In situ Si3N4–SiC–BN composites: preparation, microstructures and properties

Boron nitride composites in Si–B–C–N system have been widely studied and applied in industry in these decades. In the present investigation, in situ reaction process was used to fabricate a new kind of silicon nitride-silicon carbide-boron nitride (Si3N4–SiC–BN) composites according to a previously proposed reaction of Si3N4, B4C, and C with extra addition of Si3N4 in the starting powder mixture. The composites were produced by hot pressing at 1800 °C in a nitrogen atmosphere. The obtained composites demonstrated relatively high density and high bending strength over those of conventionally-processed ones, although with increasing BN content the densification behavior became poorer especially for composites with BN contents higher than 25 vol.%. The growth of rodlike β-Si3N4 grains was suppressed in the composites. Different from the previously reported SiC–BN in situ composites in which the strength almost kept unchanged when the BN content was lower than 35 vol.%, the strength of the present Si3N4–SiC–BN composites decreased monotonously with increase in BN content due to the decreased relative density and limited grain growth of rodlike β-Si3N4 grains.