Existence patterns of Dy in β-NiAl from first-principles calculations

Intermetallic compound β-NiAl is a promising material in high temperature applications due to its high melting temperature, high strength, low density, and good oxidation resistance. However, its application remains limited because of its relatively poor cyclic oxidation resistance. Addition of reactive element (RE) Dy can improve the cyclic oxidation of NiAl alloys significantly. However, the mechanism of Dy addition is not clear. Even the existence pattern of Dy in NiAl is unspecified. Therefore, in the present study, the impurity formation energies of Dy in stoichiometric NiAl, Ni-rich, and Al-rich NiAl for the substitution cases were studied by first-principles density functional theory. The results show that Dy could hardly substitute for either Ni or Al atoms in NiAl. However, calculations for dissolution energies show that Dy could be easily dissolved in Al vacancies in all three types of NiAl, which provides a new existence pattern of Dy in NiAl beyond experimental detection.