Tailoring the Tribomechanical and Corrosion Behavior of Reverse Pulse Deposited Ni–Co–P Coating Through Cobalt Content Modulation

Abstract

This study explores the influence of cobalt content on the tribomechanical and corrosion properties of Ni–Co–P coatings deposited through reverse pulse electroplating. The ratio of Co salt concentration to the total Ni and Co salt concentration was varied in the electrolyte to achieve different Co levels within relatively low cobalt (≤36 wt%) regime. X-ray diffraction revealed crystallite sizes of 1–3 nm in the deposited layers suggesting a mixture of amorphous and nanocrystalline structure. Critical loads in scratch adhesion tests are found to be in between 10.5 N and 15.1 N implying adequate adhesive bonding between the deposits and the substrates. Microhardness and pin-on-disc tribo test results demonstrate a positive correlation between Co content and both hardness and wear resistance of the coatings. However, incorporating small amounts of Co (≤6.2 wt%) exhibited minimal impact on these properties. Interestingly, corrosion resistance in saline medium peaked at the second-highest Co level (26.2 wt% of Co), followed by a decrease with further increase of Co. These findings indicate an optimal Co concentration for achieving a balance between wear resistance and corrosion protection in Ni–Co–P coatings.