Grain boundary sliding and migration: Effect of temperature and vacancies - art. no. 024104

Monte Carlo simulations combined with the embedded-atom method potential ha ve been employed to investigate the microscopic process of the Sigma5 tilt grain boundary sliding in aluminum. We have studied the atomic structures a nd the grain boundary sliding/migration energy profile at elevated temperat ures in the absence or presence of vacancies. The annealing temperature is found to play an important role in determining the grain boundary energetic s and mobility. Contrary to "static" simulations, the simulated annealing ( SA) produces new lower energy states of the complex and low-symmetry grain boundary structure. The vacancy formation energy at the first layer from th e interface is found to be significantly lower than that at the other layer s and the bulk. On the other hand, the vacancy at the interface has a signi ficantly higher formation energy compared to bulk, in very good agreement w ith recent ab initio electronic-structure calculations. For both "static" a nd SA simulations, the grain boundary sliding energy profile is smooth, exh ibiting several energy peaks and valleys, where the latter are associated w ith grain boundary migration. The SA scheme reduces the grain boundary slid ing/migration energy barrier by about a factor of 3 and increases the rate of migrations. The distribution of atomic energies helps identify the atoms that play a key role in the grain boundary sliding and migration. The grai n boundary sliding energy profile in the presence of a vacancy placed at th e first layer is very similar to that of the clean boundary, while the vaca ncy at the interface increases the grain boundary energy and leads to no mi gration.