MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF SI3N4/SIC COMPOSITES

Si3N4/SiC composites containing up to 30 vol% SiC were fabricated by hot-pressing the mixtures of submicron-sized alpha-Si3N4 and beta-SiC powders. As the SiC content increased, the alpha-beta transformation and grain growth of beta-Si3N4 were inhibited and the equiaxed grain increased. The observed enhancement of mechanical properties was rationalized by these microstractural changes. The high-temperature mechanical properties were also improved significantly by SiC dispersions. This improvement was mainly attributed to the suppression of grain boundary sliding by intergranular SiC particles banded directly with the Si3N4 grain in the atomic scale without any impurity phases.