Driving force induced transition in thermal behavior of grain boundary migration in Ni

Abstract

Grain boundaries (GBs) that show higher mobility at lower temperatures (i.e., anti-thermal or non-Arrhenius behavior) have attracted significant interest in recent years. In this study, we use atomistic simulations to systematically investigate the effect of driving force on GB mobility based on a set of bicrystalline models in Ni. It is found that the thermal behavior of GB migration strongly depends on temperature and the magnitude of driving forces. When the driving force is at the zero-driving force limit as induced solely by thermal fluctuations, the mobility of all GBs investigated in the current study shows a transition from thermally activated to anti-thermal behavior when the temperature is increased. As the driving force increases, the transition temperature at which the mobility peaks would gradually decrease so that for some GBs only the anti-thermal behavior would be detected. Energy analysis further reveals that the transition temperature (Ttrans) is linearly related to both energy barrier per area (E) from NEB simulation and the fitted apparent activation (Q) energy, and both E and Q are lowered as the driving force increases. Our work supports the previous theoretical models for GB migration based on both classical thermal activation and disconnection nucleation. Furthermore, the current study can be used to improve both models by considering the influence of driving force with a simple fix to how the energy barrier for GB migration should be considered. It is expected that this work advances the current understanding of general GB migration and sheds some light on a unified theoretical framework in the near future