Preparation and effect of vanadium addition on the mechanical properties of CoCrFeNiVx high-entropy alloy

Abstract

High-entropy alloys (HEAs) have attracted considerable attention due to their unique phase structures and excellent properties. However, the existing preparation processes for HEAs involve high temperatures, lengthy procedures, and high costs, which limit their practical applications and confine them to the realm of fundamental research. Here, a novel method combining low-temperature solid-phase molten salt electrolysis and hot-press sintering was proposed to prepare CoCrFeNi HEA. Moreover, the study explored the addition of metal V, to modulate the composition of the HEA and improve its mechanical properties. The results showed that the molten salt electrolysis process could achieve the direct deoxidation of metal oxide mixtures, enabling one-step preparation of HEAs. During the early stages of deoxidation, the metals Ni and Co were obtained first and, under the influence of the mixed entropy, formed a non-stoichiometric NiCoCr alloy. As deoxidation progressed, Cr and Fe were successively reduced and further alloyed with the NiCoCr to form the non-stoichiometric CoCrFeNi HEA. Eventually, the aggregated dendritic metal Fe diffused and solid-solved into the non-stoichiometric CoCrFeNi HEA, resulting in the formation of a stoichiometric CoCrFeNi HEA. The CoCrFeNiVx (x = 0, 0.5, 1, 1.5) alloy maintained a single-phase FCC structure, where V effectively improved the hardness of the CoCrFeNi HEA, with minimal impact on its phase structure. V played a role in solid-solution strengthening, grain refinement, and reducing Cr segregation in the alloy. Additionally, the appropriate addition of V simultaneously increased the tensile strength, hardness, and ductility of the CoCrFeNi HEA.