High-Temperature Oxidation Behavior of Cu0.3Cr2Fe2Ni3Mn2Nbx High-Entropy Alloys

The high-temperature oxidation performance of Cu0.3Cr2Fe2Ni3Mn2Nbx (x = 0, 0.2, 0.4 mol, named Nb0, Nb0.2, and Nb0.4, respectively) high-entropy alloys (HEAs) was investigated using a constant-temperature oxidation discontinuous weighing method at 800°C. The high-temperature oxidation of the three HEAs follows a parabolic law. After 50 h of oxidation, the Nb0.4 alloy has the lowest oxidation weight gain, approximately 0.016 mg/cm2. As the Nb content increases, the Kp value of HEAs decreases. The Kp value of the Nb0.4 alloy is smallest, about 1.52 × 10−11 g2·cm–4·s–1, indicating that an increase in Nb content can effectively improve the oxidation resistance of Cu0.3Cr2Fe2Ni3Mn2Nbx HEAs. The outer layer primarily contains O and Mn, while the inner layer includes O, Cr, Mn, and/or Nb. The oxidation mechanism is mainly the outward diffusion of metal cations and the inward permeation of O ions. The Nb element improves the high-temperature oxidation resistance of the alloy through the dual effects of thermodynamic stability and kinetic diffusion inhibition.