Chromium and tantalum site substitution patterns in Ni3Al (L12) γ′-precipitates

The site substitution behavior of Cr and Ta in the Ni3Al (L1(2))-type gamma(')-precipitates of a Ni-Al-Cr-Ta alloy is investigated by atom-probe tomography (APT) and first-principles calculations. Measurements of the gamma(')-phase composition by APT suggest that Al, Cr, and Ta share the Al sublattice sites of the gamma(')-precipitates. The calculated substitutional energies of the solute atoms at the Ni and Al sublattice sites indicate that Ta has a strong preference for the Al sites, while Cr has a weak Al site preference. Furthermore, Ta is shown to replace Cr at the Al sublattice sites of the gamma(')-precipitates, altering the elemental phase partitioning behavior of the Ni-Al-Cr-Ta alloy. (C) 2008 American Institute of Physics.