High-Temperature Oxidation Behavior of AlxCoCr0.5NiPt0.1 (x = 0.5, 1.0) Multi-Principal Element Alloys at 1100 °C

The microstructure, phase composition, and high-temperature oxidation behavior of Al0.5CoCr0.5NiPt0.1 and AlCoCr0.5NiPt0.1 multi-principal element alloys (MPEAs) at 1100 °C in air were investigated. Depending on the content of aluminum, the microstructure of as-cast samples contains FCC and BCC solid solutions. Similarly, the ratio of two solid solutions varies depending on the aluminum content in the alloy. When the content of aluminum is x = 0.5, the microstructure is dominated by the FCC solid solution, while a BCC solid solution is dominated when the concentration of aluminum is increased to x = 1.0. Moreover, in both MPEAs, platinum exists as a part of solid solutions rather than a separate phase. High-temperature oxidation was carried out in a Plavka.Pro PM-1 SmartKiln muffle furnace under isothermal conditions at 1100 °C for 100 h exposure in air, and weighing was performed every 10 h. The maximum specific weight gain for the Al0.5CoCr0.5NiPt0.1 alloy was 0.965 mg/cm2, and 0.675 mg/cm2 for the AlCoCr0.5NiPt0.1 alloy. Based on the high-temperature oxidation experiment results, it was established that AlCoCr0.5NiPt0.1 MPEA exhibits greater resistance towards high-temperature dry air corrosion with the formation of an exclusive Al2O3 scale on the surface with 3–5 μm thickness; the parabolic oxidation rate constant for this alloy is kp = 20.2 × 10–13 (g2/cm4s). Introduction of platinum into the composition of the Fe-free AlCoCr0.5Ni alloy reduces the value of the parabolic oxidation rate constant by half.