Microstructure formation of α/β-sialons prepared via an aqueous processing route and from cost effective silicon nitride powders

High quality α/β-Sialon materials were reproducible prepared using cost effective silicon nitride powders and an aqueous processing route. The influence of the powder quality (SN-E10, Silzot HQ, SicoNide P95H) on sintering and phase formation was investigated. With all 3 powders dense Sialon materials with nominal composition RxSi12-(m + n)Alm + nOnN16-n and m = 0.5 and n = 1 and 4 wt% excess rare earth additives could be prepared. The material based on Silzot HQ exhibits the highest α-Sialon content and subsequently the highest hardness due to the lower oxygen content of the starting powder. The microstructural analysis using XRD, FESEM including EDX- and EBSD-mapping reveal, that the α-Sialon grains are formed on existing α-Si3N4 grains of the starting powder. Anisotropic grain growth of the α-Sialon takes place therefore the differences in the microstructure depend strongly on the oxygen content but not from the α/β-content of the starting powders.