Experimental and Computational Study of Grain Growth in AlN Based Ceramics

Abstract

As a model experiment, the grain growth of aluminum nitride (AlN) was studied at different fractions of yttrium aluminate (7-31%) to compare to the results of computer simulation using Monte Carlo method (MC simulation) of grain growth in presence of a liquid phase. In the model experiment, the time dependence of mean grain size for sintered AlN ceramics was measured from scanning electron photomicrographs. At 2123K, yttrium aluminate appears to be a liquid. The liquid fraction remained relatively constant over the time intervals studied. The cube of mean grain size was observed to be proportional to heat treatment time. The mean AlN grain size decreased as the yttrium aluminate fraction increased. Results of these observations indicated that the solution-reprecipitation process is the dominant growth mechanism in this system and that the rate of grain growth is controlled by AlN diffusion in the liquid phase. On the other hand, microstructures obtained by MC simulation were isotropic and the dependence of grain size in simulated microstructures on fraction of liquid phase and Monte Carlo steps showed similar ones in the model experiment. As a result, it was concluded that MC simulation could express isotropic grain growth and the mechanism that was observed in AlN grain growth.