Effect of alloying elements on stacking fault energies of γ and γʹ phases in Ni-based superalloy calculated by first principles

The first-principle calculations were employed to investigate the effect of alloying elements on stacking fault energies of γ-Ni and γʹ-Ni₃Al phases in Ni-based single crystal superalloys. The results showed that Co, Cr, Mo, Ta, Ti, W, Re and Ru elements decreased the stacking fault energy of γ-Ni phase with increasing the concentration, but increased the stacking fault energy of γʹ-Ni₃Al phase except Co and Cr elements. And, Co had a more significant effect than Cr in decreasing the unstable stacking fault energies of two phases. Furthermore, the interaction effect of Co and Cr elements was calculated that it significantly reduced the stable stacking fault energy of γ′ phase but had no obvious effect on the that of γ phase. Finally, two alloys with different Co contents were crept at 750 °C/750 MPa condition, and the creep life in 12Co alloy was about 118 h, which was basically half of that in 9Co alloy (242 h). The microstructure observation indicated that the width of stacking fault in γ′ phase in 12Co alloy was increased by 51.8 nm, and the stable stacking faults energy of γ′ phase was reduced by 9.1 mJ/m² compared to those in 9Co alloy.