Strengthening mechanisms in heterostructured copper films with highly (220)-oriented vertical nanotwins.

In this study, heterostructured copper films containing different proportions of highly (220)-oriented vertical nanotwins were prepared by direct current (DC) electroplating. Uniaxial tensile tests showed that the mechanical properties improved notably when the volume ratio of the vertical nanotwins increased—the film with the 88% vertical twins exhibited the ultimate tensile strength of 455 MPa, approximately 83% higher than those of the equiaxed Cu films. Postmortem electron microscopy characterizations, assisted by molecular dynamics simulations, revealed that these special heterostructures of the equiaxed grains and vertical nanotwins facilitated the activation of multi-mode slip systems. The activation of multi-mode slip systems leads to higher dislocation density, thus endowing the material with enhanced mechanical strength and work hardening rate without significant loss of ductility. [ABSTRACT FROM AUTHOR]