Experimental and Computational Study of Grain Growth and Microstructures in AlN Composite Ceramics.

Abstract

Grain growth of AlN-TiN composite ceramics was studied under conditions where the AlN/Al2O3/Y2O3 grain boundary phase is presumed to be liquid. It was found that the growth of AlN grains was strongly inhibited as the level of TiN additions increased. Compared to AlN, TiN particles showed very little grain growth under the conditions studied. AlN grain growth in both monolithic and composite systems proceeded at a rate of one-third the sintering time, and it was postulated that AlN grain growth proceeded by the “solution-reprecipitation” mechanism. Microstructure observation showed that TiN particles were present at grain boundaries and within AlN grains. Heat treatment of the composite resulted in a severe microstructural change in which the grain boundary phase was isolated at triple points of AlN grains. Computational studies of grain growth in the presence of both, a liquid phase and dispersoids, similar to the AlN-TiN composite system, were undertaken using Monte Carlo simulation based on the Potts model. The simulation effectively expressed the dependency of grain growth on the size and amount of dispersoid as well as predicting the inclusion of dispersoid particles into matrix grains. Adjusting the γsl/γss value from 0.5 to 1.0 yielded microstructural changes that were similar to those observed upon annealing experiments.