Wet oxidation of TiZrHfNbTaV high-entropy alloys: Role of grain-boundary and interdendritic diffusion

Refractory high-entropy alloys (RHEAs) are sensitive to thermal oxidation, significantly restricting their service performance and potential applications. However, the wet oxidation behavior of RHEAs has remained poorly understood despite the potential risk of catastrophic oxidation caused by water vapor. In this study, the oxidation mechanism of an equiatomic TiZrHfNbTaV high-entropy alloy (HEA) has been investigated in a wet atmosphere at elevated temperatures. Synchronous oxidation of all elements occurs at temperatures below 800 °C. At temperatures above 800 °C, preferential oxidation of Nb, Ti, and Zr, and internal oxidation of V occur on HEAs, which are thermodynamically less preferred as compared with oxidations of more reactive Hf and Ta. Experimental and theoretical analyses show that the oxide grain boundaries and substrate interdendritic regions of HEAs act as diffusion pathways for V and oxidizing species during preferential and internal oxidation processes. This work provides a fundamental understanding of the oxidation of multicomponent alloys in wet environments, which is helpful in the development of effective oxidation resistance strategies and innovative surface engineering techniques.