Towards enhanced strength-ductility in pure copper by fabricating hetero grain composite laminates

Due to the contradictory relationship between strength and toughness, many novel structures have been designed to overcome the tradeoff dilemma. In this paper, pure copper hetero grain composite laminates (HGCLs) composed of fine /coarse /fine grain bands were fabricated via rolling bonding and annealing. Microstructure characterizations indicated the grain size and hardness differences among different layers of HGCLs, and the interfaces were well bonded. When compared to the tensile results of the reference specimen (non-composite laminates), it is clear that the well-bonded interface facilitated HGCLs to achieve ductility and strength beyond that anticipated by the rule of mixture. A series of loading−unloading−reloading tests, quasi-in-situ EBSD and TEM tests were performed in order to explore the evolution of hetero-deformation induced (HDI) stress and dislocation of HGCLs, and the results demonstrated that mechanical incompatibility occurred during deformation and dislocation density at the interface was higher than the layer interior, resulting in a strain gradient. Additionally, the good ductility of HGCLs can be attributed to the coexistence of multiple factors, including annealing, slip bands, formation of deformation twins and stacking faults, and dislocation hardening. The findings provide a promising avenue for the design of a new generation metals with high-performance.