Site occupancy of chromium in the γ′-Ni3Al phase of nickel-based superalloys: a combined 3D atom probe and first-principles study

Transition-metal dopants play a critical role in the high-temperature mechanical strength and corrosion resistance of nickel-based superalloys. In this article, the site occupancy behavior of chromium in gamma'-Ni3Al has been investigated by combining three-dimensional (3D) atom probe and high-resolution transmission electron microscopy characterizations with ab initio density functional theory (DFT) calculations. The 3D atom probe data show a clear preference of chromium on the aluminum sublattice over the nickel sublattice in Rene88 super alloys. First-principles DFT total-energy calculations were performed to understand the site occupancy of chromium in the L1(2) structured gamma-Ni3Al. The obtained chromium site preference energies have been compared using the anti-site and vacancy-based substitution formation mechanism, as well as using the standard defect formation formalism. It was found that chromium prefers aluminum site, consistent with the 3D atom probe result. In addition, interaction energies between two chromium atoms have also been determined from first-principles calculations. Our results show that chromium atoms prefer to be close by on either nickel or aluminum sublattices or on a nickel-aluminum mixed lattice, suggesting a potential tendency of chromium segregation in the gamma' phase.