Promising pathways for balancing strength and ductility in chemically complex alloys with medium-to-high stacking fault energies

Emerging chemically complex alloys (CCAs) with medium-to-high stacking fault energies (SFEs) offer significant potential as advanced materials, yet achieving the balance between strength and ductility remains challenging. This study explores the strategic control of partial recrystallization in Al_8.3Co_16.7Cr_13.3Fe_16.7Ni_41.7V_3.3 CCAs to engineer micron-scale heterogeneous structures featuring unevenly distributed L1₂ nanoprecipitates. The optimized microstructure comprises finely recrystallized regions with high-angle grain boundaries (HAGBs), coarsely unrecrystallized regions with low-angle grain boundaries (LAGBs), and deformation-defect-rich transition (DDRT) zones where both grain boundary types coexist. This architecture enables synergistic strengthening mechanisms, including grain boundary strengthening, precipitation strengthening, dislocation strengthening, and hetero-deformation-induced (HDI) strengthening, resulting in an exceptional yield strength of up to 1623 MPa. During plastic deformation, the dislocation pile-up and accumulation aided by interactions with nanoprecipitates and GBs balance strain softening caused by shear band propagation, leading to relatively low but steady work-hardening rates (WHRs). As deformation progresses, increasingly complex interactions further promote the formation of pronounced dislocation pile-ups, multiplication, SFs, Lomer-Cottrell (L-C) lock networks, and the 9R phase transformation within DDRT zones, collectively contributing to continuous WHRs. As a result of these synergistic mechanisms, the material achieves an ultimate tensile strength of ∼1700 MPa and a total elongation of ∼17.2 %, demonstrating enhanced ductility without sacrificing strength. This work highlights the potential of localized DDRT zones to enable controlled phase transformations in CCAs with medium-to-high SFEs, providing a promising pathway for designing high-performance materials.