Improvement of strength and conductivity in Cu-alloys with the application of high pressure torsion and subsequent heat-treatments

Quenched and slowly cooled (annealed) Cu- 0.7 %Cr, Cu-0.9 %Hf, and Cu-0.7 %Cr-0.9 %Hf alloys were processed by high pressure torsion (HPT). The microstructures of the alloys were studied immediately after HPT and subsequent annealing. It has been shown that the microhardness and the thermal stability of the severely deformed microstructure increase, while the average grain size decreases in the order of Cu-0.7 %Cr, Cu-0.9 %Hf, and Cu-0.7 %Cr-0.9 %Hf alloys. The microhardness in all alloys is higher after quenching and HPT, than after annealing and HPT. The largest dislocation density is achieved by quenching and HPT in Hf-containing samples. Cu5Hf phase precipitations in Hf-containing alloys are more effective in retarding grain growth in comparison with Cr particles and lead to additional hardening during aging. It has been demonstrated that HPT-processing with subsequent heat-treatment might yield the combination of large hardness and high electrical conductivity in Cu alloys.