Coupling effect of Ni and Ta on the antiphase boundary energy in γ’ phase of CoNi-based superalloys

Anti-phase boundaries (APBs) significantly influence the yield strength and creep resistance of CoNi-based superalloys. However, the effect of Ni on the anti-phase boundary energy (APBE) of the γ’ phase remains under debate. In this work, a comprehensive investigation combining density functional theory (DFT), cluster expansion (CE), and Monte Carlo simulations was carried out to clarify this issue. The analysis of equilibrated configurations reveals that Ni plays a key role in suppressing anti-site defect formation, thereby enhancing the stability of the γ’ phase. In addition, short range order (SRO) phenomena were observed within the γ’ phase, further stabilizing the γ’ phase. With respect to APBE, both Ni and Ta are found to increase the APBE within a reasonable compositional range. Notably, their co-addition exhibits a synergistic effect, leading to a further increase in APBE. However, in CoNi-based superalloys, an increased Ni content leads to a reduced Ta concentration in the γ′ phase, resulting in a decrease in the APBE. These findings offer new insights into the compositional tuning of APBE and provide a solid foundation for designing alloys with controlled shear deformation mechanisms in γ’ phases.