Co-alloying effects on the site preference and the elastic properties of γ′-Ni3Al from first-principles calculations

The influences of co-alloying atom pairs Ta-X (X: Ta, Mo, W, Cr, Co, and Re) on the site preference and elastic properties of gamma ' -Ni3Al precipitate phase were studied using first-principles calculations, and the underlying mechanism for the strengthening effect is determined. It is found that the site preferences of Ta-X co-alloying atom pairs are in the sequence of Al-Al, Al-Ni, Ni-Al, and Ni-Ni sites except for Ta-Co. The atom pair Ta-Co does not display a strong site preference tendency. The elastic properties for the Al-Al configuration were examined, and the results were compared with those of single-alloying to investigate the co-alloying effect. It is shown that the elastic modulus and hardness are obviously improved by co-alloying. Moreover, the effect of co-alloying is stronger than that of single-alloying. The further analyses by the charge density difference and the electronic density of states reveal that the strong effect of the co-alloying is attributed to the enrichment of the charge density between X and its nearest-neighbor Ni, as well as the orbital hybridization between Ta/X-d and Ni-d which acts as covalentlike bonds. Our results can provide an in-depth insight into the physics in the strengthening effect of co-alloying elements on the mechanical properties of single crystal superalloys.