材料成型金屬學(xué)ch01-1位錯(cuò)理論

1、1.位錯(cuò)理論基礎(chǔ) 1.1 晶體缺陷概論n晶體中的缺陷缺陷： 原子排列偏離完整性的區(qū)域n點(diǎn)缺陷在三個(gè)方向上尺寸都很小 n線缺陷在二個(gè)方向上尺寸很小 n面缺陷在一個(gè)方向上尺寸很小 點(diǎn)缺陷 point defectsn空位 vacancyn間隙原子 interstitial atomn雜質(zhì)原子 impurity atomSchematic illustration of types of defects in a single-crystal lattice: self-interstitial, vacancy, interstitial, and substitutional.Extra ato

2、mMissing atomExtra atomForeign atomPoint Defects in a Single Crystal LatticePoint Defects 點(diǎn)缺陷Substitutional atom 替換原子Self- interstitial atomInterstitial atom間隙原子Vacancy空位 Equilibrium concentration varies with temperature! How?空位平衡濃度Boltzmanns constant (1.38 x 10-23 J/atom K) (8.62 x 10-5 eV/atom K)

3、NDN=exp-QDkT No. of defectsNo. of potential defect sites.Formation energyTemperatureEach lattice site is a potential vacancy siteSelf Diffusion Via Vacancy Mechanism點(diǎn)缺陷對(duì)晶體性能的影響n間隙原子體積膨脹12個(gè)原子體積n 空位體積膨脹0.5個(gè)原子體積n屈服強(qiáng)度 n對(duì)擴(kuò)散、高溫形變和熱處理等過(guò)程均有重要影響 面缺陷 plane defectn小角度晶界 low angle grain boundaryn大角度晶界 high angl

4、e grain boundaryn相界面 interphase boundary小角度晶界特點(diǎn)*10 由位錯(cuò)構(gòu)成 *位錯(cuò)密度 位向差晶格畸變晶界能大角度晶界 10 小角度晶界 類型（1）對(duì)稱傾側(cè)晶界相鄰晶粒各轉(zhuǎn)/2同號(hào)刃位錯(cuò)垂直排列（2）不對(duì)稱傾側(cè)晶界相互垂直的兩組刃位錯(cuò)垂直排列 Low Angle Grain Boundary 小角晶界grain boundariesSchematicAdapted from Fig. 4.7, Callister 6e. GRAIN BOUNDARIES 晶界晶界特點(diǎn) 1） 晶界畸變晶界能向低能量狀態(tài)轉(zhuǎn)化晶粒長(zhǎng)大、晶界變直晶界面積減??； 2） 阻礙位錯(cuò)運(yùn)動(dòng)

5、 b 細(xì)晶強(qiáng)化； 3） 位錯(cuò)、空位等缺陷多晶界擴(kuò)散速度高； 4） 晶界能量高、結(jié)構(gòu)復(fù)雜容易滿足固態(tài)相變的條件固態(tài)相變首先發(fā)生地； 5） 化學(xué)穩(wěn)定性差晶界容易受腐蝕； 6） 微量元素、雜質(zhì)富集Variation in Grain Boundary Energy With Misorientation for Copper. 晶界能角度00.10.20.30.40.50.60102030405060DegreesEnergy (J/m2)相界面n兩個(gè)不同相之間的界面 共格界面 半共格界面 非共格界面彈性能 與 界面能？晶界處新晶粒晶界與亞晶界新晶粒與位錯(cuò)Laminar structure 片層狀組

6、織High resolution TEM 高分辨電子顯微鏡高分辨電子顯微鏡成百上千個(gè)原子成百上千個(gè)原子單個(gè)原子排列單個(gè)原子排列ELECTRON MICROSCOPYnJuan Villegas, Ph.D. thesis (UConn MSE)advancing twin001110Nickel alloy線缺陷 line defectn刃型位錯(cuò) Edge dislocationn螺型位錯(cuò) Screw dislocation n混合位錯(cuò) Mixed dislocation1.2 位錯(cuò)概念的引入n1934 解釋實(shí)測(cè)的晶體臨界切應(yīng)力值與理論計(jì)算值相差千倍以上的問(wèn)題理想晶體的臨界切應(yīng)力實(shí)際晶體的逐步

7、滑移2Gm= Effect of dislocations in the lattice structure under stressIn the series of diagrams, the movement of the dislocation allows deformation to occur under a lower stress than in a perfect lattice1.3 位錯(cuò)的原子模型及柏氏矢量Edge Dislocation 刃型位錯(cuò)刃型位錯(cuò)From A. G. Guy, Elements of Physical Metallurgy, Addison-We

8、sleyPublishing Co., Inc., Reading, Mass., 1959.Contains an additional plane of atoms which extends indefinitely along the crystal 多余原子面Edge Dislocation 刃型位錯(cuò)刃型位錯(cuò)Screw Dislocation 螺型位錯(cuò) From J.F. Shackelford, Introduction to Material Science for Engineers,MacMillan Publishing Co, New York, NY, 1985Spir

9、al Stacking of crystal planes. The direction of motion is perpendicular to the shearing stress. Screw Dislocation 螺型位錯(cuò) Mixed Dislocation 混合位錯(cuò) From J.F. Shackelford, Introduction to Material Science for Engineers,MacMillan Publishing Co, New York, NY, 1985Has both edge andscrew character.Screw Disloc

10、ationEdge DislocationMixed Dislocation 混合位錯(cuò) n柏氏矢量的確定 （1）包含位錯(cuò)線做一封閉回路柏氏回（2） 將同樣的回路置于完整晶體中不能閉合 （3） 補(bǔ)一矢量（終點(diǎn)指向起點(diǎn)）使回路閉合柏氏矢量BURGERS VECTOR 柏氏矢量nEdge dislocation: Burgers vector perpendicular to dislocation linenScrew dislocation: Burgers vector parallel to dislocation linenMixed dislocation: Orientation of

11、 Burgers vector with respect to dislocation changes with positionEdge dislocationScrew dislocationDislocation line: into pageDislocation lineBurgers vectorBurgers vector特性（1） 滿足右螺旋規(guī)則時(shí)，柏氏矢量與柏氏回路路徑無(wú)關(guān) 唯一性 （2） 用柏氏回路求得的柏氏矢量為回路中包圍的所有位錯(cuò)柏氏矢量的總和（矢量和） 可加性 （3） 同一位錯(cuò)，柏氏矢量處處相同 同一性位錯(cuò)密度n單位體積中位錯(cuò)的總長(zhǎng)度：3/,cmcmVL=3/1 ,c

12、mAnALnL=將位錯(cuò)線看作于垂直某一平面的直位錯(cuò)線位錯(cuò)的觀察Etching to Reveal Dislocation MotionMovement of dislocations in LiF.“A” are sessile dislocations & “B” are glissile dislocations.When a stress is applied the glissile dislocation slides, hence, when it is etched again it leaves a new trace where as the old trace gets wider, but not deeper.Sessile dislocations do not move and the etch pits get deeper and wider on repeated