Strengthening of Cu–Ni–Si alloy using high-pressure torsion and aging

• Grain refinement is achieved in Corson alloy the size of ~150nm by HPT.
• Aging at 300°C after HPT leads to further increase in the mechanical property.
• Electrical conductivity reaches 40% IACS after aging for 100 h.
• 3D-APT revealed the formation of nanosized-precipitates during aging treatment.
• Simultaneous hardening in both grain refinement and precipitation is achieved.

An age-hardenable Cu–2.9%Ni–0.6%Si alloy was subjected to high-pressure torsion. Aging behavior was investigated in terms of hardness, electrical conductivity and microstructural features. Transmission electron microscopy showed that the grain size is refined to ~ 150 nm and the Vickers microhardness was significantly increased through the HPT processing. Aging treatment of the HPT-processed alloy led to a further increase in the hardness. Electrical conductivity is also improved with the aging treatment. It was confirmed that the simultaneous strengthening by grain refinement and fine precipitation is achieved while maintaining high electrical conductivity. Three dimensional atom probe analysis including high-resolution transmission electron microscopy revealed that nanosized precipitates having compositions of a metastable Cu3Ni5Si2 phase and a stable NiSi phase were formed in the Cu matrix by aging of the HPT-processed samples and these particles are responsible for the additional increase in strength after the HPT processing.