a Schematic illustration of rotary swaging technique. b Vickers micro-hardness measured from center to edge along the radial direction (the error bar represents the standard deviation of hardness). c EBSD crystal orientation map (filled with orientation information of cross section) with ε = 2.5. d, e EBSD crystal orientation maps and GB maps in the rod center (d-i, d-ii, d-iii) and at the edge (e-i, e-ii, e-iii) with ε = 2.5 from top (d-i, d-ii, e-i, and e-ii) and side (d-iii and e-iii) views. The insets are inverse pole figures and color code, respectively. Black and red lines in d-ii and e-ii represent high angle GBs (>15°) and low angle GBs between 2° and 15°, respectively. f, g TEM images of the swaged copper with ε = 2.5 from top (g) and side (h) views. The insets are selected area electron diffraction (SAED) patterns.