Investigation of the High-Temperature Oxidation Behavior of the Al0.5CoCrFeNi High Entropy Alloy

As a new class of materials, High Entropy Alloys (HEAs), have been recently used for various usages such as high-temperature applications. High entropy alloys have such unique properties as high strength, high-temperature phase stability, good fracture resistance, and excellent softening resistance at high temperatures. Studies on the oxidation behavior of as-cast high entropy alloys are, however, currently limited. The oxidation behavior of Al0.5CrCoFeNi HEA was investigated at three different temperatures of 800, 900, and 1000°C, and in the air. The results showed that the oxidation kinetics of this alloy followed the parabolic rate law. However, at 1000°C, two-step oxidation kinetics was found: in the first step, it followed the almost linear oxidation rate law (n=0.97); in the second one, the predominant mechanism followed the parabolic rate law (n=0.56). Analysis of the morphology and phase composition of the oxide layers was done using the Scanning Electron Microscopy (SEM) and X-ray diffraction. At all temperatures, the results showed that the oxide layers consisting of Cr2O3/Al2O3 and spinel of Ni, Co, and Fe were formed in the Al depleted zone.