Effect of oxygen pressure on the oxidation behavior of NiCoCr medium-entropy alloy at 800 °C

Highlights: • The oxidation of the NiCoCr meduim-entropy alloy was studied in various oxygen pressures at 800 °C. • The oxidation kinetics of the alloy obeyed the parabolic-rate law. • The oxidation mechanism of the alloy was due to outward cation diffusion. • The main diffusing species were doubly- and triply-ionized cation vacancies. The oxidation behavior of NiCoCr medium-entropy alloy was investigated at 800 °C in various oxygen pressures from 10 to 10⁵ Pa. The results showed that the oxidation kinetics of NiCoCr followed the parabolic rate law, regardless of oxygen pressure. The oxidation rate constants of the alloy steadily increased with increasing oxygen pressure. The oxidation mechanism of the MEA was mainly controlled by outward cation diffusion to form an exclusive Cr₂O₃ layer although minor amounts of Co- or Ni-Cr spinels were observed at PO₂ = 10⁵ Pa under TEM analyses. The main diffusing species were doubly- and triply-ionized cation vacancies.