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第六章淬火与时效(2).ppt
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第六章无多型性转变合金的淬火与时效(2)6.5时效前后合金性能的变化6.6影响时效过程及材料性能的因素6.7淬火(固溶处理)与时效规程6.5时效前后合金性能的变化6.5.1力学性能时效时间硬度合金成分、时效温度、力学性能的变化关系IIIGenerally,apeakcorrespondstoakindofprecipitate.ForAl-Cualloys,therecanbemorethan4peaksresultedfromtheformationofGP,’’,’and’.However,thereisalsothecasewheredifferentpeakscannotbediscriminated,oronepeakcorrespondstoseveralkindsofprecipitates.时效强化机制解析:位错与脱溶质点间的相互作用Orowan机制:位错绕过机制切割机制:短程作用(界面,反相畴)、长程作用Interpretation:Microstructurecontainsanumberofheterogeneities,whichcancontributebothtolocalizationofplasticflow,andtoinitiationandpropagationofcrack.Inorderofdecreasingsize,theheterogeneitiesincludeintermetallicparticles,quenchinducedintergranularandintragranularprecipitates,andprecipitate-freezonessituatedatthegrainboundaries.FailureModes:intermetallicdecohesion,intergranularfractureandintragranularfracture.Orowan机制:位错绕过机制位错环绕机制(Orowan机制)强化理论Dislocationtheory:K=1forscrew,K=1-forknife,ispoissoncoefficient,Gisshearmodule,bburgersvector,r0radiusofdislocation,Rhalfofthedistancebetweenparticles,fvolumefraction,rradiusofparticle.切割机制强化作用(以10b为界限,小于10b为短程作用;大于10b为长程作用)-----短程作用--------(1)界面能增加导致的额外切应力计算:新增面积:新增能量:ount,estoforallparticlesinaunitarea.(2)反相畴界能增加导致的附加切应力机算:orderedparticles可见短程作用中,增加的切应力具有以下形式Parabolic-type-----长程作用-----(3)长程作用计算:两应变场的相互作用whereEisYoung’smodule,,afunctionofthemismatchoflatticesofthe2phase.Theotherparametershavetheconventionalmeanings.Iftheincreaseofthestressneededtoincisetheparticlesexcessesthatintroducedbythelong-rangeeffect,thenthelong-rangeeffectistobeneglected.两种机制的相互作用---强化与沉淀粒子尺寸的关系质点半径强化增量开始阶段:粒子小、共格,易被切割后阶段:大、半共格或非共格,绕过Inrealalloys,largervolumeandfinerparticles;strainfield 内容来自淘豆网www.taodocs.com转载请标明出处.