Atom site preference and γ′/γ mismatch strain in Ni-Al-Co-Ti superalloys

The structure and chemistry of Ni-Co-Al-Ti quaternary superalloys are investigated at the micro structural and atomic scale. Atom probe tomograghy (APT) is used to quantify phase compositions and elemental partitioning behavior. Using aberration corrected electron microscopy, the site occupancy of the atoms within the A(3) B structure (L1(2)-type) gamma' phase is determined via atomic resolution energy dispersive X-ray spectroscopy (EDX). Ni is observed to preferentially occupy the A sub-lattice positions for all alloys, while Al and Ti occupy the B sub-lattice. In contrast, Co's site preference changes from a random distribution to the A sub-lattice as the alloy composition changes, in agreement with theoretical predictions from literature. Finally, the lattice strain across the 771, interfaces is measured as a function of alloy composition. (C) 2016 Elsevier Ltd. All rights reserved.