PROPERTIES AND MICROSTRUCTURE OF MOLYBDENUM DISILICIDE BETA'-SIALON PARTICULATE CERAMIC COMPOSITES

Particulate ceramic composites that were composed of a combustion-synt hesized beta'-SiAlON matrix and dispersed MoSi2 particles were hot pre ssed at 1600 degrees C in a nitrogen atmosphere, The physical and mech anical 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 o f 500-600 MPa, 3-4 MPa.m(1/2), and 11-13 GPa, respectively, The measur ed mechanical strength and hardness were very similar to the values th at were predicted from the rule of mixtures. The fracture toughness of the combustion-synthesized beta'-SiAlON (2.5 MPa.m(1/2)) was apparent ly enhanced by the MoSi2 particles that were added. The increase in th e fracture toughness was predominately attributed to the residual ther mal 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 monoli thic beta'-SiAlON. High-resolution transmission electron microscopy ex amination of the composites indicated that the MoSi2 was chemically we ll compatible with the beta'-SiAlON.