Abstract
The formation of Y-alpha-sialon from fine or coarse beta-Si3N4 was examined to eliminate the effect of sialon nucleation on alpha-Si3N4 grains. The addition of a small amount of Y-alpha-sialon powder as nuclei was also studied. Full transformation from beta-Si3N4 to alpha-sialon was only performed with fine beta-powder containing alpha-sialon seed. It was shown that not only the nucleation process but also the driving force for grain growth have a large influence on alpha/beta ratios and the microstructures of the sintered materials. The addition of alpha-sialon powder is also useful for the formation of Ce-alpha-sialon. Without this addition, no alpha-phase forms due to the thermodynamic metastability of Ce-alpha-sialon. The results indicate that not only thermodynamic stability but also the nucleation process have a decisive effect on the formation of alpha-sialons. Even unstable phases can be formed by controlling the nucleation process and the transient state. 18 refs.