Strength-ductility mechanism of combined heterostructured CoCrFeMnNi high-entropy alloy prepared by laser heat-treatment process

Abstract

Two types of typical combined heterostructured CoCrFeMnNi high-entropy alloys with superior mechanical properties that evade the strength-ductility trade-off are fabricated using laser heat-treatment process. The lamellar grain structure with relatively high microhardness can hardly be observed due to the short time annealing at low temperature (873 K for 5 min) before laser scanning. The hetero-deformation induced strengthening, as well as the excellent deformation ability of the bottom hard region which can enhance the interaction between nanotwin-dislocation and maintains the large microhardness difference among the soft-hard layers, are the main factors that improve the yield strength of CoCrFeMnNi high-entropy alloy. Moreover, the combined heterostructured structure without lamellar deformed bands is demonstrated to have a relatively better uniform elongation, which is attributed to the stronger deformation ability of the non-recrystallized grains in the bottom hard region and the effective delay of the crack growth. Consequently, the combined heterostructured structure without lamellae is a promising way to simultaneously improve the strength and ductility, which can be efficiently prepared by the laser surface heat-treatment technique.