Achieving excellent strength-ductility synergy in pure copper via dual heterostructures

Heterogeneous structured metals have demonstrated superior strength-ductility synergy. In this work, pure copper samples with a single gradient structure, a bimodal grain structure, and an inhomogeneous core were fabricated via cold rolling, annealing, and surface mechanical attrition treatment (SMAT). The 700-SMAT sample possesses a single gradient structure, while the 350-SMAT sample features a gradient structure with an inhomogeneous core, and the 450-SMAT sample combines a gradient structure with a bimodal grain core. Both dual-heterostructured samples exhibit outstanding tensile properties: the 350-SMAT sample achieves a yield strength (YS) of ∼217 MPa and a uniform elongation (UE) of ∼18.9%, whereas the 450-SMAT sample shows a YS of 182.3 MPa and a UE of ∼27.8%, outperforming the single-gradient 700-SMAT sample (YS: 143 MPa, UE: 26.1%). They also demonstrate stronger hetero-deformation induced (HDI) strengthening, with the 350-SMAT sample showing more pronounced effects due to its abundant core inhomogeneity. EBSD analysis reveals that although mechanical incompatibility decreases during deformation, the inhomogeneous structure in 350-SMAT and the interaction between bimodal grains and the gradient zone in 450-SMAT effectively enhance strength without compromising ductility. This dual-heterogeneous structure design provides a new paradigm for microstructural engineering towards superior strength–ductility synergy.