A composite nature of cyclic strain accommodation mechanisms of accumulative roll bonding (ARB) processed Cu sheet materials

A systematic investigation of the cyclic deformation behavior of OFHC copper processed by 7 cycles of accumulative roll bonding has been carried out. The ARB copper shows a unique composite natured microstructure with components of various grain sizes. Upon cyclic deformation, a general cyclic softening trend was observed. Due to the composite natured of the ARB copper microstructure, several micro-mechanisms have been observed to have activated for cyclic strain accommodation. These mechanisms were found to be activated in sequence rather than concurrently. The first of the mechanisms to activate is believed to be slip found in the pre-existing large equiaxed grains. Following the exhaustion of the above, the pre-existing shear bands were re-activated and further developed. It is believed that the strain incompatibility between the grains within the shear band and those outside was partially responsible for the coarsening of grains along the shear bands. The cyclic softening observed is believed to be related to the grain coarsening along the path of strain localization. However, due to the limited ductility and the abundance of crack nucleation sites, the cyclic lifespan of this ARB material was found not long enough for the extensive grain coarsening necessary in the development of a macro shear band. In an attempt to understand the behavior observed, the consideration of using a composite model is also discussed.