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

Abstract

The oxidation behavior of NiCoCr medium-entropy alloy was investigated at 800 degrees C in various oxygen pressures from 10 to 10(5) 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 = 10(5) Pa under TEM analyses. The main diffusing species were doubly- and triply-ionized cation vacancies.