Metallurgical Fundamentals 冶金学.ppt

MetallurgicalFundamentals MetallurgicalFundamentals CrystalGeometryMetallicPropertiesPlasticDeformationSingleCrystalsvs PolycrystalsPhaseDiagramsStrengtheningMechanismsSofteningProcessesTopicsonSolidificationDiffusion CrystalGeometry CrystalGeometry Crystallinesolidshaveperiodic ordered3 DarraysThesearrayscanbedescribedintermsofaunitcellSevenbasiccrystalsystems interatomicdistancesandanglesCubic tetragonal orthorhombic rhombohedral hexagonal monoclinic triclinicFurthersymmetriesresultin14differentspace orBravais lattices BravaisLattices CrystalGeometry MostengineeringmetalshaveBCC FCC orHCPBravaislattices Face CenteredCubic HighestatomicpackingfactorPropertiesarefairlyisotropicExamplesAluminumCopperNickelGoldSilverGamma iron 911 1392 C Body CenteredCubic LoweratomicpackingfactorPropertiesarefairlyisotropicExamplesAlpha iron RT 911 C Delta iron 1392 C MT VanadiumMolybdenumChromiumTungsten HexagonalClosePacked PackingfactorvarieswithplaneofinterestAnisotropicExamplesTitaniumMagnesiumCobaltZincCadmiumZirconium MetallicProperties Structure Properties Similarcrystalstructure similarpropertiesBCCshowDBTTdeformmoreeasilyathighTFCClowerdiffusionrate goodcreepresistanceHCPpropertiesareanisotropic MeltingPoint Strength PureAnnealedMetalsMeltingpointsgroupedbycrystalstructureRoomtemperaturestrengthcorrelatestomeltingpointAtsamefractionofMP allmetalshavesimilarstrength MeltingPoint Strength MeltingPoint Strength PureAnnealedMetalsMeltingpointsgroupedbycrystalstructureRoomtemperaturestrengthcorrelatestomeltingpointAtsamefractionofMP allmetalshavesimilarstrengthWorkedandAlloyedMetalsTheserulesarethrownoutthewindow asweshallsee Density DensityImportantconsiderationfordesignValuesformetalsrange1 74g ccformagnesiumto19 30g ccforgoldValuesfornon metals polymers elastomers generally1 0to3 0g ccSpecificStrengthorStiffnessBetterdesigncriteria Density Strength Weight Density Strength Weight SingleCrystalsvs Polycrystals SingleCrystalsvs Polycrystals MostdiscussionsofarhasconcernedsinglecrystalsThetendenciesrelatedthusfarareamplifiedornegatedinpolycrystallinematerials SingleCrystalMaterials AtomsinBravaislatticearrangedinsamedirection crystallographicorientation Showisotropy anisotropyofBravaislatticeDifficulttoproduceinlargecomponentsImportantincreep resistantapplications turbineblades PolycrystallineMaterials Madeupofgroupsofsinglecrystals grains 10 100micronsEachcrystalhasit sowncrystallographicorientationRegionsbetweencrystals grainboundaries havehigherenergyduetolocaldistortionofatomicorder Polycrystals cont RandomcrystallographicorientationresultsinisotropyCommonengineeringmetalsarepolycrystallineEaseofproduction isotropicpropertiesProductionmethodseffectgrainsizeandorientationGrainsizeandorientationcaneffectisotropy PhaseDiagrams PhaseDiagrams PhasediagramsdescribethephasespresentinanymixtureoftwoelementsatstandardpressureovertherangeoftemperaturesexceedingthemeltingpointAssumeeverythinghappensinequilibriumNOTHINGhappensinequilibrium butwe lldealwiththatlater CompleteSolidMiscibility ElementsarecompletelysolubleatallconcentrationsExample Cu NisystemTerminology liquidus solidusLeverRule PartialSolidMiscibility OneelementissolubleintheotheronlytoacertainextentBasisforprecipitationhardeningAtintermediateconcentrationsintheliquidstate athree phasereactionoccursEutectic L Pb SnsystemPeritectic L Fe Csystem PartialSolidMiscibility PartialSolidMiscibility PartialSolidMiscibility Three phasereactionsalsooccurinsolidstateAnalogoustoliquidstatereactionsEutectiod Fe CsystemPeritectiod SolidStateReactions StrengtheningMechanisms Deformation Whensubjecttostress interatomicdistanceincreases elasticdeformationBeyondtheelasticlimit yieldpoint nofurtherincreaseininteratomicdistanceAdditionaldeformationisduetoatomicmovement plasticdeformationSlipTwinning Slip PrimarymechanismofplasticdeformationEntireplanesofatomsmoverelativetooneanother SlipSystems SlipSlipoccursonclose packedplanesinclose packeddirections slipsystems FCC 12systems 4planes 3directions BCC 24systems 6pl 2dir 12pl 1dir HCP 3systems 1plane 3directions However slipispossibleonnon closepackedplanes Twinning CooperativemotionofplanesrelativetoeachotherAtomiclocationismirroredacrossatwinboundary Twinning CanoccuronanyplaneordirectionHigherstressthanslipisnormallyrequiredEspeciallyimportantforHCPmetalsSomewhatmorefavorableatlowerdeformationtemperatures Twinning Thisis deformationtwin Alsooccursasalatticedistortionduringgraingrowth esp duringrecrystallizationCalled annealingtwin OftenseeninFCCmetals copperalloys stainlesssteels Twinning AnnealingtwininC26000brass LatticeDefects Howcanthishappen atomicscale Crystallatticesareimperfect point line planedefectsMovementoflinedefects called dislocations EdgeScrewMixed LatticeDefects EdgeDislocation ScrewDislocation DislocationMotion Dislocations glide untiltheymeetanobstacletomovement thencan climb or cross slip tocontinuemoving StrengtheningMechanisms Deformationoccursbyslip soneedtomakeslipmoredifficultGrainboundariesHighdislocationdensityParticlestoinhibitglideIfslipistoodifficult metalsbecomebrittleandcleaveratherthanyield StrengtheningMechanisms WorkHardeningAlloyingSolidsolutionsSecondphaseparticlesPhaseTransformation WorkHardening Atomicscale DislocationinteractionsDislocation dislocationDislocation particleDislocation grainboundaryOtherslipsystemscanbecomeactive WorkHardening MacroscaleDeformation elongationisobservedEffectscanbeillustratedbystress straincurve Stress StrainCurves Stress StrainCurves Stress StrainCurve Engineeringvs true ImportantpointsYieldPoint Upper LowerYieldPointElongation0 2 OffsetYieldStrengthUltimateTensileStrengthElongation ReductionofAreaModulusofElasticityEvidenceofWorkHardening Alloying SolidSolutions MacroscaleTwoelementscompletelydissolveineachother asinglephasesolidistheresultElementsoftenhavesamecrystalstructureCu Ni bothFCCMicroscaleDifferentelementshavedifferentatomicsizes impedingdislocationmotion Alloying SolidSolutions Alloying 2ndPhaseParticles MacroscaleTwoelementsdonotdissolveineachotherTwoelementsformintermediatephases particles richerinoneelementortheotherSolubilityvarieswithtemperatureElementsoftenhavedifferentcrystalstructuresAl MgMicroscaleSecondphaseshavecompletelydifferentcrystalstructure impedingdislocationmotion Alloying 2ndPhaseParticles PhaseTransformations MacroscaleSomemetals alloysexistindifferentphasesatdifferenttemperaturesHeatingtoabovethephasechange thenrapidlycoolingcreatesaphasethatis metastable atroomtemperatureFe CMicroscaleTheresultingdistortedcrystalstructureimpedesdislocationmotionThemetastablephasehasahighdislocationdensity againimpedingdislocationmotion PhaseTransformations SofteningProcesses SofteningProcesses TwotypesAnnealing followscoldworkTempering followshardeningandquenchinginsteels Annealing ThermaltreatmentperformedaftercoldworkDislocationsfromworkhardeningbecomeordered recoveryAmountoforderincreasesastimeprogresses recrystallizationCriticalamountofcoldworkmustbedoneforrecrystallizationtooccurAtime temperaturephenomenon Annealing MacroHeatinginfurnacetoreducehardnessMicroDislocationspropagatedduringcoldworkUponheatingDislocationsorganizeinto subgrain boundariesSubgrainscombineintodistinctnewgrainsWithsufficientcoldworkandadditionalheating grainscontinuetogrow resultinginfurthersoftening Annealing Annealing As Rolled 400C1280min 600C1280min 800C5min Tempering Steels reducethehardnessofas quenchedmartensiteMacroHeat furnace induction afteraustenitizeandquenchReducehardnessandtensilestrength increaseelongation drawing temperMicro Metastable martensitephasehasinherentstrainduetocrystalstructure BCTTemperingreducesstrain crystalstructurerevertstowardstableferritephase BCCAlsoresultsinFe3Cprecipitation Tempering Aluminum StainlessSteel etcPrecipitatesecondphaseparticlesaftersolutiontreatment notreally tempering TopicsonSolidification HeatTransferShrinkageSegregationNucleationandGrowthPlanarvs DendriticSolidificationGasEvolution HeatTransfer Forsolidificationtooccur heatmustberemovedSensibleheatofliquidLatentheatoffreezingSensibleheatofsolid HeatTransfer HeatTransfer HeatTransfer HeatisremovedthroughthemoldSurface volumeratioofcastingThermalconductivityofmetalandmoldingmaterialsInitiallyhighrateofcoolingduetocoldmold slowsdependingonheattransferbetweenmoldandenvironmentImportantprecursorofcastingproperties Shrinkage MostmetalsexperiencevolumetriccontractionuponsolidificationFe 10 5 Al 11 4 Linearcontractionis1 3ofvolumetriccontractionMetalssolidifyfrommoldwallinward soshrinkagecavitiesmayformunlessliquidmetalissuppliedReservoirsofliquidmetalmustbeavailableSolidificationmustbecontrolledsoliquidmetalcanbefedCAEmodelingofsolidificationcanhelpavoidshrinkage Shrinkage Segregation Phasediagramspredictmicroconstituentsupon equilibrium solidificationKineticsandthermodynamicsdon thappenfastenough Segregation describesnon equilibriumsolidification aka Coring Microscale diffusionofsoluteinsolventcreatescoringPhasediagramcanshowtheeffectsofcoring Segregation Segregation NucleationandGrowth SoliddoesnotimmediatelyformoncoolingfromliquidTemperaturemustgobelowliquidusbeforecrystalsformDrivingforceforcrystalgrowthincreaseswithincreasedundercooling resultinginlarge coredgrainsTypically meltsare inoculated withcrystalnucleijustpriortopouring Planarvs DendriticSolidification Withsufficienttimefordiffusionandheattransferatthesolid liquidinterface growthisalongaplanarfrontAsyoudepartfromequilibriumconditions dendriticgrowthoccurs3D pinetree growthintoliquidOccursbecauseofthesymmetryofcubiccrystalsDe