On the tribological behavior of cobalt-based nanocomposite coatings containing ZnO@Graphene oxide core-shell nanoparticles

A hybrid nanocrystalline cobalt-based coating was prepared by cathode plasma electrolytic deposition (CPED). Zinc oxide and graphene oxide (GO) nanoparticles were mixed to form a core-shell structure through electrostatic self-assembly by using (3-aminopropyl)triethoxysilane (APTES) modifier. ZnO@GO nanoparticles were used as additives to improve wear and friction properties of deposited coatings. The concentration effect of core-shell ZnO@GO addition (0.1, 0.2 and 0.3 %wt) on the friction, wear, coating thickness and mechanical properties was investigated. The composition and microstructure of deposited coatings were studied by scanning electron microscope (SEM), X-ray diffraction (XRD), Raman spectroscopy and energy dispersive spectroscopy (EDS). Reciprocating sliding wear tests using a ball-on-plate configuration were carried out on a PLINT TE67 tribometer. AISI 52100 steel was used as ball and the coating deposited onto a AISI 304 stainless steel substrate was used as plate. Coatings were dense, nanocrystalline and uniform with a FCC metastable cobalt structure. Core-shell concentration above to 0.2 %wt resulted in a decrease of grain size and an increase of hardness and wear resistances. Nanoparticles act as nucleation sites for grain formation, decreasing grain sizes. Samples using 0.3% ZnO@GO displayed the lowest wear and friction coefficients. ZnO@GO nanoparticles enables the formation of a protective layer consisting of oxide and exfoliated GO on the top of worn surfaces.