Fabrication and characterization of SiC rod-particulate-reinforced reaction-bonded Si3N4 composites

Reaction-bonded Si3N4 composites reinforced by whisker-like SiC rod particulates have been fabricated by nitriding SiCrod-containing Si powder compacts, which were presintered to a controlled density by spark plasma sintering (SPS). The effects of processing parameters, including presintered density, SiCrod content, nitriding temperature, atmosphere pressure and heating rate on the nitridation reaction were investigated. It was found that the addition of SiCrod to Si powders led to easier control of complete nitridation compared to the case of pure Si powder compacts, probably because the SiCrod not only acted as diluting filler to suppress the rapid rise in temperature resulting from an SHS-like reaction between Si and N2, but also provided paths for diffusion of reactant gases. The density of the reaction-bonded Si3N4–50 vol% SiCrod composites was increased up to near 90% which is quite a lot higher than that of conventional reaction-bonded Si3N4 ceramics, by using SPS to improve the density prior to nitridation. The relative density increased from ∼70 to 90% after the nitridation without appreciable dimensional change, being characteristic of reaction-sintering. As the reinforcement in the reaction products, the SiCrod improved Youngʹs modulus and bending strength both at ambient and elevated temperatures, as well as thermal and electric conductivity.