Abstract
Si3N4 sintered body was obtained by pressureless sintering and then post-HIPing with addition of small amount of TiO2 (3mass%). Sintering additives were 5mass% Y2O3, 3mass% Al2O3 and 3mass% AlN. It was found that round-shaped particles with diameter 0.2-0.5μm were distributed within the grain-boundary phase. The particles contained high density crystalline imperfections. They contained Ti and N, and were identified as TiN by energy-dispersive-type 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 contain Ti. Formation of TiN from TiO2 by reduction and nitridation was suggested based on thermodynamic calculations and crystal chemical considerations. High density crystalline imperfections may be introduced during reduction of TiO2 particles. It is believed that the grain-boundary distribution of round-shaped TiN particles contributes to the improvement of wear resistance of Si3N4 ceramics.
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