EXPERIMENTAL AND COMPUTATIONAL STUDY OF GRAIN-GROWTH IN ALN BASED CERAMICS

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