晶体相场法模拟纳米晶材料反霍尔—佩奇效应的微观变形机理

Phase field crystal simulation of microscopic deformation mechanism of reverse Hall-Petch effect in nanocrystalline materials

采用晶体相场模型模拟获得了平均晶粒尺寸从11.61—31.32nm的纳米晶组织,研究了单向拉伸过程纳米晶组织的强化规律的微观变形机理.模拟结果表明:晶粒转动、晶界迁移等晶间变形行为是纳米晶材料的主要微观变形方式,纳米晶尺寸减小,有利于晶粒转动,使屈服强度降低,显示出反霍尔-佩奇效应.当纳米晶较小时,变形量超过屈服点达到4%,位错运动开启,其对变形的直接贡献有限,主要通过改变晶界结构而影响变形行为,位错运动破坏三叉晶界,引发晶界弯曲,促进晶界迁移.随纳米晶增大,晶粒转动困难,出现晶界锯齿化并发射位错的现象.

The nanocrystalline （NC） materials of several average grain sizes ranging from 11.61 to 31.32 nm were obtained by using the phase field crystal model （PFC）, and the microscopic deformation mechanism of strengthening law for the uniaxial tensile deformation was discussed. Simulated results show that grain rotation and grain boundary （GB） migration are mainly responsible for the microscopic deformation. Since small grain size is favorable for grain rotation so that it can make the yield strength reduced; and the NC materials would show a reverse Hall-Petch effect. When the grain size is so small and the strain exceeds the yield point to about 4%, dislocation activities begin to occur. Mainly by the change of GB structure （disorganizing triple grain boundary junction and then promoting grain migration）, the GB can play a finite contribution to deformation. With increasing grain size, grain rotation becomes difficult, and the grain serration and emission of dislocations are observed.