Plastic displacement as a collective variable to study shear-coupled grain boundary migration and grain boundary phase transitions

In absence of dislocation activity, grain boundary (GB) migration can operate as an efficient vector of plasticity. The shear-coupled grain boundary migration (SCGBM) mechanism has focused a peculiar attention due to its conservative nature and ability to operate at low temperature. Nucleation and motion of disconnections constitute the elementary mechanisms of the GB migration. Using atomistic models, the nudge elastic-band method has revealed to be a powerful tool to quantitatively characterize the disconnection properties. However, this method only operates at 0 K which significantly limits the comparison of its results with experimental data. In this manuscript, we propose to use the plastic displacement as a collective variable in order to compute the free-energy barrier for the SCGBM at different temperatures. This method allows to account for entropic effects during the process. Furthermore, we demonstrate that the GB transition phases may be examined and characterized thanks to this novel approach.