Vacancy effect on the generalized stacking fault energy of alloyed γ-Ni system: A first-principles study

It is of great importance to explore alternative alloying elements to replace rhenium (Re)for the design of low-cost Ni-based single crystal (SC)superalloys. Due to the partitioning of Re to γ matrix, the individual and the combined effects of the single (vacancy, Mo, W and Re)and solute-vacancy complex (Mo-Va, W-Va and Re-Va)defects on the plasticity of γ-Ni have been studied by the first-principles calculations of generalized stacking fault energies (GSFE). It is found that a single vacancy and an alloying solute Mo/W/Re at the fault plane decreases the intrinsic stacking fault energy of Ni from 131 mJ/m² to 106 mJ/m² and ∼97 mJ/m² respectively. Further reductions are made by the introduction of a solute-vacancy complex defect (∼80 mJ/m²). Furthermore, the unstable planar fault energies tuned by the Mo-Va and W-Va complex defects are almost identical, which are both slightly smaller than those by Re-Va. Finally, the calculated values of three twinnability measures elucidate that W and Mo provide similar enhancements in the twinning propensity of γ-Ni to that by Re. This result suggests a possibility of partly replacing Re by Mo or W in Ni-based SC superalloys.