Unraveling the oxidation mechanism of Y-doped AlCoCrFeNi high-entropy alloy at 1100 °C

Equimolar AlCoCrFeNi high entropy alloy (HEA) with a coherent dual-phase structure commonly exhibits good strength at high temperatures. Regretfully, the poor oxidation resistance greatly limits its practical application space. In this work, the effect of the reactive element (RE) Y on the oxidation resistance of AlCoCrFeNi HEA is explored. (AlCoCrFeNi)_100−xY_x (x = 0, 0.1, 0.5 and 1, at.%) were designed and their oxidation mechanisms were unravelled at 1100 °C. Besides the two original B2 phase and A2 phase, the Y-doped HEAs contain (Y, Ni)-rich phase. An appropriate amount of Y blocks the outward Al diffusion and meanwhile inhibits the laterally grown oxides within the existing scale, thereby suppressing the formation of interface pores and rumplings and contributing to superior resistance to oxide scale spallation. However, excessive Y doping causes the formation of (Y, Al)-rich oxide intrusions, which result in the nucleation of cracks near them and thus degrade the interface adherence. The generation and failure mechanisms of oxide scales formed on Y-doped HEAs during 100 h oxidation have been revealed. The presented information proposes new insights to improve the high-temperature oxidation resistance of AlCoCrFeNi HEA and may be useful for assessing the possibility of the practical application of HEAs in aerospace engine components.