材料物理导论Chapter .ppt

《材料物理导论Chapter .ppt》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

1、1.Diffusionphenomenon、essence、studymethodDiffusion:Transportationofatomsormolecules,theonlytransportationfortheatomsinsolidsDiffusionessence:AtomstransportfromoneplacetoanotherbythermalmovementStudymethod：a)representationtheory一Describingthespeedandquantityofthemattertransportationaccord

2、ingtothemeasuredparametersb)Atomtheory一Howtotransportoftheatomsduringthediffusionprocess2.DiffusionconditionforsolidmetalsDiffusionismoredifficultforsolidmetalthangasandliquidduetothelargebondingforce,thediffusionconditioncontains:HighTemperature(T):Hightemperatureleadstoalargediffusiona

3、ctivationenergytoovercomethebindingofthearoundatoms.Fe:diffusiontemperature:500oC;CdiffusiontemperatureinFe:100oCLongtime(t):thelongestdiffusiondistanceofatomsincrystallatticeverytime0.3～0.5nm，1nmdistancerequireaboutonehundredmillionoftransportationAtomsSolutedinmetals:asolidsolubilityfo

4、rtheatomsinthemetalsrequiredfordiffusionDiffusiondrivenforce:thedirectionaldiffusionneedadiffusiondrivenforce3.Diffusiontypes(1)Dividedbyconcentrationchangeornot:Self—diffusion：diffusioninpurematter,noconcentrationchange,independentondρ/dx,relativewiththermalvibration,onlyinpuremetalsand

5、uniformsolidsolutionse.g.crystalgraingrowthinpuremetals；graingrowthinuniformsolutiosmutual/chemicaldiffusion：concentrationchange,mutualdiffusiondependsonthedifferentatomsolution,thediffusionbetweenthedifferentatomse.g.chemicalheattreatment;materialscompositionuniformity(2)Dividedbythedif

6、fusiondirectiondependentondρ/dx(concentrationvarietytrend)Downhilldiffusion：diffusionalongconcentrationdecrease,concentrationuniformitye.g.uniformityannealing,chemicalheattreatmentUphilldiffusion:diffusionalongconcentrationincrease,concentrationchangealongtwodirectionsdecidedbychemicalgr

7、ads：a)Effectofelasticitystress.uphilldiffusiondecreasetheenergyinducedbyelasticitydeformation.。b)Absorbatinterface.Decreasethefreeenergyofthewholesystemc)Differentchemicalpotential.Dominatingfactord)Formingcompouds.e.g.Fe3Ce)Specialcondition.e.g.eletricfield,magneticfield