Effect of pulse duty cycle on mechanical properties and microstructure of nickel-graphene composite coating produced by pulse electrodeposition under supercritical carbon dioxide

Nickel (Ni) and nickel-graphene oxide (Ni-GO) composite coatings were produced by pulse electrodeposition technique under supercritical carbon dioxide (SC-CO2). The GO and resulting nanocomposites were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), Raman spectra and zeta potential. It was found that GO was reduced to reduced graphene oxide (RGO) using this method. Effect of duty cycle on surface morphology, microstructure, phase structure, microhardness and wear resistance of the resulting coatings were compared and researched in detail. The results show that the Ni-GO composite coating electrodeposited under SC-CO2 fluid exhibits brighter surface appearance, lower surface roughness and smaller grain size. In addition, the preferred orientation plane of (200) for the coating is changed to be close-packed (111) plane for the addition of RGO. The microhardness of Ni-GO composite coating electrodeposited under SC-CO2 fluid reaches the maximum of 756.4HV0.2. Moreover, the wear tests show that the incorporations of RGO in the coating improve the wear resistance and friction reduction of the deposit.