On the Microstructure and Hardness of Cu-GO Nanocomposite Produced by Accumulative Roll Bonding Processing

Nanocomposites have attracted significant attention in recent years due to their unique microstructure and exceptional mechanical properties. Accumulative roll bonding (ARB) processing is one of the severe plastic deformation methods used for producing the nanocomposites. Accordingly, this research was conducted to investigate the effects of ARB processing on the microstructure and hardness of the Cu-GO (wt.%) nanocomposite. In order to fabricate the nanocomposite, the graphene oxide (GO) particles with nanometer sizes were sprayed between the annealed copper sheets and then, the prepared collection was subjected to the ARB processing by 2 cycles, leading to produce a Cu-GO nanocomposite with a thickness of 500 µm. The microstructure of the Cu-GO nanocomposite was examined using field emission scanning electron microscopy (FE-SEM) and optical microscope (OM). The FE-SEM images revealed a uniform distribution of GO within the copper matrix, resulting in an ultrafine-grained microstructure. The microstructure of GO was evidently laminar. In the metallography images of the ARB-processed specimen, it was observed that the grains undergo significant elongation in the rolling direction, which could be attributed to the considerable levels of strain involved in the process. The images prove good level of bonding during the ARB process. It is imperative that when two sheets are stacked to form a solid metallurgical bond, the boundary between them should be free from any voids or imperfections. This ensures the structural integrity and reliability of the final product, as well as upholding industry standards for quality control. The mechanical properties of the Cu-GO nanocomposite were evaluated through hardness testing. The Vickers microhardness measurements demonstrated a significant improvement compared to pure copper. This enhancement can be attributed to several factors, including grain refinement, dispersion strengthening, and the presence of GO particles. The uniform dispersion of GO between the copper matrix contributes to dispersion strengthening. The graphene oxide layers act as obstacles to dislocation movement, impeding plastic deformation and increasing the strength of the nanocomposite. The considerable enhancement in microhardness after the initial cycle due to high rate of strain hardening, results in an increased dislocation density. The hardness saturation in the nanocomposite may be attributed to the steady-state density of dislocations. This is due to the establishment of a balance between the formation of dislocations during the ARB process and their annihilation through the presence of dynamic restoration events. The copper and GO combination results in a nanocomposite with improved hardness, suitable for various applications in industries such as aerospace, electronics, and renewable energy.