Synthesis of Si₃N₄ composite nano-powders and evaluation of sintered bodies

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 Si ₃N₄ 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.