Enhanced synergy of strength-ductility and low-cycle fatigue resistance of high-entropy alloy through harmonic structure design

Compared with homogeneous structured materials, heterogeneous structured materials exhibit unprecedented performances. In the present work, a series of harmonic structured CoCrFeMnNi high-entropy alloys (HEAs) with different shell fractions were prepared by mechanical milling (MM) and spark plasma sintering (SPS) process. The effects of shell fraction on mechanical properties and low-cycle fatigue (LCF) performances were investigated at room temperature. Results show that the harmonic structured HEAs with a shell fraction between 20% and 40% demonstrate a combination of superior strength-ductility synergy and good LCF resistance. Development and rearrangement of dislocations dominantly occur in the coarse-grained areas (cores) during LCF process, while the ultrafine-grained areas (shells) show good cyclic stability. The enhanced strain hardening leads to a good balance of high strength and high ductility in the harmonic structured HEAs. Moreover, the enhanced ductility also restrains LCF failure.