第2章晶体缺陷讲解.ppt

123 * 123 * 123 * * Figure 2-19 A sketch illustrating dislocations, slip planes, and etch pit locations. 图2-19 位错、滑移面和蚀坑关系的示意图 * Figure 2-20 Optical image of etch pits in silicon carbide (SiC). The etch pits correspond to intersection points of pure edge dislocations with Burgers vector a/3 and the dislocation line direction along [0001] (perpendicular to the etched surface). Lines of etch pits represent low angle grain boundaries 图2-20 碳化硅（SiC）晶体表面的蚀坑分布的光学图像 * Figure 2-21 Electron photomicrographs of dislocations in Ti3Al: (a) Dislocation pileups (x26,500). (b) Micrograph at x 100 showing slip lines and grain boundaries in AI. (c) Schematic of slip bands development. 图2-21 TiAl3中位错的透射电镜照片： （a）位错塞积，×36500; （b）Al的滑移线和晶界 （c）滑移带形成的示意图 * Plastic deformation refers to irreversible deformation or change in shape that occurs when the force or stress that caused it is removed. Elastic deformation - Deformation that is fully recovered when the stress causing it is removed. Dislocation density - The total length of dislocation line per cubic centimeter in a material. Section 2.？ Significance of Dislocations * Section 2.3 Surface Defects 面缺陷 Surface defects - Imperfections, such as grain boundaries, that form a two-dimensional plane within the crystal. Hall-Petch equation - The relationship between yield strength and grain size in a metallic material—that is, ASTM grain size number (n) - A measure of the size of the grains in a crystalline material obtained by counting the number of grains per square inch a magnification ? 100. Small angle grain boundary - An array of dislocations causing a small misorientation of the crystal across the surface of the imperfection. 晶体的面缺陷包括晶体的外表面(表面或自由界面)和内界面两类，其中的内界面又有晶界、亚晶界、孪晶界、堆垛层错和相界等。 * 2.3.1 晶体表面 晶体表面是指金属与真空或气体、液体等外部介质相接触的界面。表面原子会偏离其正常平衡位置，并因此牵连到邻近的几层原子，造成表面层的晶格畸变，其能量升高，将单位面积上升高的能量称为比表面能，简称表面能(J/m2 )。表面能也可以用单位长度上的表面张力(N/m )表示。影响表面能的因素主要有： 外部介质的分子或原子对晶体界面原子的作用力与晶体内部原于对界面原子的作用力相差越悬殊，则表面能