Enhanced strengthening effect via nano-twinning in cryo-rolled FeCoCrNiMo0.2 high-entropy alloys

Abstract

High-entropy alloys (HEAs) with face-centered cubic (FCC) structure generally exhibit extraordinary ductility but relatively low strength, which limits its widespread applications as engineering structural materials. Enhancing the strength of FCC HEAs is crucial to broaden its application. In present work, by performing rolling at cryogenic temperature (77 K), we obtained a significantly enhanced ultimate strength as high as 1557.7 MPa in a typical single-phase FCC FeCoCrNiMo0.2 HEA. A high intensity of Brass texture and Goss texture are formed in the cryo-rolled specimens. With the increasing of cryo-rolling reduction, twins are generated inside grains with the Copper texture, forming the Copper-twin texture. Due to the low stacking fault energy of FeCoCrNiMo0.2 HEA, abundant nanoscale deformation twins and stacking faults are generated inside the cryo-rolled specimens. Besides, a high density of dislocation networks and Lomer-Cottrell dislocation locks are also observed. Hence, the interactions among the dislocations, nano-twins, stacking faults, and Lomer-Cottrell dislocation locks are speculated to effectively contribute to the enhanced ultimate strength and work hardening. Our results are forward to improve the strength of single-phase FCC HEAs as structural materials.