Tuning the plasticity of Ni-Mo solid solution in Ni-based superalloys by ab initio calculations

The generalized stacking fault energies of face centered cubic Ni-Mo solid solutions are calculated using the exact muffin-tin orbital method in combination with coherent potential approximation. The alloying of Mo in Ni is found to decrease the intrinsic stacking fault energy of the solid solution from 150 mJ/m² (pure Ni) to 50 mJ/m² (17.5 at.% Mo) almost linearly. At the same time, the unstable stacking fault energy (the unstable twin fault energy) of the Ni-based solid solution increases (decreases) in a small extent with increasing Mo concentration. Three different twinnability measures are adopted and all indicate a substantially enhanced twinning mechanism in Ni-Mo solid solutions with increasing concentration of Mo. The weaker Ni-Ni bonding at high Mo concentrations is considered to be the main mechanism behind the disclosed phenomena. Segregation of Mo to the fault plane is proved to have strong effect on the generalized stacking fault energy of Ni-based solid solution.