High strength and good electrical conductivity in Cu–Cr alloys processed by severe plastic deformation

• Bronzes containing 0.75%, 9.85% and 27% Cr were subjected to high pressure torsion.
• With increasing Cr content the hardness rises due to grain size reduction to 40 nm.
• Heat-treatment after HPT increases electrical conductivity of the alloys.
• With increasing Cr content the stability of UFG microstrcucture was improved.
• Heat-treatment after HPT yields both high hardness and good conductivity.

Ultrafine-grained (UFG) microstructures in Cu–Cr alloys were processed by high pressure torsion (HPT). The improved hardness was accompanied by a reduced electrical conductivity due to the large amount of grain boundaries. The effect of heat-treatment after HPT-processing on the hardness and the electrical conductivity was studied for different chromium contents (0.75, 9.85 and 27 wt%). For low Cr concentration (0.75%) the electrical conductivity increased considerably above 250 °C, however the hardness decreased concomitantly. At the same time, for high Cr content (9.85% and 27%) the hardness was only slightly reduced even at 500 °C, while the electrical conductivity increased to a similar level as before HPT due to grain boundary relaxation and decomposition of Cu–Cr solid solution. Our study demonstrates the capability of SPD-processing and subsequent heat-treatment to achieve a combination of high strength and good electrical conductivity.