1、IntroductionofMaterialsScienceIntroductionofMaterialsScienceChapter1Introduction1.1HistoricalPerspectiveMaterialsaremoredeep-seatedinourculturethanmostofusrealize.Transportation,housing,clothing,communication,recreation,andfoodproduction-virtuallyeverysegmentofoureverydaylivesisinfluencedtoonedegree
2、oranotherbymaterials.Chapter1IntroductionHistorically,thedevelopmentandadvancementofsocietieshavebeenintimatelytiedtothemembersabilitytoproduceandmanipulatematerialstofilltheirneeds.Earlycivilizationshavebeendesignatedbytheleveloftheirmaterialsdevelopment(StoneAge,BronzeAge,etal.,)Chapter1Introducti
3、onFirstly,theearliesthumanhadaccesstoonlyaverylimitednumberofmaterials,thosethatoccurnaturally:stone,wood,clay,skins,andsoon.Secondly,thehumandiscoveredtechniquesforproducingmaterialsthathadpropertiessuperiortothoseofthenaturalones,thesenewmaterialsincludedpotteryandvariousmetals.Chapter1Introductio
4、nFurthermore,itwasdiscoveredthatthepropertiesofamaterialscouldbealteredbyheattreatmentsandbytheadditionofothersubstances.Nowthescientistscometounderstandtherelationshipsbetweenthestructuralelementsofmaterialsandtheirproperties.Chapter1IntroductionThus,tensofthousandsofdifferentmaterialshaveevolvedwi
5、thratherspecializedcharacteristicsthatmeettheneedsofourmodernandcomplexsociety;theseincludemetals,plastics,glasses,andfibers.Thedevelopmentofmanytechnologiesthatmakeourexistencesocomfortablehasbeenintimatelyassociatedwiththeaccessibilityofsuitablematerials.Chapter1IntroductionAnadvancementintheunder
6、standingofamaterialtypeisoftentheforerunnertothestepwiseprogressionofatechnology.In our contemporary era,sophisticatedelectronic devices rely on componentsthat are made from what are calledsemiconductingmaterials.Chapter1Introduction1.2MaterialsScienceandEngineeringThedisciplineofmaterialsscienceinv
7、olvesinvestigatingtherelationshipsthatexistbetweenthestructuresandpropertiesofmaterials.Materialsengineeringis,onthebasisofthesestructure-propertytoproduceapredeterminedsetofproperties.Chapter1Introduction“Structure”is a nebulous term thatdeservessomeexplanation.In brief,the structure of a materialu
8、suallyrelatestothearrangementofitsinternalcomponents.Subatomic structure involves electronswithintheindividualatomsandinteractionswiththeirnuclei.(ElectronicStructure)Chapter1IntroductionOnanatomiclevel,structureencompassestheorganizationofatomsormoleculesrelativetooneanother.(AtomicStructure)Thenex
9、tlargerstructuralrealm,whichcontainslargegroupsofatomsthatarenormallyagglomeratedtogether,istermed“microscopic”.(MicroscopicStructure)Chapter1IntroductionFinally,structuralelementsthatmaybeviewedwiththenakedeyearetermed“macroscopic.”(Macroscopicstructure)Thenotionof“property”deserveselaboration.Whil
10、einserviceuse,allmaterialsareexposedtoexternalstimulithatevokesometypeofresponse.Chapter1IntroductionApropertyisamaterialtraitintermsofthekindandmagnitudeofresponsetoaspecialimposedstimulus.Generally,definitionsofpropertiesaremadeindependentofmaterialshapeandsize.Virtuallyallimportantpropertiesofsol
11、idmaterialsmaybegroupedintosixdifferentcategories:Chapter1Introduction1.Mechanicalproperties2.Electricalproperties3.Thermalproperties4.Magneticproperties5.Opticalproperties6.DeteriorativepropertiesChapter1IntroductionForeachthereisacharacteristictypeofstimuluscapableofprovokingdifferentresponses.Mec
12、hanicalpropertiesrelatedeformationtoanappliedloadorforce(includingelasticmodulusandstrength).Chapter1IntroductionForelectricalproperties,suchaselectricalconductivityanddielectricconstant,thestimulusisanelectricfield.Thethermalpropertiesofsolidscanberepresentedintermsofheatcapacityandthermalconductiv
13、ity.Magneticpropertiesdemonstratetheresponseofamaterialtotheapplicationofmagneticfield.Chapter1IntroductionForopticalproperties,thestimulusiselectro-magneticorlightradiation.(indexofrefractionandreflectivity)Deteriorativecharacteristicsindicatethechemicalreactivityofmaterials.Chapter1IntroductionIna
14、dditiontostructureandproperties,twootherimportantcomponentsareinvolvedinthescienceandengineeringofmaterialsnamely“processing”and“performance.”Withregardtotherelationshipsofthesefourcomponents,thestructureofamaterialwilldependonhowitisprocessed.Chapter1IntroductionFurthermore,amaterialsperformancewil
15、lbeafunctionofitsproperties.Theinterrelationshipbetweenprocessing,structure,properties,andperformanceisshownasFigure1.1Chapter1IntroductionStructureProcessingPropertiesPerformanceFigure 1.1 The relationships of structure,properties,precessing and performanceChapter1IntroductionWenowpresentanexampleo
16、ftheseprocessing-structure-properties-performanceprinciples.Allofthesespecimensareofthesamematerials:aluminumoxide(Al2O3)Chapter1IntroductionAsinglecrystal-thatis,itishighlyperfect-whichgivesrisetoitstransparency,soitistransparent;Theotheroneiscomposedofnumerousandverysmallsinglecrystalsthatareallco
17、nnected(polycrystals);Chapter1Introductiontheboundarybetweenthesesmallcrystalsscatteraportionofthelightreflectedfromtheprintedpage,whichmakesthismaterialsopticallytranslucent.Finally,thethirdspecimeniscomposednotonlyofmanysmall,interconnectedcrystals,butalsoofalargenumberofverysmallporesorvoidspaces
18、.(Ceramics)Chapter1IntroductionTheseporesalsoeffectivelyscatterthereflectedlightandrenderthismaterialopaque.Thus,thestructuresofthesethreespecimensaredifferentintermsofcrystalboundariesandpores,whichaffecttheopticaltransmittanceproperties.Chapter1IntroductionFurthermore,eachmaterialwasproducedusinga
19、differentprocessingtechniques.Andofcause,ifopticaltransmittanceisanimportantparameterrelativetotheultimatein-serviceapplication,theperformanceofeachmaterialwillbedifferent.Chapter1Introduction1.3WhystudyMaterialsScienceandEngineering?Manyanappliedscientistorengineer,whethermechanical,civil,chemical,
20、orelectrical,willatonetimeoranotherbeexposedtoadesignprobleminvolvingmaterials.Chapter1IntroductionOfcourse,materialsscientistsandengineersarespecialistswhoaretotallyinvolvedininvestigationanddesignofmaterials.Manytimes,amaterialsproblemisoneofselectingtherightmaterialfromthemanythousandsthatareavai
21、lable.Thereareseveralcriteriaonwhichthefinaldecisionisnormallybased.Chapter1IntroductionFirstofall,thein-serviceconditionsmustbecharacterized,forthesewilldictatethepropertiesrequiredofthematerial.Ononlyrareoccasionsdoesamaterialpossessthemaximumoridealcombinationofproperties.Chapter1IntroductionThus
22、,itmaybenecessarytotradeoffonecharacteristictoanother.Chapter1Introduction The classic example involves strengthandductility;normally,amaterialhavingahigh strength will have only a limitedductility.A second selection consideration isany deterioration of material propertiesthatmayoccurduringserviceop
23、eration.Chapter1IntroductionForexample,significantreductionsinmechanicalstrengthmayresultfromexposuretoelevatedtemperaturesorcorrosiveenvironments.Finally,theoverridingconsiderationisthat of economics:what will the finishproductcost?Chapter1IntroductionAmaterialmaybefoundhastheidealset of properties
24、 but is prohibitivelyexpensive.Hearagain,somecompromiseisinevitable.The cost of a finished piece alsoincludes any expense incurred duringfabricationtoproducethedesiredshape.Chapter1Introduction1.4ClassificationofMaterialsSolidmaterialshavebeenconvenientlygroupedintothreebasicclassifications:metals,c
25、eramicsandpolymers.Thisschemeisbasedprimarilyonchemicalmakeupandatomicstructure.Chapter1IntroductionInaddition,therearethreeothergroupsofimportantengineeringmaterials-composites,semiconductorsandbiomaterials.METALSMetallicmaterialsarenormallycombinationsofmetallicelements.They have large numbers of
26、nonlocated electrons:that is,these electrons are notboundtoparticularatoms.Chapter1IntroductionMany properties of metals are directlyattributabletotheseelectrons.Metals are extremely good conductorsof electricity and heat and are nottransparenttovisitlight;apolishedmetalsurfacehasalustrousappearance
27、.Metalsarequitestrong,yetdeformable,whichaccountsfortheirextensiveuseinstructureapplicationsChapter1IntroductionCERAMICSCeramicsarecompounds betweenmetallic and nonmetallic elements;theyaremostfrequentlyoxides,nitrides,andcarbides.The wide range of materials that fallwithinthisclassificationincludes
28、ceramicsare composedof clay minerals,cement,andglass.Chapter1IntroductionCeramicsaretypicallyinsulativetothepassage of electricity and heat,and aremoreresistanttohightemperaturesandharsh environments than metals andpolymers.With regard to mechanical behavior,ceramicsarehardbutverybrittle.Chapter1Int
29、roductionPOLYMERSPolymersincludethefamiliarplasticandrubbermaterials.Many of them are organic compoundsthat are chemically based on carbon,hydrogen,andothernonmetallicelements;theyhaveverylargemolecularstructures.Thesematerialstypicallyhavelowdensitiesandmaybeextremelyflexible.Chapter1IntroductionCO
30、MPOSITESAnumberofcompositematerialshavebeenengineeredthatconsistofmorethanonematerialtype.Acompositeisdesignedtodisplayacombinationofthebestcharacteristicsofeachofthecomponentmaterial.Chapter1IntroductionFiberglass is a familiar example,inwhichglassfibersareembeddedwithinapolymericmaterial.Fiberglas
31、s acquires strength from theglassandflexibilityfromthepolymer.Chapter1IntroductionSEMICONDUCTORSemiconductorshaveelectricalpropertiesthatareintermediatebetweentheelectricalconductorsandinsulators.Furthermore,the electrical characteristicsofthesematerialsareextremelysensitivetothe presence of minute
32、concentrations ofimpurityatoms;theseconcentrationsmaybecontrolledoververysmallspatialregions.Chapter1IntroductionBIOMATERIALSBiomaterialsareemployedincomponents implanted into the humanbody for replacement of diseased ordamagedbodyparts.Thesematerialsmustnotproducetoxicsubstancesandmustbecompatiblew
33、ithbodytissues.Chapter1IntroductionAll of the above materials-metals,ceramics,polymers,composites,and semiconductors-may be used as biomaterials.1.5 Advanced Materials Materials that are utilized in high-technology(or high-tech)application are sometimes termed advanced materials.Chapter1Introduction
34、By high technology we mean a device or product that operates or functions using relatively intricate and sophisticated principles;examples include electronic equipment(VCRs,CD players,etc.),computers,fiberoptical systems,spacecraft,aircraft,and military rocketry.Chapter1IntroductionThese advanced ma
35、terials are typicallyeithertraditionalmaterialswhosepropertieshavebeenenhancedornewlydeveloped,high-performancematerials.Chapter1IntroductionFurthermore,they may be of all material types(e.g.,metals,ceramics,polymers)and are normally relatively expensive.For example,advanced materials are materials
36、that used for lasers,integrated circuits,magnetic information storage,liquid crystal displays(LCDs),fiber optics and the thermal protection system for the Space Shutter Orbiter.Chapter1Introduction1.6METRIALSOFTHEFUTURESMARTMATERIALSSmart(or intelligent)materials are agroupofnewandstate-of-the-artma
37、terials now being developed that willhave a significant influence on many ofourtechnologies.Chapter1IntroductionTheadjective“smart”impliesthatthesematerialsareabletosensechangesintheirenvironmentsandthenrespondtothesechangesinpredeterminedmanners-traitsthatarealsofoundinlivingorganisms.Chapter1Intro
38、ductionInaddition,this“smart”conceptisbeingextendedtorathersophisticatedsystemsthatconsistofbothsmartandtraditionalmaterials.Componentsofasmartmaterial(orsystem)includesometypeofsensor(thatdetectsaninputsignal),andanactuator(thatperformsaresponsiveandadaptivefunction).Chapter1IntroductionActuators m
39、ay be called upon to changeshape,position,naturalfrequency,ormechanical characteristics in response tochange in temperature,electric fields,and/ormagneticfields.Fourtypesofmaterialsarecommonlyusedforactuators:shapememoryalloys,piezo-electricceramics,magnetostrictivematerials,Chapter1Introductionande
40、lectrorheological/magnetorheologicalfluids.Shapememoryalloysaremetalsthat,afterhavingbeendeformedrevertbacktotheiroriginalshapeswhentemperatureischanged.Piezoelectricceramicsexpandandcontractinresponsetoanappliedelectricfield(orvoltage);conversely,theyalsogenerateanChapter1Introductionelectricfieldw
41、hentheirdimensionsarealtered.Thebehaviorofmagnetostrictivematerialsisanalogoustothatofthepiezoelectricceramics,exceptthattheyareresponsivetomagneticfields.Chapter1IntroductionAlso,electrorheological and magneto-rheologicalfluidsareliquidsthatexperiencedramaticchangesinviscosityupon the application o
42、f electric andmagneticfield,respectively.Forexample,onetypeofsmartsystemisusedinhelicopterstoreduceaerodynamiccockpitnoisethatiscreatedbytherotatingrotorblades.Chapter1Introduction Piezoelectricsensorsinsertedintotheblades,monitorbladestressanddeformations;feedbacksignalsfromthesesensorsarefedintoac
43、omputer-controlledadaptivedevice,whichgeneratesnoise-cancelingantinoise.Chapter1IntroductionNANOTECHNOLOGYUntilveryrecenttimesthegeneralprocedureutilizedbyscientiststounderstandthechemistryandphysicsofmaterialshasbeentobeginbystudyinglargeandcomplexstructures,andthentoinvestigatethefundamentalbuildi
44、ngblocksofthesestructuresthataresmallerandsimpler.Chapter1IntroductionThisapproachissometimestermed“top-down”science.However,withtheadventofscanningprobemicroscopes,whichpermitobservationofindividualatomsandmolecules,ithasbecomepossibletomanipulatesandmoveatomsandmoleculestoformnewstructuresand,thus
45、,designnewmaterialsthatarebuiltfromsimpleatomicleveltoconstituents(i.e.,”materialsbydesign”).Chapter1IntroductionThisabilitytocarefullyarrangeatomsprovidesopportunitiestodevelopmechanical,electrical,magnetic,andotherpropertiesthatarenototherwisepossible.Wecallthisthe“bottom-up”approach,andthestudyof
46、thepropertiesofthesematerialsistermed“nanotechnology”;the“nano”prefixdenotesthatarethedimensionsofthesestructuralentitiesareontheorderofanano-meter(10-9m)-asarule,lessthan100nano-meters(equivalenttoapproximately500atomdiameters).Chapter1IntroductionOneexampleofamaterialofthistypeisthecarbonnanotube.
47、In the future,we undoubtedly find thatincreasinglymoreofourtechnologicaladvanceswillutilizethesenano-engineeredmaterials.Chapter1Introduction1.7MODERNMATERIALS”NEEDSIn spite of the tremendous progressthat has been made in the discipline ofmaterialsscienceandengineeringwithinthe past few years,there
48、still remaintechnological challenges,including thedevelopmentofevenmoresophisticatedand specialized materials,as well asconsiderationoftheenvironmentalimpactofmaterialsproduction.Chapter1IntroductionNuclear energy holds some promise,but the solutions to the many problemsthatremainwillnecessarilyinvo
49、lvematerials,from fuels to containmentstructurestofacilitiesforthedisposalofradioactivewaste.Significantquantitiesofenergyareinvolvedintransportation.Chapter1IntroductionReducingtheweightoftransportationvehicles(automobiles,aircraft,trains,etc.),as well as increasing engineoperating temperatures,wil
50、l enhancedfuelefficiency.Newhigh-strength,low-densitystructurematerialsremaintobedeveloped,aswellasmaterialsthathavehigher-temperaturecapabilities,foruseinenginecomponents.Chapter1IntroductionFurthermore,there is a recognizedneedtofindnew,economicalsourcesofenergyandtousepresentresourcemoreefficient
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