Extraordinary strength-ductility combination in bidirectional heterostructured CoCrFeMnNi high-entropy alloy

Despite abundant types of heterogeneous structures, no optimal strength-ductility combination of high-entropy alloys has been achieved yet; designing heterogeneous structures to stimulate the greater potential of high-entropy alloys in terms of mechanical properties still needs to be explored. Here, we prepare a bidirectional heterostructured CoCrFeMnNi high-entropy alloy using partial recrystallization annealing and subsequent laser surface heat treatment. The average grain size exhibits a gradient distribution along the depth, while each gradient layer maintains a partially recrystallized microstructure consisting of coarse and ultrafine grains, accompanied by a superior yield strength of ∼979 MPa and a considerable uniform elongation of ∼15.1%. The research indicates that the excellent strength-ductility combination of the bidirectional heterogeneous structure mainly originates from the coupling action of remarkable soft-hard layer strength differences and abundant geometrically necessary dislocation storage interfaces, as well as the blunting effect of dislocations, stacking faults, and nanotwins on cracks.