The Effects of Grain Size on the Mechanical Properties of Nanocrystalline NiCoFe Nickel-Based Medium Entropy Alloys

Abstract

The effects of nanocrystalline NiCoFe nickel-based medium entropy alloys on tensile mechanical properties as a function of increasing Fe/Co ratio are investigated by simulation methods. Ni₆₀Co₁₀Fe₃₀ exhibits higher strength and is employed to investigate the effects of grain size on mechanical properties. The results reveal that a decrease in grain size leads to a reduction in Young's modulus, and the work-hardening phenomenon is more pronounced in larger grain size samples compared to those with smaller grain sizes. The critical grain size for the transition from the Hall-Petch relationship to the inverse Hall-Petch effect is ≈9.65 nm. In the former region, the hindering effect of grain boundaries on dislocations results in an increase in average flow stress as grain size decreases, with dislocation motion serving as the primary deformation mechanism. In the latter phase, the softening effect associated with grain boundary migration leads to a decrease in alloy strength as grain size diminishes, indicating that grain boundary migration serves as the dominant deformation mechanism. These findings elucidate the critical role of grain size in the mechanical properties of NiCoFe alloys and have significant implications for the design of high-performance medium entropy alloys.