Deformation behavior of a Co-Cr-Fe-Ni-Mo medium-entropy alloy at extremely low temperatures

We report the mechanical and microstructural characteristics of a medium-entropy alloy, Co17.5Cr12.5Fe55Ni10Mo5 (atomic percent, at%) at cryogenic temperatures, down to a record low temperature of 0.5 K. The alloy exhibits excellent strength and ductility combined with a high strain-hardening rate in the entire temperature range investigated. Its property profile, including the yield strength, ultimate tensile strength, strain hardening capability, and absorbed mechanical energy, is better than those of most alloys and HEAs used in cryogenics. Within the interval of extremely low temperatures considered (0.5-4.2 K), the alloy exhibits several unusual features, including anomalies of the temperature dependence of the yield strength and tensile ductility, discontinuous plastic deformation (DPF), and a change in the propensity for the deformation-induced martensitic transformation. While the occurrence of these effects in the same temperature interval may be fortuitous, we hypothesize that they are interrelated and provide a tentative explanation of the observed phenomena on this basis.

Automated summary

The medium-entropy alloy Co17.5Cr12.5Fe55Ni10Mo5 demonstrates excellent mechanical properties at cryogenic temperatures, showing high strength, ductility, and strain hardening. It exhibits several unusual features within the extremely low temperature range of 0.5-4.2 K, including anomalies in the temperature dependence of yield strength and tensile ductility, discontinuous plastic deformation (DPF), and changes in deformation-induced martensitic transformation tendency. The observed phenomena may be interrelated and require further investigation.