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

Abstract Results of a systematic investigation of the oxidation in a Mo–Si–B alloy containing the three phases, Mo, Mo 3 Si, and Mo 5 SiB 2 (T2) are presented. The relative kinetics of B-containing silica-scale formation, permeation of MoO 3 through the viscous scale, the viscosity of the B-containing SiO 2 scale, volatilization of MoO 3 and B 2 O 3 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 MoO 3 begins to volatilize but B 2 O 3 does not, resulting in gaseous MoO 3 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.