The dependence of accumulative roll bonded copper mechanical properties on grain sub-division, stacking faults, and lattice strains

Commercial pure copper was processed at room temperature by accumulative roll bonding (ARB) up to 7 cycles. High-Resolution-Transmission-Electron-Microscope (HRTEM), X-Ray Diffraction (XRD) analyses, tensile and hardness measurements were carried out to interpret the interplay between lattice strain, stacking faults, microstructure evolution and mechanical properties of pure copper during ARB. ARBed Cu was obtained with 27 nm crystallite size achieving 351%, 137%, and 159% enhancements in yield strength, tensile strength, and hardness, respectively. XRD analyses revealed an increase in the dislocation density with reductions in the lattice strain and the effective Stacking Fault Energy (SFE). The decrease in the SFE promoted the generation of new dislocations and extended the dislocation saturation limit up to 6 cycles. Moreover, it was revealed that the grain subdivision significantly influences the lattice strain and the rate of dislocation increase. The decrease in the lattice strain was accompanied with an increase in ductility. Due to a reduction in the SFE of the processed copper, stacking faults were observed in the lattice structure and ∼60% enhancement in ductility over cold rolled samples was obtained. The assessment of strengthening mechanisms revealed that 55% of the strengthening is due to grain subdivision and 45% is due to strain hardening.