Fine Si3N4 powder, Si3N4-TiN composite powder and Si3N4-BN-TiN composite powder were prepared by a vapor phase reaction method, and hot-pressed to investigate the effects of TiN inclusion in Si3N4-TiN composites and BN inclusion in Si3N4- BN-TiN composites on the microstructure and mechanical properties of sintered bodies. The prepared powders were fine with a size of about 80-100 nm. Hot pressing was carried out for 2h at 1800°C and 50 MPa in N2 with 6 wt%Y2O3 and 2 wt%Al2O3 as sintering aids. When the content of TiN was small, Si3N4-TiN composites included rod-like Si3N4 grains dispersed in a fine Si3N4 matrix, having a high thermal shock resistance whilst retaining their fracture toughness. The thermal shock resistance of Si3N4-TiN composites was not improved by addition of the BN and the fracture toughness was reduced.

Keywords: silicon nitride, nano-composite, composite powder, thermal shock resistance, fracture toughness