Electrodeposition of gradient Ni/SiO₂ nanocomposite coatings on St.37 steel: Microstructure, mechanical properties, and corrosion resistance

This research focused on the possibility of fabricating a gradient Ni/SiO 2 nanocomposite coating on a St. 37 substrate using the electrodeposition method from a Watts bath. The effects of applied current density and nanoparticle (NP) concentration on the coatings' composition, microstructure, microhardness, and corrosion resistance were investigated. GDS and EDS analyses were used to quantify the NP concentration and evaluate the NP dispersion in the coating, respectively. Response Surface Methodology (RSM) was employed via Design-Expert software for process optimization. Following the determination of optimized parameters, a gradient coating was successfully produced under three distinct deposition conditions. The microstructure of the coatings was studied using XRD, and the mechanical and electrochemical properties were evaluated through microhardness measurements and potentiodynamic polarization tests, respectively. Findings confirmed the successful production of a gradient coating, with SiO 2 content precisely controlled from 0.69 wt% at the interface to a maximum of 3.49 wt% at the surface. The incorporation of SiO 2 NPs induced significant grain refinement, reducing the average crystallite size from 138 nm to 90 nm. This microstructural modification resulted in a corresponding increase in microhardness to 359 Hv. The corrosion current density decreases by up to 8.9 times compared to low-nanoparticle content layers.