Enhanced fracture toughness and strength in bulk nanocrystalline Cu with nanoscale twin bundles

Bulk nanocrystalline pure Cu samples with embedded nanoscale twin bundles were prepared by means of dynamic plastic deformation (DPD) at cryogenic temperature. By adjusting the DPD parameters, we increased the volume fraction of nanotwin bundles, resulting in an increase in both tensile strength and fracture toughness. The enhanced strength is attributed to the strengthening effect of the nanotwin bundles. The highly anisotropic nanotwin lamellar structures are found to be effective in energy absorption and arresting crack propagation during fracture. Coarse and deep dimples associated with obvious recrystallization underneath were detected in the fracture surfaces, owing to the presence of the nanotwin bundles. The enhancement of fracture toughness is closely correlated with the formation of these deep dimples.