Yb_2Si_2O_7粒界相を持つMo_5Si_3粒子強化Si_3N_4複合材料の酸化特性

概要

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The influences of oxidation treatment on the microstructure and strength retention of a Mo_5Si_3 particle reinforced Si_3N_4 composite with a crystallized grain boundary phase of Yb_2Si_2O_7 were studied. When the Mo_5Si_3-Yb_2Si_2O_7-Si_3N_4 composite was oxidized at 1400℃, an oxide layer containing cristobalite and Yb_2Si_2O_7 was created on the surface. The thickness of the oxide layer increased with oxidation time, but was only 1.8μm when oxidized at 1400℃ for 100h. 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 100h of oxidation at 1400℃ in air, the weight gain of the Mo_5Si_3-Yb_2Si_2O_7-Si_3N_4 composite was 0.07mg/cm^2, is considerably less than that of other Si_3N_4-based materials. The crystallization of the grain boundary phase and the incorporation of the submicrometer Mo_5Si_3 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 Si_3N_4.
2006-12-01