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

High quality a/v-Sialon materials were reproducible prepared using cost effective silicon nitride powders and an aqueous processing route. The influence of the powder quality (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 4wt% excess rare earth additives could be prepared. The material based on Silzot HQ exhibits the highest a-Sialon content and subsequently the highest hardness due to the lower oxygen content of the starting material. The microstructural analysis using XRD, FESEM including EDX- and EBSD- mapping reveal, that the a-Sialon grains are formed on existing a-Si3N4 grains of the starting powder. Anisotropic grain growth of the a-Sialon takes place therefore the differences in the microstructure depend strongly on the oxygen content but not from the a/v-content of the starting powders.