Learning Objectives After studying this chap his chapter ter you should should be able to do the following: 1. List six different property classifications of materials that determine their applicability. 2. Cite the four components that are involved in the design, production, and utilization of materials, and briefly describe the interrelation ponents. ts. ships between these com ponen 3. Cite three criteria that are important in the proces cess. s. materials selection pro
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HISTORICAL
4. a! List the three primary classifications of solid materials, and then cite the distinctive h. chemical feature of eac each. b! "ote the four types of advanced materials and, for each, its distinctive features!. 5. a! #riefly define $smar t material%system.& b! #riefly explain the concept of $nanotechnology& as it applies to materials.
PERSPECTIVE
'aterials are prob probably ably more deep seated in our culture than most of us realize. communication, ication, recreation, and food produ (ransportation, housing, clothing, commun production) ction) virtually every segment of our everyday lives is influenced to one degree or another by materials. *istorically, the development and advancement of societies have been intimately tied to the members+ ability to produc produce e and manipulate materials to fill their needs. n fact, early civilizations have been designated by the level of their materials development tone Age, #ronze Age, ron Age!. (he earliest earliest humans had access to only a very limited limited number of materials, those and so on. 0ith time they discovered that th at occur naturally: stone, wood, clay, s/ins, and techni1ues for producing materials that had prop properti erties es supe superior rior to those of the natural ones2 these new materials inc includ luded ed pot pottery tery and var various ious met metals. als. 3urthermore, it was discovered that the properties of a material could be altered altered by by heat treatments and by the addition of other substances. At this point, materials utilization was totally a selection process that involved deciding from a given, rather limited set of materials the one best suited for an application by virt virtue ue of its characteristics. t was not until relatively recent times that scientists came to understand the relationships between the structural elements of materials and their pro propp- erties. (his /nowledge, ac1uired over approximately the past 44 years, has empowered them to fashion, to a large degree, the characteristics of evolved with rather materials. (hus, tens of th thous ousand andss of different materials have evolved specialized characteristics that meet the needs of our modern and complex society2 these include metals, plastics, glasses, and fibers. (he development of many technologies that ma/e our existence so comfortable has been intimately associated with the accessibility of suitable materials. An advancement in the understanding of a material type is often the forerunner to the stepwise progressio progression n of a technology. 3or example, automobiles would not have been poss ible with without out the avai availabil labil ity of inexpensive steel or some other comparable substitute. n the contemporary era, sophisticat sophisticated ed electronic devices rely on components that are made from what are called semiconducting materials.
1.2
ATERIALS SCIE!CE
A!" E!#I!EERI!#
ometimes it is useful to subdivide the discipline of materials science and engineering into materials science and materials engineering subdisciplines. trictly spea/ing, materials science involves investigating the relationships that exist between the structures and
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1.2 ateria%s Science an& Engineering
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properties of materials. n contrast, materials engineering involves, on the basis of these structure8property correlations, designing or engineering the structure of a material to 5 produce a predetermined set of properties. 3rom a functional perspective, the role of a materials scientist is to develop or synthesize new materials, whereas a materials engineer is called upon to create new products or systems using existing materials and%or to develop techni1ues for processing materials. 'ost graduates in materials programs are trained to be both materials scientists and materials engineers . Structure is at this point a nebulous term that deserves some explanation. n brief , the structure of a material usually relates to the arrangement of its internal components. ubatomic structure involves electrons within the individual atoms and interactions with their nuclei. 9n an atomic level, structure encompasses the organization of atoms or molecules relative to one another . (he next larger structural realm, which contains large groups of atoms that are normally agglomerated together, is termed microscopic, meaning that which is subect to direct observation using some type of microscope. 3inally, structural elements that can be viewed with the na/ed eye are termed macroscopic. (he notion of property deserves elaboration. 0hile in service use, all materials are exposed to external stimuli that evo/e some type of response. 3or example, a specimen subected to forces will experience deformation, or a polished metal surface will reflect light. A property is a material trait in terms of the /ind and magnitude of response to a specific imposed stimulus. ;enerally, definitions of properties are made independent of material shape and size.
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(he four components of the discipline of materials science and engineering and their interrelationship . 5
(hroughout this text we draw attention to the relationships between material properties and structural elements.
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(hree thin-dis/ specimens of aluminum oxide that have been placed over a printed page in order to demonstrate their differences in light-transmittance characteristics . (he dis/ on the left is transparent i.e., virtually all light that is reflected from the page passes through it!, whereas the one in the center is translucent meaning that some of this reflected light is transmitted through the dis/!. (he dis/ on the right is opa1ue)that is, none of the light passes through it. (hese differences in optical properties are a conse1uence of differences in structure of these materials, which have resulted from the way the materials were processed. pecimen preparation, =. A. Lessing2 photography by . (anner .!
each of the three materials are different2 the one on the left is transparent i.e., virtually all of the reflected light passes through it!, whereas the dis/s in the center and on the right are, respectively, translucent and opa1ue. All of these specimens are of the same material, aluminum oxide, but the leftmost one is what we call a single crystal) that is, has a high degree of perfection)which gives rise to its transparency. (he center one is composed of numerous and very small single crystals that are all connected2 the bound- aries between these small crystals scatter a portion of the light reflected from the printed page, which ma/es this material optically translucent. 3inally, the specimen on the right is composed not only of many small, interconnected crystals, but also of a large number of very small pores or void spaces. (hese pores also effectively scatter the reflected light and render this material opa1ue. (hus, the structures of these three specimens are different in terms of crystal boundaries and pores, which affect the optical transmittance properties. 3urthermore, each ma- terial was produced using a different processing techni1ue. f optical transmittance is an important parameter relative to the ultimate in-service application, the performance of each material will be different.
1.3
)H* ST+"* ATERIALS SCIE!CE
A!" E!#I!EERI!#,
0hy do we study materials> 'any an applied scientist or engineer, whether mechanical, civil, chemical, or electrical, will at one time or another be exposed to a design problem involving materials. ?xamples might include a transmission gear, the superstructure for a building, an oil refinery component, or an integrated circuit chip. 9f course, materials scientists and engineers are specialists who are totally involved in the investigation and design of materials. 'any times, a materials problem is one of selecting the right material from the thou- sands that are available. (he final decision is normally based on several criteria. 3irst of all, the in-service conditions must be characterized, for these will dictate the properties re1uired of the material. 9n only rare occasions does a material possess the maximum or ideal combination of properties. (hus, it may be necessary to trade one characteristic for another . (he classic example involves strength and ductility2 normally, a material having a high strength will have only a limited ductility. n such cases a reasonable compromise between two or more properties may be necessary. A second selection consideration is any deterioration of material properties that may occur during service operation. 3or example, significant reductions in mechanical strength may result from exposure to elevated temperatures or corrosive environments.
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3inally, probably the overriding consideration is that of economics: 0hat will the fini- shed product cost> A material may be found that has the ideal set of properties but is pro- hibitively expensive. *ere again, some compromise is inevitable. (he cost of a finished piece also includes any expense incurred during fabrication to produce the desired shape. (he more familiar an engineer or scientist is with the various characteristics and structure8property relationships, as well as processing techni1ues of materials, the more proficient and confident he or she will be in ma/ing udicious materials choices based on these criteria.
1.4
CLASSI'ICATIO! O' ATERIALS olid materials have been conveniently grouped into three basic categories: metals , ceramics, and polymers. (his scheme is based primarily on chemical ma/eup and atomic structure, and most materials fall into one distinct grouping or another. n addition, there are the composites, which are engineered combinations of two or more different materi- als. A brief explanation of these material classifications and representative characteristics is offered next. Another category is advanced materials)those used in high-technology applications, such as semiconductors, biomaterials, smart materials, and nanoengineered materials2 these are discussed in ection .6.
eta%s 'aterials in this group are composed of one or more metallic elements e.g., iron, aluminum, copper, titanium, gold, and nic/el!, and often also nonmetallic elements 7 e.g., carbon, nitrogen, and oxygen! in relatively small amounts. Atoms in metals and their alloys are arranged in a very orderly manner as discussed in Chapter 7! and are relatively dense in comparison to the ceramics and polymers 3igure .7!. 0ith regard to mechani- cal characteristics, these materials are relatively stiff 3igure .@! and strong 3igure .6!, yet are ductile i.e., capable of large amounts of deformation without fracture! and are resistant to fracture 3igure .!, which accounts for their widespread use in structural applications. 'etallic materials have large numbers of nonlocalized electrons2 that is, these electrons are not bound to particular atoms. 'any properties of metals are directly @4 54 ! e 4 l a c s B c i m h t @ i r a g o l 5 ! 7 m c % g .4 y 4.B t i s 4. n e E4.@
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attributable to these electrons. 3or example, metals are extremely good conductors of electricity 3igure .F! and heat and are not transparent to visible light2 a polished metal surface has a lustrous appearance. n addition, some of the metals i.e., 3e, Co, and "i! have desirable magnetic properties. 3igure .B shows several common and familiar obects that are made of metallic materials. 3urthermore, the types and applications of metals and their alloys are discussed in Chapter 7.
Cera2ics Ceramics are compounds between metallic and nonmetallic elements2 they are most fre1uently oxides, nitrides, and carbides. 3or example, common ceramic materials include aluminum oxide or alumina, Al597!, silicon dioxide or silica, i95!, silicon carbide iC!, silicon nitride i 7 "@!, and, in addition, what some refer to as the traditional ceramics )those composed of clay minerals i.e., porcelain!, as well as cement and glass. 0ith regard to mechanical behavior, ceramic materials are relatively stiff and strong) stiffnesses and strengths are comparable to those of the metals 3igures .@ and .6!. n addition, they are typically very hard. *istorically, ceramics have exhibited extreme 'etals
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brittleness lac/ of ductility! and are highly susceptible to fracture 3igure .!. *owever , newer ceramics are being engineered to have improved resistance to fracture2 these mate- rials are used for coo/ware, cutlery, and even automobile engine parts. 3urthermore, ceramic materials are typically insulative to the passage of heat and electricity i.e., have low electrical conductivities2 3igure .F! and are more resistant to high temperatures and harsh environments than are metals and polymers. 0ith regard to optical characteristics , ceramics may be transparent, translucent, or opa1ue 3igure .5!, and some of the oxide ceramics e.g., 3e 79@! exhibit magnetic behavior . everal common ceramic obects are shown in 3igure .K. (he characteristics, types, and applications of this class of materials are also discussed in Chapter 7.
P0% ers =olymers include the familiar plastic and rubber materials. 'any of them are organic compounds that are chemically based on carbon, hydrogen, and other nonmetallic elements
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3amiliar obects that are made of metals and metal alloys from left to right!: silverware for/ and /nife!, scissors, coins, a gear, a wedding ring, and a nut and bolt.
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Common obects that are made of ceramic materials: scissors, a china teacup, a building bric/, a floor tile, and a glass vase.
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everal common obects that are made of polymeric materials: plastic tableware spoon, for/, and /nife!, billiard balls, a bicycle helmet, two dice, a lawn mower wheel plastic hub and rubber tire!, and a plastic mil/ carton.
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ne common item that presents some interesting material property re1uirements is the container for carbonated beverages. (he material used for this application must satisfy the following constraints: ! provide a barrier to the passage of carbon dioxide, which is under pressure in the container2 5! be nontoxic, unreactive with the beverage, and, preferably, recyclable2 7! be relatively strong and capable of surviving a drop from a height of several feet when containing the beverage2 @! be inexpensive, including the cost to fabricate the final shape2 6! if optically transparent, retain its optical clarity2 and ! be capable of being produced in different colors and%or adorned with decorative labels. All three of the basic material types)metal aluminum!, ceramic glass!, and polymer polyester plastic!)are used for carbonated beverage containers per the chapter-opening photographs for this chapter!. All of these materials are nontoxic and
unreactive with beverages. n addition, each material has its pros and cons. 3or example, the aluminum alloy is relatively strong but easily dented!, is a very good barrier to the diffusion of carbon dioxide, is easily recycled, cools beverages rapidly, and allows labels to be painted onto its surface. 9n the other hand, the cans are optically opa1ue and relatively expensive to produce. ;lass is impervious to the passage of carbon dioxide, is a relatively inexpensive material, and may be recycled, but it crac/s and fractures easily, and glass bottles are relatively heavy. 0hereas plastic is relatively strong, may be made optically transparent, is inexpensive and lightweight, and is recyclable, it is not as impervious to the passage of carbon dioxide as aluminum and glass. 3or example, you may have noticed that beverages in aluminum and glass containers retain their carbonization i.e., $fizz&! for several years, whereas those in two-liter plastic bottles $go flat& within a few months.
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C020sites A composite is composed of two or more! individual materials, which come from the categories previously discussed)metals, ceramics, and polymers. (he design goal of a composite is to achieve a combination of properties that is not displayed by any single material and also to incorporate the best characteristics of each of the component materials. A large number of composite types are represented by different combinations of metals, ceramics, and polymers. 3urthermore, some naturally occurring materials are composites)for example, wood and bone. *owever, most of those we consider in our discussions are synthetic or human-made! composites. 9ne of the most common and familiar composites is fiberglass, in which small glass @ fibers are embedded within a polymeric material normally an epoxy or polyester!. (he glass fibers are relatively strong and stiff but also brittle!, whereas the polymer is more flexible. (hus, fiberglass is relatively stiff, strong 3igures .@ and .6!, and flexible. n addition, it has a low density 3igure .7!. carbon Another technologically important material is the fiber8reinforced polymer C3D=! composite)carbon fibers that are embedded within a polymer. (hese materials are stiffer and stronger than glass fiber8reinforced materials 3igures .@ and .6! but more expensive. C3D= composites are used in some aircraft and aerospace applications , as well as in high-tech sporting e1uipment e.g., bicycles, golf clubs, tennis rac/ets, and s/is%snowboards! and recently in automobile bumpers. (he new #oeing FBF fuselage is primarily made from such C3D= composites. Chapter 6 is devoted to a discussion of these interesting composite materials .
1.5
A"VA!CE" ATERIAL S 'aterials that are utilized in high-technology or high-tech! applications are sometimes termed adanced materials! #y "ig" tec"nology we mean a device or product that operates or functions using relatively intricate and sophisticated principles2 examples include electronic e1uipment camcorders, CE%E
Se2ic0n&(ct0rs emiconductors have electrical properties that are intermediate between those of electrical conductors i.e., metals and metal alloys! and insulators i.e., ceramics and polymers!)see 3igure .F. 3urthermore, the electrical characteristics of these materials are extremely sensitive to the presence of minute concentrations of impurity atoms, for which the concentrations may be controlled over very small spatial regions. emiconductors have made possible the advent of integrated circuitry that has totally revolutionized the electronics and computer industries not to mention our lives! over the last three decades.
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1.5 A&vance& ateria%s $ 11
9i02ater ia%s #iomaterials are employed in components implanted into the human body to replace diseased or damaged body parts. (hese materials must not produce toxic substances and must be compatible with body tissues i.e., must not cause adverse biological reactions!. All of the preceding materials)metals, ceramics, polymers, composites, and semiconductors) may be used as biomaterials.
Sart ateria%s Smart or intelligent ! materials are a group of new and state-of-the-art materials now being developed that will have a significant influence on many of our technologies. (he adective smart implies that these materials are able to sense changes in their environment and then respond to these changes in predetermined manners)traits that are also found in living organisms. n addition, this $smart& concept is being extended to rather sophisticated systems that consist of both smart and traditional materials. Components of a smart material or system! include some type of sensor that detects an input signal! and an actuator that performs a responsive and adaptive function!. Actuators may be called upon to change shape, position, natural fre1uency, or mechanical characteristics in response to changes in temperature, electric fields, and%or magnetic fields. 3our types of materials are commonly used for actuators: shape-memory alloys, piezoelectric ceramics, magnetostrictive materials, and electrorheological%magnetorheological fluids. hape-memory alloys are metals that, after having been deformed, revert bac/ to their original shape when temperature is changed see the 'aterials of mportance box following ection .K!. =iezoelectric ceramics expand and contract in response to an applied electric field or voltage!2 conversely, they also generate an electric field when their dimensions are altered see ection 5.56!. (he behavior of magne- tostrictive materials is analogous to that of the piezoelectrics, except that they are responsive to magnetic fields. Also, electrorheological and magnetorheological fluids are li1uids that experience dramatic changes in viscosity upon the application of electric and magnetic fields, respectively. 'aterials%devices employed as sensors include optical fibers ection K.@!, piezoelectric materials including some polymers!, and microelectromechanical systems '?'2 ection 7.4!. 3or example, one type of smart system is used in helicopters to reduce aerodynamic coc/pit noise that is created by the rotating rotor blades. =iezoelectric sensors inserted into the blades monitor blade stresses and deformations2 feedbac/ signals from these sensors are fed into a computer-controlled adaptive device, which generates noisecanceling antinoise.
!an02ateria%s 9ne new material class that has fascinating properties and tremendous technological promise is the nanomaterials! "anomaterials may be any one of the four basic types) metals, ceramics, polymers, and composites. *owever, unli/e these other materials, they are not distinguished on the basis of their chemistry but rather their size2 the nano prefix denotes that the dimensions of these structural entities are on the order of a K nanometer 4 m!)as a rule, less than 44 nanometers nm! e1uivalent to approximately 644 atom diameters!. =rior to the advent of nanomaterials, the general procedure scientists used to understand the chemistry and physics of materials was to begin by studying large and complex structures and then to investigate the fundamental building bloc/s of these structures that are smaller and simpler. (his approach is sometimes termed $top-down& science. 9n
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Intr0&(cti0n the other hand, with the development of scanning probe microscopes ection 6.5!, which permit observation of individual atoms and molecules, it has become possible to design and build new structures from their atomic-level constituents, one atom or molecule at a time i.e., $materials by design&!. (his ability to carefully arrange atoms provides opportunities to develop mechanical, electrical, magnetic, and other properties that are not otherwise possible. 0e call this the $bottom-up& approach, and the study of 6 the properties of these materials is termed nanotec"nology . ome of the physical and chemical characteristics exhibited by matter may experience dramatic changes as particle size approaches atomic dimensions. 3or example, materials that are opa1ue in the macroscopic domain may become transparent on the nanoscale2 some solids become li1uids, chemically stable materials become combustible, and electrical insulators become conductors. 3urthermore, properties may depend on size in this nanoscale domain. ome of these effects are are re- lated to surface phenomena)the 1uantum mechanical in origin2 others proportion of atoms located on surface sites of a particle increases dramatically as its size decreases. #ecause of these uni1ue and unusual properties, nanomaterials are finding niches energy production, and other in electronic, biomedical, sporting, industrial applications. ome are discussed in this boo/2 these include the following: L
Catalytic converters for automobiles)'aterials of mportance box, Chapter 6
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Carbon nanotubes)'aterials of mportance box, Chapter 7
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=articles of carbon blac/ as reinforcement for automobile tires)ection 6.5
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"anocomposites in tennis balls)'aterials of mportance box, Chapter 6
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'agnetic nanosize grains that are used for hard dis/ drives)ection B.
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'agnetic particles that store data on magnetic tapes)ection B.
0henever a new material is developed, its potential for harmful and toxicological interactions with humans and animals must be considered. mall nanoparticles have exceedingly large surface area8to8volume ratios, which can lead to high chemical reactivities. Although the safety of nanomaterials is relatively unexplored, there are concerns that they may be absorbed into the body through the s/in, lungs, and digestive tract at relatively high rates, and that some, if present in sufficient concentrations, will pose health ris/s)such as damage to E"A or promotion of lung cancer .
1.
O"ER!
ATERIALS:
!EE"S
n spite of the tremendous progress that has been made in the discipline of materials science and engineering within the last few years, technological challenges remain, including the development of even more-sophisticated and specialized materials, as well as consideration of the environmental impact of materials production. ome comment is appropriate relative to these issues so as to round out this perspective. "uclear energy holds some promise, but the solutions to the many problems that remain will necessarily involve materials, such as fuels, containment structures, and facilities for the disposal of radioactive waste. ignificant 1uantities of energy are involved in transportation. Deducing the weight of transportation vehicles automobiles, aircraft, trains, etc.!, as well as increasing engine operating temperatures, will enhance fuel efficiency. "ew high-strength, low-density structural materials remain to be developed, as well as materials that have higher temperature capabilities, for use in engine components. 6
9ne legendary and prophetic suggestion as to the possibility of nanoengineered materials was offered by Dichard 3eynman in his K6K American =hysical ociety lecture titled $(here+s =lenty of Doom at the #ottom.&
1. Pr0cessing/Str(ct(re/Pr0erties/Per0r2ance C0r re%ati0ns $ 13 3urthermore, there is a recognized need to find new, economical sources of energy and to use present resources more efficiently. 'aterials will undoubtedly play a significant role in these developments. 3or example, the direct conversion of solar power into electrical energy has been demonstrated. olar cells employ some rather complex and expensive materials. (o ensure a viable technology, materials that are highly efficient in this conversion process yet less costly must be developed. (he hydrogen fuel cell is another very attractive and feasible energy-conversion technology that has the advantage of being nonpolluting. t is ust beginning to be implemented in batteries for electronic devices and holds promise as a power plant for automobiles. "ew materials still need to be developed for more efficient fuel cells and also for better catalysts to be used in the production of hydrogen. 3urthermore, environmental 1uality depends on our ability to control air and water pollution. =ollution control techni1ues employ various materials. n addition, materials processing and refinement methods need to be improved so that they produce less environmental degradation)that is, less pollution and less despoilage of the landscape from the mining of raw materials. Also, in some materials manufacturing processes, toxic substances are produced, and the ecological impact of their disposal must be considered. 'any materials that we use are derived from resources that are nonrenewable)that is, not capable of being regenerated. (hese include most polymers, for which the prime raw material is oil, and some metals. (hese nonrenewable resources are gradually becoming depleted, which necessitates ! the discovery of additional reserves, 5! the development of new materials having comparable properties with less adverse environmental impact, and%or 7! increased recycling efforts and the development of new recycling technologies. As a conse1uence of the economics of not only production but also environmental impact and ecological factors, it is becoming increasingly important to consider the $cradle-to-grave& life cycle of materials relative to the overall manufacturing process. (he roles that materials scientists and engineers play relative to these, as well as other environmental and societal issues, are discussed in more detail in Chapter 54.
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PR OCESSI!#/STR+CT+RE/PR OPER TIES/ PER'ORA!CE CORRELATIO!S As mentioned previously ection .5!, the science and engineering of materials involves four interrelated components: processing, structure, properties, and perform- ance 3igure .!. nasmuch as the remainder of the boo/ discusses these components for the different material types, it has been decided to direct the readers+ attention to the treatment of individual components for several specific materials. 0hereas some of these discussions are found within single chapters, others are spread out over mul- tiple chapters. 3or the latter, and for each material we have selected, a $topic timeline& has been created that indicates the locations by sections! where treatments of the four components are to be found. 3igure . presents topic timelines for the following materials: stee ls, glass-ceramics, polymer fibers, and silicon a 3urthermore, semiconductors. processing%structure%properties%performance summary appears at the end of that chapter in which the last item on the topic timeline appears)for example, Chapter @ for steels, for glass-ceramics and polymer fibers, and Chapter 5 for silicon semiconductors . n addition, near the end of each chapter that has some discussion of processing, structure, properties, and%or performance for at least one of these four materials, a sum- mary is provided in the form of one or more concept maps! A concept map is a diagram that illustrates the relationships among concepts. 0e represent these relationships by connecting arrows fre1uently horizontal!2 each arrow points left to right! from one
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Pr0cessing
tructure
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?lectronic structure, interatomic bonding
=olymer molecules, polymer crystals
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P0%42eri>ati0n; a&&itives; 2e%ting; 1iber 0ring ➣
(hermoplastic 'echanical 'echanical properties, 'elting temperature, polymers factors that affect properties factors that affect =roperties
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Eegradation
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Applications =erformance
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ch 5
ch @
ch F
ch B
ch
ch 7
ch @
ch
(c)
'ig(re 1.11
=rocessing%structure%properties%performance topic timelines for a! steels, b! glass-ceramics, c! polymer fibers, and d ! silicon semiconductors.
S(ar $ 15
C00siti0n seciicati0n
SILICO! SEICO!"+CTORS
Pr0cessing
tructure
"i(si0n
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➣
Integrate& circ(its ➣
?lectronic structure, interatomic bonding
?lectronic band structure
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➣ ➣ ?lectrical
properties
=roperties ntegrated circuits =erformance
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ch 5
ch 6
ch
ch 5
(d)
'ig(re 1.11 continued ! concept to another . (he organization of these connections is hierarchical)that is, a concept to the left of an arrow should be mastered before a concept to the right can be under- stood. 3or each map, at least one of its concepts is discussed in its chapter2 other concepts may be treated in previous and%or later chapters. 3or example, 3igure .5 presents a portion of a concept map for the processing of steel alloys that appears in Chapter . Ir0n?ir0n carbi&e -ase &iagra @C-ater 18A
'ig(re 1.12
Is0t-er2a% trans0rati0n &iagras @C-ater 11A
C0ntin(0(s
Heat treat2ent 0 stee%s @C-ater 14A
=ortion of a concept map for the processing of a steel alloy that is found in
Chapter .
S+AR * 'aterials cience and ?ngineering
Classification of 'ater ials
L
(here are six different property classifications of materials that determine their applicability: mechanical, electrical, thermal, magnetic, optical, and deteriorative.
L
9ne aspect of materials science is the investigation of relationships that exist between the structures and properties of materials. #y structure we mean how some internal components! of the material is are! arranged. n terms of and with increasing! dimensionality, structural elements include subatomic, atomic, microscopic, and macroscopic.
L
0ith regard to the design, production, and utilization of materials, there are four elements to consider)processing, structure, properties, and performance. (he per- formance of a material depends on its properties, which in turn are a function of its structures!2 furthermore, structures! is are! determined by how the material was processed.
L
(hree important criteria in materials selection are in-service conditions to which the material will be subected, any deterioration of material properties during operation, and economics or cost of the fabricated piece .
L
9n the basis of chemistry and atomic structure, materials are classified into three general categories: metals metallic elements!, ceramics compounds between metallic and nonmetallic elements!, and polymers compounds composed of carbon, hydrogen, and other nonmetallic elements!. n addition, composites are composed of at least two different material types.
$ C-ater 1 Advanced 'ater ials
/
Intr0&(cti0n L Another materials category is the advanced materials that are used in high-tech applications. (hese include semiconductors having electrical conductivities intermediate between those of conductors and insulators!, biomaterials which must be com patible with body tissues!, smart materials those that sense and respond to changes in their environments in predetermined manners!, and nanomaterials those that have structural features on the order of a nanometer, some of which may be designed on the atomic%molecular level!.
RE'ERE!CES Ashby, '. 3., and E. D. *. Jones, Engineering Materials 1, An Introduction to #"eir Properties and Applications, 7rd edition, #utterworth-*einemann, 0oburn, MN, 5446. Ashby, '. 3., and E. D. *. Jones, Engineering Materials $, An Introduction to Microstructures, Processing and Design, 7rd edition, #utterworth-*einemann, 0oburn, MN, 5446. Ashby, '., *. hercliff, and E. Cebon, Materials Engineering , Science, Processing and Design, #utterworth-*einemann, 9xford, 544F. As/eland, E. D., =. =. 3ulay, and 0. J. 0right, #"e Science and Engineering of Materials, th edition, Cengage Learning, tamford, C(, 54. #aillie, C., and L.
B+ESTIO! 1.1 elect one or more of the following modern items or devices and conduct an nternet search in order to determine what specific materials! is are! used and what specific properties this these! materials! possesses! in order for the device%item to function properly. 3inally, write a short essay in which you report your findings. Cell phone%digital camera batteries Cell phone displays olar cells 0ind turbine blades 3uel cells Automobile engine bloc/s other than cast iron!
'c'ahon, C. J., Jr., Structural Materials, 'erion #oo/s, =hiladelphia, 544@. 'urray, ;. (., C. <. 0hite, and 0. 0eise, Introduction to Engineering Materials, 5nd edition, CDC =ress, #oca Daton, 3L, 544F. chaffer, J. =., A. axena, . E. Antolovich, (. *. anders, Jr., and . # . 0arner, #"e Science and Design of Engineering Materials, 5nd edition, 'c;raw-*ill, "ew Hor/, KKK. hac/elford, J. 3., Introduct ion to Materials Science for Engineers, Fth edition, =rentice *all =(D, =aramus, "J, 544K. mith, 0. 3., and J. *ashemi, 'oundations of Materials Science and Engineering, 6th edition, 'c;raw-*ill, "ew Hor/, 544.
Automobile bodies other than steel alloys! pace telescope mirrors 'ilitary body armor ports e1uipment occer balls #as/etballs /i poles /i boots nowboards urfboards ;olf clubs ;olf balls Naya/s Lightweight bicycle frames
Chapter
5
Atomic -tr ucture and nteratomic #onding
(
he photograph at the bottom of this page is of a
gec/o.
;ec/os, harmless tropical lizards, are extremely fascinating and extraordinary animals. (hey have very stic/y feet one of which is shown in the third photograph! that
cling to virtually any surface. (his characteristic ma/es it possible for them to rapidly run up vertical walls and along the un- dersides of horizontal surfaces. n fact, a gec/o can suppor t its body mass with a single toeO (he secret to this
remar/- able ability is the presence of an extremely large
number of microscopically small hairs on each of their toe pads. 0hen these hairs come in contact with a surface, wea/ forces of attraction i.e., van der 0aals
forces! are established between hair molecules and molecules on the surface. (he fact that
these hairs are so small and so numerous explains why the gec/o grips surfaces so
tightly. (o release its grip, the gec/o simply curls up its toes and peels the hairs away from the sur face. Msing their /nowledge of this mechanism of adhesion, scientists have developed several ultra-strong synt hetic adhesives. 9ne of these is an adhesive tape shown in the second photograph!, which is an
especially promising tool for use in surgical procedures as a replacement for sutures and staples to close wounds and incisions. (his material retains its adhesive nature in wet environments, is
biodegradable, and does not release toxic substances as it dissolves during the healing process. 'icroscopic features of this adhesive tape are shown in the top photograph.
Adhesive tape: Courtesy Jeffrey Narp, D ober t Langer and Alex ;ala/atos2 ;ec/o foot: ?manuele #iggi%;etty mages, nc.2 ;ec/o: #arbara =eacoc/%=hotodisc%;etty mages, nc.!
$ 1
)H* ST+"* Atomic Structure and Interatomic Bonding , An important reason to have an understanding of interatomic bonding in solids is that in some instances, the type of bond allows us to explain a mat er ial+s properties. 3or example, consider carbon, which may exist as both graphite and diamond. 0hereas graphite is relatively soft and has a $greasy& feel to it, diamond is the hardest /nown material. n addition, the electrical properties of
diamond and graphite are dissimilar: diamond is a poor conductor of electricity, but graphite is a reasonably good conductor. (hese disparities in properties are directly attributable to a type of interatomic bonding found in graphite that does not exis t in diamond see ection 7.K!.
Learning Objectives After studying this chapter you should be able to do the following: 1. "ame the two atomic models cited, and note the differences between them. 2. Eescribe the important 1uantum-mechanical principle that relates to electron energies. 3. a! chematically plot attractive, repulsiv e, and net energies versus interatomic separation for two atoms or ions.
2.1
b! "ote on this plot the e1uilibrium separation and the bonding energy. 4. a! #riefly describe ionic, covalent, metallic, hydrogen, and van der 0aals bonds. b! "ote which materials exhibit each of these bonding types.
I!TRO"+CTIO! ome of the important properties of solid materials depend on geometrical atomic arrangements and also the interactions that exist among constituent atoms or molecules. (his chapter, by way of preparation for subse1uent discussions, considers several fundamental and important concepts)namely, atomic structure, electron configurations in atoms and the periodic table, and the various types of primary and secondary interatomic bonds that hold together the atoms that compose a solid. (hese topics are reviewed briefly, under the assumption that some of the material is familiar to the reader .
Atomic -tr ucture 2.2
'+!"AE!TAL CO!CEPTS
at0ic n(ber @ Z A
?ach atom consists of a very small nucleus composed of protons and neutrons, which is encircled by moving electrons. #oth electrons and protons are electrically charged, the K charge magnitude being .45 4 C, which is negative in sign for electrons and positive for protons2 neutrons are electrically neutral. 'asses for these subatomic particles are extremely small2 protons and neutrons have approximately the same mass, .F 4 5F /g, which is significantly larger than that of an electron, K. 4 7 /g. ?ach chemical element is characterized by the number of protons in the nucleus, or the at0ic n(ber @ Z A. 3or an electrically neutral or complete atom, the atomic num ber also e1uals the number of electrons. (his atomic number ranges in integral units from for hydrogen to K5 for uranium, the highest of the naturally occurring elements. (he atomic mass A! of a specific atom may be expressed as the sum of the masses of protons and neutrons within the nucleus. Although the number of protons is the same
(erms appearing in b0%&ace type are defined in the ;lossary, which follows Appendix ?.
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