microstructure evolution in deform

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1、MicrostructureModelinginDEFORMTMOutlineMicrostructureModelingPhenomena(graingrowth,recrystallization,phasetransformation)MicrostructureModelingwiththeJMAKequationTMJMAKModelingspecifictoDEFORMHowtocomputeyourownJMAKconstantsfromexperimentTypesofMic

2、rostructureEvolutionGrainGrowthgrainsizeincreaseswithtimeandtemperatureRecrystallizationsomeorallofthedeformedmicrostructurebecomes“recrystallized”therecrystallizedfractionhasanewgrainsize(generallysmaller)dynamicmetadynamicstaticThe“average”gr

3、ainsizeisa“rule-of-mixtures”computationbetweentheunrecrystallizedfractionandtheinitialgrainsize,andtherecrystallizedfraction(s)andtherecrystallizedgrainsizeTransformation(beyondthescopeofthispresentation)afractionofthemicrostructuretransformsintoanewp

4、hasePhasePhasePhase+PhasePhasePhasePhase+PhaseGrainGrowthGrainboundariesarehigh-energyregionsofthemicrostructure,andsincesystemstendtoseeklowerenergy,thereisadrivingforcetoreducethegrainboundaries.Thisresultsinanaverageincreaseingrainsize.•M

5、anygrainboundaries=•Fewergrainboundaries=SmallaveragegrainsizeLargeraveragegrainsizeGrainGrowthThedrivingforceforgraingrowthisnotasstrongasthedrivingforceforrecrystallizationThus,graingrowthonlyoccursbeforeanyrecrystallizationmaytakeplace,orafterallre

6、crystallizationisfinishedGraingrowthincreasestheaveragesizeofgrains(inrealmicrostructuregrainsizedistributions,somegrainsmaygrowsmallerattheexpenseoflargergrowinggrains,buttheaveragesizeincreases)Recrystallization(Rex)Asamicrostructureisdeformed,itbec

7、omesdisordered,andhencebecomesahigherenergymicrostructurethantheundeformedstateThereisadrivingforcetoreturnthishigher-energystatebacktothelower-energyundeformedstate:thisiscalledrecrystallization(rex)Thiscanoccurduringdeformation(dynamicrex),immediate

8、lyafterdeformationstops(metadynamicrex),orafteradelayedperiodafterdeformationstops(staticrex)RecrystallizationNucleationRecrystallizationtransformsadeformedmicrostructurebacktoan“undeformed”microstructureintwosteps:(1)creatingre