材料科學與工程導論總復習課件

Aboutthiscourse(cont’d)4.

Courseevaluation—

Howtoassessthelearningquality?

?Finalexam—70%weight(multiplechoice,analysisandcalculation,English/Chinesealternatively)?In-classquiz—30%weight(1quiz/Per2weeks,totally6quizzes)

?Homework—Byyourchoice,notamust

5.Textbook:D.R.AskelandandP.P.Phule,EssentialsofMaterialsScienceandEngineering(材料科學與工程基礎(chǔ)),TsinghuaUniversityPress,2005(影印本).EvolutionofmaterialsOurtasks,challengesandgoalsCompositionStructures

ProcessingProperties/performance

StrongerTougherLighterCheaperSaferSmarterFriendly

Ourtasks—4componentsinmaterialsresearch&thelinearinterrelationship

Ourchallenges&goals:

—TomakematerialsMaterialsscienceMaterialsengineeringMaterialsfamily—

classification(bybond)X.P.Zhang(張新平)X.Ma(馬驍)Z.M.Yang(楊中民)HuiHe(何慧)PE,PP,PCPA(Nylon)PolymersButylrubberNeopreneGFRPCFRPCompositesKFRPPlywoodAluminaSi-CarbideInorganicmat./CeramicsSoda-glassPyrexFe,Cu,Al,Ni,Au,Metals&AlloysSteels,castironMaterialsfamily—

classification(byuse)MaterialsStructuralmaterialsFunctionalmaterialsMagneticmaterials

Opticalmaterials

Electronicmaterials

Superconductivematerials

:Metallicmaterials

Plasticmaterials

Woodstructuralmaterials

Otherstructuralmaterials

:Whatisametal?Whatisaceramic?

—Natural&syntheticrock:hard,brittle&heat-resistantWhatisapolymer?

—Thewordpolymerliterallymeans"manyparts"

Betterknowas“plastics”bygeneralpublic

Thegreatmajorityofelementsintheperiodictablearemetals.

Ametalhasaparticulartypeofbondingknownasmetallicbonding(asdistinctfromionicbondingandcovalentbonding).

MetalstendtobeductilestrongshinymaterialsthatcorrodeeasilyWhatisacompositematerial?

—AnengineeringmaterialwhichconsistsofmorethanonematerialtypeStructureof“Metal&Alloys”—

Part1Chapt.1IntroductiontoMaterialsSci.&Eng.Chapt.2AtomicStructureChapt.3Atomic&IonicArrangementsChapt.4ImperfectioninA.&I.ArrangementsChapt.5Atom&IonMovementsinMaterialsChapt.6MechanicalProperties&BehaviorChapt.7FractureMechanics:Fatigue,CreepChapt.8StrainHardeningandAnnealingChapt.9Principle&ApplicationofSolidificationChapt.10SolidSolutionandPhaseEquilibriumChapt.11DispersionStrengthening&PhaseDiag.Chapt.12DispersionStrengtheningbyPT&HTChapt.13HeatTreatmentofSteels&CastIronsChapt.14NonferrousAlloysChapt.17CompositesPart2:Controllingthemicrostructure&mechanicalpropertiesofmaterialsPart1:Atomstructure,arrangements&movementPart3:EngineeringMaterialsLect.1Lect.2Lect.3Lect.4Lect.8Lect.5Lect.6Lect.7Atomic&IonicArrangements—

Lattice(晶格),unitcells(晶胞),basis(陣型)

andcrystalstructure

(晶體結(jié)構(gòu))AnIntroductiontoMaterialsScience&Engineering

—Lecture2(Chapters2+3)Today’sobjectives:

?Whydowestudystructureofmaterials—

Significance

?Theelectronicstructureoftheatom

?Theperiodictable&atomicbonding

?Bindingenergy&inter-atomicspacing

?Classificationofmaterialsbasedonatom/ionarrangement

?Thearrangementsincrystallinesolidsbasedonlattice,

basis,andcrystalstructure

?Points,directions&planesinunitcellsorcrystalstructure

Atomicstructure,atomic&ionicArrangement(原子結(jié)構(gòu)、原子和離子的排列)Lattice–Acollectionofpointsthatdividespaceintosmallerequallysizedsegments.Basis–Agroupofatomsassociatedwithalatticepoint.Unitcell–Asubdivisionofthelatticethatstillretainstheoverallcharacteristicsoftheentirelattice.Atomicradius–Theapparentradiusofanatom,typicallycalculatedfromthedimensionsoftheunitcell,usingclose-packeddirections(dependsuponcoordinationnumber).Packingfactor(堆積因數(shù))–

Thefractionofspaceinaunitcelloccupiedbyatoms.Atomic&IonicArrangements—

Lattice(晶格/點陣),basis(陣型),unitcells(晶胞),&crystalstructure

(晶體結(jié)構(gòu))(c)2003Brooks/ColePublishing/ThomsonLearning?

14typesofBravaislatticesgroupedin7crystalsystems

(七個晶系中的14個布拉菲點陣)Atomic&IonicArrangements—

SimpleCubic(SC),BCC&FCCSimpleCubic(SC):1atomperunitcellBodyCenteredCubic(BCC):2atomsperunitcellFaceCenteredCubic(FCC):4atomsperunitcell體心立方點陣面心立方點陣簡單立方Determinethenumberoflatticepointspercellinthecubiccrystalsystems.Ifthereisonlyoneatomlocatedateachlatticepoint,calculatethenumberofatomsperunitcell.SOLUTION:IntheSCunitcell:latticepoint/unitcell=(8corners)1/8=1InBCCunitcells:latticepoint/unitcell=(8corners)1/8+(1center)(1)=2InFCCunitcells:latticepoint/unitcell=(8corners)1/8+(6faces)(1/2)=4Thenumberofatomsperunitcellwouldbe1,2and4,forsimplecubic,body-centeredcubic,andface-centeredcubic,unitcells,respectively.Example:DeterminingthenumberoflatticepointsincubiccrystalsystemsBCCFCCSCAtomic&IonicArrangements—

Points,DirectionsandPlanesintheUnitCellMillerindices―Ashorthandnotationtodescribecertaincrystallographicdirectionsandplanesinamaterial.Denotedby[]brackets.Anegativenumberisrepresentedbyabaroverthenumber.Directionsofaform―Crystallographicdirectionsthatallhavethesamecharacteristics,althoughtheir‘‘sense’’isdifferent.Denotedbyhibrackets.Repeatdistance―Thedistancefromonelatticepointtotheadjacentlatticepointalongadirection.Lineardensity―Thenumberoflatticepointsperunitlengthalongadirection.Packingfraction―Thefractionofadirection(linear-packingfraction)oraplane(planar-packingfactor)thatisactuallycoveredbyatomsorions.ExampleSOLUTION:DirectionA1.Twopointsare1,0,0,and0,0,02.1,0,0,-0,0,0=1,0,03.Nofractionstoclearorintegerstoreduce4.[100]DirectionB1.Twopointsare1,1,1and0,0,02.1,1,1,-0,0,0=1,1,13.Nofractionstoclearorintegerstoreduce4.[111]DirectionC1.Twopointsare0,0,1and1/2,1,02.0,0,1-1/2,1,0=-1/2,-1,13.2(-1/2,-1,1)=-1,-2,2ExampleSOLUTION:PlaneA1.x=1,y=1,z=12.1/x=1,1/y=1,1/z=13.Nofractionstoclear4.(111)PlaneB1.Theplaneneverinterceptsthezaxis,sox=1,y=2,andz=2.1/x=1,1/y=1/2,1/z=03.Clearfractions:1/x=2,1/y=1,1/z=04.(210)PlaneC1.Wemustmovetheorigin,sincetheplanepassesthrough0,0,0.Let’smovetheoriginonelatticeparameterinthey-direction.Then,x=,y=-1,andz=2.1/x=0,1/y=1,1/z=03.Nofractionstoclear.AnIntroductiontoMaterialsScience&Engineering

—Lecture3(Chapters4+5)Today’sobjectives:

?Pointdefect,linedefect&areadefectinmaterials

?Themovementofdislocation

?

Importanceofdefectsformaterialsproperties

?HowAtom&ionmoveinmaterials?—Diffusion

?Howtodescribe“diffusion”rule—Fick’slaw

?Diffusion&materialsprocessing—Applications

Imperfectionsinatomic&ionicarrangementsofmaterials;atom&ionmovement(材料中原子和離子的排列缺陷,以及原子和離子的運動)Pointdefects—Imperfections,suchasvacancies,thatarelocatedtypicallyatone(insomecasesafew)sitesinthecrystal.Extendeddefects—Defectsthatinvolveseveralatoms/ionsandthusoccuroverafinitevolumeofthecrystallinematerial(e.g.,dislocations,stackingfaults,etc.).Vacancy—Anatomoranionmissingfromitsregularcrystallographicsite.Interstitialdefect—Apointdefectproducedwhenanatomisplacedintothecrystalatasitethatisnormallynotalatticepoint.Substitutionaldefect—Apointdefectproducedwhenanatomisremovedfromaregularlatticepointandreplacedwithadifferentatom,usuallyofadifferentsize.Threebasictypesofimperfection—1:PointdefectsDislocation—Alineimperfectioninacrystallinematerial.Edgedislocation—Adislocationintroducedintothecrystalbyaddingan‘‘extrahalfplane’’ofatoms.Screwdislocation—Adislocationproducedbyskewingacrystalsothatoneatomicplaneproducesaspiralrampaboutthedislocation.Mixeddislocation—Adislocationthatcontainspartlyedgecomponentsandpartlyscrewcomponents.Slip—Deformationofametallicmaterialbythemovementofdislocationsthroughthecrystal.Threebasictypesofimperfection—

2:Linedefects—Dislocation(位錯)Etchpits—Tinyholescreatedatareaswheredislocationsmeetthesurface.Theseareusedtoexaminethepresenceandnumberdensityofdislocations.Slipline—Avisiblelineproducedatthesurfaceofametallicmaterialbythepresenceofseveralthousanddislocations.Slipband—Collectionofmanysliplines,ofteneasilyvisible.Observingdislocations(a)Theatomsneartheboundariesofthethreegrainsdonothaveanequilibriumspacingorarrangement.(b)Grainsandgrainboundariesinastainlesssteelsample.Surfacedefects(cont’d)ApplicationsofdiffusionAtomandIonMovementsinMaterialsNitriding

—CarburizationforSurfaceHardeningofSteelsp-njunction—

DopantDiffusionforSemiconductorDevicesManufacturingofPlasticBeverageBottles/MylarTMBalloonsSputtering,Annealing—MagneticMaterialsforHardDrivesHotdipgalvanizing—CoatingsandThinFilmsThermalBarrierCoatingsforTurbineBladesDiffusionandmaterialsprocessingSintering

—Ahigh-temperaturetreatmentusedtojoinsmallparticles.Powdermetallurgy

—Amethodforproducingmonolithicmetallicparts.Dielectricresonators

—Hockeypuck-likepiecesofceramicssuchasbariummagnesiumtantalate(BMT)orbariumzinctantalate(BZN).Graingrowth

—Movementofgrainboundariesbydiffusioninordertoreducetheamountofgrainboundaryarea.Diffusionbonding

—Ajoiningtechniqueinwhichtwosurfacesarepressedtogetherathighpressuresandtemperatures.AnIntroductiontoMaterialsScience&Engineering

—Lecture4-1(Chapters6+7+8)Today’sobjectives:

?Introductionofbasicconceptsonmaterials’

mechanicalproperties.

?Somebasicmaterialsproperties&importancein

materialsselectionanddesign;materialstesting.

?Whatisfracturemechanics&howtouseit?

?Applicationoffracturemechanics

?Fatiguebehaviourofmaterials

?Creep,stressrupture&stresscorrosion

?ColdworkandannealingeffectonmaterialsMechanicalpropertiesofmaterialsandfracturebehavior(材料的力學性能及斷裂行為)Terminologyformechanicalproperties

Stress—Forceorloadperunitareaofcross-sectionoverwhichtheforceorloadisacting.Strain—Elongationchangeindimensionperunitlength.Young’smodulus—Theslopeofthelinearpartofthestress-straincurveintheelasticregion,sameasmodulusofelasticity.Shearmodulus(G)—Theslopeofthelinearpartoftheshearstress-shearstraincurve.Viscosity—Measureofresistancetoflow,definedastheratioofshearstresstoshearstrainrate.

Thixotropicbehavior—Materialsthatshowshearthinningandalsoanapparentviscositythatataconstantrateofsheardecreaseswithtime.(a)Tensile,compressive,shearandbendingstresses.(b)Young’smodulusofelasticmaterial.(c)Fornonlinearmaterials,theslopeofatangentisavariablequantitythatreplacesYoung’smodulusconstantConventionalmechanicalpropertiesAunidirectionalforceisappliedtoaspecimeninthetensiletestbymeansofthemoveablecrosshead.Thecross-headmovementcanbeperformedusingscrewsorahydraulicmechanismTensiletest:Equipment&specimenThemicrographshowsneckedregioninafracturedsampleStress&strainindeformation

(tension&compression)

Strain:=l/lo

(100%)

l

―changeinlength

lo

―originallength(gagelength)

Stress:=P/Ao

P―Loadappliedtothesample

Ao

―Cross-sectionareaofthesample

ModulusE=Stress/Strain=/

E―ElasticmodulusorYoung’smodulusNotethat:ThesearequalitativeTensilestress-straincurvesfordifferentmaterials

Stress-straincurveoftheAlalloyfromaboveTablePropertiesobtainedfromthetensiletestElasticlimitTensilestrength,NeckingHooke’slawPoisson’sratioModulusofresilience(Er)TensiletoughnessDuctilityBendtestforbrittlematerials?Bendtest—Applicationofaforcetothecenterofabartodeterminetheresistanceofthematerialtoanappliedload.?Thebendtest—Oftenusedformeasuringthestrengthofbrittlematerials;?Flexuralstrengthormodulusofrupture—Thestressrequiredtofractureaspecimeninabendtest.?Flexuralmodulus—Themodulusofelasticitycalculatedfromtheresultsofabendtest,givingtheslopeofstress-deflectioncurve.Three-pointbend(TPB)test:(a)Beforetest;(b)DuringtestingHardnessofmaterials?Hardnesstest—Measurestheresistanceofamaterialtopenetrationbyasharpobject.?Macrohardness—Overallbulkhardnessofmaterialsmeasuredusingloads>2N.?Microhardness—Hardnessofmaterialstypicallymeasuredusingloadslessthan2NusingsuchtestasKnoop(HK).?Nano-hardness—Hardnessofmaterialsmeasuredat1–10nmlengthscaleusingextremelysmall(~100μN)forces.IndentersfortheBrinell&Rockwellhardnesstests(a)Charpy&Izodtests;(b)dimensionsoftypicalspecimensImpacttestsFracturemechanics(斷裂力學)?Fracturemechanics—Thestudyofamaterial’sabilitytowithstandstressinthepresenceofaflaworacrack（裂紋）.?Fracturetoughness（斷裂韌性）—Theresistanceofamaterialtofailureinthepresenceofaflaworacrack.?Itistotallydifferentfromconventionaltensiletestorimpacttest,andgivesmuchmoreaccurateevaluationofamaterial’sproperties.Charpyspecimen:V-notch—LesstoseeinpracticeAcrackwiththesharptip—MoreoftentoseeinpracticeSchematicoffracturetoughnessspecimensEdgeflaws（邊裂紋）Internalflaws（內(nèi)部裂紋）Stressintensityfactor:（應(yīng)力強度因子）Kc:Fracturetoughness（斷裂韌性）

—Itisamaterial’spropertyImportanceoffracturemechanics?Selectionofamaterial?Designofacomponent?Designofamanufacturingortestingmethod?Brittlefracture（脆斷）&Griffithflaw（格里菲思微裂紋）—Acrackorflawinamaterialthatconcentrates（集中）&magnifies（放大）theappliedstress.SchematicdiagramofaGriffithflawinaceramicTheactualstressatthecracktip:Micro-structuralfeaturesoffractureinmetallicmaterials?Ductilefracture(韌/塑/延性斷裂)–Ametalfractureswithgoodductilityandtoughness.Itnormallyoccursinatransgranular（穿晶斷裂）manner(throughthegrains),i.e.,thecrackswouldgothruthegrains.Microvoids(微孔)forminfractureprocess.?Brittlefracture(脆性斷裂)–Ametaloralloyfractureswithpoorductilityandtoughness.Itoccurswithoutplasticdeformationandtakesanintergranularpath（沿晶斷裂）(alongthegrainboundaries).Cleavagefracture（解理斷裂）isoftenobserved.?Chevronpatternfracture(人字紋形斷裂)–Acommonfracturefeatureproducedbyseparatecrackfrontspropagating（擴展）atdifferentlevelsinthematerial.Fatigue（疲勞）ofmaterialsFatigue–Itmeansthatthematerialistiredfromtheappliedcyclicload（循環(huán)載荷）.Itistheloweringofstrengthorfailureofamaterialduetorepetitivestress（反復應(yīng)力）whichmaybeaboveorbelowtheyieldstrength.80%offailuresofengineeringparts&structuresarerelatedtofatigue,moreorless!!!Creep（蠕變）–Atimedependent,permanentdeformationathightemperatures,occurringatconstantload（恒載荷）orconstantstress（恒應(yīng)力）.Beach（海灘紋）orclamshell（蛤殼紋）marks–Patternsoftenseenonacomponentsubjectedtofatigue.Rotatingcantileverbeam（懸臂梁）test–Anoldertestforfatiguetesting（P.197）.S-Ncurve(alsoknownastheW?hlercurve)–Agraphshowingstressasafunctionofnumberofcyclesinfatigue.Creep（蠕變）,stressrupture（應(yīng)力斷裂）&stresscorrosion（應(yīng)力腐蝕）Stress-rupturecurve（應(yīng)力斷裂曲線）—Amethodofreportingtheresultsofaseriesofcreeptests（蠕變試驗）byplottingtheappliedstressversustherupturetime.Stress-corrosion—Aphenomenoninwhichmaterialsreactwithcorrosive（腐蝕性）

chemicalsintheenvironmentleadingtotheformationofcracksandloweringofstrength.Creep（蠕變）–Atimedependent,permanentdeformationathightemperatures,occurringatconstantload（恒載荷）orconstantstress（恒應(yīng)力）.StrainHardeningandAnnealing（應(yīng)變/加工硬化與退火）Strainhardeningandannealingrelationshipofcoldworking（冷加工）tothestress-straincurve:Manufacturingprocessesthatmakeuseofcoldworkingaswellashotworking.Commonmetalworkingmethods軋制rolling擠出extrusion拉拔wiredrawing沖壓stamp/punch鍛造forgingThreestagesofannealingRecovery（回復）—Alow-temperatureannealingheattreatmentdesignedtoeliminateresidualstresses（殘余應(yīng)力）introducedduringdeformationwithoutreducingthestrengthofthecold-workedmaterial.Recrystallization（再結(jié)晶）—Amedium-temperatureannealingheattreatmentdesignedtoeliminatealloftheeffectsofthestrainhardeningproducedduringcoldworking.Graingrowth（晶粒長大）—Movementofgrainboundariesbydiffusioninordertoreducetheamountofgrainboundaryarea.AnIntroductiontoMaterialsScience&Engineering

—Lecture5(Chapters9+10)Today’sobjectives:

?Whatissolidification凝固?whysolidificationcanoccur?

?Solidificationmechanismandtheory;

?Solidificationdefects&howtopreventthedefects;

?Someapplication(glass-making,joiningmetalsetc);

?Whatisaphase相andwhatisaphasediagram相圖(PD)?

?Solid-solutionstrengthening固溶強化andother;

?Typicalsolidificationofsolid-solutionalloybyPDSolidificationofmaterials&Phaseequilibrium(材料的凝固及相平衡)Developmentoftheingot（鑄錠）structureofacastingduringsolidification:Nucleationbegins,Thechillzone（激冷區(qū)）forms,PreferredgrowthproducesthecolumnarZone（柱狀區(qū)）,and(d)Additionalnucleationcreatestheequiaxedzone（等軸區(qū)）Howisasolidificationprocessgoing?

—Twosteps:nucleation&growth（形核與長大）PhasesEquilibriumandPhaseDiagram（相平衡及相圖）?Phase–Anyportionincludingthewholeofasystem,whichisphysicallyhomogeneouswithinitandboundedbyasurfacesothatitismechanicallyseparablefromanyotherportions.?Gibbsphaserule–Describesthenumberofdegreesoffreedom（自由度）,orthenumberofvariablesthatmustbefixedtospecifythetemperatureandcompositionofaphase(2+C=F+P,wherepressureandtemperaturecanchange,1+C=F+P,wherepressureortemperatureisconstant).?P-Tdiagram壓力－溫度相圖–Adiagramdescribingthermodynamicstabilityofphasesunderdifferenttemperatureandpressureconditions(sameasaunaryphasediagram一元相圖).Solubility–Theamountofonematerialthatwillcompletelydissolve（溶解）inasecondmaterialwithoutcreatingasecondphase（不產(chǎn)生第二相）.Unlimitedsolubility（無限互溶）–Whentheamountofonematerialthatwilldissolveinasecondmaterialwithoutcreatingasecondphaseisunlimited.Limitedsolubility（有限互溶）–Whenonlyamaximumamountofasolutematerialcanbedissolvedinasolventmaterial.SolubilityandSolidSolutions（固溶體）Solid-solution/alloyingstrengthening（合金強化）–Increasingthestrengthofametallicmaterialviatheformationofasolidsolution（固溶體）.Dispersionstrengthening（彌散強化）–Strengthening,typicallyusedinmetallicmaterials,bytheformationofultra-finedispersionsofasecondphase（第二相）,includingnano-sizedparticle(dispersion).Reinforcementstrengthening（復合強化）–Materialisenhancedbyaddingstrongreinforcements,suchasceramicparticlesorfibers/whispers(metalmatrixcomposites)Twinningstrengthening（孿晶強化）–Twinsareintroducedintomaterials(metalsoralloys)toincreasethestrength.Solid-SolutionStrengthening（固溶強化）Theeffectsofseveralalloyingelementsontheyieldstrengthofcopper.Ni鎳andZn鋅atomsareaboutthesamesizeascopperatoms,butberyllium鈹andtin錫atomsaremuchdifferentfromcopperatoms.Increasingbothatomicsizedifferenceandamountofalloyingelementincreasessolid-solutionstrengthening.Strengtheningbysolid-solutiondeformationThecoolingcurveforanisomorphousalloyduringsolidification.Weassumethatcoolingratesaresmallsoastoallowthermalequilibrium(熱平衡)totakeplace.Thechangesinslopeofthecoolingcurveindicatetheliquidus（液相線）andsolidus（固相線）temperatures,inthiscaseforaCu-40%Nialloy.SolidificationofabinaryalloyinPhas.Diag.liquidusAnIntroductiontoMaterialsScience&Engineering

—Lecture7(Chapters11+12)Today’sobjectives:

?Fundamentalsofdispersion（彌散）strengtheningtodeterminethemicrostructure.

?Typesofreactionsthatproducemultiple-phasealloys（多相合金）.

?Methodstoachievedispersionstrengtheningby

controllingthesolidificationprocess.

?Dispersionstrengtheningbystudyingavarietyof

solid-statetransformation（固態(tài)轉(zhuǎn)變）processes.

?Nonequilibrium（非平衡）phasetransformations—martensiticreaction（馬氏體轉(zhuǎn)變）strengthening.Materialsstrengtheningbymultiphase,Phasetransformation&heattreatment(材料的多相彌散強化、相變和熱處理強化)Dispersionstrengthening-Increasingthestrengthofamaterialbyformingmorethanonephase.Matrix-Thecontinuoussolidphaseinacomplexmicrostructure.Precipitate（沉淀/析出物）-Asolidphasethatformsfromtheoriginalmatrixphasewhenthesolubilitylimitisexceeded.Eutectic（共晶）-Athree-phaseinvariant（不變、平衡）reactioninwhichoneliquidphasesolidifiestoproducetwosolidphases.Principlesandexamplesofdispersionstrengthening(彌散強化)Thefivemostimportantthree-phasereactionsinbinaryphasediagrams共晶反應(yīng)包晶反應(yīng)偏晶反應(yīng)共析反應(yīng)包析反應(yīng)Lead-tin(Pb-Sn)equilibriumphasediagramThePb-2%Snalloyisasingle-phasesolidsolution.Solidificationµstructureofasolid-solutionalloySolidification凝固,precipitation析出,andmicrostructureofaPb-10%Snalloy.Somedispersionstrengthening彌散強化occursastheβsolidprecipitates.Solidificationµstructureofasolid-solutionalloySolidificationµstructureoftheeutecticalloy共晶合金Pb-61.9%Sn.Example:PhasesinPb-SnphasediagramThecoolingcurveforaeutecticalloyisasimplethermalarrest熱轉(zhuǎn)變,sinceeutecticsfreezeormeltatasingletemperature,similartothatofapuremetal.ThecoolingcurveforaeutecticalloyAgehardening（時效強化）—Aspecialdispersion-strengtheningheattreatment.Bysolutiontreatment,quenching淬火（快速冷卻）,andaging（時效）,acoherentprecipitateformsthatprovidesasubstantialstrengtheningeffect.Alsoknownasprecipitationhardening（沉淀強化）,itisaformofdispersionstrengthening.Ageorprecipitationhardening時效強化或沉淀強化Step1:SolutionTreatment固溶處理Step2:Quench淬火（快速冷卻）Step3:Age時效Guinier-Preston(GP)zones（GP區(qū)）—Tinyclustersofatomsthatprecipitatefromthematrixintheearlystagesoftheage-hardeningprocess.MicrostructuralevolutioninageorprecipitationhardeningThethreestepsintheage-hardeningheattreatmentandthemicrostructuresthatareproduced.鋁合金的時效強化Schematicofthreestepsintheage-hardeningheattreatmentSupersaturatedSolidSolutionAnIntroductiontoMaterialsScience&Engineering

—Lecture7(Chapter13)Today’sobjectives:

?Designations(牌號)&classificationsofsteels

?Whyisheattreatmentnecessaryforasteel?

?Whatareconventionalheattreatments?

?Discusshowtousetheeutectoidreaction(共析反應(yīng))to

controlthestructureandpropertiesofsteels

throughheattreatmentandalloying.

?Examinetwospecialclassesofferrousalloys:

stainlesssteels(不銹鋼)andcastirons.Heattreatmentofsteels&castirons(鋼和鑄鐵的熱處理)Designations&classificationofsteelsDividingpointofSteel&Iron—2.11%Cisthedividingpointbetween“Steels”&“Castirons”:C%below2.11isSteel,above2.11isCastiron.Differentnationshavedistinctdesignationsofsteels,USA:AISI+SAE+ASTM,China:GB(國標),Germany:DIN,Japan:JIS,UK:BSetc.Designations(牌號)—TheAISI(AmericanIronandSteelInstitute)andSAE(SocietyofAutomotiveEngineers)providedesignationsystemsforsteelsthatuseafour-orfive-digitnumber.Classifications—Steelscanbeclassifiedbasedontheircompositionorthewaytheyhavebeenprocessed:Carbonsteels(碳鋼),alloysteels(合金鋼)andspecialtysteels(特種鋼)etc.TheeutectoidportionofFe-Fe3CphasediagramAnexpandedversionoftheFe-Cdiagram.ProcessAnnealing(工藝退火)—EliminatingColdWork:Alow-temperatureheattreatmentusedtoeliminateallorpartoftheeffectofcoldworkinginsteels.AnnealingandNormalizing

(退火和正火)—DispersionStrengthening:Annealing-Aheattreatmentusedtoproduceasoft,coarse

pearlite(珠光體)insteelbyaustenitizing(奧氏體化),thenfurnacecooling(隨爐冷卻).Normalizing-Asimpleheattreatmentobtainedbyaustenitizingandaircooling(空冷)toproduceafine

pearliticstructure.Spheroidizing(球化處理)—Improvingmachinability(可加工性):Spheroidite-Amicroconstituentcontainingcoarsespheroidal

cementiteparticlesinamatrixofferrite(鐵素體),permittingexcellentmachiningcharacteristicsinhigh-carbonsteels(高碳鋼).SimpleheattreatmentsRetainedaustenite