Oxidation behavior of Mo5SiB2-based alloy at elevated temperatures

A Mo5SiB2-based alloy having composition of Mo–12.3 mol% Si–24.9 mol% B was produced by arc-melting in an Ar atmosphere, and its oxidation behavior was investigated at temperature between 973 and 1673 K. At and above 1273 K, transient and steady state oxidation stages were clearly observed. The occurrence of the transient and steady state oxidation is interpreted in terms of rapid volatilization of MoO3 and B2O3 under ambient O2 pressure at the initial stage and the passive oxidation after completely sealing the substrate by silicate glass. Development of two layers onto the substrate, i.e. SiO2 glass scale and Mo solid solution interlayer including SiO2 dispersions, strongly supports the interpretation. Dissolution of B into the SiO2 scale was not confirmed because of low B concentration that was under a detectable limit of EPMA and TEM-EDS. It is suggested that the SiO2 glass scale formed on the Mo5SiB2-based alloy is more protective than as expected.