Abstract: Heterogeneous laminated structure (HLS) design offers new opportunities to enhance the mechanical performance of high-entropy alloys (HEAs) through synergistic effects from heterogeneity. However, it remains challenging to introduce the HLS into HEAs via severe plastic deformation due to their strong work-hardening capacity. In this study, a specially designed multi-level HLS, characterized by alternatively stacked micro-grained soft CoCrFeNi layers and nanostructured ultra-hard Al_0.3CoCrFeNi layers containing a three-phase microstructure (composed of nanograined face-centered cubic matrix, (Al, Ni)-rich B2 precipitates, and Cr-rich σ precipitates), is controllably introduced into FCC HEAs via a conventional thermo-mechanical processing involving hot-pressing, cold-rolling, and annealing. Meanwhile, thermo-mechanical processing induces Al element diffusion across the layer interface, resulting in the formation of an interfacial transition layer and the establishment of a strong interface bonding between the neighboring CoCrFeNi and Al_0.3CoCrFeNi layers. As a result, the multi-level HLSed CoCrFeNi/Al_0.3CoCrFeNi composite exhibits a yield strength as high as 1127 ± 25.4 MPa while maintaining a large fracture elongation (up to (26.3 ± 2.4) %). Such an excellent strength-ductility synergy surpasses that of most previously reported high-performance monolithic bulk CoCrFeNi and Al_0.3CoCrFeNi HEAs prepared through careful chemical composition optimization and/or thermo-mechanical processing. Strong hetero-deformation induced strengthening benefited from the apparent microstructural/microhardness difference and the strong interface bonding between the neighbouring CoCrFeNi and Al_0.3CoCrFeNi layers, together with simultaneous activation of multiple strain hardening mechanisms containing mechanical twinning, stacking faults and precipitation strengthening, is responsible for the excellent strength-ductility combination. This multi-level HLS and its fabrication strategy provide an enlightening way to develop strong and ductile HEAs and can also be applied to high-performance designs of other metallic materials.

Key words: High entropy alloys, Laminated structure, Strength-ductility synergy, Hetero-deformation induced strengthening, Mechanical twinning