Although the maximal strength of Cu with a mean grain size of 10 nm has been reported as ³1000 MPa, the maximal strength of nanostructured Cu processed by severe plastic deformation (SPD) is ³450 MPa, owing to the saturation of accumulated strain caused by recovery or recrystallization during the SPD process. The strength of SPD-processed Cu can be increased by adding solid-solution atoms. A significant increase in the strength of nanostructured Cu after adding a small amount of Si solute atoms was reported in our previous study. In this study, various-composition CuZn, CuSi, and CuNi solid-solution alloys were subjected to high-pressure torsion (HPT) processing, which is one of the SPD processes. To reveal the role of solid-solution atoms on the deformation of Cu during the SPD process, the effects of Zn, Si, and Ni additions on hardness and microstructure of Cu after various HPT rotations were systematically investigated, up to the solubility limits of these atoms. It is well known that Zn and Si atoms decrease the stacking fault energy (SFE) of Cu. On the other hand, Ni atoms have the opposite effect to that of Zn and Si on the SFE of Cu. Experimental results were considered in terms of the atomic concentration of solute atoms c a , electron-atom ratio e/a, and the SFE. The hardness of 140 HV of the nanostructured Cu significantly increased with increasing addition of Zn, Si, and Ni. The maximal hardness values of the nanostructured CuZn, CuSi, and CuNi alloys were 250 HV (29.4 at%Zn), 275 HV (4.5 at%Si), and 360 HV (81.4 at%Ni), respectively. In the case of the nanostructured CuZn and CuSi alloys, the hardness increase correlated with the reduction in the SFE as a function of e/a. The decreased SFE by Zn and Si additions increased strain hardening during the SPD process. This strengthened the nanostructured CuZn and CuSi alloys. On the other hand, hardening of the nanostructured CuNi alloys is related not to the SFE changes, but to dislocation pinning or dragging by Ni solute atoms followed by suppression of recovery or recrystallization during the SPD process.

Tensile deformation behavior of high-strength nanostructured CuSi solid-solution alloys processed by high-pressure torsion (HPT) with 5 rotations was investigated at room and low temperatures. With increasing Si concentration, tensile strength of the nanostructured CuSi solid-solution alloys was significantly increased. The maximal tensile strengths were 980 MPa at room temperature, and 1350 MPa at 77 K in a Cu2.04 wt.%Si alloy. This significant strengthening was achieved by grain refinement and increased dislocation density through severe plastic deformation (SPD) with the effect of Si addition on the decreasing stacking fault energy of the CuSi alloy. With increasing Si concentration, strain-rate sensitivity m of the nanostructured CuSi solid-solution alloys was decreased due to the increased dislocation density, resulting in accelerating plastic instability of tensile specimens, caused by the diminishing strain-rate hardening capacity after necking.