Properties and microstructure of molybdenum disilicide beta'-SiAlON particulate ceramic composites

Particulate ceramic composites that were composed of a combustion-synthesized beta'-SiAlON matrix and dispersed MoSi2 particles were hot pressed at 1600 degrees 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 beta'-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 beta'-SiAlON matrix. The composites showed improved electrical conductivity and oxidation resistance over monolithic beta'-SiAlON. High-resolution transmission electron microscopy examination of the composites indicated that the MoSi2 was chemically well compatible with the beta'-SiAlON.