Effects of tantalum on the partitioning of tungsten between the gamma- and gamma '-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 gamma (face-centered cubic)- and gamma' (LI2)-phases in Ni-based alloys. APT observations indicate that whereas W partitions preferentially to the gamma'-phase in a ternary Ni-Al-W alloy, its partitioning behavior is reversed in favor of the gamma-phase in multi-component alloys. Furthermore, the degree of W-partitioning to the gamma'-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 gamma'-phase, whereas Ta has a larger tendency to partition to the gamma'-phase than does W. This implies that Ta displaces W from the gamma'-phase Into the gamma-phase in multi-component Ni-based alloys. (C) 2010 Acta Materialia Inc Published by Elsevier Ltd. All rights reserved.