High-Temperature Oxidation Behavior of Cu_0.3Cr₂Fe₂Ni₃Mn₂Nb_x High-Entropy Alloys

The high-temperature oxidation performance of Cu_0.3Cr₂Fe₂Ni₃Mn₂Nb_x (x = 0, 0.2, 0.4 mol, named Nb₀, Nb_0.2, and Nb_0.4, 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 Nb_0.4 alloy has the lowest oxidation weight gain, approximately 0.016 mg/cm². As the Nb content increases, the K_p value of HEAs decreases. The K_p value of the Nb_0.4 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 Cu_0.3Cr₂Fe₂Ni₃Mn₂Nb_x 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.