Effect of Modified Graphene on the Tribotechnical Characteristics of Electrolytic Nickel-Molybdenum Coatings

The effect of co-deposited graphene oxide (GrO) modified with COOH groups on the tribological characteristics of electrolytic nickel-molybdenum coatings has been studied. The coatings were formed on the surface of polished high-carbon steel by electrodeposition from an aqueous electrolyte based on nickel sulfate (NiSO₄) and sodium molybdate (Na₂MoO₄) with dispersed graphene oxide. The coatings were obtained at current densities 2,5 A/dm² and GrO concentrations from 0.05 to 0.2 g/L. Tribotechnical tests have shown that introduction of GrO at a concentration of 0.1 g/L promotes the formation of a coating with a uniform structure, ensuring a minimum friction coefficient (0.38—0.45) and a wear track width (25—110 µm) under a load of 0.25—1.0 N. A dependency of tribological characteristics on the concentration of graphene particles in the working solution was revealed: at 0.1 g/L, a uniform distribution of GrO particles is achieved, leading to a 30—40 % reduction in the friction coefficient and a 40—55 % decrease in wear track width compared to the base Ni–Mo coating. When the particle concentration exceeds 0.1 g/L, an increase in coating roughness is observed, likely caused by agglomeration and excessive inclusion of filler particles in the coating structure, which results in the formation of a rougher and more heterogeneous surface, thereby degrading the tribological properties of the coating. The obtained results confirm the promising use of GrO in the composition of electrolytic Ni-Mo coatings to reduce friction and increase wear resistance.

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