Reaction sintering of AlN-AlON composites

Sintering behavior of three different compositions in the AlN-Al2O3 system using Y2O3 as a sintering aid was investigated. Samples with various ratios of AlN/Al2O3 were sintered in nitrogen atmosphere using a gas pressure furnace in the temperature range 1750-1950 °C. The densification of the samples was studied by shrinkage and relative density measurements. Results showed that samples containing 1 and 70 wt.% alumina were sintered to near theoretical density at 1800 °C; whereas the sample with 20 wt.% alumina never reached densities higher than 93% in the temperature range considered. It was found that the AlN/Al2O3 ratio and the sintering temperature had a great influence on the microstructure and crystalline phases present in the samples, namely, AlN, γ-AlON, 27R, and YAG. In the sample with 20 wt.% alumina, porosity formation prevented further densification. These porosities were probably due to the release of oxygen during sintering.