Concurrent grain growth and coarsening of two-phase microstructures; large scale phase-field study

Abstract

A thermodynamically consistent phase-field model is exploited to demonstrate the influence of relative volume fractions and bulk diffusivity on the grain growth phenomena in two-phase polycrystalline systems. For very small and high volume fractions, the simulated morphology consists of a dispersion of isolated minor phase grains embedded in the matrix of major phase grains. At intermediate fractions, the obtained microstructure resembles an interpenetrating network-like structure. The performed large-scale 2-D simulations elucidate the governing mechanisms for the concurrent two-phase growth at low and high volume fractions, and the continuous transition between interface-controlled and diffusion-limited regimes. While the slowest kinetics is observed for the 50/50 volume fraction case, irrespective of the diffusivity, the fastest kinetics is displayed by the pure systems, with a slight difference, which is due to relative interfacial energies. The relative growth rates of the individual phases and the maximum attainable grain size to mean size ratio are observed to follow the well-known trends for isotropic systems. The obtained results for the concurrent growth of a minor phase with various diffusivities, reveal that it is difficult to reconcile all observed behaviors with a universal Zener relation, in contradiction to the previously made claims in the literature. A need for the full-fledged growth law, which takes into consideration the role of the diffusivity, the volume fractions, and the relative interfacial energies in multiphase polycrystalline systems, is pointed out.