Microstructures and mechanical properties of Cu–Ti alloys with ultrahigh strength and high ductility by thermo-mechanical treatment

To synergistically improve the strength-ductility of copper alloys used in the miniaturized component, Cu-3.2Ti-0.2Fe-0.2V alloy with heterogeneous structure was obtained by thermo-mechanical treatment (namely, short-time annealing). The heterogeneous structure was composed of the non-uniform grains formed due to Laves phase inhibiting grain growth and FCC structured Cu4Ti phase with good coherent interface precipitated on the grain boundaries in sub-micro size. After aging at 400 °C for 2 h and then 450 °C for 4 h, the ultimate tensile strength and elongation of the heterogeneous-structured alloy were 976.8 MPa and 18.8% respectively, which was approximately 120 MPa more than that of the coarse-grained alloy after complete annealing, but both alloys had comparable ductility. When cold-rolling with 5% reduction was carried out before the aging of 450 °C, the strength increased to 1057 MPa and corresponding elongation was still over 10%. The strengthening mechanism of alloy with heterogeneous structure was analyzed and the hetero-deformation induced hardening of 284.5 MPa was the other significant reinforcement. The semi in-situ observation of tensile deformation behavior shown that the superior ductility in coarse-grained alloy was mainly attributed to the slipping and twinning. While grain rotation and grain boundary sliding were additional deformation mechanism in heterogeneous-structured alloy during tensile deformation, meanwhile, the texture of S, {110}<1 1‾ 1> and {331}<12‾ 3> components converted to the texture of {441}<1‾1‾ 8>, Goss, Copper and {012}<82‾1 > components. The deteriorative ductility after rolling with the reduction of 5% was owing to the S and Cube components converted to the strong texture of {032}<223‾> components.