Overcoming the strength ductility trade off in nanostructured copper alloys

Nanotwinned copper (Cu) exhibits an exceptional combination of strength (∼1 GPa) and ductility, challenging the conventional strength–ductility trade-off in nanostructured metals. However, subsequent efforts on nanostructured Cu and its alloys have led to only incremental gains, with yield strength largely plateauing. Here, we demonstrate a major advancement with a Cu–2.4 at.% Ag–0.8 at.% P alloy that achieves a yield strength of 1.9 ± 0.1 GPa, nearly double that of prior nanostructured Cu alloys. Notably, it ranks among the hardest Cu-based materials reported in over three decades of comparative data, while retaining deformability comparable to coarse-grained Cu. Notched microcantilever tests reveal dynamic toughening driven by back stress arising from plasticity and microstructural evolution ahead of the crack tip, with the effect quantified via stiffness changes during unloading cycles. Segregation of Ag to grain boundaries reduces this back stress, leading to a slight decrease in the toughening response. Unnotched beams endure ∼85% strain without failure, underscoring exceptional ductility. Deformation-induced twinning, secondary twinning, and 9R phase formation enable high strength without sacrificing ductility. These findings highlight the potential of nanoscale structuring combined with minimal alloying to achieve transformative mechanical performance, offering a cost-effective alternative to complex, heavily alloyed high-entropy materials.