Graphene enforced copper matrix composites fabricated by in-situ deposition technique

Due to the outstanding mechanical and electronic properties, graphene has been widely investigated as the nano-filler for fabricating metallic matrix composites. The key point in these studies is how to realize a uniform distribution of graphene in the metallic powders. The traditional methods mainly include ball-milling and colloidal processing. However, both of them result in massive structural defects on graphene flakes and further degrade its strengthening effects. Therefore, it is meaningful to explore a new method. In this study, we present a new way, i.e. in-situ growth of graphene on copper powders in the plasma enhanced chemical vapor deposition system (PECVD). The scanning electron microscope(SEM) images indicate that the powder is fully covered by graphene nanoflakes, realizing uniform mixing on a micro-scale. Further research finds that there exists a competition between growth and etching at the initial stage of the graphene growth. Methane is dissociated into various active species (CHx, atomic H and C) by the radio frequency. The C atoms self-assemble into graphene islands, yet the H atoms tend to etch these islands away. At a lower temperature, the etching effect takes a dominant position and then only the bigger islands are able to survive in this process, resulting in bigger graphene nanoflakes. As a contrast, it is a growth-dominant process at higher temperature, resulting in a much higher nucleation density and smaller graphene sheets. Therefore, the size of graphene sheets can be well controlled by tuning the growth temperature, for example, the sizes are 300 and 100 nm at 500 degrees C and 600 degrees C respectively. Moreover, the X-ray photoelectron spectroscopy(XPS) spectra show that the oxide layer at the surface of copper powder can be removed as the graphene flakes grow, which contributes to a fine interface between the two parts and further leads to outstanding performance of the final composite. The powder is consolidated by spark plasma sintering(SPS) technique, and several properties of this composite are tested. The results indicate that compared with the pure copper, the copper with the addition of graphene can reduce the resistivity by one order of magnitude and increase the hardness and yield strength by 15.6% and 28.8%, respectively. This work provides an alternative way to fabricate graphene-enforced composite and shows promising application prospects.