Fig. 1 TEM images showing the microstructures of Cu-10 at%Mn a, b, Cu-15 at%Mn c, d, and Cu-20 at%Mn e, f alloys after one-pass ECAP. Note that, the grain refinement mechanism during one-pass ECAP is jointly undertaken by dislocation subdivision and SRO-stimulated twin fragmentation

Fig. 2 Optical microscope images showing the original microstructures of Cu-10 at%Mn a, Cu-15 at%Mn b, and Cu-20 at%Mn c alloys. Note that, the mean grain size of the three FG Cu-Mn alloys is almost the same

Fig. 3 Tensile behavior of Cu-Mn alloys with different Mn contents at room temperature: a engineering stress-strain curves; b work hardening rate curves. Note that, the strength of Cu-Mn alloys is improved without a loss of ductility with the increase in Mn content

Fig. 4 TEM images showing the typical microstructures in Cu-Mn alloys tensioned at room temperature: a, b Cu-10 at%Mn; c, d Cu-15 at%Mn; e, f Cu-20 at%Mn. Note that, the deformation microstructures are mainly manifested by a decrease in the size of dislocation cells

Fig. 5 Optical microscope images showing the microstructures of Cu-Mn alloys tensioned at 250 °C: a Cu-10 at%Mn; b Cu-15 at%Mn; c Cu-20 at%Mn. Note that, the average grain size of three FG Cu-Mn alloys still basically keeps unchanged even after tension to fracture at 250 °C

Fig. 6 Tensile behavior of Cu-Mn alloys with different Mn contents at 250 °C: a engineering stress-strain curves; b work hardening rate curves. Note that, the FG Cu-Mn alloys exhibit an excellent strength-ductility synergy and an abnormal multi-stage work hardening characteristic

Fig. 7 Variations in the ultimate tensile strength and uniform elongation with the Mn content for the FG Cu-Mn alloys at RT and 250 °C. Obviously, the FG Cu-Mn alloys exhibit a better strength-ductility synergy at 250 °C rather than RT

Fig. 8 TEM images showing the typical microstructures in Cu-Mn alloys tensioned at 250 °C: a, b Cu-10 at%Mn; c, d Cu-15 at%Mn; e, f Cu-20 at%Mn. Note that, the deformation microstructures transform from dislocation cells to planar slip bands and even to deformation twins with increasing Mn content

Fig. 9 Schematic diagram showing the effect of SRO on the mechanical behavior and deformation microstructures of fine-grained Cu-Mn alloys. At RT, the strength of the present FG Cu-Mn alloys is greatly improved without a loss of ductility with the increase in Mn content, resulting from a decrease in the size of dislocation cells. At 250 °C, the FG Cu-Mn alloys exhibit a superior strength-ductility synergy, originating from an obvious transformation in deformation microstructures from dislocation cells to planar slip bands and even to deformation twins with increasing Mn content