Simulating Three-dimensional Microstructure Evolution in the Region of Ultrahigh Volume Fractions of Coarsening Phase

A three-dimensional (3D) phase-field model is developed to study the kinetic behavior and microstructure evolution by phase coarsening in the region of ultrahigh volume fractions. In this model, a two-phase system is described by concentration and orientation variables. The microstructure evolution is tracked by solving the time-dependent Cahn-Hilliard equation and Ginzburg-Landau equation.;By employing the phase-field model, the 3D microstructure evolution by phase coarsening is studied over a series of volume fractions (V V) between 0.9 and 1. The results from small-scale simulations show that the morphology of particles in the simulated microstructure shares some characteristic of that in grain growth. The scaling exponent m gradually decreases from 3 to 2, when VV approaches 1. These predictions are different from previous research over lower volume fraction (VV < 0.9) where m is always 3. The shape of particle size distribution (PSD) is broad and nearly symmetric. In addition, our simulations show that having different mobility for the two phases does not affect the kinetics of phase coarsening. However, the large uncertainties in scaling exponent and PSD prevent decisive conclusion.;To increase the statistical significance of these results, parallel code for large-scale simulation is developed. It is scripted based on 1D decomposition method and message passing paragraphs. Detailed performance analyses are carried out over speed up and scalability, that shows both of them improve with the increased problem size. A runtime prediction formula is developed, which shows a satisfactory match with the actual runtime.;Large-scale simulations are executed base on parallel algorithm. It is found that the simulation scale does not change the tendency of decreasing scaling exponent. However, large-scale simulations yield smooth data points, which generate more reliable predictions of scaling exponent. Besides, smooth PSDs are obtained due to the increased number of particles.;All of these results elucidate that the phase coarsening behavior in the region of ultrahigh volume fractions may be a crossover from Ostwald ripening to grain growth.;A systematic comparison between experimental and computational results is performed. The kinetics parameter, shape of PSD and morphology of particles are in reasonable agreement.