Atomistic simulations of grain boundary migration under recrystallisation conditions

We present details of an approach to simulating the migration of grain boundaries using classical molecular dynamics (MD) in a regime in which the boundary motion is driven by the presence of dislocation defects resulting from plastic deformation. By simulating the shrinkage of spherical grains of deformed material embedded in a perfect crystal, we create conditions in which grain boundary motion takes place on time scales accessible to MD simulations, in which the defect free energy acts as a driving force additional to the capillary force due to excess grain boundary energy. This approach is particularly flexible in allowing arbitrary choices of misorientation axis and angle and providing an interface in which all grain boundary plane orientations are represented. This flexibility is at the cost of additional complexity in the system under study and we establish an approach suitable for analysing the excess grain boundary energy and the components of the force for boundary motion on a local basis over the surface of the shrinking grain. We demonstrate that this approach is able to resolve variation in the grain boundary energy related to the intrinsic grain boundary dislocation network in lower angle boundaries and to detect local maxima in the driving force due to the dislocation structure within the deformed grain. We show that the variation in measured grain boundary velocities is accounted for by the excess energy of the dislocations. We further show that the presence of dislocations in the shrinking grain has a tendency to reduce the anisotropy in grain boundary behaviour. Indicative evidence is presented that the dislocation network may act as a focal point for mechanisms of grain boundary migration.