Effect of Pt Addition on the Oxidation and Corrosion Resistance of Al0.25CoCrFeNi High-Entropy Alloy

The effect of minor platinum alloying on the microstructure, phase composition, oxidation and corrosion resistance of Al0.25CoCrFeNi high-entropy alloy (HEA) has been studied. It was observed that Pt does not segregate as a separate phase, but it is incorporated into the fcc solid solution. High-temperature oxidation of the as-cast Al0.25CoCrFeNi and Al0.25CoCrFeNiPt0.1 high-entropy alloys was carried out in a muffle furnace under isothermal conditions at 900 °C for 0–50 h (weighing was carried out every 10 h) in air atmosphere. The specific weight gain decreased from 0.58 mg/cm2 for Al0.25CoCrFeNi to 0.31 mg/cm2 for the platinum-doped Al0.25CoCrFeNiPt0.1 sample. It was determined that Pt triggers the formation of an interlayer Al-rich oxide phase between the outer Cr-rich oxide layer and the interior of the alloy, significantly reducing the oxidation rate of Al0.25CoCrFeNiPt0.1 HEA. Electrochemical tests in 0.5 M H2SO4 solution demonstrated passive behavior with anodic control of the process.