In Situ synthesis of TiN-reinforced Si3N4 matrix composites using Si and sponge Ti powders

Dense Si3N4-TiN composites from Si and sponge Ti (0–40 wt %) powders were produced by in situ reaction-bonding and post-sintering under N2 atomosphere. The fracture strength and toughness of Si3N4-17% TiN composite were found to be 537.9 MPa and 10.4 MPa m1/2, respectively. In the reaction-bonded bodies, Si3N4 grains were constructed with α- and β-Si3N4 structure as well as TiN and some amounts of residual Si phase. After post-sintering, the residual Si and α-Si3N4 grains were transformed to β-Si3N4 grains with rod-like shape. No intermetallic compounds (e.g., TiSi2, Ti5Si3 and Ti5Si4) were formed at the interfaces between Si3N4 and TiN grains. The main toughening mechanisms were crack deflection and crack bridging caused by rod-like Si3N4 grains which were randomly dispersed in sintered body. Microcracking due to the dispersion of in situ formed TiN particles also contributed to the toughening of the sintered body.