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