Breaking the trade-off between strength and ductility in nanostructured CrCoNi-based medium-entropy alloys by promoting twinning kinetics

The ternary equiatomic CrCoNi medium-entropy alloys (MEAs) generally suffer from a low strength, which can be improved by mechanical nanotwins induced by cryogenic deformation. After adding Si and reducing the content of Ni, the mechanical twinning in the CrCoNiSi MEA is easy to occur at room temperature (RT), resulting in a higher strain hardening rate to delay necking. After 30% tensile deformation, a lot of thinner mechanical nanotwins are introduced into the CrCoNiSi MEA. After annealing at 773 K for 30 min, the mechanical nanotwins in the nanostructured CrCoNiSi MEA are retained. The production of strength and ductility of the nanostructured CrCoNiSi MEA is 42 GPamiddot%, which is 26% higher than that of the nanostructured CrCoNi MEA. In addition, the phase transformation from FCC phase to HCP phase in the CrCoNiSi MEA during tensile deformation is responsible for a higher strain hardening rate and a better elongation.(c) 2022 Published by Elsevier B.V.

Automated summary

The addition of Si and reduction of Ni content in the CrCoNiSi medium-entropy alloy promote the occurrence of mechanical twinning at room temperature, resulting in a higher strain hardening rate and delayed necking. Tensile deformation introduces a large amount of thinner mechanical nanotwins into the CrCoNiSi alloy, which can be retained after annealing. The strength and ductility of the nanostructured CrCoNiSi alloy is increased by 26% compared to the nanostructured CrCoNi alloy.