The crystallography of interphase boundaries between silicon carbide and silicon nitride in silicon nitride - Silicon carbide particulate composites

Abstract

Interphase boundaries between 3C SiC grains and two different beta-Si3N4 morphologies in Si3N4-SiC composites have been studied by transmission electron microscopy. In general, boundaries between small beta-Si3N4 intragranular precipitates and surrounding SiC grains were relatively free of intergranular films, whereas boundaries between large beta-Si3N4 grains and adjacent SiC grains were invariably covered with thin intergranular films. Orientation relationships approximating to [110] 3C SiC parallel to [0001] beta-Si3N4 and (001) 3C SiC parallel to (10 (1) over bar 0) beta-Si3N4 were found to dominate between 3C SiC grains and the intragranular beta-Si3N4 precipitates, but there was no evidence of any favoured orientation relationship between the large beta-Si3N4 grains and adjacent SiC grains. The rationale for 'special' orientation relationships arising when there is no intergranular film present at 3C SiC-beta-Si3N4 interfaces is explored geometrically using the near-coincidence site lattice model, with the significant result that the dominant orientation relationships between 3C SiC grains and the intragranular beta-Si3N4 precipitates have low misfits relative to all other possible orientation relationships between 3C SiC and beta-Si3N4.