Fine Si
3N
4 powder and Si
3N
4-TiN composite powder were prepared by vapor phase reaction method, and hot-pressed to investigate the effects of sintering condition and TiN inclusion on the microstructure and mechanical properties of sintered bodies. The prepared powders were fine with the size below 0.05μm. Hot-pressing was conducted at 1800-1850°C in N
2 (1 atm) with 6wt% Y
2O
3 and 2wt% Al
2O
3 as sintering aid. When fine Si
3N
4 powder was sintered at 1800°C, the sintered body had a fine-grained microstructure. By increase in temperature to 1850°C, rod-like grains grew in the fine matrix, resulting in an increase in fracture toughness. Fine TiN particles were dispersed in Si
3N
4 matrix by sintering of Si
3N
4-TiN composite powder, indicating the formation of nanocomposite. In the composite system, the growth of rod-like grains was observed even at 1800°C. This suggests the acceleration of Si
3N
4 grain growth by TiN inclusion. The composite had a high fracture toughness.
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