The influence of vanadium element on the microstructure and mechanical properties of (FeCoNi)100-xVx high-entropy alloys

Despite their unique thermodynamic and kinetic features, Face-centered cubic (FCC) high-entropy alloys (HEAs) are well known to usually possess superior ductility at room temperature but relatively low strength, which greatly limits their structural application. To address this issue of strength-ductility tradeoff, we have systematically investigated in the present work the crystallographic structure, microstructural evolution, and tensile properties of (FeCoNi)100-xVx (x = 10, 15, 20, 25, and 30) HEAs in both as-quenched and annealed conditions. A single-phase solid solution was still obtained by quenching from high temperature when the V concentration was up to 25%. It is interesting to find in that the microstructure of this family of HEA alloys varies with the content of V element and pre-annealing, showing an unusual single phase with L12 chemically ordered structure for (FeCoNi)75V25, but otherwise a composite consisting of a L12 phase coherent with disordered FCC phase matrix for the other V doped FeCoNi alloys such as (FeCoNi)80V20. Owing to the presence of the ordered phase, both (FeCoNi)80V20 and (FeCoNi)75V25 display a remarkable work hardening capability, leading to the enhanced ultimate tensile strengths up to 1.1 and 1.4 GPa, respectively, and the resultant excellent deformability with uniform plastic strain of >30%.