20111219_固态转变-非扩散型相变

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1、SOLID-SOLIDTRANSFORMATIONS固态转变Displacive(Diffusionless)Transformations主讲：刘国权教授材料优化设计与生物医用材料研究室北京科技大学材料科学与工程学院2.3.2Classificationsbasedonmechanisms•Buerger(1951)hasintroducedaclassificationbasedonmechanisms,namely,(a)reconstructiveand(b)displacivetransformations.•Inthecurrentmetallurgicalliterat

2、ure,however,amechanisticclassificationgroupstransformationsinto(a)diffusionaland(b)displacive(whichincludesmartensitic)transformations.•Inordertodifferentiatethemechanismsofatommovementsacrossthetransformationfront,Christian(1965,1979)hascomparedthemovementsinvolvedindiffusionalanddisplacivetra

3、nsformationswithcivilianandmilitarymovements,respectively.PhaseTransformations:ExamplesfromTitaniumandZirconiumAlloys.PergamonMaterialsSeriesVol12,2007H.K.D.H.Bhadeshia.Fromwww.msm.cam.ac.uk/.ThermodynamicPhaseTransformations:ExamplesfromTitaniumandZirconiumAlloys.PergamonMaterialsSeriesVol12,2

4、007DisplacivePartitionlessPergamonMaterialsSeriesVol12,2007DiffusionlessTransformationsAdiffusionless/displacivetransformationisaphasechangethatoccurswithoutthelong-rangediffusionofatomsbutratherbysomeformofcooperative,homogeneousmovementofmanyatomsthatresultsinachangeincrystalstructure,butpart

5、itionless.Theseatomicmovementsaresmall,usuallylessthantheinteratomicdistances,andtheatomsmaintaintheirrelativerelationships.Theorderedmovementoflargenumbersofatomsleadsometorefertotheseasmilitarytransformationsincontrasttociviliandiffusion-basedphasechanges.Atrulydisplacivetransformationoccurst

6、hroughthepassageofaglissileinterfacewhichisessentiallyadisplacement(orshear)front,themovementofwhichisnotassistedbythermalactivation.Themostcommonlyencounteredtransformationofthistypeisthemartensitictransformationwhich,whilebeingthebestknown,isactuallyonlyonesubsetofnon-diffusionaltransformatio

7、ns.Themartensitictransformationinsteelrepresentsthemosteconomicallyimportantexampleofthiscategoryofphasetransformations.(Displacive)马氏体相变http://en.wikipedia.org/wiki/File:Diffusionless_classification.svghttp://en.wikipedia.org/wik