Revealing the elemental fluctuations and deformation mechanisms in VCoNi medium entropy alloy

The superior mechanical properties and specific deformation mechanisms of VCoNi medium-entropy alloy have attracted increasing interest. In this study, we conducted hybrid Monte-Carlo and molecular dynamics (MC/MD) simulations based on a machine learning potential to investigate the elemental fluctuations in both defect-free and planar-defect-containing (with initial stacking faults, twins) VCoNi alloys, along with their impacts on deformation behaviors. In addition to the short-range ordering (SRO) of V-Co and V-Ni pairs after hybrid MC/MD simulation, stronger V-Ni ordering within the planar defect regions is also detected. The introduction of SRO transforms the dislocation nucleation behavior from multi-site in the random solid solution (RSS) sample to single-site events at the end of elastic deformation stage, and reaching a yield strength increment of approximately 40%. The pre-existing planar defects enhance the peak stress by ∼ 5% in the RSS sample, while their effects become negligible in SRO samples. Moreover, defects evolution analysis and twinnability parameters calculation both indicate the suppression effects of SRO on nanotwins formation. These results advance the fundamental understanding of how SRO governs defect evolution in VCoNi and establish it as a decisive microstructural parameter for tailoring mechanical performance.