Manipulating the microstructure of Cu from direct current electrodeposition without additives to overcome the strength-ductility trade-off

Abstract

The attainment of both high strength and ductility has been a long-standing quest for most metallic materials in engineering. However, these properties were generally mutually exclusive. In this study, columnar nanotwinned Cu (col-nt-Cu) with a hexagonal pyramid surface morphology was fabricated using direct current (DC) electrodeposition in an additive-free electrolyte. The formation mechanism of col-nt-Cu was studied from the perspective of surface morphology, and the results indicated that both nanotwins and hexagonal pyramids were the result of screw dislocation-driven growth. This unique microstructure is at the basis of excellent mechanical properties, including a high ultimate tensile strength up to 443 MPa and superior elongation to failure (∼21%), thereby overcoming the strength-ductility trade-off. This unusual strengthening is caused by the synergy of multiple deformation mechanisms, including dislocation transfer across twin boundaries (TBs) and threading dislocation gliding in the confined twin lamella. In particular, the interaction between dislocations and TBs exhibited variability in the spatial distribution of col-nt-Cu. The TBs in the top grains dominate the strength of the sample, whereas the grain boundaries (GBs) in the core grains dominate the ductility of the sample. These results not only provide new insight to overcome the strength-ductility trade-off, but also steer the way for optimization of mechanical properties through the design of nanotwinned structures in spatial distribution.