Simultaneous grain boundary migration and grain rotation

The energy of a polycrystalline network can be reduced by both grain boundary migration and grain rotation. We perform a series of molecular dynamics (MD) simulations of a circular grain embedded in an otherwise single-crystal matrix and monitor both the grain size and the misorientation of the two grains as a function of time. The MD simulations show that grain boundary migration and grain rotation occur simultaneously. The grains rotate toward local minima or cusps in the grain boundary energy versus misorientation plots. The rate of rotation decreases with increasing grain size. The boundary migration rate is a maximum at the orientations corresponding to cusps in the boundary energy. We use the MD results to fit parameters in a sharp interface limit of a phase field model of simultaneous grain boundary migration and grain rotation. With this parameterization, the phase field model is able to reproduce simultaneously the time dependence of the grain size and misorientation of the initially circular grain. The MD simulations are consistent with the phase field prediction of the grain size dependence of the rotation rate. The implications of the results for grain growth are discussed.