The influences of vanadium addition and temperature on the microstructure, and mechanical properties of Al0.1CoCrFeNiV multi-principal element alloys

The study aimed to examine the crystal structure, microstructure, microhardness, and tensile properties of Al0.1CoCrFeNiVx (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) multi-principal element alloys. Both Al0.1CoCrFeNi and Al0.1CoCrFeNiV0.2 alloys were single FCC phase solid solutions. σ-phase precipitated in Al0.1CoCrFeNiV0.4 alloy. The volume fraction of σ-phase increased as V content increased from x = 0.4 to 1.0. The volume fraction of σ-phase in Al0.1CoCrFeNiV alloy was found to be 48.4 vol.%. It was shown that to predict the phase composition of multi-principal element alloys containing σ-phase employing solid solution formation model, coupling it with criteria of σ-phase formation was necessary. Moreover, when the V content was x ≤ 0.4, the alloys showed good toughness and ductility (> 49%). However, a continuous increase in V content led to a higher volume fraction of σ-phase, which enhanced the strengthening/hardening effect until reaching the embrittlement threshold. At x = 0.4, the alloy exhibited a better balance between strength and plasticity. Uniaxial tensile tests were performed on the annealed Al0.1CoCrFeNiV0.4 alloy at different temperatures. Results suggested that the alloy retains excellent plasticity (> 45%) at 500 ℃. Nevertheless, it exhibited a decrease in strength and plasticity with elevated temperatures. The addition of V caused a significant increase in ultimate strength and elongation at mid-temperatures (500~700 ℃) compared to Al0.1CoCrFeNi alloy. The engineering stress-strain curves of the Al0.1CoCrFeNiV0.4 alloy displayed serrated flow at temperatures from 300 ℃ to 700 ℃. The serration type transitioned from A-type to C-type as the temperature rose.