Molecular dynamics simulations of crystal rearrangement at grain boundaries and the vicinity

Molecular dynamics simulations of rearrangement of atoms around the grain boundaries are carried out. The purpose of this study is to estimate the stability of grain boundaries and to observe their motion based on the atomistic considerations, so that the results are able to be applied for multi-scale scheme such as the phase field model. First, the grain-boundary energy is calculated as a function of misorientation angle, which revealed that several specific angles exhibit cusp-like low values, for both symmetric and non-symmetric grain boundaries. Secondly, changes in morphology of a square grain embedded in a bulk single crystal are simulated. Grains surrounded by specific grain boundaries having low energy are stable and do not incorporate rotation or migration, while unstable grains change their shape or orientation. A circular-grain model is also applied for the simulations, and similar tendency is obtained. Finally, a simulation at a high temperature for the model which consist of a grain stable at low temperature is carried out, which reveals that grain contraction occurs resulting in disappearance of the grain.