Microstructural observation of silicon nitride ceramics sintered with addition of titania

Si3N4 sintered body was obtained by pressureless sintering and then post-HI Ping with addition of small amount of TiO2(3 mass%). Sintering additives we re 5 mass%Y2O3, 3 mass%Al2O3 and 3 mass%AlN. It was found that round-shaped particles with diameter 0.2-0.5 mum were distributed within the grain-boun dary phase. The particles contained high density crystalline imperfections. They contained Ti and N, and were identified as TiN by energy-dispersive-t ype X-ray microanalysis and X-ray diffractometry. The grain-boundary phase was mainly an amorphous phase containing Si, Y, Al and O, but it did not co ntain Ti. Formation of TiN from TiO2 by reduction and nitridation was sugge sted based on thermodynamic calculations and crystal chemical consideration s. High density crystalline imperfections may be introduced during reductio n of TiO2 particles. It is believed that the grain-boundary distribution of round-shaped TiN particles contributes to the improvement of wear resistan ce of Si3N4 ceramics.