Mechanical Properties and Microstructure of Si3N4 Matrix Composite with Nano-Meter Scale SiC Particles

Si3N4 matrix composites with dispersed SiC particles were prepared by hot-pressing compacts of powder mixtures of sub-micron size SiC and Si3N4 particles. SiC particles in nano-meter scale were dispersed uniformly inside Si3N4 grains. After adding SiC particles, the configuration of β-Si3N4 grains changed from equiaxed/platelet-like to rod-like structure. At 20vol% SiC, grains were fine and equiaxed. With increasing SiC content, the α- to β-phase transformation was suppressed, and relative density was decreased. On the other hand, the bending strength reached a maximum value at 10vol% SiC and fracture toughness was maximum at 5vol% SiC. These changes are related closely to the shape of Si3N4 grains and relative density. Young's modulus was minimum at 5vol% SiC. This seems to be caused by the disorder of the interface structure between SiC and Si3N4. Vickers hardness was constant up to 10vol% SiC and increased beyond it.