Effects of tantalum on the partitioning of tungsten between the γ- and γ′-phases in nickel-based superalloys: Linking experimental and computational approaches

Atom probe tomography (APT) and first-principles calculations are implemented to study the partitioning of W to the γ (face-centered cubic)- and γ′ (L12)-phases in Ni-based alloys. APT observations indicate that whereas W partitions preferentially to the γ′-phase in a ternary Ni–Al–W alloy, its partitioning behavior is reversed in favor of the γ-phase in multi-component alloys. Furthermore, the degree of W-partitioning to the γ′-phase decreases with the addition of Ta to a Ni–Al–Cr–W alloy, a trend which is consistent with Thermo-Calc simulations. First-principles calculations of the substitutional formation energies of W and Ta at 0 K predict that both elements prefer energetically sharing the Al-sublattice sites of the γ′-phase, whereas Ta has a larger tendency to partition to the γ′-phase than does W. This implies that Ta displaces W from the γ′-phase into the γ-phase in multi-component Ni-based alloys.