Vacancy-enhanced oxidation resistance of Fe2CrAl high-temperature alloy

Although Fe2CrAl ternary alloy is a promising high temperature material, the oxidation mechanism of Fe2CrAl is unknown. To solve the problem, here, we apply the first-principles method to study the oxidized behavior of Fe2CrAl ternary alloy. In particular, the influence of vacancies on the oxidation resistance of Fe2CrAl is further studied. The calculated results shows that the oxygen prefers to occupy the octahedral interstitial (OI) site because of the interaction of O-Al, O-Cr and O-Fe atoms. It is found that these vacancies are thermodynamic stability in Fe2CrAl ternary alloy. In particular, the Cr-vacancy has better thermodynamic stability compared to the Fe-vacancy and Al-vacancy. Importantly, the Cr-vacancy has strongest the oxidation resistance because the Cr-vacancy enhances the localized hybridization between O atom and Al atom, which form the Al2O3 oxide. The formation of Al2O3 is demonstrated by the bond length of Al-O bond in Al2O3. In addition, the calculated elastic modulus of the oxidized Fe2CrAl is lower than the unoxidized Fe2CrAl whether the parent Fe2CrAl or Fe2CrAl with three vacancies. However, the Fe2CrAl with Cr-vacancy retains the high elastic stiffness compared to the Fe-vacancy and Al-vacancy. Therefore, we believe the Cr-vacancy is beneficial to improve the oxidation resistance of Fe2CrAl ternary alloy.