Boron nitride–silicon carbide interphase boundaries in silicon nitride–silicon carbide particulate composites

Interphase boundaries between SiC and h-BN grains in hot isostatically pressed Si3N4–SiC particulate composites made from both as-received powders and deoxidised powders, in which sub-micron size h-BN particles occur as a contaminant, have been characterised using transmission electron microscopy techniques. Most of the h-BN grains observed were aligned with respect to SiC grains so that (111) 3C SiC and (0001) α-SiC planes were parallel to (0001) h-BN planes. The h-BN–SiC interphase boundaries in the composites made from as-received powders were covered with thin silica-rich intergranular films, in contrast to the interphase boundaries in the composites made from deoxidised powders. These observations are discussed in the light of models for the formation of intergranular amorphous films in ceramic materials, geometric considerations for low interfacial energies and the possible bonding at h-BN–SiC interphase boundaries free of intergranular films.