Post-Hot-Pressing and High-Temperature Bending Strength of Reaction-Bonded Silicon Nitride-Molybdenum Disilicide and Silicon Nitride-Tungsten Silicide Composites

Abstract

A hot-pressing technique was used for the further densification of reaction-bonded silicon nitride-molybdenum disilicide and silicon nitride-tungsten silicide (Si3N4-MoSi2 and Si3N4-WSi2, respectively) compacts that were prepared via a presintering step and a nitriding process from silicon-molybdenum or silicon-tungsten powders. After hot pressing was performed at 1650°C (25 MPa for 1 h), most of the alpha-Si3N4 that formed during the reaction-bonding process was transformed to β-Si3N4 and, moreover, a very small amount of Mo5Si3 (W5Si3) was formed in addition to MoSi2 (WSi2). Three- and four-point bend tests were performed at room temperature (25°C), 1000°C, 1200°C, and 1400°C. The bend strength of the Si3N4-WSi2 composite increased slightly from room temperature up to 1000°C, whereas the Si3N4-MoSi2 composite showed a more-pronounced increase up to 1200°C. Microstructural analysis was performed on the fracture surfaces of both composites that were tested at different temperatures.