High strength nanocrystalline Cu–Co alloys with high tensile ductility

A supersaturated single-phase Cu–26 at.% Co alloy was produced by high-pressure torsiondeformation, leading to a nanocrystalline microstructure with a grain size smaller than 100 nm.The nonequilibrium solid solution decomposed during subsequent isothermal annealing. In situhigh-energy X-ray diffraction was used to map changes linked to the separating phases, and thedevelopment of a nanoscale Cu–Co composite structure was observed. To gain further informationabout the relationship of the microstructure and the mechanical properties after phase separation,uniaxial tensile tests were conducted on as-deformed and isothermally annealed samples. Based onthe in situ diffraction data, different isothermal annealing temperatures were chosen. Miniaturizedtensile specimens with a round cross section were tested, and an image-based data evaluationmethod enabled the evaluation of true stress–strain curves and strain hardening behavior. The mainresults are as follows: all microstructural states showed high strength and ductility, which wasachieved by a combination of strain-hardening and strain-rate hardening