Abrasion Tests on Nanotwinned and Graphene-Doped Ag Films Prepared by Cyanide-Free Ag Electroplating

A cyanide-free Ag plating process was developed to fabricate nanocrystalline (nc) Ag and nanotwinned (nt) Ag films with a (111)-preferred orientation. Graphene-doped nt-Ag films were prepared through the incorporation of varying graphene powder concentrations (i.e., 250, 375, and 500 ppm) into the Ag plating solution. The graphene powder (with an average size of 260 nm) and a proper graphene dispersant (1-pyrene sulfonic acid sodium) were added to the cyanide-free Ag plating solution. X-ray photoelectron spectroscopy (XPS) depth profiling analysis showed that the graphene in the graphene-doped nt-Ag films was uniform in thickness. The highest average C weight percentage (6.70 wt%) occurred in the graphene-doped nt-Ag film plated with a graphene powder concentration of 375 ppm in the Ag plating solution. Abrasion tests were conducted on the nc-Ag, nt-Ag, and graphene-doped nt-Ag films. Three abrasion stages were observed in the abrasion force curves. The co-doped graphene in the graphene-doped Ag films caused a substantial reduction in the abrasion force across all three stages. The graphene-doped nt-Ag film with the highest co-doped graphene concentration exhibited the lowest maximum abrasion force (18.33 N). The co-doped graphene reduced the plastic deformation in the graphene-doped nt-Ag films, which contributed to the lower plastic deformation. The nanotwinned structure and co-doped graphene reduced wear debris production and plastic deformation during the friction process.