The oxidation behavior of Ni₂FeCoCrAl_x high-entropy alloys in dry air

The oxidation behavior of three Ni₂FeCoCrAl_x high-entropy alloys (where x = 0, 0.5, and 1.0) was studied at 600–900 °C in dry air. The oxidation kinetics of all the alloys obeyed the parabolic rate law at T ≥ 700 °C, with their oxidation rates steadily increasing with either increasing temperature or decreasing Al content. Discontinuous oxide particles grew on the alloys at 600 °C, while multiple layered scales and an exclusive Al₂O₃ layer formed on the Al-free and the Al-containing alloys, respectively at T ≥ 700 °C. In addition, an internal nitrogen attack to form AlN was also observed for the Al-containing alloys at 900 °C.