High-temperature oxidation of Mo-rich (Mo1−xNbx)Si2 pseudo-binary compounds

The oxidation behaviours of arc-melted (Mo1−xNb1−x)Si2 pseudo-binary alloys were investigated at temperatures between 1473 and 1773 K with emphasis on the Mo-rich portion. C11b/C40 duplex-phase microstructure was formed in the composition range of x = 0.05–0.2. In Mo-rich alloys (x ⩽ 0.5), the near-parabolic law of oxidation kinetics was followed at all investigated temperatures. The oxidation resistance of alloys depends on chemical composition as well as microstructure. An anomalous increase in weight gain was observed in the C11b/C40 two-phase region, where the peak weight gain shifts to the Mo-rich side with an increase in temperature. The C40 single phase (Mo0.7Nb0.3)Si2 was found to have a low oxidation weight gain which is even less than that of the binary MoSi2. However, when the Nb content x exceeds 0.4, the oxidation resistance becomes poor and Nb2O5 is formed in the oxide scale.