreversal images. Stereomicroscopes can produce meaningful overall magnifications of up to about 250 times the original. Figure 15.20 shows a modern stereomicroscope.

16 Electron Microscopy—Scanning Probe Microscopy AN IN-DEPTH DESCRIPTION OF ELECTRON MICROSCOPY AND SCANNING probe microscopy falls outside the scope of this book, but in this chapter a short introduction is given to the transmission electron microscope 共TEM兲, the scanning electron microscope 共SEM兲, the focused ion beam techniques 共FIB兲, and a number of scanning probe microscopes 共SPM兲.

16.1 The Transmission Electron Microscope „TEM… Electron beams penetrate thin layers and, in doing so, are diffracted at the crystal lattice and interferences arise. One can make these visible, after amplification with electromagnetic lenses and electronic processing, as bright-dark effects. With an acceleration voltage of up to 1 million volts, magnifications of up to 106 with a resolution below 1 nm can be attained. Disruptions in the crystal lattice, such as dislocations, eliminations, grain boundaries, and other lattice defects, are detectable; they appear mostly dark. Specimens for the TEM examinations must be thin enough for the electrons to pass through and thick enough for their structural features to remain verifiable. Various methods can be used for the preparation. With metallic materials and ceramic basic materials, thinning procedures are preferred. Using this method, the specimen 共diameter 3 mm兲 is made sufficiently thin, through either ion bombardment 共see Section 16.3兲 or electrolytically, that a hole is produced in the middle. Areas next to the hole are sufficiently thin to be suitable for TEM examination 共see Section 8.5兲. For purposes of imaging the surfaces, carbon or lacquer is used to take a replica of the specimen. The peeled-off layer of lacquer is then vapor-coated in a vacuum chamber with carbon or metal 共Au, Pt兲 to bring out the contrast. After the layer of lacquer has been removed, the metal foil or carbon foil can be transluminated. Fine powder, dust, or smoke particles are applied directly to a backing film 共carbon, lacquer兲. With extraction replicas, individual particles of a specimen, their size, and distribution can be identified. With the use of ultramicrotomes one can produce thin sections from embedded powders or synthetics. Synthetic materials that tend to smudge must be worked with at low temperatures 共cryomicrotomy兲.

16.1.1 The Scanning Transmission Electron Microscope „STEM…

This microscope is a combination of a TEM and a SEM 共see below兲 and gives the advantages of both microscope types. A STEM is a very high cost investment and primarily used for research.

16.2 The Scanning Electron Microscope „SEM… In the scanning electron microscope, the surface of the specimen is linearly scanned with the electron beam 共ca. 0.01 ␮m兲. Secondary electrons are emitted and captured by 558

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an electron detector. The spatial distribution of these secondary electrons can be made visible, after electronic amplification, on a monitor. Depending on the acceleration voltage of the primary electrons, magnifications of up to 200 000⫻ are possible. With magnification of 1000⫻ the depth of field is about 35 ␮m; the resolution power amounts up to 0.01 ␮m. Differences in levels on the surface of the specimen result in differences in contrast. Moreover, shadow formations can arise as a result of the slant with which the electron beams fall on the specimen. As a result, an image of high resolution and great depth of field is obtained. The SEM is used preferably for the examination of rough surfaces and investigations of damage or loss, e.g., fractured surfaces. Preparation of the specimen for SEM examinations is simple: the specimen must be free of volatile elements like water, oil, or grease. Loose particles must also be removed. If the specimen does not consist of electricity-conducting material, the surface must be coated with a layer of electro-conductive material 共C, Pt, Au兲 to prevent charging. In case of mounting, care should be taken that metal powder, like copper, contained in the mounting material, is not contaminating the specimen.

16.2.1 Energy Dispersive Spectroscopy „EDS…

An SEM can be equipped with additional equipment like EDS and EBSD 共see below兲. Besides the electrons emitted from the specimen mentioned above, also X-rays are emitted. As high-energy electrons produced with an SEM interact with the atoms within the top few micrometres of a specimen surface, X-rays are generated with an energy characteristic of the atom that produced them. The intensity of these X-rays is proportional to the mass fraction of that element in the specimen. In EDS, X-rays from the specimen are detected by a solid-state spectrometer that converts them to electrical pulses proportional to the characteristic X-ray-energies. If the X-ray intensity of each element is compared to that of a standard of known composition and suitably corrected for the effects of other elements present, then the mass fraction of each element can be calculated.

16.2.2 Electron Backscatter Diffraction „EBSD…

Electron Backscatter Diffraction 共EBSD兲 has become popular among materials scientists since the first commercial automatic systems were available in 1994. The main advantage of this method is the possibility to link morphology 共grain size and shape兲 with crystallographic features 共phase, orientation, disorientation兲 on the microscopic scale, but still in a representative specimen area. During the examination, an electronic backscatter pattern 共EBSP兲 is produced, an image consisting of relatively intense bands 共Kikuchi bands兲 intersecting one another and overlying the normal distribution of backscattered electrons, as a result of Bragg diffraction of electrons by atomic planes in the crystal lattice. The results can be compared to TEM, but the specimen preparation is much simpler than the preparation of thin foils. The specimens, however, are considerably more difficult to prepare than for normal imaging in SEM, because of the very low information depth of the EBSD signal based on channeling effects. This means that the very thin deformed layer, often left on the specimen after mechanical preparation, cannot be tolerated to obtain a good pattern quality, and therefore the specimen preparation shall be improved. In general, classic etching is not needed for EBSD because the contrast is defined through the orientation differences. Etching should even be avoided, as the induced surface roughening is disturbing due to

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the high specimen tilt 共70°兲 during the examination process. The specimen preparation for EBSD is discussed in Section 7.10.4.

16.2.3 The Electron Probe Microanalyzer „EPMA… This instrument, also called the microprobe is closely related to the SEM, only the X-ray detectors are not analyzing only the energy as in EDS mentioned above, but the wavelength of the X-rays generated from the interaction of the primary and backscattered electrons and the specimen. This is called wavelength dispersive spectroscopy 共WDS兲 and compared to EDS, WDS gives much more accurate quantitative data for the single components in the specimen surface.

16.3 Focused Ion Beam „FIB… A focused ion beam system 共FIB兲 is in principle built like an SEM. In the SEM an electron beam is used for scanning, but in the FIB a beam from a liquid metal ion source 共mostly gallium, Ga+兲 is used. This beam is focused so that it can be scanned like an electron beam. This allows for sputtering material from the sample or for depositing material on the sample if gases are used 共see Section 9.6.5兲. Also, imaging is possible by ion-induced secondary electrons, as it is known from the SEM. As the FIB can remove material with a very high precision, it is used for preparation of samples for TEM. This covers both samples of electronic devices and samples for material research. The TEM samples can be made either by using a pre-prepared sample in the form of a thin strip of material, which then is further thinned by the FIB, or by the newer lift-out technique. With this technique no mechanical preparation is needed, the ion beam cuts into the base material and the sample is lifted out using a special manipulator. The great advantage of using FIB for preparation of samples for TEM is the shorter times compared to conventional methods 共see Section 8.6兲, and the very high rate of success.

16.4 Scanning Probe Microscopes „SPM… In addition to the methods of optical metallography/materialography already mentioned 共LM, TEM, SEM兲, we will briefly discuss scanning probe microscopy. In the past few years it has gained increasingly greater significance in the area of metallography/ materialography. All scanning probe microscopes work according to the following principle: the surface of the specimen is scanned with the sharp tip of a needle that is mounted on a flexible cantilever. The interactive force that is present between the tip and the surface serves as a measurement signal and can be evaluated. Through the use of piezoelectrical actuators, movements of the measuring tip in the magnitude of atomic diameters can be initiated, with a resolution of less than 1 nm. Scanning probe microscopes are used in biology, physics, and materials science to characterize surfaces. The first device of this kind, the Scanning Tunneling Microscope 共STM兲, was developed by Binnig and Rohrer and used for the first time in 1981. It makes use of the quantum-mechanical tunneling effect for measurement of distance. For this purpose, voltage is applied between the tip and the specimen. If one brings the tip closer to the surface without actually touching it 共noncontact mode兲, a current begins to flow. Inas-

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much as the amplitude of this current depends exponentially on the distance it can be used to regulate the distance. With STM the surface topographies of conductive samples and images in the atomic range can be shown. With the Atomic Force Microscope 共AFM兲, the tip is positioned at the free end of a cantilever. The interaction between tip and surface, e.g., a repulsive force, is registered through the vibration of the cantilever. Its detection occurs in accordance with the light conducting principle: a laser beam focused on the backside of the flexible cantilever is reflected and registered by a photo diode. The measured values in the nanometre range can be used to guide piezoelectric actuators in the x-, y-, z-direction of the tip. In this manner one can obtain a three-dimensional image of the surface on the computer. AFM is suited for electrical-conductive and nonconductive materials such as metals, ceramics, glasses, and synthetics. Samples, either unprocessed or processed, can be examined in air, in a gaseous environment, or in liquids. The field to which ATM is applied is constantly growing and now this technique is also used for measuring of nano hardness and elastic modulus 共Young’s modulus兲共see Section 21.6.1兲. If the specimen is to be prepared metallographically/materialographically, one must take care that it has been polished with as little resulting deformation as possible 共electrolytic polishing may be an advantage兲, and that through chemical etching only a minimal level contrast in the nanometre range arises between the individual phases. Very small structural elements, e.g., the very finest precipitates, can then be identified that can no longer be seen with a light microscope because of its limited resolution power. Nevertheless, other local interactive forces can be detected with the AFM procedure. With magnetic force microscopy 共MFM兲, the surface of the sample is scanned with a nickel or iron tip in noncontact mode. One obtains an image of the local magnetic characteristics with a resolution in the nanometre range. Adhesion force microscopy conveys perceptions with regard to the local structurespecific adhesive force between measuring tip and specimen surface. With friction force microscopy, the local frictional forces can be measured and imaged. This is performed in contact mode by letting the tip move across the surface of the specimen and measuring the deflection of the cantilever. Good contrasts can be obtained especially with synthetics.

References „Part III… 关1兴

Courtesy of Carl Zeiss, Germany.

关2兴

Courtesy of Olympus, Germany.

关3兴

Courtesy of Leica Microsystems, Germany.

关4兴

Courtesy of E. Bischoff, Max-Planck-Institut für Metallforschung, Stuttgart, Germany.

Part IV: Quantitative Metallography/Materialography— Automatic Image Analysis

17 Quantitative Metallography/ Materialography—An Introduction WHEN MAKING A QUALITATIVE EXAMINATION OF A MICROSTRUCTURE, the interpretation of the structure is to a high degree based on the knowledge and experience of the observer. In quantitative metallography/materialography the constituents in the microstructure are measured to provide more reliable data for materials engineering and quality control purposes. Typical microstructural measurements include the length, width, and area of features or the relative amount of a structure or phase. The application of stereological principles enables two-dimensional measurement data extracted from metallographic/materialographic specimens to provide accurate information about three-dimensional structures increasing the usefulness and importance of quantitative microstructural analysis. It can be tedious to implement quantitative methods. Digital image analysis equipment and software have been developed as tools to automate the collection and reporting of quantitative data. In this chapter, the most important uses of quantitative metallography/materialography and corresponding ASTM standards are discussed briefly. Automatic image analysis is described in Chapter 18. Both chapters should be considered as introductions to quantitative metallography/materialography and image analysis 共see the References and Literature List for further study of these subjects兲.

17.1 Quantitative Metallography/Materialography In short, quantitative metallography/materialography can be defined as the measurement of microstructural parameters. This may be linear measurements when examining layer thickness, case depth, etc., or measurements of area, when analysis of volume fraction or grain size is required. Both manual quantitative methods, including measurements using point counting screens or templates, and automatic image analysis are defined in a number of standards.

17.1.1 Stereology–Table 17.1 Stereological methods are procedures used to characterize three-dimensional microstructural features based on measurements made on two-dimensional sectioning planes.1 For the stereological calculations, the International Society for Stereology recommends a number of symbols and notations. The most important are stated in Table 17.1.1,2

Basic Measurements A number of the above-mentioned parameters are simple counting measurements that are relatively easy to measure and are used in a number of equations 共see below兲. 565

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TABLE 17.1—Principal Symbol and Combined Notations for Quantitative Metallography/Materialography. Symbol P PP

Units ¯ ¯

L PL LL

mm mm−1 mm/mm

A S

mm2 mm2

V

mm3

AA

mm2/ mm2 mm2/ mm3 mm3/ mm3 ¯ mm−1

SV VV N NL PA LA NA

mm−2 mm/ mm2 mm−2

NV

mm−3 mm/ mm3 mm−3

L A S V

mm mm2 mm2 mm3

PV LV

Description Number of point elements or test points Point fraction (number of point elements per total number of test points). Length of linear elements or test line length Number of point intersections per unit length of test line Sum of linear intercept lengths divided by total test line length Planar area of intercepted features or test area Surface area or interface area, generally reserved for curved surfaces Volume of three-dimensional structure elements or test volume Sum of areas of intercepted features divided by total test area Surface or interface area divided by total test volume (surface-to-volume ratio) Sum of volumes of structural features divided by total test volume Number of features Number of interceptions of features divided by total test line length Number of point features divided by total test area Sum of lengths of linear features divided by total test area

Common Name ¯ Point Count ¯ ¯ Lineal fraction ¯ ¯ ¯ Area fraction ¯ Volume fraction ¯ Lineal density ¯ Perimeter (total)

Number of interceptions of features divided by total test area Number of points per test volume Length of feature per test volume

Area density

Number of features per test volume

Volumetric density ¯ ¯ ¯ ¯

Mean linear interception distance, LL/NL Mean area intercept, AA/NA Mean particle surface area, SV/NV Mean particle volume, VV/NV

¯ ¯

PP is the ratio P␣ / PT, where P␣ is the number of points that fall in the ␣-phase and PT is the total number of test points 共see also below兲. PL is the number of points of intersections generated per unit length of test line. An intersection count is the number of boundaries between the matrix phase and the phase or constituent of interest that are crossed by the lines of a test grid. For isolated particles in a matrix, the number of feature intersections will equal twice the number of feature interceptions. The total length of the test line is determined in advance to facilitate calculations. NL is the number of interceptions of features divided by total test line length. The part of the test line superimposed on the feature constitutes the intercept. The number of interceptions equals the number of particles 共or clusters of particles兲 of a phase or

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constituent of interest that are crossed by the lines of a test grid. For all microstructures with more than a single phase, PL = 2 NL and for a single phase, PL = NL. PA is the number of point features, such as grain boundary junctions, inside a given area, divided by this area. NA is the number of interceptions of features, such as grains or graphite nodules, inside a given area, divided by this area. See also ASTM Standard Terminology Relating to Metallography 共E 7兲 for standard stereological terminology definitions. To obtain a true measurement, the instrument used must be calibrated 共see Section 17.1.3兲.

Basic Equations Based on the measurements mentioned above, a number of equations are developed for covering the calculation of points, lines, areas, and volumes used for metallographic/materialographic analysis. The most important measurements such as volume fraction, inclusion rating, etc., with the covering ASTM standards are described in short below, and the relevant equations will be stated there.

Use of Comparison Charts and Grids Comparison charts were developed for the evaluation of a given microstructure. An example is the so-called JK charts 共developed by the Swedish Jernkontoret兲 depicting a series of typical inclusion configurations 共size, type, and number兲 to be used for direct comparison with the microscopical field in view. Comparison charts can be used also for determination of volume fraction and grain sizes, but a grid is used normally 共see the relevant standards below兲.

17.1.2 Specimen Preparation Selection of Specimens The selection of specimens, sampling, for quantitative analysis is very important because if the measured results are to be of value, the specimens must be representative of the material that is being analyzed. The number of specimens and the selection depends on the type of examination to be performed. As described in ASTM Standard Practice for Calculating Sample Size to Estimate, with a Specified Tolerable Error, the Average for Characteristic of a Lot or Process 共E 122兲共see Section 12.4兲, random sampling should be performed. As an example, the sampling procedure for the ASTM Test Method for Determining the Inclusion Content of Steel 共E 45兲, should be described in short: To obtain a reasonable estimate of inclusion variations within a lot, at least six locations, chosen to be as representative of the lot as possible, should be examined. For cases in which a definite location within a heat, ingot, or other unit lot is unknown, statistical random sampling with a greater number of specimens should be employed. Very often the geometry of the work piece plays a role; in examination of inclusions, the polished surface must be parallel to the longitudinal axis of the product. In case of rolled or other hot worked material, the microstructure to be measured will vary strongly according to the plane of the prepared surface 共see also Section 2.1兲.

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Reproducibility It is very important that the specimen surfaces examined in quantitative metallography/materialography are prepared with the highest degree of reproducibility; only then can the measured results be compared. In case of manual image analysis, the operator might be able to compensate for minor artifacts in the prepared microstructure, but when using digital imaging equipment to delineate structures with image segmentation, artifacts may be included in the measurements producing inaccurate results 共see below兲.

Preparation of the Specimen Surface As a general rule the goal of specimen preparation is to consistently show the “True Structure,” free of all artifacts. A specimen for automatic image analysis should also be plane, without relief and edge rounding. All phases should be visible without smearing or other artifacts; in inclusion rating even small scratches can disturb the measuring 共see Section 13.6兲. Preparation of specimens suitable for quantitative analysis is described in Section 13.2.3 and in every quantitative standard under the jurisdiction of the ASTM Committee E-4 共see Section 12.4兲.

Etching For a number of quantitative examinations, such as inclusion rating, etching should not be used; the contrast developed obscures the features to be measured. In other cases, etching has to be performed to obtain the contrast necessary to show the structures of interest such as in steel grain size and banding measurements. Reproducibility of the etching is very important in automatic image analysis so that a uniform contrast can be developed. Variable and inconsistent etching will produce contrast irregularities which influence the measurements.

17.1.3 Calibration Before making any measurement, it is essential to create calibrations for each instrument 共microscope, video system, etc.兲 used to deliver an image. Calibration is the process of establishing the graphical or mathematical relationship relating the desired property 共expressed in a standard unit of measure such as ␮m兲 to the instrument output 共instrument units such as filar divisions or pixels兲. Although the operational requirements for equipment calibration differ widely, the ASTM Standard Guide for Calibrating Reticles and Light Microscope Magnifications 共E 1951兲 provides an overview of calibration concepts and generalized calibration procedures.

17.1.4 Field Selection—Bias Quantitative measurement of a specimen surface will take place in microscopic fields only representing a small part of the surface. To obtain a specific measurement accuracy, a number of fields must be examined. This number depends on the homogeneity of the microstructure and the magnification. The higher the magnification observed and the lower the homogeneity of the specimen, the higher the number of fields that will be needed to accurately evaluate the microstructure, because at higher magnification the area covered by the field is smaller and with a heterogeneous microstructure the variations of the surface are higher. The number of fields is stated very often in the

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specific standards. If not, the number should be calculated to obtain a reasonable relative accuracy. As a rule, the fields should be placed randomly on the specimen surface. This can be performed easily on an upright microscope, the specimen surface being visible 共see Section 15.6兲. It is important that the operator does not look at the image when the placement of the fields is decided on. This is the only way bias can be avoided.

17.2 Volume Fraction—Point Count The volume fraction of a given phase or constituent in an alloy is one of the most important and most common measurements in quantitative metallography/materialography. This is because the amount of a second phase can have a strong influence on the properties of the material. The amount of a specific constituent 共second phase兲 is quantified by the volume fraction. The volume fraction of a component ␣ is designated by VV, and is the ratio of the volume of this component V␣ referred to the test volume VT 共total volume of the specimen兲. This can be expressed: VV = V␣/VT

共1兲

VV corresponds to the area fraction of the structural component ␣ that is visible in the polished specimen surface and can be determined by planimetry. Because of the valid relationship in the range of statistical scatter, AA 共area fraction兲 = LL 共lineal fraction兲 = PP 共point count兲, the volume fraction can also be determined from LL. This is done by measurement of the fraction L␣ of a straight line LT that falls within the component, or from the point fraction PP by counting the points P␣ of a point grid with the point count PT that fall on the component. This can be expressed: VV = V␣/VT = A␣/AT = L␣/LT = P␣/PT

共2兲

In ASTM Test Method for Determining Volume Fraction by Systematic Manual Point Count 共E 562兲共see below兲, an efficient way for statistically estimating the volume fraction of an identifiable constituent or phase from sections through the microstructure by means of a point grid, is described.

17.2.1 ASTM Test Method for Determining Volume Fraction by Systematic Manual Point Count „E 562…

The test method may be used for all opaque materials 共see Section 12.4.3兲. The test method is based on the stereological principle that a clear plastic test grid with a number of regularly arrayed points, when systematically placed over an image of a twodimensional section through the microstructure, can provide, after a representative number of placements on different fields, an unbiased statistical estimation of the volume fraction of an identifiable component or phase. A grid of lines or curves is superimposed on a magnified image of a metallographic/materialographic specimen, and the number of points falling within the microstructural component of interest is counted and averaged for a selected number of fields. These points divided by the total points in the grid is the point fraction PP 共see above兲. Based on PP the volume fraction VV can be calculated.

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17.3 Inclusion Rating Inclusions can significantly influence the properties of a material. For this reason inclusion rating, especially of steel, is a very important quantitative method. Inclusions can be exogenous like slag particles or indigenous, oxides, sulfides, silicates, etc., developed in the material during the manufacturing process. Normally only the indigenous inclusions, sulfides and oxides, are measured, quantifying the amount, size, shape, and distribution. In a number of standards, ASTM E 45 共see below兲, SAE J422a, and the German standard SEP 1570 共DIN 50602兲, the inclusions are determined by using manual comparison chart methods based on volume fraction and point counting. Since this involves a vast amount of counting time, image analyzers are often used for inclusion rating 共see below兲.

17.3.1 ASTM Standard Test Method For Determining the Inclusion Content of Steel „E 45… ASTM E 45 covers a number of recognized methods for determining the nonmetallic inclusion content of wrought steel. The methods are both macroscopical and microscopical; only the latter shall be shortly described here. Comparison charts, mostly based on JK charts, as described above in this chapter, are used. The inclusions are separated into four categories, A, B, C, and D and are graded by calculating a severity level based on width and length 共for D types the count兲 of inclusions in 0.50 mm2 fields within a 160 mm2 specimen surface area. In Method A 共Worst Field兲 the inclusions are assessed qualitatively, seeking out and reporting only the field with the highest severity rating. In Method D the length or count and the width of inclusions are examined and the severity level of each inclusion type for each field of view is determined and reported for a 160 mm2 specimen surface area. The Methods B and C require that a specimen area be surveyed and inclusions greater than a certain length and those of the maximum length be reported. Manual performance of E 45 共especially Method D兲 involves much work to obtain an acceptable measurement accuracy; therefore, the use of digital image analysis equipment has become more common 共see Section 18.5.2兲.

17.3.2 ASTM Practice for Obtaining JK Inclusion Ratings Using Automatic Image Analysis „E 1122… „withdrawn 2006, replaced by E 45… This practice covers procedures to perform JK-type inclusion ratings using automatic image analysis in accordance with microscopical methods A and D of E 45. E 1122 is further described in Section 18.5.2.

17.3.3 ASTM Practice for Determining the Inclusion or Second-Phase Constituent Content of Metals by Automatic Image Analysis „E 1245… The practice describes a procedure for obtaining stereological measurements that quantify basic characteristics of the morphology of indigenous inclusions in steels and other metals using image analysis. The practice can be applied to provide such data for any discrete second-phase constituent in any material. ASTM E 1245 is further described in Section 18.5.2.

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17.4 Grain Size A very high number of metallographic/materialographic examinations are performed to determine the grain size of the material; this parameter to a high degree influences the material properties. Three procedures for determining grain size are described in ASTM E 112 共see below兲, the comparison procedure does not require counting of either grains, intercepts, or intersections but only involves comparison of the grain structure to a series of graded images. The planimetric procedure involves an actual point count of the number of grains within a known area, NA. NA is used to determine the ASTM grain size number, G 共see below兲. The intercept procedure involves an actual count of the number of grains intercepted by a test line or the number of grain boundary intersections with a test line, per unit length of line, used to calculate the mean lineal intercept length, l. l is used to determine the ASTM grain size number, G 共see below兲.

17.4.1 ASTM Test Methods for Determining Average Grain Size „E 112… ASTM E 112 includes the comparison procedure, the planimetric procedure, and the intercept procedures. The methods apply chiefly to single-phase grain structures in metallic materials, but they can be applied to determine the average grain, crystal, or cell size in nonmetallic materials like ceramics. ASTM E 112 is a very comprehensive standard covering the earlier mentioned procedures, a description of the ASTM Grain Size Number, and a number of annexes describing how to establish the grain size for a number of materials.

ASTM Grain Size Number This number, the G number, is defined as: NAE = 2G−1

共3兲

where NAE is the number of grains per square inch at 100⫻ magnification. To obtain the number per square mm at 1⫻, NA, NAE is multiplied by 15.50. The International Standard Organization (ISO) and in several national standards, the metric grain size number, GM, is based on the number of grains per mm2, at 1⫻, and this gives the equation: NA = 8共2GM兲

共4兲

The metric grain size number, GM, is a little lower than the ASTM grain size number, G, for the same microstructure: G = GM + 0.046

共5兲

Comparison Procedure The comparison procedure, as mentioned above, does not require counting of grains, intercepts, or intersections, but involves comparison of the grain structure to a series of graded images, either in the form of a wall chart, clear plastic overlays, or an eyepiece reticle. Experience has shown that unless the standard image reasonably well approaches that of the specimen, errors may occur. To minimize such errors, the comparison charts are presented in four categories: Plate I—Untwinned grains 共flat etch兲 1 1 1 1 1 1 1 1 1 includes grain size numbers 00, 0, 2 , 1, 1 2 , 2, 2 2 , 3, 3 2 , 4, 4 2 , 5, 5 2 , 6, 6 2 , 7, 7 2 , 8, 8 2 , 9, 1 9 2 , 10, at 100⫻. Plate II—Twinned grains 共flat etch兲 includes grain size numbers 1, 2, 3,

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4, 5, 6, 7, 8, at 100⫻. Plate III—Twinned grains 共contrast etch兲 includes nominal grain diameters of 0.200, 0.150, 0.120, 0.090, 0.070, 0.060, 0.050, 0.045, 0.035, 0.025, 0.020, 0.015, 0.010, 0.005 mm at 75⫻. Plate IV—Austenite grains in steel 共McQuaid-Ehn兲 includes grains size numbers 1, 2, 3, 4, 5, 6, 7, 8, at 100⫻. As an example, Plate III is used for twinned copper and brass with a contrast etch. Repeatability and reproducibility of comparison chart ratings are generally ±1 grain size number.

Planimetric Procedure As mentioned above, the planimetric procedure, also called Jeffries’ procedure, involves an actual count of the number of grains within a known area 共circle or rectangle兲. The number of grains per unit area, NA, is used to determine the ASTM grain size number, G. The precision of the method is a function of the number of grains counted, and a magnification shall be selected which gives at least 50 grains in the field to be counted 共a minimum of three fields兲. When the counting is done, the figure is multiplied by Jeffries’ multiplier, f, that is a factor relating to the magnification used, M. The number of grains per square mm at 1⫻, NA is calculated from: NA = f共NInside + NIntercepted/2兲

共6兲

where f is the Jeffries' multiplier taken from a table in the standard, NInside is the number of grains completely inside the test circle and NIntercepted is the number of grains that intercept the test circle. A precision of ±0.25-grain size units can be attained with a reasonable amount of effort. Results are free of bias and repeatability and reproducibility are less than ±0.5-grain size units. An accurate count does require marking off the grains as they are counted.

Intercept Procedure The intercept procedure, also called Heyn’s procedure, is more convenient to use than the planimetric procedure. With the intercept method an accurate estimate of the grain size can be obtained in a fraction of the time used with the planimetric method. As mentioned above, the intercept method involves an actual count 共at least 50 intercepts兲 of the number of grains intercepted by a test line or the number of grain boundary intersections with a test line, per unit length of test line, used to calculate the mean lineal intercept length, l−. l− is used to determine the ASTM grain size number, G. The precision of the method is a function of the number of intercepts and intersections counted. An intercept is a segment of test line overlaying one grain. An intersection is a point where a test line is cut by a grain boundary. Experiments have shown that a test pattern consisting of three concentric and equally spaced circles having a total circumference of 500 mm gives satisfactory results. Based on the calculation of the number of intercepts, NL and the number of intersections, PL, the mean lineal intercept value for each field, l can be calculated: l = l/NL = 1/PL

共7兲

A precision of better than ±0.25-grain size units can be attained with a reasonable amount of effort. Results are free of bias; repeatability and reproducibility are less than ±0.5-grain size units. Because an accurate count can be made without the need of

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marking off intercepts and intersections, the intercept method is, as mentioned, faster than the planimetric method for the same level of precision. ASTM E 1382 describes determining average grain size using semiautomatic and automatic image analysis 共see below兲.

17.4.2 ASTM Test Methods for Estimating the Largest Grain Observed in a Metallographic Section „ALA Grain Size… „E 930… Commercial material specifications sometimes include, in size limits for grain structures, the need for identification of the largest grain observed in a sample, often expressed in ALA 共as large as兲 grain size. ASTM E 930 is used when the number of large grains is too few for measurement with ASTM E 112. The test methods are simple manual procedures, using comparison and measuring. The measuring procedure is recommended for greater accuracy.

17.4.3 ASTM Test Methods for Characterizing Duplex Grain Sizes „E 1181… The above-mentioned test methods for determination of average grain size covers materials assumed to contain a single log-normal distribution of grain sizes. ASTM E 1181 is set forth to characterize grain size in products with any other distributions of grain size. The term “duplex grain size” is chosen to describe any of these other distributions of grain size, because of its common usage and familiarity. However, the use of that term does not imply that only two-grain size distributions exist. Duplex grain size may occur in some metals and alloys as a result of their thermomechanical processing history, and these methods are made for these materials, but they can also be used for other materials with a similar microstructure. Duplex grain structures 共for example, multiphase alloys兲 are not necessarily duplex in grain size, and as such not covered by these methods. The test methods use a comparison procedure, a point count procedure based on ASTM E 562 共see above兲, a planimetric procedure, and a direct measurement procedure.

17.4.4 ASTM Test Methods for Determining Average Grain Size Using Semiautomatic and Automatic Image Analysis „E 1382… These test methods may be used to determine the mean grain size, or the distribution of grain intercept lengths, or areas in metallic and nonmetallic polycrystalline materials. The methods may be applied to specimens with equiaxed or elongated grain structures with either uniform or duplex grain distribution. Either semiautomatic or automatic image analysis devices may be utilized to perform the measurements. The semiautomatic procedure is based on a digitizing tablet with a measurement resolution of at least 0.1 mm. A variety of approaches can be employed: The simplest is to fix a photograph to the tablet surface and place a suitable grid over the photograph, tape down the corners of the grid, and use the cursor, fitted, with fine cross hairs, to measure the appropriate features. Alternatively, the grid can be placed on an eyepiece reticle. The cursor is moved over the table surface and the microscopist can see the illuminated cross hairs in the cursor through the eyepieces over the field of view and grid pattern. A third approach is to transfer the microstructural image, the test grid image, and cursor image to a television monitor. The microscopist moves the cursor across the tablet surface while watching the monitor to make the appropriate measurements. The automatic procedure is described in Section 18.5.3.

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17.5 Banding A banded microstructure is caused by segregation that occurs during the dendritic solidification of metals and alloys and is aligned by subsequent deformation. Solid-state transformations may be influenced by the resulting microsegregation pattern leading to development of a layered or banded microstructure. The most common example of banding is the layered ferrite-pearlite structure of wrought low-carbon and low-carbon alloy steels. Other examples of banding include carbide banding in hypereutectoid tool steels and martensite banding in heat-treated alloy steels. Microstructural banding influences the uniformity of mechanical properties of the material, and ASTM E 1268 describes a number of procedures for testing of banded microstructures.

17.5.1 ASTM Practice for Assessing the Degree of Banding or Orientation of Microstructures „E 1268… This practice describes a procedure to qualitatively describe the nature of banded microstructures and stereological procedures for quantitative measurement of the degree of microstructural banding or orientation. The practice also includes a procedure using microindentation hardness testing. Only the stereological procedure will be discussed here. The stereological measurements are made on an etched specimen by superimposing a test grid 共consisting of closely spaced parallel lines of known length兲 on the projected image of the microstructure or on a photomicrograph. Measurements are made with the test lines parallel and perpendicular to the deformation direction. The stereological measurements may be made using a semiautomatic tracing type image analyzer. The test grid is placed over the image projected onto the digitizing tablet and a cursor is used for counting. For certain microstructures where the contrast between the banded or oriented constituents is adequate, an automatic image analyzer may be used for counting 共see Section 18.5.4兲.

17.6 Porosity in Thermal Spray Coatings Thermal spray coatings are susceptible to the formation of porosity due to a lack of fusion between sprayed particles or the expansion of gases generated during the spray process. The determination of area percent porosity is important to monitor the effect of variable spray parameters and the suitability of a coating for its intended purpose. Depending on application, some or none of this porosity may be tolerable. In Test Methods for Determining Area Percentage Porosity in Thermal Sprayed Coatings 共E 2109兲, two methods are indicated for the determination of the porosity 共see below兲.

17.6.1 ASTM Test Methods for Determining Area Percentage Porosity in Thermal Sprayed Coatings „E 2109… These test methods cover the determination of the area percentage porosity of thermal sprayed coatings. Method A is a manual, direct comparison method using seven standard images shown on figures in the standard. These figures depict typical distributions of porosity in thermal spray coatings. Method B is an automated technique requiring the use of a computerized image analyzer 共see Section 18.5.1兲. The methods quantify area percentage porosity only on the basis of light reflectivity from a metallo-

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graphically polished cross section. In ASTM Guide E 1920 共see Section 12.4.3兲, a number of preparation procedures are recommended 共see also Material/Preparation Tables 12–15兲.

17.7 Decarburization—Case Depth—Coatings The measurement of thickness 共depth兲 of surface phenomena like decarburization, carburizing, nitriding, and coatings 共surface layers兲 is a common metallographic/ materialographic procedure. Normally a specimen is prepared and examined in an optical microscope using an ocular micrometre reticle or other measuring instrument 共see below兲. The automatic image systems are also able to measure these surface phenomena 共see Section 18.5.5兲.

17.7.1 Specimen Preparation For all measurements on layers, etc., mentioned above, the quality of the prepared specimen is of utmost importance. The plane of the cross section must be perpendicular to the plane of the surface phenomenon to secure measurement of the true thickness. The preparation must be performed so that the specimen surface is flat without edge rounding and the surface shall be without artifacts such as smearing of a softer coating. For correct preparation see Table 11.1 and Section 13.5/6.

17.7.2 ASTM Test Methods for Estimating the Depth of Decarburization of Steel Specimens „E 1077… These test methods cover procedures for estimating the depth of decarburization of steels irrespective of the composition, matrix microstructure, or section shape. The following basic procedures may be used: Screening methods, microscopical methods, microindentation hardness methods, and chemical analysis methods. Only the microscopical methods will be discussed here. Microscopical methods are most suitable for measuring the depth of decarburization of as-hot rolled, as-forged, annealed, or normalized specimens. These methods can also be applied to heat-treated specimens, although with less certainty in determining the maximum affected depth. Spheroidized-annealed or cold-worked specimens can also be evaluated, but detection of structural variations due to decarburization is more difficult than with hot-worked or fully annealed structures. Measurement is done on an etched specimen and based on evaluation of the variation in the microstructure at the surface due to change in carbon content. Measurements are made on a microscope using an ocular reticle, a screw 共Filar兲 micrometre ocular, or with a scale placed against a ground glass projection screen. For use of automatic image analysis see Section 18.5.5.

17.7.3 Case Depth The measurement of the often very thin zone developed by carburizing, nitriding, etc., is done in much the same way as decarburization and coatings 共see below兲. The specimen preparation can be difficult because the often very hard zone will create problems with the planeness of the specimen 共see above兲. For very low depths, taper sectioning may be used 共see Section 3.11.1兲. For the use of automatic image analysis see Section 18.5.5.

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17.7.4 ASTM Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of a Cross Section „B 487… This test method covers measurement of the local thickness of metal and oxide coatings by the microscopical examination of cross sections using an optical microscope. Under good conditions, when using an optical microscope, the method is capable of giving an absolute measuring accuracy of 0.8 ␮m. A carefully prepared specimen 共cross section兲 is used 共see above兲. A special problem when preparing specimens with soft coatings is embedded abrasives 共see Section 13.5/6兲. The measuring device may be a screw 共Filar兲 micrometre ocular or a micrometre eyepiece. An image splitting eyepiece is advantageous for thin coatings on rough substrate layers. The measuring device shall be calibrated at least once before and once after the measurement using a stage micrometre. The magnification should be chosen so that the field of view is between 1.5 and 3⫻ the coating thickness. For the use of automatic image analysis see Section 18.5.5.

17.7.5 ASTM Test Methods for Thickness of Diffusion Coating „C 664… These test methods cover two procedures for measuring the thickness of diffusion coatings. Method A is the determination of the difference in the thickness of the part before and after coating. Method B is the determination of total coating thickness, defined as the distance between the observably unaffected substrate and the exterior surface of the coating. The total coating thickness is determined by cross-sectioning the coating, preparing a metallographic/materialographic specimen, and microscopically measuring the coating thickness. For the use of automatic image analysis see Section 18.5.5.

17.8 Other ASTM Standards for Quantitative Materialography Below follows the designations of a number of ASTM standards relating to quantitative metallography/materialography. For further information see the Document Summaries in Section 12.4 共the CD-ROM included with this manual兲. For other standards 共ISO, DIN, BSI, etc.兲 see Appendix I. ASTM Practice for Petrographic Examination of Hardened Concrete 共C 856兲 ASTM Test Method for Quantitative Analysis of Textiles 共D 629兲 ASTM Test Method for Fiber Analysis of Paper and Paperboard 共D 1030兲 ASTM Test Method for Microscopical Determination of the Reflectance of Vitrinite in a Polished Specimen of Coal 共D 2798兲 ASTM Practice for Calculating Sample Size to Estimate, with a Specified Tolerable Error, the Average for Characteristic of a Lot or Process 共E 122兲

18 Automatic Image Analysis 18.1 Introduction THE NEED TO CONSIDER DIGITAL IMAGING SYSTEMS IS PREDICATED ON recognition of stereological principles and quantitative metallography/materialography as essential concepts in materials science. The application of quantitative metallography/materialography in materials science requires the measurement of microstructures. It may be argued that the study of materials cannot be termed a “science” if it does not use quantitative methods. Equipment using digital imaging technology is not essential to the implementation of quantitative metallographic/materialographic methods. Quantitative metallography/materialography can be practiced using nondigital methods 共see Chapter 17兲. Digital imaging technology is applied to materials science to expeditiously produce the structural measurements required by quantitative metallographic/materialographic standards. Performing image analysis is not a goal; rather it is a means of achieving a goal. To hear a laboratory technician or manager discuss the need to “do image analysis” is disturbing. What actually needs to be performed in a materials science laboratory is the measurement of microstructures, i.e., quantitative metallography/materialography. The required products of quantitative metallography/ materialography are the measured dimensions of microstructural features, numerical values that describe the physical extent of the structures. The goals of quantitative metallography/materialography can be more easily achieved through the use of digital image measurement technologies to simplify and maximize control of the measurement process. In the most basic sense an image analysis system is nothing more than a gage; principally no different than a micrometre, scale, or other device used to extract physical dimensions from any object. An image analysis system is nothing more than a tool designed to deliver digital images, extract the structural measurement data required by quantitative metallography/materialography and, as a bonus, process and manage the data. Primarily, such a system offers the possibility of making accurate and reproducible measurements of microstructural features. The availability of relatively inexpensive digital imaging equipment greatly facilitates the extraction of data from microstructural images as well as producing data that are immediately ready to be stored and analyzed using a wide variety of common information management tools.

18.2 Qualitative and Quantitative Metallography/ Materialography 18.2.1 The Transition to Quantitative Standards The barriers to implementing quantitative methods are primarily the continued existence of qualitative standards; lack of cost effective and efficient instrumentation; and perhaps most significantly, the existence of procedural obstacles. Bringing rigorous quantitative methods to metallography/materialography necessitates the existence of specifications and standards requiring these methods, the equipment and operational 577

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procedures to produce the results specified in the standards, and, finally, the organizational desire to institute these methods. Nearly all of the more recent standard test methods produced by ASTM International, as well as other standards organizations and private industry, are quantitative in nature and require the actual measurement of structural features rather than the traditional chart comparison or other subjective methods. New standards generally tend to eliminate the use of chart comparison and rating or indexing schemes. Instead they report the actual measured values for length, width, area, etc., as well as appropriate statistical values. In many cases, the quantitative standard actually simplifies the test method. The equipment necessary to perform the operations required by quantitative methods is readily available. In addition to a microscope, the components needed to assemble an image analysis system generally include: computer with monitor, camera, and printer. Early implementations of image analysis systems required specialized and relatively expensive hardware components. Fortunately, the exponential rise in consumer use of computers and digital cameras has benefited the use of image analysis in materials science. Many of the technologies used in consumer imaging products are directly transferable to microstructural image analysis systems. For example, the availability of mass-produced personal computer components and image sensor chips have resulted in dramatically lower system hardware costs. A certain symbiosis exists between the advancement of digital imaging component technology and the propagation of quantitative standards. Technological developments and component cost reductions have facilitated the adoption of more quantitative standards by virtue of easing the efforts and costs of implementing the standards. Conversely, the increased number of quantitative standards has expanded industry demand for more efficient and cost-effective systems to perform the measurements incorporated in these standards. Perhaps the most significant remaining barrier to the use of quantitative methods is organizational 共procedural兲 in nature. While the imprecision and the shortcomings of nonquantitative methods are widely recognized, there remains in many metallographic/materialographic laboratories a strong inertia slowing the adoption of new standards. The advancement of quantitative materials science often suffers from a burdensome process of new standards approval. In many organizations the effort required to secure organizational approval of new standards is difficult, tedious, and presents a formidable barrier to what is technically and logically obvious. None the less, quantitative methods and standards are gradually replacing qualitative procedures, driven by the issuance by industry leaders, both public and private, of quantitative standards and the constantly improving price/performance ratio of the equipment necessary to conveniently implement the standards.

18.2.2 Structure, Stereology, and Statistics What structural parameters should be quantified? Physical metallurgy and the study of microstructure property relationships provide the answers. An obvious problem is that the preparation of materials for microscopic observation and quantification yields a planar, two-dimensional surface on which three-dimensional phase and structural features are displayed in some cross-sectional views. The solution lies in the body of stereological principles that provide a scientific basis extrapolating planar measurement data to yield valid volumetric material structure information.1 The physical extent of microstructures as shown by metallographic preparation including feature number,

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length, width, and area, are the primary structural dimensions of importance. Nearly all standards for the measurement of materials microstructures call for the determination of some or all of these parameters. Several other measurements are sometimes required including perimeter as well as calculated data such as percent area, density, distance from a surface, aspect ratio, and shape factor. For most quantitative standards the data extraction requirements are very basic. Commonly, in the implementation of quantitative standards using image analysis software, far more effort is required in the processing of the measurement data to provide reporting in the format required by the standard. This situation is particularly encountered when translating the older qualitative standards 共for example, ASTM Standard Test Method for Determining the Inclusion Content of Steel 共E 45兲兲 that rely on rating or other manipulations to produce results expressed as an index or relative value rather than as stereological data. An extremely important aspect of quantitative standards is the role of statistical concepts. Not only is the validity of stereological principles predicated on meeting certain statistical conditions, but the results to be calculated also consist almost entirely of statistical parameters, such as mean standard deviation and confidence interval. It is vital that the laboratory personnel who are engaged in the performance and use of quantitative methods have a basic understanding of statistical concepts in order to obtain accurate results. This chapter will cover the basic elements of image analysis systems and their practical application to several of the most common quantitative standards. The sections below present an overview of image analysis functions that are frequently found to be useful in quantitative metallography/materialography. This overview is not designed to be a detailed examination of the vast array of image processing functions. For a thorough discussion of many of these processing functions see the work of John C. Russ.3

18.3 Principles of Digital Imaging 18.3.1 What is Digital Image Analysis? Because the terminology used in describing digital imaging equipment and systems is confusing, often ambiguous, and because of rapid changes in technology, prone to short-term obsolescence the discussion that follows minimizes reference to specific components. How is digital image analysis applied to materials science? Image analysis is a set of software functions that can be used to extract quantitative data from microstructural images. Digital imaging technology integrated into a “system” is used as a tool to provide the measurement of microstructures as required by quantitative methods. Employing the power of digital imaging technology, the extraction of data is accomplished in a more timely and efficient manner.

18.3.2 Image Acquisition Generally an image of materials microstructure consists of a rectangular or square area showing physical structure 共voids or grain boundaries兲 or material phases embedded in a matrix. In most cases the objective of quantitative analysis is to measure the physical extent of the structure or phase, most commonly length, width, or area. In doing so it is necessary to remove the matrix portion of the image from consideration. For this reason all of image processing is essentially a data reduction problem. Even for

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a standard NTSC format camera the number of pixels in an image is 307 200. Every step in the image acquisition and processing is performed with the objective of removing pixels representing matrix material information from consideration. Ironically the large format digital cameras capable of delivering images having more than 1 000 000 pixels 共one mega pixel兲 provide an even greater amount of data that must be eliminated to produce the quantitative information required. The argument can be made that more pixels are not always a benefit in the extraction of measurements from materials microstructure. Very little work has been done on identifying the level on imaging digitization that is optimal for the data extraction job at hand. The assumption that more pixels are better is not a universal truth, i.e., it should not be applied to all analysis situations. Rather, the minimum number of pixels needed to quantify the structure, based on the requirements of the standard should be taken into account when selecting a camera. The more image data captured beyond that required to provide the measurement tolerances required by the standard, the more elaborate and, therefore, more exposed to error the image processing 共data reduction兲 will be.

18.3.3 Image Digitization—Gray Scale Digitization is the process of converting a continuous scene 共microscopic field of view兲 into a block of numerical values 共a number of horizontal rows and a number of vertical columns兲. Individual units in the rows and columns are picture elements 共pixels兲. Pixels are the basic unit of digital images. Pixels have a location within the image. X is the horizontal position and Y is the vertical position. Each pixel also has a brightness, illumination intensity, or color value. These numerical values associated with each pixel constitute a digital image. After a structural field of view has been digitized, all image processing and measurement is based on the quantitative values of each pixel. A discussion of the details of image digitization can easily fill a volume, but an in-depth knowledge of the technology is not necessary. See the excellent work of Inoue and Spring for a detailed discussion of image digitization.4 The X, Y positional information associated with a pixel is straightforward. The pixels into which the image is divided form an array or grid. The relative position of each pixel within the overall grid 共image兲 can be expressed as a coordinate location. Once a calibration has been established the position of each pixel can be expressed as a real distance from the coordinate system origin or from any other point 共pixel兲 in the array. The least common denominator for an image pixel array as produced from an NTSC standard video camera has dimensions of 640 pixels in each horizontal row and 480 pixels in each vertical column. A so-called mega pixel image has upwards of 1000 horizontal by 1000 vertical pixels. The third value possessed by every pixel is a measure of its illumination level. This value is a quantification of the relative amount of light found at that location of the image. The range of values possibly varies and is dependent on technical specifications of the camera and digitizing components used to perform digitizing. In digitizing the total range of illumination from no light 共pure black兲 to the maximum amount of light 共pure white兲 is divided into an equal number of levels. Commonly, an image from a monochrome camera is digitized into 256 distinct levels, beginning with 0 for no light up to a maximum of 255 for the maximum amount of light. In this scheme every level of illumination has a value from 0–255. This range of digital illumination values is called the gray scale. A gray scale having a range of from 0–255 is an 8-bit gray scale, since a digital computer represents numbers as “bits” and to count to 255 requires 8 bits. Image illumination may be digitized into ranges other than 0–255. The wider the range of

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Fig. 18.1a—Base line image.

digital illumination levels, the more bits are required to count them. The number of bits used in digitizing illumination is called the bit depth. To digitize a true color image requires at least 24 bits and produces a total of 16.7 million possible illumination 共or color兲 levels.

18.3.4 The Histogram Digitization of the illumination levels within a microstructural field of view is in fact a measurement of the illumination. Taken together, the pixel illumination measurements show a pattern of variation representing the various phases and structures within the image. By counting the number of pixels at each illumination value in a digitized image, an illumination frequency distribution can be produced. The frequency or quantitative distribution is a basic statistical method for summarizing data. Once a microstructural field of view has been digitized its distribution of illumination values can be viewed graphically by constructing a histogram.5 The typical image illumination histogram uses the gray scale range as the horizontal, X axis, and the count of pixels falling into each of the gray scale levels as the vertical, Y axis. In fact, the frequency distribution of illumination presents the raw image data upon which all image processing is based and from which all materials structure measurements are extracted. If the structural features to be measured are not represented in the initial raw data of the illumination quantitative distribution, then measurement of those features will not be possible. The shape and position of the illumination histogram provides important information about the brightness, contrast, and measurability of the image.

18.3.5 The Effects of Brightness and Contrast on Illumination Distribution The effects of different illumination 共brightness兲 levels on quantitative distribution can be seen as measurability by considering the example of an image of a thermally sprayed coating structure digitized to a depth of 8 bits, having a possible range of measured illumination values of 0–255 共displayed in Fig. 18.1共a兲兲. A histogram of the pixel brightness distribution of this field of view is shown at the right in Fig. 18.1共b兲. Digitized pixel brightness values are shown on the horizontal X axis beginning with a value of 0 at the left end of the axis. The vertical Y axis shows the number of pixels at each gray scale value. An inspection of the distribution reveals several things. First, notice that this distribution is approximately normal; it has the shape of the classic “bell” curve of a normal distribution. There is also a small but prominent

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Fig. 18.1b—Base image illumination.

“spike” or relatively high number of pixels at the 0 or black gray scale level. Additionally, the majority of the brightness measurements are clustered somewhat to the right, or bright end of the distribution, at around the 180 level. To show the effects of a change in illumination levels on the resultant distribution, the brightness level was decreased by 15 % for the same field of view. The image and its associated histogram are shown in Fig. 18.2. Notice that the distribution is basically the same shape but it has shifted to the left or darker end of the scale and that the most frequent illumination value is now approximately 140. Also, the number of pixels at the 0 illumination level has increased nearly three times. Next the image brightness level was increased by 15 %. The average brightness level of the resultant image is approximately 213 and the brightest areas within the image have been set to 255, the highest possible level 共saturation兲. Note in Fig. 18.3 that the distribution is shifted so far to right end of scale that a portion of the distribution has been clipped. This means that at the higher illumination levels some data representing the brightest structural features have been lost. In most cases the loss of raw image illumination data due to excessive or insufficient image brightness should be avoided.

Fig. 18.2a—Brightness decreased.

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Fig. 18.2b—Histogram shifted left.

Now let us examine the effects on the image illumination distribution of changes to the field of view contrast. Contrast is a measure of the range of illumination values

Fig. 18.3a—Brightness increased.

Fig. 18.3b—Histogram shifted right.

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Fig. 18.4a—Contrast decreased.

between the darkest and lightest areas within the field of view. Again, referring to the distribution shown in Fig. 18.1共a兲, the range of brightness values extends across the entire 0–255 gray scale range. The result of decreasing the contrast by 10 % is displayed in Fig. 18.4共a兲. Notice in Fig. 18.4共b兲 that the range of illumination values has been reduced and the distribution no longer fills the gray scale with the lowest value somewhat above 0 and the highest values somewhat below the 255 maximum. A decrease in contrast has the effect of compressing the illumination distribution. Increasing the contrast by 10 % produces the image and distribution displayed in Fig. 18.5. In this case, the distribution range has been expanded or stretched. Note the gaps in the bars plotted in Fig. 18.5共a兲, indicating that after increasing contrast some illumination levels are not present in the image. See more on “stretching” in the Image Processing section of this chapter. Based on these examples, several generalizations can be made about the optimal illumination conditions for extracting measurement data from digital images. First, the illumination 共brightness兲 level selected for the image should provide the broadest possible range of values in the distribution histogram while avoiding clipping at either end of the gray scale. Also the contrast level should be selected to maximize the range of illumination values present in the gray scale distribu-

Fig. 18.4b—Distribution decreased.

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Fig. 18.5a—Contrast increased.

tion. The reason for seeking these conditions is simply to create an image that provides the maximum amount of raw data to be used to define and measure the material microstructure. Controlling illumination is essential. And while image processing software includes many powerful methods for altering digital image brightness and contrast, these mathematical techniques must be considered as secondary tools. The primary and most powerful control for controlling microstructure illumination is the microscope or metallograph used to obtain the images. No software alteration of image illumination characteristics should be undertaken prior to a thoughtful use of microscope illumination controls including illumination level, aperture, filtering, etc., to produce an image possessing the illumination conditions optimal for the intended use of the image. During the process of setting illumination conditions with the microscope the operator may quickly digitize candidate images and use the imaging software to display a distribution histogram. A series of microscope illumination adjustments should be made and checked by viewing the histogram until the illumination distribution is optimized. Only after such a process should additional software illumination adjustment be undertaken if necessary. The state of the image illumination distribution along with the intended uses of

Fig. 18.5b—Distribution stretched.

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the digitized image determines what, if any, image processing can or should be performed.

18.3.6 Image Processing and True Microstructure The phrase image processing describes a wide range of operations, implemented by software programs and designed to transform a digital image into another image by performing one or more mathematical calculations upon the image pixel data. There is only one goal in applying any image processing function and that is to produce an image that more clearly represents the microstructure of interest. To achieve this single result, image processing functions are commonly used in microstructural images for the removal of artifacts that obscure the image structures of interest and to enhance or exaggerate image structures so as to maximize the possibility of uniquely delineating 共and therefore more accurately measuring兲 the structures. The goals of image processing should be identical to those of materialography, that is, to produce a visible microstructure with no artifacts that is the truest possible depiction of the material structure for the intended purpose. The application of modern controlled metallographic/materialographic processes results in observable microstructures that optimally reveal the material structural or phase constituents, or both. Consequently, materialography or metallography is actually the most powerful image processing tool available, in that the mechanical or chemical processes employed are designed to physically produce “true microstructure,” whereas software-based image processing relies on mathematical calculations performed upon an image to produce a new image displaying a structure which in fact does not exist physically. All applications of image processing will alter the image illumination distribution. Therefore, any image that exists as the result of image processing is not “true microstructure.” Such an image is not necessarily bad. But recognizing this simple truth leads to the inescapable conclusion that in all cases electronic image processing should be strictly limited to only those operations without which the original image would remain unmeasureable or for purposes of human visualization to enhance the structure visibility. In regard to quantitative materials science, image processing operations should be applied only in so far as they render the image more measurable or more viewable. So the application of image processing processes is determined by the state of the real world image and the use to which the digital image is to be put. In furthering the purpose of materialography or metallography, that is to reveal microstructure for subsequent measurement or examination, digital image manipulation is nothing more than another process for materials specimen preparation. Digital 共image兲 preparation should be used as a secondary class of techniques to be applied only if the primary class 共physical metallographic/materialographic methods兲 has failed to provide the required structural visibility. There are a very large number of image processing functions available in most image analysis software products. Of the many possible image processing operations a relatively few provide useful results in preparation of materials microstructure images. Presented here is a short list of several image processing functions that are frequently applied to improving microstructural images. For an extensive discussion of many more image processing techniques see Russ.3

Background Correction A common artifact resulting from poor microscope illumination alignment is observable as bright or dark areas within the image. Background correction is an image pro-

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Fig. 18.6a—Unevenly illuminated image.

cessing program that is used to reduce uneven image illumination due to misalignment of microscope lighting. Microscope illumination alignment must always be centered. All possible physical positioning and optical path alignment adjustments must be made to the microscope or metallograph prior to performing software-based background correction. A common method of software background correction performs a subtraction of a poorly illuminated image with a second copy of the same image showing only the background. The background-only image can be produced by digitizing an image of a uniform white surface or by defocusing the optics to obliterate all image features. A background correction operation yields a resultant image that has been corrected. The images in Fig. 18.6 illustrate this process. Figure 18.6共c兲 clearly shows that the dark edge seen in Fig. 18.6共a兲 has been removed by the background correction. Also note that several dust particles present within the lenses of the microscope or camera used to capture the image are visible in both Fig. 18.6共a兲 and 18.6共b兲 and have been removed by the correction software. A side effect or artifact of the background correction process is that the right edge of the image is now slightly brighter than the balance of the image. It is a near universal truth that the application of image processing functions seldom provides results that are wholly without artifacts. The existence of some degree of nonuniform image illumina-

Fig. 18.6b—Background only copy of Fig. ???

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Fig. 18.6c—Resultant image after applying background correction.

tion may be acceptable provided it does not interfere with the measurement of the structures of interest.

Contrast Stretching Once digitized the image brightness and contrast may be altered using image processing software. Again, it is important to use the illumination controls found on the imaging system microscope being able to optimize image brightness and contrast before resorting to software processing functions. Adjustments to brightness and contrast should always be performed to increase the amount of illumination data available. See Section 18.3 for examples of brightness and contrast changes to the amount and range of data in the digitized image. Stretching techniques increase image contrast by expanding the brightness values found in the original image into a wider range of values. Stretching is generally applied to images that display a narrow range of illumination levels in their initial digitized state. One approach to stretching determines the minimum and maximum illumination levels within the image and mathematically extrapolates these values to cover the maximum possible range, 256 values in an 8-bit gray scale image, as seen in Fig. 18.7. Notice that there are no 0 or 255 brightness level pixels within the image 共extreme left and right ends of the distribution in Fig. 18.7共a兲兲. Figure 18.7共b兲 displays the same image after applying a contrast-stretching program to radically expand the illumination range 共contrast兲. In addition to increasing contrast across the entire image illumination range, it is possible to increase the contrast within a specific part of the illumination range. Stretching of this type may be helpful if several material phases have nearly contiguous or slightly overlapping illumination ranges. This enhancement is performed by dividing the histogram into three sections: brightness values that have a value below a dark-end threshold 共some value greater than the minimum illumination values in the image兲; brightness values above a bright-end threshold 共some illumination level less than the maximum兲; and brightness values lying between the dark and bright thresholds. brightness values that lie below the dark threshold are assigned a new value of 0. Similarly, values that lie above the bright threshold are assigned a value of 255. The remaining values between the dark and bright threshold are assigned new brightness levels between 0 and 255, according to a linear mathematical extrapolation and are thereby stretched slightly to provide a calculated set of structural brightness levels. The histograms in Fig. 18.8 display the effects of this type of stretching.

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Fig. 18.7a—Narrow illumination range.

This form of histogram stretching eliminates low and high pixel brightness values that do not represent the structures of interest by setting them to 0 or 255. Notice the high pixel counts at the extreme ends of the distribution.

Fig. 18.7b—Entire range stretched.

Fig. 18.8a—Original image.

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Fig. 18.8b—Middle values expanded.

Watershed Filter The watershed filter is a mathematical function that transforms an image containing individual particles that are touching or fused together into a new image wherein the touching or fused objects have been separated. This is a very useful tool because several quantitative metallography/materialography standards require the measurement of individual objects. In material microstructure analysis the watershed filter can be applied to grain size measurement as well as to other structures where it is desirable to measure individual particles within the unprocessed image that are touching. ASTM Standard Test Methods for Determining Average Grain Size Using Semiautomatic and Automatic Image Analysis 共E 1382兲 for grain size measurement by image analysis describe procedures incorporating individual grain area measurement. To achieve maximum accuracy each grain must be separated. Figure 18.9共a兲 shows a steel grain boundary structure. Notice that the dark linear grain boundaries are broken and do not completely delineate the individual grains. Frequently the condition of uneven and incomplete grain boundary definition is pro-

Fig. 18.9a—Gray scale image showing incomplete grain boundaries.

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Fig. 18.9b—Binary version of Fig. ??? after watershed separation operation to fill in missing boundaries.

duced when revealing grain boundaries by chemical etching. The watershed filter can be applied to such images and ideally will produce an image such as seen in Fig. 18.9共b兲, which shows all the grain boundaries completed. Such an image can be easily measured using automated methods 共see Section 18.5.3 for additional discussion of grain size measurement兲. Another example will illustrate risks of applying image processing functions as well as demonstrate another function that occasionally is useful in materials measurement. In Fig. 18.10共a兲 below, a materials image showing darker second phase particles within a light gray matrix has been digitized. To accurately count or measure the individual particles a watershed separation processes has been performed. The resultant binary image with particles assigned to white and the matrix to black is shown in Fig. 18.10共b兲. The separation function has been fairly successful, having split many of the previously touching particles by constructing a black line between them. Note that the con-

Fig. 18.10a—Touching particles.

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Fig. 18.10b—After separation.

structed separations tend to give angular and geometric rather than smoothly curving edges to the particles. This type of mathematical artifact is typical of many image processing operations and while the results are less than perfect, the slight distortion in particle boundaries is more than offset by the overall improvement in particle measurability. However, the separation has produced two relatively serious errors. In one instance, near the upper center part of the image, a small triangular “particle” has been created in the separation process that clearly does not exist in reality. Also, near the lower right corner of the image a small particle has been incorrectly cracked in half. Close examination of the Fig. 18.10共a兲 image reveals that small bright dots are found within the particles at the site of the incorrect separations. In fact, just as in materials where small voids or impurities can produce structural weaknesses that act as origin sites for failures, these bright spots within the image have served as nuclei for the failure of the separation process. Caution should be used in the application of the separation function since the manufactured boundaries may result in the separated particles having slightly altered dimensions. As discussed below, applying additional image processing operations prior to running the separation program can minimize the occurrence of these errors.

Smoothing There are a large number of processing operations designed to alter individual pixel brightness values based upon the values of surrounding pixels. Such spatial filtering operations exist for increasing or decreasing illumination changes within pixel neighborhoods. When separating touching particles, a prior filtering operation that reduces or smoothes illumination variability can eliminate bright spots that may lead to errors. Applying such a filter results in the image shown in Fig. 18.10共c兲. Compare Fig. 18.10共c兲 with Fig. 18.10共a兲, nothing that the smoothing filter has remove the bright spots. Applying the watershed separation operation to the image in Fig. 18.10共c兲 yields the image shown in Fig. 18.10共d兲. Figure 18.10共d兲 displays a very good separation of the particles with no grossly inaccurate particle shapes. This example has demonstrated the ability of image processing programs to both reduce as well as increase artifacts present within an image as

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Fig. 18.10c—Smoothed image.

well as the potential benefits of performing a series of image processing operations to achieve an optimal result. Developing a multi-stage image processing procedure is much like developing a metallographic/materialographic specimen preparation procedure. It is extremely important to note, however, that since the outcome of any given image processing operation is directly dependent upon the level of illumination in the original image, any change to the illumination level may result in an entirely different result.

Sharpening Sharpening is an image processing operation that is designed to accentuate the edges of objects within the image. It can be thought of as a way to bring an object into sharper focus. The figures below illustrate the visual as well as quantitative effects of sharpening. Figure 18.11共a兲 shows a portion of a micron scale. Figure 18.11共b兲 is a plot of the pixel brightness levels measured along the horizontal section line drawn in Fig. 18.11共a兲. Note that the brighter scale lines result in spikes on the illumination value plot.

Fig. 18.10d—More accurate separation.

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Fig. 18.11a—Scale with section line.

A typical sharpening function has been applied to the same image and the results are displayed in Figs. 18.11 and 18.11共c兲 and 18.11共d兲. Visually the scale lines in Fig. 18.11共c兲 are more prominent and show more contrast between the lines and the gray matrix areas. The plot in Fig. 18.11共d兲 shows a distinct dip at the base of the spikes indicating a greater illumination difference in the pixels at the boundary where the scale lines and the matrix meet. These visual and quantitative changes are characteristic of the image sharpening process. By blowing up a section of the image the effects of sharpening can be seen in detail. Note the exaggerated black to white illumination transition along the edges of the sharpened image scale line in Fig. 18.11共f兲. Also notice the visible pixel brightness artifacts created in the matrix area immediately above the scale line in the sharpened image. Exaggerating minor image brightness variations may cause difficulties depending on the ultimate goals of the analysis. Sharpening filters can be valuable in enhancing images for human viewing and can be helpful in reducing the so-called halo effect when performing automatic detection of objects for measurement 共see ASTM Standard Practice for Obtaining JK Inclusion Ratings Using Automatic Image Analysis 共E 1122兲兲.

Fig. 18.11b—Plot of illumination along section line.

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Fig. 18.11c—Sharpened image.

Many other image processing functions including filters and morphological operations exist and are commonly found in commercially available image processing software. For a thorough discussion of many of these processing functions see the work of John C. Russ.2

18.3.7 Image Calibration To measure the physical extent of structural features within a digital image, it is necessary to create a spatial calibration. The process of calibration is the method by which actual measurements may be extracted from any object displayed within an image. A calibration is a numerical ratio that defines the relationship between a pixel and a real world measurement unit such as a millimetre. Recall that a pixel is the unit building block from which the entire digital image is formed. Spatial calibration provides a height and width dimension for the image pixel. Within any digital image, all pixels are identical in horizontal and vertical dimension. By assigning horizontal and vertical pixel dimensions, structural features can be measured by counting the number of pixels within the feature and multiplying by the appropriate spatial calibration factors. Pixel calibration factors are generally created for each of the magnification options

Fig. 18.11d—Exaggerated illumination at edges.

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Fig. 18.11e—Unsharpened blowup.

available through the microscope or other device that is used to acquire images for analysis. A calibration must be associated with an image prior to performing any measurements within the image. A notable exception to this requirement is the case of percent area or other relative measurements wherein the desired data are expressed as a ratio and can be calculated by pixel counting. The general process of creating a calibration involves the digitization of an image of a scale or other object for which a dimensional distance is known. In microscopy this is usually a slide micrometre having an etched scale in inches, millimetres, or microns, or a geometric shape such as a circle or square with a known dimension. Figures 18.12共a兲, 18.12共b兲, 18.12共c兲, and 18.12共d兲 illustrate the calibration process. First a slide micrometre is placed on the microscope stage, aligned, and the image is digitized. After the scale image is digitized the operator initiates a series of steps that include

Fig. 18.11f—Sharpened blowup.

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Fig. 18.12a—Image of portion of slide micrometre scale.

drawing a calibration line on the image across some distinct distance on the scale as seen in Fig. 18.12共b兲. Next the software prompts the operator to enter the length of the calibration line in real world units, such as millimetres, as shown in Fig. 18.12共c兲. The image analysis system software uses this information to calculate the calibration factor. Figure 18.12共d兲 shows a typical software control where the resultant calibration factor is displayed as a ratio of pixels per unit measurement. Note that in the example a calibration factor is shown for both the X 共horizontal兲 and Y 共vertical兲 pixel dimensions. If the image pixels are square and have an aspect 共height to width兲 ratio of 1 then the X and Y calibration factors are the same. The pixel aspect ratio is a function of the camera and digitizing hardware. It is very important to

Fig. 18.12b—Scale with calibration line overlay.

Fig. 18.12c—Operator input of calibration line distance.

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Fig. 18.12d—Typical operator for control for creating spatial calibration.

determine the pixel aspect ratio and if it is not 1 then the X and Y calibration factors must be calculated independently. Another feature on the calibration display panel of importance is the name of the calibration. This name could include information about how the calibration is configured, including optics, measurement units, etc. An additional essential item of information displayed and adjustable from this control is the origin of the XY coordinate grid of pixels into which the image is divided. Although not specifically written for use with digital imaging systems, ASTM Standard Guide for Calibrating Reticles and Light Microscope Magnifications 共E 1951兲, provides relevant information on the calibration process 共see Section 12.4兲.

18.4 Image Measurement Once calibration has been established it becomes possible to extract data from an image. It is at this point that digital image analysis becomes a tool to implement quantitative metallography/materialography. Assuming that the metallographic/materialographic specimen preparation and digitization processes have yielded an image that displays the microstructure clearly, the next task to be performed is the delineation of the features to be measured. A typical materials image is composed of a relatively large area of matrix or background material within which one or more structural features having one or more individual occurrences are distributed. To extract measurements it is necessary to separate the pixels that represent the features of interest from the pixels that represent the matrix or background material. This is a data reduction operation to separate pixel data that are associated with the microstructure of interest from all other pixel data. It is interesting to note that from this point forward what is taking place is data processing—not image processing. There are two basic approaches to defining and separating the features within the

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Fig. 18.13a—Grain diameters measured.

image to be measured. In the more basic method the equipment operator interactively delineates the points, lines, or areas to be measured.

18.4.1 Manual Measurements „Operator Defines Points, Lines, or Areas… Manually indicating what is to be measured by operator interaction is a simple yet useful method of extracting measurements from microstructural images. In general there are three possible forms to be delineated by direct operator interaction, points, lines, and areas. Figure 18.13共a兲 shows an image of a grain boundary structure. Exercising the line feature creation tool available with nearly all image measurement software the operator can use the computer system mouse to position the cursor on a grain boundary, then click the mouse button and drag the cursor to another point on the grain boundary. Another mouse click and the image measurement software immediately counts the number of pixels in the line, calculates the length of the line, and notes the distance on the image. A slightly different implementation of the same techniques allows the operator to trace an outline of a complete grain boundary and the measurement software can immediately calculate the grain area as shown in Fig. 18.13共b兲. While manual measurement techniques are basic and require operator input, they should not be overlooked as a viable means for accurately extracting measurement data from materials structure.

Fig. 18.13b—Grain boundaries traced and grain areas measured.

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Fig. 18.14a—Segmentation control showing distribution of image illumination.

18.4.2 Automatic Measurements „Objects Defined by Image Segmentation… Of all the many advantages of digital image analysis, possibly the single most powerful is the process of delineating and measuring structural features over multiple fields of view without the necessity of operator interaction. The ability to measure dozens, hundreds, and even thousands of individual occurrences of structural features without constant operator involvement is a strong incentive for the implementation of image analysis for quantitative metallography/materialography. Such automation of extracting data from materials images based upon the concept of image segmentation. Segmentation provides a means whereby, after initial operator setup, features can be delineated and thus measured without additional operator input. In segmentation the image is divided into the structural features of interest and the matrix or image background based upon the pixel illumination values. The division is based on the histogram showing the distribution of image pixel illumination values. The process of segmentation produces a range of values having a lower limit and an upper limit within the overall image illumination distribution. The segmentation range is set to match as closely as possible the pixel illumination values of the structure to be measured. The success of this process is directly dependent upon the degree to which the structures to be measured are represented by an exclusive set of pixel brightness values. Ideally the structure to be measured is represented within the image by a distinct range of the pixel illumination values different from the pixel illumination values of the matrix. All image analysis software provides a control mechanism to allow the operator to interactively adjust the segmentation levels to detect the features of interest. Commonly, the control will display a histogram showing the image illumination distribution with the upper and lower segmentation range limits superimposed as a pair of vertical lines. The image itself may also be shown with a color overlay corresponding to the current segmentation range settings. In effect, the color will show exactly what part of the image is being detected. Figure 18.14共a兲 shows a portion of a typical segmentation control panel provided with image analysis software. In this example the histogram of an image digitized to 8 bits 共0 = black to 255 = white兲 is displayed. Notice also the bar along the top of the control; the size and position of this bar relative to the distribution histogram is a visual indicator of the current segmentation range setting. The 0–255 setting shown is actually detecting the entire image and is simply the starting point for segmentation adjustment. The operator, using a combination of cursor positioning and mouse clicks, must move either or both of the segmentation limits set to achieve detection of the features of interest. Figure 18.14 共b兲 shows the image under analysis. The darker gray objects are to be detected for measurement. Since the objects are

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Fig. 18.14b—Segmentation control showing the image under analysis.

relatively darker than the surrounding matrix material, the upper segmentation limit must be adjusted to a lower level to exclude the brighter pixels representing the matrix. Using the software control the upper segmentation limit can be reduced. As the limit is moved lower, the pixels falling within the range are indicated by the bar and with a color overlay on the actual image. This color-coding method allows the operator to clearly see the results of segmentation at each possible level. The segmentation limit must be lowered until the best possible delineation of the objects is achieved. Figures 18.14共c兲 and 18.14共d兲 show the final segmentation setting on the distribution plot and the image with the red overlay indicating objects detected for measurement. It is important to note two items regarding the setting of segmentation levels. First, while automatic software-controlled segmentation can be performed by virtually all image analysis software, the accuracy of the segmentation operation and therefore all subsequent measurements, are primarily the responsibility of the operator and in most cases are based upon a subjective judgment concerning the optimal limit settings. Secondly, if a relatively clear distinction between object feature illumination levels and matrix illumination levels does not exist, the process of segmentation may be difficult and in some cases it may be impossible to set with adequate accuracy to produce meaningful measurement results. If the structures to be measured cannot be cleanly delineated by segmentation further metallographic/materialographic specimen preparation or additional image processing must be considered. It is possible that microstructures of certain materials, regardless of preparation and processing, do not lend themselves to the use of segmentation to delineate features for measurement. In such

Fig. 18.14c—Illumination distribution with segmentation range set.

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Fig. 18.14d—Image showing detected objects with red overlay.

cases extraction of measurements must be accomplished interactively. Once structural objects have been defined by segmentation, the extraction of measurement data are almost trivial. All image analysis software includes a variety of measurements that may be extracted from defined objects. In most cases the variety of measurements possible greatly exceeds the requirements of common quantitative metallographic/materialographic standards. Structure area, diameter, length, width, perimeter, and many other measurement types can be made. In the next section the application of these measurement methods to several of the most commonly employed quantitative standards will be discussed.

18.5 Digital Imaging Applied to Quantitative Materialography This section is composed of a series of detailed discussions of several of the most commonly practiced quantitative materials standards. The Annual Book of ASTM Standards, Volume 03.01—Standards Relating to Metals-Mechanical Testing; Elevated and Low-Temperature Tests; Metallography 共see Part II, Section 12.4兲 contains the majority of standards written by this body that are applied to quantitative materials microstructural analysis. Other standards not found in this volume but applicable to microstructural measurements include: ASTM Standard Test Method for Evaluating the Microstructure of Graphite in Iron Castings 共A 247兲 and ASTM Standard Specification for Compacted Graphite Iron Castings 共A 842兲. One or two other quantitative methods for which specific standards do not exist are included based upon their widespread use.

18.5.1 Percent Area „Volume Fraction… One of the simplest and most widely used forms of quantitative metallography/ materialography is area, or volume fraction. To perform percent area measurements requires image digitization but does not require calibration, since the required outcome is a ratio. The manual standard for implementing this quantitative method is ASTM Standard Test Method for Determining Volume Fraction by Systematic Manual Point Count 共E 562兲. This standard relies upon the use of a grid consisting of “equally spaced points formed by the intersection of fine lines.” This, of course, is a method of

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digitizing the microstructure. Interestingly, ASTM E 562 references ASTM Practice for Inclusion or Second-Phase Constituent Content of Metals by Automatic Image Analysis 共E 1245兲 for the “use of automatic image analysis to determine the volume fraction.” Another standard, ASTM Test Methods for Determining Area Percentage Porosity in Thermally Sprayed Coatings 共E 2109兲, describes the use of digital imaging to measure percent area of a specific structural feature. Performed either manually or by computer, the point counting technique is the essence of percent area or volume fraction measurement. By definition a digitized image is composed of a number of pixels that are, in fact, a grid of equally spaced points. All that is necessary is to count the pixels 共grid points兲 that fall within the structure of interest and divide that value by the total number of pixels in the entire field of view. In order for the software to calculate the percentages, the operator must use the system segmentation control to detect the phase 共or phases兲 to be measured. The detection operation is the key step in the procedure and all concerns relative to segmentation discussed in Section 18.3.6 apply. Inevitably, microstructures will be encountered in which the pixel illumination values of the structure to be measured and the matrix have some overlap with no distinct boundary. In these cases setting the segmentation range necessarily requires a subjective judgment on the part of the operator. The reliability of the calculated volume fraction may be improved by employing a technique of setting several segmentation ranges to detect the same structure. Since most imaging systems have the capability of measuring more than one segmented range simultaneously, it is a simple matter to set several ranges for the same structure and take the statistical average for the reported result. This approach of taking a larger sample of data is consistent with statistical thinking and the additional measurements and calculations necessary are easily performed by analysis software. There are other advantages to using digital image measurement software for percent area 共volume fraction兲 as well as other measurements. The possibility of applying a color overlay to the image to highlight the measured phases provides an excellent visual aid to the operator and yields highly informative images for inclusion in the results report. Another advantage is the capability of the image measurement software to produce data that may be exported directly to external analysis and reporting software such as database, statistical process control, and spreadsheet programs.

18.5.2 Inclusion Rating Inclusions are occurrences of precipitates or other products of indigenous processes that result in random distributions of observable particles in the matrix material. Because of the significance of inclusions in influencing material properties, methods of classifying and determining the level of inclusions present in materials have been developed and widely used, primarily in steel, as a major determining factor of quality. A number of published standards employing manual comparison as well as quantitative methods for determining the content of inclusions exist. ASTM Volume 03.01 includes three standards, ASTM Standard Test Methods for Determining the Inclusion Content of Steel 共E 45兲, ASTM Standard Practice for Obtaining JK Inclusion Rating Using Automatic Image Analysis 共E 1122兲共withdrawn 2006, replaced by E 45兲 and ASTM Standard Practice for Determining the Inclusion or Second Phase Constituent Content of Metals by Automatic Image Analysis 共E 1245兲 for determining inclusion content. ASTM E 45 is the original manual comparison method. Of the several methods found in this standard by more widely practiced microscopic methods are Method A

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and Method D. The heart of these methods involves classifying inclusions into four types 共A, B, C, and D兲 based upon inclusion morphology, separating each type into a thin and heavy series based upon inclusion width and assigning each type a Severity Level 共1 / 2 to 5兲 based upon the total length or number of inclusions in a field of view. The Method A requires the reporting of the inclusion rating for the field of view with the most severe rating for each inclusion type. The compilation of these four ratings is the “worst field.” In Method D a specimen surface area of 160 mm2 must be covered using individual fields of view of 0.05 mm2. This results in the requirement to cover 320 fields of view, each to be rated for the severity level of all types. ASTM E 45 includes a series of drawings showing the amount of inclusions at each severity level for each inclusion type and requires that the operator judge the best comparison and record the observations. Obviously this manual approach is quite labor intensive and has the potential to generate subjective results particularly in the Method D rating of 320 fields. ASTM E 45 is one of the best examples of a standard that has been significantly improved by converting to more quantitative and automatable methods. While incorporating the methods of E 45, ASTM E 1122 defines inclusion typing and rating in a sufficiently quantitative way so as to enable these classifications to be performed by image analysis software. Although eliminating the reliance on chart comparison, ASTM E 1122 preserves the traditional severity level-rating scheme rather than requiring a more statistically robust results report. In recognition of this short-coming ASTM E 1245 has been published and provides a thoroughly quantitative method with statistically relevant reporting of results. Following the ASTM E 45/E 1122 standard to perform the severity level rating of inclusions using digital imaging software requires first the separation of the inclusions from the matrix by the process of segmentation. The matrix of the steel microstructure after specimen preparation has a very high illumination level nearly white. The type A sulfide inclusions are generally quite high in illumination levels and appear in a gray scale digital image as light gray. A-type inclusions may be close to the matrix in illumination level and therefore the requirements for specimen preparation and lighting optimization are critical. Background correction may be required to ensure that the A types can be successfully segmented without detection of bits of the matrix. Inclusion types B, C, and D are the oxide types and generally appear as black objects in the matrix. The B types are sometimes described as broken stringers and occur as a series of three or more particles strung out in a line; C types are single particles called stringers having an elongated form with an aspect ratio of greater than designated in the standard. The D types are globular oxides and are circular with aspect 共length to width兲 ratios of less than designated in the standard. The B, C, and D oxide type inclusions must also be separated from the matrix by segmentation. Normally segmentation to separate the B, C, and D types is not difficult due to their high contrast with the bright matrix. Separation of the sulfide A type inclusions from the B, C, and D oxide types is generally straightforward since the A types appear as brighter objects than the darker oxide types. Once segmentation is established the measurement of length and width of all inclusion types and counting of the D types must be performed. These data are then used to calculate the severity levels for each inclusion type. For many image analysis systems, the specimens must be oriented on the microscope stage such that the elongated inclusions are aligned horizontally or parallel to the X axis of stage movement. Several difficulties can be encountered when implementing this standard. To begin

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with, inclusion ratings must be made for a specific field area 共0.05 mm2兲. If this area cannot be displayed in a single digitized image, it is necessary to digitize and measure a sequence of images until the 0.50 mm2 area has been achieved before a rating can be calculated. The need to measure and accumulate data over multiple images requires more complex software and will be more time consuming. To improve efficiency an attempt should be made to choose a combination of camera lens and microscope objective magnification to yield a digitized image area of 0.50 mm2. Another difficulty may be encountered because of the standard requirement that inclusions as thin as 2 ␮m be measured. Such small objects can be difficult to distinguish from commonly occurring artifacts that possess illumination levels similar to the inclusion types. Any scratches visible on the specimen surface after materialographic preparation may be detected as an elongated A or C type inclusion, although generally imaging software is designed to eliminate such artifacts due to their orientation. A more common problem is the misdetection of small circular artifacts as D type inclusions. It is nearly impossible to separate with software filtering legitimate D types from artifacts of this class and therefore it is absolutely essential to perform inclusion measurement only on specimens that are freshly prepared in order to minimize the occurrence of corrosion, oxidation, or staining. Another issue arises from the requirement to measure a relatively large specimen area, 160 mm2. As mentioned earlier 320 images are needed to cover this area at 0.50 mm2 per image. Obtaining such a large number of images can obviously take a significant amount of time and has naturally led to the use of motorized microscope stages that can be programmed to move the necessary number of fields without the need for manual operator interaction. While without question an improvement, the use of motorized stage movement along with motorized focusing procedures to eliminate operator interaction during the inclusion measurement process can also lead to problems. It is inevitable that an unattended, fully motorized, and automatic inclusion rating process will produce some field ratings that are incorrect. Two types of errors are commonly encountered. Excessively high severity levels can be calculated because image artifacts 共scratches, dust, oxidation spots, stains, etc.兲 have been measured as inclusions. Also slightly out-of-focus images can be digitized to display inclusions with exaggerated dimensions that produce results higher than actual severity levels. More rarely, the focus is so far off so as to cause complete failure to detect any inclusions present in the image. Falsely high field measurements can be flagged and the images stored separately so at the conclusion of specimen measurement the operator may check the list of suspect rating data and review the associated images. Any images displaying obvious artifacts may then be removed from the rating database. Incorrectly under rated images are impossible to discover, short of an operator examination of every image rated. This of course is impractical and completely defeats the desire to eliminate direct operator involvement in the measurement process. Several additional error sources can be identified including misclassification of inclusion type by the software. In contrast to ASTM E 45 and ASTM E 1122 the ASTM E 1245 provides another approach to inclusion rating. ASTM E 1245 is a primary example of a stereologically and statistically robust quantitative microstructural quality standard. The Procedures Section of E 1245 lists the Measurement of Stereological Parameters including volume fraction of the inclusions, the number of inclusions per field, and the number of interceptions of the inclusions per unit length of test line. Additional individual inclusion feature measurements may be made. From these basic measurements, statistical parameters such as aver-

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ages, standard deviations, 95 % confidence interval, and percent relative accuracy are to be calculated for each type of inclusion detected. An important aspect of this standard that is significantly different from its predecessors is the elimination of separating inclusion types into thin and heavy and calculation of severity levels. The stereological and statistical procedures embodied in the ASTM E 1245 standard make it an important addition to the traditional severity rating level methods.

18.5.3 Grain Size Grain size is a key determiner of materials properties. Several standards, both qualitative and quantitative exist that describe methods for determining grain sizes 共see Section 17.3兲. ASTM Standard Test Methods for Determining Average Grain Size Using Semiautomatic and Automatic Image Analysis 共E 1382兲 is a quantitative standard written for implementation via digital image analysis that is based on many of the same measurement parameters described in the quantitative methods of the ASTM Standard Test Methods for Determining Average Grain Size 共E 112兲. The several variations in methods described in both of these standards are derived from measurement of either grain interior areas, grain boundary lengths, or the interceptions of these features with some pattern of test lines. The chief difficulty in applying digital image analysis to grain size determination arises from the problem of grain boundary delineation. To show the grain boundaries in most materials requires some form of chemical etching. Acidic etch compounds may erode the material at the structurally weaker boundary between grains producing a slight “groove” that has a lower illumination level when viewed with a microscope 共see Part II, Chapter 13兲. Some acidic etchants, such as Nital, when applied to steel, chemically dissolve grains at different rates based on each grain’s crystal orientation. This difference in attack creates differences in elevations at the boundaries between adjacent grains resulting in what appears to be, in bright-field illumination, black lines at the boundaries between grains. In practice the precise and uniform application of etchants is difficult to achieve and along with naturally occurring variations in material etching rates, results in grain boundary visibility and appearance that is highly variable. Even within a single microscopic field of view it is common to observe strongly etched boundaries immediately adjacent to areas that display faintly or incomplete boundary delineation. In fact, the preparation of microstructural specimens with 100 % grain boundary delineation is uncommon. The boundary delineation issue is so significant that the ASTM E 1382 standard prefaces all discussion of digital image measurement methods with the statement “The precision … of grain size measurements using automatic image analysis is highly dependent on the quality of the etch delineation of the grain boundaries. The grain boundaries should be fully and uniformly delineated.” If the boundary between adjacent grains is incomplete when using a grain area method, the separate grain areas will be measured as one, resulting in erroneously high grain area data. Similarly, missing boundaries will produce an inaccurately low measurement when employing a grain boundary length method of grain size determination. In nearly every case the application of a watershed type digital image filter must be applied to improve grain boundary delineation before measuring grain features with digital imaging systems. This process is commonly referred to as grain boundary reconstruction; see Section 18.3.6 for a discussion of the watershed filter. It is important to note that the watershed filter can be too aggressive in defining boundaries; the filter typically connects truncated grain boundaries but also tends to connect any dots ap-

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pearing in the grain interiors to form boundary networks. This action can result in a virtual “fracturing” of grains into small pieces. Minimization of this effect can be achieved by careful operator adjustment of the segmentation levels. Most implementations of this filter require that the operator set the segmentation levels to select the grain interiors. In practice it may be advantageous to set the segmentation range to over detect the grains, i.e., include some of the lighter boundaries 共and grain interior artifacts兲 along with the grain interiors. Observing the results of boundary reconstruction at several different segmentation levels and selecting the most accurate level should be a part of the standard analysis procedure. It may also be necessary to run one or more digital image processing functions designed to eliminate grain interior artifacts that can serve as sites for nonexistent boundary construction. Ultimately, it may be necessary for the operator to manually insert, via a software drawing function, missing boundary sections. This operation obviously lacks efficiency and should be avoided. In reality, boundaries have no dimensions, but in any graphical representation they will have some width. Depending on the magnification, the grain size and the width of the boundaries, an area reduction introduced by the boundary delineation could be significant, thus the boundary thickness should be kept to a minimum. After performing the appropriate image processing steps to “reveal” the complete grain boundary network in a specific image, the image processing software can produce a binary, or black and white image with only the boundaries shown. An image composed of only test lines in any orientation and density, linear or circular 共or virtually any other configuration兲 can be constructed by software. This test line image can be mathematically combined with the grain boundary image using a class of image processing functions commonly termed “image arithmetic.” The imaging software can produce a resultant image showing just the points where the test lines intercept the boundaries. This is accomplished by checking pixels at exactly the same coordinate location in both images and if the location is occupied by a boundary and by a test line it is counted. Alternatively other image arithmetic functions may be performed to yield an image showing just the lengths of the test lines falling within the grain interiors. The grain intercept lengths displayed in these images can be measured to provide the mean lineal intercept length, a method of grain measurement described in ASTM E 1382 as well as in ASTM Standard Test Methods for Characterizing Duplex Grain Sizes 共E 1181兲. In reality, perfect grain boundary delineation is not necessary. It is perfectly acceptable that over any given number of fields measured there will be some over and some under-measured grain areas or boundary lengths. Since the statistical reporting requirements of the quantitative standards provide methods for determining measurement accuracy based on statistical parameters such as confidence interval and percent relative accuracy, if, after measuring a specimen area, appropriate statistical significance levels are not produced, then it is necessary to measure more grains in more images. Typically, imaging system software accumulates the grain feature measurements, as they are collected over multiple images. Based on these raw measurements the required statistical parameters are calculated. One advantage in delineating and collecting individual grain areas for average grain size determination is that in the same dataset the largest grain area and clusters of grains can be found. The largest grain area can be used to satisfy the requirements of ASTM Standard Test Methods for Estimating the Largest Grain Observed in a Metallographic Section 共ALA Grain Size兲共E 930兲. Even Table 1 of ASTM E 930 listing the relationship of the ALA grain area to the grain size

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number can be created easily in software such that the grain size number can be automatically reported, further streamlining the performance of ALA grain size analysis. Grain area cluster data can be useful in characterizing duplex grain sizes as described in ASTM E 1181.

18.5.4 Degree of Banding The nature and importance of quantifying banding in microstructures is discussed in Section 17.5. ASTM Standard Practice for Assessing the Degree of Banding or Orientation of Microstructures 共E 1268兲 provides quantitative as well as qualitative methods for assessing the degree of banding. The standard requires the measurements of volume fraction and count of feature interior interceptions or feature boundary intersections with superimposed test grid lines. Both of these operations have been discussed 共see Sections 18.5.1 and 18.5.3兲; they can be performed using digital imaging techniques providing the banded structures exhibit a sufficiently high degree of illumination contrast to enable successful segmentation. Application flexibility is increased and segmentation requirements relaxed if the imaging software provides the option for direct operator insertion or deletion of the test line-feature interceptions or intersections. The only other condition to be satisfied for banding measurements is to orient the image so that the deformation axis seen in the structure is aligned horizontally or vertically in the digitized image. While image rotation can be performed by software to avoid introduction of image processing artifacts, it is preferable to achieve the required structure alignment by physically rotating the material specimen on the microscope stage.

18.5.5 Depth or Thickness Measurements Several standards exist that address the linear measurement of depth or thickness of structures, zones, and layers. These include ASTM Standard Test Methods for Estimating the Depth of Decarburization of Steel Specimens 共E 1077兲 and ASTM Standard Test Method for Measurement of Metal or Oxide Coating Thickness by Microscopical Examination of a Cross Section 共B 487兲. These standards rely primarily on the use of eyepiece reticles or filar micrometres to perform the necessary measurements. Digital imaging offers several approaches to emulate the nondigital quantitative procedures. When measuring the depth or thickness of structures that exhibit a strong contrast with surrounding or adjacent material the “segment and combine” techniques described in Section 18.5.3 may be used. Briefly, an image of the segmented layer to be measured is mathematically combined with an image of a set of section lines. A resultant image is produced that displays only that portion of each section line that lies on the segmented layer and these lines are measured. While section lines may be discontinuous, the image analysis software calculates the overall length of each horizontal row of line segments no matter how many segments into which the line is broken. The actual thickness measurement is made starting from the left end point of the left-most segment in each row and finishes at the right end point of the right-most segment in the row. Figures 18.15共a–e兲 depict this process. For structures lacking the contrast to use the segmentation approach the measurements can be made using operator interactive methods to construct point-to-point distances or parallel lines that are measured by the software. These methods are the digital equivalents of positioning filars for thickness measurement, with the operator using the computer mouse to position filar lines on the digital image as displayed in Figs. 18.16共a兲 and 18.16共b兲.

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Fig. 18.15a—Image of coating.

Fig. 18.15b—Binary 共segmented兲

Fig. 18.15c—Binary section line image.

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Fig. 18.15d—Combined 18.15b and c.

One of the additional advantages in using digital imaging systems for thicknesstype measurements is that annotations showing measurement lines as well as the measured distances can be added to the image automatically by the software.

18.5.6 Graphite in Iron Castings ASTM Standard Test Method for Evaluating the Microstructure of Graphite in Iron Castings 共A 247兲 is essentially a qualitative chart comparison standard, applied to ductile, gray and malleable irons. For nodular 共ductile兲 and flake 共gray兲 iron particles a size 共maximum diameter or length兲 classification chart is given. Much could be done to improve this standard by introducing additional quantitative procedures. The highly contrasted nature of microscopically observed graphite in prepared cast iron specimens make the use of segmentation-based digital image measurement of these structures quite straightforward. Well prepared specimens that do not exhibit graphite smearing seldom require extensive image processing since the dark 共nearly black兲 graphite shapes are strongly contrasted with the bright white of the cast iron ferrite matrix. One problem that may hinder automatic measurement is the possibility, particularly in gray iron, of touching graphite particles. The application of a separation filter

Fig. 18.15e—Section lines over coating.

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Fig. 18.16a—Vertical filar.

may reduce these occurrences and as a final solution manual editing of the image may be undertaken to separate massively touching particles.

Ductile Cast Iron Although not incorporated into any ASTM standard, an important factor in determining ductile or nodular iron product acceptability is the percentage of graphite particles that are nodular. Digital imaging systems provide outstanding capabilities for calculating the percent nodularity. The classic function used to calculate particle roundness 共nodularity兲 is the shape factor. While several equations exist for calculating shape factor the most commonly used is: Shape Factor = 4*Pi* Particle Area/Particle Perimeter2 To calculate nodule shape factor the area and perimeter of each graphite particle is

Fig. 18.16b—Horizontal point-to-point.

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Fig. 18.17a—8-line perimeter.

measured. These values are entered into the equation and the shape factor number is produced. Possible shape factor values range from 1.0 for a perfectly circular particle downward towards 0 for increasingly “uncircular” shapes. Some shape factor level must be chosen as a lower limit to define the most “uncircular” shape to be considered nodular. This value is often set to 0.6, so that graphite particles have a shape factor equal to 0.6 or greater are nodules, and those with shape factors less than 0.6 are not. Percent nodularity can then be easily calculated by dividing the total count of nodules by a count of all graphite particles. The precision with which the imaging software defines the particle perimeter length has a significant effect on the outcome of the calculations. In particular, the measuring of small undulations in perimeter can significantly alter the percent nodularity since the perimeter is squared in the calculation of shape factor. Figure 18.17共a兲 shows a nodule in an enlarged portion of a digital image. In this view the imaging software was adjusted to measure the graphite perimeter using just eight line segments seen as dark lines around the perimeter. In Fig. 18.17共b兲 the software was readjusted to use 128 line segments to define the object perimeter. The 8-line delineation yields a perimeter of 0.47953 mm while the

Fig. 18.17b—128-line perimeter.

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128-line perimeter is 0.51311 mm in length. The shape factor of Fig. 18.17共a兲 is 0.929 while the shape factor of Fig. 18.17共b兲 is 0.869, a significant difference. This example illustrates the importance of the software algorithms used to define objects and extract measurements. The algorithms are in fact critical functions in the process of data production. As such their contribution to the end result must be understood and controlled if reproducible structure measurements are to be achieved. Attention to such internal software methods is especially important when results produced by several separate digital imaging systems are to be compared.

Gray Cast Iron The length of graphite flakes in gray iron can normally be readily measured from digital images. The lengths can be input to calculations of the percentage of the flakes falling in each of the size classes listed in ASTM A 247. However, the task of digitally classifying the “Graphite Distribution Patterns” as types of graphite flakes described in the standard is beyond the capability of common image analysis techniques.

Compacted Graphite Compacted graphite cast iron contains graphite particles in shapes that are intermediate between flake and spheroid shapes. This type is defined by the ASTM Standard Specification for Compacted Graphite Iron Castings 共A 842兲 as “The acceptable graphite formation in the microstructure shall contain 80 % minimum Type IV graphite as depicted in ASTM A 247 which may be arrived at by using…automatic image analysis methods.” Also, this type is “described as cast iron with the graphite in compacted 共vermiform兲 shapes and essentially free of flake graphite.” Based upon these guidelines it is possible to produce imaging software to calculate the percentage of graphite that is not spheroid 共calculate shape factor as in ductile cast iron except the percent particles that are not spherical is found兲. Also, to ensure that there is no flake graphite present, the aspect 共length to width兲 ratio may be calculated. In this case since the standard does not provide a quantitative value to separate compacted from flake graphite, a reasonable value must be assumed and used in the software to calculate the presence of any flake graphite.

18.6 Digital Imaging Technology 18.6.1 Hardware Several distinct hardware components are required to perform image digitization, processing, and analysis. Microscopes and other optical devices are not discussed here. The basic imaging system hardware components are: computer, camera, and printer. Recently all hardware components needed for image digitization have become available as “off-the-shelf” items and the need for specialized hardware components for all common materials structure measurements is nonexistent. A general philosophy concerning selection of digital imaging systems should be based upon using the most standard components available. It is no longer necessary or even desirable to purchase proprietary, single purpose, single source, and fully integrated systems. Such systems inevitably have limited shelf life, provide functionality that is behind the curve of hardware capabilities available on the open market, and provide very limited 共and expensive兲 upgrade possibilities. With the possible exception of image measurement soft-

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ware there is no component necessary for assembling a state-of-the-art digital imaging system that is not widely available commercially. Because the same technologies developed and priced for mass-marketed consumer cameras, computers, and printers are used in industrial grade digital imaging systems, the cost of the hardware components needed to provide image digitizing functions continues to decline while the capabilities of the components continue to improve.

Computer Today, computers designed for normal business 共or even home兲 use have more than adequate power and information processing capabilities to run even the most sophisticated materials analysis software. It is not necessary or even desirable to procure custom designed or nonstandard computers to power digital imaging systems. All of the computer peripherals present in a typical home computer system designed for Internet access and game playing should in most cases be present on a system for image measurement. Several specific components can be briefly commented upon. For viewing images 共especially those delivered by large format digital cameras兲, relatively large monitors are helpful. Monitors of 19 in. or larger display size and to save laboratory bench space 共albeit at a premium price兲 flat, active matrix LCD monitors should be considered. Efficient management of digital images does require relatively large capacity computer memory, high processing speed, and extensive file storage space. Fortunately, computer processors, memory chips, and disk drive components are among the most cost effective of all equipment needed for digital imaging. Rapid technological development and a long history of downward trending prices in these devices are primary reasons to avoid imaging systems based upon private label and custom designed hardware that cannot be readily upgraded or enhanced with standard components.

Cameras No other single component required to perform digital imaging is more widely available than the camera. There are literally hundreds of camera models available. Of this vast array there are two basic types: analog and digital. The analog camera outputs an analog electronic signal that is essentially a television signal; it is not in digital form and requires that image digitization be performed by a video digitizing or frame grabber circuit board installed in the computer.4 Digital cameras are designed to digitize the image signal internally and output a digital format data stream to the computer. The key element in cameras is the sensor that converts light into an electronic signal. At this time the predominant sensor technology is the charged coupled device or CCD silicon chip. Another type of image sensor becoming increasingly available is the Complementary Metal Oxide Semiconductor or CMOS. Among the specifications that differentiate cameras, the physical size of the chip is one of the more significant. Chip sizes generally range from 41 , 31 , 21 , 32 , up to 1 in. or more. Chip size is important because all other components remaining equal, the size of the chip is directly proportional to the size of the digital image field of view. A system equipped with a camera featuring one of 1 1 the smaller chip sizes 共 4 or 3 in.兲 may not be capable of delivering the required field of view area. Obviously the quality of the image produced by the camera is important. But other factors such as image size, ease of operation, cost, and most importantly, how the im-

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ages are to be used should be considered.

Analog Cameras Analog cameras output a video signal that can be displayed in real time, that is, the image signal is output fast enough to refresh the monitor display at approximately 30 times a second. For viewing images on a monitor at a display rate that produces no noticeable delay or jerky movement when the field of view is moved or the image focus is adjusted, in general an analog camera performs better than a digital camera. Since analog cameras contain a minimal amount of circuitry the physical size of the camera can be relatively small. In general, the more digitizing and signal processing that is done within the camera, the larger the camera body. To digitize an image the analog camera must be connected to a digitizing circuit board mounted inside the computer. Digitizing boards can display a live signal from the camera along with digitizing the image for storage, processing, and measurement 共see Inoue and Spring for a detailed discussion of digitizing boards4兲. There are a wide variety of digitizing boards available. When selecting a digitizing board it is important to match the board input and digitizing capabilities with the signal output of the analog camera. Many digitizing boards are available with the capability of being connected to multiple cameras. This feature is useful in laboratories requiring cameras to be mounted on a microscope, a stereoscope, a microhardness tester, and more. Digitizing boards are supplied with software for adjusting the board to accept various camera signal formats, for capturing images, and perhaps for image file management. Digitizing board products may also include software programs called drivers that are designed to enable the board to work directly with specific digital imaging software. There is an industry standard digitizer-to-imaging software driver called TWAIN. Digitizing boards and imaging software products providing the TWAIN interface can work together and do not require any additional special software drivers. Analog camera/digitizing board combinations provide a fast and efficient means for digitizing images. For most material microstructure digitizing applications high-resolution analog camera/digitizing board combinations are the best all around choice.

Digital Cameras Digital cameras digitize the image signal output from the image sensor chip before it enters the computer. Digital cameras connect to the computer using a variety of computer ports or circuit boards, some standard and some custom designed. Digital cameras are available with large format image sensor chips and can digitize images into a very large number of pixels. With their high pixel counts digital cameras can provide excellent quality images and are generally capable of displaying fine structural details more sharply than an analog camera/board combination. As with digitizing boards, digital cameras will be supplied with software for image acquisition and the availability of TWAIN software is equally important. While providing high quality images, it should be noted that many digital cameras are slower to capture images than analog cameras. The real time image display rate is 30 times a second for analog output while digital cameras may require up to several seconds to display a full image. In general, the greater the number of pixels the digital camera offers, the longer the image capture time. Delays in refreshing the computer image display are particularly noticeable during focusing of the image. Additionally, digital cameras may be more complex to oper-

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ate than analog systems. Digital cameras should be considered when the primary use for the digitized images is viewing, particularly when the images are to be printed. Of course, the quality of printed images is also a function of the printer used and printers are briefly discussed in this section.

Black and White or Color For extracting structural measurements from most materials a gray scale 共8 bit or 256 levels of pixel illumination兲 is adequate. In a few materials segmentation to separate a structure for automatic delineation may require the use of a 24 bit 共16.7 million levels兲 true color image. Due to the increased difficulty in setting color segmentation levels and inefficiencies attendant to managing color images, the use of color images for extracting measurements is only recommended if the measurements are not possible with gray scale images. Color images are recommended when the primary use of the image is for publication and human viewing.

Printers As with cameras, a very large number of computer printers are available for use with digital imaging systems. The growth in consumer digital photography has impacted the quality of prints and the price of image printers very positively. Inkjet type printers that can produce “photographic quality” images continue to become less expensive. The primary printer specification used to judge the potential quality of printed images is the number of ink dots per inch the printer is capable of putting on the paper. A count of 2400 by 1200 dots per inch is dense enough to produce high quality prints. For the highest quality images coated photographic type paper must be used. Another type of printer technology known as thermal dye diffusion can produce a continuous-tone print with resolution of 300 pixels-per-inch. The quality of these prints is termed “professional grade” and these printers have prices in the range of one order of magnitude higher than ink jet printers. Specifications and pricing level aside, it is recommended that actual prints of material microstructures be viewed prior to making a decision on printer acquisition.

18.6.2 Software There is an enormous variety of digital imaging software available. A recent search of the Internet yielded the following results: Search Phrase: digital imaging software Web Page Matches over 50 000 Search Phrase: image acquisition software Web Page Matches over 2400 Search Phrase: imaging editing software Web Page Matches over 400 Search Phrase: image archiving software Web Page Matches over 400 Search Phrase: image measurement software Web Page Matches over 300 Although not designed specifically for materialographic structure imaging, the number of “image software” product sources is significant. Many of the products, concepts, techniques, and software modules developed for other digital imaging applications can be used in metallographic/materialographic systems. This results in the availability of constantly improving software functionality at competitive prices. Of course, several software systems have been designed particularly for materials science applications. These should provide minimum basic image processing functions as well as the modules to perform one or more of the metallographic/materialographic test methods described in Section 18.5, depending on the requirements of the individual laboratory.

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It is a near certainty that most imaging software packages will provide far more processing and measurement capabilities than are normally needed in all but the most diverse research and development environments. One of the challenges in selecting software for materials analysis uses is in identifying products that provide the functions needed to perform structural imaging tasks without the presence of extraneous software capabilities that may complicate operation and inflate costs. A few general guidelines can be suggested. Obviously the most important consideration is that the software is capable of performing the required tasks. What may not be so apparent is what those tasks are 共see Section 18.7 for additional comments concerning software selection兲. The same general criteria used in selecting any type of software are applicable. Avoid software that can only be used with a specific computer or other hardware components. The software should provide an open architecture that permits exchange of data and interaction with other software products such as database, spreadsheet, and statistical process control programs. The software must also follow industry standards for data and image file formats, user interface control designs, and device connectivity. In most cases it is advisable to avoid proprietary designs that create a “sole source” supplier dependency.

Open Source/Public Domain Software It is possible to obtain open source/public domain software like NIH Image from National Institutes of Health for image processing/analysis. However, it should be noted that the basic philosophy of open source software requires a strong commitment to maintain and support the software on the part of the user. Often the typical metallographic/materialographic laboratory is not able or willing to perform such tasks.

18.7 Digital Imaging System Implementation The selection of software should always be based on a thorough and realistic study of current organizational tasks, established laboratory procedures and a realistic appraisal of future requirements. A digital imaging system is not a stand-alone device; it is a tool to facilitate the operation of a quantitative microstructural quality control program. The same care and attention to detail should be accorded the selection of a digital imaging system as to other organizational information management or quality control systems. An imaging system is part of a bigger organizational structure. In a well designed system implementation project three distinct phases can be identified. The purpose of Phase 1 is to produce a master plan based on an analysis of existing metallographic/materialographic operations and a definition of objectives. Part of this phase is actually a traditional systems analysis study, undertaken to define in some detailed and formal manner the procedures and work flow of the existing metallographic/materialographic operations. This information can serve as a base line for integration of new equipment. A clear understanding of the standards to be followed, the type of measurements necessary, and the volume of current as well as projected work are among the many questions to be answered. It is also essential to consult with engineers, information technology personnel, and others within the organization who will be in any way impacted by the new system. A very important factor in the successful implementation of a digital imaging system is the skill level required by the system operator. Efficient operation of the imaging system may require a more techni-

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cal background than general lab work; in particular a firm understanding of basic computer operation techniques is essential. Since quantitative metallography/materialography is based on stereological and statistical principles the system operators must also possess an understanding of these subjects. If an evaluation of potential system operators reveals a deficiency in these areas, suitable training programs should be required. The system suppliers should provide training in the operation of specific imaging systems and software. However, general computer and quantitative methods knowledge are a prerequisite and remedial instruction in these topics, if necessary, is not the responsibility of equipment vendors. One important result of the initial phase should be the generation of a set of expectations or specifications that define the functions required of the imaging system. The purpose of Phase 2 is to use the requirements, priorities, and specifications generated in Phase 1 to determine which of the many commercially available systems will best meet the current and future requirements of the company. This phase may include identification of potential suppliers, compilation of a list of products available, demonstrations, circulation of a Request for Quotation, and of course, final system selection. Phase 3, the last step of the process, is actually placing the system into operation. The process of converting to digital imaging from qualitative or manual quantitative methods should have been defined in Phase 1. Implementation of new technology will almost certainly necessitate changes in the procedures used to employ that technology. Common procedural points that may need changing include: 1. Specific orientation and positioning of specimen may be required by standards or by equipment. 2. Selection of microscope objective magnification may be significant, i.e., field of view area required by standard. 3. Upgrading of preparation standards to eliminate artifacts that defeat automatic imaging. Often results obtained from image analysis equipment will not match historical results based on qualitative estimates or chart comparison methods. In these cases it may become necessary to devise a strategy to correlate pre-and post-digital imaging results. Ideally, major issues arising during implementation will have been identified, and the new system will be placed into operation in an efficient and cost-effective manner. Even with flawless planning it is to be expected that the full use of the system at maximum efficiency will require a “learning” period. ASTM Standard Guide for Laboratory Information Management Systems 共LIMS兲共E 1578兲, offers many insightful guides for the selection of a Laboratory Information Management System. Many of these concepts may be adapted for use in selecting a system for digital imaging and an examination of ASTM E 1578 is suggested. A particularly useful idea found in ASTM E 1578 is the need to focus on functions, not technology. Additionally, see ASTM E 2066-00 Standard Guide for Validation of Laboratory Information Management Systems. In conclusion, the objective of this chapter was to highlight some of the digital imaging functions that are commonly applied to materials structure images and to provide an overview of the use of image measurement techniques to implement selected standard test methods. It is also hoped that these comments have initiated an awareness of the necessity of quantitative metallography/materialography and also that digital imaging systems are but a part of an overall program for the improvement of product quality.

19 Digital Image Management „Archiving… A DIGITAL IMAGE ARCHIVING SYSTEM MAY INCLUDE ALL OF THE FEAtures and components of a full image measurement system, the difference being that the primary purpose of archiving is to provide efficient and convenient yet powerful methods for capturing, identifying, storing, and retrieving digital images and associated information rather than to extract structure measurement data. Such a system may include sophisticated database software or simple filing schemes for identifying images by a range of user definable classifications and keyword associations. As with digital image measurement systems the selection of archiving must be based upon an evaluation of existing and projected needs. A broader view of laboratory digital imaging possibilities must include consideration of the ASTM Standard Guide for Laboratory Information Management Systems 共LIMS兲共E 1578兲共see Sections 12.4.2/3兲. ASTM E 1578 provides a detailed discussion of LIMS concepts. Laboratory information management systems are designed to provide total data management from initial material sample receipt through logging of all specimen preparation procedures, recording of image acquisition parameters such as microscope magnification brightness, contrast, segmentation levels, calibration, and any image processing functions performed along with the original, intermediate, and final images as well as final structural measurements data and many others. In short, these systems aspire to compile a complete record of all possible information related to the processing of the specimen within the laboratory along with the ability to search, retrieve, and report selected views or dynamic combinations of the information from these records. These systems represent the most ambitious and sophisticated level of digital system possible in the laboratory. The demands of design and implementation of digital systems are increased by levels of magnitude when considering a LIMS. At the most advanced implementation level, the LIMS must provide electronic integration of the technologies of many diverse instruments, requires the use of local as well as wide area networking, and employs sophisticated database technologies. And because they provide the several functional LIMS components as defined in ASTM E 1578 such as data/information capture, data analysis, and reporting, systems for digital image archiving and structural measurement may be considered components or subsystems of a LIMS.

References „Part IV… 关1兴关2兴关3兴关4兴关5兴

Underwood, E. E., Quantitative Stereology, Addison-Wesley Publishing Company, Reading, MA, USA, 1970. Friel, J. J., et al., Practical Guide to Image Analysis, ASM International, Materials Park, OH, USA, 2000. Russ, J. C., The Image Processing Handbook, 3rd ed., CRC Press, Boca Raton, FL, USA, 1998. Inoue, S. and Spring, K. R., Video Microscopy, Plenum Press, New York, NY, USA, 1997. Freund, J. E., Statistics: A First Course, 2nd ed., Prentice Hall Inc., Englewood Cliffs, New Jersey, USA, 1970.

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Part V: Hardness Testing

20 Introduction HARDNESS IS AN IMPORTANT PROPERTY WHEN JUDGING THE QUALITY and possible applications of a material. It can also give indications concerning the tensile strength, ductility, or wearing quality of the material. Beginning in approximately 1822, quantitative evaluation of hardness was carried out based on the hardness scale developed by F. Mohs. He ordered known minerals so that the harder mineral scratched the one preceding it. TABLE 20.1—Mohs Hardness Scale. Mohs Scale 1 2 3 4 5 6 7 8 9 10

Mohs Standard Mineral Talc Gypsum Calcite Fluorite Apatite Feldspar Quartz Topaz Corundum Diamond

Equivalent Knoop Hardness Number 2 32 120 150 400 560 700 1300 1800 6000

It must be noted that the differences in hardness between the individual steps of the scale are not equal. For example, the difference between steps 9 and 10 is substantially greater than that between 1 and 9. Around 1900, further testing procedures were developed for technical purposes. In these procedures, hardness is not determined by scratching, but rather by indenting the material to be tested with very hard objects of a specified size and shape. The Brinell, Rockwell, Vickers, and Knoop hardness testing procedures are the best known of these techniques. Already in 1900, Martens suggested the following definition of hardness for technical purposes: Hardness is the resistance of a material to penetration by another 共harder兲 material. This simple conceptualization remains the basis of our understanding of hardness even today.

20.1 Indentation Hardness Figure 20.1 schematically shows the significant elements of indentation hardness testing. A particular indenter 共1兲, attached to the lower end of a press, is pressed into the 623

624


Fig. 20.1—Schematic drawing of hardness tester indicating force, indenter 共1兲 specimen 共2兲 and support 共3兲.

specimen surface 共2兲 with a particular test force 共in N or kgf兲 and then pulled back. The indentation that is created can then be measured. The shape and size of the indenter are decisive for indentation resistance. With ball-shaped indenters, the specimen material is pushed away sideways and downwards through plastic and elastic deformation. Angular or needle-shaped indenters can, in addition to the deformation, cause separation processes like cracks, especially in brittle materials 共ceramics兲. Depending on the characteristics of the material being tested, various mostly nonhomogeneous deformation processes with multiple axes and varying degrees of elasticity and plasticity occur with penetration. The speed of penetration also influences the behavior of the material being tested. For these reasons, the guidelines for the hardness testing procedures, including equipment construction, indenter, penetration speed, optical system, and evaluation are of particular importance. Hardness is a distinguishing feature of a material. It is usually measured quantitatively according to the following general relationship: Hardness value = Test force/indentation size

共1兲

Beginning in 1940, hardness testing procedures in which the penetration depth is measured during application of a test force and then used to determine hardness were developed. These procedures quickly gained in importance. We differentiate among: Hardness testing procedures with static load action. Hardness testing procedures with dynamic load action. Special hardness testing procedures.

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Introduction

625

The most important of these will be shortly described below.

20.2 ASTM Standards To be able to compare hardness values, the equipment, testing procedures, testing method, and evaluation must correspond to particular standards. The following ASTM standards describe the various hardness testing procedures. See Section 12.4.2 for more standards on hardness. Standard Practices for Force Verification of Testing Machines 共E 4兲 Standard Test Method for Brinell Hardness of Metallic Materials 共E 10兲 Standard Test Methods for Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials 共E 18兲 Standard Test Method for Rapid Indentation Hardness Testing of Metallic Materials 共E 103兲 Standard Test Method for Indentation Hardness of Metallic Materials by Portable Hardness Testers 共E 110兲 Hardness Conversion Tables for Metals 共Relationship Between Brinell Hardness, Vickers Hardness, Rockwell Hardness, Rockwell Superficial Hardness, Knoop Hardness and Scleroscope Hardness兲共E 140兲 Standard Practice for Scleroscope Hardness Testing of Metallic Materials 共E 448兲 Standard Test Method for Microindentation Hardness of Materials 共E 384兲 Standard Test Method for Vickers Hardness of Metallic Materials 共E 92兲

21 Static Hardness Testing Procedures 21.1 Brinell Hardness Testing THE FIRST STATIC HARDNESS TESTING METHOD WAS INTRODUCED BY J. A. Brinell, a Swedish researcher, at the 1900 Paris World Exposition. A hardened steel ball or tungsten carbide ball with a diameter 共D兲 of 1, 2, 2.5, 5, or 10 mm was used as indenter. This was pressed into the smooth, clean specimen surface with a test force 共F兲. Figure 21.1 shows the principle of test with test force F 共N兲, D the diameter of the ball 共mm兲, d the mean diameter of the indentation 共mm兲, and h the depth of the indentation 共mm兲. It is important that the specimen rests on a rigid support, and that the indenter contacts the specimen without being shaken or jolted. The test force is then increased to the predetermined maximum value within 2 – 10 s and held for 10– 15 s. If the duration of load application falls outside of this range, this must be indicated. For example, for nonferrous materials, the duration may be as long as 180 s. Depending on the elastic-plastic behavior of the material, the indentation may vary. Figure 21.2 shows an ideal indentation, 共a兲, an indentation with sink-in due to a high degree of elasticity 共b兲 and an indentation with pile-up due to a high degree of plasticity 共c兲.

21.1.1 Calculations and Procedures The spherically shaped indentation that is created is measured. The Brinell hardness is calculated from the mean indentation diameter according to the following equation: HBS or HBW = 0.102

2F F = 0.102 ⫻ A ␲D共D − 冑D2 − d2兲

共1兲

where HBS= Brinell hardness with steel ball as indenter HBW= Brinell hardness with tungsten carbide ball as indenter F = test force in N A = indentation surface in mm2

Fig. 21.1—Brinell hardness testing, test principle. Force, kgf 共F兲, diameter of ball, mm 共D兲, mean diameter of indentation, mm 共d兲, depth of indentation, mm 共h兲共ASTM Standard E 10兲.

626

Chapter 21

Static Hardness Testing

627

Fig. 21.2—Ball-shaped indentation shapes. Ideal indentation 共a兲, indentation with sink-in 共b兲 and indentation with pile-up 共c兲.

D = ball diameter in mm d = arithmetical mean value of two measured indentation diameters in mm The test force F is multiplied by 0.102 共⬃1 / 9.80665= 1 / g兲 to get the calculated hardness as a unitless numerical value. Specimen thickness should be at least ten times the expected indentation depth. If the expected hardness of a material can be estimated, then the minimum specimen thickness can also be estimated. For the indentation depth, it can be assumed that A = D␲h

共2兲

The minimum thickness S of the specimen is then S = 8共0.102F/␲DHB . . . 兲

共3兲

Steel balls can be recommended as indenters for Brinell hardness values of up to 350. They are permitted up to HBS= 450. When testing harder materials, elastic deformations of the ball must be expected. These lead to increased indentation diameters and thus to erroneously elevated measured values. Tungsten carbide balls may be used up to HBW 650. Test results are given as follows: Duration of test load application 共25兲 Test force identifying value 0.102 F 共3000兲 Ball diameter in mm 共10兲 Identifying marking of indenter 共in this case tungsten carbide兲共W兲 Abbreviation for Brinell hardness 共HB兲 Determined Brinell hardness value 共410兲 The relatively large indentations are an advantage of the Brinell hardness testing method. They ensure representative hardness values even when heterogeneous materials are tested.

628


TABLE 21.1—Stress Level and Recorded Hardness Range for Various Materials. Stress Level 30 10 5

Hardness Range, HB 70–600 22–315 11–158

2.5 1.25

6–78 3–39

Material Steel, Iron ⬎140 HB Ti, Ni-, Co, Cu-Alloys ⬎200 HB Nonferrous metals and their alloys Bearing metals Lead, tin

It is important that the ball creates an easily measurable indentation. For that reason, it is stipulated that the indentation diameter lies between 0.24 D and 0.6 D. If different ball diameters are used on the same material, the measured values can only be compared when the indentations are geometrically similar. Accordingly, the test force F must be appropriate for the ball diameter D. For comparison of hardness values, the optimum stress level 0.102F / D must therefore be closely adhered to. Table 21.1 shows the relationship between stress level and measured hardness range for various material categories. If the material to be tested, and therefore the load ratio and the diameter D of the test ball selected 共10, 5, 2.5, or 1.25 mm兲, are known, then the test force F can be set on the testing apparatus. The minimum distance from the middle of an indentation to the edge of the specimen should be at least 2.5 d for steel, gray cast iron, copper, and copper alloys. The distance between adjacent indentations must be ⬎4 d. For light alloys, Pb, Zn, and their alloys, the respective distances should be ⬎3 d 共specimen edge兲 and ⬎6 d 共adjacent indentations兲.

21.1.2 Brinell Hardness Testers Figure 21.3 schematically shows the construction of a Brinell hardness testing machine with hand wheel 共1兲, support 共2兲, specimen 共3兲, objective 共4兲, indenter 共5兲, loading system 共7兲, and screen for measuring the projected Brinell indentation 共6兲. Figure 21.4 shows a modern Universal Hardness Tester for Vickers, Knoop, Brinell, and Rockwell. It has unattended testing and analysis cycle via fully automated image analysis for Brinell/Vickers and automatic focusing. The test load ranges are 9.81 N to 2450 N or 49 N to 7350 N. Testing procedure details can be found in the directions for use of the equipment and in the procedural and material-specific norms, for example, the ASTM Test Method for Brinell Hardness of Metallic Materials 共E 10兲. Internal company procedural guidelines should also be observed.

21.2 Vickers Hardness 21.2.1 Calculations and Procedures Smith and Sandland developed the Vickers method 共named for the English company Vickers兲 in 1925. The reason for this development was the fact that Brinell hardness only provided usable results up to HBS= 450, because higher test forces cause deformation of the steel ball to begin to occur. In Vickers Hardness Testing, the indenter is a regular four-sided diamond pyramid

Chapter 21


629

Fig. 21.3—Schematic drawing of Brinell hardness testing machine with hand wheel 共1兲, support 共2兲, specimen 共3兲, objective 共4兲, disengaged indenter 共5兲, screen for projection of the indentation 共6兲, and loading system 共7兲.1

with an interfacial angle, ␣, of 136°. The geometry of this Vickers pyramid produces a good correlation between the Vickers values HV and the Brinell hardness values HBS between 350 and 400. The Vickers pyramid is pressed vertically into the specimen with a test force P 共kgf兲共2兲 shown schematically in Fig. 21.5. ␣ 共1兲 is the face angle of the diamond 共136°兲, d1 and d2 共3兲 are the diagonals of the impression 共mm兲. The mean diagonal diameter d of the indentation is used to calculate the Vickers hardness. HV = 0.9272 where HV= Vickers hardness P = test force in kgf

P 2P sin共136 ° /2兲 P ⬇ 1.8544 2 = A d2 d

共4兲

630


Fig. 21.4—Universal hardness tester for all standard testing processes such as Vickers, Knoop, Brinell, and Rockwell. Unattended testing and analysis cycle via fully automated image analysis for Brinell and Vickers. Automatic focusing. Test load ranges: 9.81 N to 2450 N or 49 N to 7350 N.2

A = indentation surface in mm2 d = arithmetical mean value of the measured indentation diagonals in mm For Vickers Hardness, given in GPa units, we find that HV = 0.0018544 ⫻ P2/d22

共5兲

with force P2 in N and the mean length of indentation diagonals in mm. Because of the pyramidal geometry, the relationship between the indentation depth and the indentation diagonals is h = d / 7.0006. For Vickers macrohardness testing, the test load must normally also be selected such that the indentation diagonals are relatively large in comparison to the phase components. The diagonal d should be a maximum of 2 / 3 of the specimen thickness, and the penetration depth thus 1 / 10 of the specimen thickness, to exclude influence from the specimen support. This is important when testing thin sheets or layers 共see below兲.

Chapter 21


631

Fig. 21.5—Vickers hardness testing, test principle 共ASTM Standard E 92兲.

Test results are given as follows: Duration of test load application in s 共25兲 Test load identifying value 共100兲 Abbreviation for Vickers hardness 共HV兲 Measured Vickers hardness value 共780兲 Figure 21.6 shows the ideal indentation 共a兲 and possible undesirable indentations with sink-in 共b兲, pile-up 共c兲 formation and “kite” shape 共d兲. For high-test forces, determination of Vickers hardness is independent of the test force. However, for test forces P ⬍ 5N the calculated Vickers hardness becomes test force dependent. This phenomenon is known as Indentation Size Effect 共ISE兲. Its influence is particularly disruptive in microhardness testing, where HV values that have been measured for the same specimen with differing test forces are no longer comparable. The cause can be tension induced when the Vickers pyramid is imposed or surfaces that have stabilized dissimilarly during metallographic/materialographic preparation. For this reason, hardness value classification is divided into test ranges. Following the ASTM Standard Test Method for Vickers Hardness of Metallic Materials 共E 92兲, Vickers Hardness Tests are performed with test forces of from 1 to 120 kgf. The ASTM Standard Test Method for Microindentation Hardness of Materials 共E 384兲 specifies a test force range of 1–1000 gf for microindentation hardness testing with Vickers indenters 共see Section 21.5兲. At Vickers hardness testing 共E 92兲 the distance between the center of the indentation and the specimen edge and between the center of two indentations should be ⬎2.5d. When laminated material is tested, a bond surface shall be considered as an edge for spacing of indentation calculations. In hardness testing of small parts, thin sheets, layers or foils, low-test forces should be used to avoid the so-called anvil effect. The anvil effect is caused by use of a test force

632


Fig. 21.6—Vickers indentation shapes. Ideal indentation 共a兲, indentation with sink-in 共b兲, indentation with pile-up 共c兲, and kite-shaped indentation 共d兲.

that is too high when testing a thin specimen, resulting in a bulge or shiny spot on the underside of the specimen. Also a force that is too high may cause edge effects, a plastic deformation in the direction towards the edge. For this reason an indentation shall be in a certain distance to the edge as mentioned above. The use of low-test forces also applies to the determination of hardness of individual structural constituents. As the test force or indentation size, or both, decrease, the influence of the specimen surface increases. A carefully smoothed and cleaned surface is sufficient when macro testing, but when micro testing, the specimen must be metallographically/ materialographically prepared to remove any disruptive roughness or solidified surface layers. If smoothing and polishing are insufficient, the surface can be electrolytically or chemically treated to have access to mechanically undisrupted areas. If individual structural constituents are to be tested, additional phase contrasting, for example by means of etching, is necessary.

21.2.2 Vickers Hardness Tester The hardness tester shown in Fig. 21.4 can easily be converted for use in Vickers macrohardness measurements. The indenter is exchanged and the appropriate test force increments selected. Measurement takes place on the screen or automatically. Depending on the producer, the machines differ in various ways. For example, the test force may be produced mechanically or hydraulically in different increments, the test method may be more or less automated and special testing needs may be met by means of additional equipment.

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633

Fig. 21.7—Knoop diamond pyramid and indentation 共ASTM Standard E 384兲.

21.3 Knoop Hardness Testing 21.3.1 Calculations and Procedures Special machines were developed for low load, microindentation hardness, and ultramicroindentation hardness testing in order to further decrease potentially disruptive device-related influences and better measure very small indentations. Essentially, however, the testing procedure corresponds to that of macrohardness testing. In 1932, Knoop, Emerson, and Peters introduced a method developed specifically for low load and microindentation hardness testing. In Knoop hardness testing, a rhombic-based pyramidal-shaped diamond indenter with edge angles of 172° 30⬘ 共⬔A兲 and 130° 共⬔B兲 is used. In Fig. 21.7, the pyramidal-shaped diamond is shown with the two angles and the long diagonal, d 共␮m兲. As in the Vickers method, this pyramid is pressed vertically into the specimen surface. Knoop hardness in kgf/ mm2 is calculated by means of the long indentation diagonal d in ␮m, which is 7.114 times longer than the short diagonal of the Knoop indentation. The following equation applies: HK = 14.229P1/d12

共6兲

where HK= Knoop hardness in kgf/ mm2 P1 = test force in kgf d1 = long indentation diagonal in mm Knoop hardness in GPa units is determined as follows: HK = 0.014229 ⫻ P2/d22 where P2 = test force in N d2 = long indentation diagonal in mm Test results are given as follows: 650 HK 0.5/ 30

共7兲

634


Duration of test force application in seconds; not recorded if between 10 and 15 s 共30兲 Test force identifying value: 0.102F 共F in N兲共0,5兲 Abbreviation for Knoop hardness 共HK兲 Measured Knoop hardness value 共650兲 Knoop hardness measurements are primarily taken using hardness testers developed for low load and microindentation hardness testing. In such machines, the load system is changed accordingly and adjusted for small test forces. The screen onto which the indentation is projected is exchanged for a measuring ocular. Due to the measurement length that is greater than that of a comparable Vickers indentation, measurement error is smaller in the Knoop method. Therefore, even very thin layers or foils can be tested better. The Knoop method is also advantageous with brittle materials, as cracks form more easily around a Vickers indentation. The Knoop indenter does not produce a geometrically similar indentation as a function of test force. Consequently, the Knoop hardness will vary with test force. Due to the elongated shape of the Knoop diamond, any anisotropy that may exist in individual structural constituents can be ascertained. When this is the case, different measurements of the crystallite are taken and the specimen is appropriately rotated before every new measurement. Knoop hardness testing is described in ASTM Standard Test Method E 384 共see Section 21.5兲.

21.4 Rockwell Hardness Testing 21.4.1 Calculations and Procedures Due to a number of disadvantages of the Brinell hardness test and the limitations regarding testing of steels with high hardness, Stanley P. Rockwell developed a hardness testing method in 1919. In this method, the hardness of a material is determined by means of measured indentation depth. A diamond indenter is used for Rockwell C 共see Fig. 21.8兲 or a tungsten carbide/steel ball is used for Rockwell B. In Fig. 21.8 the following symbols and designations are used: 1: Angle of the top of the diamond indenter 共120°兲; 2: Radius of the curvature at the tip of the cone 共0.200 mm兲; 3: P0, Preliminary test force; 4: P1, Additional force; 5: P, Total test force 共P0 + P1兲; 6: Depth of penetration under preliminary test force; 7: Increase in depth under additional force; 8: e, Permanent increase in depth of penetration under preliminary test force after removal of additional force, the increase being expressed in units of 0.002 mm; 9: xxHRC, Rockwell C hardness= 100− e. It can be seen that the indenter is first pressed a small distance into the material; in this way the influence of the specimen surface can be excluded. Rockwell hardness value is calculated by means of a process internal to the machine with the help of a scale division factor S and a numerical value N. The simple equation for determining Rockwell hardness is: HR = N − e/S where HR= Rockwell hardness N = Numerical value tied to S e = Remaining indentation depth in mm

共8兲

Chapter 21


635

Fig. 21.8—Rockwell C hardness test with diamond indenter, test principle, see text 共ASTM Standard E 18兲.

S = Scale division in mm The standard indenters are a diamond cone with 120° apical angles and tungsten carbide balls with diameters of 1.588, 3.175, 6.350, and 12.70 mm. The preliminary test force for the Rockwell Standard Method is 98 N 共10 kgf兲; the possible total force is 589 N 共60 kgf兲, 981 N 共100 kgf兲, 1471 N 共150 kgf兲. For the Rockwell Superficial Hardness test, the preliminary force is 29 N 共3 kgf兲 and the possible total force is 147 N 共15 kgf兲, 294 N 共30 kgf兲 and 441 N 共45 kgf兲. Corresponding scales are available for different application purposes and material groups 共see Table 21.2兲. Lower test forces are used in Rockwell Superficial Hardness Testing. The preliminary test force is 29 N and the total test force can be 147 N, 294 N, and 441 N. Rockwell scales B 共for the steel ball of 1.588 mm diameter兲 and C 共for the diamond cone兲 are the most frequently used. As in Brinell hardness testing, however, it must be noted that deformation of the ball can occur in very hard materials with HRB. Therefore, use of the B steel ball for materials harder than 100 HRB is not recommended. The test object should lie solidly on the support table 共anvil兲 so that it cannot slip during the test method. Care must be taken to select the correct indenter and force when working with thin specimens so that the hardness value of the specimen is not falsified due to the influence of the support table, the so-called anvil effect. Specimen thickness should be ⬎15 times the depth of indentation when using a ball indenter and ⬎10 times the depth of indentation with a diamond cone. As a rule, no deformation should be visible on the back of the work piece after the test. Indentations should be made at a distance of at least 2.5 times the indentation diameter from the specimen edge. The distance between adjacent indentations should be three times the indentation diameter. The preliminary test force F should be produced within 3 s. The usual duration of stress by the additional force is 1 – 8 s. Further information about the method can be found in ASTM Standard Test Method E 18.

636


TABLE 21.2—Rockwell Scales and Test Conditions for Various Groups of Materials. Scale Symbol B

Indenter (Diam.) Steel 共1.588 mm兲

Total Test Force kgf 100

C

Diamond

150

A

Diamond

60

D E F G H K L M

Diamond Steel 共3.175 Steel 共1.588 Steel 共1.588 Steel 共3.175 Steel 共3.175 Steel 共6.350 Steel 共6.350

mm兲 mm兲 mm兲 mm兲 mm兲 mm兲 mm兲

100 100 60 150 60 150 60 100

P R S V

Steel 共6.350 Steel 共12.70 Steel 共12.70 Steel 共12.70

mm兲 mm兲 mm兲 mm兲

150 60 100 150

Application Example Moderately hard, soft steels; brass, bronze, Al alloys Hardened, tempered steel; hard casting, materials harder than HRB 100 Sintered carbides as well as HRC with low specimen thickness Thin steel sheets, case-hardened layers Cast iron, Al and Mg alloys, bearing metals Thin, soft steel sheets, annealed copper alloys Copper-nickel-zinc, hard bronzes Aluminum, zinc, lead

Soft bearing metals and thin specimens, very small balls and heaviest load that does not give an anvil effect

Designation of Rockwell hardness is made by supplying the hardness value followed by the abbreviation HR 共for Rockwell hardness兲 and the scale symbol. This gives information about the indenter and the force. For example, 80 HRC means a Rockwell hardness value of 80 on the C scale using the diamond cone as indenter.

21.4.2 Rockwell Hardness Testers Figure 21.9 shows a basic Rockwell hardness testing machine. The testing procedure differs in two significant ways from the Brinell and Vickers methods described previously. First, with the help of a hand wheel, the specimen is pressed against the indenter until the meter indicates the desired preliminary force F0. Then, the additional force F1 is applied for the specified length of time. A further difference lies in the fact that the Rockwell hardness value HR can be read from the meter immediately after withdrawing the major force. The significant advantages of Rockwell hardness testing compared to the Vickers and Brinell procedures include the simpler machine construction without optical measuring equipment, the direct readability of the hardness values, and the less stringent quality requirements for the specimen surface. For these reasons, the Rockwell method was quickly adopted and is used primarily for simple and fast quality control in production.

21.5 Microindentation Hardness 21.5.1 Methods Measuring methods and machines must be appropriately adapted to perform hardness measurements on very small objects, thin layers, surface-treated materials, or individual structural constituents.

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Fig. 21.9—Rockwell hardness tester.2

Microindentation hardness, also often called microhardness, means the determination of hardness values with low test forces. Compared to the macrohardness testing methods described previously, the test force range in microhardness testing is very small. Following the ASTM Standard Test Method for Microindentation Hardness of Materials 共E 384兲 the range is between 1 and 1000 gf 共9.8⫻ 10−3 and 9.8 N兲, and the indentations are correspondingly small. In practice, the geometric forms of the Vickers and Knoop diamond indenters have proved successful. In addition, the Berkovich diamond indenter must be mentioned. This is a regular three-sided pyramid with an angle of 142° between the lateral edge and the opposite lateral face. The indentation surface is an equilateral triangle; the lengths of its sides are measured. The hardness value that has already been described, is in any case ascertained by dividing the test force by the remaining indentation surface. It is especially important to monitor the loading system regularly, since the hardness error percentage is directly proportional to force error. The total force should be applied within 10 s, while the duration of the force can range from 10 to 15 s. For steels, 10 s are sufficient. If longer load times are necessary for softer materials, this must be indicated in the test protocol. Vibrations and shaking of the machine must be avoided during measurement.

21.5.2 Specimen Preparation To achieve precise measurement values, the polished and cleaned specimen surface should be set up perpendicularly to the direction of indentation. This is the only way to achieve clearly defined indentations that can be evaluated to a microscopically exact degree. The smaller the test force and the indentation, the greater the influence of specimen preparation. For example, excessive polishing can cause cold work of the surface material 共see Part II, Section 13.16兲. Whenever possible, the surface should not be

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etched since the indentation otherwise becomes uneven due to the attacked surface and may be difficult to measure. See Part II, Table 11.1 and Chapter 13.2.3 for information regarding suitable specimen preparation. Small unevenly shaped specimens must be mounted or fastened into specimen holders. It is important to ensure that the specimen cannot move under the effects of the force.

21.5.3 Taking the Measurements The microindentation hardness measurement method takes place in the following way: Turn on lighting system and the calibrated hardness tester Select, carefully clean and apply an indenter Set or fasten specimen material on table surface Focus a low-enlargement lens on the specimen surface Select indentation area, adjust contrast and resolution to optimal values Remove lens from and move indenter into the operating position Select force Activate test, adhere to specified force times After withdrawing the force, disengage indenter and move lens into measuring mode Check indentation for desired position and symmetry Evaluate Nonsymmetrical indentations can be caused by the following: Indenter does not penetrate specimen surface perpendicularly Specimen surface is not level Material is textured Anisotropy of structural constituents Because microindentation hardness values are strongly influenced by different components and their size and distribution in the material, it is advisable, depending on the task at hand, to make several indentations under otherwise identical conditions. The distance between two Knoop indentations shall lengthwise be ⱖ1.5 d 共length of Knoop diagonal兲, side by side be ⱖ4 w 共width of Knoop diagonal兲 and the distance to the edge of the specimen shall be ⱖ3w. The distance between the center of two Vickers indentations shall be ⱖ4 d 共length of Vickers diagonal兲, and the distance to the edge of the specimen shall be ⱖ2d. In ceramics or other brittle substances, the indentation can cause cracks. The ASTM Test Method for Knoop Hardness for Advanced Ceramics 共C 1326兲 and the ASTM Test Method for Vickers Hardness for Advanced Ceramics 共C 1327兲 address more closely the consideration of such special circumstances. When test forces and indentations are so small, high demands are placed on the indenter in terms of precision, particularly where the four faces meet. For the Knoop indenter the line of junction between opposite faces 共offset兲 shall be not more than 1 ␮m in length for indentations greater than 20 ␮m in length, as shown in Fig. 21.7. For Vickers indenters the offset shall be not more than 0.5 ␮m. Formation of an offset between the faces cannot occur with the Berkovich indenter, as it has only three faces. Indenters should be examined periodically and replaced if they become worn, dulled, chipped, cracked, or separated from the mounting material.

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Fig. 21.10—Microhardness testing machine.3

21.5.4 Microindentation Hardness Testers Figure 21.10 shows a modern microhardness tester. With this machine, Vickers, Knoop, Berkovich, and Brinell testing procedures can be carried out with adherence to the most recent ISO and ASTM standards. Machines of this kind operate completely automatically with motorized lens carousel and autofocus 共motorized z-axis兲. The load production and the load changes among nine increments 共from 98.07 mN to 19.61 N兲 take place automatically when the duration of load application is between 5 and 999 s. With the help of a video camera and appropriate measuring and controlling software, the image of the indentation surface can be transferred to a PC and evaluated there. Serial measurements are possible in addition to individual tests. Measurement values can be statistically evaluated 共maximum, minimum, mean values, standard deviation, histogram兲. Conversion of hardness values 共HR, HB, MPa, etc.兲 occurs automatically.

21.5.5 Examples of Indentations Figure 21.11 gives four examples of indentations. In Fig. 21.11 共a兲 shows three indentations in differential interference contrast 共DIC兲; 共b兲 shows Vickers indentations in steel, indicating the softer ferrite and the harder pearlite; 共c兲 shows the hardness progression in case hardened steel; and 共d兲 the indentation is in a ceramic material, Si3N4. The brittle material causes cracks at the corners of the indentation.

21.6 Universal Hardness—Martens Hardness—Instrumented Indentation Testing—Nano Indentation The extent of elastic and plastic deformation varies greatly among technical materials. In rubber, for example, elasticity predominates, and the indentation regresses almost completely when the load is removed, whereas in materials like lead the hardness indentation is retained. The hardness values of the two materials can therefore not be compared to each other. Comparison is possible when the Universal hardness, HU, is calculated. In this procedure that has been known since 1940, the Vickers hardness is measured under force. The Universal hardness is calculated from the maximal test force Pmax and the indentation depth hmax. Universal hardness is now known as Martens hardness, HM 共see below兲.

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Fig. 21.11—Examples of Vickers and Knoop indentations. Three Vickers indentations in DIC, 220X 共a兲, indentations in steel indicating ferrite and pearlite, BF 500X 共b兲, progression of hardness in a case hardened steel, BF, 100X 共c兲, and a Vickers indentation in silicon nitride with cracks at the corners, DIC, 200X 共d兲.

By means of this procedure, hardness values from all material types can be compared on one scale, which is a great advantage, particularly for industrial purposes. The Vickers procedure’s visual evaluation of the indentation, along with its possibility of error, is hereby eliminated. The indentation depth is recorded by measuring techniques that make possible the automation of the procedure. Additional valuable quantitative information about a material’s elastic and plastic behavior can be extracted from load-indentation depth curves, Fig. 21.12, that are a schematic representation of the test force 共indentation-load兲, F, versus depth of indentation 共displacement兲, h. The diagram shows that the depth of indentation 共displacement兲 increases with increasing load. At unloading only the elastic portion of the displacement is recovered, which allows for separation of the elastic properties of the material from the plastic properties. Based on the maximum depth, hmax and the maximum load, Fmax, the Martens hardness, HM, previously Universal hardness, can be defined 共see below兲. It is also possible from Fig. 21.12 to calculate the elastic modulus 共Young’s modulus兲 based on the slope of the unloading curve.

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Fig. 21.12—Schematic representation of indentation force—depth of indentation 共displacement兲 data during one complete cycle of loading and unloading.

21.6.1 Instrumented Indentation Testing—Nano Indentation In classical light-optical microhardness testing, even when using automatic machines with high-grade optical measurement systems, a Vickers or Knoop diagonal length is recordable to at most 2 – 3 ␮m. This is due to the limited resolution capability. When working with microcrystalline materials and extremely thin layers, however, hardness indentations of substantially smaller indentation size are required. This is achieved by using the testing principle, Instrumented Indentation Testing 共IIT兲, also called nano indentation. IIT is used for determination of Martens hardness, HM, Indentation hardness, HIT, and Indentation modulus, EIT. The indentation depth 共h兲 is measured and used to calculate the hardness value. In this way, indentation depths to 0.1 nm can be recorded and evaluated in adherence to international standards 共see below兲. Martens Hardness Scale: The Martens hardness value is calculated by dividing the test force F by the surface area of the indenter penetrating beyond the original surface of the test piece As共h兲. For Vickers indenter: HM = F/As共h兲 = F/26.43h2

共9兲

HM = F/As共h兲 = F/26.44h2

共10兲

For Berkovich indenter:

Indentation Hardness Scale: The indentation hardness HIT is calculated from the test force, F, divided by the projected area of the indenter in contact with the test piece at maximum load: HIT = F/A共hc兲

共11兲

where the projected contact area A共hc兲 is calculated from knowledge of the geometry of the indenter and the stiffness of the contact. During the indentation the force-trajectory progression can be recorded that gives significantly more information about elastic-plastic behavior than does a classical indentation for which the size is evaluated. In this way, hardness, elasticity, or viscoelas-

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tic properties of paint, varnish, or synthetic layers, galvanized layers, carbide layers of TiN or TiC, diamond and anodized layers as well as fibers and foils can be determined and compared. Also, the hardness and elastic modulus of a single grain in a microstructure can be measured. Fully automated measurement and evaluation ensure high reproducibility and prevent subjective error. Instruments for IIT work with test forces down to 1 nN and indentation depths 共displacement兲 down to 0.1 nm. HM can be measured with Vickers and Berkovich indenters. For measurements in the nano range the Berkovich indenter, having only three faces 共see Section 21.5.3兲 is preferred, but other geometries like sphero-conical indenters are also used. Instrumented Indentation Testing is described in ASTM Work Item, Practice for Instrumented Indentation Testing 共WK 382兲 and in the Standard ISO 14577.

21.7 Precision of Hardness Values The hardness testing procedure takes place in two steps: The production of the hardness indentation and its measurement. The measurement value that is obtained in the presence of known standard testing machine and specimen conditions is influenced by the geometric precision of the indentation specimen and by penetration direction, test force, test time, penetration speed, and temperature. This can lead to constant or variable errors. For this reason the testing machine shall be verified. The direct verification of the hardness tester includes the inspection of the force application, the indenters, and the measuring device at regular intervals. If the test force or the indenter is changed, a new verification must be performed. Indirect verification takes place by making a series of at least five test impressions on a standardized hardness test block. The closer the mean values of the test impressions are to the hardness of the test block, the more exact the hardness tester functions. The difference in hardness values around a mean value may be an indication of the precision of the hardness tester: The less difference the higher precision. A verification report often should be worked out after the verification. The test report should contain the following information: Reference to the ASTM test method. Method of verification. Identification of the hardness testing machine. Means of verification. Type of indenter and test force. The result obtained. Date of verification and reference to the calibration institution. Identity of the person performing the verification. For specification regarding the single hardness testing method, see the relevant ASTM standard stated in Section 20.2.

21.8 Conversion of Hardness Values The conversion back and forth among Brinell, Vickers, or Rockwell hardness values is possible with the help of conversion tables 共see below兲. The conversion values are solely empirical in nature. In certain cases the following equations can be used; these should be considered as rules of thumb, not as exact as the equations stated in the conversion tables mentioned below. Simple Hardness Conversion Equations:

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From HB to HV: HB⬃ 0.95 HV From HRB to HB: HRB⬃ 176– 1165/冑HB From HRC to HV: HRC⬃ 116– 1500/冑HV From HV to HK: HV⬃ HK 共in low load range兲 Procedural information can be found in the ASTM Standard Hardness Conversion Tables for Metals 共Relationship between Brinell Hardness, Vickers Hardness, Rockwell Hardness, Rockwell Superficial Hardness, Knoop Hardness, and Scleroscope Hardness 共E 140兲. Please refer to ASTM E 140 in the CD-ROM included with this manual. Values that have been estimated using the equations given above or taken from the conversion tables should be indicated, stating the original hardness value.

22 Dynamic Hardness Testing Procedures IN DYNAMIC HARDNESS TESTING PROCEDURES, THE INDENTER HITS the specimen surface with impact. The specimen material can thereby be elastically and unelastically deformed. Deformation that arises due to the kinetic energy of the indenter and remains can be measured. In such dynamic-plastic procedures, the hardness value is the quotient of the test force and the indentation size. We distinguish between fall hardness testing and impact hardness testing 共see Fig. 22.1兲. In the fall hardness testing method 共a兲, an object of defined mass falls freely onto the specimen along with the indenter 共ball兲 and creates an indentation. In the impact hardness testing method 共b兲, the ball rests on the specimen surface. Triggered by a hammer blow or by spring force, an object of known mass is thrust onto the indenter, which then penetrates the specimen. One such instrument is the Poldi impact hardness tester, Poldi hammer for short. The indenter is pressed, by means of a hammer blow, simultaneously into the specimen and into a comparison rod of known Brinell hardness. The HBP hardness can then be determined by comparison. With the Baumann hammer, the indenter is driven into the specimen surface by means of spring force. The indentation is measured and assigned a corresponding Brinell hardness value.

Fig. 22.1—Principles of dynamic hardness testing procedures, schematic. Rebound with drop 共a兲, and rebound with spring loaded hammer and ball placed on the work piece 共b兲.

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Fig. 22.2—Types of rebound hardness testers, schematic. Hardness value based on height of rebound 共a兲, and hardness value based on rebound angle 共b兲.

In dynamic-elastic hardness test procedures, the rebound height, or rebound angle is measured 共see Fig. 22.2兲. In materials with low deformation potential, such as tungsten carbide or rubber, the indenter, which hits the specimen surface at a defined velocity, springs back. We can infer a hardness value from the rebound height that is proportional to the rebound energy. Such dynamic-elastic procedures also include the Shore hardness testing method and the Equotip method. The Scleroscope functions according to the drop hammer principle. The indenter is either a rounded diamond point of a particular size and shape or a steel ball that rests on a drop hammer. This falls through a pipe vertically onto the specimen and rebounds again up to a particular height 共Fig. 22.2共a兲兲. This rebound height is a measure of hardness that is given in Shore hardness values. In the Model C Scleroscope, a highprecision, low-friction glass pipe is used. The rebound height can be recorded on a scale of 0–140, and the hardness can be read in HSc. In the Model D Scleroscope, the hammer is automatically detained after reaching the rebound height, and height and hardness are then recorded using technical measuring instruments. Since the hammer is larger and heavier compared to the one used for the Model C, the fall height can be reduced without changing the impact energy. The hardness values are given in HSd. Depending on the machine model, application, and test material, various indenters and scales are used. More exact guidelines are found in the ASTM Standard Practice E 448. The Equotip tester functions according to the drop hammer principle. A carbide ball 3 mm in diameter is used as indenter. After the release of a preloaded spring, the indenter is thrust against the test specimen. Impact and rebound velocity of the ball are electronically measured at a distance of 1 mm above the test surface. From the relationship between these two velocities we can ascertain an L hardness value 共named after D. Leeb, the machine’s inventor兲. Hardness measurements of up to approximately 1200 HV can be calculated with this method. The advantages of the portable machines described above include their suitability for use on slanted surfaces and the short duration 共only a few seconds兲 of the test procedure. The disadvantage is that these methods do not supply the hardness values with the same high precision as the static hardness testers.

23 Special Methods for Hardness Testing SPECIAL HARDNESS TESTING PROCEDURES INCLUDE THE MARTENS scratch hardness determination as well as the Mohs scratch hardness. In the Martens procedure, a specimen surface under a specified test force is scratched by a diamond cone with a 90-deg apical angle. The test force F is varied until a scratch width of 10 ␮m is microscopically measured. In this way, a particular scratch hardness value can be attributed to the specimen. There are continuous test procedures that allow us to record hardness progression curves for case-hardened or nitrided steels. In these, the width of the scratch that appears is evaluated, at a constant test force, in light of the scratch length. Or, the force trajectory-dependent indentation process may be recorded by means of technical measurement instruments, much as is done in instrumented indentation testing 共see Section 21.6.1兲.

References „Part V… 关1兴

Courtesy of Deutscher Verlag für Grundstoffindustrie.

关2兴

Courtesy of Emco-Test Prüfmaschinen GmbH.

关3兴

Courtesy of Struers A/S.

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Part VI: The Metallographic/Materialographic Laboratory

24 Introduction 24.1 Establishing a Metallographic/Materialographic Laboratory WHEN ESTABLISHING A METALLOGRAPHIC/MATERIALOGRAPHIC LABOratory, many conditions have to be taken into consideration. The two main conditions are: 共1兲What is the purpose of the metallographic/materialographic examination? Is it quality control, research, education, etc.?; 共2兲 What is the specimen volume; few or many specimens per day? Another important condition is the degree of automation of the preparation process. This really depends on the volume of specimens to be prepared and the size of the specimens, as well as the specimen quality 共reproducibility兲. The occupational situation for the persons performing the preparation should also be taken into consideration. Chapter 25 discusses the above-mentioned conditions and other important matters connected to planning for and establishing a metallographic/materialographic lab, and suggestions for a number of laboratories suited for different purposes and capacities will be given.

24.2 Running a Metallographic/Materialographic Laboratory The metallographic/materialographic laboratory should be considered a production unit, producing specimens of the desired quality at the lowest price. This means that correct planning must be made, covering both the day-to-day operation and preventive maintenance.

24.3 Occupational Safety and Health The work in the laboratory involving machines, chemicals, etc., makes it imperative that all relevant rules and regulations covering occupational safety are followed. This subject is described in Chapter 26.

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25 How to Build a Metallographic/ Materialographic Laboratory A LABORATORY IS SELDOM BUILT FROM SCRATCH. AN EXISTING LABORAtory should usually be changed, possibly moved to other locations, etc. In all these cases it is very useful to analyze a number of factors regarding the laboratory so that the right changes, gradually, can be made.

25.1 Purpose The purpose of the laboratory as part of a larger organization should be considered. The purpose may be quality inspection of parts from a running production, meaning that the preparation with examination result should be finished in a short time, or a research lab with large test series that can be prepared at a steady speed with ample time available. Three purposes together with the capacity, number of specimens to prepare per week, should be discussed here.

25.1.1 Quality Control „QC… The laboratory performing quality inspection ranges from the relatively small subsupplier, who prepares a few specimens per week, to the large lab with several hundred specimens per week. In both cases, the specimen size and the materials to be prepared are known and often of a limited number. This means that fixed documented procedures can be established. This ensures the reproducibility that is very important if the analysis over a period of time shall provide a true picture of the product quality. Although a smaller lab with few specimens per week could prepare the specimens by hand and still be rational, the preparation should be performed with a small semiautomatic grinder/polisher to secure the reproducibility. This also makes it possible to use a rather untrained person for the preparation, which can be of advantage, when the specimen volume is low, and it is not possible to have a full-time person on the job. A lab with higher volume will use semiautomatic or fully automatic equipment to have rational specimen production, at the same time securing reproducibility and a programmed process. The “cost per specimen” is important 共see Section 25.2.2兲. If preparation time is important, electrolytic polishing should be considered if the materials are suited for this 共see Chapter 8兲. A QC lab often will have the advantage of digital imaging connected to a system for registration, connecting the metallographic/materialographic analysis with other tests like hardness, etc. 共see Chapter 19兲. If a QC lab also makes failure analysis, this might indicate other types of equipment 共see below兲. 650

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25.1.2 Research and Education Research Like the QC lab, the research lab needs a high reproducibility to secure correct interpretation of the materials being developed. For this reason, semiautomatic equipment should be used. This equipment should have a reasonable capacity, but the production of specimens can usually be planned for and “high-production” equipment is not needed. For research, typically a wide spectrum of materials should be prepared and the equipment should preferably be for mechanical preparation. Electrolytic polishing and thinning 共TEM兲 could be interesting also, electrolytic polishing resulting in “deformation-free” specimens 共see Chapter 8兲.

Education As part of education in physical metallurgy, the students often have to prepare one or more materials, both to experience the metallographic/materialographic process and to be able to see a prepared microstructure in a microscope with their own eyes. A group of students usually works with specimen preparation at the same time, and this can be done on a number of small grinder/polishers, either by hand or with a simple semiautomatic specimen mover. Education is often connected to a research lab, but equipment used for research should not be used by the students for educational purposes.

25.1.3 Testing and Inspection Laboratories—Failure Analysis Laboratories established for preparation of specimens for customers should be able to prepare “all materials” for a wide number of examinations. The job may be just one specimen representing a failure, a special case 共archaeology, forensic兲, or a series of specimens. For this reason, equipment for both mechanical preparation and electrolytic polishing should be available, “high productivity” playing a minor role, with the possibility of preparing all difficult materials playing a major role. Preparation of specimens for failure analysis is often difficult because the specimen is not “regular,” but has to be taken from a work piece at a special location, and the area to be prepared is often difficult to establish. In certain cases hand preparation is preferred, but in most cases the specimen can be mounted so that a semiautomatic grinder/polisher can be used. Therefore, even large laboratories with advanced automatic equipment, sometimes engaged in failure analysis, need a small semiautomatic machine for single specimens.

25.2 Rationalization and Automation The demand for more cost-efficient processes and procedures has been increasing in all parts of the society for a long time. In the metallographic/materialographic lab, the focus is on “cost per specimen,” including all the costs covering manpower, equipment, consumables, locations, administration, energy consumption, etc. Examples are changes in the production, the organization, or the requirements to documentation. As a result, the lab has to produce more specimens without increasing the personnel, or the quality of the specimens should be improved because an auto-

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matic image analyzer has been installed. Improvements in quality have to be made very often without a similar increase to the budget. The demand for a higher specimen quality and a better reproducibility is also increasing because of quality standards like ISO 9000 and IS 9000. Rationalization can often be made in all steps from the work piece/specimen arriving in the lab to the finished report leaving the lab. This can be in specimen handling, choice of equipment, preparation procedures, and administrative routines, including writing of reports and filing the micrographs. At the same time the occupational safety can very often be improved. Automation according to the “state-of-the-art” is limited to the preparation process from plane grinding to the finished specimen and to the automatic printing of microphotographs through digital systems 共see below兲. In case of image analysis, this can also be automatic 共see Part IV兲.

25.2.1 Reproducibility—Standards—Occupational Safety Basically the only assurance that a microstructure is “true” depends on the evaluation done by the person who is interpreting the structure. In most technical matters, the result can be measured and the correctness be verified, but this is not possible with a microstructure. A high element of subjectivity is present when it should be decided whether a microstructure is “true.” It is very possible, of course, to measure the structure using image analysis, but whether the microstructure being measured is the true structure representing the work piece material, or not, is based on the evaluation of an experienced person. For this reason, it is very important that methods are developed, documented, and followed when making a preparation. A proven method “guaranteeing” the true structure, executed on a machine with constant parameters and uniform consumables, makes it possible 共with a high certainty兲 to say that a running production of specimens is correct. As soon as human treatment is involved, the risk of an incorrect result will increase. In modern quality control 共QC兲, according to standards like ISO 9000 and IS 9000, the correct measurement of all results is very important. Therefore, in the case of metallography/materialography, the microscope should be calibrated regularly to ensure that the analysis is correct. It is very difficult, however, to give correct “measuring data” for the preparation process, securing a correct preparation, as mentioned above. Therefore, the responsibility of the correct structure is transferred to the skilled person evaluating the microstructure, and to support this, a documented procedure using semiautomatic or automatic preparation equipment should be worked out. In a number of ASTM standards, such as Standard Test Methods for Determining Average Grain Size Using Semiautomatic and Automatic Image Analysis 共E 1382兲, the preparation is part of the standard, spelling out that the “true structure” must be available at a high reproducibility. In most cases, however, the methods for a given material must be worked out in the laboratory 共see Section 13.2.3兲. Occupational safety and health play an increasing role, both regarding the physical work done by the operator and the total laboratory environment 共see Chapter 26兲. Using semiautomatic or fully automatic equipment for cutting-off, mounting, and preparation will reduce the amount of physical power needed and, when possible, the equipment can be connected to an exhaust system to avoid contaminating the air.

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25.2.2 Productivity—Cost Per Specimen Essentially the preparation of a specimen can be seen as a “production” as any other item made in a production facility. This means that preparation should be constantly analyzed according to the following demands: • Increased productivity • Improved quality • Cost reduction The increase in productivity can be obtained by analyzing the whole preparation process and calculating the cost per specimen 共see below兲. Improved quality can often be achieved by using semiautomatic or automatic equipment. This also usually provides increased productivity. Cost reduction can often be obtained by reducing the cost per specimen, but other factors should also be analyzed to give the most cost-efficient function of the total metallographic/materialographic lab. The following should be taken into consideration: Development of the correct application for each material: It is very important that the optimum process is found for a given material. One or more preparation steps can often be omitted or times can be reduced. Training of Personnel: The persons responsible for the preparation should be trained to optimize the use of equipment and consumables. Service: The equipment should be serviced regularly 共preventive servicing兲 to avoid breakdowns. If breakdowns happen, a service support should be available from the supplier, keeping the downtime short.

Cost per Specimen A cost-savings analysis must be made to decide on the present cost per specimen and a possible lower cost per specimen. The analysis is supposed to show all costs involved in making a specimen. • Operator costs • Consumable costs • Depreciation of equipment The first step in the analysis is to decide on the actual costs. Operator costs are calculated for the total operator time used per specimen from receiving the work piece 共specimen兲 through to a prepared specimen that is ready for the microscope. Consumable costs are calculated by listing all consumables used for each preparation step and calculating the amount used per step. For the equipment, the service costs and depreciation costs are calculated, the latter based on the total investment in equipment, time of depreciation, and the interest rate. The cost per specimen will usually be lower when using more automatic preparation equipment, and often depends on the number of specimens made per day. In Fig. 25.1, two curves are shown indicating the cost per specimen for a highly automated machine 共Equipment 1兲 and a relatively simple piece of equipment 共Equipment 2兲. It can be seen that around 55 specimens per day, the price per specimen is lower using the expensive machinery. The Payback Time is interesting too. This indicates the time for how long the new equipment should operate before the savings are so high that the investment is “paid back.” Figure 25.2 shows an example of Equipment 1 mentioned earlier. The Payback

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Fig. 25.1—Cost per specimen. Comparison between preparation with a highly automated machine 共Equipment 1兲 and a relatively simple piece of equipment 共Equipment 2兲.

Time shows that the expensive 共automatic兲 equipment 共Equipment 1兲 is paid back in one year when approximately 38 specimens are prepared per day. Additionally, the advantage of having a higher certainty for correctly prepared specimens should be taken into consideration also, supporting the procurement of automatic equipment.

25.3 Planning the Metallographic/Materialographic Laboratory 25.3.1 Basic Planning The metallographic/materialographic lab, like all other investments, should be subject to a total cost-benefit analysis. It is, however, not as easy to calculate as the more straightforward processes like a production facility. The lab is a mixture of production 共specimen preparation兲, analysis, reporting, and other administrative work, often with a high variation in the work load. The metallographic/materialographic lab is established like any other lab, but a number of specific features should be evaluated. The lab should be split into several rooms, the basic parts including a room for cutting, a room for preparation, and a microscope room.

Fig. 25.2—Payback time. Payback time in years in relation to number of specimens per day for Equipment 1 in Fig. 25.1.

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A good workflow should be secured. Considering the number of apparatus, the installation of electric power 共both 1-phase and 3-phase兲, compressed air, water drains, and ventilation should be made flexible and easy to maintain The floor load should also be taken into consideration. Because of the relatively large machines used in materialographic preparation, the passages and doors need to be wide enough so that machines up to 1.3 m 共4.3 ft兲 can pass through. A person’s workplace in the lab should have the best possible lighting 共daylight兲, low noise level, and correctly placed fume hoods. A 20–25 % spare area should be designed, if possible, to make room for future expansion. It is important to consider all demands regarding safety 共cupboard for first aid, etc.兲共see Chapter 26兲. With both basic and detailed planning it is important that the personnel already using the lab, or intending to work in the new lab, participate in the planning work. This ensures that a lot of problems are solved in the planning stage and the most efficient function is obtained.

25.3.2 Detailed Planning Factors like type of specimen material, number of specimens to prepare, etc., will influence the details in the lab.

Specimen Material The specimen material influences the type of equipment used. If only one type of material is to be prepared, relatively simple machinery may be used. In the case of a vast spectrum of materials, more machinery may be needed because of the different preparation methods needed.

Number of Specimens The average number of specimens per day will vary very much from lab to lab. A QC lab might have a hundred or more specimens per day, maybe in working shifts. In this case, a very rational preparation can take place 共see Section 25.2兲. In a research lab perhaps only ten specimens per day are made on average, but the materials span widely so that several types of preparation processes are available. In some cases with very few specimens, the preparation might be performed in the “Chemical Lab” or “Materials Testing Lab.”

The Specimen Size and Shape In some cases the lab receives the specimens cut to the right size. In other cases large work pieces, machine parts, or stock material are received and the lab should take care of cutting out the specimen. This may require a special room for cutting, often with large machines. The mounting of the specimen will vary. In mounting a large number of specimens, a special room for hot mounting presses should be considered. In the case of cold mounting, fume hoods must be available.

Type of Examination For labs working with QC or other types of inspection, the lab might be under time pressure, being required to deliver an analysis result in a given period of time. This

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influences how the lab is organized, securing fast results and reporting, effective communication, etc. In some cases, the metallographic/materialographic analysis is combined with other examinations, like hardness testing, and care should be taken that these other instruments are integrated in the best possible way in the lab. In some laboratories, the specimens, before or after preparation, have to be treated in other laboratories and a rational cooperation must be secured. Using a digital camera, the images often necessary for reporting can easily be communicated, avoiding the more tedious photographic work.

Personnel Persons with different educational background and training are needed in the metallographic/materialographic lab. Cutting, mounting, and preparation work can be done by persons with little or no metallographic/materialographic background. For persons without knowledge of metallography/materialography, they should be trained thoroughly before starting the work because lack of knowledge may jeopardize the preparation result. Interpreting the microstructure, working out reports, etc., should be performed by persons with the necessary education in metallography/materialography. In spite of the increasing use of semiautomatic equipment, it should be emphasized that the personnel should be well trained and be allowed to develop experience over a long period of time.

25.4 Equipment and Laboratory Layout A large selection of equipment for preparation, examination, and reporting 共IT兲 is available in the market. The tendency goes towards automation both regarding preparation and analyzing, where the result will now be electronically communicated in IT networks. It is important to select the right equipment, both to secure a high quality, costefficient production of specimens and to secure a certain flexibility 共increase兲 in the number of specimens to be prepared and analyzed. Table 25.1 gives an overview of the equipment needed for a metallographic/materialographic lab, and in the following sections examples for different labs are given. The layout of the lab with several rooms and the correct installations, etc., also plays an important role to ensure an efficient specimen production. This will be discussed below.

25.4.1 Equipment—Table 25.1 The basic equipment is stated in Table 25.1, but in each category several models are available, e.g., a grinder/polisher can be hand-operated or automatic 共see Chapter 7兲. In the following sections some examples are given for different sizes of labs, indicating the types of machines.

Small Laboratory A laboratory with only one to ten specimens per day can be defined as a small lab. This type of lab can be at a sub-supplier to a large company, where a metallographic/ materialographic examination is part of the specifications for the supplied product. The following equipment should be available:

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TABLE 25.1—Equipment, Accessories, and Consumables for a Metallographic/Materialographic Laboratory. Preparation Stage Sectioning

Mounting

Marking Surface preparation— mechanical

Equipment Cut-off machine Precision cutter

Shearing Sawing

Shear Hacksaw Bandsaw Wire cutter Hot mounting press

Saw blades Saw bands, cutting fluid Wire Hot mounting resins

Mounting molds

Cold mounting resins

Small oven Clamp Vacuum impregnation apparatus Vacuum pump Engraver Plane grinder with grinding stone Grinder/Polisher/ sample mover

Cold mounting epoxy

Wire cutting Hot compression mounting Cold (castable) mounting Heating of epoxy Clamping (sheets) Impregnation

Engraving Grinding

Mechanical polishing

Surface preparation— electrolytic Thinning for TEM Cleaning

Belt grinder Grinder/polisher/sample mover Vibratory polisher

Dispensing of diamond suspension Electrolytic polishing

Dosing unit

Electrolytic polishing Ultrasonic cleaning

Jet-thinning apparatus Ultrasonic apparatus

Drying

Drying apparatus (hair dryer) Desiccator Special cupboard Plastic container, pair of tongs DC-power supply with pair of tongs

Conservation Etching

Accessory/ Consumable Cut-off wheels, additive for cooling fluid

Process Wet abrasive cutting Precision cutting

Chemical etching Electrolytic etching

Electropolisher

Resins with low viscosity Dye Engraving needless Grinding stones, additive for cooling fluid Disks (platens), rigid composite disks (RCD), wet grinding papers, diamond disks Grinding belts Disks (platens), polishing cloths, diamond consumables, lubricants, oxide consumable (Al2O3, SiO2) Diamond suspension Electrolytes Electrolyte containers Electrolytes Cleaning liquids Ethanol, cotton

Desiccants Protective media Etchants Etchants

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TABLE 25.1—(Continued.) Preparation Stage

Examination

Process Potentiostatic etching Thermal etching Vapor deposition Sputtering Ion etching Optical microscopy

Electron microscopy

Documentation

Microscopy

Indentation hardness testing

Vickers/Knoop microindentation hardness Brinell/Vickers hardness Rockwell hardness

Equipment Potentiostat Oven Vacuum chamber

Magnifying glass, Light microscope, small, medium, large Stereomicroscope Image analysis system SEM EPMA TEM STEM Macro camera Micro camera Polaroid camera Digital camera PC with monitor Video equipment Printer Cutter Refrigerator Microhardness tester

Universal hardness tester Rockwell hardness tester

Accessory/ Consumable

Objectives Eyepieces

Sample mounts

Sample mounts Films, paper

Indenters

Indenters Indenters

Sectioning: Cut-off machine, table top, hand operated, cut-off wheel diameter 200– 250 mm 共8 – 10 in兲. For an examination of sheet products, a hand shear should be available. A vertical band saw might be useful also. Mounting: Cold mounting materials with mounting cups or a hot mounting press, or both, if the investment is justified. In the case of sheet specimens, a clamp can be used for manual preparation. Plane grinding/Fine grinding/Polishing: Rotating grinder/polisher 共2 speeds兲, 200 or 250 mm 共8 or 10 in兲 disk diameter. This is sufficient for manual preparation, but to ensure highest reproducibility and avoid tedious work, a small specimen mover for three or six specimens should be mounted on the grinder/polisher. This also ensures a relatively high quality of the specimens, even with a relatively unskilled operator. A dosing unit, adding diamond suspension and lubricant in an optimal way, will also improve quality and economy. Microscope/Documentation: A small or medium-sized light microscope with bright field/dark field and differential interference contrast 共DIC兲 is recommended 共see

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Part III兲. For making images for reporting, a Polaroid 共4 in⫻ 5 in兲 or digital camera should be used, the latter in connection to a PC and a printer.

Medium-Sized Laboratory A medium-sized lab will prepare three to fifty specimens a day, mounted or unmounted 共see Table 25.1兲. The following equipment can be recommended: Sectioning: Cut-off machine, table top or floor model, automatic feed, cut-off wheel diameter 250– 350 mm 共10– 14 in兲. For large work pieces, larger automatic machines with a wheel diameter up to 600 mm 共24 in兲 are needed 共see Section 2.5兲. If precision cutting or cutting with lowest possible deformation of the cut surface is needed, a precision cutter should be available. A bandsaw can also be useful, and a hand shear can be used for sheet products. Mounting: One or two hot mounting presses and consumables for cold mounting. A vacuum impregnation apparatus and a small oven for accelerating the curing of epoxy cold mounting resins might be included. Plane grinding: With large specimens and a relatively high production with the specimens fixed in holders, a special plane grinding machine is recommended using a grinding stone. In most cases, however, the plane grinding can take place on the same machine as for fine grinding/polishing. Fine grinding/polishing: This is preferably done on a table model, semiautomatic system, consisting of a grinder/polisher with a 250 or 300 mm 共10 or 12 in兲 disk and specimen mover with specimen holders for fixed or single specimens, or both, which can prepare up to six to eight specimens at a time. To obtain the highest reproducibility a semiautomatic, programmable system with a dosing unit included is recommended. In case of a relatively high production of larger specimens, a floor-based, programmable grinder/polisher, using specimens fixed in a holder is recommended. To save manpower and increase the reproducibility, a fully automatic preparation system could be used. A fully automatic system might show a favorable cost/benefit 共see Section 25.2兲, especially for difficult to prepare materials. An electropolisher could be of advantage as a supplement to the mechanical preparation equipment, depending on the type of material to be prepared 共see Chapter 8兲. Etching: Chemical etching is typically used and needs only a very low investment 共see Table 25.1兲. If other contrasting methods should be used, like thermal etching or interference layers, special equipment must be procured 共see Table 25.1 and Chapter 9兲. Microscopy/Documentation: A good quality light microscope with good optics should be available. This shall have bright field/dark field, polarized light, differential interference contrast 共DIC兲, and fluorescence. For documentation one or more of the following cameras should be available: A normal, single lens reflex camera 共35 mm兲, a Polaroid camera 共4 in⫻ 5 in兲, or a digital camera. For all types, an automatic control unit should be connected to the microscope. For a digital camera, a PC with monitor should be available and a printer. For macro work, a stereomicroscope with camera connection should be available. A camera for macrophotography should be available also.

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Large-Sized Laboratory The large laboratory has from 10– 100/ 200 specimens per day, and the specimens produced are very often for quality control relating to a production. Therefore, the main concern is to have a fast, efficient flow of prepared specimens. The following equipment can be recommended: Sectioning: The conditions are the same as mentioned above under the MediumSized Laboratory. Mounting: The conditions here are also close to the medium-sized lab, only a larger number of mounting presses may be needed. Plane grinding: With a large number of specimens and using specimen holders with fixed specimens, plane grinding can be a bottleneck; therefore, a special plane grinding machine is recommended, using a grinding stone. In some cases, the plane grinding will be part of a fully automatic system 共see below兲. Fine Grinding/Polishing: With a large number of specimens, handling, manual cleaning, etc., should be avoided to save time. Therefore, fully automatic systems with a high number of preparation programs and built-in dosing and cleaning are recommended. These systems can be used for both “normal” specimen sizes and for large, unmounted specimens. The only manual handling is placing the specimens in a holder and removing the finished specimen ready for etching/microscopy from the holder. An alternative is one or more of the systems described above under Medium-Sized Labs. Electropolishing may be useful also, as mentioned above. Etching/Microscopy/Documentation: This is the same as mentioned under Medium-Sized Labs.

25.4.2 Layout—Furniture—Installations The layout of a metallographic/materialographic lab should include several rooms, making it possible to keep the different activities separated. The furniture should be appropriate and the installations specifically made to ensure an effective working procedure. The space between tables and machines should be so that several persons can work and move around in the lab without disturbing each other. During planning, space should also be reserved for extension considering a period of three to five years, often, a relatively new lab gets crammed after a few years.

Rooms A metallographic/materialographic lab should have at least three rooms, each connected with a door for easy passage from room to room. A lab for quality control purposes could have three rooms, and a research lab, covering a wide material field and many different processes might have four rooms. Room 1: This is the room for “dirty” processes, sectioning, and mounting. If cold mounting is performed in this room, a fume hood should be installed. Plane grinding also may be done in this room if a special machine is available for plane grinding. A sink should be installed in this room, and the idea is that a specimen, leaving the room, is clean and ready for the proper preparation in Room 2. Room 2: This is the main area of the lab, containing a preparation area and possibly an area for the personnel for working out preparation reports, etc. 共see below兲. Machines for preparation should be placed so that persons passing by do not disturb the operator. Table space around a machine should be 80– 100 cm 共3 – 4 ft兲 to ensure an

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efficient working order and make room for possible service work on the machine. At least one or two sinks should be placed very close to the grinder/polisher. It must be understood that cleaning is a very important part of the preparation process, and the operator should be able to clean the specimens when only moving a few steps. Another sink is placed under a fume hood to be used for chemical etching. The same hood, if large enough, can be used for electrolytic polishing, with the polishing table being placed under the hood. A small, low cost, upright or inverted microscope, placed near the preparation machines, is also useful to examine the specimens between the preparation steps. Other instruments like hardness testers are also placed in this room. Space should be available for desks with PCs for the personnel, preferably separated from the machine area, if these are not placed in connection with Room 3 together with the microscopes. Room 3: This is the microscope room with a large microscope and possibly a stereomicroscope and other examining instruments. The working places for the personnel can be placed in this room also, separated from the microscopes, preferably as a separate “office.” In the ideal microscope room, an air conditioning system keeps a constant temperature. Specimens can also be stored in this room in a desiccator 共one for each metallographer兲 or a special cupboard. Room 4: In certain cases, a fourth room may be recommended. This room will take over the “etching functions” of Room 2. The room will have one or two fume hoods for etching, electro polishing, and other processes that must be kept under strict control. Darkroom: For photographic work, one or two darkrooms will be necessary, but this won’t be necessary if only digital photography is used.

Furniture Laboratory furniture is available from many suppliers, but it should be taken into consideration that this furniture is made typically for chemical labs, not metallographic/ materialographic labs. The most important points to observe are the following: The metallographic/materialographic machine has a certain height, and the working area of the machine is often too high for convenient work if the table is a normal lab table. The surfaces of tables, etc., should be resistant to acids, alcohol, etc. Drawers for the grinding/polishing disks should be available, preferably placed under the tabletops very close to the machines. Shelves for consumables like cut-off wheels, grinding paper, etc., and storing space for other consumables, specimen holders, etc., should be close to the machines, and correctly made storage space for chemicals, glass articles, etc., should be close to fume hoods. Channels for taking pipes, tubes, and cables to the machines should be made in the tables. Other furniture is solid tables for microscopes, special cupboards for storing of specimens, cupboards for archiving, etc., shelves for a small library, and a refrigerator for storing of polaroid films, etc.

Installations The metallographic/materialographic lab should have the following installations: Hot/cold water at all sinks and compressed air preferably at all sinks and at all tables and places to be used for equipment. The compressed air should be clean, passing a water/oil separator and a particle filter. Adequate three-phase and one-phase electricity should be taken to all tables and places to be used for equipment, especially cutoff machines require a high amperage. Drainage should be installed in all tables and places to be used for equipment. The

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drainage should be made according to the regulations of the local authorities, taking into consideration that acid and other chemicals together with debris from the preparation process will flow in the drainage system. For installations regarding protection of personnel see Chapter 26.

25.5 Maintenance The most obvious reason for maintaining the laboratory in good working order is economy. A badly organized laboratory that cannot carry out its work properly and timely can cause unnecessary additional lab expenses and costs due to delayed production. Another important reason to focus on quality inspection and competitiveness is that the laboratory is a showcase for the company. Any manufacturing company that wants to attract customers and convince them of the quality of its goods needs a well equipped and presentable laboratory. A well run metallographic/materialographic laboratory with a good working atmosphere will reflect positively on the company’s image. The maintenance can be split into organizing, cleaning, and servicing.

25.5.1 Organizing Accessories and consumables for machines should be in easy reach of the operators. Special lab furniture or wall shelves help to keep grinding paper, cut-off wheels, polishing cloths, and disks out of the way but still accessible. In a metallographic/materialographic lab a large variety of small items are needed in everyday operation. Small tool or tackle boxes help to keep screws, tweezers, springs, rings, “dummy” samples in order. Wire racks over the sink are essential for storing wet glassware. It is always important to have enough consumables available to guarantee uninterrupted work. Large quantities of consumables should not be stocked in the laboratory, but in the main storeroom because they take up too much of the valuable space in the lab.

25.5.2 Cleaning Keeping the machines and work area clean is one of the most important matters in a metallographic/materialographic laboratory. Every machine should be wiped clean with a wet cloth before the staff leaves in the afternoon. This should also be done before shift change, so that the incoming operators start with clean machines. If this routine is not possible, a specific day or time should be set aside each week for cleaning the machines. Recirculation cooling units have to be cleaned and refilled at regular intervals, at least once a month depending on the workload. The spray nozzles of certain automatic diamond dispensing systems must be cleaned occasionally to avoid drying of the diamond suspensions inside the nozzles. As a rule, rigid composite disks 共RCDs兲 and polishing cloths should not be cleaned regularly. However, they can be cleaned with water/soap or ethanol, or both, if too much debris has built up on the surface and stops them from grinding/polishing properly, or if they are contaminated.

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25.5.3 Servicing Regular service checks ensure that the equipment is always in a correct working condition. This is crucial because correct maintenance is the basis of reliability, avoiding irritating stops, and reproducibility, and securing the correct preparation result, even over a long period of time.

26 Occupational Safety and Health in the Metallographic/ Materialographic Laboratory OCCUPATIONAL SAFETY AND HEALTH ARE IMPORTANT IN A METALLOgraphic/materialographic labs considering the use of machines, chemicals, plastics, etc. The dangers in the metallographic/materialographic laboratory will be discussed, and a special section will describe dangerous and hazardous materials. In Section 26.1.8 the ASTM Guide for Metallographic Laboratory Safety 共E 2014兲 will be shortly described, the only standard specifically covering the safety in the metallographic/ materialographic lab. The standard is stated in full in the CD-ROM included in this manual. At the end of this chapter, the most important rules and regulations for safety and health covering the metallographic/materialographic lab will be stated.

26.1 Dangers in the Metallographic/Materialographic Laboratory The laboratory having functions like cut-off, specimen preparation, and etching involves a number of potential dangers. In the following the most important precautions regarding safety and health are mentioned, not claiming that all potential dangers and necessary safety and health measures are mentioned.

26.1.1 Sectioning Eye protection and gloves should be used when working with machines and tools for sectioning. Abrasive cut-off machines will have a hood 共shield兲 protecting the operator against cooling fluid, pieces from a broken cutting wheel, etc. According to safety regulations, the machine can only be started when the hood is closed. When cutting with bakelite or rubber wheels, fumes develop, and at larger machines the cutting chamber should be connected to an exhaust system. For bandsaws, the operator will guide the work piece into the band, and it is very important that this is done indirectly using a distance piece or a special holder for the work piece. A Standard Operating Procedure 共SOP兲, including a Job Safety Analysis 共JSA兲共see Section 26.2.3/4兲 should be completed for each piece of equipment being used for sectioning.

26.1.2 Mounting With hot compression mounting, the main danger is the high temperatures used in the mounting presses. Gloves should be used for handling of the hot mounts, and when 664

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filling mounting material such as bakelite powder into the press, inhalation of dust should be avoided. A SOP, including a JSA, should be completed for each piece of equipment. At cold 共castable兲 mounting there are several potential dangers. The cold mounting resins are potentially dangerous to health 共see Section 26.1.7兲, and therefore all handling should be done with rubber 共latex兲 gloves to avoid skin contact and the mixing and hardening shall take place under a fume hood. When using an oven for accelerating the hardening of epoxy, gloves should be used. MSDS information should be available for all mounting resins 共see Section 26.2.2兲.

26.1.3 Mechanical Preparation The semiautomatic preparation machines are basically safe to use. If a specimen is slung away from the specimen holder during rotation, the specimen will usually be kept inside the machine, and the speeds of the disks and holders are relatively low. To avoid dirty hands, especially when using rigid composite disks that create a very fine sludge that is difficult to remove from the skin, rubber or plastic gloves should be used. For large machines using a flammable alcohol-based lubricant, the alcohol fumes can be rather strong, and the machine should be placed in connection to a fume exhaust system. A better solution might be to change the lubricant to a water-based type. When working with semiautomatic machines, a laboratory coat should be used to avoid that ties or other pieces of clothing get into contact with the rotating specimen holder. Fully automatic systems are totally enclosed and will not operate if the protective shields are not closed. At manual grinding/polishing, care should be taken that a specimen released by the operator and flying from the grinding/polishing disk will not injure other persons. A SOP, including a JSA, should be completed for all mechanical and polishing equipment.

26.1.4 Electrolytic Polishing/Etching The most serious potential danger at electrolytic polishing and etching is the mixing, handling, use, and storing of electrolytes 共see Section 26.1.5兲. During the polishing process, care should be taken to avoid heating of the electrolyte that may cause a fire or even an explosion. It is important to keep a correct level of electrolyte in the electrolyte container because too little electrolyte might give air pockets in the polishing chamber causing a spark between anode and cathode, which might ignite the alcohol in the electrolyte. A SOP, including a JSA, should be completed for each electropolisher.

26.1.5 Etching—Etchants—Electrolytes The etching procedure should be performed using gloves and eye protection under a fume hood. The most serious potential dangers are connected to the mixing, handling, and storing of the chemicals used for etchants, and the same is the case for electrolytes. The user should have sufficient information on all the chemicals used from training and MSDSs, which should be available in the laboratory 共see Section 26.2兲. Etchants/ electrolytes are mostly solution mixtures of different materials mixed in the laboratory. During the mixing, very dangerous reactions can be established like fire, explosion, and dissolution, creating dangerous substances. The etchants are generally more danger-

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ous than the electrolytes because they contain very oxidizing substances. As a rule, the mixing should always start with the water 共alcohol兲 and then mix the other ingredients into this. A special procedure, however, should often be followed to obtain the necessary safety, and certain combinations of chemicals are known to be dangerous. Information on this must be available in the laboratory. A number of the most hazardous materials are mentioned below, and further information can be obtained in the Standard Guide on Metallographic Laboratory Safety 共E 2014兲 in Section 26.1.8 of this book. Acetic Acid: Extreme care should be taken when mixing with other acids like perchloric acid and nitric acid. Mixtures of acetic acid and perchloric acid should be avoided. Chromic Acid: Very strong oxidation substance, very strong reaction with organic or easy to oxidize material and it cannot be safely mixed with acetic acid and most organic liquids, such as alcohols or glycerol. Poisonous. Nitric Acid: Strong oxidizing acid, creating gases with many organic materials and metals. Do not store solutions of more than 3 % nitric acid in ethanol. Perchloric Acid: Very aggressive acid that can cause serious explosions at higher concentrations. Very dangerous at contact with metals that oxidize easily, such as bismuth. Contact to organic material should also be avoided; if absorbed in organic material the material must be placed in water. Organic material should never be used to wipe up perchloric acid. Picric Acid: Aggressive oxidizer and should always be stored in wet condition. In dry condition the risk of explosion is high. Storage should be cool and fire safe.

Toxic Substances Toxic materials are substances that, when inhaled or taken in by the mouth or by the skin, can lead to death or serious damage to the health. These substances are listed by official organizations like the National Institute for Occupational Safety and Health 共NIOSH兲共see Section 26.5兲, and rules are defined for their use, storing, handling and disposal. Also, for many substances the permissible exposure through air and skin is stated 共see Section 26.5兲. A number of toxic substances with CAS Nos. 共see Section 26.5.1兲 often used in a metallographic/materialographic laboratory are mentioned below. Chemicals based on the metals Be, Pb, Cr, Cu, Ag, U, Sn, Zn 共not ZnO2兲: Poisonous as liquids or as vapor. Chlorinated Carbohydrates: These solvents are very dangerous to inhale. Cyanides 共CAS No. 460-19-5兲: These react strongly with acids, even the CO2 content in humid atmospheric air gives a reaction. Very poisonous. Hydrofluoric Acid, Anhydrous 共CAS No. 7647-01-0兲: In concentration higher than 0.5 % the acid is very dangerous, making very serious damage to tissue. Attacks almost all metals and glass. Very dangerous. Mercury 共CAS No. 7439-97-6兲: Chemicals bond on mercury and mercury vapor are poisonous. Methanol 共CAS No. 67-56-1兲: Poisonous. Oxalic Acid 共CAS No. 144-62-7 共Anhydrous兲兲共CAS No. 6153-56-6 共Dihydrate兲兲: In concentrations higher than 5 % oxalic acid is poisonous. Phosgen 共Carbonyl Chloride兲共CAS No. 75-44-5兲: Very dangerous to the respiratory system.

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Flammable Liquids Flammable liquids are used in metallographic/materialographic preparation for electrolytic polishing, lubrication, etching, and cleaning. OSHA 共see Section 26.5兲 defines flammable liquids. “Class I liquids” as any liquid having a flashpoint below 100° F 共37.8° C兲, except any mixture having components with flashpoints of 100° F 共37.8° C兲 or higher, the total of which make up 99 % or more of the total volume of the mixture. Liquids, which are somewhat harder to ignite, with a flash point above 100° F 共37.8° C兲 are called combustible liquids, “Class II liquids.” These are defined by OSHA as liquids with flashpoints at or above 100° F 共37.8° C兲 and below 140° F 共60° C兲, except any mixture having components with flashpoints of 200° F 共93.3° C兲 or higher, the volume of which make up 99 % or more of the total volume of the mixture. “Class III liquids” are even harder to ignite and are defined by OSHA as “liquids.” Class IIIA liquids include those with flashpoints 140° F 共60° C兲 or above and below 200° F 共93.3° C兲, except any mixture having components with flashpoints of 200° F 共93.3° C兲, or higher, the total volume of which make up 99 % or more of the total volume of the mixture. Class IIIB liquids include those with flashpoints at or above 200° F 共93.3° C兲. When a combustible liquid is heated for use to within 30° F 共16.7° C兲 of its flashpoint, it should be handled in accordance with the requirements for the next lower class of liquids. All containers with flammable liquids should be marked 共see Section 26.5.3兲. The number of flammable liquids stored in the lab should be kept at a minimum and carefully protected against heat and against possible ignition. All rules and regulations should be followed carefully when handling flammable liquids. Heating in open containers should be done with special care, using a fume hood and special electric heating plates. The flammable liquids are also very often dangerous to health and precautions should be taken according to the MSDS for the liquid 共see Section 26.2.2兲. Disposal can be a problem and should be done according to rules and regulations by local authorities.

26.1.6 Dust Dust can be developed from specimen material, abrasives, or powders used for mounting. This should be suppressed as much as possible, because even if not toxic, the dust can give respiratory problems. Dust from metals can be toxic and should be avoided.

26.1.7 Cold „Castable… Mounting Resins

All the cold 共castable兲 mounting resins described in Section 3.8 are potentially dangerous to health.

Epoxy This material, both resin and hardener, can damage the skin, causing allergic reactions. The material should never come in contact with skin and the vapors should not be inhaled. All work with epoxy should take place under a fume hood using personal protective equipment 共PPE兲 specified in the MSDS. It is recommended that containers and stirring pins are disposed of after mixing. The epoxy is not dangerous when it has fully hardened.

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Fig. 26.1—The NFPA diamond symbol: 1兲 Indication of color and type of hazard of the four small diamonds. 2兲 Example of number ratings and symbol.

Acrylics and Polyesters Mixing should always take place under a fume hood and gloves should be used when handling these materials to avoid inhalation and skin contact.

26.1.8 Standard Guide on Metallographic Laboratory Safety „E 2014… This ASTM guide covers the outline of the basic safety guidelines to be used in a metallographic/materialographic laboratory. Safe working habits are discussed for various tasks performed in the laboratory and the guide goes into more details of the work than stated above in this chapter. Please refer to ASTM E 2014 in the CD-ROM included with this book.

26.2 Safety Information It is very important that the user of a chemical substance is informed on all important facts regarding the substance. According to the OSHA Standard 29 CFR 1910.1200 共see Section 26.5.3兲, any chemical should be labeled for safe identification and a Material Safety Data Sheet 共MSDS兲 should be available on the working place for any chemical.

26.2.1 Identification It is important that the dangerous materials can be identified. Materials that are in one way or another hazardous should be marked with a label according to a system, as stated in the standards 共see Section 26.5兲. This label must express a number of facts regarding the substance so that the user is able to evaluate the possible hazard. The container with the substance is usually labeled by the supplier, but in cases where chemicals are taken into smaller containers in the lab and in other cases where the original container is not used, a new label must be used. Below two “official” identification systems, NFPA and EU 共EC兲, used by suppliers of chemicals and one system, HMIS, developed for use in the laboratory, are described.

NFPA 704 Hazard Identification Ratings System This identification system, developed by the National Fire Protection Association 共NFPA兲 uses the “Hazard Diamond” 共see Fig. 26.1兲 for identification of health, flamma-

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bility and instability 共reactivity兲共see also Section 26.5.11兲. The diamond is broken into four smaller diamonds one each blue, red, yellow, and white. The numbers in the three colored diamonds range from 0 共least severe hazard兲 to 4 共most severe hazard兲. The fourth 共white兲 diamond is left blank and is used only to devote special fire fighting measures/hazards, indicated with special symbols.

Meaning of Colors—Ratings of Numbers Red: FLAMMABILITY 共Instability兲 is the degree of susceptibility to burning. 0 1 2 3 4

Will not burn. Must be preheated to burn. Flash point above 200° F 共93.5° C兲. WARNING: Ignites with moderate heat. Flash point 100° F – 200° F 共38– 93.5° C兲. HAZARDOUS: Ignites at room temperature. Flash point 73° F – 99° F 共23– 37° C兲. EXTREMELY DANGEROUS: Highly flammable liquids and explosive gases. Flash point below 73° F 共23° C兲.

Yellow: REACTIVITY 共Instability兲 is the degree of susceptibility of materials to release energy. 0 1 2 3 4

Normally stable at all temperatures. Not reactive with water. CAUTION: May become unstable when heated or mixed with water. HAZARDOUS: Normally unstable or may have violent chemical change when mixed with water. DANGEROUS: Explodes with exposure to confined heat, shock, or when mixed with water. EXTREMELY DANGEROUS: Explodes at room temperature. Blue: HEALTH HAZARD is the degree of injury from burning materials.

0 1 2 3 4

Creates no unusual hazard. CAUTION: Causes irritation or minor injury. HAZARDOUS: Intense exposure may be harmful. EXTREMELY DANGEROUS: Avoid skin contact and inhalation. FATAL: Too dangerous to enter without specialized protective equipment. White: OTHER indicates special warnings.

ACID ALK COR OXY 䊏䊏 P — W

acid alkali corrosive oxidizing chemicals radiation subject to polymerization when mixed with water do not use water

EU „EC… Identification System

The European Union 共EU兲 has issued a directive, Council Directive 67/548/EEC of 27 June 1967, covering classification, packaging, and labeling of dangerous substances.

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According to this directive, all dangerous substances sold in the EU, the European Economic Area and selected other countries, should be marked with a labeling symbol and one or more Risk Phrases and Safety Phrases.

Labeling Symbols The symbols indicate the basic serious dangers, expressed in a figure, and a short text expressing the Category of Danger, Symbol Letter, and Indication of Danger 共see Fig. 26.2兲.

Risk Phrases—Safety Phrases To give further information to the user of the substance, one or more Risk Phrases 共R Phrases兲 and Safety Phrases 共S Phrases兲 should be indicated. The phrases are often combined 共see below兲. A high number of R and S phrases are available and a few examples are given below, indicating the number of the phrase. Examples of R Phrases: R1 R10 R20 R21 R20/21 R24 R25 R24/25

Explosive when dry Flammable Harmful by inhalation Harmful in contact with skin Harmful by inhalation and in contact with skin Toxic in contact with skin Toxic if swallowed Toxic in contact with skin and if swallowed

Examples of S Phrases: S1 S15 S20 S24 S25 S24/25 S36 S37

Keep locked up Keep away from heat Do not eat or drink when using Avoid contact with the skin Avoid contact with eyes Avoid contact with skin and eyes Wear suitable protective clothing Wear suitable gloves

HMIS: Hazardous Materials Identification System In case the user makes the labeling, this can be supported by systems developed for this purpose. HMIS® is a complete program that helps employers comply with OSHA’s Hazard Communication Standard 共HCS兲. The program uses a numerical hazard rating system, labels with colored bars giving information on health, flammability, and reactivity hazards. Training material is provided to inform workers of chemical hazards in the workplace 共see Section 26.5.12兲.

26.2.2 Material Safety Data Sheet „MSDS…

A Material Safety Data Sheet 共MSDS兲 is designed to provide both laboratory personnel and emergency personnel with the proper procedures for handling or working with a

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Fig. 26.2—EU labeling system. Symbols 共pictograms兲 with words and letters indicating categories of danger.

particular substance. MSDSs include information such as physical data, health effects, first aid, reactivity, storage, disposal, protective equipment, and spill/leak procedures. These are of particular use if a spill or other accidents occur. MSDSs are made according to the OSHA Standard on Hazard Communication 共HCS兲 or the EC Directive on Safety Data Sheets 共see Section 26.5兲. MSDSs are meant for:

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Employees who may be occupationally exposed to a hazards at work. Employers who need to know the proper methods for storage, etc. Emergency responders such as fire fighters, hazardous material crews, emergency medical technicians, and emergency room personnel. MSDSs are not meant for consumers. An MSDS reflects the hazards of working with the material in an occupational fashion. For example, an MSDS for a given paint is not highly pertinent to someone who uses a can of paint once a year, but is extremely important to someone who does this in a confined space for 40 hours a week.

The MSDS Format The formats of MSDSs tend to vary, but they usually convey the same basic kinds of information.

Supply of MSDS MSDSs should be kept at the workplace. They are usually delivered by the supplier of a given product. If it is not delivered, ask the supplier for immediate delivery. For commonly known substances, MSDSs can be obtained from an OSHA office or science library. Many organizations and chemical suppliers, like Cornell University and SigmaAldrich have databases with MSDS on the Internet.

26.2.3 Standard Operating Procedure „SOP…

Standard Operating Procedures 共SOPs兲 can be made for chemicals or processes and shall contain the operating procedure in relative detail so that an operator can perform the procedure in a satisfactory way without risk. Often at procedures involving hazardous materials or other potential risks a Job Safety Analysis 共JSA兲 is included in the SOP 共see below兲.

26.2.4 Job Safety Analysis „JSA…

The Job Safety Analysis 共JSA兲 is a very effective means of helping reduce accidents and injuries in the workplace. Any job that has hazards or potential hazards is a candidate for a JSA. Based on the operating procedure 共SOP兲, the potential hazards for each step in the working process are identified. It is very important to look at the entire environment to determine every hazard that might exist. Based on the steps in the working process and potential hazards, it is decided what actions are necessary to eliminate, control, or minimize hazards that could lead to accidents, injuries, damage to the environment, or possible occupational illness.

26.3 Disposal of Chemicals Disposal of chemicals should follow the local rules and regulations. These can vary very much from place to place and therefore it is very important to obtain the rules from the local authorities. As a common rule, the chemicals should be kept separated. Strongly oxidizing chemicals especially should not be mixed with other chemicals. The chemicals for disposal should be carefully categorized so that no mistake can take place when the waste is transported and treated further. Typical categories could be: 共1兲 Chlorinated hydrocarbons like trichloroethylene

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共2兲共3兲共4兲共5兲共6兲共7兲

Hydrocarbons containing aromatic solvents like xylene, terpentine, kerosene Hydrocarbons not containing aromatic solvents like acetone, ketones, alcohols Acidic, aqueous solutions containing chromium compounds Acidic, aqueous solutions containing nitric acid, but not hydrofluoric acid Acidic, aqueous solutions containing hydrofluoric acid or HF salts Acidic, aqueous solutions containing hydrochloric acid, sulfuric acid or phosphoric acid 共8兲 Basic aqueous solutions containing metal compounds but not cyanide 共9兲 Metal sludge containing chromium, copper, nickel, zinc, lead, cadmium and silver

26.4 Occupational Safety in General 26.4.1 Standards In the sections above, the hazards of chemicals and machines have been discussed. As a rule, the machines and apparatus are designed and manufactured according to relevant standards. These are the “technical” standards, “safety” standards, and “occupational” standards. The “occupational” standards, describing the conditions, when working in the laboratory concerning machines and chemicals, can be the OSHA standards No. 29 CFR 1910.212, General Requirements for All Machines, No. 29 CFR 1910.215, Abrasive Wheel Machinery, No. 29 CFR 1910.95, Occupational Noise Exposure, No. 29 CFR 1910.120, General Description and Discussion of the Levels of Protection and Protective Gear, and the important Hazard Communication standard, No. 29 CFR 1910.1200 共see Section 26.5兲.

26.4.2 Training It is very important that the personnel be trained, both in using the machines and other equipment, and in health and safety precautions. Not only the training in the practical use, but an education in the correct attitudes is also important.

26.4.3 Maintenance and Service It is important that all equipment, building parts, and installations are kept in good working order and repair is made immediately in case of failure. Unauthorized personnel should not perform repair work.

26.5 Standards and Regulations—Organizations A number of American and International organizations are responsible for issuing standards and regulations connected to occupational safety and health in the metallographic/materialographic laboratory. The first section below states a number of abbreviations used in connection with safety and health.

26.5.1 Designations and Abbreviations Used to Describe a Chemical Substance Ca: A substance NIOSH 共see below兲 considers a potential occupational carcinogen CAS Number: Chemical Abstract Service Registry Number. This number identifies each chemical. The Chemical Abstracts Service is a division of the American Chemical Society

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IDLH: Immediately Dangerous to Life or Health Concentrations PEL: Permissible Exposure Limit PPE: Personal Protective Equipment REL: Recommended Exposure Limit RTECS: Registry of Toxic Effects of Chemical Substances 共see Section 26.5.4兲 STEL: Short-Term Exposure Limit as designated by “ST” preceding the value TLV: Threshold Limit Value, issued by ACGIH 共see Section 26.5.8兲 TWA: Time-Weighted Average 共used in REL兲 UN Number: Four digit number to identify hazardous chemicals 共transport兲.

26.5.2 ASTM Standard The only standard that directly describes the safety in the metallographic/materialographic laboratory is issued by ASTM. Standard Guide on Metallographic Laboratory Safety 共E 2014兲 covers the outline of the basic safety guidelines to be used in a metallographic/materialographic laboratory. This standard is stated with its full text in the CD-ROM included with this book 共see Section 26.1.8兲. All other standards 共see below兲 are directed towards the problems in general and specific matters inside and outside the metallographic/materialographic lab. E 2014, being specific regarding metallographic/materialographic labs, makes it an important document that should be followed by all metallographic/materialographic laboratories.

26.5.3 OSHA—OSHA Standards In 1970, the Occupational Safety and Health Act was passed by the U.S. Congress, establishing NIOSH 共see below兲 and OSHA. Occupational Safety and Health Administration 共OSHA兲 in the U.S. Department of Labor has issued a number of regulations 共standards兲 covering occupational safety and health in laboratories in general, these also covering the metallographic/materialographic laboratory. In the following, the most important standards are described in short form, with the important Hazard Communication Standard in relative detail.

Standard Title: Hazard Communication Standard Standard Number: 29 CFR 1910.1200 The Hazard Communication Standard 共HCS兲, sometimes called the Right to Know law or HazCom, is a set of regulations first promulgated in 1988 by the Office of Occupational Safety and Health Administration 共OSHA兲. HCS’s purpose is to ensure that the hazards of workplace chemicals are evaluated, and that information on the hazards is provided to employers and employees. Details of the standard are provided in parts 1910.1200 of the Code of Federal Regulations 共CFR兲 of Chapter XVII of Title 29 under the Department of Labor. HCS covers nearly all employers and is applicable to most work operations where hazardous materials are present.

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Contents: In short, the standard requires that every affected employer must establish a program to inform the employees of the hazards associated with the materials in their workplace. The program must have five main components as follows: • Written Hazard Communication Program documentation • Identifying and keeping an inventory of hazardous chemicals • Obtaining and keeping material safety data sheets 共MSDS兲 on the identified hazards • Ensuring that the hazardous materials are labeled with name and hazard • Training employees on the standard, safety information, labeling, and protective measures

Hazardous Chemicals/Materials The HCS covers chemicals in all physical forms—liquids, solids, gases, vapors, fumes, and mists—whether they are “contained” or not. The hazardous nature of the chemical and potential for exposure are the factors that determine whether a chemical is covered. If it is hazardous and there is potential for exposure, the rule applies.

Written Program Under the standard each laboratory 共employer兲 must complete and keep a written Hazard Communication Program. The written program describes how the requirements for labels and other forms of warning, material safety data sheets 共MSDSs兲, and employee information and training are implemented in the workplace. It indicates who is responsible for MSDSs, labels, warning signs, and training, as well as the location of the inventory. MSDSs and other information and resources pertaining to hazardous chemicals and safety measures. An inventory list of hazardous chemicals is required to be maintained as part of the written program.

Chemical Inventory The person working in the laboratory needs to know about the hazards to be able to protect oneself. The leader of the laboratory is responsible for establishing an inventory of hazardous chemicals. All potentially hazardous chemicals in containers should be registered and chemicals possibly generated in work operations should be included, including vapor, fumes, dust, etc. In the inventory, information based on the labels and the MSDSs made available by the supplier of the chemical is stated.

MSDS The role of the MSDS is to provide detailed information on each hazardous chemical, including its potential hazardous effects, its physical and chemical characteristics, and recommendations for appropriate protective measures. This information is useful for designing protective programs, as well as informing the chemical user of the hazards. MSDSs must be readily accessible to users when they are in their work areas. Some laboratories keep the MSDSs in a binder in the individual work area or in a central location in the department. An MSDS should be available for each hazardous chemical used in the lab. The MSDS must be in English. The MSDS should be delivered by the supplier, and it should include all of the information required under the rule. If an MSDS is not supplied auto-

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matically it should be requested for. If an MSDS is obviously inadequate an appropriately complete one should be requested. Employees should not use or be exposed to any chemicals for which the safety data have not been reviewed and appropriate safety measures implemented.

Labels Containers of hazardous chemicals must be labeled, tagged, or marked with the identity of the material and appropriate hazard warnings. The original label must include the identity of the material, appropriate hazard warnings, and the manufacturer name and address. The identity used by the supplier may be a common or trade name, or a chemical name. The hazard warning is a brief statement of the hazardous effects of the chemical 共“flammable,” “causes lung damage”兲. Labels frequently contain other information, such as precautionary measures 共“do not use near open flame”兲. Labels must be legible and prominent.

Secondary Containers Label and Signs If materials are transferred from the original container into other containers, these must be labeled as well. Depending on the employers written plan, the secondary labels may be warning symbols, text, or use a numerical hazard rating system, such as HMIS and NFPA 共see Section 26.2兲. Large containers or storage units containing hazardous chemicals or mixtures must also be labeled or have warning signs. It is strongly recommended that other warning or caution signs be placed in the work areas to remind individuals of the hazards and of the protective equipment that may be necessary in the area.

Employee Information and Training An employee working with hazardous chemicals must receive both information and training on the hazard communication. Information and training may be done either by individual chemical, or by categories of hazards 共such as flammability or carcinogenicity兲. If there are only a few chemicals in the laboratory, each chemical may be discussed individually. Where there are large numbers of chemicals, or the chemicals change frequently, training may be based on the hazard categories 共e.g., flammable liquids, corrosive materials, carcinogens兲. Employees must have access to the substance-specific information on the labels and MSDSs. The underlying purpose of the HCS is to reduce the incidence of chemical source illnesses and injuries. In general, the most important aspects of training are to ensure employees are aware that they are exposed to hazardous chemicals, that they know how to read and use labels and material safety data sheets, and that, as a consequence of learning this information, they are following the appropriate protective measures 共e.g., personal protective equipment, safe procedures, engineering controls兲.

Frequently Asked Questions on HCS „HAZCOM… HCS being an important standard, the answers to a number of questions can be of interest.

What are the containers labeling requirements under HCS? Under HCS, the manufacturer, importer, or distributor is required to label each container of hazardous chemicals. If the hazardous chemicals are transferred into un-

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marked containers, these containers must be labeled with the required information, unless the container into which the chemical is transferred is intended for the immediate use of the employee who performed the transfer.

Can MSDSs be stored in a computer to meet the accessibility requirements of HCS? If the employee’s work area includes the area where the MSDSs can be obtained, then maintaining MSDSs on a computer would be in compliance. If the MSDSs can only be accessed out of the employee’s work area共s兲, then the employer would not be in compliance with HCS.

When is the supplier required to distribute MSDSs? Hazard information must be transmitted on Material Safety Data Sheets 共MSDSs兲 that must be distributed to the customer at the time of first shipment of the product. The Hazard Communication Standard also requires that MSDSs be updated by the chemical manufacturer or importer within three months of learning of “new or significant information,” regarding the chemical’s hazard potential.

What is considered proper training under HCS? Employees are to be trained at the time they are assigned to work with a hazardous chemical. The intent of this provision is to have information prior to exposure to prevent the occurrence of adverse health effects. This purpose cannot be met if training is delayed until a later date. The training provisions of the HCS are not satisfied solely by giving the employee the data sheets to read. An employer’s training program is to be a forum for explaining to employees not only the hazards of the chemicals in their work area, but also how to use the information generated in the hazard communication program. This can be accomplished in many ways 共audiovisuals, classroom instruction, interactive video兲, and should include an opportunity for employees to ask questions to ensure that they understand the information presented to them. Training need not be conducted on each specific chemical found in the workplace, but may be conducted by categories of hazard 共e.g., carcinogens, acutely toxic agents兲 that are or may be encountered by an employee during the course of his duties. Furthermore, the training must be comprehensible. If the employees receive job instructions in a language other than English, then the training and information to be conveyed under the HCS will also need to be conducted in a foreign language.

What are the requirements for refresher training or retraining a new hire? Additional training is to be done whenever a new physical or health hazard is introduced into the work area, not a new chemical. For example, if a new solvent is brought into the workplace, and it has hazards similar to existing chemicals for which training has already been conducted, then no new training is required. As with initial training, and in keeping with the intent of the standard, the employer must make employees specifically aware which hazard category 共i.e., corrosive, irritant, etc.兲 the solvent falls within. The substance-specific data sheet must still be available, and the product must be properly labeled. If the newly introduced solvent is a suspect carcinogen, and there has never been a carcinogenic hazard in the workplace before, then new training for

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carcinogenic hazards must be conducted for employees in those work areas where employees will be exposed. It is not necessary for the employer to retrain each new hire if that employee has received prior training by a past employer, an employee union, or any other entity. General information, such as the rudiments of the HCS could be expected to remain with an employee from one position to another. The employer, however, maintains the responsibility to ensure that their employees are adequately trained and are equipped with the knowledge and information necessary to conduct their jobs safely. It is likely that additional training will be needed since employees must know the specifics of their new employer’s programs such as where the MSDSs are located, details of the employer’s in-plant labeling system, and the hazards of new chemicals to which they will be exposed.

Do you need to keep MSDSs for commercial products such as Windex® and “White-out®”? OSHA does not require that MSDSs be provided to purchasers of household consumer products when the products are used in the workplace in the same manner that a consumer would use them, i.e., where the duration and frequency of use 共and therefore exposure兲 is not greater than what the typical consumer would experience. This exemption in OSHA’s regulation is based, not on the chemical manufacturer’s intended use of his product, however, but on how it actually is used in the workplace. Employees who are required to work with hazardous chemicals in a manner that results in a duration and frequency of exposure greater than what a normal consumer would experience have a right to know about the properties of those hazardous chemicals.

What are the requirements and limits to use generic MSDSs? The requirements for MSDSs are found in paragraph 共g兲 of the standard. MSDSs must be developed for hazardous chemicals used in the workplace, and must list the hazardous chemicals that are found in a product in quantities of 1 % or greater, or 0.1 % or greater if the chemical is a carcinogen. The MSDS does not have to list the amount that the hazardous chemical occurs in the product. Therefore, a single MSDS can be developed for the various combinations of chemicals, as long as the hazards of the various mixtures are the same. This “generic” MSDS must meet all of the minimum requirements found in HCS, including the name, address, and telephone number of the responsible party preparing or distributing the MSDS who can provide additional information.

What is the application of HCS to an office environment? Office workers who encounter hazardous chemicals only in isolated instances are not covered by the rule. OSHA considers most office products 共such as pens, pencils, adhesive tape兲 to be exempt under the provisions of the rule, either as articles or as consumer products. OSHA has previously stated that intermittent or occasional use of a copying machine does not result in coverage under the rule. However, if an employee handles the chemicals to service the machine, or operates it for long periods of time, then the program would have to be applied.

Is an MSDS required for a nonhazardous chemical? MSDSs that represent nonhazardous chemicals are not covered by the HCS. Paragraph 29 CFR 1910.1200 共g兲共8兲 of the standard requires that “the employer shall main-

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tain in the workplace copies of the required MSDSs for each hazardous chemical, and shall ensure that they are readily accessible during each work shift to employees when they are in their work area共s兲.” OSHA does not require nor encourage employers to maintain MSDSs for nonhazardous chemicals. Consequently, an employer is free to discard MSDSs for nonhazardous chemicals.

Standard Title: Occupational Exposure to Hazardous Chemicals in Laboratories Standard Number: 29 CFR 1910.1450

Scope and Application The standard covers all laboratories engaged in the laboratory use of chemicals defined as hazardous by this standard, generally, superseding provisions of all other health standards except in specific instances. The obligation to maintain employee exposures at or below the permissible exposure limits 共PELs兲 specified in the air contaminants standard and in substance specific standards is retained. It does not apply to users of hazardous chemicals, which do not meet the definition of laboratory use, and in such cases, the employer must comply with the relevant standard even though use occurs in a laboratory. The standard does not apply for laboratory use of hazardous chemicals that provide no potential for employee exposure such as procedures using chemically impregnated test media and commercially prepared test kits.

Employee Exposure Determination The employer must measure the employee’s exposure periodically to any substance regulated by a standard which requires monitoring if there is reason to believe that exposure levels for that substance routinely exceed the action level 共or in the absence of an action level, the PEL兲. The employer must notify the employee of the results within 15 working days after receipt of the monitoring results.

Chemical Hygiene Plan Where hazardous chemicals are used a laboratory covered by this standard the employer must develop and carry out the provisions of a written Chemical Hygiene Plan 共CHP兲. The CHP must include the necessary work practices, procedures, and policies to ensure that employees are protected from all potentially hazardous chemicals in use in their work area. The plan must be available to employees, to employee representatives, and to the Assistant Secretary for Occupational Safety and Health.

Employee Training and Information The employer must provide employees with information and training to ensure that they are aware of the hazards of the chemicals present in their work area. This information must be provided at the time of an employee’s initial assignment to a work area where hazardous chemicals are present and prior to assignments involving new exposure situations. Employees must be informed of: • The contents of this standard and its appendices must be made available to them • The location and availability of the employer’s Chemical Hygiene Plan • The permissible exposure limits for OSHA

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Signs and symptoms associated with exposures to hazardous chemicals used in the laboratory The location and availability of known reference material on the hazards, safe handling, storage, and disposal of hazardous chemicals found in the laboratory including, but not limited to Material Safety Data Sheets 共MSDS兲 received from chemical suppliers

Medical Consultation and Examinations All employees who work with hazardous chemicals must be given the opportunity to receive medical attention, including any follow-up examinations, which the examining licensed physician determines to be necessary under certain circumstances. Medical examinations and consultants must be provided without cost to the employee, without loss of pay, and at a reasonable time and place. The employer must provide certain information to the physician, including the identity of the hazardous chemicals, a description of the conditions under which the exposure occurred, and a description of the signs and symptoms of exposure that the employee is experiencing.

Hazard Identification Labels on incoming containers of hazardous chemicals must not be removed or defaced. MSDSs on incoming hazardous chemicals must be retained and made available to lab employees.

Respirator Use Where the use of respirators is necessary to maintain exposure below permissible exposure limits, the employer must provide, at no cost to the employee, the proper respirator equipment.

Record Keeping The employer must establish and maintain for each employee an accurate record of any measurements taken to monitor employee exposure and any medical consultation and examination including tests or written opinions.

Standard Title: List of Highly Hazardous Chemicals, Toxics and Reactives Standard Number: 29 CFR 1910.119 App A The standard contains a listing of toxic and reactive highly hazardous chemicals that present a potential for a catastrophic event at or above the treshold of quantity. Chemical name, CAS number 共Chemical Abstract Service Number兲 and Treshold Quantity in Pounds are stated in the list.

Standard Title: Flammable and Combustible Liquids Standard Number: 29 CFR 1910.106. The standard defines “flammable” and “conbustible” 共see Section 26.1.5兲 and states the rules and regulations regarding safety and health, using flammable liquids in general.

Standard Title: General Description and Discussion of the Levels of Protection and Protective Gear Standard Number: 29 CFR 1910.120 App B

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Scope and Application The standard gives information about personal protective equipment 共PPE兲 protection levels, which may be used to assist employers in complying with the PPE requirements. As required by the standard, PPE must be selected, which will protect employees from the specific hazards, which they are likely to encounter during their work on-site. Selection of the appropriate PPE is a complex process, which should take into consideration a variety of factors. Key factors involved in this process are identification of the hazards, or suspected hazards; their routes of potential hazard to employees 共inhalation, skin absorption, ingestion, and eye or skin contact兲; and the performance of the PPE materials 共and seams兲 in providing a barrier to these hazards. The amount of protection provided by PPE will protect well against some hazardous substances and poorly, or not at all, against others.

Standard Title: Availability of NIOSH Registry of Toxic Effects of Chemical Substances „RTECS… „non-mandatory…. Standard Number: 29 CFR 1910.1020 App. B The standard applies to all employee exposure and medical records, and analyses thereof, of employees exposed to toxic substances or harmful physical agents 共paragraph 共b兲共2兲. The term “toxic substance or harmful physical agent” is defined by paragraph 共c兲共13兲 to encompass chemical substances, biological agents, and physical stresses for which there is evidence of harmful health effects. The regulation uses the latest printed edition of the National Institute for Occupational Safety and Health 共NIOSH兲共see below兲, Registry of Toxic Effects of Chemical Substances 共RTECS兲 as one of the chief sources of information as to whether evidence of harmful health effects exists. If a substance is listed in the latest printed RTECS, the regulation applies to exposure and medical records 共and analyses of these records兲 relevant to employees exposed to the substance. It is appropriate to note that the final regulation does not require that employers purchase a copy of RTECS, and many employers need not consult RTECS to ascertain whether their employee exposure or medical records are subject to the rule. Employers who do not currently have the latest printed edition of the NIOSH RTECS, however, may desire to obtain a copy. The RTECS is issued in an annual printed edition as mandated by section 20 共a兲共6兲 of the Occupational Safety and Health Act 共29 U.S.C. 669 共a兲共6兲兲.

26.5.4 National Institute for Occupational Safety and Health „NIOSH…

National Institute for Occupational Safety and Health 共NIOSH兲 is, like OSHA established according to the Occupational Safety and Health Act of 1970. They are, however, two distinct agencies with separate responsibilities, NIOSH is in the U.S. Department of Health and Human Services. NIOSH is the Federal agency responsible for conducting research and making recommendations for the prevention of work-related disease and injury. NIOSH works with the Health Hazard Evaluation Program, investigating potentially hazardous working conditions and with the NIOSH Publications Office supplying information on hazardous materials. NIOSH has a number of other activities.

NIOSH Pocket Guide NIOSH Pocket Guide to Chemical Hazards is a useful book that can be obtained from NIOSH. It includes the following:

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Chemical Names, synonyms, trade names, conversion factors, CAS, RTECS, and DOT Numbers NIOSH Recommended Exposure Limits 共NIOSH, RELS兲 Permissible Exposure Limits 共PELs兲 NIOSH Immediate Dangerous to Life and Health values 共NIOSH IDLHs兲. A physical description of the agent with chemical and physical properties Measurement methods Personal Protection and Sanitation Recommendations Respirator Recommendations Information on Health Hazards including route, symptoms, first aid, and target organ information.

RTECS® Database The Registry of Toxic Effects of Chemical Substances 共RTECS®兲 is a database of toxicological information compiled, maintained, and updated by the NIOSH. RTECS® contains over 133 000 chemicals as NIOSH strives to fulfill the mandate to list “all known toxic substances … and the concentrations at which … toxicity is known to occur.” RTECS® is a compendium of data extracted from the open scientific literature. The data are recorded in the format developed by the RTECS® staff and arranged in alphabetical order by prime chemical name. No attempt has been made to evaluate the studies cited in RTECS®. The user has the responsibility of making such assessments.

26.5.5 International Chemical Safety Cards „ICSCS… The International Chemical Safety Cards are worked out by an international group of experts under The International Programme on Chemical Safety under the World Health Organization 共WHO兲. The ICSCs are based on standard phrases, the criteria for which are given in the Compiler’s Guide. A certain number of Cards are available in 22 languages and their translation into a further eight languages is on-going. The first edition of the Compiler’s Guide and ten series, representing over 900 Cards, have been published as hard copies in English, Spanish, Japanese, Chinese, and Polish, and about 1300 Cards are available in electronic form. Cards in English are available on the ILO Web site: www.ilo.org/public/english/protection/safework/cis/ products/icsc An ICSC summarizes essential health and safety information on chemicals for their use at the “shop floor” level by workers and employees in factories, agriculture, construction, and other work places. ICSCs are not legally binding documents, but consist of a series of standard phrases, mainly summarizing health and safety information collected, verified, and peer reviewed by internationally recognized experts, taking into account advice from manufacturers and Poison Control Centers. The identification of the chemicals on the Cards is based on the UN numbers, the Chemical Abstracts Service 共CAS兲 number, and the Registry of Toxic Effects of Chemical Substances 共RTECS/NIOSH兲 numbers. It is thought that the use of those three systems assures the most unambiguous method of identifying the chemical substances concerned, referring as it does to numbering systems that consider transportation matters, chemistry, and occupational health.

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ICSCs and Material Safety Data Sheets Great similarities exist between the various headings of the ICSC and the manufacturers’ Safety Data Sheet 共SDS兲 or Material Safety Data Sheet 共MSDS兲 of the International Council of Chemical Associations. However, MSDSs and the ICSCs are not the same. The MSDS, in many instances, may be very complex technically and too expensive for shop floor use, and secondly it is a management document. The ICSCs, on the other hand, set out peer-reviewed information about substances in a more concise and simple manner. Although not a legal document, the ICSC is an authoritative document emanating from WHO/ILO/UNEP. This is not to say that the ICSC should be a substitute for an MSDS, nothing can replace management’s responsibility to communicate with workers on the exact chemicals, the nature of those chemicals used on the shop floor and the risk posed in any given work place. Indeed, the ICSC and the MSDS can even be thought of as complementary. If the two methods for hazard communication can be combined, then the amount of knowledge available to the safety representative or shop floor workers will be more than doubled.

26.5.6 Environmental Protection Agency „EPA… The U.S. Environmental Protection Agency is to protect human health and to safeguard the natural environment—air, water, and land—which life depends on. EPA administrates important laws like Occupational Safety and Health Act and Toxic Substances Control Act, both important in relation to metallographic/materialographic laboratories.

26.5.7 National Technical Information Service „NTIS…

The National Technical Information Service 共NTIS兲 is the largest, central resource for government-funded scientific, technical, engineering, and business information available in United States. Toxic Substances Control Act 共TSCA兲 Chemical Substances Inventory—Revised Inventory Synonym and Preferred Name File: This inventory list covers more than 65 000 chemicals as defined under TSCA.

26.5.8 American Conference of Government Industrial Hygienists „ACGIH…

The American Conference of Governmental Industrial Hygienists, Inc. 共ACGIH兲, is an organization open to all practitioners in industrial hygiene, occupational health, environmental health, or safety. ACGIH publishes over 400 titles in occupational and environmental health and safety. They are best known for their Treshold Limit Values publication that lists the TLVs for over 700 chemical substances and physical agents, as well as 50 Biological Exposure Indices for selected chemicals.

26.5.9 National Toxicology Program „NTP… The National Toxicology Program is an organization under U.S. Department of Health and Human Services 共DHHS兲 to coordinate toxicological testing programs. NTP has collected health and safety data on over 2000 chemicals.

26.5.10 Agency for Toxic Substance and Disease Registry „ATSDR…

The Agency for Toxic Substances and Disease Registry 共ATSDR兲 is an agency under U.S. Department of Health and Human Services.

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The mission is to prevent exposure and advise human health effects associated with exposure to hazardous substances. ATSDR TOX FAQs is a series of summaries about hazardous substances. Each fact sheet serves as a quick and easy to understand guide, 共www.atsdr.cdc.gov/toxfaq.html兲.

26.5.11 National Fire Protection Association „NFPA…

The National Fire Protection Association 共NFPA兲 is a nonprofit organization that is responsible for over 300 codes covering basic fire safety, electricity, and other topics. The NFPA 704 Hazard Identification Ratings System is described in Section 26.2.

26.5.12 National Paint and Coatings Association „NPCA…—HMIS

The National Paint and Coatings Association 共NPCA兲 has established a complete program, HMIS, 共Hazardous Materials Identification System兲 that helps employers comply with OSHA’s Hazard Communication Standard 共HCS兲共see Section 26.2兲.

26.5.13 BSI—ISO British Standards Institution is the independent national body responsible for preparing British Standards. BSI cooperates with ISO 共International Standard Organization兲 and EU 共European Union兲. The British Standard BS 7750 on Environmental Management has been used as the basis for the standard, BS EN ISO 14001: 1996, Environmental Management Systems. This standard covers all sides of environmental management and connects to the quality standard BS EN ISO 9000: 2000. The standard BS 8800: 1996, Guide to Occupational Health and Safety Management Systems, puts emphasis on OHS management. Two standards are established based on this standard: OHSAS 18001: 1999, Occupational Health and Safety Management Systems Specifications. OHSAS 18002: 2000, Occupational Health and Safety Management Systems. Guidelines for the implementation of OHSAS 18001. An important factor in OHSAS 18001: 1999 is “Risk Assessment” defined as “The overall process of estimating the magnitude of risk and deciding whether or not the risk is tolerable or acceptable.” Risk assessment involves three basic steps: 共1兲 identify hazards; 共2兲 estimate the risk from each hazard—the likelihood and severity of harm; 共3兲 decide if the risk is tolerable.

26.5.14 EU The European Union 共EU兲共European Community 共EC兲兲 has established a number of directives, covering occupational safety. The directive 67/548/EEC on dangerous substances is described further in Section 26.2.

26.6 Literature on Laboratory Safety Literature can be seen in References of the Standard Guide on Metallographic Laboratory Safety 共E 2014兲 in the CD-ROM included with this manual 共see Section 26.1.8兲. In addition the books by Petzow and Vander Voort 共Refs 2 and 9, Part I兲 can be recommended.

27 Literature 27.1 Books THE BOOKS LISTED BELOW COVER THE FIELD OF METALLOGRAPHIC/ materialographic preparation and examination. They are intended as a supplement to this book and should not be considered as a complete list of books on these subjects. Amelinckx, S., Van Dyck, D., Van Landuyt, J., and Van Tendeloo, G., Handbook of Microscopy: Applications in Materials Science, Solid-State Physics, and Chemistry. Wiley-VCH, New York, N.Y., USA, 1997. Beraha, E. and Shipgler, B., Color Metallography, ASM Materials Park, Ohio, USA, 1977. Bjerregaard, L., Geels, K., Ottesen, B., and Rückert, M., Metalog Guide, Struers A/S, Copenhagen, Denmark, 2000. Bousfield, B., Surface Preparation and Microscopy of Materials, John Wiley & Sons, Chichester, UK, 1992. Bramfitt, B. L. and Benscoter, A. O., Metallographer’s Guide—Practices and Procedures for Iron and Steels, ASM International, Metals Park, Ohio, USA, 2001. Burgess, D. and Blanchard, R. A., Wafer Failure Analysis for Yield Enhancement, Accelerated Analysis, Half Moon Bay, California, USA, 2001. Bühler, H. E. and Hougardy, H. P., Atlas of Interference Layer Metallography, Deutsche Gesellschaft für Metallkunde, Oberursel, Germany, 1980. Durand-Charre, M., Microstructure of Steels and Cast Irons, Springer-Verlag New York, Inc., New York, NY, USA, 2004. Durand-Charre, M. and Durand-Charre, M., Microstructure of Superalloys, Taylor & Francis, Inc., Philadelphia, PA, USA, 1998. Elssner, G., Hoven, H., Kiessler, G., and Wellner, P., Ceramics and Ceramic Composites: Materialographic Preparation, Elsevier Science, Inc., New York, NY, USA, 1999. Freund, J. E., Statistics: a First Course, 2nd ed., Prentice Hall, Englewood Cliffs, New Jersey, USA, 1970. Friel, J. J., et al., Practical Guide to Image Analysis, ASM International, Materials Park, Ohio, USA, 2000. Handbook of Thermal Spray Technology, ASM International, Materials Park, Ohio, USA, 2004. Higginson, R. L. and Sellars, C. M., Worked Examples in Quantitative Metallography, Maney Publishing, Cambridge MA, USA, 2003. Inoue, S. and Spring, K. R., Video Microscopy, Plenum Press, New York, NY, USA, 1997. Kapitza, H. G., Microscopy from the Very Beginning, Carl Zeiss, Jena, Germany, 1994. Metals Handbook, Metallography and Microstructures, Vol. 9, ASM International, Materials Park, Ohio, USA, 2004. Petzow, G., Metallographic Etching, ASM International, Materials Park, Ohio, USA, 1999. Ross, Boit, and Staab, 共edit.兲, Microelectronics Failure Analysis, ASM International, Materials Park, Ohio, USA, 1999. Rostoker, W. and Dvorak, J. R., Interpretation of Metallographic Structures, Elsevier Science, Inc., New York, NY, USA, 1990. Russ, J. C., The Image Processing Handbook, 3rd ed., CRC Press, Boca Raton, FL, USA, 1998. Samuels, L. E., Metallographic Polishing by Mechanical Methods, ASM International, Materials Park, Ohio, USA, 2003. Schumann, H. and Oettel, H., Metallografie, Wiley-VCH Verlag, Weinheim, Germany, 2004 共In German兲. Tegart, Mc.G., The Electrolytic and Chemical Polishing of Metals in Research and Industry, Pergamon Press, London, UK, 1959. Tomer, A., Structure of Metals through Optical Microscopy, ASM International, Materials Park, Ohio, USA, 1990. Underwood, E. E., Quantitative Stereology, Addison-Wesley Publishing Company, Reading, MA, USA, 1970.

685

686


Vander Voort, G. V., Metallography Principles and Practice, ASM International, Materials Park, Ohio, USA, 1999. Waschull, H., Präparative Metallographie, Wiley-VCH Verlag, Weinheim, Germany, 1993 共In German兲. Weck, E. and Leistner, E., Metallographic Instructions for Colour Etching by Immersion, Part I 共1982兲, II 共1983兲, III 共1986兲, Deutscher Verlag für Schweisstechnik GmbH, Düsseldorf, Germany.

27.2 Periodicals THE PERIODICALS STATED IN THIS LIST COVER THE FIELD OF METALLOgraphic/materialographic preparation and interpretation, but it should not be considered a complete list of all periodicals covering these subjects. Advanced Functional Materials, English/18 issues yearly, Wiley-VCH, P.O. Box 191161, D-69451, Weinheim, Germany. Advanced Materials, English/24 issues yearly, Wiley-VCH, P.O. Box 191161, D-69451, Weinheim, Germany. Advanced Materials and Processes, English/monthly, ASM International, Materials Park, OH 44073, USA. Advanced Engineering Materials, English/monthly, Wiley-VCH, P.O. Box 191161, D-69451, Weinheim, Germany. Alloy Digest, English/bimonthly, ASM International, Materials Park, OH 44073, USA. Electronic Device Failure Analysis, English/quarterly, ASM International, Materials Park, OH 44073, USA. International Materials Reviews, English/bimonthly, ASM International, Materials Park, OH 44073, USA. JOM, English/monthly, TMS 共The Minerals, Metals and Materials Society兲, 184 Thorn Hill Road, Warrendale, PA 15086, USA. Journal of Electronic Materials, English/monthly, TMS 共The Minerals, Metals and Materials Society兲, 184 Thorn Hill Road, Warrendale, PA 15086, USA. Journal of Failure Analysis and Prevention, English/bimonthly, ASM International, Materials Park, OH 44073, USA. Journal of Materials Engineering and Performance, English/bimonthly, ASM International, Materials Park, OH 44073, USA. Journal of Phase Equilibria and Diffusion, English/bimonthly, ASM International, Materials Park, OH 44073, USA. Journal of the American Ceramic Society, English/monthly, American Ceramic Society, P.O. Box 6136, Westerville, OH 430866136, USA. Journal of Thermal Spray Technology, English/quarterly, ASM International, Materials Park, OH 44073, USA. Materials Characterization, English/10 issues yearly, Elsevier Science Publishing Co. Inc., 655 Avenue of the Americas, New York, NY 10010, USA. Metallurgical and Materials Transactions A, English/bimonthly, ASM International, Materials Park, OH 44073, USA. Metallurgical and Materials Transactions B, English/bimonthly, ASM International, Materials Park, OH 44073, USA. Praktische Metallographie/Practical Metallography, bilingual, German/English/monthly, Carl Hanser Verlag, Kolbergstrasse 22, 81679 München, Germany. SlipLines, newsletter, English/quarterly, IMS 共International Metallographic Society兲, ASM International, Materials Park, OH 44073, USA. Structure, English/German/French editions, twice a year, Struers A/S, Pederstrupvej 84, 2750 Ballerup, Denmark. Welding Journal, English/monthly, AWS 共American Welding Society兲, 550 N.W. LeJeunne Road, Miami, FL 33126, USA.

Appendixes Appendix I: Other Standards on Metallography/ Materialography A NUMBER OF STANDARDS, OTHER THAN ASTM, COVERING METALLOgraphy/materialography from ISO 共International Standard Organization兲 and a number of important industrial countries are listed below. The list is not complete. ISO standards/National standards: The national standards, which are local versions of ISO standards, are not indicated below. CEN 共European Committee for Standardization兲 is involved in European Stan-

Chapter 27

Books

687

dards 共EN兲, Technical Specifications 共CEN TS兲, Technical Reports 共CEV TR兲 and CEN Work Agreements 共CWA兲. All documents are supplied by the national members of CEN. ISO 共INTERNATIONAL STANDARD ORGANIZATION兲 ISO 643 Steels—Micrographic determination of the ferritic or austenitic grain size ISO 945 Cast iron—Designation of microstructure of graphite ISO 1083 Spheroidal graphite cast irons—Classification ISO 1463 Metallic and oxide coatings—Measurements of thickness— Microscopical method ISO 2064 Metallic and other inorganic coatings—Definitions and conventions concerning the measurement of thickness ISO 2624 Copper and copper alloys—Estimation of average grain size ISO 2639 Steel—Determination and verification of the effective depth of carburized and hardened cases ISO 3057 Nondestructive testing—Metallographic replica techniques of surface examination ISO 3082 Iron ores—Sampling and sample preparation procedures ISO 3085 Iron ores—Experimental methods for checking the precision of sampling, sample preparation and measurement ISO 3754 Steel—Determination of effective depth of hardening after flame or induction hardening ISO 3763 Wrought steels—Macroscopic methods for assessing the content of nonmetallic inclusions ISO 3887 Steels—Determination of depth of decarburization ISO 4499 Hard metals—Metallographic determination of microstructure ISO 4505 Hard metals—Metallographic determination of porosity and uncombined carbon ISO 4524-1 Metallic coatings—Test methods for electrodeposited gold and gold alloy coatings—Part 1 Determination of coating thickness ISO 4967 Steel—Determination of content of nonmetallic inclusions— Micrographic method using standard diagrams ISO 4968 Steel—Micrographic examination by sulfur prints 共Baumann method兲 ISO 4969 Steel—Macroscopic examination by etching with strong mineral acids ISO 4970 Steel—Determination of total or effective thickness of thin surface-treated layers ISO 5949 Tool steels and bearing steels—Micrographic method for assessing the distribution of carbides using reference photomicrographs ISO 6196 Micrographics—Vocabulary—Part 1: General terms

688


ISO 8036 ISO 9042

ISO 9220 ISO 11567 ISO 13520 ISO 14250 ISO/TR 14321 ISO 14703

ISO 14923 ISO 16793

ISO 17642-2

ISO 20160 ISO 21227 FRANCE NF A04-105

NF A04-106

NF A04-107 NF A04-108

NF A04-110 NF A04-111

Optics and photonics—Microscopes—Immersion liquids for light microscopy Steels—Manual point counting method for statically estimating the volume fraction of a constituent with a point grid Metallic coatings—Measurement of coating thickness— Scanning electron microscope method Carbon fibre—Determination of filament diameter and cross-sectional area Determination of ferrite content in austenitic stainless steel castings Steel—Metallographic characterization of duplex grain size and distribution Sintered metal materials, excluding hardmetals— Metallographic preparation and examination Fine ceramics 共advanced ceramics, advanced technical ceramics兲—Sample preparation for the determination of particle size distribution of ceramic powders Thermal Spraying—Characterization and testing of thermally sprayed coatings Nuclear fuel technology—Guide for ceramographic preparation of UO2 sintered pellets for microstructure examination Destructive tests on welds in metallic materials—Cold cracking tests for weldments—Arc welding processes—Part 2: Self-restraint tests Implants for surgery—Metallic materials—Classification of microstructures for alpha⫹beta titanium alloy bars Paints and varnishes—Evaluation of defects on coated surfaces using optical imaging—Part 1: General guidance Iron and steel. Methods of determination of the nonmetallic inclusion content of wrought steels. Part 1: Macroscopic methods. Iron and steel. Methods of determination of content of nonmetallic inclusions in wrought steel. Part II: Micrographic method using standards diagrams. Iron and steel. Micrographic method of dtermination of the nonmetallic inclusion content of unalloyed wire rod. Iron and steel. Characterization of sulfide shapes in structural steels with improved machinability using standard diagrams. Micrographic method. Iron and steel. Wire rods of non-alloy general purpose steel for wire drawing. Surface examination. Iron and steel. Micrographic determination of the extent of decarburization of non-alloy high carbon steel wire rod.

Chapter 27

NF A04-112

NF A04-113

NF A04-114

A04-115

NF A04-203 NF A04-204 NF A04-503

NF A05-150 NF A05-151 NF A05-152 NF A05-153 NF A05-154 NF A05-156 A05-165

NF A95-342 NF EN 1321 NF EN 12797 NF EN 24499 NF EN 24505 XP ENV 10247 GERMANY

Books

689

Iron and steel. Macrographic method of showing and describing the chemical heterogeneity of effervescent steel wire rod. Iron and steel. High carbon steel wire rod derived from ingots. Macrographic method of showing and describing the chemical heterogeneity. Iron and steel. High carbon continuous cast steel wire rod. Macrographic method of showing and describing the chemical heterogeneity. Iron and steel. Characterization of sulfide shapes in free-cutting steels using standards diagrams. Micrographic method. Steel products. Determination of the effective hardening after flame or induction hardening. Steel products. Determination of the total or conventional thickness of surface hardened thin layers. Semi-products made from aluminum, copper, nickel and their alloys. Determination of grain size. Aluminium and aluminium alloys. Steel products. Techniques of micrographic examination. Steel products. Macrographic examination by sulfur print 共Baumann method兲. Steel products. Macroscopic examination by etching with strong mineral acids. Iron and steel. Macroscopic examination by means of copper salt etching. Steel products. Metallographic replica techniques 共optical examination兲. Iron and steel. Macrographic examination by sodium sulfur print 共so-called lead print method兲. Steel products. Manual point counting method for statistically estimating the volume fraction of a constituent with a point grid. Powder metallurgy. Sintered materials including hardmetals. Micrographic examination techniques. Destructive tests on welds in metallic materials. Macroscopic and microscopic examination of welds. Brazing—Destructive tests of brazed joints. Hard metals. Metallographic determination of microstructure. Hard metals. Metallographic determination of porosity and uncombined carbon. Micrographic examination of the nonmetallic inclusion content of steels using standard pictures.

690


DIN V ENV 1071-5 DIN CEN/TS 1071-10 DIN EN 1321 DIN EN 2004-10 DIN EN 2007

DIN EN 3684

DIN EN 10247 DIN 50192 DIN 50600 DIN 50601 DIN 50602

DIN 54150 JAPAN JIS H 0501 JIS G 0551 JIS G 0552 JIS G 0553 JIS G 0555 JIS Z 6014 UNITED KINGDOM BS M 37 BS EN 1321

共Pre-standard兲 Advanced technical ceramics—Methods of test for ceramic coatings—Part 5: determination of porosity Advanced technical ceramics—Methods of test for ceramic coatings—Part 10: determination of coating thickness by cross sectioning Destructive tests of welds in metallic materials— macroscopic and microscopic examination of welds Aerospace series—Test methods for aluminium and aluminium alloy products; Part 10: preparation of micrographic specimens for aluminium alloys Aerospace series—Test methods for aluminium and aluminium alloy products—metallographic determination of cladding thickness and copper diffusion in the cladding for rolled products Aerospace series—Test methods—titanium alloy wrought products—determination of beta transus temperature; metallographic method Micrographic examination of the nonmetallic inclusion content of steels using standard pictures Determination of the depth of decarburization Testing of metallic materials; metallographic micrographs; picture scales and formats Metallographic examination; determination of the ferritic or austenitic grain size Metallographic examination; microscopic examination of special steels using standard diagrams to assess the content of non-metallic inclusions Nondestructive Testing Impression Methods for Surface Examination Methods for estimating average grain size of wrought copper and copper alloys Steels—Micrographic determination of the apparent grain size Method of ferrite grain size test for steel Macrostructure detecting method for steel, Edition 1 Microscopic testing method for the non-metallic inclusions in steel Micrographics—Test charts for digitizing image— Description and use in electronic imagery Method for the etch inspection of metallic materials and components Destructive test on welds in metallic materials. Macroscopic and microscopic examination of welds

Chapter 27

BS 4490 BS 5710 BS 6285 BS 6286 BS 6479 BS 6481 BS 6533 BS 6617

BS 7590

BS 7590 A BS 10247 BS EN 10328 93/7105316 DC

94/710839 DC

94/710840 DC

Books

691

Methods for micrographic determination of the grain size of steel Macroscopic assessment of the nonmetallic inclusion content of wrought steels Macroscopic assessment of steel by sulfur print Measurement of total or effective thickness of thin surface-hardness layers in steel Determination and verification of effective depth of carburized and hardened cases of steel Determination of effective depth of hardening of steel after flame or induction hardening Guide to microscopic examination of steel by etching with strong acids Determination of decarburization in steel. Methods for determining decarburization by microscopic and microhardness techniques Method for statistically estimating the volume fraction of phases and constituents by systematic manual point counting with a grid Worksheet for the determination of volume fraction by systematic manual point count Micrographic examination of the nonmetallic inclusion content of steels using standard pictures Iron and steel—determination of the conventional depth of hardening after surface heating Aerospace series. Test methods for aluminium and aluminium alloy products. Metallographic determination of cladding thickness and copper diffusion in the cladding for rolled products 共prEN 2007兲 Aerospace series. Test methods. Titanium alloy wrought products. Determination of primary ␣ content. The point count method and line intercept method 共prEN 3683兲 Aerospace series. Test methods. Titanium alloy wrought products. Determination of ␤ transus temperature. Metallographic method 共prEN 3684兲

Appendix II: Other Standards on Hardness Testing A number of standards, other than ASTM, covering hardness testing from ISO 共International Standard Organization兲 and a number of important industrial countries are listed below. The list is not complete. ISO standards/National standards: The national standards, which are local versions of ISO standards, are not indicated below. CEN 共European Committee for Standardization兲 is involved in European Standards 共EN兲, Technical Specifications 共CEN TS兲, Technical Reports 共CEV TR兲 and CEN Work Agreements 共CWA兲. All documents are supplied by the national members of CEN.

692


ISO „International Standard Organization… A number of standards covering hardness testing from ISO are listed below. The list is not complete. ISO 共INTERNATIONAL STANDARD ORGANIZATION兲 ISO 48 Rubber, vulcanized or thermoplastic—Determination of hardness 共hardness between 10 IRHD and 100 IRHD兲 ISO 3738-1 Hard metals—Rockwell hardness test 共scale A兲—Part 1: Test method ISO 3738-2 Hard metals—Rockwell hardness test 共scale A兲—Part 2: Preparation and calibration of standard test blocks ISO 3878 Hard metals—Vickers hardness test ISO 4384-1 Plain bearings—Hardness testing of bearing metals—Part 1: Compound materials ISO 4384-2 Plain bearings—Hardness testing of bearing metals—Part 2: Solid materials ISO 4498 Sintered metal materials, excluding hardmetals— Determination of apparent hardness and microhardness ISO 4498-1 Sintered metal materials, excluding hardmetals— Determination of apparent hardness—Part 1: Materials of essentially uniform section hardness ISO 4498-2 Sintered metal materials, excluding hardmetals— Determination of apparent hardness—Part 2: Case-hardened ferrous materials, surface enriched by carbon or carbon and nitrogen ISO 4507 Sintered ferrous materials, carburized or carbonitrided— Determination and verification of hardening depth by a microhardness test ISO 4516 Metallic and other inorganic coatings—Vickers and Knoop microhardness tests ISO 4545 Metallic materials—Hardness test—Knoop test ISO 4546 Metallic materials—Hardness test—Verification of Knoop hardness testing machines ISO 4547 Metallic materials—Hardness test—Calibration of standardized blocks to be used for Knoop hardness testing machines ISO 6506-1 Metallic materials—Brinell hardness test—Part 1: Test method ISO 6506-2 Metallic materials—Brinell hardness test—Part 2: Verification and calibration of testing machines ISO 6506-3 Metallic materials—Brinell hardness test—Part 3: Calibration of reference blocks ISO 6507-1 Metallic materials—Vickers hardness test—Part 1: Test method ISO 6507-2 Metallic materials—Vickers hardness test—Part 2: Verification of testing machines

Chapter 27

ISO 6507-3 ISO 6508-1 ISO 6508-2

ISO 6508-3

ISO 9015-1 ISO 9015-2 ISO 9385 ISO 14271 ISO 14577-1 ISO 14577-2

ISO 14577-3

ISO 18571 France NF A95-329 NF A95-348

Germany DIN EN 1043-2 DIN CEN/TS 1071-7

DIN CEN/TS 1071-8 Japan JIS Z 2255 JIS Z 2255

Books

693

Metallic materials—Vickers hardness test—Part 3: Calibration of reference blocks Metallic materials—Rockwell hardness test—Part 1: Test method 共scales A, B, C, D, E, F, G, H, K, N, T兲 Metallic materials—Rockwell hardness test—Part 2: Verification and calibration of testing machines 共scales A, B, C, D, E, F, G, H, K, N, T兲 Metallic materials—Rockwell hardness test—Part 3: Calibration of reference blocks 共scales A, B, C, D, E, F, G, H, K, N, T兲 Destructive test on welds in metallic materials—Hardness testing—Part 1: Hardness test on arc welded joints Destructive tests on welds in metallic materials—Hardness testing—Part 2: Microhardness testing of welded joints Glass and glass-ceramics—Knoop hardness test Vickers hardness testing of resistance spot, projection and seam welds 共low load and microhardness兲 Metallic materials—Instrumented indentation test for hardness and materials parameters—Part 1: Test method Metallic materials—Instrumented indentation test for hardness and materials parameters—Part 2: Verification and calibration of testing machines Metallic materials—Instrumented indentation test for hardness and materials parameters—Part 3: Calibration of reference blocks Rubber, vulcanized or thermoplastic—Hardness testing— Introduction and guide Powder metallurgy. Sintered metal materials excluding hardmetals. Measurement of Vickers microhardness Powder metallurgy. Sintered ferrous materials, carburized or carbonitried. Determination of effective case depth by the Vickers microhardness testing method. Destructive test on welds in metallic materials—Hardness test—Part 2: Micro hardness testing on welded joints 共Pre-standard兲 Advanced technical ceramics—Methods of test for ceramic coatings—Part 7: Determination of hardness and Young’s modulus by instrumented indentation testing 共Pre-standard兲 Advanced technical ceramics—Methods of test for ceramic coatings—Part 8: Rockwell indentation test for evaluation of adhesion Method for ultra-low loaded hardness test Method for ultra-low loaded hardness test

694


JIS R 1623:1995 JIS B 7724:1999 JIS B 7726 JIS B 7727:2000 JIS B 7730 United Kingdom BS DD ENV 843-4 BS 1881 P 202 BS 2782 P3 METH 3665 C BS 3900-E12.1

BS 4443 P2 BS 5411 P6 BS 5600 P4 S4.5

BS 6431 P13 BS 6617

BS 7442 P3 S3.2 BS EN 23878 BS EN 24428-1

Testing method for Vickers hardness of fine ceramics at elevated temperatures Brinell hardness test—Verification of testing machines Rockwell hardness test—Verification of testing machines Shore hardness test—Verification of testing machines Rockwell hardness test—Calibration of reference blocks Advanced technical ceramics—monolithic ceramics— mechanical properties at room temperature—Part 4. Vickers, Knoop and Rockwell superficial hardness tests Recommendations for surface hardness testing by rebound hammer Determination of Rockwell hardness Methods of test for paints—determination of Knoop hardness by measurement of the indentation length using a microscope Method 7, indentation hardness tests Vickers and Knoop microhardness tests Powder metallurgical materials and products—methods of testing and chemical analysis of hardmetals—Rockwell hardness test 共scale A兲 Method for determination of scratch hardness of surface according to Mohs Determination of decarburization in steel. Method for determining decarburization by microscopic and micro-hardness techniques Determination of Shore hardness Hardmetals—Vickers hardness test Sintered metal materials, excluding hardmetals— determination of apparent hardness—Part 1. Materials of essentially uniform section hardness

Appendix III: Hardness Conversion Tables for Metals „E 140… 共Included on CD-Rom in back of this book.兲

Appendix IV: SI Quick Reference Guide: International System of Units „SI… 共Included on CD-Rom in back of this book.兲

Glossary Abrasion

The process of rubbing, grinding, or wearing away by the use of abrasives; a roughening or scratching of a surface due to abrasive wear [1]. Abrasive A substance capable of removing material from another substance in machining, abrasion, or polishing that usually takes the form of several small, irregular shaped particles of hard material [1]. Abrasive disk (1) Grinding wheel mounted on a steel plate, with the exposed flat side being used for grinding. (2) Grinding disk with a layer of abrasive product [1]. Abrasive paper See Grinding paper. Abrasive wet cutting Cutting method for almost all solid materials using mechanical friction and wear with abrasives bonded in a cut-off wheel (similar to grinding) [3]. Achromatic Literally, color-free. A lens or prism is said to be achromatic when corrected for two colors. The remaining color seen in an image formed by such a lens is said to be secondary chromatic aberration [2]. See Achromatic objective. Achromatic objective An objective that is corrected chromatically for two colors, and spherically for one, usually in the yellow-green part of the spectrum [2]. Acid A chemical substance that yields hydrogen ions 共H+兲 when dissolved in water gives a pH of less than 7 [1]. See also Base. Age hardening Hardening through aging, usually after rapid cooling or cold working [1]. See also Precipitation hardening. Aging A change in the property of certain metals and alloys that occurs at room temperature or slightly elevated temperatures, after hot working or heat treatment, or after cold working. The aging is usually due to phase changes (precipitation) [1]. See also Precipitation hardening. Air-hardening steel A steel containing sufficient carbon and other alloying elements to harden fully during cooling in air or other gaseous media from a temperature above its transformation range. Same as self-hardening steel [1]. Alloy A substance having metallic properties and being composed of two or more chemical elements of which at least one is an elemental metal [1]. Alloying element An element added to a metal (and which remains within the metal) to effect changes of properties [1]. Alloy steel Steel containing significant quantities of alloying elements (other than carbon and the commonly accepted amounts of manganese, copper, silicon, sulfur, and phosphorus) to improve the mechanical properties [1]. Alpha brass Solid solution phase of one or more alloying elements in copper and having the same crystal lattice as copper [2]. Alpha iron „Fe… Solid phase of pure iron [2]. Amalgam Alloy with mercury and one or more other metals [3]. Amorphous Not having a crystal structure; noncrystalline [1].

695

696


Anisotropy Annealing

Anode

Anode corrosion Anodic etching Anvil effect

Aperture, optical Apochromatic objective

Arc cutting

Artifact

Attack polishing

Austenite Austenitic steel Automatic image analysis

Characterized by having different values of a property in different crystallographic directions [1]. Heating to and holding metals and alloys at a suitable temperature followed by cooling at a suitable rate, used primarily to soften metals, but also to simultaneously produce desired changes in properties or in microstructure [3]. Electrode where electrons leave (current enters) an operating system (battery, X-ray tube, electrolytic cell) [3]. See also Cathode. The dissolution of a metal acting as an anode [3]. See Electrolytic etching. The effect caused by use of too high a load, or when testing the hardness of too thin a specimen, resulting in a bulge or shiny spot on the underside of the specimen [2]. The working diameter of a lens or a mirror [2]. An objective with longitudinal chromatic correction for red, green, and blue, and spherical chromatic correction for green and blue. This is the best choice for high resolution or color photomicrography [2]. A group of cutting processes that melts the metals to be cut with the heat of an arc between an electrode and the base material [1]. A false microstructural feature that is not an actual characteristic of the specimen; it may be present as a result of improper or inadequate preparation, handling methods, or optical conditions for viewing [2]. Simultaneous etching and mechanical polishing by adding a weak etching solution to the polishing compound [1]. See also Chemical mechanical polishing. A face-centered cubic solid solution of carbon or other elements in gamma iron [2]. An alloy steel whose structure is austenitic at room temperature [1]. A device which can be programmed to detect and measure features of interest in an image. It may include accessories such as automatic focus and an automatic traversing stage to permit unattended operation [2].

Glossary

Bainite—upper, lower, intermediate

Banded structure „banding… Band saw Base Base metal

Beilby layer

Beta structure

Binder Blow torch

Bond

697

Metastable microstructure or microstructures resulting from the transformation of austenite at temperatures between those which produce pearlite and martensite. These structures may be formed on continuous (slow) cooling if the transformation rate of austenite to pearlite is much slower than that of austenite to bainite. Ordinarily, these structures may be formed isothermally at temperatures within the above range by quenching austenite to a desired temperature and holding for a period of time necessary for transformation to occur. If the transformation temperature is just below that at which the finest pearlite is formed, the bainite (upper bainite) has a feathery appearance. If the transformation temperature is just above that at which martensite is produced, the bainite (lower bainite) is acicular, resembling slightly tempered martensite. At the higher resolution of the electron microscope, upper bainite is observed to consist of plates of cementite in a matrix of ferrite. These discontinuous carbide plates tend to have parallel orientation in the direction of the longer dimension of the bainite areas. Lower bainite consists of ferrite needles containing carbide platelets in parallel array cross-striating each needle axis at an angle of about 60°. Intermediate bainite resembles upper bainite; however, the carbides are smaller and more randomly oriented [2]. Alternate bands parallel with the direction of working resulting from the elongation of segregated areas [2]. Mechanical cutting method using an endless steel saw blade. A chemical substance that yields hydroxyl ions 共OH−兲, when dissolved in water gives a pH of more than 7 [1]. (1) After welding, that part of the metal which was not melted. (2) A metal that readily oxidizes, or that dissolves to form ions [1]. See also Noble metal. A layer of amorphous or amorphous-like character developed on the surface of a specimen during mechanical polishing. Theory by G. Beilby, but later research has shown that the layer does not exist. Structurally analogous body-centered cubic phases (similar to beta brass), or electron compounds, that have ratios of 3 valence electrons to 2 atoms [2]. Cementing medium holding together mixtures of particles or powder [3]. Method for cutting metal using an acetylen burner, with the possibility of adding an extra flow of oxygen, melting, and blowing away the material. Also called oxyacetylen torching. The material that binds the abrasive in a cut-off wheel and in other abrasive products.

698


Brass Brightfield illumination

Brinell hardness testing Brittleness

Bronze Burning metallography/ materialography… Calibration

Carbide

Carbide tools

Carbon steel Carbonitriding

Carburizing

Case

Alloy consisting of copper (over 50 %) and zinc, to which small amounts of other elements may be added [3]. For reflected light, the illumination which causes specularly reflected surfaces normal to the axis of a microscope to appear bright. For transmission electron microscopy, the illumination of an object so that it appears on a bright background [2]. Hardness test performed by forcing a hard steel or tungsten carbide ball of specified diameter into a material [3]. The tendency of a material to fracture without first undergoing significant plastic deformation [1]. See also Ductility. Copper-tin alloy with or without small amounts of other alloying elements such as phosphorus and zinc [3]. Can occur in cutting and grinding, when sufficient heat is generated on the surface of the work piece to cause discoloration or a change of the microstructure by tempering or hardening [1]. (1) The act or process of determining the relationship between a set of standard units of measure and the output of an instrument or test procedure. (2) The graphical or mathematical relationship relating the desired property (expressed in a standard unit of measure such as micrometres or Kg/ mm2) to the instrument output (instrument units such as filar divisions or pixels) [2]. A compound of carbon with one or more elements, which, in customary formulation, are considered as being more positive than carbon [2]. Cutting or forming tools, usually made of tungsten, titanium, tantalum, or niobium carbides or a combination of them in a matrix of cobalt, nickel, or other metals. Carbide tools are characterized by high hardness and compressive strength and may be coated to improve wear resistance [1]. Steel containing carbon up to 2 % [3]. A case-hardening process by which a suitable ferrous metal is heated in a gaseous atmosphere. Through the gas, the metal surface will absorb carbon and nitrogen by diffusion and form a very hard compound layer [1]. Absorption and diffusion of carbon into solid ferrous alloys by heating to a temperature usually above Ac3, in contact with a suitable carbonaceous material. A form of case hardening [1]. See also Case hardening. In a ferrous alloy, the outer portion that has been made harder than the inner portion as a result of altered composition, or structure, or both, from treatments such as carburizing, nitriding, and induction hardening [2]. See also Core.

Glossary

Case hardening

Cast iron

Cast structure Cathode Cemented carbides „sintered carbides… Cementite

Ceramic

Cermets CG iron Chemical deposition

Chemical etching

Chemical polishing

699

A generic term covering several processes applicable to steel that change the chemical composition of the surface layer by absorption of carbon, nitrogen, or a mixture of the two by diffusion. It is also called carburizing, nitriding, carbonitriding, cyaniding, nitrocarburizing, and quench hardening [1]. Generic term of a large family of cast ferrous alloys containing 2.5–4 % carbon and about 1–3 % silicon. The carbon content exceeds the solubility of carbon in austenite that exists at the eutectic temperature, which is usually more than 2 % [3]. The structure, on a macroscopic or microscopic scale, of a casting [2]. See also Dendrites. Electrode where the electrons enter (current leaves) an operating system [3]. See also Anode. Material made by pressing and sintering a powder of one or more metallic carbides with a small amount of metal (cobalt) serving as a binder [1]. A very hard and brittle compound of iron and carbon corresponding to the empirical formula Fe3C. It is commonly known as iron carbide and possesses an orthorhombic lattice. In “plain-carbon steels” some of the iron atoms in the cementite lattice are replaced by manganese, and in “alloy steels” by other elements such as chromium or tungsten. Cementite will often appear as distinct lamellae or as spheroids or globules of varying size in hypo-eutectoid steels. Cementite is in metastable equilibrium and has a tendency to decompose into iron and graphite, although the reaction rate is very slow [2]. Inorganic, nonmetallic material with crystalline and noncrystalline structures (for instance: metal carbides, oxides, nitrides, and borides are ceramics) [3]. Powder metallurgy product consisting of ceramic particles bonded with metal [1]. Same as compacted graphite cast iron [1]. See also Compacted cast iron. Precipitation of a metal from solutions of its salts through the introduction of another metal or reagent to the solution [1]. Develops the microstructure by using an electrochemical process, which takes advantage of the differences in the electrochemical potentials of the various constituents in the structure [3]. Improving the surface luster of a metal by chemical treatment [1]. See also Chemical mechanical polishing.

700


Chemical mechanical polishing Chips Clad metal

Clay

Cold etching Cold rolled sheet Cold worked structure Combined carbon Comet tails

Compacted graphite cast iron Component

Composite material

Condenser

Constant feed speed

Using a combination of a chemical solution (usually an etchant) with an oxide suspension on a polishing cloth, resulting in a scratch free surface. Mainly used for very soft or ductile metals [3]. See also Oxide polishing. Pieces of material removed from a work piece by cutting tools or by an abrasive medium [3]. A composite metal containing two or three layers that have been bonded together. The bonding may have been accomplished by co-rolling, welding, casting, heavy chemical deposition, or heavy electroplating [1]. Earthy or stony mineral aggregate, which is plastic when sufficiently pulverized and wetted, rigid and dry, and vitreous when fired at a sufficiently high temperature [3]. Reveals the microstructure at room temperature and below [4]. Sheets of metal made by feeding metal through mill rolls at room temperature [3]. A microstructure resulting from plastic deformation of a metal or alloy below its recrystallization temperature [1]. That part of the total carbon in steel or cast iron that is present as other than free carbon [1]. See also Free carbon. Artifact in the form of unidirectional scratches developed by mechanical polishing of a metallographic/materialographic surface. Cast iron having a graphite shape intermediate between the flake form typical of gray cast iron and the spherical form of fully spherulitic cast iron. Also known as CG iron [1]. One of the independently variable substances by means of which the composition of each phase of a system of heterogeneous equilibrium may be described completely; usually an element, or a compound that remains undissociated throughout the range of temperature and pressure concerned [2]. A heterogeneous, solid structural material consisting of two or more distinct components that are mechanically or metallurgically bonded together (such as a cermet, or boron wire embedded in a matrix of epoxy resin) [1]. See also Cermet. A term applied to lenses or mirrors designed to collect, control, and concentrate radiation in an illumination system [2]. In cutting: Cutting principle where the movement of the specimen or the cut-off wheel is kept constant throughout the cutting process. This cutting principle is preferred to the principle of Constant force as it will produce the least deformation possible while still achieving the shortest cutting times [3]. See also Constant force.

Glossary

Constant force

Constituent Contamination „metallography/ materialography…

Continuous phase Controlled etching

Conversion, hardness Coolant Core

Corrosion Corrosion embrittlement Corrosion fatigue Coupon

Creep Crystal Crystallite Cut-off wheel Cutting „metallography/ materialography… Cutting fluid

701

In cutting: Cutting principle where the force applied is kept constant throughout the cutting process. Constant force can produce damage to the sample especially at sample entry and exit [3]. A phase, or combination of phases, which occurs in a characteristic configuration in an alloy microstructure [2]. (1) Debris from grinding or dust from the lab environment contaminating a polishing cloth resulting in scratches of the specimen surface. (2) Material from a source other than the specimen itself, which is deposited on the specimen surface during preparation [3]. The phase forming the matrix or background in which other phases may be dispersed as isolated units [2]. Electrolytic etching with selection of suitable etchant and voltage, resulting in a balance between current and dissolved ions [4]. The exchange of a hardness number determined by one method for an equivalent hardness number of a different scale [2]. See Cutting fluid. (1) Case hardening—interior portion of unaltered composition, or microstructure, or both, of a case-hardened steel article. (2) Clad products—the central portion of a multilayer composite metallic material [2]. Deterioration of a metal by chemical or electrochemical reaction with its environment [1]. The chemical or electrochemical reaction between a material, usually a metal, and its environment that produces a deterioration of the material and its properties [1]. Cracking produced by the combined action of repeating and fluctuating stress and a corrosive environment [1]. A piece of material especially made for testing. Known from printed circuit boards, where a coupon is made together with the board. Time-dependent strain occurring under stress [1]. A solid composed of atoms, ions, or molecules arranged in a pattern which is periodic in three dimensions [2]. A crystalline grain not bounded by habit planes [2]. Abrasive wheel consisting of an abrasive in a bond for cutting any material or part [3]. Sectioning of a piece of material to obtain a specimen [3]. See also Cut-off wheel. Fluid used to cool a work piece, wash chips away, and improve surface finish and cut-off wheel lifetime [3].

702


Cutting speed

Darkfield illumination

Decarburization

Deep drawing Deep etching

Deformation „metallography/ materialography…

Deformation bands

Dendrites

Depth of field Diamond polishing

Diamond wheel Diaphragm

The linear or peripheral speed of relative motion between the tool and work piece in the principal direction of cutting [1]. The illumination of an object such that it appears illuminated with the surrounding field dark. This results from illuminating the object with rays of sufficient obliquity so that none can enter the objective directly. As applied to electron microscopy, the image is formed using only electrons scattered by the object [2]. Loss of carbon from the surface of a carbon-containing alloy due to a reaction with one or more chemical substances in a medium that contacts the surface. Decarburization may be either (1) partial. That is, where carbon content is less than the unaffected interior but greater than the room temperature solubility limit of carbon in ferrite or (2) complete. That is, where carbon content is less than the solubility limit of carbon in ferrite so that only ferrite is present [2]. Forming of deeply recessed parts by means of plastic flow of the material [1]. Macroetching; etching preliminary to macro-examination, intended to develop gross features such as segregation, grain flow, cracks, or porosity [2]. See also Macroetching. Plastic deformation, which may also be referred to as cold work, can result in subsurface defects after grinding, lapping, or polishing. Remaining plastic deformation can first be seen after etching. Plastic deformation (deformed layer) is an artifact that has to be removed during sample preparation [3]. Bands produced within individual grains during cold working which differ variably in orientation from the matrix [2]. Crystals, usually formed during solidification or sublimation, which are characterized by a tree-like pattern composed of many branches; pine-tree or fir-tree crystals [2]. The depth or thickness of the object space that is simultaneously in acceptable focus [2]. Polishing using diamond as abrasive. Removes scratches introduced during fine grinding. Makes the specimen suitable for microscopic observation [3]. See also Final polishing, Polishing. A grinding wheel in which crushed and sized industrial diamonds are held in a resinoid, metal, or vitrified bond [1]. A fixed or adjustable aperture in an optical system. Diaphragms are used to intercept scattered light, to limit field angles, or to limit image-forming bundles or rays [1].

Glossary

Differential interference contrast illumination „DIC…

Diffraction

Diffusion Direct cut „metallography/ materialography… Dislocation Dislocation etching Dissolution etching Double etching Drawing

Drop etching Dry etching Ductile cast iron

Ductility

Duplex microstructure Dye penetrant

703

A microscopical technique employing a beam-splitting double-quartz prism; that is a modified Wollaston prism placed ahead of the objective with a polarizer and analyzer in the 90° crossed positions. The two light beams are made to coincide at the focal plane of the objective, thus rendering height differences visible as variations in color. The prism can be moved, shifting the interference image through the range of Newtonian colors [2]. (1) A modification which radiation undergoes, as in passing by the edge of opaque bodies or through narrow slits, in which the rays appear to be deflected. (2) Coherent scattering of X-radiation by the atoms of a crystal which necessarily results in beams in characteristic directions. Sometimes called reflection. (3) The scattering of electrons, by any crystalline material, through discrete angles depending only on the lattice spacings of the material and the velocity of the electrons [2]. The spontaneous movement of atoms or molecules to new sites within a material [1]. Cutting mode in which the cut-off wheel cuts directly through the work piece; also called chop cutting [3]. A linear imperfection in a crystalline array of atoms [1]. Reveals exit point of dislocations on the specimen surface [4]. Reveals the microstructure by surface removal [4]. Two etchants are used sequentially; the second one will accentuate a particular microstructural feature [4]. Forming recessed parts of metal by pressing them in or through a die. Reducing cross section of a wire or tube by pulling it through a die [1]. Placing a drop of an etchant on a selected area of the specimen surface to develop the microconstituents [4]. Develops the microstructure by gaseous exposure [4]. A cast iron that has been treated while molten with an element such as magnesium or cerium to induce the formation of free graphite as nodules or spherulites, which imparts a measurable degree of ductility to the cast metal. Also known as nodular cast iron, cast iron with spheroidal graphite and SG iron [1]. Ability of a material to deform plastically without fracturing, measured by elongation or reduction of area in a tensile test [1]. See also Brittleness. A two-phase structure [2]. Color spray used in nondestructive testing to find cracks in surface of parts [3].

704


Elastic deformation

Elasticity Electrical discharge machining „EDM… Electrolyte Electrolytic cell

Electrolytic etching

Electrolytic polishing

Electron microscopy Embedded abrasives

Equiaxed grain Equilibrium diagram

Etchant Etch figures

Etching Eutectic

Eutectic structure

Change of dimensions of a piece of material under stress. Upon release of stress original dimensions are restored again (example: elastic band which takes its original shape after it has been stretched) [3]. Ability of a solid to deform in direct proportion to and in phase with increases or decreases in applied force [3]. Removal of stock from an electrically conductive material by rapid, repetitive spark discharge through a dielectric fluid flowing between the work piece and a shaped electrode [1]. Liquid, most often a solution, that will conduct an electric current [1]. An assembly consisting of a vessel, electrodes (anode and cathode) and an electrolyte in which electrolysis can be carried out [1]. Development of microstructure by selective dissolution of the polished surface under application of a direct current [1]. Also called anodic etching. A metallographic preparation procedure where metal is preferentially dissolved from high points on an anodic surface by passage of an electric current through a conductive bath, to produce a specular reflecting surface. Used as an alternative to mechanical polishing [2]. The study of materials by means of the electron microscope [2]. See also SEM and TEM. Loose abrasive particles pressed into the surface of a specimen. This happens mainly with soft or ductile materials, or both. Abrasives can be embedded when using a small abrasive particle size, the grinding or polishing cloth used has a low resilience or a lubricant with a low viscosity is used or a combination of these conditions takes place [3]. A polygonal crystallite, in an aggregate, whose dimensions are approximately the same in all directions [2]. A graphical representation of the temperature, pressure, and composition limits of phase fields in an alloy system, as they exist under conditions of complete equilibrium [1]. Chemical substance or mixture used for etching [1]. Markings formed on a crystal surface by etching or chemical solution and usually related geometrically to the crystal structure [2]. Controlled preferential attack on a metal surface for the purpose of revealing structural details [2]. Phase consisting of intermixed solid constituents formed by a eutectic reaction, (pearlite= ferrite end cementite). The number of solids being the same as the number of components in the system [3]. The structure resulting when an alloy has passed through a eutectic equilibrium upon freezing [2].

Glossary

Exogenous inclusions Eyepiece Fatigue Feed speed Ferrite

FG Field Field metallography

Filar

Filler Final polishing Flame spraying

Flow lines

Fluorescent screen Foil Forging

Formability „workability, drawability… Fractography

705

A nonmetallic constituent produced by entrapment of foreign material in the melt [2]. See also Inclusions, Nonmetallic inclusions. The lens system used in an optical instrument for magnification of the image formed by the objective [2]. Process by which repeated or fluctuating stress, or both, leads to fracture [3]. Rate by which a tool or cut-off wheel advances along or into the surface of a work piece [3]. Designation commonly assigned to alpha iron containing alloying elements in solid solution. Increasing carbon content markedly decreases the high-temperature limit of equilibrium [2]. Fine Grinding. Reduces surface roughness of a specimen to a degree that is suitable for polishing [3]. The portion of the object in view [2]. Metallographic techniques carried out in the field when the part or component is too large to bring to a metallographic laboratory or a specimen cannot be removed [1]. An eyepiece equipped with a fiducial line in its focal plane, which is movable by means of a calibrated micrometre screw, in order to make accurate measurements of length [2]. Material used to increase the bulk of a product without adding to its effectiveness in functional performance [3]. The final step in a specimen preparation process producing a surface suitable for microscopic examination. Coating technique in which the coating material is fed as wire or powder into a flame and sprayed in the molten state against the surface to be coated [3]. A fiber pattern, frequently observed in wrought metal, which indicates the manner in which the metal flowed during deformation [2]. A sheet of material which emits visible light when exposed to invisible radiation [2]. A thin sheet of a material, usually a metal, not exceeding 0.13 mm 共0.005 in.兲 in thickness [2]. Process of plastically deforming metal, usually hot, into a desired shape with compressive force, with or without dies [1]. Relative ease with which a metal can be shaped through plastic deformation [1]. Description of fractures with macrographs 共⬍25⫻ 兲 and micrographs at high magnification 共⬎25⫻ 兲 from the optical microscope and the SEM [3].

706


Fracture test

Free carbon Free machining

Galvanizing Goniometer Grain Grain boundary

Grain boundary etching

Grain size

Grain-contrast etching Graphite

Graphitic carbon Graticule

Test in which a specimen is broken and its fracture surface examined to determine such factors as composition, grain size, case depth, or soundness [1]. Part of the total carbon in steel or cast iron that is present in elemental form as graphite [1]. See also Combined carbon. Machining capabilities of an alloy to which one or more ingredients have been introduced to produce small broken chips, better surface finish, and longer tool lifetime during the machining process [1]. Coating the surface of iron or steel with zinc applied electrolytically or by hot dipping [3]. An instrument devised for measuring the angle through which a specimen is rotated [1]. An individual crystallite in metals [2]. An interface separating two grains, where the orientation of the lattice changes from that of one grain to that of the other. When the orientation change is very small the boundary is sometimes referred to as a subboundary [2]. Reveals the intersections of the individual grains. Grain boundaries have a higher dissolution potential than the individual grains because of their high density of structural defects. Accumulation of impurities in grain boundaries increases this effect [4]. (1) Measure of the areas or volume of grains in a polycrystalline material, usually expressed as an average when the individual sizes are fairly uniform. In metals containing two or more phases, grain size refers to that of the matrix unless otherwise specified. Grain size is reported in terms of number of grains per measuring unit area or volume, average diameter, or as a grain size derived from area measurements. See also ASTM Standard E 112. (2) Dimension of one individual particle of an abrasive, measured in micrometres, ␮m [1]. See also Grit size. Etching the surface of the grains according to their crystal orientation. They become distinct by the different reflectivity caused by reaction layers or surface roughness [4]. The polymorph of carbon with a hexagonal crystal structure [1]. See also CG iron, Gray cast iron, Nodular cast iron, Spheroidal cast iron. Free carbon in steel or cast iron [1]. A scale on glass or other transparent material placed in the eyepiece or at an intermediate plane on the optic axis of a light microscope for the location and measurement of objects (a graticule is different than a reticle) [2]. See also Reticle.

Glossary

Gray cast iron or gray iron Grinding

Grinding paper Grit size

Half moon phenomenon

Hardening Hardness „indentation…

Heat-resistant alloy

Heat tinting

Heat treatment Heterogenous High alloy steel

Homogenizing

707

Cast iron that looks gray on the fractured surface due to the presence of free graphite. Contains carbon as graphite in form of flakes or nodules [3]. The removal of material from the surface of a specimen by abrasion through the use of randomly oriented hard-abrasive particles bonded to a suitable substrate, such as paper or cloth, where the abrasive particle size is generally in the range of 60 to 600 grit (approximately 150 to 15 ␮m) but may be finer [2]. Coated abrasive product in which paper is used as a backing material [3]. Nominal size of abrasive particles in a grinding wheel, corresponding to the number of openings per linear inch in a screen through which the particles can just pass. Sometimes but inadvisably called “grain size” [1]. See Grain size. Appears mainly when using wet grinding disk and coarse SiC-paper for plane and fine grinding of specimens clamped in a specimen holder. This phenomenon is due to the fact that the abrasive grains of the SiC-paper are not getting worn down at the edge of an SiC-paper as fast as in the middle, combined with the higher speed at the periphery of the disk [3]. Increasing hardness of a metal with a suitable treatment, usually through heating and fast cooling [1]. Resistance of a metal to plastic deformation, usually by indentation. However, the term may also refer to resistance to scratching, abrasion, or cutting. Indentation hardness may be measured by various hardness testing methods, such as Brinell, Rockwell, Vickers, Knoop, and Scleroscope [3]. Alloys used for applications for which resistance against high temperature and corrosion, combined with high stresses are required. They are usually high nickel alloys [1]. Coloration of a metal surface through a thin oxide film, formed by heating in oxidizing atmosphere, to reveal details of the microstructure [1]. Heating and cooling a solid metal or alloy in such a way that desired properties are obtained [1]. Nonuniform in microstructure or composition [2]. Contains up to 2.5 % carbon and more than 6 % metallic alloying elements, mainly chromium (Cr), nickel (Ni), vanadium (V), tungsten (W), and manganese (Mn). Very hard tool steels and ductile stainless steels are high alloy steels [3]. Holding at high temperature to eliminate or decrease chemical segregation by diffusion [1].

708


Hot dip coating Hot etching Identification „selective… etching Image Image processing, in image analysis Immersion etching

Immersion objective

Impact test

Impregnation „metallography/ materialography… Impression

Impurities Inclusions

Indentation hardness

Indigenous „endogenous… inclusion Induction hardening

Ingot

Metallic coating obtained by dipping the basic metal into a molten metal [1]. Development and stabilization of the microstructure at elevated temperature in etching solutions or gases [4]. Etching for the identification of particular microconstituents without attacking any others [4]. A representation of an object produced by means of radiation, usually with a lens or mirror system [2]. The computer modification of a digitized image on a pixel-by-pixel basis to emphasize or de-emphasize certain aspects of the image [2]. See also Automatic image analysis. The specimen is immersed in the etchant with the polished surface up and is agitated. This is the most common etching method [4]. An objective in which a medium of high refractive index is used in the object space to increase the numerical aperture and hence the resolving power of the lens [2]. A test to determine the behavior of materials when subjected to high rates of loading, usually bending, tension, and torsion. The quantity measures the energy absorbed in breaking the specimen by a single blow, as in Charpy and Izod tests [1]. Process of filling voids and cracks under vacuum with a sealing medium, for instance, epoxy cold mounting resin [3]. (1) Electron microscopy. The reproduction of the surface contours of a specimen formed in a plastic material after the application of pressure and heat, or both. (2) Hardness. The imprint or dent made in the specimen by the indenter of a hardness-measuring device [2]. Elements or compounds whose presence in a material is undesired [1]. Foreign material held mechanically, usually referring to nonmetallic particles, such as oxides, sulfides, silicates, etc. [2]. See also Exogenous inclusions, Nonmetallic inclusions. Resistance of a material to indentation. This is the usual type of hardness test, in which a pointed or rounded indenter is pressed into a surface under a substantially static load [3]. See also Hardness. A nonmetallic material that precipitates from the melt [2]. See Inclusions. Surface hardening in which only the surface layer of a suitable ferrous work piece is heated by electrical induction to hardening temperature and then quenched [3]. Casting of a simple shape suitable for hot working or remelting [1].

Glossary

Intercrystalline Intercrystalline cracks Interdendritic corrosion Interface Intergranullar corrosion Intracrystalline Inverted microscope Ion etching Iron Isotropy Kikuchi lines

Koehler illumination

Knoop hardness

Lamellar structure Laminate

Lapping Lapping tracks

709

Between crystals, or between grains of a metal, the same as intergranular [1]. Cracks or fractures that occur between the grains or crystals in a polycrystalline aggregate [2]. Corrosive attack that progresses preferentially along an interdendritic path [1]. Surface that forms the boundary between phases or systems, or both [1]. A preferential attack at the grain boundaries [2]. Within or across the crystals or grains of a metal, same as transcrystalline and transgranular [1]. A microscope so arranged that the line of sight is directed upwards through the objective to the object [2]. Surface removal by bombardment with accelerated ions in a vacuum 共1 to 10 kV兲 [4]. Iron-based metals not falling into the steel category, such as pure iron, gray iron, pig iron, white cast iron, etc. [3]. The condition of having the same values of properties in all directions [2]. Light and dark lines superimposed on the background of a single crystal electron diffraction pattern caused by diffraction of diffusely scattered electrons within the crystal [2]. A specular illumination system. In reflected-light microscopy, used directly for the brightfield mode, and as a preliminary setup for all other modes except darkfield. The image of the field diaphragm is focused on the specimen surface and the image of an undiffused lamp source is focused in the plane of the aperture diaphragm [2]. Microhardness determined from resistance of a metal to indentation using a rhombic-based pyramidal diamond indenter, which makes an impression with one long and one short diagonal [3]. A microstructure consisting of parallel plates of a second phase [3]. See Pearlite. (1) A composite material, usually in the form of sheet or bar, composed of two or more materials bonded to form a solid structure. (2) Product of two or more bonded metal layers [3]. The abrasive removal of material using graded abrasive particles in a loose form as in a liquid slurry on a platen [2]. Indentations on the specimen surface made by abrasive particles moving freely on a hard surface. These are not scratches from a cutting action, but are the distinct tracks of particles tumbling over the surface without removing material [3].

710


Light metal Light micoscopy Long-term etching Lubricant

Machining Macroetching

Macroscopic Macrostructure Magnetic-particle inspection

Malleability Malleable cast iron

Martensite

Low density metal such as aluminum, magnesium, titanium, beryllium, or their alloys [1]. See Optical microscope. Etching times of a few minutes to several hours [4]. Any substance used to reduce friction between surfaces in contact. Liquid used for cooling and lubricating. Depending on the type of material and the preparation stage, different types of lubricants can be used for grinding and polishing [3]. Removing surface material in the form of chips, usually with a mechanical tool [3]. Controlled etching of the surface of a metallic specimen, intended to reveal a structure which is visible at low magnifications (not usually greater than ten times) [2]. See also Deep etching. Observation using the naked eye or magnifications up to 10–30 times [3]. Structure of metals as revealed by macroscopic examination of the etched surface of a polished specimen [1]. A nondestructive method of inspection for determining the existence and extent of possible defects in ferro-magnetic materials. On the surface of a magnetized part fine magnetic particles are attracted to areas where the magnetic field is displaced or interrupted, such as cracks or pores [1]. The characteristic of metals that permits plastic deformation in compression without rupture [1]. A cast iron made by prolonged annealing of white cast iron in which decarburization or graphitization, or both, takes place to eliminate some or all of the cementite [1]. Metastable phase resulting from the diffusionless athermal decomposition of austenite below a certain temperature known as the Ms temperature (martensite start temperature). It is produced during quenching when the cooling rate of a steel, in the austenitic condition, is such that the pearlite and bainite, or both, transformation is suppressed. The composition of the martensite is identical with that of the austenite from which it transformed. Hence, martensite is a super-saturated solid solution of carbon in alpha iron (ferrite) having a body-centered tetragonal lattice. It is a magnetic plate-like constituent formed by a diffusionless shear type of transformation. These plates may appear needle-like or veriform in cross section [2].

Glossary

Materialography

Matrix Mechanical polishing Mechanical properties

Mechanical testing Mechanical twin Metallograph

Metallography

Metallurgy Metastable

Microetching

Micrograph

Micro indentation hardness „microhardness… Micro penetration hardness Microscopy

711

Materialography is defined as an investigative method of materials science. It emcompasses the optical examination of microstructures, and its goal is a qualitative and quantitative description of the microscopic structural analysis of solid materials. Materialography includes metallography, ceramography, plastography, and mineralogy [4]. See also Metallography. The continuous phase [2]. See Continous phase. Specimen preparation process using finer and finer abrasives, mostly diamond, to obtain a surface suited for microscopic examination. The properties of a material that reveal its elastic and inelastic behavior when force is applied, by indicating its suitability for mechanical applications; for example, modulus of elasticity, tensile strength, elongation, hardness, and fatigue limit [1]. Compare with Physical properties. Determination of mechanical properties [1]. A twin formed in a crystal by simple shear under external loading [1]. See also Twin bands. An optical instrument for the examination of metallographic/ materialographic specimens. In principle it consists of a light source, a microscope, and a camera. That branch of science which relates to the constitution and structure, and their relation to the properties, of metals and alloys [2]. See also Materialography. The science and technology of metals and alloys [1]. A state of apparent equilibrium which has a higher free energy than has the true equilibrium state; usually applied to a phase existing outside its temperature and pressure span of equilibrium existence, by reason of a greatly delayed transformation [2]. Development of microstructure for microscopic observation.The usual magnification exceeds 25⫻ (50⫻ in Europe) [1]. A graphic reproduction of an object as seen through the microscope or equivalent optical instrument, at magnifications greater than ten diameters [2]. Hardness of a material determined by forcing an indenter into the polished surface of a material under very light load using a microhardness tester [3]. See also Micro penetration hardness. The hardness number obtained by use of a low load tester whose indentation is usually measured with a high power microscope [2]. See also Micro indentation hardness. The science of the interpretive use and applications of microscopes [1].

712


Microstructure Mineralogy Modulus of elasticity „E…

Monochromatic „homogeneous… Monocrystalline Morphology Mounting

Multiple etching Nitriding

Nitrocarburizing

Noble metal

Nodular cast iron

Nonmetallic inclusions

Nondestructive testing Normalizing

The structure of a suitably prepared specimen as revealed by a microscope [2]. Scientific study of minerals [3]. See also Petrographic examination. The measure of rigidity or stiffness of a metal; the ratio of stress, below the proportional limit, to the corresponding strain. In terms of stress-strain diagram, the modulus of elasticity is the slope of the stress-strain curve in the range of linear proportionality of stress to strain. Also known as Young's modulus [1]. Of the same wavelength [2]. A solid composed of a unique crystal [3]. The shape characteristics of a structure; the form and orientation of specific phase or constituent [2]. To embed the specimen in resin to facilitate the further handling during grinding and polishing, and to improve the preparation result [3]. A specimen is etched sequentially with the specific etchants to reveal certain constituents [4]. Nitriding is a form of surface hardening. By exposing a ferrous part at a certain temperature to nitrogenous materials, nitrogen will diffuse into the surface of the part and form hard nitrides [3]. Any of several case-hardening processes in which both nitrogen and carbon are absorbed into the surface layers of a ferrous material at a certain temperature. Nitrocarburizing improves fatigue resistance [1]. (1) A metal whose potential is highly positive relative to the hydrogen electrode. (2) A metal with marked resistance to chemical reaction, particularly to oxidation and to solution by inorganic acids. The term as often used is synonymous with precious metal [1]. Also called ductile cast iron; trace amounts of magnesium are added to the melt to induce formation of free graphite in the form of nodules. See also Spheroidal cast iron. Particles of impurities (usually oxides, sulfides, silicates, and such) that are held mechanically or are formed during solidification or by subsequent reaction within the solid metal [2]. See also Exogenous inclusions, Inclusions. Inspection by methods that do not destroy the part in order to determine its suitability for use [1]. See also Field metallography. Heating a ferrous alloy to a suitable temperature above the transformation range and then cooling it in air to a temperature substantially below the transformation range [1].

Glossary

Numerical aperture „NA… Objective Ocular Optical etching

Optical microscope

Ore

Organic materials Orientation

Overheating

Oxide polishing

Oxidation

P

Particle size

713

The sine of half the angular aperture of an objective lens multiplied by the refractive index of the medium between the lens and the sample [2]. The primary magnifying system of a microscope [1]. See Eyepiece. Develops the microstructure by using special illumination techniques (dark field, interference contrast, polarized light, phase contrast) [4]. Instrument containing one or more lenses which uses artificial light to produce an enlarged image of an object placed in the focal plane of the lens(es) [3]. A natural mineral that may be mined and treated for the extraction of any of its components, metallic or otherwise [3]. For example, wood, bone, tissue, teeth, paper. The angular position of a crystal described by the angles which certain crystallographic axes make with the frame of reference. In hardness measurements, the relationship between the direction of the axes of the indenter of a hardness tester and the direction of nonhomogeneous properties of the specimen [2]. (1) In ferrous alloys, heating to an excessively high temperature such that the properties/structure undergo modification. The resulting structure is very coarse-grained. Unlike burning, it may be possible to restore the original properties/structure by further heat treatment or mechanical working, or a combination thereof. (2) In aluminum alloys, overheating produces structures that show areas of resolidified eutectic or other evidence that indicates the metal has been heated within the melting range [2]. Process used for the final polishing of a specimen with a suspension containing fine abrasive particles of oxides (aluminum oxide, silicon dioxide) with or without chemicals of different pH. See also Final polishing. (1) A reaction in which there is an increase in valence resulting from a loss of electrons. (2) A corrosion reaction in which the corroded metal forms an oxide; usually applied to reaction with a gas containing elemental oxygen, such as air [1]. Polishing (mechanical) taking place as the last steps (P1, P2, P3, etc.) of metallographic/materialographic preparation to obtain a surface suited for microscopic examination. See also Final polishing, Oxide polishing, Polishing. The controlling linear dimension of an individual particle, such as of a powdered metal, as determined by analysis with screens or other suitable instruments [1].

714


Pearlite

Petrographic examination

PG

pH

Phase Phase contrast microscopy

Photo micrograph Physical etching

Physical properties

A metastable microstructure formed when local austenite areas attain the eutectoid composition in alloys of iron and carbon containing greater than 0.025 % but less than 6.67 % carbon. The structure is an aggregate consisting of alternate lamellae of ferrite and cementite formed on slow cooling during the eutectoid reaction. In an alloy of given composition, pearlite may be formed isothermally at temperatures below the eutectoid temperature by quenching austenite to a desired temperature (generally above 550° C) and holding for a period of time necessary for transformation to occur. The interlamellar spacing varies directly with the transformation temperature; that is, the higher the temperature the greater the spacing [2]. Methods of examining nonmetallic matter under suitable microscopes to determine structural relationships and to identify the phases or minerals present. With transparent materials, the determination of the optical properties, such as the indices of refraction and the behavior in transmitted polarized light, serve as means of identification. With opaque materials, the color, hardness, reflectivity, shape, and etching behavior in polished sections serve as means of identification. Metallographic applications include examination of particles mechanically or chemically separated from the metal by these methods [2]. Plane (planar) grinding. Removes damage introduced by cutting, and levels specimens clamped in a holder for automatic grinding [3]. See also Planar grinding. The negative logarithm of the hydrogen-ion activity. It denotes the degree of acidity or basicity of a solution. At 25° C 共77° F兲, 7.0 is the neutral value. Lower values than 7.0 indicate acidity and higher values increasing basicity [1]. A physically homogeneous and distinct portion of a material system [1]. A special method of controlled illumination, ideally suited for observing thin, transparent objects whose structural details vary only slightly in thickness or refractive index. This can also be applied to the examination of opaque materials to determine surface elevation changes [2]. See Micrograph. Develops the microstructure through removal of surface atoms, lowering the grain surface potential and deposition of interference layers [4]. Properties, other than mechanical properties, that pertain to the physical nature of a material; for example, density, electrical conductivity, thermal expansion, reflectivity magnetic susceptibility, and so on [1]. See also Mechanical properties.

Glossary

Physical testing Pig Pitting „metallography… Pixel „picture element… Planar grinding

Plane grinding Plasma spraying

Plastic

Plastic deformation Plasticity Plating

Plowing Polarized light illumination Polishing

Polishing artifact Polishing cloth

Polishing rate

Polycrystalline

715

Determination of physical properties [1]. Metal casting poured from the melting furnace, used for remelting [3]. Forming small sharp cavities in a metal surface if electrolytic polishing is not performed correctly. Smallest spatial unit of an image [2]. The first step in a preparation procedure used to bring all specimens into the same plane of polish. It is unique to semi or fully automatic preparation equipment that utilize specimen holders [2]. See also PG. See PG. Coating technique in which the coating material is fed as powder into an ionized gas atmosphere (plasma) and sprayed in the molten state onto the surface to be coated [3]. Any of various organic compounds produced by polymerization, capable of being molded, extruded, cast into various shapes and films, or drawn into filaments used as textile fibers [3]. Deformation that remains or will remain permanent after release of the stress that caused it [1]. The capacity of a material to deform nonelastically without rupturing [1]. Forming an adherent layer of metal on metal, usually through a galvanic process. Any adherent layer of metal on other material can also be called plating [3]. In tribology, the formation of grooves by plastic deformation of the softer of two surfaces in relative motion [1]. A method of illumination in which the incident light is plane polarized before it impinges on the specimen [2]. A mechanical, chemical, or electrolytic process or combination thereof used to prepare a smooth reflective surface suitable for microstructure examination, free of artifacts or damage introduced during prior sectioning or grinding [2]. See also Final polishing, Oxide polishing, Polishing cloth. A false structure introduced during a polishing stage of a surface preparation sequence [1]. See also Artifact. A substrate, mostly a textile or a nonwoven material, used for polishing of specimens with selected abrasives. See also Final polishing, Oxide polishing, Polishing. The rate of which material is removed from a surface during polishing. It is usually expressed in terms of the thickness removed per unit of time or distance traversed [1]. Characteristic of an aggregate composed of more than one, and usually of a large number, of crystals [2].

716


Polymers Pores Porosity Potentiostatic etching Powder Powder metallurgy Precious metals Precipitation

Precipitation etching Precipitation hardening Primary crystals Primary etching Pull-out

Quantitative metallography

Quenching Quenching crack

Ram Rare earth metals

RCD Recarburize

Plastics, for instance polyethylene, epoxy, polyester and polyacryl, and polyamide (Nylon) [3]. Small voids in the body of a material [1]. Holes in a solid, not necessarily connected [2]. Anodic development of the microstructure at a constant potential enables a defined etching of singular phases [4]. Particles of a solid characterized by small size, nominally within the range from 0.1 to 1000 ␮m [3]. Production and use of metal powders, which are hot pressed and sintered into solid materials and shaped objects [1]. Gold, silver, and platinum-group metals [3]. Separation of a new phase from solid, liquid, or gaseous solutions, usually with changing conditions of temperature or pressure, or both [2]. Develops the microstructure by the formation of reaction products at the specimen surface [4]. Hardening caused by precipitation of a constituent from a supersaturated solid solution [1]. See also Age hardening, Aging. The first type of crystals that separates from a melt on cooling [2]. Develops the cast microstructures including coring [4]. See also Secondary etching. Void existing on the plane of polish of a metallographic specimen caused by the dislodging of a particle or constituent during the grinding or polishing operation [2]. Determination of specific characteristics of a microstructure by making quantitative measurements on micrographs or metallographic/materialographic images. Quantities so measured include volume concentration of phases, grain size, particle size, and surface-area-to-volume ratios of micro-constituents, particles, or grains [1]. See also Automatic image analysis. Rapid cooling, usually in water [3]. A crack formed as a result of thermal stresses produced by rapid cooling from a high temperature, not to be confused with fire crack [2]. Moving part in e.g, the cylinder of a mounting press [3]. One of the group of 15 chemically similar metals with atomic numbers 57 through 71, commonly referred to as the lanthanides [1]. Rigid composite disk, hard or soft, used for fine grinding. See also Rigid grinding disk. (1) Increase the carbon content of molten cast iron or steel by adding carbonaceous material, high-carbon pig iron or a high carbon alloy. (2) Carburize a metal part to return surface carbon loss in processing [1].

Glossary

Recrystallization

Reflected light

Refractory

Refractory alloy

Refractory metal Relief

Removal rate

717

The formation of a new grain structure through nucleation and growth commonly produced by subjecting a metal, that may be strained, to suitable conditions of time and temperature [3]. In the metallographic/materialographic microscope the specimen is illuminated with reflected (incident) light. For examination of mineralogical thin sections and in biology the transmitted light is used. (1) Material of very high melting point with properties that make it suitable for furnace linings and kiln construction. (2) Quality of resisting heat [1]. (1) Heat-resistant alloy. (2) Alloy having an extremely high melting point. (3) An alloy difficult to work at elevated temperatures [1]. Metal with an extremely high melting point, above the range of iron, cobalt, and nickel (Mo, V, W, Ta, Nb) [3]. Due to varying hardness or wear rate of a matrix or individual phases, or both; material is removed at different rates, and relief is developed [3]. The rate at which material is removed from a surface during grinding and polishing. See also Polishing rate.

718

Replica


A reproduction of a surface in a material, for example, a plastic. (1) Atomic. A thin replica devoid of structure on the molecular level, prepared by the vacuum or hydrolytic deposition of metals or simple compounds of low molecular weight. (2) Cast. A reproduction of a surface in plastic made by the evaporation of the solvent from a solution of the plastic or by polymerization of a monomer on the surface. (3) Collodion. A replica of a surface cast in nitro-cellulose. (4) Formvar. A reproduction of a surface in a plastic Formvar film. (5) Gelatin. A reproduction of a surface prepared in a film composed of gelatin. (6) Impression. A surface replica which is made by impression. The results of making an impression. (7) Molecular. The reproduction of a surface in a high polymer such as collodion and other plastics. (8) Negative. That replica which is obtained by the direct contact of the replicating material with the specimen. In it, the contour of the replica surface is reversed with respect to that of the original. (9) Oxide film. A thin film of an oxide of the specimen to be examined. The replica is prepared by air, oxygen, chemical, or electrochemical oxidation of the parent metal and is subsequently freed either mechanically or chemically for purposes of examination. (10) Plastic. A reproduction in plastic of the surface to be studied, prepared by evaporation of the solvent from a solution of plastic, by polymerization of a monomer, or solidification of a plastic on the surface. (11) Positive. A replica, the contours of which correspond directly to the surface being replicated; that is, elevations on the surface are elevations on the replica. (12) Preshadowed. A replica formed by the application of the shadowing material to a surface to be replicated, before the thin replica film is cast or otherwise deposited on the surface. (13) Pseudo. A replica which has portions of the material being replicated embedded in it. (14) Tape replica method (faxfilm). A method of producing a replica by pressing the softened surface of a tape or sheet of a plastic material on the surface to be replicated. (15) Vapor deposited—a replica formed of a metal or a salt by the condensation of the vapors of the material onto the surface to be replicated [2].

Glossary

Reproducibility

Resolution

719

The ability to achieve the same result every time. In specimen preparation reproducibility is crucial, as specimen preparation is often employed in quality inspection and failure analysis. Reproducibility can be ensured by using consumables of high standard and uniform quality, and by using automatic preparation equipment which controls preparation parameters, e.g., rotational speed, force, dosing levels, and time [3]. The fineness of detail in an object which is revealed by an optical device. Resolution is usually specified as the minimum distance by which two lines or points in the object must be separated before they can be revealed as separate lines or points in the image. The theoretical limit of resolution is determined from the equation: d = 0.61␭/共n sin A.A./2兲 where d

=

minimum distance between object points observed as distinct points in the image;

␭

=

wavelength of the radiation employed;

n

=

the minimum refractive index of the media between the object and the objective lens;

the angular aperture 关2兴. See also Resolving power. The ability of a given lens system to reveal fine detail in an object 关2兴. See also Resolution. A system of lines, circles, dots, cross hair or wires, or some other pattern, placed in the eyepiece or an intermediate plane on the optic axis which is used as a measuring reference, focusing target, or to define a camera field of view 共a reticle is different than a graticule兲关2兴. See also Graticule. A nonfabric support surface, such as a composite of metal/ceramic or metal/polymer, charged during use with an abrasive 共usually 6 to 15 micrometre diamond particles兲 and used for grinding operations in a metallographic preparation 关2兴. See also RCD. Indentation hardness test based on the depth of penetration of a specified penetrator 共cone or ball兲 into a specimen under a specified load 关3兴. Relatively finely spaced surface irregularities, the heights, width, and directions of which establish the predominant surface pattern 关1兴.

A.A. Resolving power Reticle

Rigid grinding disk

Rockwell hardness test Roughness

=

720


Rough polishing

Scanning microscope

Scratches Secondary etching

Segregation Segregation „coring… etching SEM

SG iron Shear

Short-term etching Shrinkage Shrinkage cavity Shrinkage gaps Single specimen

A polishing process after fine grinding to remove the layer of significant damage caused by the grinding. Rough polishing is followed by the steps polishing and final polishing to finish the specimen preparation. See also Final polishing, Oxide polishing, Polishing. An electron microscope in which the image is formed by a beam operating in synchronism with an electron probe scanning the object. The intensity of the image forming beam is proportional to the scattering or secondary emission of the specimen where the probe strikes it 关2兴. See also SEM. A groove produced in a surface by an abrasive point 关1兴. Develops the microstructures that differ from primary structures through transformation and heat treatment in the solid state 关4兴. See also Primary etching. Concentration of alloying elements in specific regions in a metallic object 关2兴. Develops segregation 共coring兲 mainly in macrostructures and microstructures of castings 关4兴. Scanning Electron Microscope is a type of electron microscope capable of producing high resolution images of a specimen surface. Due to the manner in which the image is created, SEM images have a characteristic three-dimensional appearance and are useful for judging the surface structure of the specimen 关3兴. See also Scanning microscope. See Ductile cast iron. 共1兲 That type of force that causes or tends to cause two contiguous parts of the same body to slide relative to each other in a direction parallel to their plane of contact. 共2兲 A type of cutting tool with which a material in the form of wire, sheet, plate, or rod is cut between two opposing blades. 共3兲 The type of cutting action produced by rake so that the direction of chip flow is other than at right angles to the cutting edge 关1兴. Etching time of seconds to a few minutes 关4兴. Reduction in volume of a material from beginning to end of solidification 关3兴. A void left in cast metals as a result of solidification shrinkage 关1兴. Gaps are voids between the mounting resin and sample material caused by shrinkage of the mounting resin 关3兴. Single specimens can be prepared on preparation systems using specimen mover plates. The specimens are not clamped and force is applied to each individual specimen 关3兴.

Glossary

Sintering Slag

Slip Slip lines

Smearing

Soldering Specimen

Specimen holder „metallography/ materialography… Spheroidal cast iron „SG… Spheroidite

Spheroidizing Stage Stage micrometre Staining

721

Bonding of particles in a mass of metal powder by heating, usually with prior compacting 关3兴. Nonmetallic product resulting from the dissolution of flux and nonmetallic impurities in smelting, refining, and certain welding operations 关1兴. See also Inclusions. Translation of a portion of a crystal relative to the adjacent portion 关2兴. Traces of slip planes observed at low magnifications on the polished surface of a crystal which has been deformed after polishing; since no differences in orientation exist, repolishing will remove the traces. With increasing resolving power and magnification, an individual line may be revealed as a series of parallel lines. The “line” which is visible at low magnifications is then described as a slip band 关2兴. Plastic deformation of a soft matrix or soft phases. Instead of being cut, the material is pushed, moved across the surface. Smearing occurs when the abrasive is too small or when using the wrong lubricant or polishing cloth, or a combination of these conditions, which reduces the cutting effect of the abrasive 关3兴. Bonding of metals using filler metals at temperatures below 450° C 关3兴. A test object, often of standard dimensions or configuration, or both, which is used for destructive and nondestructive testing. One or more specimens may be cut from each unit of a sample 关1兴. A holder in which 3–12 specimens are clamped. During specimen preparation force is applied to the center of the holder 关3兴. Same as nodular cast iron or ductile cast iron. See also Nodular cast iron. A coarse aggregate of carbide and ferrite usually produced by tempering martensite at temperatures slightly below the eutectoid temperature. Generally, any aggregate of ferrite and large spheroidal carbide particles no matter how produced 关2兴. Heating and cooling to produce a spheroidizing or globular form of carbide in steel 关1兴. A device for holding a specimen in the desired position in the optical path 关2兴. A graduated scale used on the stage of a microscope for calibration 关2兴. Staining is a discoloration of the specimen surface, typically caused by water, alcohol, or etching solutions 关3兴.

722


Stainless steel Steel

Stereology

Stereomicroscope

Strain hardening

Stringer

Structure

Subgrain

Substrate Superalloy

Swab etching

Swarf Technical ceramics

Any of several steels containing 12 to 30 % chromium as the principal alloying element 关1兴. Malleable iron-base alloy, containing carbon and other alloying elements. Carbon and low-alloy steels contain a maximum of 2 % carbon, high-alloy steels up to 2.5 % carbon and over 8 % metallic alloying elements 关3兴. The study of mathematical procedures used to derive three-dimensional parameters describing a structure from two-dimensional measurement 关2兴. A light optical microscope that permits each eye to examine the specimen at a slightly different angle, thereby retaining its three-dimensional relationship 关2兴. An increase in hardness and strength caused by plastic deformation at temperatures below the recrystallization range 关1兴. A single, high-aspect ratio, elongated inclusion, two or more elongated inclusions, or a number of small nondeformable inclusions aligned in a linear pattern due to deformation 关2兴. See also Inclusions. As applied to a crystal, the shape and size of the unit cell and the location of all atoms within the unit cell. As applied to microstructure, the size, shape, and arrangement of phases 关2兴. See also True structure, Polishing. A portion of a crystal or grain, with an orientation slightly different from the orientation of neighboring portions of the same crystal or grain 关1兴. 共Substratum兲 that which lies under 关2兴. Same as heat-resistant alloy; superalloys are heat and corrosion resistant and ductile and contain up to 20 % chromium 共Cr兲关3兴. See also Heat-resistant alloy. Wiping the specimen surface with cotton saturated with an etchant. This will simultaneously remove undesired reaction products 关4兴. Mixture of chips, abrasive material, and lubricating medium developing during grinding/polishing. Pressed and sintered oxides, carbides, and nitrides. They are very dense, insulators, highly wear resistant, and resistant against chemicals: aluminum oxide 共Al2O3兲, silicon carbide 共SiC兲, silicon nitride 共Si3N4兲, tungsten carbide 共WC兲, titanium carbide 共TiC兲, boron carbide 共B4C兲, titanium boride 共TiB2兲, zirconium oxide 共ZrO2兲关3兴.

Glossary

TEM

Tensile testing

Thermal Thermal etching

Thermoplastic resins Thermosetting resins Thin foil Tool steel

Traditional ceramics Transmission microscope True structure

Twin bands

Ultrasonic cleaning

723

The Transmission Electron Microscope is an imaging instrument whereby a beam of electrons is focused onto a specimen causing an enlarged version to appear on a fluorescent screen or layer of photographic film or can be detected by a CCD camera 关3兴. See also Thin foil, Transmission microscope. To determine the strength of a material by pulling a sample applying equal and constant stress until it breaks. The elongation of the sample is also measured. Also known as tension testing 关3兴. Any physical process taking place due to heat 关3兴. Annealing the specimen in a vacuum or inert atmosphere. This is a preferred technique for high-temperature microscopy and for ceramics 关4兴. Mounting resins that soften or melt at elevated temperatures and harden during cooling 关3兴. Mounting resins that cure under heat and pressure and cannot be melted after curing. They are also called duroplastics 关3兴. A very thin specimen prepared for transmission microscopy. See also TEM. Any of a class of carbon and alloy steels commonly used to make tools. Tool steels are characterized by high hardness and resistance to abrasion, often accompanied by high toughness and resistance to softening at elevated temperature. These attributes are generally attained with medium carbon and high-alloy contents 关1兴. Earthenware, brick, clay, porcelain 关3兴. A microscope in which the image forming rays pass through 共are transmitted by兲 the specimen being observed 关2兴. See also TEM. The microstructure representing the material without any influences from the preparation of the specimen. See also Structure, Polishing. Bands across a crystal grain, observed on a polished and etched section, the crystallographic orientations of which have a mirror image relationship to the orientation of the matrix grain across a composition plane which usually is parallel to the sides of the band. 共1兲 Annealing twins— twin bands which are produced during annealing following cold work. 共2兲 Mechanical twins—twin bands which are produced by cold work. 共3兲 Neumann bands— mechanical twins in ferrite 关2兴. Immersion cleaning aided by ultrasonic waves that cause microagitation 关1兴.

724


Ultrasonic testing

Vibratory polishing

Vickers

Vickers hardness test

Weld Welding

Weld structure Wet etching

Whiskers White cast iron

White metal

Wire cutting

Workability Work hardening Working distance

Nondestructive test used on sound conductive materials to locate cavities, cracks, and structural discontinuities by means of ultrasonic impulse 关3兴. Mechanical polishing process where one or several specimens are moved around in a bowl through vibration of the bottom of the bowl. In a more restricted sense, the 136° diamond pyramid indenter used in microindentation hardness tests 关2兴. See also Micro indentation hardness, Micro penetration hardness, Vickers hardness test. Indentation hardness test using a pyramid-shaped diamond indenter and variable loads which enables the use of one hardness scale for all materials from very soft lead to tungsten carbide 关3兴. See also Micro indentation hardness, Micro penetration hardness, Vickers. Union between materials by welding 关3兴. See also Welding. Joining two or more pieces of metal by applying heat or pressure, or both, with or without a filler material, to produce a localized union through fusion or recrystallization across the interface 关1兴. The microstructure of a weld deposit and heat-affected base metal 关2兴. See also Welding. The specimen surface has to be wetted before immersion into the etching solution. This is important for color etchants 关4兴. Metallic or ceramic filaments, mostly microscopic, more or less evenly distributed in a matrix 关3兴. Cast iron that shows a white fracture because the carbon is present in the form of iron carbide, Fe3C, which gives it its very high hardness and also brittleness 关3兴. A general term covering a group of white-colored metals and their alloys of relatively low melting points 共lead, antimony, tin, cadmium, bismuth, and zinc兲 and alloys based on these metals 关1兴. A cutting method mainly used for sectioning of small specimens of various types of materials. A fine wire is drawn along the work piece with a controlled force. The abrasive is either diamond bonded to the wire, or an abrasive slurry that is dripped continuously onto the wire and drawn into the cut 关3兴. See Formability. A change in the hardness of a material as a result of plastic deformation 关2兴. The distance between the surface of the specimen being examined and the front surface of the objective lens 关2兴.

Glossary

Wrought iron

X-ray testing

Young’s modulus

725

An iron produced by direct reduction or ore or by refining molten cast iron under conditions where a pasty mass of solid iron with included slag is produced. The iron has a low carbon content 关1兴. Using X-ray radiation to check work pieces for cavities, cracks, pores, and overlaps. Especially used for checking of welds 关3兴. A term used synonymously with modulus of elasticity. The ratio of tensile or compressive stresses to the resulting strain 关1兴. See also Modulus of elasticity.

References „Glossary… [1] Benscoter, A. O. and Bramfitt, B. L., Metallographer’s Guide, Practices and Procedures for Irons and Steels, ASM International, Materials Park, Ohio, USA, 2002. Reprinted with permission of ASM International®. All rights reserved. www. asminternational.org [2] ASTM Standard, Terminology Relating to Metallography 共E 7兲, ASTM International, West Conshohocken, Pennsylvania, USA, 2003. [3] Terms defined by Struers in the on-line training material e-Education and e-Training under www.struers.com. [4] Petzow, G., Metallographic Etching, ASM International, Materials Park, Ohio, USA, 1999.

Subject Index A Abbreviations occupational safety and health, labs, 673–674 specimen preparation, 221 Abrasive cut-off machines, 36–43 design principles of wheel-work piece contact, 36–39 machine designs, 39–43 Abrasive cut-off wheels, 32–36 consumable wheels, 32–34 slow consumable wheels, 34–36 Abrasives, 18–19 aluminum oxide, 18 cubic boron nitride, 18 diamond, 18–19 polishing, 129–132 silicon carbide, 18 wet abrasive cutting, sectioning, 16–21 Acrylics occupational safety and health, labs, 668 specimen preparation, 436–439 After preparation cleaning, 82–84 Agency for Toxic Substance and Disease Registry 共ATSDR兲, 683–684 Alcohol-based grinding/polishing fluids, 97 Alumina wet grinding paper, 105–106 Aluminum electrolytic polishing and etching, 464 specimen preparation, 352–356 Aluminum alloys, 356–358 Aluminum oxide abrasive types, 18 grinding abrasives, 93 specimen preparation, 238–240 American Conference of Government Industrial Hygienists 共ACGIH兲, 683 Analog cameras, automatic image analysis, 614–615 Anodic etching, 172–173 Anodized coatings, specimen preparation, 247–251 Anodizing, etching, 173 Antimony, specimen preparation, 361–364

Arc of contact, metallographic/ materialographic cutting operation, 31 Archiving, 619 Artifacts of electrolytic polishing, selection of preparation method, 7 ASTM B 487, 576 ASTM C 664, 576 ASTM E 45, 570 ASTM E 112, 571–573 ASTM E 562, 569 ASTM E 930, 573 ASTM E 1077, 575 ASTM E 1122, 570 ASTM E 1181, 573 ASTM E 1245, 570 ASTM E 1268, 574 ASTM E 1382, 573 ASTM E 1578, 619 ASTM E 2014, 668, 674 ASTM E 2109, 574–575 ASTM standards cutting fluids, wet abrasive cutting, 29 hardness, 625 metallography, 188–193 Atomic force microscope 共AFM兲, 561 Automatic grinding equipment, 119, 135 Automatic image analysis, 577–617 analog cameras, 614–615 automatic measurements, 600–602 background correction, 586–588 banding degree, 608 brightness and contrast, 581–586 cameras, 614–615 compacted graphite, 613 computers, 614 contrast stretching, 588–589 depth measurements, 608–610 digital cameras, 615–616 digital imaging, 579, 602–613 digital imaging technology, 613–616 ductile cast iron, 611–613 grain size, 606–608 graphite in iron castings, 610–611 gray cast iron, 613 hardware, 613–616 727

728


histogram, 581 image acquisition, 579–580 image calibration, 595–598 image digitization, 580–581 image measurement, 598–602 image processing, 586–595 implementation, 617–618 inclusion rating, 603–606 manual measurements, 599–600 open source/public domain software, 617 percent area, 602–603 printers, 616 sharpening, 593–595 smoothing, 592–593 software, 616–617 thickness measurements, 608–610 volume fraction, 602–603 watershed filter, 590–592 Automatic measurements, automatic image analysis, 600–602 Automatic systems, polishing, 140–143 Automation labs, 651–654 Availability of NIOSH Registry of Toxic Effects of Chemical Substances, 681

Bias, quantitative metallography/ materialography, 568–569 Blades, bandsawing, 49–51 Bond materials cut-off wheel, 20–21 wet abrasive cutting, sectioning, 16–21 Bones, specimen preparation, 427–430 Boron carbide grinding abrasives, 97 specimen preparation, 227–232 Brass, specimen preparation, 376–380 Brightness and contrast, automatic image analysis, 581–586 Brinell hardness testing, 626–628 British Standards Institution, 684 Brittle materials, grinding, 92–93 Bronze electrolytic polishing and etching, 467 specimen preparation, 376–380 Building labs, 649, 650–663

B

Calcium oxide, specimen preparation, 241 Calibration, quantitative metallography/materialography, 568 Cameras, automatic image analysis, 614–615 Capacitors, specimen preparation, 298–300 Carbonitrided steels, specimen preparation, 339–342 Cement clinker, specimen preparation, 346–349 Cemented carbides, 187 Ceramic capacitors, specimen preparation, 281–284 Ceramic layers, specimen preparation, 268–270 Ceramic resistors, specimen preparation, 281–284 Ceramics deformation, grinding, 92–93 specimen material, 182 specimen preparation, 232–235

Background correction, automatic image analysis, 586–588 Bacteria and fungi, cutting fluids, wet abrasive cutting, 28–29 Bakelite bond, 20–21 Banding, quantitative metallography/ materialography, 574 Banding degree, automatic image analysis, 608 Bandsawing, 48–52 blades, 49–51 cutting fluids, 51 machines, 49–51 safety, 49 tips, 51–52 Barium titanate, specimen preparation, 241 Baumann hammer, 644 Before preparation start cleaning, 82 Beryllium, specimen preparation, 365–367

C

Subject Index

Cerium oxide, specimen preparation, 241 Chemical disposals, occupational safety and health, labs, 672–673 Chemical etching, 172 Chemical mechanical polishing 共CMP兲, 7, 151–152 Chemical microetching, examination purpose, 194–217 Chemical polishing, 7 electrolytic polishing/etching, 168 Chips, sliding, plowing, grinding mechanics, 22 Chromium electrolytic polishing and etching, 464–465 specimen preparation, 367–370 Chromium carbide, specimen preparation, 232–235 Chromium oxide, specimen preparation, 238–240 Circular sawing, 48 Clamping, thermal damage, wet abrasive cutting, 24–25 Classical etching, 172 Classification of materials, specimen material, 181 Cleaning, 82–84 after preparation, 82–84 drying, 83 ethanol, 83 grinding disks, 84 hand, 82–83 polishing cloths, 84 before preparation start, 82 rubbing effect, 83 ultrasonic, 83 ultrasonic apparatuses, 83 Cleanliness, 84 Cloths, polishing, 124–129 Coatings, specimen material, 182–183 Cobalt electrolytic polishing and etching, 465–466 specimen preparation, 370–373 Cobalt-based super alloys, specimen preparation, 373–376 Cold mounting resins, occupational safety and health, labs, 667

729

Color etching, 172 Color ratings system, occupational safety and health, labs, 669 Compacted graphite, automatic image analysis, 613 Comparison procedure, quantitative metallography/materialography, 571–572 Composites specimen material, 183 specimen preparation, 276–281 Compressed air, cleaning, 83 Computers, automatic image analysis, 614 Concrete, specimen preparation, 346–349 Confocal laser scan microscope, 552–555 Consumable abrasive cut-off wheels storing, 33–34 wheel dimensions, 33 wheel velocity, 32–33 Consumables, specimen preparation, 221 Contemporary grinding, 106–117 diamond film, 109 diamond pads, 109 fine grinding cloths, 116 magnetic fixation, 106–107 metal-bonded diamond-coated disks, 109 resin-bonded diamond grinding disks, 107–108 resin-bonded SiC grinding disks, 108 rigid composite disks, 109–116 Contrast stretching, automatic image analysis, 588–589 Cooling, cutting fluids, 26 Cooling system, cutting fluids, wet abrasive cutting, 27–28 Copper electrolytic polishing and etching, 466 specimen preparation, 376–380 Copper-bearing alloys, specimen preparation, 380–383 Cubic boron nitride, abrasive types, 18

730


Cubic boron nitride 共CBN兲, grinding abrasives, 97 Cut-off grinding process, wet abrasive cutting, sectioning, 15–16 Cut-off wheel abrasive types, 18–19 bond material, 20–21 grade, 20 grain size, 19–20 rpm, 30 selection, 44–45 specifications, 16–18 structure, 20 truing and dressing, 26 wear, 25–26 wet abrasive cutting, sectioning, 16–21 Cutting fluids, 26–29 ASTM standards, 29 bacteria and fungi, 28–29 bandsawing, 51 cooling system, 27–28 grinding fluid application, 27 grinding fluid concentration, 28 grinding fluid disposal, 29 health and safety aspects, 29 lubrication and cooling, 26 synthetic grinding fluids-oilbased, 26–27 water quality, 28 CVD coatings, specimen preparation, 247–251

D Dangers, occupational safety and health, labs, 664 Dark-field illumination 共DF兲, etching, 169 Decarburization, quantitative metallography/materialography, 575–576 Deformation, 89–93 brittle materials, 92–93 ceramics, 92–93 grinding, 86 metals, 89–92 polishing, 122–124

Depth measurements, automatic image analysis, 608–610 Design principles of wheel-work piece contact abrasive cut-off machines, 36–39 direct cutting, 36 oscillating cutting, 36–37 rotating work piece, 39 step cutting, 38–39 Diamond products abrasive types, 18–19 film, 109 fixed grains, 95 grinding abrasives, 94–96 loose grains, 95–96 monocrystalline, 94 pads, 109 pastes, 96 polycrystalline, 94 sprays, 96 suspensions, 96 Differential interference contrast 共DIC兲, etching, 169 Diffusion coatings, specimen preparation, 251–254 Digital cameras, automatic image analysis, 615–616 Digital image management, 619 Digital imaging, automatic image analysis, 579, 602–613 Digital imaging technology, automatic image analysis, 613–616 Diodes, specimen preparation, 281–284 Direct cutting, design principles of wheel-work piece contact, 36 Documentation, optical reflected light microscope, 550–552 Drying, cleaning, 83 Ductile cast iron, automatic image analysis, 611–613 Dust, occupational safety and health, labs, 667 Dynamic hardness testing procedures, 644–645

E Economy, grinding, traditional, 105 Edge retention, grinding, traditional, 103–105

Subject Index

Education, labs, 651 Electric discharge machining 共EDM兲, sectioning by melting, 46 Electrolytes, polishing/etching, 163–164 Electrolytic polishing and etching, 172–173, 453–475 aluminum, 464 bronze, 467 chromium, 464–465 cobalt, 465–466 copper, 466 gray cast iron, 459 hard metals, 474–475 heat treated steels, 459–460 high carbon steels, 457 high-speed steels, 462–463 iron, 462 lead, 467–468 low-alloyed tool steels, 463 low carbon steels, 457–458 magnesium, 468–469 nickel, 469 silver, 469–470 stainless steels, 460–461 super alloys, 461 tin, 470–471 titanium, 471 tungsten, 472 vanadium, 472–473 zinc, 473 zirconium, 474 Electrolytic polishing/etching, 156–168 chemical polishing, 168 electrolytes, 163–164 electrolytic thinning for transmission electron microscope 共TEM兲, 167–168 electropolishing in practice, 164–165 equipment, 165–166 field metallography, 166–167 nondestructive electropolishing, 166–167 occupational safety and health, labs, 665 process, 156–163 Electrolytic polishing etching, artifacts, 7 Electrolytic thinning for transmission

731

electron microscope 共TEM兲, 167–168 Electrolytically deposited coatings, 251–254 Electron backscatter diffraction 共EBSD兲, 559–560 polishing, 149–150 Electron microscopy, 558–561 atomic force microscope 共AFM兲, 561 electron backscatter diffraction 共EBSD兲, 559–560 electron probe microanalyzer 共EPMA兲, 560 energy dispersive spectroscopy 共EDS兲, 559 focused ion beam 共FIB兲, 560 magnetic force microscopy 共MFM兲, 561 scanning electron microscope 共SEM兲, 558–559 scanning probe microscopes 共SPM兲, 560–561 scanning transmission electron microscope 共STEM兲, 558 transmission electron microscope 共TEM兲, 558 Electron probe microanalyzer 共EPMA兲, 560 Electropolishing in practice, 164–165 Energy dispersive spectroscopy 共EDS兲, 559 Engraving, marking, 80 Environment, grinding, traditional, 105 Environmental Protection Agency 共EPA兲, 683 EPDM polymers, 430–436 Epoxy, occupational safety and health, labs, 667 Equipment electrolytic polishing/etching, 165–166 labs, 656–660 Equotip tester, 645 Etchant names, examination purpose, 217 Etching, 169–176 anodic, 172–173 anodizing, 173 chemical, 172

732


classical, 172 color, 172 dark-field illumination 共DF兲, 169 differential interference contrast 共DIC兲, 169 electrolytic, 172–173 examination purpose, 194 fluorescence, 170 grain boundary etching, 171 grain contrast etching, 170–171 heat tinting, 172 ion, 173–174 macroetching, 174–175 microetching, 169 microscope techniques, 169–170 occupational safety and health, labs, 665–666 physical, 173–174 polarized light 共POL兲, 169–170 potentiostatic, 173 precipitation, 172 preparation process, 13 reactive sputtering, 174 relief polishing, 173 reproducibility, 171–172 sputtering, 174 thermal, 174 vapor deposition, 174 Ethanol, cleaning, 83 European Union 共EU兲, occupational safety and health, labs, 669–670, 684 Examination purpose, 179, 188 ASTM standards, 188–217 chemical microetching, 194–217 etchant names, 217 etching practice, 194 Eyepieces, optical reflected light microscope, 535–536

F Failure analysis, labs, 651 Feed speed, metallographic/ materialographic cutting operation, 30–31 Ferrous metals, specimen material, 183–184 Field metallography

electrolytic polishing/etching, 166–167 polishing, 150–151 Field metallography/materialography, specimen preparation, 475–476 Field selection, quantitative metallography/materialography, 568–569 Fine grinding, 86, 119 Fine grinding cloths, 116 Fixed grains, diamond products, 95 Flammable and Combustible Liquids, 680 Flammable liquids, occupational safety and health, labs, 667 Fluorescence, etching, 170 Focused ion beam 共FIB兲, 560 Force material removal, grinding, 89 metallographic/materialographic cutting operation, 30 Fracturing, sectioning, 45 Free cutting, 31–32 automatics, 32 hand, 32

G Galvanization, specimen preparation, 251–254 General Description and Discussion of the Levels of Protection and Protective Gear, 680–681 General studies or routine work, 14 General use, machine designs, abrasive cut-off, 40–41 Generic methods, specimen preparation, 219 Germanium, specimen preparation, 288–291 Glasses, specimen preparation, 244–247 Gold, specimen preparation, 384–387 Grades cut-off wheel, 20 hard, 20 soft, 20 Grain boundary etching, 171 Grain contrast etching, 170–171

Subject Index

Grain penetration, material removal, grinding, 89 Grain shape, material removal, grinding, 88 Grain size automatic image analysis, 606–608 cut-off wheel, 19–20 quantitative metallography/ materialography, 571–573 Graphite in iron castings, automatic image analysis, 610–611 Gray cast iron automatic image analysis, 613 electrolytic polishing and etching, 459 specimen preparation, 315–318 Grinding, 85–86 chips, sliding, plowing, 22 contemporary, 106–117 deformation, 86, 89–93 fine, 86 material removal, 86–89 plane, 85 traditional, 99–106 wet abrasive cutting, sectioning, 21–22 Grinding, traditional, 99–106 alumina wet grinding paper, 105–106 economy, 105 edge retention, 103–105 environment, 105 relief, 103–105 SiC wet grinding paper, 100–105 stones/disks, 99–100 zirconia alumina wet grinding paper, 105–106 Grinding abrasives, 93–97 aluminum oxide, 93 boron carbide, 97 cubic boron nitride 共CBN兲, 97 diamond, 94–96 silicon carbide, 93 Grinding disks cleaning, 84 Grinding fluid application, 27 concentration, 28 disposal, 29

733

Grinding/polishing equipment, 117–119 automatic grinding, 119 fine grinding, 119 manual grinding, 117–119 plane grinding, 117–119 Grinding/polishing fluids, 89, 97–99 alcohol-based, 97 oil-based, 98–99 water-based, 97 water-oil based, 98 Grit number, 19

H Hacksawing, 48 Hand cleaning, 82–83 Hard grade, 20 Hard metals, electrolytic polishing and etching, 474–475 Hardness, 623–625 ASTM standards, 625 indentation, 623–624 testing special methods, 646 Hardness values conversion, 642–643 precision, 642 Hardware, automatic image analysis, 613–616 Hazard Communication Standard 共HCS兲, OSHA standard, 674–679 Health and safety aspects, cutting fluids, 29 Heat tinting, etching, 172 Heat treated steels, electrolytic polishing and etching, 459–460 High-alloy steels, specimen preparation, 325–328 High carbon steels electrolytic polishing and etching, 457 specimen preparation, 307–311 High-speed steels electrolytic polishing and etching, 462–463 specimen preparation, 343–346 Histogram, automatic image analysis, 581 HMIS, occupational safety and health, labs, 670

734


Hot dip zinc coatings, specimen preparation, 254–257 Human eye, light microscopy, 526–527 Hydroxyapatite 共HA兲 coating, specimen preparation, 223–226

I Identification tag marking, 80 Illumination, optical reflected light microscope, 536–537 Image acquisition, 579–580 calibration, 595–598 digitization, 580–581 measurement, automatic image analysis, 598–602 processing, automatic image analysis, 586–595 Implementation, automatic image analysis, 617–618 Inclusion rating automatic image analysis, 603–606 quantitative metallography/ materialography, 570 Indentation hardness, 623–624 Instrumented indentation testing, 641–642 Integrated circuits. specimen preparation, 301–305 Intercept procedure, quantitative metallography/materialography, 572–573 International Chemical Safety Cards, 682–683 Ion etching, 173–174 Iron, electrolytic polishing and etching, 462

J Job Safety Analysis 共JSA兲, 670–672

K Knoop hardness testing, 633–634

L Laboratory information management systems 共LIMS兲, 619 Labs, 649 automation, 651–654 building, 649, 650–663 education, 651 equipment, 656–660 failure analysis, 651 layout, 660–662 maintenance, 662–663 occupational safety and health, 649, 664–684 planning, 654–656 purpose, 650 quality control, 650 rationalization, 651–654 research, 651 running, 649 testing and inspection labs, 651 Laser torching, sectioning by melting, 46 Layout, labs, 660–662 Lead electrolytic polishing and etching, 467–468 specimen preparation, 387–391 Light microscopy, 525–527 human eye, 526–527 magnification, 527 magnifying lens and microscope, 527 visible light, 525–526 List of Highly Hazardous Chemicals, Toxics and Reactives, OSHA standards, 680 Literature, occupational safety and health, labs, 684–686 Loose grains, diamond products, 95–96 Low-alloy steels, specimen preparation, 336–339 Low-alloyed steels, electrolytic polishing and etching, 463 Low carbon steels electrolytic polishing and etching, 457–458 specimen preparation, 311–314 Lubricants, 97–99

Subject Index

cutting fluids, 26

M Machine designs, 39–43 general use, 40–41 polishing, 135–139 precision, 41–43 Machines, bandsawing, 49–51 Macroetching, 174–175 Magnesium electrolytic polishing and etching, 468–469 specimen preparation, 391–394 Magnesium oxide, specimen preparation, 241 Magnetic fixation, contemporary grinding, 106–107 Magnetic force microscopy 共MFM兲, 561 Magnification, light microscopy, 527 Magnifying lens and microscope, 527 Maintenance, labs, 662–663, 673 Malleable cast iron, specimen preparation, 315–318 Manganese, specimen preparation, 395–397 Manual grinding equipment, 117–119, 135 Manual measurements, automatic image analysis, 599–600 Marking, 80 engraving, 80 identification tag, 80 stamping, 80 with waterproof ink, 80 Martens scratch hardness, 646 Material exam, 179 Material removal, 86–89 force on specimens, 89 grain penetration, 89 grain shape, 88 grinding, 86 grinding/polishing fluids, 89 polishing, 120–122 rake angle, 87–88 Material Safety Data Sheet 共MSDS兲, occupational safety and health, labs, 670–672 Materialographic specimen, 7–9

735

specimen or sample, 8–9 Materialography, 3 Mechanical damage, wet abrasive cutting, 22–23 unplane surface, 23 waviness, 23 Mechanical polishing artifacts, selection of preparation method, 7 Mechanical preparation, occupational safety and health, labs, 665 Mechanical surface preparation. see grinding Medium carbon steels, specimen preparation, 307–311 Metal-bonded diamond-coated disks, contemporary grinding, 109 Metallographic/materialographic cutting operation arc of contact, 31 cut-off wheel rpm, 30 feed speed, 30–31 force, 30 free cutting, 31–32 power, 31 wet abrasive cutting, sectioning, 29–32 wheel velocity, 30 Metallographic/materialographic preparation, 5–6 Metallography, 3 Metals, deformation, grinding, 89–92 Microelectronic material, specimen preparation, 291–293 Microelectronic materials, polishing, 143–147 Microelectronic packages polishing, 147–149 specimen preparation, 295–298, 301–305 Microetching, 169 Microindentation hardness, 636–639 Microscopes options, 537–538 techniques, etching, 169–170 Microtomy, polishing, 155 Mineralogical materials, specimen material, 184 Minerals, ores, specimen preparation, 349–352

736


Mohs scratch hardness, 646 Molybdenum, specimen preparation, 398–401 Monocrystalline, diamond products, 94 Mounting occupational safety and health, labs, 664–665 preparation process, 11

N National Fire Protection Association 共NFPA兲, 684 National Paint and Coatings Association, 684 National Technical Information Service 共NTIS兲, 683 National Toxicology Program 共NTP兲, 683 NFPA 704 Hazard Identification Ratings System, 668–669 Nickel electrolytic polishing and etching, 469 specimen preparation, 402–405 NIOSH standards, 681–682 Nodular cast iron, specimen preparation, 319–321 Nondestructive electropolishing, electrolytic polishing/etching, 166–167 Nonferrous metals, specimen material, 184–186

O Occupational Exposure to Hazardous Chemicals in Laboratories, 679–680 Occupational Safety and Health Administration 共OSHA兲 standards Availability of NIOSH Registry of Toxic Effects of Chemical Substances, 681 Flammable and Combustible Liquids, 680 General Description and Discussion of the Levels of

Protection and Protective Gear, 680–681 Hazard Communication Standard 共HCS兲, 674–679 List of Highly Hazardous Chemicals, Toxics and Reactives, 680 Occupational Exposure to Hazardous Chemicals in Laboratories, 679–680 Occupational safety and health labs, 649, 664–684 abbreviations, 673–674 acrylics, 668 Agency for Toxic Substance and Disease Registry 共ATSDR兲, 683–684 American Conference of Government Industrial Hygienists 共ACGIH兲, 683 ASTM E 2014, 668, 674 British Standards Institution, 684 chemical disposals, 672–673 cold mounting resins, 667 color ratings system, 669 dangers, 664 dust, 667 electrolytic polishing/etching, 665 Environmental Protection Agency 共EPA兲, 683 epoxy, 667 etching, 665–666 EU system, 669–670 European Union 共EU兲, 684 flammable liquids, 667 HMIS, 670 International Chemical Safety Cards, 682–683 Job Safety Analysis 共JSA兲, 670–672 literature, 684–686 maintenance and service, 673 Material Safety Data Sheet 共MSDS兲, 670–672 mechanical preparation, 665 mounting, 664–665 National Fire Protection Association 共NFPA兲, 684 National Paint and Coatings Association, 684

Subject Index

National Technical Information Service 共NTIS兲, 683 National Toxicology Program 共NTP兲, 683 NFPA 704 Hazard Identification Ratings System, 668–669 NIOSH standards, 681–682 OSHA standards, 674–681 polyesters, 668 risk phrases, 670 safety information, 668–672 sectioning, 664 Standard Operating Procedure 共SOP兲, 670–672 standards, 673 toxic substances, 666 training, 673 Oil-based grinding/polishing fluids, 98–99 Open source/public domain software, image analysis, 617 Optical examination methods, reflected light microscope, 540–546 Optical fibers, specimen preparation, 244–247 Optical reflected light microscope, 528–555 confocal laser scan microscope, 552–555 documentation, 550–552 eyepieces, 535–536 illumination, 536–537 microscope options, 537–538 optical examination methods, 540–546 path of light rays, 528 practical use of microscope, 546–550 reflected-light microscope, 538–540 stereo microscopy, 555–557 Ores, specimen preparation, 349–352 Organic materials, specimen material, 186–187 Oscillating cutting, design principles of wheel-work piece contact, 36–37 Oxyacetylene torching, 46

737

P Paint layers, specimen preparation, 257–260 Palladium, specimen preparation, 406–409 Parameters, specimen preparation, 220–221 Pastes, diamond products, 96 Path of light rays, optical reflected light microscope, 528 PCB coupon, specimen preparation, 305–307 Percent area, automatic image analysis, 602–603 Phenolic bond, 20–21 Physical etching, 173–174 Pitting, 9 Plane grinding, 85, 117–119 Planimetric procedure, quantitative metallography/materialography, 572 Planning, labs, 654–656 Plasma spray coatings, specimen preparation, 265–267, 270–273 Plasma torching, sectioning by melting, 46 Plated coatings, specimen preparation, 251–254 Point count, quantitative metallography/materialography, 569 Polarized light 共POL兲, etching, 169–170 Poldi impact hardness tester, 644 Polishing, 120–155 abrasives, 129–132 automatic grinding/polishing equipment, 135 automatic systems, 140–143 chemical mechanical polishing 共CMP兲, 151–152 cloths, 84, 124–129 deformation, 122–124 dynamics, 139–140 electron backscatter diffraction 共EBSD兲, 149–150 field metallography, 150–151 machine design, 135–139 manual grinding/polishing equipment, 135 material removal, 120–122

738


microelectronic materials, 143–147 microelectronic packages, 147–149 microtomy, 155 polishing dynamics, 139–140 preparation methods, 132–134 printed circuit boards 共PCB兲, 143 rough, 120 semiautomatic systems, 140–143 thin sections, 152–154 ultramilling, 155 Polycrystalline diamond products, 94 Polyesters, occupational safety and health, labs, 668 Polymers, specimen material, 187 Porosity in thermal spray coatings, 574–575 Potentiostatic etching, 173 Powder metals specimen material, 187 specimen preparation, 439–443 Power, metallographic/ materialographic cutting operation, 31 Power hacksawing, 48 Practical use of microscope, 546–550 Precipitation etching, 172 Precision cut-off, slow consumable wheels, 35 machine designs, abrasive, 41–43 Preparation methods polishing, 132–134 selection of preparation method, 7 Preparation process, 9–13 etching, 13 mounting, 11 sectioning, 10–11 surface preparation, 11–13 Preservation, 81 Printed circuit boards 共PCB兲, polishing, 143 Printers, automatic image analysis, 616 Process, electrolytic polishing/etching, 156–163 Punching, shearing, 47

Purpose, labs, 650 PVD coatings, specimen preparation, 247–251

Q Quality control labs, 650 Quantitative metallography/ materialography, 565–576 ASTM B 487, 576 ASTM C 664, 576 ASTM E 45, 570 ASTM E 112, 571–573 ASTM E 562, 569 ASTM E 930, 573 ASTM E 1077, 575 ASTM E 1122, 570 ASTM E 1181, 573 ASTM E 1245, 570 ASTM E 1268, 574 ASTM E 1382, 573 ASTM E 2109, 574–575 banding, 574 bias, 568–569 calibration, 568 comparison procedure, 571–572 decarburization, 575–576 field selection, 568–569 grain size, 571–573 inclusion rating, 570 intercept procedure, 572–573 other standards, 576 planimetric procedure, 572 point count, 569 porosity in thermal spray coatings, 574–575 specimen preparation, 567–568 stereology, 565–567 volume fraction, 569

R Rake angle, material removal, grinding, 87–88 Rationalization, labs, 651–654 Reactive sputtering, etching, 174 Reflected-light microscope, 538–540 Relief

Subject Index

grinding, 103–105 polishing, 173 Reporting locations, 15 Reproducibility, etching, 171–172 Research labs, 651 Research studies, 14 Resin-bonded diamond grinding disks, 107–108 Resin-bonded SiC grinding disks, 108 Resistors, specimen preparation, 293–295 Rigid composite disks, grinding, 109–116 Risk phrases, occupational safety and health, labs, 670 Rockwell hardness testing, 634–636 Rotating work piece, 39 Rough polishing, 120 Rubber bonds, 21 Rubbing effect, cleaning, 83 Running labs, 649

S Safety bandsawing, 49 occupational safety and health, labs, 668–672 Sample, materialographic specimen, 8–9 Sawing bandsawing, 48–52 circular sawing, 48 hacksawing, 48 power hacksawing, 48 sectioning, 47–52 Scanning electron microscope 共SEM兲, 558–559 Scanning probe microscopes 共SPM兲, 558–561, 560–561 Scanning transmission electron microscope 共STEM兲, 558 Scleroscope, 645 Section type, selection, sectioning, 14–15 Sectioning, 14–53, 15 abrasive cut-off machines, 36–43 abrasive cut-off wheels, 32–36 fracturing, 45

739

occupational safety and health, labs, 664 other methods, 45–53 preparation process, 10–11 sawing, 47–52 sectioning by melting, 46 selection, 14–15 shearing, 46–47 wet abrasive cutting, 15–32 wet abrasive cutting tips, 43–45 wire cutting, 52–53 Sectioning by melting, 46 electric discharge machining 共EDM兲, 46 laser torching, 46 oxyacetylene torching, 46 plasma torching, 46 Selection, sectioning, 14–15 general studies or routine work, 14 reporting locations, 15 research studies, 14 section type, 14–15 study of failures, 14 Selection of preparation method, 6–7 artifacts of electrolytic polishing, 7 artifacts of mechanical polishing, 7 preparation methods, 7 Semiautomatic systems, polishing, 140–143 Semiconductors, specimen preparation, 288–291 Sharpening, automatic image analysis, 593–595 Shearing punching, 47 sectioning, 46–47 Si wafers, specimen preparation, 288–291 SiC fibers in Ti matrix, specimen preparation, 273–276 SiC wet grinding paper, 100–105 Silicon, specimen preparation, 288–291 Silicon carbide abrasive types, 18 grinding abrasives, 93

740


Silicon nitride, specimen preparation, 235–237 Silicon oxide, specimen preparation, 241 Silver electrolytic polishing and etching, 469–470 specimen preparation, 409–412 Sintered carbides specimen material, 187 specimen preparation, 443–447 Slow consumable wheels precision cut-off, 35 storing, 36 truing and dressing, 34–35 use, 35 wheel dimensions, 35 wheel velocity, 35 Smoothing, automatic image analysis, 592–593 Soft grade, 20 Software, automatic image analysis, 616–617 Solder balls, specimen preparation, 295–298 Sorby, Henry Clifton, 5–6 Special methods hardness testing, 646 Specimen material, 179, 181–187 ceramics, 182 classification of materials, 181 coatings, 182–183 composites, 183 ferrous metals, 183–184 materialographic specimen, 8–9 mineralogical materials, 184 nonferrous metals, 184–186 organic materials, 186–187 polymers, 187 powder metals, 187 sintered carbides, 187 Specimen preparation, 179–180, 218–521 abbreviations, 221 acrylics, 436–439 aluminum, 352–356 aluminum alloys, 356–358 aluminum oxide, 238–240 anodized coatings, 247–251 antimony, 361–364

barium titanate, 241 beryllium, 365–367 bones, 427–430 boron carbide, 227–232 brass, 376–380 bronze, 376–380 calcium oxide, 241 capacitors, 298–300 carbonitrided steels, 339–342 cement clinker, 346–349 ceramic capacitors, 281–284 ceramic layers, 268–270 ceramic resistors, 281–284 ceramics, 232–235 cerium oxide, 241 chromium, 367–370 chromium carbide, 232–235 chromium oxide, 238–240 cobalt, 370–373 cobalt-based super alloys, 373–376 composites, 276–281 concrete, 346–349 consumables, 221 copper, 376–380 copper-bearing alloys, 380–383 CVD coatings, 247–251 diffusion coatings, 251–254 diodes, 281–284 electrolytic polishing and etching, 453–475 electrolytically deposited coatings, 251–254 EPDM polymers, 430–436 field metallography/ materialography, 475–476 galvanization, 251–254 generic methods, 219 germanium, 288–291 glasses, 244–247 gold, 384–387 gray cast iron, 315–318 high-alloy steels, 325–328 high carbon steels, 307–311 high-speed steels, 343–346 hot dip zinc coatings, 254–257 hydroxyapatite 共HA兲 coating, 223–226 integrated circuits, 301–305

Subject Index

lead, 387–391 low-alloy steels, 336–339 low carbon steels, 311–314 magnesium, 391–394 magnesium oxide, 241 malleable cast iron, 315–318 manganese, 395–397 medium carbon steels, 307–311 microelectronic material, 291–293 microelectronic packages, 295–298, 301–305 minerals, ores, 349–352 molybdenum, 398–401 nickel, 402–405 nodular cast iron, 319–321 optical fibers, 244–247 paint layers, 257–260 palladium, 406–409 parameters, 220–221 PCB coupon, 305–307 plasma spray coatings, 265–267, 270–273 plated coatings, 251–254 powder metals, 439–443 PVD coatings, 247–251 quantitative metallography/ materialography, 567–568 resistors, 293–295 semiconductors, 288–291 Si wafers, 288–291 SiC fibers in Ti matrix, 273–276 silicon, 288–291 silicon nitride, 235–237 silicon oxide, 241 silver, 409–412 sintered carbides, 443–447 solder balls, 295–298 stainless steels, 328–333 steps, 219–220 super alloys, 333–335 teeth, 427–430 thermal spray coatings, 260–265 tin, 413–416 tin cubic boron nitride, 232–235 tissue, 427–430 titanium, 416–420 titanium carbide, 232–235 titanium nitride, 232–235

741

transistors, 301–305 trouble shooting, 476–521 tungsten carbide, 232–235 uranium, 447–450 white cast iron, 322–324 wrought aluminum alloys, 359–361 YBCO ceramic super conductors, 285–288 zinc, 420–423 zinc oxide, 241 zirconium, 424–427 zirconium dioxide, 241 Sprays, diamond products, 96 Sputtering, etching, 174 Stainless steels electrolytic polishing and etching, 460–461 specimen preparation, 328–333 Stamping, marking, 80 Standard Operating Procedure 共SOP兲, 670–672 Standards, occupational safety and health, labs, 673 Static hardness testing, 626–643 Brinell hardness testing, 626–628 hardness values conversion, 642–643 hardness values precision, 642 instrumented indentation testing, 641–642 Knoop hardness testing, 633–634 microindentation hardness, 636–639 Rockwell hardness testing, 634–636 universal hardness, 639–642 Vickers hardness testing, 628–632 Step cutting, design principles of wheel, 38–39 Steps, specimen preparation, 219–220 Stereo microscopy, 555–557 Stereology, 565–567 Stones/disks, grinding, 99–100 Storage, 81 Storing consumable abrasive cut-off wheels, 33–34 slow consumable wheels, 36

742


Structure, cut-off wheel, 20 Study of failures, selection, sectioning, 14 Super alloys electrolytic polishing and etching, 461 specimen preparation, 333–335 Surface preparation, 11–13 Suspensions, diamond products, 96 Synthetic grinding fluids-oil-based, 26–27

T Teeth, specimen preparation, 427–430 Testing and inspection labs, 651 Thermal damage, wet abrasive cutting, 23–25 clamping, 24–25 wet cutting, 25 Thermal etching, 174 Thermal spray coatings, specimen preparation, 260–265 Thickness measurements, automatic image analysis, 608–610 Thin sections, polishing, 152–154 Tin electrolytic polishing and etching, 470–471 specimen preparation, 413–416 Tin cubic boron nitride, specimen preparation, 232–235 Tissue, specimen preparation, 427–430 Titanium electrolytic polishing and etching, 471 specimen preparation, 416–420 Titanium carbide, specimen preparation, 232–235 Titanium nitride, specimen preparation, 232–235 Toxic substances, occupational safety and health, labs, 666 Traditional grinding, 99–106 Traditional versus contemporary methods, specimen preparation, 218 Training, occupational safety and health, labs, 673

Transistors, specimen preparation, 301–305 Transmission electron microscope 共TEM兲, 558 Trouble shooting, specimen preparation, 476–521 True microstructure, 5–6, 6 Truing and dressing cut-off wheel wear, wet abrasive cutting, 26 slow consumable wheels, 34–35 Tungsten, electrolytic polishing and etching, 472 Tungsten carbide, specimen preparation, 232–235

U Ultramilling, polishing, 155 Ultrasonic apparatuses cleaning, 83 Ultrasonic cleaning, 83 Universal hardness, static hardness testing, 639–642 Unplane surface, mechanical damage, wet abrasive cutting, 23 Uranium, specimen preparation, 447–450 Use, slow consumable wheels, 35

V Vanadium, electrolytic polishing and etching, 472–473 Vapor deposition, etching, 174 Vickers hardness testing, 628–632 Visible light, light microscopy, 525–526 Volume fraction automatic image analysis, 602–603 quantitative metallography/ materialography, 569

W Water-based grinding/polishing fluids, 97 Water-oil based grinding/polishing fluids, 98

Subject Index

Water quality, cutting fluids, wet abrasive cutting, 28 Waterproof ink marking, 80 Watershed filter, automatic image analysis, 590–592 Waviness, mechanical damage, wet abrasive cutting, 23 Wet abrasive cutting, sectioning, 15–32 abrasives and bond materials, 16–21 cut-off grinding process, 15–16 cut-off wheel, 16–21 cut-off wheel wear, 25–26 cutting fluids, 26–29 grinding mechanics, 21–22 mechanical damage, 22–23 metallographic/materialographic cutting operation, 29–32 thermal damage, 23–25 tips, 43–45 Wet cutting, thermal damage, 25 Wheel dimensions consumable abrasive cut-off wheels, 33 slow consumable wheels, 35 Wheel velocity consumable abrasive cut-off wheels, 32–33 metallographic/materialographic cutting operation, 30

743

slow consumable wheels, 35 White cast iron, specimen preparation, 322–324 Wire cutting, 52–53 Wrought aluminum alloys, specimen preparation, 359–361

Y YBCO ceramic super conductors, specimen preparation, 285–288

Z Zinc electrolytic polishing and etching, 473 specimen preparation, 420–423 Zinc oxide, specimen preparation, 241 Zirconia alumina wet grinding paper, 105–106 Zirconium electrolytic polishing and etching, 474 specimen preparation, 424–427 Zirconium dioxide, specimen preparation, 241

A.S.T.M.24, Metallographic and Materialographic Specimen Preparation-2006

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