3-5_线缺陷.ppt

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1、3.5Linedefect（dislocation）–Explainwhythestrengthof“real”crystallinematerialsismuchless(102to103times)thanthetheoreticalvalue.–Motionofdislocationsisthemechanismattheoriginofplasticdeformationofcrystals(ductilevs.brittlebehavior).–Allowssome“cohesion“betweencrystalsofdifferentorientations(l

2、owanglegrainboundariesarearraysofdislocations).–Explainsanumberofcrystal-crystaltransitions.1.Typesofdislocation2.Burgersvector(伯格斯矢量)anddislocationproperties3.Stressfieldarounddislocationandstrainenergyofdislocation4.Movementofdislocation5.Dislocationreaction1.Typesofdislocationa.Edgedisl

3、ocation(刃位错）b.Screwdislocation（螺位错）c.Mixeddislocationa.Edgedislocationb.ScrewdislocationAtomsarrangementarounddislocationlines（b）atomsslippingoncrystalplaneflankbyscrewdislocationslippingplane（a）shapeofcrystalplaneperpendiculartodislocationCMixeddislocation（a）Formationofmixeddislocation（b）

4、Dissociationofmixeddislocation（c）Atomsslippingaroundmixdislocationline2.BurgersvectoranddislocationpropertiesTheBurgersvectorrepresentsthemagnitudeanddirectionofthelatticedistortionofdislocationinacrystal.a.DeterminationandexpressofBurgersvectorb.ConservationofBurgersvector（a）b1＝b2＋b3（b）c.

5、Continuityanddensityofdislocation1.ContinuityofdislocationDensityofdislocation:ThetotallengthofdislocationinunitvolumecrystalL——lengthofdislocation；n——numberofdislocationlines；S——crosssectionareaofcrystalMeasurementofdislocationdensityincrystal：TEM,X-ray, metalloscopedislocationdensityincr

6、ystal:Singlecrystal﹤103~104/cm2；Metalcrystalafterannealing104~108/cm2；Metalcrystalafterquenching1012~1014/cm2。3.StressfieldarounddislocationandstrainenergyofdislocationTheoryfoundation：continuouselasticmediummodelHypothesis：1.ThecrystalobeyHook’slawabsolutely；2.Thecrystalisisotropic；3.Thec

7、rystaliscontinuousmedium。Stressfieldsaroundanedgedislocation.(ThedislocationlineisOx3),(a)σ11;(b)σ22;(c)σ33;(d)σ12.Strainenergyofdislocation(Wtot)Wtot=Wcore+Wel（1）Coreenergyofdislocation(Wcore)（2）Elasticstrainenergy(Wel)Elasticstrainenergyofedgedislocationperl