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1/4P2Materialscienceistheinvestigationoftherelationshipamongprocessing,structure,properties,andperformanceofmaterials.材料科学是研究材料的加工，组织性能和功能之间关系的学科（材料与工程之间的关系可以用图一的四面体来表示）P2Thedisciplineofmaterialsscienceinvolvesinvestigatingtherelationshipsthatexistbetweenthestructuresandpropertiesofmaterials.材料科学是研究材料的结构和性能之间的关系的学科Incontrast,materialsengineeringis,onthebasisofthesestructure-propertycorrelations,designingorengineeringthestructureofamaterialtoproduceapredeterminedsetofproperties.而材料加工是在材料组织和性能关系的基础上，对材料的组织进行设计，以获得一系列预定的性能P5Semiconductorshaveelectricalpropertiesthatareintermediatebetweentheelectricalconductorsandinsulators.Furthermore,theelectricalcharacteristicsofthesematerialsareextremelysensitivetothepresenceofminuteconcentrationsofimpurityatoms,whichconcentrationsmaybecontrolledoververysmallspatialregions.Thesemiconductorshavemadepossibletheadventofintegratedcircuitrythathastotallyrevolutionizedtheelectronicsandcomputerindustries.半导体有介于电导体和绝缘体之间的性能。此外这些材料做成的仪器对极小浓度的混杂原子特别灵敏这种混杂原子可以在非常小的空间区域控制起来半导体使集成电路有可能到来，集成电路彻底改变了电子行业和计算机行业P5Compositesareformedfromtwoormorematerials,producingpropertiesthatcannotbeobtainedbyanysinglematerials.Concreteandfiberglassaretypicalexamplesofcompositematerials.Acompositeisdesignedtodisplayacombinationofthebestcharacteristicsofeachofthecomponentmaterials.Withcompositeswecanproducelightweight,strong,ductile,hightemperature-resistantmaterialsthatareotherwiseunobtainable,orproducehardyetshock-resistantcuttingtoolsthatwouldotherwiseshatter.复合材料是由两个或两个以上的材料复合而成生成单一材料得不到的性能。混凝土和玻璃纤维都是复合材料典型的例子。一个合成物是设计用来展现每个材料成分最佳特性的组合。用复合材料我们可以生产出轻质、强度高塑性好，难获得的耐高温材料或者生产出坚硬的、的抗冲击性强而不破碎的切削工具P25Manytime,thephysicalpropertiesand,inparticular,themechanicalbehaviorofamaterialdependonthemicrostructure.Microstructureissubjecttodirectmicroscopicobservation,usingopticalorelectronmicroscopes.Inmanyalloy,microstructureischaracterizedbythenumberofphasepresent,theirproportions,andthemannerinwhichtheyaredistributedorarranged.Themicrostructureofanalloydependsonsuchvariablesasthealloyingelementspresent,theirconcentration,andtheheattreatmentofthealloyP36Inadditiontopearlite,othermicroconstituentsthatareproductsofthe2/4austenitictransformationexist;oneoftheseiscalledbainite.Themicrostructureofbainiteconsistsofferriteandcementitephases,andthusdiffusionalprocessesareinvolvedinitsformation.Bainiteformsasneedlesorplates,dependingonthetemperatureofthetransforrnation除了珠光体之外，其他的微观结构也是奥氏体转变的产物。其中一个就叫做贝氏体。贝氏体的微观结构是由铁素体和渗碳体所组成，因此在它的形成中包括的扩散的过程。贝氏体的外形是针状还是板条状取决于转变时的温度P37Anothermcroconstituentorphasecalledisformedwhenaustenitizediron-carbonalloysarerapidlycooledtoarelativelylowtemperature.Martensiteisanonequilibriumsinglephasestructurethatresultsfromadiffusionlesstransformationofaustenite.Themartensitictransformationoccurswhenthequenchingrateisrapidenoughtopreventcarbondiffusion.Anydiffusionwhatsoeverwillresultintheformationofferriteandcementitephases.当奥氏体化的铁碳合金被快速的冷却到一个相对低的温度时，另外一个叫做马氏体的微观结构或者说是相就会形成。马氏体是一个非平衡单相组织，它是由奥氏体的非扩散转变而形成的。当淬火时的速度快的足以去阻止碳扩散时，马氏体的转变就会发生。无论什么样的扩散（转变）都会导致铁素体相和渗碳体相的形成P40Afteryielding,thestressnecessarytocontinueplasticdeformationinmetalsincreasestoamaximum,pointMinFigure1.26,andthendecreasestotheeventualfracture,pointF.Thetensilestrengthisthestressatthemaximumontheengineeringstressstraincurve.Thiscorrespondstothemaximumstressthatcanbesustainedbyastructureintension.Ifthisstressisappliedandmaintained,fracturewillresult.Alldeformationuptothispointisuniformthroughoutthenarrowregionofthetensilespecimen.However,atthismaximumstress,asmallconstrictionorneckbeginstoformatsomepoint,andallsubsequentdeformationisconfinedatthisneck,asindicatedbytheschematicspecimeninsetsinFigure1.26.Thisphenomenonistermed“necking,”andfractureultimatelyoccursattheneck抗拉强度屈服之后，金属持续发生塑性变形的应力会达到一个最大值，图表1.2中的M点，然后减小直到最终断裂F点。抗拉强度σb就是工程应力—应变曲线上最大值时的应力。这和组织所能维持的拉力的最大应力相一致。如果这应力施加并保持就会引起断裂。在受拉试样的狭小区域整个范围内达到这一点时的所有变形都是均匀的。然而在这个最大应力处，有小的或缩颈开始在某一处形成，随后的变形就限制在缩颈处如插图1.26中的试样，这种现象叫做颈缩，并且断裂基本上就在经缩处。一般的当材料的强度被用以设计时就要利用屈服强度，这是因为当施加的应力达到抗拉强度时，组织会因发生强烈的塑性变形而改变而不能使用P72Steelswithacarbonrangeof0.05to.0.30percentarecalledlow-carbonsteels.Steelsinthisclassaretough,ductile,andeasilymachined,formed,andwelded.Mostofthemdonotrespondtoanyheattreatingprocessexceptcasehardening.碳含量从0.05%到0.30%的钢被称为低碳钢。这类钢韧性好塑性好容易加工形成和焊接。除了表面渗碳硬化大部分对任何热处理没有回应。P72Thosesteelshaveacarbonrangefrom0.30to0.45percent.Theyarestrong3/4andhardbutcannotbeworkedorweldedaseasilyaslow-carbonsteels.Becauseoftheirhighercarboncontent,theycanbeheattreated.Successfulweldingofthesesteelsoftenrequiresspecialelectrodes,buteventhengreatercaremustbetakentopreventformationofcracksaroundtheweldarea.这类钢的碳含量从0.30%到0.45%。他们强度和硬度很高，但不能像低碳钢一样容易被加工和焊接。因为他们有更高的碳含量他们可以进行热处理。通常需要采用特殊焊条才能成功地焊接这类钢材P74Theadditionofmanganesetosteelproducesafinegrainstructurewhichhasgreatertoughnessandductility.Manganesealwayspresentsinasteeltosomeextentbecauseitisusedasadeoxidiser.在钢中加入锰会生成使金属有很好的韧性和塑性的细晶组织。锰总是一定程度出现在钢中因为它被用作脱氧剂。P74Alwayspresenttosomeextent,becauseitisusedwithmanganeseasadeoxidiser.总是一定程度的存在因为它和锰共同作为脱氧剂。P74Whenquantitiesofchrom