Fabrication of Si3N4-based composite containing needle-like TiN synthesized using NH3 nitridation of TiO2 nanofiber

A Si3N4 composite containing needle-like TiN particles (7 vol%) was fabricated. Needle-like TiN particles several micrometers long were synthesized using NH3 nitridation of TiO2 nanofiber, which was obtained using hydrothermal treatment. A mixed powder of α-Si3N4 and the needle-like TiN particles with additives was hot pressed at 24 MPa and 1850 °C for 1 h in N2 atmosphere. Mechanical properties of the composite were compared with those of a composite containing rounded TiN particles and a monolithic β-Si3N4 ceramic. The Si3N4 matrix of the composites containing TiN was mainly a-phase, suggesting that the α–β phase transformation of Si3N4 was inhibited by the presence of TiN. Although fracture strength of the composites was lower, fracture toughness was comparable to that of monolithic β-Si3N4 ceramics. Hardness of the composites was about 19 GPa and was greater than that of the monolithic β-Si3N4 ceramic.