Role of Al and Cr on cyclic oxidation behavior of AlCoCrFeNi2 high entropy alloy

In this work, cyclic oxidation behavior of AlCoCrFeNi2, Al1.5CoCrFeNi2, AlCoCr1.5FeNi2, and Al1.5CoCr1.5FeNi2 High Entropy Alloys (HEAs) has been studied at 1050 °C for 10 cycles to understand the effect of Al and Cr in AlCoCrFeNi2 based HEAs. X-ray photoelectron spectroscopy, X-ray diffraction, electron backscattered diffraction, scanning electron microscopy with energy dispersive spectroscopy were used to study the base metals and oxidized samples. It was found that in all the samples, face centered cubic, and body centered cubic phases were present in different phase fractions. Al1.5CoCrFeNi2 alloy shows lower oxidation rate with oxidation rate constant (Kp) in the order of 10−13 g2cm−4s−1. The lowest oxidation rate of Al1.5CoCrFeNi2 alloy is attributed to the presence of higher Al content as it forms protective continuous thin Al2O3 oxide layer which suppress further oxidation by preventing ingress of oxygen into the substrate. Presence of higher Cr content results in forming protective Cr2O3 oxide layer but eventually it spalls off leading to the exposure of substrate for further oxidation.