Effect of solid-solution strengthening on deformation mechanisms and strain hardening in medium-entropy V1-xCrxCoNi alloys

High- and medium-entropy alloys (HEAs and MEAs) possess high solid-solution strength. Numerous investigations have been conducted on its impact on yield strength, however, there are limited reports regarding the relation between solid-solution strengthening and strain-hardening rate. In addition, no attempt has been made to account for the dislocation-mediated plasticity; most works focused on twinning- or transformation-induced plasticity (TWIP or TRIP). In this work we reveal the role of solidsolution strengthening on the strain-hardening rate via systematically investigating evolutions of deformation structures by controlling the Cr/V ratio in prototypical V 1- x Cr x CoNi alloys. Comparing the TWIP of CrCoNi with the dislocation slip of V 0.4 Cr 0.6 CoNi, the hardening rate of CrCoNi was superior to slip-band refinements of V 0.4 Cr 0.6 CoNi due to the dynamic Hall-Petch effect. However, as V content increased further to V 0.7 Cr 0.3 CoNi and VCoNi, their rate of slip-band refinement in V 0.7 Cr 0.3 CoNi and VCoNi with high solid-solution strength surpassed that of CrCoNi. Although it is generally accepted in conventional alloys that deformation twinning results in a higher strain-hardening rate than dislocation-mediated plasticity, we observed that the latter can be predominant in the former under an activated huge solid-solution strengthening effect. The high solid-solution strength lowered the cross-slip activation and consequently retarded the dislocation rearrangement rate, i.e., the dynamic recovery. This delay in the hardening rate decrease, therefore, increased the strain-hardening rate, results in an overall higher strain-hardening rate of V -rich alloys. (c) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

High- and medium-entropy alloys with high solid-solution strength have significant effects on strain-hardening rate. In this study, the role of solid-solution strengthening on strain-hardening rate was revealed by controlling the Cr/V ratio in V1-xCrxCoNi alloys and investigating the evolution of deformation structures. The results showed that under the activated huge solid-solution strengthening effect, dislocation-mediated plasticity can be predominant over twinning, leading to an overall higher strain-hardening rate in the V-rich alloys.