First-principle calculation of APB energy in Ni-based binary and ternary alloys

An ab initio method based on density functional theory has been employed to compute the zero-temperature anti-phase boundary (APB) energies for Ni3Al1−xRx (R = Nb, Ta, Ti) system over a range of compositions. The computation is limited to the APB on the (1 1 1) plane for L12 crystal structure, allowing only the volume relaxation, appropriate for the γ' precipitate in Ni-based superalloy. For the limiting case of the binary system Ni3Al, the APB energy has also been calculated for the (1 0 0) plane. We find that the APB energy for the (1 1 1) plane in Ni3Al is 181 mJ m−2, and substitution of Nb, Ta or Ti at the Al site increases the APB energy to over 600 mJ m−2, leading to higher strengths. While the peak APB energy values for all the ternary systems are quite similar, they are achieved over very different compositional ranges. Nb and Ta are found to have almost identical strengthening effect on Ni3Al. The selected compositional space is of direct relevance to the commercially important family of Ni-based superalloys, and our results provide important guidelines for alloy design strategies.