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中文摘要：
采用晶体相场模型模拟了小角度对称倾转晶界结构及其在外加应力作用下的晶界演化消失过程，从位错的运动形式和体系自由能的变化，分析晶界的消失过程和位错的反应机理，并计算了位错分解的激活能．研究表明，具有二维三角晶格原子点阵结构形成的小角度对称倾转晶界是由配对的双位错按直线规则排列构成，可以看成由2套位错Burgers矢量组成．晶界的消失演化过程主要分为6个特征阶段，包括如下几方面的特征过程：首先晶界位错攀移，然后发生位错分解，晶界发射位错，位错由攀移运动转化为作滑移运动；接着滑移位错穿过晶粒内部，直到对面晶界上湮没，即被晶界吸收与合并；剩余的晶界位错继续作攀移运动，然后又出现位错分解，晶界再次发射位错，使得位错转为作滑移运动，与其它作滑移运动的位错在晶内相遇湮没消失．最后，所有晶界和位错全部消失，双晶结构变成为完整的单晶结构．应用三角晶系的点阵位错的2套基本Burgers矢量的组合，可以有效地表示位错的发射、分解、合并、吸收、湮没的反应过程，并能够揭示出这些反应过程的新Burgers矢量的产生和原有的Burgers矢量的消失，以及Burgers矢量方向发生变化的机理．
英文摘要：
Transformations of grain boundaries often strongly influence both the structure and the properties of polycrystalline and nanocrystalline materials. Thus, plastic deformation processes in fine-grained polycrystals and nanocrystalline solids are associated with transformations of grain boundaries, which crucially affect the struc- ture and mechanical characteristics of such solids. Motion of grain boundary dislocations in plastically deformed materials is commonly considered to be the absorption of lattice dislocations by grain boundaries. In order to reveal the mechanism of motion of a low-angle symmetric tilt grain boundary （STGB） associated with the emission and absorption of lattice dislocation, the emission and evolution of a STGB under strain were simulated by phase-field crystal （PFC） model. The decay of STGB and dislocation reactions of separation, annihilation and mergence and their mechanisms were analyzed from the energy point of view, furthermore, the active energy of the dislocation separation was calculated. The research results show that the low-angle STGB is composed of pair dislocations in a line arrangement in two dimensions of triangular atomic lattice, in which there are two sets of basic Burgers vec- tors. The evolution process of STGB decay can be divided into six typical stages which includes the detail features as： dislocation climbs firstly along the STGB under strain, then the dislocation occurs to break up into two new dislocations after it gets enough energy to overcome the active potential barrier of dislocation, at this time the STGB emits pair dislocations to move in gliding in grain instead of climbing along STGB; gliding for while, the dislocation crosses the grain until it is annihilated by another dislocation at the STGB right in the front, i.e. the Grain boundary absorbs or merges the gliding dislocation. The remain of dislocation in the STGB can still climb along the grain boundary in which splits off again into two dislocations when it gets enough energy, at the same
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