Compositional effects on stacking fault energies in Ni-based alloys using first-principles and atomistic simulations

Stacking fault energy (SFE) in fcc materials is a fundamental property that is closely related to Shockley partial dislocations and deformation twinning, the latter of which is potentially responsible for some of the exceptional mechanical properties observed in Ni-based high/medium-entropy alloys. In this study, the SFEs and twinning energies over a wide range of compositions are systematically determined in model Ni-based binary alloys using both first-principles density functional theory (DFT) and atomistic simulations with interatomic potentials. Particularly, different compositional dependences of SFEs are observed in the selected binary alloys (Ni-Cu, NiCo, and Ni-Fe) from DFT calculations. We find that SFEs of Ni-Co follow a linear-mixing rule while Ni-Cu and NiFe systems exhibit non-linear compositional dependences, especially in the concentrated region towards the center of the phase diagram. Analyses of the magnetic structures help clarify the origins of the non-linear dependences. The fidelity of existing interatomic potentials for these alloys is evaluated against DFT. Using the interatomic potentials with the overall highest fidelity, the SFE calculations are extended to Cantor-related ternary alloys (Ni-Co-Cr and Ni-Co-Fe) and the spatial features of the fault energies in atomistic simulations are also discussed. These results provide the basis for a systematic understanding of the compositional effects on the SFEs and twinning energies, which could be useful for a systematic tuning of mechanical properties in nonequimolar alloys, thus leading to a broad field in alloy design.