High temperature oxidation behavior of directionally solidified NiAl–31Cr–2.9Mo–0.1Hf–0.05Ho eutectic alloy

The isothermal oxidation behavior of NiAl–31Cr–2.9Mo–0.1Hf–0.05Ho directional eutectic alloy was investigated with the help of scanning electron microscopy and X-ray diffraction. The results revealed that a continuous Al2O3 scale was formed and owned excellent oxidation resistance in the temperature range of 900–1100 °C. When the temperature was up to 1150 °C, the continuous Al2O3 oxide film ruptured. Trace rare earth element Ho distributed uniformly in the alloy and relatively high level of Al in Cr(Mo) phase are beneficial to the formation of continuous and compact Al2O3 scale. During the oxidation, a phase transformation from θ-Al2O3 to α-Al2O3 existed on the surface of oxidation film. It resulted in the abnormal oxidation mass gain happening when the alloy was oxidized at 1000 °C or 1050 °C.