Abstract
The influences of oxidation treatment on the microstructure and strength retention of a Mo5Si3 particle reinforced Si3N4 composite with a crystallized grain boundary phase of Yb2Si2O7 were studied. When the Mo5Si3-Yb2Si2O7-Si3N4 composite was oxidized at 1400°C, an oxide layer containing cristobalite and Yb2Si2O7 was created on the surface. The thickness of the oxide layer increased with oxidation time, but was only 1.8 μm when oxidized at 1400°C for 100 h. The formation of the oxide layer caused the weight gain of the composite, and a parabolic weight gain with respect to oxidation time was observed. After 100 h of oxidation at 1400°C in air, the weight gain of the Mo5Si3-Yb2Si2O7-Si3N4 composite was 0.07 mg/cm2, is considerably less than that of other Si3N4-based materials. The crystallization of the grain boundary phase and the incorporation of the submicrometer Mo5Si3 particles into the grain boundaries decreased the driving force for the diffusion of oxygen and the additive cation, and contributed to the high oxidation resistance of Si3N4.
