Oxidation behavior of Al15Fe20Co20Ni20Cr25-xNbx high-entropy alloys at elevated temperatures

In this work, dual-phase solid solution structures including disordered and ordered FCC and BCC were obtained in Al15Fe20Co20Ni20Cr25-xNbx (x = 1, 1.5, 2, at.%) HEAs. With the addition of Nb, Al15Fe20Co20Ni20Cr25-xNbx HEAs were strengthened, and good trade-offs of strength and strain were achieved. Notably, the designed Nb-containing Al15Fe20Co20Ni20Cr25-xNbx HEAs exhibited excellent oxidation resistance at the temperatures of 750–1000 °C. Compared with Nb-free Al15Fe20Co20Ni20Cr25 HEA, the oxidation rate coefficients (kp) of H6N-1 alloy reduced by 81.70% (±1.32%) and 94.92%(±0.75%) respectively after oxidizing at 750 °C and 900 °C. When H6N-1 alloy was oxidized at 1000 °C, a low oxidation rate coefficient of 3.80 × 10−12 g2/cm4∙s was achieved. Moreover, H6N-1.5 and H6N-2 alloys show smaller mass gains than H6N-1 alloy, and obvious plateau can be observed in the oxidation kinetics curves, indicating the occurrence of oxidation passivation. Significantly, the kp values of Al15Fe20Co20Ni20Cr25-xNbx HEAs at 1000 °C are smaller than that of most of the reported AlCoCrFeNi HEAs oxidized at 900 °C. In summary, the partial substitution of Cr by Nb can remarkably promote oxidation resistance of Al15Fe20Co20Ni20Cr25-xNbx HEAs without obvious damaging the mechanical properties. It indicates that Al15Fe20Co20Ni20Cr25-xNbx (x = 1, 1.5, 2, at.%) HEAs can be promising candidates for multi-component superalloys.