Segregation of tungsten at γ′ (L 12) /γ (fcc) interfaces in a Ni-based superalloy: An atom-probe tomographic and first-principles study

γ (fcc) / γ′ (L 12) heterophase interfaces in a Ni-based superalloy are investigated using atom-probe tomography and first-principles calculations. Flat {100} interfaces exhibit a confined (nonmonotonic) Gibbsian interfacial excess of tungsten, ΓW =1.2±0.2 nm-2, corresponding to a 5 mJ m-2 decrease in interfacial free energy. Conversely, no measurable segregation of W is detected at curved interfaces. First-principles calculations for a Ni-Al-W system having a {100} interface indicate a decrease in the interfacial energy of 5 mJ m-2 due to W segregation. Similar calculations for {110} and {111} interfaces predict an increase of 1 and 9 mJ m-2 in their energies, respectively, and therefore no heterophase segregation.