金属镍内典型晶界的迁移热力学分子动力学模拟

Molecular Dynamics Simulation of Migration Thermodynamics for Typical Grain Boundary in Ni

为进一步揭示温度对晶界迁移行为的复杂影响,本研究基于分子动力学模拟探究了Ni 36.9˚ {310}001对称倾斜晶界在100~1000 K范围内的迁移热力学、迁移率和剪切耦合迁移等内容。结果表明,在100~600 K时晶界启动迁移所需临界驱动力将随温度升高而逐渐降低,但在600~1000 K时则保持稳定,因而晶界迁移的热力学行为将从热激活模式转变为无热激活。在所探究的温度范围内,晶界迁移率随温度的变化趋势与临界驱动力对应趋势并不相反或相同,因而认为较难启动迁移的晶界会具有相对较低迁移率的已有观点并不正确。该晶界沿晶界面法向迁移的同时还在晶界面内发生剪切运动,也即呈现剪切耦合迁移的特征,在100~800 K时的耦合强度最高,随后因晶界结构改变而导致耦合强度持续降低。

In order to further reveal intricate influences of temperature on the migration behaviors of grain boundary, we investigated the migration thermodynamics, mobility and shear-coupled migration of Ni 36.9˚ {310}001 symmetrical tilt grain boundary at 100~1000 K based on molecular dynamics simulations. The results show that the threshold driving force of initiating boundary migration at 100~600 K gradually decreases with the increasing the temperature, but keeps stable at 600~1000 K. This indicates a transition of the migration thermodynamics from thermally activated model to athermally activated model. The tendencies shown in the variation of grain boundary mobility with the temperature are not contrary or consistent with the counterpart of threshold driving force. Therefore, the existing viewpoint that the grain boundary being hard to initiate migration will be of relatively low mobility is not correct. This grain boundary will make migration along the boundary normal direction and also the shear motion in the boundary plane, i.e., exhibiting the characteristic of shear-coupled migration. The coupled strength keeps the maximum at 100~800 K and then continuously declines due to alteration of grain boundary structure.