Effect of ceramic particle pretreatment and surface chemistry on electrocomposite coatings

The quantity of embedded ceramic particles within an electroplated metal matrix plays a major role in the wear resistance of an electrocomposite coating (ECC). Increasing the ceramic content of an ECC may improve its wear resistance, and thus provide longer coating service life. There are several ways to enrich the ceramic content of an electrocomposite: optimize solution hydrodynamics, decrease current density or modify the charge of particles. This paper reports on the third method by presenting a study of the effect of various acidic particle pretreatments; and the addition of anionic, cationic or amphoteric surfactants on the ceramic particle codeposition efficiency. The work focuses on two plating systems: (1) nickel/silicon carbide and (2) nickel/silicon oxide, using a sulfamate-based electrolyte. It has been demonstrated that a SiC powder pretreated with 15 vol% hydrofluoric acid (HF) and without a surfactant in the plating solution, produces coatings with the highest percentage of embedded particles. For a SiO2 powder, the best conditions were obtained with an HNO3 pretreatment and a cationic surfactant in the plating solution. The presence of impurities on the two types of particle influences both the particle inclusion probability and surfactant adsorption.