Microstructures and Mechanical Properies of Si₃N₄-SiC Composites Prepared by Combustion Synthesis and HIP Sintering

Abstract

The microstructures and mechanical properties of Si₃N₄-SiC composites containing 8 to 46 vol% Sic, which were prepared from combustion synthesis and HIP sintering without additives, were studied and compared with those of Si₃N₄ prepared from conventional methods. Transmission electron microscopic observation revealed the existence of some small SiC particles within the Si₃N₄ matrix grains. The fracture toughness of the Si₃N₄-SiC composite was independent of Si, C content, probably because the SiC grains were smaller than the critical size for effective toughening and the formation of elongated Si₃N₄ grains was not promoted by the Sic dispersions. But SiC additions modified the high-tempera-ture strength of the Si₃N₄-SiC composites and increased the microhardness at all temperatures.