Fabrication of Si ₃N ₄-based composite containing needle-like TiN synthesized using NH ₃ nitridation of TiO ₂ nanofiber

A Si ₃N ₄ composite containing needle-like TiN particles (7vol%) was fabricated. Needle-like TiN particles several micrometers long were synthesized using NH ₃ nitridation of TiO ₂ nanofiber, which was obtained using hydrothermal treatment. A mixed powder of α-Si ₃N ₄ and the needle-like TiN particles with additives was hot pressed at 24MPa and 1850°C for 1h in N ₂ atmosphere. Mechanical properties of the composite were compared with those of a composite containing rounded TiN particles and a monolithic β-Si ₃N ₄ ceramic. The Si ₃N ₄ matrix of the composites containing TiN was mainly a-phase, suggesting that the α-β phase transformation of Si ₃N ₄ was inhibited by the presence of TiN. Although fracture strength of the composites was lower, fracture toughness was comparable to that of monolithic β-Si ₃N ₄ ceramics. Hardness of the composites was about 19GPa and was greater than that of the monolithic β-Si ₃N ₄ ceramic.