Effect of cryo-deformation on structure and properties of CoCrFeNiMn high-entropy alloy

Microstructure evolution in high-entropy alloy CoCrFeNiMn during plane-strain multipass rolling to a thickness strain of 80% at 293 and 77 K was studied. Deformation at both temperatures was found to be accompanied by twinning. At 77 K, twinning was more extensive in terms of the fraction of twinned grains and the length of the twinning stage thereby providing faster kinetics of the microstructure evolution. Micro-shear bands formed in the microstructure of the alloy at the late stages of rolling (at ε ≈ 80% at 293 K and ε ≈ 40% at 77 K). The ultimate tensile strength of specimens rolled at 77 K or 293 K was found to be 1500 or 1200 MPa, respectively while the strength in the initial homogenized condition was 440 MPa. The contribution of various mechanisms to the hardening of the alloy following rolling at 77 K and 293 K was analyzed quantitatively.