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Designation: E384 − 11
Standard Test Method for
Knoop and Vickers Hardness of Materials 1 This standard is issued under the fixed designation E384; the number immediately following the designation indicates the year of original origin al adoption or, in the case of revis revision, ion, the year of last revision. revision. A number in paren parenthese thesess indicates the year of last reappr reapproval. oval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval. This standard has been approved for use by agencies of the U.S. Department of Defense. 1
NOTE—Sections 8.3 8.3 and A1.1.4 A1.1.4 were were editorially corrected in March 2012. ε NOTE—Sections
1. Scope*
standard d doe doess not purport purport to add addre ress ss all of the 1.6 This standar safety safe ty co conc ncern erns, s, if an anyy, as asso soci ciat ated ed wit with h its us use. e. It is th thee responsibility of the user of this standard to establish appro priate safety and health practices and determine the applicability of regulatory limitations prior to use.
1.1 This test method covers covers determination determination of the Knoop Knoop and Vickers hardness of materials, the verification of Knoop and Vicke ickers rs har hardne dness ss tes testing ting mach machine ines, s, and the cal calibr ibratio ation n of standardized Knoop and Vickers test blocks. 1.2 This test metho method d covers Knoop and Vickers Vickers hardn hardness ess tests made utilizing test forces in micro (9.807 × 10 -3 to 9.807 N ) ( 1 to 1000 gf ) and macro (>9.807 to 1176.80 N) ( >1kg to 120 kgf ) ranges.
2. Referenced Documents 2.1 ASTM Standards: 2 C1326 Test Meth Method od for Kno Knoop op Ind Indent entatio ation n Har Hardne dness ss of Advanced Ceramics C1327 Test Meth Method od for Vick ickers ers Ind Indenta entatio tion n Har Hardne dness ss of Advanced Ceramics E3 Guide E3 Guide for Preparation of Metallographic Specimens E7 Terminology E7 Terminology Relating to Metallography E29 Pra Practic cticee for Using Sig Signifi nifican cantt Dig Digits its in Test Data to Determine Conformance with Specifications E74 Practice E74 Practice of Calibration of Force-Measuring Instruments for Verifying the Force Indication of Testing Machines E92 Test E92 Test Method for Vickers Hardness of Metallic Materials (Withdrawn 2010) 3 E122 Practice E122 Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or Process E140 Hardness E140 Hardness Conversion Tables for Metals Relationship Among Brinell Hardn Hardness, ess, Vi Vickers ckers Hardn Hardness, ess, Rockw Rockwell ell Hardness, Superficial Hardness, Knoop Hardness, Scleroscope Hardness, and Leeb Hardness E175 Terminology E175 Terminology of Microscopy E177 Practice E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods E691 Practic Practicee for Condu Conducting cting an Interl Interlabora aboratory tory Study to Determine the Precision of a Test Method E766 Practice E766 Practice for Calibrating the Magnification of a Scanning Electron Microscope
NOTE 1—Previous versions of this standard limited test forces to 9.807 N (1 kgf).
1.3 This tes testt met method hod includes includes all of the req requir uireme ements nts to perform macro Vickers hardness tests as previously defined in Test Method E92 Method E92,, Standard Test Method for Vickers Hardness Testing. 1.4 Thi Thiss test method method incl include udess an ana analys lysis is of the possible possible sourcess of err source errors ors tha thatt can occ occur ur dur during ing Kno Knoop op and Vicker Vickerss testing and how these factors affect the accuracy, repeatability, and reproducibility of test results. NOTE 2—While Committee E04 is primarily concerned with metals, the test procedures described are applicable to other materials.
1.5 Units— When When Knoop and Vickers hardness tests were developed, the force levels were specified in units of gramsforce (gf) and kilograms-force kilograms-force (kgf). This stand standard ard specifi specifies es the units of force and length in the International System of Units (SI); that is, force in Newtons (N) and length in mm or µm. However, because of the historical precedent and continued ue d co comm mmon on us usag age, e, fo forc rcee va valu lues es in gf an and d kg kgff un units its ar aree provided for information and much of the discussion in this standar stan dard d as wel welll as the method method of reportin reporting g the test res result ultss refers to these units. 1
Thiss tes Thi testt met method hod is und under er the jur jurisd isdict iction ion of AS ASTM TM Com Committ mittee ee E04 on Metallography Metallograp hy and is the direct respo responsibil nsibility ity of Subco Subcommitte mmitteee E04.05 E04.05 on on Microindentation Hardness Testing.With this revision the test method was expanded to include the requirements previously defined in E28.92, Standard Test Method for Vickers Hardness Testing of Metallic Material that was under the jurisdiction of E28.06 Current Curre nt editio edition n approv approved ed Aug. 1, 2011 2011.. Publi Published shed August 201 2011. 1. Origin Originally ally approved in 1969. Last previous edition approved in 2010 as E384 – 10 2. DOI: 10.1520/E0384-11E01.
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For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at
[email protected]. For Annual Book of ASTM Standards volume information, refer to the standard’s Document Summary page on the ASTM website. 3 The last app approv roved ed ver versio sion n of thi thiss his histor torica icall sta standa ndard rd is refe referen renced ced on www.astm.org.
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*A Summary of Changes section appears at the end of this standard Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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E384 − 11 2.2 ISO Standards: 4 ISO 6507 6507-1 -1 Metallic Materia Materials—V ls—Vickers ickers hardn hardness ess Test— Part 1: Test Method ISO/IEC 17011 Conformity 17011 Conformity Assessment—General Requirements for Accreditation Accreditation Bodies Accrediting Accrediting Confo Conformity rmity Assessment Bodies. ISO/IEC 17025 General Requirements for the Competence of Testing and Calibration Laboratories
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recovery after force removal. The test results are normally in the Knoop or Vickers scales. 3.2.5 macroindention hardness test, n— a hardness test using a calibrated machine to force an indenter of specific geometry into the surface of the material being evaluated, in which the test forces are normally higher than 9.807 N (1 kgf). Macroindentation test scales include Vickers, Rockwell and Brinell. NOTE 3—Use of the term microhardness should be avoided because it implies that the hardness, rather than the force or the indentation size, is very low.
3. Terminology 3.1 Definitions— For For the standard definitions of terms used in this test method, see Terminology E7 E7..
3.2.6 verifying, checking g or test testing ing the ins instru trumen mentt to verifying, v— checkin assure conformance with the specification.
3.2 Definitions of Terms Specific to This Standard: 3.2.1 calibrating, v— determining determining the values of the significantt par can paramet ameters ers by com compar pariso ison n wit with h val values ues indicated indicated by a reference instrument or by a set of reference standards.
Vickers har hardness dness numbe numberr, HV HV,, n— an 3.2.7 Vickers an exp expres ressio sion n of hardness obtained by dividing the force applied to a Vickers indenter by the surface area of the permanent indentation made by the indenter.
3.2.2 Knoop an exp expres ressio sion n of Knoop har hardne dness ss num number ber,, HK, n— an hardness obtained by dividing the force applied to the Knoop indent ind enter er by the pro project jected ed are areaa of the per perman manent ent ind indent entatio ation n made by the indenter.
3.2.8 Vickers indenter, n— a square-based pyramidal-shaped diamond indenter with face angles of 136° (see Fig. 1). 1). 3.2.9 scale, n— a specific combination of indenter (Knoop or Vick ickers ers)) and the test force. force. For example, example, HV1 HV10 0 is a sca scale le defined as using a Vickers indenter and a 10 kgf test force and HK 0.1 is a scale defined as using a Knoop indenter and a 100 gf test force. See 5.8 5.8 for for the proper reporting of the hardness level and scale.
Knoop p ind indente enterr, n— a rho 3.2.3 Knoo rhombic mbic-bas -based ed pyr pyramid amidalalshaped diamond indenter with edge angles of / A = 172° 30' and / B = 130° 0' (see Fig. 2) 2 ). microindent indentation ation har hardness dness test, n— a ha 3.2.4 micro hard rdne ness ss tes testt using usi ng a cali calibra brated ted mac machin hinee to for force ce a dia diamon mond d ind indente enterr of spec sp ecific ific ge geom ometr etry y in into to th thee su surf rfac acee of th thee ma mater terial ial be bein ing g evaluated, in which the test forces are 9.807 × 10 -3 to 9.807 N (1 to 1000 gf) and the indentation diagonal, or diagonals are measured with a light microscope after load removal; for any test, it is assumed that the indentation does not undergo elastic
3.3 Formulae— The The formulae presented in 5.5 and 5.6 for calcula calc ulating ting Kno Knoop op and Vickers Vickers har hardne dness ss are bas based ed upo upon n an ideal ide al test tester er.. The mea measur sured ed val value ue of the Kno Knoop op and Vicker Vickerss hardness of a material is subject to several sources of errors. Based on Eq on Eq 1-9, 1-9, variations in the applied force, geometrical variations variati ons between diamond indenters, indenters, and human errors in measuring indentation lengths can affect the calculated material hardness. The influence each of these parameters has on the calcu ca lcula lated ted va valu luee of a Kn Knoo oop p or Vic icke kers rs me meas asur urem emen entt is discussed in Section 10 10..
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Available from International Organization for Standardization (ISO), 1, ch. de la Voie oie-Cr -Creus euse, e, Cas Casee pos postal talee 56, CHCH-121 1211, 1, Gen Geneva eva 20, Sw Switz itzerl erland and,, htt http:/ p:// / www.iso.org.
FIG. 1 Vickers Indenter
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E384 − 11
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FIG. 2 Knoop Indenter Indenter
4. Significance and Use
elastic recovery. Thus, the Knoop indenter is very useful for evalua eva luating ting har hardne dness ss gra gradien dients ts or thi thin n coa coatin tings gs of sec section tioned ed samples.
4.1 Har Hardne dness ss test testss hav havee bee been n fou found nd to be very use useful ful for material mate rialss eva evalua luation tion,, qua quality lity con contro troll of man manufa ufactu cturin ring g pro pro-cesses cess es and res resear earch ch and dev develo elopme pment nt ef effor forts. ts. Har Hardne dness, ss, although empirical in nature, can be correlated to tensile strength for many metals, and is an indicator of wear resistance and ductility.
5. Principle of Test 5.1 In this test method, a Knoop or Vickers Vickers hardness number is det determ ermine ined d bas based ed on the formation formation of a rela relativ tively ely sma small ll indentation made in the test surface of samples being evaluated.
4.2 Micro Microinden indentation tation hardness hardness tests extend testing to materials th rials that at ar aree to too o th thin in or to too o sm small all fo forr ma macr croi oind nden enta tatio tion n hardne har dness ss tes tests. ts. Mic Microi roinde ndenta ntatio tion n har hardne dness ss test testss als also o allo allow w specific spe cific pha phases ses or con constit stituen uents ts and reg region ionss or gra gradie dients nts too small for macroindentation hardness testing to be evaluated.
5.2 A Kno Knoop op or Vick ickers ers ind indent enter er,, mad madee fro from m dia diamon mond d of specific geometry, is pressed into the test specimen surface by an accu accurate rately ly con contro trolled lled app applied lied for force ce usi using ng test mac machin hines es specifically designed for such work.
4.3 Bec Becaus ausee the Kno Knoop op and Vicker Vickerss har hardne dness ss will rev reveal eal hardness variations that may exist within a material, a single test value may not be representative of the bulk hardness.
5.3 Knoop Knoop and Vickers Vickers har hardne dness ss test testing ing is div divide ided d int into o micro and macro-test force ranges as defined:
4.4 The Vickers Vickers indenter usually produces produces a geomet geometrically rically similar indentation at all test forces. Except for tests at very low forces that produce indentations indentations with diagonals smaller than about 25 µm, the hardness number will be essentially the same as produced by Vickers machines with test forces greater than 1 kgf, as long as the material being tested is reasonably homogeneous. For isotropic materials, the two diagonals of a Vickers indentation indentation are equal in size. Recommendations Recommendations for low force microindentation testing can be found in Appendix X5.. X5
Range Micro Macro
Test Force 9.807 × 10-3 to # 9.807 N ( 1 to # 1000 gf) > 9.807 to # 1176.80 N ( > 1 to # 120 kgf)
5.3.1 Knoop 5.3.1 Knoop sca scale le test testing ing is nor normal mally ly per perfor formed med usi using ng micro-range test forces (1kg and less) while the Vickers scale is used over both the micro and macro-ranges. NOTE 4—The user should consult with the manufacturer before applying test forces in the macro-ranges (over 1 kg) with diamond indenters previously used for micro-range testing. The diamond mount may not be strong enough to support the higher test forces and the diamond may not be large enough to produce the larger indentation sizes.
4.5 The Knoop indenter indenter does not prod produce uce a geomet geometrically rically similar indentation as a function of test force. Consequently, thee Kn th Knoo oop p ha hard rdne ness ss wi will ll va vary ry wi with th te test st fo forc rce. e. Du Duee to its rhombic shape, the indentation depth is shallower for a Knoop indentation compared to a Vickers indentation under identical test conditions. The two diagonals of a Knoop indentation are markedly different. Ideally, the long diagonal is 7.114 times longer than the short diagonal, but this ratio is influenced by
5.4 The size of the ind indent entatio ation n is mea measur sured ed usi using ng a lig light ht microscope equipped with a filar type eyepiece, or other type of measur measuring ing device (see Termino erminology logy E175). E175). Micro Micro-rang -rangee inde in dent ntss ar aree ty typi pica cally lly mea measu sure red d in µm (m (micr icrom omet eter ers) s) an and d macro-range indents are measured in mm. The formulas for both units are given below. 3
E384 − 11 5.5 The Knoop Knoop har hardne dness ss num number ber is bas based ed upo upon n the force divided by the projected area of the indentation 5.5.1 For Knoop hardness hardness testing, testing, test loads are typical typically ly in grams-force gramsforce (gf) and inden indentation tation diagonals are in microm micrometers eters (µm). The Knoop hardness number, in terms of gf and µm, is calculated using the following: 3
HK 5 1.000 3 10
or
3
~ P / A p ! 5 1.000 3 10
3
~ c p 3 d !
3 P /
2
HK 5 14229 3 P / d d 2 tan
contained in Appendix in Appendix X6. X6. To obtain HV values when other test forces are employed, emplo yed, multiply the HV value from Table from Table X6.2 for X6.2 for the d value by the actual test force, gf.
5.6.2 Macro range range Vickers Vickers hardness hardness is typically typically determined determined using kgf and mm and is calculated as follows: HV 5 1.8544 3 P 1 / d d 1 2
(1 )
where:
(2 )
force, ce, kgf kgf,, and and P1 = for d 1 = mean diagonal diagonal length length of of the indentatio indentations, ns, mm.
/ B
Indenter constant 5 c p 5
2 tan
2 / A
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5.6.3 The Vicker 5.6.3 Vickerss har hardne dness ss rep report orted ed wit with h uni units ts of GPa is determined as follows:
(3 )
HV 5 0.0018544 3 P 2 / d d 2 2
2
where:
where:
P d A p / A / B
P2 d 2
= = = = =
force fo rce,, gf, length len gth of lon long g dia diagon gonal, al, µm, projected proje cted area of indent indentation, ation, µm 2 included includ ed longitudi longitudinal nal edge edge angle, angle, 172° 172° 30’ 30’ includ inc luded ed transve transverse rse edge edge angle, angle, 130° 130° 0’ (see Fig. 2 and, = inden indenter ter const constant ant relatin relating g projecte projected d area area of the indentation to the square of the length of the long diagonal, ideally 0.07028.
c p
(4 )
where:
= force, force, kgf kgf,, and = len length gth of lon long g diago diagonal, nal, mm.
5.5.3 The Knoop hardnes 5.5.3 hardnesss rep report orted ed with units of GPa is determined as follows: HK 5 0.014229 3 P 2 / d d 2 2
(5 )
5.9 The reported Knoop Knoop and Vickers Vickers hardness number shall be reported rounded to three significant digits in accordance with Practice E29 E29 (for (for example, 725 HV 0.1, 99.2 HK 1).
where: P2 d 2
= fo forc rce, e, N, an and d = length of the the long diago diagonal nal of the indentatio indentation, n, mm.
6. Apparatus
5.6 The Vickers Vickers hardness hardness number is based upon the force divided by the surface area of the indentation. 5.6.1 For the micromicro-range range Vickers Vickers hardness hardness test loads are typically in grams-force (gf) and indentation diagonals are in micrometers (µm). The Vickers hardness number, in terms of gf and µm, is calculated as follows: HV 5 1.000 3 103 3 P / A s 5 2.000 3 103 3 Psin~ α / d 2 /2 2 ! / d
(6 )
HV 5 1854.4 3 P / d d 2
(7 )
6.1 Test Machine— The The test machine shall support the test specimen and control the movement of the indenter into the specimen under a preselected test force, and should have a light optical microscope to select the desired test location and to measure the size of the indentation produced by the test. The plane of the surface of the test specimen should be perpendicular to the axis of the indenter and the direction of the force application. Vibration Control— During 6.1.1 Vibration During the entire test cycle, the test machine should be protected from shock or vibration. To minimize vibrations, the operator should avoid contacting the machine in any manner during the entire test cycle.
or
where: P As d α
= = = =
force, gf, force, surfac sur facee area of the the indentat indentation ion,, µm2, mean diagon diagonal al length length of the the indentat indentation ion,, µm, and facee angle fac angle of the the indente indenter, r, 136° 136° 0’ 0’ (see (see Fig. 1) 1). –3
NOTE 6—HV 6—HV nu numb mber erss fo forr a 1 gf (9 (9.8 .807 07 × 10
= fo forc rce, e, N, an and d = mean diagona diagonall length length of the the indentations indentations,, mm.
5.8 Th 5.8 Thee sy symb mbol olss HK fo forr Kn Knoo oop p ha hard rdne ness ss,, an and d HV fo forr Vick ickers ers har hardne dness ss sha shall ll be use used d wit with h the rep report orted ed num numeri erical cal values. 5.8. 5. 8.1 1 Fo Forr th this is st stan anda dard rd,, th thee ha hard rdne ness ss te test st re resu sults lts can be reported in several different ways. For example, if the Knoop hardness was found to be 400, and the test force was 100 gf, the test results may be reported as follows: 5.8.1.1 5.8.1 .1 In the kilogram force system: system: 400 HK 0.1. 5.8.1.2 5.8.1 .2 In the gram force system: system: 400 HK 100 gf. 5.8.1.3 5.8.1 .3 In the SI system: 3.92 GPa. 5.8.1.4 5.8.1 .4 For nonstanda nonstandard rd dwell times, times, other than 10 10 to 15 s, the hardness would be reported as 400 HK 0.1 /22. In this case, 22 would be the actual time of full load dwell time in seconds.
5.5.2 5.5. 2 Th Thee Kn Knoo oop p ha hard rdne ness ss,, in ter terms ms of kg kgff an and d mm mm,, is determined as follows:
P1 d 1
(9 )
5.7 It is assumed that elastic recovery does does not occur when the indenter is removed after the loading cycle. That is, it is assumed that the indentation retains the shape of the indenter after the force is removed. In Knoop testing, it is assumed that thee ra th ratio tio of th thee lo long ng di diag agon onal al to th thee sh shor ortt di diag agon onal al of th thee indentation is the same as for the indenter.
NOTE 5—HK values for a 1gf (9.807 × 10 –3 N) test force are contai contained ned in Appendix Appendix X6 X6.. To To ob obta tain in HK va valu lues es wh when en ot othe herr te test st fo forc rces es ar aree employed, multiply the HK value from Table from Table X6.1 for X6.1 for the d value by the actual test force, gf.
HK 5 14.229 3 P 1 / d d 1 2
(8 )
6.2 Vickers Indenter— The The ideal Vickers indenter (see Fig. 1) is a hig highly hly pol polish ished, ed, poi pointe nted, d, squ square are-ba -based sed pyr pyramid amidal al
N) te test st lo load ad ar aree
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E384 − 11 diamond with face angles of 136° 0'. The effect that geometrical variations of these angles have on the measured values of Vickers hardness are discussed in Section 10 10.. 6.2.1 The four faces of the Vickers Vickers indenter indenter shall be equally inclined to the axis of the indenter and shall meet at a sharp point. The line of junction (offset) between opposite faces shall not exceed the limits defined in A1.3.5.1 in A1.3.5.1..
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indentation size, the more critical is the surface preparation. Specimen preparation should be performed in accordance with applicable applic able section of Guide E3 E3.. In all test tests, s, the pre prepar paratio ation n should be such that the indentation perimeter and the indentation tips in particular, can be clearly defined when observed by the measuring system. 7.1.1. 7.1 .1.1 1 The test sur surface face shall be fre freee of any def defects ects that could affect affect the indentation or the subsequent subsequent measur measurement ement of the dia diagon gonals als.. It is wel welll kno known wn tha thatt imp improp roper er gri grindi nding ng and polishing methods can alter test results either due to excessive heating or cold work. Some materials are more sensitive to prepar pre paratio ation-i n-indu nduced ced dam damage age tha than n oth others ers;; the theref refore ore spe specia ciall precautions must be taken during specimen preparation. Specimen preparation must remove any damage introduced during these steps. 7.1.1.2 7.1.1 .2 The specimen surface surface shou should ld not be etched before making an indentation. Etched surfaces can obscure the edge of the indentation, making an accurate measurement of the size of the indentation difficult. However, when determining the microindentation hardness of an isolated phase or constituent, a light etch can be used to delineate the object of interest. 7.1.2 Alignment— To obt obtain ain usa usable ble inf inform ormatio ation n fro from m the test, the specimen should be prepared or mounted so that the test surface is perpendicular to the axis of the indenter. This can readily rea dily be acco accompl mplish ished ed by sur surfac facee gri grindi nding ng (or oth otherw erwise ise machining) the opposite side of the specimen parallel with the sidee to be test sid tested. ed. Non-para Non-parallel llel samples samples can be test tested ed usi using ng clamping and leveling fixtures designed to align the test surface properly to the indenter. 7.1.3 Mounted Samples— In In many instances, it is necessary to mount the specimen for convenience in preparation and to maintain a sharp edge when surface gradient tests are to be perfor per formed med on the sam sample ple.. Whe When n mou mountin nting g is req requir uired, ed, the specim spe cimen en mus mustt be ade adequa quately tely sup suppor ported ted by the mou mountin nting g medium med ium so tha thatt the spe specime cimen n doe doess not move dur during ing force appl ap plic icati ation on,, th that at is is,, av avoi oid d th thee us usee of po poly lymer meric ic mo moun untin ting g compounds that creep under the indenter force. 7.1.4 Thickness— the the thickness of the specimen tested shall be such that no bulge or other marking showing the effect of the test force appears on the side of the piece opposite the indentation. The thickness of the material under test should be at least ten times the depth of the indentation. This is also to be used as a guideline for the minimum depth of a coating on a material. 7.1.5 Radius of Curvature— due due caution should be used in interpreting or accepting the results of tests made on spherical or cylindrical surfaces. Results will be affected even in the case of th thee Kn Knoo oop p tes testt wh wher eree th thee ra radi dius us of cu curv rvatu ature re is in th thee direction of the short diagonal. Table 1, 1, Table 2 and Table 3 provid pro videe cor correc rection tion fac factor torss tha thatt sha shall ll be app applied lied to Vick ickers ers hardness values obtained when tests are made on spherical or cylind cyl indric rical al sur surfac faces. es. The cor correc rectio tion n fac factor torss are tab tabula ulated ted in terms of the ratio of the mean diagonal d of the indentation to the diamete diameterr D of the sphere or cylinder. Examples of the use of these tables are given in Example 1 and 2:
6.3 Knoop Indenter— The The ideal Knoop (see Fig. 2) 2) indenter is a highly polished, pointed, rhombic-based, pyramidal diamond. The included longitudinal edge angles are 172° 30' and 130° 0'. The ideal indenter constant, c p, is 0.07028. The effect that geometrical variations of these angles have on the measured values of Knoop hardness are discussed in Section 10 10.. 6.3.1 The four faces of the Knoop Knoop indenter shall shall be equally inclined to the axis of the indenter and shall meet at a sharp point. The line of junction (offset) between opposite faces shall not exceed the limits defined in A1.3.5.2 in A1.3.5.2.. 6.4 Whe When n meas measuri uring ng ind indent entatio ation n dia diagon gonal al len length gthss 40 µm and larger the test machine’s measuring device shall be capable of reporting the diagonal lengths to within 0.5 µm or 0.5% which ever is larg larger er.. When measuring indentation indentation diago diagonal nal lengths less than 40 µm the measuring device shall be able to report the diagonal lengths within 0.25 µm. In all cases, smaller measurement increments may be reported if the equipment is capable of displaying smaller measurement increments. NOTE 7—This is the reported length and may not be the resolution of the system used for performing the measurements. As an example, if a length of 200 µm corresponds corresponds to 300 filar units or pixels, the corres correspondponding calibration constant would be 200/300 = 0.6667. This value would be used to compute diagonal lengths, but the reported length may only be reported to the nearest 0.5 or 0.25 µm.
6.4.1 6.4 .1 The measurin measuring g dev device ice may be an int integr egral al par partt of the tester or a stand alone instrument. 6.4.2 6.4 .2 The opt optical ical portion portion of the meas measuri uring ng dev device ice sho should uld have Köhler illumination (see Appendix X1). X1 ). 6.4.3 To obtain maximu maximum m resolution, the measuring microscope should have adjustable illumination intensity, adjustable alignment, aperture, and field diaphragms. 6.4.4 Magnifi Magnification cationss should be provi provided ded so that the diagonal can be enlarged to greater than 25 % but less than 75 % of the field width. The device may be built with single or multiple magnifying objectives. 6.5 Verifications— All All testers and indenters used to perform Knoop and Vickers hardness tests shall meet the requirements defined in Annex in Annex A1 prior to performing hardness tests.
7. Test Specimen 7.1 Th 7.1 Ther eree is no sta stand ndar ard d sh shap apee or siz sizee fo forr a Kn Knoo oop p or Vickers test specime specimen. n. The specim specimen en on which the indentation is made should conform to the following: 7.1.1 Preparation— For For optimum accuracy of measurement, the test should be performed on a flat specim specimen en with a polish polished ed or oth otherw erwise ise sui suitabl tably y pre prepar pared ed sur surfac face. e. The qua quality lity of the required surface finish can vary with the forces and magnificatio cat ions ns us used ed.. Th Thee lo lowe werr th thee tes testt fo forc rcee an and d th thee sm smal aller ler th thee
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