剪切应变下刃型位错的滑移机理的晶体相场模拟∗

摘要

针对刃型位错的滑移运动，构建包含外力场与晶格原子密度耦合作用的体系自由能密度函数，建立剪切应变作用体系的晶体相场模型。模拟了双相双晶体系的位错攀移和滑移运动，计算了位错滑移的Peierls势垒和滑移速度。结果表明：施加较大的剪切应变率作用，体系能量变化为单调光滑曲线，位错以恒定速度做连续运动，具有刚性运动特征；剪切应变率较小时，体系能量变化出现周期波动特征，位错运动是处于低速不连续运动状态，运动出现周期“颠簸”式滑移运动，具有黏滞运动特征；位错启动运动，存在临界的势垒。位错启动攀移运动的Peierls势垒要比启动滑移Peierls势垒大几倍。位错攀移和滑移运动特征与实验结果相符合。%Structural kinetics in crystalline solids is driven heterogeneously at an atomic level by localized defects, which in turn drive mesoscopic and macroscopic phenomena such as structural phase transformation, fracture, and other forms of plastic flows. A complete description of such processes therefore requires a multiscale approach. Existing modeling methods typically operate exclusively either on an atomic scale or on a mesoscopic scale and macroscopic scale. Phase-field-crystal model, on the other hand, provides a framework that combines atomic length scale and mesoacpoic/diffusive time scale, with the potential reaching a mesoacpoic length through systemic multiscale expansion method. In order to study the dislocation movement under shear strain, the free energy density functional including the exerting shear force term is constructed and also the phase field crystal model for system of shear stain is established. The climb and glide of single dislocation in two-grain system are simulated, and the glide velocity of dislocation and the Peierls potential for dislocation gliding are calculated. The results show that the energy curve changing with time are monotonically smooth under a greater shear strain rate, which corresponds to dislocation movement at a constant speed, which is of rigorous characteristic;while under less shear strain rate, the energy change curve of system presents a periodic wave feature and the dislocation movement in the style of periodic“jerky”for gliding with the stick-slip characteristic. There is a critical potential for dislocation starting movement. The Peierls potential wall for climbing movement is many times as high as that for gliding movement. The results in these simulations are in a good agreement with the experimental ones.