Dependence of mechanical properties on the site occupancy of ternary alloying elements in γ′-Ni3Al: Ab initio description for shear and tensile deformation*

Abstract

The site occupancy behavior of ternary alloying elements in γ′-Ni3Al (a key strengthening phase of commercial Ni-based single-crystal superalloys) can change with temperature and alloy composition owing to the effect of entropy. Using a total-energy method based on density functional theory, the dependence of tensile and shear behaviors on the site preference of alloying elements in γ′-Ni3Al were investigated in detail. Our results demonstrate that Fe, Ru, and Ir can significantly improve the ideal tensile and shear strength of the γ′ phase when occupying the Al site, with Ru resulting in the strongest enhancement. In contrast, elements with fully filled d orbitals (i.e., Cu, Zn, Ag, and Cd) are expected to reduce the ideal tensile and shear strength. The calculated stress–strain relationships of Ni3Al alloys indicate that none of the alloying elements can simultaneously increase the ideal strength of the γ′ phase for both Ni1-site and Ni2-site substitutions. In addition, the charge redistribution and the bond length of the alloying elements and host atoms during the tensile and shear processes are analyzed to unveil the underlying electronic mechanisms.