Achieving a strength-ductility combination in VCoNi medium-entropy alloy via N alloying

Abstract

Single-phase FCC-structured medium-entropy alloys (MEAs) have excellent ductility, but the low strength limits their applications in engineering. In this study, non-equiatomic V32Co33Ni33Cr1N1 MEA was prepared by vacuum arc melting, and its comprehensive mechanical properties were improved by nitrogen alloying and subsequent thermo-mechanical processing. Compared with the VCoNi MEA, it was observed that nitrogen alloying inhibited the recrystallization process and contributed to the formation of nitride precipitates at the grain boundaries, significantly refining the grains. Among them, the alloy subjected to cold rolling and annealing at 900 ℃ exhibited a high yield stress of ∼ 1.1 GPa, an ultimate tensile stress of ∼ 1.5 GPa, and possessed a high fracture elongation of ∼ 25.3 %. The outstanding mechanical properties were mainly attributed to the grain refinement strengthening resulting from the nitrogen alloying and multiple twins strengthening containing annealing twins, deformation twins and multiple twinning systems. This work was expected to aid in understanding the effect of nonmetallic elements alloying on the microstructures and mechanical properties of MEAs, high-entropy alloys and traditional alloys.