Oxidation mechanisms in Mo-reinforced Mo5SiB2(T2)–Mo3Si alloys Original Research Article

Results of a systematic investigation of the oxidation in a Mo–Si–B alloy containing the three phases, Mo, Mo3Si, and Mo5SiB2 (T2) are presented. The relative kinetics of B-containing silica-scale formation, permeation of MoO3 through the viscous scale, the viscosity of the B-containing SiO2 scale, volatilization of MoO3 and B2O3 from the silica scale, are identified as key parameters that determine the kinetics of the oxidation of the alloy in the temperature range of 500–1300 °C. The oxidation is worst in the intermediate temperature range, 650–750 °C, where MoO3 begins to volatilize but B2O3 does not, resulting in gaseous MoO3 bubbling through a low viscosity borosilicate scale. In this temperature range, the scale provides insufficient protection suggesting that attempts to improve the oxidation resistance of this system must focus on this temperature range.