Compositional control of chemical short-range order and yield strength in NiCoCr medium-entropy alloys

This study employs a hybrid Monte Carlo/Molecular Dynamics (MC/MD) method to systematically investigate the effects of varying atomic ratios (Ni/Co/Cr contents ranging from 20 to 60 at.%) on the formation of Short-Range Order (SRO) and the mechanical properties of the NiCoCr ternary system. The degree of SRO was quantified by calculating Warren-Cowley parameters, and the deformation behaviors of structures with SRO were compared against Random Solid Solution models under uniaxial tension. The results indicate that SRO structures significantly enhance the alloy's unstable stacking fault energy and yield strength. Microstructural analysis reveals that Ni-Ni clusters play a dual role in SRO structures: dislocations preferentially nucleate along the edges of Ni-Ni clusters, while these clusters simultaneously exert a pinning effect, hindering dislocation slip and propagation. Furthermore, the investigation into atomic ratio variations reveals that as Ni content increases, the system tends to form a continuous network of Ni-Ni clusters. Based on the simulation results, this study establishes a theoretical prediction model incorporating lattice friction, elastic misfit strengthening, and chemical bond-breaking strengthening. This model successfully captures the variation laws of yield strength with respect to atomic ratio and SRO degree. This work not only reveals the physical origins of SRO strengthening but also provides a theoretical basis for the compositional design of high-performance medium-entropy alloys.