Si<sub>3</sub>N<sub>4</sub>-Matrix Composite with TiN Particles Formed by In-situ Reaction

Si3N4 matrix composite reinforced with 5vol% TiN particles was fabricated by the in-situ reaction: 4TiO2+4AlN→4TiN+2Al2O3+O2, followed by hot-pressing. The internal TiN formation reaction was studied using TiO2 powders with three different particle sizes (0.28, 0.35 and 1.19μm). The reaction is likely to start from nearly 1150°C and finishes at 1450°C, before the Si3N4 matrix is sintered, and TiN formation is confirmed from the unit cell dimension. TiN particle sizes in the composites sintered at 1600°C and 1850°C were measured. When the TiO2 particle size was large (1.19μm), the particle crumbled into fragments and underwent nitridation to TiN with a smaller size than that of the original TiO2. Smaller TiO2(0.28μm) was converted into TiN particles of nearly the same size. These results suggest that the in situ TiN formation proceeds through nitridation of TiO2 particles.