Effect of Hf on high-temperature oxidation behavior of chromia-forming Al CoCrFeNi alloys

Nanodispersion of HfO 2 is deposited on the surfaces of chromia-forming Al x (CoCrFeNi) 100− x high entropy alloys ( x = 3; 6; 9) to improve their resistance to high-temperature oxidation in air at 900 °C. A strong effect of Hf as a reactive element is well-confirmed through several-fold reduction in mass gains, suppressed scale spallation, simplified oxide scale composition (mainly Cr 2 O 3 ), and inhibited internal oxidation and nitridation, compared to the unmodified reference materials. Its beneficial influence is visible particularly during the especially challenging long-term thermal cycling. The study proves the wide possibilities for obtaining highly efficient HEA-based materials for high-temperature industrial applications. • Surface dispersion of HfO 2 radically improves the high-temperature oxidation resistance of Al x CoCrFeNi alloys. • The mass gains are several times reduced, scales’ constitution is simplified and thickness is decreased. • The modified materials exhibit also excellent resistance to thermal shocks during thermal cycling. • Addition of HfO 2 enables transformation of the oxidation behavior from poor to highly protective.