ch2位錯(cuò)-24位錯(cuò)與晶體缺陷作用課件

Ch2位錯(cuò)2.1位錯(cuò)理論的產(chǎn)生2.2位錯(cuò)的幾何性質(zhì)2.3位錯(cuò)的彈性性質(zhì)2.4位錯(cuò)與晶體缺陷的相互作用2.5位錯(cuò)的動(dòng)力學(xué)性質(zhì)2.6實(shí)際晶體中的位錯(cuò)12.1位錯(cuò)理論的產(chǎn)生一、晶體的塑性變形方式二、單晶體的塑性變形三、多晶體的塑性變形四、晶體的理論切變強(qiáng)度五、位錯(cuò)理論的產(chǎn)生六、位錯(cuò)的基本知識(shí)22.2位錯(cuò)的幾何性質(zhì)一、位錯(cuò)的幾何模型二、柏格斯矢量三、位錯(cuò)的運(yùn)動(dòng)四、位錯(cuò)環(huán)及其運(yùn)動(dòng)五、位錯(cuò)與晶體的塑性變形六、割階32.3位錯(cuò)的彈性性質(zhì)一、彈性連續(xù)介質(zhì)、應(yīng)力和應(yīng)變二、刃型位錯(cuò)的應(yīng)力場(chǎng)三、螺型位錯(cuò)的應(yīng)力場(chǎng)四、位錯(cuò)的應(yīng)變能五、位錯(cuò)的受力六、向錯(cuò)七、位錯(cuò)的半點(diǎn)陣模型42.4位錯(cuò)與晶體缺陷的相互作用一、位錯(cuò)間的相互作用力二、位錯(cuò)與界面的交互作用三、位錯(cuò)與點(diǎn)缺陷的交互作用5InteractionsBetweenDislocationsWewillfirstinvestigatetheinteractionbetweentwostraightandparalleldislocationsofthesamekind.Ifwestartwithscrewdislocations,wehavetodistinguishthefollowingcases:

6Inanalogy,wenextmustconsidertheinteractionofedgedislocations,ofedgeandscrewdislocationsandfinallyofmixeddislocations.Thecaseofmixeddislocations-thegeneralcase-willagainbeobtainedbyconsideringtheinteractionofthescrew-andedgepartsseparatelyandthenaddingtheresults.

Withtheformulasforthestressandstrainfieldsofedgeandscrewdislocationsonecancalculatetheresolvedshearstresscausedbyonedislocationontheglideplaneoftheotheroneandgeteverythingfromthere.Butforjustobtainingsomebasicrules,wecandobetterthanthat.Wecanclassifysomebasiccaseswithoutcalculatinganythingbyjustexaminingoneobviousrule:Ifthesuperpositionofthestrainfieldsofdislocationsadduptovaluesofthecompressiveortensilestrainlargerthanthoseofasingledislocations,theywillrepulseeachother.Ifthecombinedstrainfieldislowerthanthatofthesingledislocation,theywillattracteachother.7Thisleadstosomesimplecases:1.Arbitrarilycurveddislocationswithidentical

bonthesameglideplanewillalwaysrepeleachother.

82.Arbitrarydislocationswithopposite

bvectorsonthesameglideplanewillattractandannihilateeachother

EdgedislocationswithidenticaloroppositeBurgersvectorbonneighboringglideplanesmayattractorrepulseeachother,dependingontheprecisegeometry.Thebluedoublearrowsinthepicturebelowthusmaysignifyrepulsionorattraction.9ThegeneralformulafortheforcesbetweenedgedislocationsinthegeometryshownaboveisFx

=

[Gb2/2p(1–n)]

·

[x·(x2–y2)/(x2+y2)2]Fy

=

[Gb2/2p(1–n)]

·[

y·(3x2+y2)/(x2+y2)2]

Fory=0,i.e.thesameglideplane,wehavea1/xor,moregenerallya1/rdependenceoftheforceonthedistancerbetweenthedislocations.Fory<0ory>0wefindzonesofrepulsionandattraction.Atsomespecificpositionstheforceiszero-thiswouldbetheequilibriumconfigurations;itisshownbelow.TheformulaforFy

isjustgivenforthesakeofcompleteness.Sincethedislocationscannotmoveiny-direction,itisoflittlerelevancesofar.10Theillustrationinthelinkgivesaquantitativepictureoftheforcesactingononedislocationonitsglideplaneasafunctionofthedistancetoanotherdislocation.11一、位錯(cuò)間的相互作用力1213（一）相互平行的兩個(gè)螺位錯(cuò)間的作用力（二）相互平行的兩個(gè)刃位錯(cuò)間的作用力（三）其它情況的位錯(cuò)之間的作用力（四）位錯(cuò)運(yùn)動(dòng)的晶格阻力－P-N力14（一）相互平行的兩個(gè)螺位錯(cuò)間的作用力15上式說明，兩平行螺位錯(cuò)之間只有徑向交互作用，因而交互作用力是一中心力。（即Fθ=Fz=0,Fr≠0）16（二）相互平行的兩個(gè)刃位錯(cuò)間的作用力σyy

與σzz

不考慮，它們對(duì)位錯(cuò)運(yùn)動(dòng)無影響σxx

使b2攀移σyx使b2滑移17根據(jù)F=τb有：Fyx=σyx?b，F(xiàn)xx=σxx?b1819202122ForcesbetweenEdgeDislocationsShownistheforcebetweenedgedislocationsofidenticalandoppositeBurgersvectorsasafunctionoftheirnormalizeddistance.Thedistancexbetweenthedislocationsisexpressedinunitsofy,thedistanceoftheglideplanes.23Theforcechangesfromrepulsivetoattractiveorviceverseforadistancex=y;i.e.ifthedislocationsareatanangleof45orelativetotheglideplane.The45opositionisastableequilibriumpositionforoppositeBurgersvectors,becauseatthispositionF=0,and

dF/dx<0.Fordislocationswithidenticalbvectors,thestablepositionisatx=0.24示。25（三）其它情況的位錯(cuò)之間的作用力1.兩相互垂直的螺位錯(cuò)之間的作用力2.相互垂直的螺位錯(cuò)與刃位錯(cuò)之間的作用力3.平行螺位錯(cuò)與刃位錯(cuò)之間的相互作用4.具有任意伯格斯矢量的平行位錯(cuò)261.兩相互垂直的螺位錯(cuò)之間的作用力恒值。272.相互垂直的螺位錯(cuò)與刃位錯(cuò)之間的作用力283.平行螺位錯(cuò)與刃位錯(cuò)之間的相互作用因?yàn)闊o驅(qū)使對(duì)方運(yùn)動(dòng)的應(yīng)力分量，所以無交互作用。＝A?b1

?b2=0294.具有任意伯格斯矢量的平行位錯(cuò)具有任意伯格斯矢量的平行位錯(cuò)大于30Thedislocationannihilationbycross-slipAnnihilationofascrewdipolebycross-slip:Twodislocationsofoppositesignglideinneighbouringparallelslipplanesandannihilateeachotherbychangingtheirslipplanes.

31Thedislocationdoublecross-slipObstacleby-passing:Ascrewdislocationcanby-passanobstacle,hereasessiledislocationsegmentofsamesign,byadoublecross-slipprocess.32（四）位錯(cuò)運(yùn)動(dòng)的晶格阻力－P-N力33上34表,與實(shí)驗(yàn)數(shù)據(jù)相符。35二、位錯(cuò)與界面的交互作用3637三、位錯(cuò)與點(diǎn)缺陷的交互作用（一）刃位錯(cuò)與點(diǎn)缺陷的交互作用（二）螺位錯(cuò)與點(diǎn)缺陷的交互作用（三）關(guān)于空位與位錯(cuò)的作用38（一）刃位錯(cuò)與點(diǎn)缺陷的交互作用設(shè)置換式溶質(zhì)原子R`>基體原子R柯垂耳(Cottrell)處理:假設(shè)(1)晶體為連續(xù)彈性介質(zhì);(2)溶質(zhì)原子為剛球;(3)溶質(zhì)原子引起的點(diǎn)陣畸變是球形對(duì)稱畸變.則溶質(zhì)原子溶入,相當(dāng)于在(r,θ)處挖一個(gè)R的球形洞,再擠入一個(gè)R`的剛球.交互作用能=剛球擠入過程中反抗位錯(cuò)應(yīng)力場(chǎng)做的功=位錯(cuò)應(yīng)力場(chǎng)做的負(fù)功由3940溶質(zhì)原子R`>基體原子R,即4142（二）螺位錯(cuò)與點(diǎn)缺陷的交互作用因?yàn)槁菸诲e(cuò)是純切應(yīng)力場(chǎng)，所以當(dāng)點(diǎn)缺陷引起球形對(duì)稱畸變時(shí)，兩者無交互作用；若點(diǎn)缺陷引起的是非球形對(duì)稱畸變時(shí)，則溶質(zhì)原子與位錯(cuò)仍發(fā)生交互作用，結(jié)果使溶質(zhì)原子向位錯(cuò)偏聚，形成溶質(zhì)原子氣團(tuán)；例如，鋼中的C、N溶入bcc鐵的八面體間隙時(shí)，引起非球形對(duì)稱畸變（稱為四方畸變），其應(yīng)力場(chǎng)既有正應(yīng)力，又有切應(yīng)力，能與位錯(cuò)發(fā)生交互作用；螺型位錯(cuò)的純切應(yīng)力場(chǎng)可以等效一個(gè)正應(yīng)力場(chǎng)，使溶質(zhì)原子擇優(yōu)分布，形成史諾克（Snock）氣團(tuán)，對(duì)位錯(cuò)有強(qiáng)烈的釘扎作用。4344（三）關(guān)于空位與位錯(cuò)的作用45ThefundamentalinteractionsbetweendislocationsandelasticobstaclesThegoaloftheworkistounderstandthefundamentalinteractionsbetweendislocationsandelasticobstacles.Theprimarytoolthatwillbeusedisthein-situTEMdeformationtechnique.Withthistechniqueitispossibletodirectlyobservetheinteractionbetweendislocationsandelasticobstaclesathighspatialresolution.Fromtheseobservations,themagnitudeofthepinningstrength,thebypassmechanism,andtheprocessbywhichdislocationloopsaredestroyedcanbeascertained.Copperwasselectedsimplyforeaseofcomparisonwithcomputersimulationstudies.In-situTEMstrainingspecimensof99.999%purepolycrystallineCuwerecutfrom250mmthickcoldrolledstripinto11mmby2.7mmpieces.Holesforthestrainingpinsinthestageweredrilledintheendsofthetensilebarsfollowedbypolishingthesurfacestoa600-gritfinish.Sampleswerethenannealedat750°