Compositional effects on dislocation properties in NiCo and NiFe alloys using atomistic simulations

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The equiatomic face-centered cubic NiCoCrFeMn high entropy alloy has exhibited a rare but desired combination of the strength and ductility at cryogenic temperatures, and a similar phenomenon has been observed in equiatomic subsets of the alloy. To obtain a fundamental understanding of the underlying deformation processes, here we investigate the compositional effects on dislocation properties in the model NiCo and NiFe alloys using atomistic simulations. First, the fidelity of the employed interatomic potential is examined by comparing calculated material properties with available experimental data and first principles calculations. Then, we systematically examine the dislocation energy, core radius, core width, Peierls stress, and separation distance between the Shockley partial dislocations for edge and screw dislocations, as a function of the composition. The core energy of a screw dislocation is found to be lower than that of an edge dislocation, suggesting screw dislocations are more energetically stable in both alloys. It is found the compositional dependence of the core width is not relevant to that of the Peierls stress in the alloys, in contradiction with the classical Peierls–Nabarro model. The results suggest local atomistic environment plays a significant role in the Peierls stress. The separation distance increases with decreasing Ni concentration, except for a screw dislocation in the NiFe, which is attributed to the compositional dependence of the stacking fault energy and shear modulus. This study provides fundamental insights into the dislocation properties of these alloys, which can serve as a basis for understanding many dislocation features and underlying deformation mechanisms in compositionally complex alloys.