Role of grain rotation during grain growth in a columnar microstructure by mesoscale simulation

We use a mesoscopic simulation approach to study the coupling and competition between grain-boundary-curvature driven and grain-rotation-coalescence induced grain growth in a {l_angle}001{r_angle} textured columnar microstructure. The well-known variational formulation for the total dissipated power, due to Needleman and Rice, provides the formal basis for our two-dimensional simulations. A stochastic velocity Monte-Carlo algorithm is used to minimize the functional in each time step. The competition between grain-boundary migration and grain rotation introduces a physical length scale, Rc, into the system, enabling the growth process to be characterized by two regimes. If the average grain size is smaller than Rc, as is the case in nanocrystalline materials, grain growth is dominated by the grain-rotation-coalescence mechanism. By contrast, if the average grain size is greater than Rc, then growth is dominated by curvature-driven grain-boundary migration. The growth exponents characterizing the power-law time dependence of the average grain size are different for the two growth regimes. An extended von Neumann-Mullins relation, based on averaged grain-boundary properties, is further extended to include the effect of grain rotations.