Nano-grained copper strip produced by accumulative roll bonding process

Accumulative roll bonding (ARB) process is a severe plastic deformation (SPD) process that has been used for pure copper (99.9%). The ARB process up to 8 cycles was performed at ambient temperature under unlubricated conditions. Microstructural characterizations were done by transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD). It was found that continuous recrystallization resulted in microstructure covered with small recrystallized grains with an average diameter below 100 nm. The tensile strength and hardness of the ARB processed copper has become two times higher than initial value. On the other hand, the elongation dropped abruptly at the first cycle and then increased slightly. Strengthening in ARB processed copper may be attributed to strain hardening and grain refinement. In order to clarify the failure mode, fracture surfaces after tensile tests were observed by scanning electron microscopy (SEM). Observations revealed that failure mode in ARB processed copper is shear ductile rupture with elongated small dimples.