Effect of Mo Dispersion Size and Water Vapor on Oxidation of Two-Phase Directionally Solidified NiAl-9Mo In-Situ Composites

Oxidation of NiAl–9Mo eutectics with three different second-phase Mo dispersion sizes was investigated at 900 °C in dry and wet air. Good oxidation resistance via alumina formation was observed in dry air, with MoO 3 volatilization minimized by submicron Mo dispersions. However, although mass change measurements were similar in dry/wet air, extensive volatilization and in-place internal oxidation of prior Mo phase regions was observed in wet air. The ramifications of this phenomenon for the development of multiphase high-temperature alloys are discussed.