High-cycle fatigue and tensile deformation behaviors of coarse-grained equiatomic CoCrFeMnNi high entropy alloy and unexpected hardening behavior during cyclic loading

High entropy alloy (HEA), a new class of materials, has received attention as a substance that can potentially replace conventional alloys. Equiatomic CoCrFeMnNi HEA is an attractive material with excellent strength-ductility combination and corrosion resistance, and it achieves greater performance in low temperatures. This study investigated the HCF and tensile deformation behavior of equiatomic CoCrFeMnNi HEA. In order to suggest the possibility of the material's application in an as-homogenized state, coarse-grained (CG) equiatomic CoCrFeMnNi HEA was prepared. Microstructural observation measured an average grain size of 245.5 mu m, and it was confirmed to have a face-centered cubic (FCC) random solid solution. A tensile test confirmed that the yield strength and tensile strength are 293.1 MPa and 625.6 MPa, respectively, and change in the work hardening rate according to deformation twin (DT) evolution during tensile deformation was observed. A high-cycle fatigue results shows fatigue strength of 280 MPa, which is close to its yield strength, and this confirmed that the material has outstanding high-cycle fatigue properties considering its yield strength. DT is uniquely formed at cycle loading with a stress level lower than the critical twinning stress (sigma(T)), and this can improve yield strength by approximately 95% and tensile strength by approximately 17%. Based on the above findings, this study discussed the role of DTs which affect the high-cycle fatigue and deformation behavior of coarse-grained HEA.