Abstract: AlCoCrFeNi_2.1 (Ni2.1) eutectic high-entropy alloy emerges as a promising candidate for strength-ductility breakthrough, owing to its lamellar architecture of soft face-centered cubic (FCC) + hard body-centered cubic (BCC, B2), semi-coherent phase boundaries (PBs), and nano-coherent precipitates. However, these structural characteristics can hardly be simultaneously achieved via current mainstream structure-refinement techniques, limiting strengthening capabilities and leaving deformation mechanisms unclear. To address these, this study for the first time integrates thermomechanical processing and laser treatment to craft Ni2.1 with unprecedented complex heterogeneities: (1) macroscale sandwich layers, (2) microscale FCC/B2 eutectic lamellae and dual-phase grains, and (3) coherent nano L12 & BCC precipitates, along with (4) non-uniformly distributed semi-coherent Kurdjumov-Sachs (K-S) PBs. Compared with the as-cast counterpart (sample C), severe plastic deformation followed by laser treatment (sample L) simultaneously amplifies strength and plasticity, while further annealing (sample LA) even more than doubles the yield strength (YS) and improves ultimate tensile strength by over 40 % with still substantial plasticity. Sample L demonstrates more pronounced multi-scale hetero-deformation-induced effects for enhanced YS and prolonged work hardening, with K-S boundaries effectively retarding necking. Whereas, precipitate-induced dislocation hindrance dominates in sample LA, significantly strengthening the matrices. This work successfully preserves and leverages all structural characteristics of Ni2.1, providing a novel design paradigm and theoretical support for engineering complex heterogeneities to achieve superior strength-ductility synergy.

Key words: Sandwich-structured complex heterostructures, Heterogeneous deformation, Multiple strengthening and hardening, Eutectic high-entropy alloy