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1、第二章 晶体结构的缺陷Chapter 2 The Crystal Structures Defects本章重点及难点1、点缺陷的平衡浓度公式2、位错类型的判断及其特征、柏氏矢量的特征3、位错源、位错的增殖（F-R源、双交滑移机制等）和运动、交割4、位错的应力场、位错的应变能、线张力等5、晶界的特性（大、小角度晶界） 、孪晶界、相界的类型Questions for chapter 21. How many types of point defects? What are their effects on diffusion?2. What are the characteristics of d
2、islocations and Burgers vector?3. How to understand the knowledge about dislocation resources and movements?4. what are the stress field, strain energy and tension forces of dislocations?5. what are the characteristics of grain boundaries?Metal crystals are never perfect. It is now well understood t
3、hat they may contain many defects. For all materials, it is necessary to consider the existence of defects and impurities, collectively known as imperfection, as they affect materials properties. In this chapter, we introduce the three basic types of imperfections: point defects, line defects （or di
4、slocations）, and surface defects.原子的不规则排列产生晶体缺陷。晶体缺陷在材料组织控制（如扩散、相变）和性能 控制（如材料强化）中具有重要作用。晶体缺陷：实际晶体中与理想点阵结构发生偏差的区域。 晶体缺陷可分为以下三类: 点缺陷：在三维空间各方向上尺寸都很小的缺陷。如空位、间隙原子、异类原子等。 线缺陷：在两个方向上尺寸很小，而另一个方向上尺寸较大的缺陷。主要是位错。 面缺陷：在一个方向上尺寸很小，在另外两个方向上尺寸较大的缺陷。如晶界、相界 表面等。2-1 点缺陷Section 2.1 Point Defects1 点缺陷的类型 the types of po
5、int defectsA.空位：VACANCIESThese are classified according to a few important types. One of the most important is called a vacancy. The existence of vacancies in crystals was originally postulated to explain solid-state diffusion in crystals.肖脱基空位（Q Schottky你c。一离位原子进入其它空位或迁移至晶界或表面。 弗兰克尔空位（a Frenkel def
6、ect）离位原子进入晶体间隙。A.间隙原子：INTERSTITIAL ATOMSAn interstitial defect is formed when an extra atom or ion is inserted into the crystal structure at a normally unoccupied position. Interstitial atoms or ions, although much smaller than the atoms or ions located at the lattice points, are still larger than t
7、he interstitial sites that they occupy, consequently, the surrounding crystal region is compressed and distorted.位于晶体点阵间隙的原子。B.置换原子：SUBSTITUTIONAL ATOMSA substitutional defect is introduced when one atoms or ion is replaced by a different type of atoms or ion. The substitutional atoms or ions may ei
8、ther be larger than the normal atoms or ions in the crystal structure, in which case the surrounding inter-atomic spacings are reduced, or smaller causing the surrounding atoms to have larger inter-atomic spacings. In either case, the substitutional defects disturb the surrounding crystal.位于晶体点阵位置的异
9、类原子。2 点缺陷的平衡浓度(1) 点缺陷是热力学平衡的缺陷在一定温度下，晶体中总是存在着一定数量的点缺 陷(空位)，这时体系的能量最低具有平衡点缺陷的晶体比理想晶体在热力学上更为稳定。 (原因：晶体中形成点缺陷时，体系内能的增加将使自由能升高，但体系熵值也增加了，这 一因素又使自由能降低。其结果是在G-n曲线上出现了最低值，对应的n值即为平衡空位 数。)(2) 点缺陷的平衡浓度C=Aexp(-Ev/kT)3 点缺陷的产生及其运动1) 点缺陷的产生 平衡点缺陷：热振动中的能力起伏。 过饱和点缺陷：外来作用，如高温淬火、辐照、冷加工等。2) 点缺陷的运动 (迁移、复合浓度降低；聚集浓度升高塌陷)
10、(A)(B)(C)Fig 2.1 Three steps in motions of a vacancy through a crystalDiffusionin crystals is explained, in terms of vacancies, by assuming that thevacancies move through the lattice, thereby producing random shifts of the atoms from one lattice position to another. The basic principle of vacancy di
11、ffusion is illustrated in Fig.2.1, where three successive steps in the movement of a vacancy are shown.It can be seen that the vacancy moves as a result of an atom jumping into a hole from a lattice position bordering the hole. In order to make the jump, the atom must overcome the net attractive for
12、ce of its neighbors on the side opposite the hole. Work is therefore required to make the jump into the hole, or, as it may also be stated, an energy barrier must be overcome. Energy sufficient to overcome the barrier is furnished by the thermal or heat vibrations of the crystal lattice. The higher
13、the temperature, the more intense the thermal vibrations, and the more frequently are the energy barriers overcome. Vacancy motion at high temperatures is very rapid and, as a consequence, the rate of diffusion increases rapidly with increasing temperature.4 点缺陷与材料行为（1）结构变化：晶格畸变（如空位引起晶格收缩，间隙原子引起晶格膨胀
14、，置换原子 可引起收缩或膨胀。）（2）性能变化：物理性能（如电阻率增大，密度减小。） 力学性能（屈服强度提高。）2-2 线缺陷位错Sec.2.2 Linear Defects: Introduction to DislocationsAn important category of defects is the line defect, defined as a one-dimensional （linear） region in the lattice characterized by local faults in the atomic arrangement. One important
15、 consequence of the inevitable presence of such defects, usually called dislocations, is that they enable atoms to slip and slide past one another under applied forces that are much lower than would otherwise be predicted.位错：晶体中某处一列或若干列原子有规律的错排。意义：（对材料的力学行为如塑性变形、强度、断裂等起着决定性的作用，对材料的扩 散、相变过程有较大影响。）位错的
16、提出：1926 年，弗兰克尔发现理论晶体模型刚性切变强度与与实测临界切应力 的巨大差异（24个数量级）。1934 年，泰勒、波朗依、奥罗万几乎同时提出位错的概念。1939 年，柏格斯提出用柏氏矢量表征位错。1947 年，柯垂耳提出溶质原子与位错的交互作用。1950 年，弗兰克和瑞德同时提出位错增殖机制。 之后，用TEM直接观察到了晶体中的位错。1 位错的基本类型1.1 刃型位错 edge dislocations模型：滑移面/半原子面/位错线（位错线丄晶体滑移方向，位错线丄位错运动方向, 晶体滑移方向/位错运动方向。）分类：正刃型位错（丄）负刃型位错（丁）。Fig. 2.2 An edge dislocationFig.2.2A represents a simple cubic crystal
