Properties and microstructure of molybdenum disilicide-β′-SiAlON particulate ceramic composites

Particulate ceramic composites that were composed of a combustion-synthesized β′-SiAlON matrix and dispersed MoSi₂ particles were hot pressed at 1600°C in a nitrogen atmosphere. The physical and mechanical properties of the composites that contained 15, 30, and 45 vol% MoSi₂ were evaluated. The average four-point bend strength, fracture toughness, and Vickers hardness of the composites were in the ranges of 500-600 MPa, 3-4 MPa·m^1/2 and 11-13 GPa, respectively. The measured mechanical strength and hardness were very similar to the values that were predicted from the rule of mixtures. The fracture toughness of the combustion-synthesized β′-SiAlON (2.5 MPa·m^1/2) was apparently enhanced by the MoSi₂ particles that were added. The increase in the fracture toughness was predominately attributed to the residual thermal stress that was induced by the thermal expansion mismatch between the MoSi₂ particles and the β′-SiAlON matrix. The composites showed improved electrical conductivity and oxidation resistance over monolithic β′-SiAlON. High-resolution transmission electron microscopy examination of the composites indicated that the MoSi₂ was chemically well compatible with the β′-SiAION.