Stick-slip behavior of grain boundaries studied by accelerated molecular dynamics

We apply parallel-replica molecular-dynamics (MD) simulations to study the peak stress versus velocity relation during stress-driven grain-boundary (GB) migration coupled to shear deformation. Because of the limited time scale of regular MD, all previous atomistic simulations of GB migration were implemented at velocities orders of magnitude higher than experiment. By accelerating MD simulations, the parallel-replica method has allowed us to greatly expand the velocity range and finally approach the experimental velocities. The GB motion observed in this work follows the general stress-velocity relation characteristic of stick-slip dynamics over a wide velocity interval. At the high-velocity end of this interval, the finite damping rate causes a reversal of the stress-velocity curve. At low velocities, we begin to see reverses of GB displacements, indicating the approaching crossover between the stick-slip and driven Brownian regimes. This study points to a close analogy between couple GB motion in crystals and other known cases of stick-slip dynamics, including the tip movements in atomic friction microscopy.