Breakthrough the strength-ductility trade-off in a high-entropy alloy at room temperature via cold rolling and annealing

Abstract

Simultaneous strength–ductility enhancement of a high-entropy alloy via cold rolling and annealing is difficult. Cold rolling and annealing were performed on an as-cast Fe35Co21Ni6Cr18Mn20 high entropy alloy (HEA), the microstructure showed single phase face centered cubic (fcc) solid solution without phase transformation and the grains were fully recrystallized accompanied by additional grain growth. The grain size decreased significantly from 179.4 ± 15.3 μm to 15.2 ± 1.4 μm. A large number of annealing twins and twin boundaries (TBs) (fraction up to 44.2%) were observed. The dislocation slip and twinning were observed as the dominant plastic deformation mechanism. Meanwhile, dislocations plugging was also seen near the twin boundaries. Tensile tests revealed for the first time that the rolling-annealing HEA overcame the strength-ductility trade-off because the yield strength dramatically increased from 516.7 ± 3.4 MPa to 725.4 ± 4.7 MPa and ductility retained excellent (from 0.51 ± 0.01 to 0.53 ± 0.01) as compared with as-cast HEA, this behavior was attributed to the grain refinement and substantial annealing twins including transgranular annealing twins and suspened annealing twins.