High-temperature oxidation behaviors of an equiatomic CrMnFeCoNi high entropy alloy

Due to the limited information in the literature on the oxidation mechanism of high-entropy alloys, we have investigated the high temperature oxidation behavior of an equiatomic Cr20Mn20Fe20Co20Ni20 high-entropy alloy (CrMnFeCoNi HEA) to demonstrate the oxidation mechanism. The evolution of the surface morphology and the specific oxide growth processes and elemental distributions were analyzed by scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), and X-ray diffractometer (XRD). The findings reveal that the alloy undergoes three oxidation stages, which are i) surface reaction between O2- ions and metal ions at low temperatures (750–850 °C), ii) thickening of the sample surface due to chemosorption of O2 atoms at moderate temperatures (950–1050 °C), and iii) thinning of the sample due to oxide spalling at high temperatures (1050–1150 °C). Three oxide layers were detected, extending from the outside to the inside of the cross sections of the sample and were composed of MnFe2O4 +Mn3O4, (Mn,Cr)xO4, and Cr2O3, respectively. Subsequently, the high-temperature oxidation behavior of the alloy was determined by thermodynamic and kinetic calculations. As a result, an oxidation mechanism model was established. The results of this study have paved the way for new applications of HEAs.