Effect of double reinforcements on elevated-temperature strength and toughness of molybdenum disilicide

Abstract

Flexural strength and fracture toughness of molybdenum disilicide and its composites with 10 wt% TiB₂ and 10 wt% TiB₂+ 10 wt% SiC, synthesized by the hot-pressing technique, were evaluated as a function of temperature, ranging from ambient temperature to 1600° C. Results show that the composites have higher strength and slightly lower toughness as compared with monolithic MoSi₂ at room temperature. At high temperatures, the composites exhibit higher strength as well as higher toughness vis-à -vis monolithic MoSi₂. Among the composites, the double reinforcement of SiC and TiB₂ was found to be more effective in improving the mechanical properties. A transition from brittle to ductile behavior was observed at temperatures greater than 1300°C for all materials tested. The high-temperature mechanical behavior was found to be significantly influenced by the flow of an intergranular glassy phase and the attendant cavity nucleation and growth along the grain boundaries. Micromechanisms responsible for the ambient as well as the elevated-temperature property improvement in composites are discussed with the aid of fractography.