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Influence of Interatomic Interactions on the Mechanical Properties of Face-Centered Cubic Multicomponent Co-Ni-Cr-Mo Alloys

The composition of a multicomponent solid solution has a significant influence on its mechanical and microstructural properties. Herein, the microstructures, phase stabilities, mechanical properties, and interatomic interactions of multicomponent Co-(5-55)Ni-19Cr-9Mo (mass%) alloys with varying Ni contents were investigated based on correlative experimental and computational methods. First-principles calculations were performed to predict the mechanical properties, electron distributions, atomic bonding states, and density of states (DOS) of the alloy system. The local charge distribution revealed that the alloying elements exhibit stronger bonds with Co atoms than with Ni atoms, and the Ni-Ni bond is the weakest; accordingly, an increase in the Ni content generally diminishes the interatomic interactions in the Co-Ni-Cr-Mo alloy system, which is consistent with the experimental results. Meanwhile, significant augmentations in the strength, hardness, and elastic modulus were observed at 45 mass% Ni. This can be attributed to the additional interactions between the second-nearest Ni atoms with vacant 3d-states, which are prevalent in 45-55 mass% Ni alloys, in the unit form of quartets of four Ni atoms or three Ni atoms and one Co atom. An axial next-nearest-neighbor Ising (ANNNI) model was employed to calculate the stacking fault energies (SFEs) and elucidate the strain-hardening behaviors. A similar trend in the SFE variations was obtained using a parameter-updated thermodynamic model under special consideration of the concentration dependence of the Co-Ni interaction, which indicated the significant influence of interatomic interactions at elevated temperatures.