Chapter4ImperfectionsinCrystal.pptVIP

Chapter 4 Imperfections in Crystal 4.1 Point defects and Equilibrium concentration 4.2 Impurity atoms 4.3 Origin and Concept of dislocations ~ Linear defects 4.4 Burgers vectors and movement of dislocation 4.5 Elastics properties of dislocation 4.6 Formation and proliferations of dislocation 4.7 Dislocations in real crystal 4.8 Dislocation reaction 4.9 Outer surface 4.10 Grain boundaries and sub-grain boundaries 4.11 Phase boundaries Ideal or perfect crystal：the arrangements of atoms that can regularly and repetitively fill space Real or defective crystal： A very tiny fraction of the atom sites, often less than one in a million, the atoms arrangement is not perfect.~ discrepancy structure According to dimension, types: point defect: vacancies, interstitial atoms, impurity atoms line defect: dislocation planar defect: stacking fault volume defect: mosaic structure 晶体缺陷：实际晶体中存在原子排列偏离理想状态的不完整区域。 按晶体缺陷的几何特征，分为：点缺陷、线缺陷（位错）、面缺陷和体缺陷。 即按照晶体缺陷在空间所占的维度，分为零维、一维、二维和三维缺陷。 晶体缺陷赋予材料丰富内容 晶体中的位错： Dislocation 刃型位错 edge dislocation 螺型位错 screw dislocation 混合型位错 mixed dislocation The dislocation can’t be seen by eyes. How did people originally realise the dislocation? What is dislocation? x: displacement of atoms 原子位移 The shearing force required to deform a crystal solidcan be a facter of about 103-104 smaller than the theoretical shearing force. The dramatic discrepancy was solved by assumed presence of lattice defects called Dislocation. 1934,Orowam,Taylor and Polanyi independently applied the concept of edge dislocations. 1939, Burgers described the lattice distortion associated with a dislocation by the so-called Burgers vector. 1947, Cottrell suggested the interaction between the dislocation and solute Atoms~ Cottrell atmosphere. 1950, mechanism of Frank-Read Source has been applied.