The deformation behavior and strain rate sensitivity of ultra-fine grained CoNiFeCrMn high-entropy alloys at temperatures ranging from 77 K to 573 K

In this study, CoCrFeMnNi (Cantor alloy) high-entropy alloy (HEA) with ultra-fine grained (UFG) structure were prepared using cryogenic (liquid nitrogen, 77 K) rolling followed by short time annealing. The deformation behavior and strain rate sensitivity (SRS) of processed material were investigated by tensile test at temperatures ranging from 77 K to 573 K. It was found that the critical twinning stress of the UFG alloy decreased at 77 K, which was attributed to the decrease of stacking fault energy with the temperature. In addition, the UFG alloy exhibited plastic instability and was prominently strengthened with increasing testing temperature from 293 K to 473 K, which was related to obviously grain boundaries relaxation in HEAs. The strain rate jump test revealed that the SRS change of UFG specimen with the decrease of grain size was inversely proportional to the associated strength enhancement, and exhibited a stronger temperature dependence than that of CG specimens especially from 293 K to 473 K. The stronger temperature dependence of SRS of UFG Cantor alloys was due to the increased grain boundary relaxation, which was a thermal activation process and depended on strain rate and temperature.