Phase identification in reactively sintered molybdenum disilicide composites

The objective of this research was to identify and quantify the phases formed in reactively sintered MoSi2 and MoSi2 composites made from carbon coated MoSi2 powders. The purpose of adding carbon was to form silicon carbide particles (SiCp) in situ and reduce the inherent presence of SiO2 in MoSi2. The carbon additions were made via polymeric coatings on MoSi2 particles by two processes, Phenolic Resin Based Carbon by Solvent Evaporation (PRBCSE) and Aqueous Dispersion Flocculation (ADF). The sintering temperatures and times ranged from 1600 to 1800°C, and from 1 to 100 h, respectively. The addition of carbon did reduce the presence of SiO2 and there was formation of SiCp. However, the SiCp formation was less than expected, a maximum of 1.4 vol.% SiCp was formed. The Nowotny phase (Mo≤4 8Si3C≤0.6) was observed in the sintered samples. The in situ formation of SiCp would increase the toughness of MoSi2 by serving as a reinforcement. The reduction in the amount of SiO2 would reduce the incidence of grain boundary sliding caused by viscous flow of SiO2 at elevated temperatures.