Computer simulation of microstructural evolution in multiphase materials using a diffuse-interface field model

A novel diffuse-interface field model was formulated by advancing and combining the diffuse-interface theory and the kinetic field theory. One of significant features of the new model is its ability to deal with complex microstructures and diffusion in multiphase polycrystalline materials. By employing this diffuse-interface field model, the kinetics of grain growth in 2-D single phase systems have been systematically investigated. It is found that the kinetics follow power growth law {dollar}Rsbsp{lcub}t{rcub}{lcub}m{rcub}-Rsbsp{lcub}0{rcub}{lcub}m{rcub}=kt{dollar} with {dollar}m=2.0.{dollar} In contrast to the general belief, we found that 4-sided and 5-sided grains may directly vanish. Theoretical predictions on the grain growth kinetics, topological features and correlations have been critically examined. The characteristics of Ostwald ripening in 2-D two-phase mixtures were studied over a range of volume fractions of the coarsening phase. The kinetics of Ostwald ripening follows the power growth law with m = 3. It is predicted that the kinetic coefficient k increases as the volume fraction of the coarsening phase increases. The skewness continuously changes from negative to positive while the kurtosis decreases in the low fraction regime and increases in the high volume fraction regime as the volume fraction increases. The microstructural evolutions in volume-conserved 2-D two-phase polycrystalline materials were systematically simulated. The stabilities of microstructural features in these systems are mainly dependent on the ratios of grain boundary energies to interphase boundary energy. The coupled grain growth is controlled by long-range diffusion and follows the power growth law with m = 3. It was proven that quadrijunctions cannot stop the coupled grain growth in two-phase systems. The effects of volume fractions, energetic ratios and initial microstructures on the kinetics, size distributions and topologies were studied. By incorporating the long-range elastic interaction the coherent phase transformations in {dollar}rm ZrOsb2{dollar}-{dollar}rm Ysb2Osb3{dollar} alloys were studied. Our thermodynamic stability analysis and computer simulations predict three different transformation sequences for a cubic phase aged within the cubic + tetragonal two-phase field.; 2...