Electrochemical crystallization and functional properties of nickel-based composite coatings

The electrochemical crystallization of nickel/graphene oxide composite electrochemical coatings was researched by the chronovoltamperometry method. The microstructure of the composite electrochemical coatings was studied by scanning electron microscopy and X-ray diffraction analysis. The microhardness and corrosion rate of nickel/graphene oxide composite electrochemical coatings obtained at different cathode current densities were measured. It was revealed that in the presence of a dispersed phase of multilayer graphene oxide, the rate of the cathode process increases. Based on scanning electron microscopy and X-ray diffraction data, it was found that the dispersed phase affects the crystal structure of the nickel matrix. In the presence of graphene oxide, the nickel deposit is formed uniform and fine-grained. It was found that the microhardness of the nickel/graphene oxide composite electrochemical coatings increases ~ 1.20 times compared with pure nickel. This is a consequence of the formation of fine crystalline deposits with long grain boundaries, which prevents the movement of dislocations and plastic deformation of the crystal lattice. Tests in 3.5% NaCl showed that the inclusion of graphene oxide particles in the composition of electrolytic nickel deposits leads to a decrease in their corrosion rate by 1.35−1.60 times. This effect is due to the fact that graphene oxide particles ensure a uniform distribution of corrosion currents over the coating surface, and in the structure of composite electrochemical coatings, the dispersed phase forms compounds that are more corrosion resistant than the metal matrix.