Combined atom probe tomography and first-principles calculations for studying atomistic interactions between tungsten and tantalum in nickel-based alloys

We investigate the partitioning behavior of tungsten to the γ(face-centered cubic) and γ′(L12) phases in Ni-based alloys employing atom probe tomography (APT), first-principles calculations and computational thermodynamics. Several APT studies of Ni-based alloys indicate that the partitioning of tungsten atoms to the γ′(L12) phase is reversed in favor of the γ phase due to tantalum atom additions. First-principles calculations of substitutional formation energies at 0 K indicate that tungsten and tantalum atoms share the aluminum sublattice sites of the γ′(L12) phase, and that tantalum has a larger tendency to partition to the γ′(L12) phase than does W. We also calculate the binding energies of W-W and Ta-W dimers in the γ(fcc) and γ′(L12) phases, respectively, and use these values in a quantitative model to demonstrate that interatomic interactions between tungsten and tantalum atoms play a significant role in the partitioning reversal of tungsten.