Preparation and Characterization of Co-Diamond Composite Coatings Obtained in a Single-Step Hybrid Electrophoretic Deposition Process

The electrochemical co-deposition of various hard particles with metals or metal alloys has been recently studied, especially for developing wear-resistant coatings. In the current work, pure cobalt and cobalt-diamond composite coatings were electrochemically deposited onto a low-alloy steel substrate and further investigated in terms of microstructure, corrosion behavior, and tribological characteristics. The electrodeposition process was carried out using direct current, from an additive-free electrolyte containing 300 g L^-1 CoSO₄, 50 g L^-1 CoCl_2, and 30 g L^-1 H₃BO₃ with and without diamond particles. Scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDS) was used for the microstructural characterization correlated with the chemical composition identification of the resulting coatings. The pure Co coatings showed a dense microstructure with a nodular morphology. In contrast, for the Co-diamond composite coatings, more elongated grains were observed containing a uniform distribution of the reinforcing diamond particles. The corrosion resistance was evaluated by potentiostatic polarization measurements in 3.5 wt.% NaCl solution, while the sliding wear resistance was assessed using the ball-on-disk testing method. The experimental results demonstrated that incorporating diamond particles into the cobalt deposition electrolyte positively impacted the tribological performance of the resulting composite coatings without significantly affecting the corrosion properties. Both cobalt and the composite coatings demonstrated substantially superior wear characteristics and corrosion resistance compared to the steel substrate.