高温预熔化晶界位错的结构组态转变的探究

Study on Transformation of Configuration Structure of Grain Boundary Dislocation in High Temperature Pre-melting

晶体材料的性能受其内部晶界特性的影响。在高温下,晶体材料在晶界上易发生预熔化。本研究采用晶体相场(PFC)方法模拟高温二维六角晶体的晶界预熔化区在双轴加载作用下的结构演化情况。结果显示,晶界位错会发生配对,形成具有对称结构的位错团,一对位错上下排列,另一对位错左右排列,构成4个位错的组合。随着施加的应变增大,晶界位错预熔化区域横向扩展,其形状最初为棒状,逐渐转化为六边形,再转变成“V”形,最后又收缩为六边形。晶界预熔化区的形状变化伴随着内部位错结构的转变,从而发生位错芯扩展,原来上下配对的位错转变为并行排列的位错,左右排列的位错发生扩展滑移,并在左右两端萌生出一对新的位错。当预熔化区域扩展达到横向最宽时,该区域发射一对位错,随后预熔化区域开始收缩,最后又恢复到初始的形状。上述结果表明,位错结构的组态转变对晶体材料的高温变形机制能产生强烈的影响。

The properties of crystal materials are affected by their internal grain boundary characteristics.At high temperature,crystal materials are prone to pre-melt at grain boundaries.In this study,the phase field crystal method is used to simulate the structural evolution of the grain boundary pre-melting zone of two-di-mensional hexagonal crystals under biaxial applied strain.The results show that the grain boundary disloca-tions will be paired to form a dislocation group with a symmetrical structure.One pair of dislocations is ar-ranged up and down,and the other pair of dislocations is arranged left and right,forming a combination of four dislocations.As the applied strain increases,the pre-melting zone of grain boundary dislocation expands laterally.The initial pre-melting zone of the grain boundary is rod-shaped,which gradually transforms into a hexagon,then transforms into a"V"shape,and finally shrinks into a hexagon.The shape change of the grain boundary pre-melting zone is accompanied by the transformation of the internal dislocation structure,thus the dislocation core expansion occurs.The original upper and lower paired dislocations are transformed into paral-lel dislocations.The left and right dislocations are extended and slipped,and a pair of new dislocations is gen-erated at the left and right ends.When the pre-melting zone extends to the widest lateral width,a pair of dis-locations is emitted,and then the pre-melting zone begins to shrink and eventually returns to the initial shape.The above results show that the configuration transformation of the dislocation structure strongly af-fects the deformation mechanism of crystal materials at high temperature.