Structural transformation and energy analysis for pile-up dislocations at triple junction of grain boundary

晶界三叉处位错塞积的结构转变与能量分析

An energy model for the structure transformation of pile-ups of grain boundary dislocations(GBD)at the triple-junction of the grain boundary of ultrafine-grain materials was proposed.The energy of the pile-up of the GBD in the system was calculated by the energy model,the critical geometric and mechanical conditions for the structure transformation of head dislocation of the pile-up were analyzed,and the influence of the number density of the dislocations and the angle between Burgers vectors of two decomposed dislocations on the transformation mode of head dislocation was discussed.The results show when the GBD is accumulated at triple junction,the head dislocation of the GBD is decomposed into two Burgers vectors of these dislocations unless the angle between the two vectors is less than 90°,and the increase of applied external stress can reduce the energy barrier of the dislocation decomposition.The mechanism that the ultrafine-grained metal material has both high strength and plasticity owing to the structure transformation of the pile-up of the GBD at the triple junction of the grain boundary is revealed.

提出超细晶材料的三叉晶界处晶界位错塞积的结构转变能量模型。运用该能量模型,计算体系的晶界位错塞积能量,分析塞积头位错的结构转变的临界几何条件和力学条件,讨论塞积位错的数密度和三叉晶界处的二个分解位错Burgers矢量之间的角度对头位错转变模式的影响。结果表明,当晶界位错在三叉晶界处塞积,只要这二个位错Burgers矢量夹角小于90°,头位错就能够分解为二个新的位错;外加应力的增加能够减少位错分解的阻力。另外,还揭示出超细晶材料同时具有高的强度和塑性的机理,归因于三叉晶界处的塞积位错的结构转变。