Computer simulation of grain growth and ostwald ripening in alumina-zirconia two-phase composites

The kinetics of grain growth and Ostwald ripening in Al₂O₃-ZrO₂ two-phase composites was systematically investigated using two-dimensional (2-D) computer simulations, based on a diffuse-interface field model. Using average values for the experimentally measured ratios of the grain boundary energies to the interphase boundary energy as the input, the predicted 2-D microstructural features and their evolution are in excellent qualitative agreement with experimental observations on 2-D cross sections of 3-D Al₂O₃-ZrO₂ two-phase composite microstructures. It was found that the coupled grain growth in Al₂O₃-ZrO₂ composites is controlled by long-range diffusion and the average size (R_t) as a function of time (t) follows the power-growth law, R^m_t - R^m₀ = kt with m = 3, which is independent of the initial microstructures and volume fractions of the two phases. The predicted variation of the kinetic coefficient (k) on the volume fraction follows a trend similar to that experimentally measured through the entire range of volume fractions. The scaling of grain size distributions is observed at a given volume fraction, i.e., they are time-invariant in the steady state. However, the characteristics of size distributions vary with the initial microstructures and the volume fractions. The relationship between matrix grain size and second-phase grain size is discussed.