Molecular dynamics simulation of triple junction migration

We present a molecular dynamics simulation study of the migration of grain boundaries with triple junctions. We have monitored the grain boundary profile, triple junction angles and rate of grain boundary migration with and without triple junctions as a function of grain size, grain misorientation, direction of migration and temperature in a series of configurations designed to ensure steady-state migration. The present results demonstrate that triple junction mobility is finite and can be sufficiently small to limit the rate of grain boundary migration. The drag on grain boundaries due to limited triple junction mobility is important at small grain sizes, low temperature and near high symmetry grain misorientations. This drag limits the rate of grain boundary migration and leads to triple junction angles that differ substantially from their equilibrium value. Simulation data suggest that triple junction drag is much more a factor at low temperature than at high temperature. The triple junction mobility is shown to depend upon the direction of triple junction migration. The present results are in excellent qualitative agreement with experimental observations.