Oxidation behavior and effect of oxidation on mechanical properties of Mo5Si3 particle-reinforced Si3N4 composites

The influence of oxidation treatment on the microstructures and the mechanical properties of Mo5Si3 particle-reinforced Si3N4 composites was studied. When the Mo5Si3-Si3N4 composites were oxidized below 801 degreesC in air, the Mo5Si3 particles were oxidized to generate the nanometer-sized MoO3 particles and the amorphous silicon oxide, but the MoO3 particles were volatized when the oxidation temperature was higher than 801 degreesC. When the Mo5Si3-Si3N4 composites were oxidized at elevated temperatures, the oxidation products of the cristobalite and Y2Si2O7 were detected, and an oxide layer was created on the surface of the MoO5Si3-Si3N4 composites. After 300h of oxidation at 1400 degreesC in air, the weight gains in the Mo5Si3-Si3N4 composites were considerably less than those in Si3N4. Oxygen diffusion through the grain boundary path into the material and the segregation of the yttrium cations from the grain boundary phase into the surface oxide scale were prevented by the sub-micrometer-sized Mo5Si3 particles, and the composites had a higher oxidation resistance than Si3N4. The strength and fracture toughness of the Mo5Si3-Si3N4 Composites decreased with the oxidation temperature and duration, but were higher than those of Si3N4. (C) 2004 Elsevier B.V. All rights reserved.