Safe and Sustainable by Design Electrolytic Ni Nanocomposite Coatings: An Eco-Conscious Alternative to Hard Chromium

Hard chromium (HC) coatings are widely used in the metal finishing industry due to their excellent wear and corrosion resistance. However, their production involves hexavalent chromium ions, a substance classified by the European Commission as toxic, carcinogenic, and mutagenic. Moreover, boric acid, which is widely used in nickel (Ni) electroplating, has been recently restricted under REACH regulations. In response, this chapter explores the development of boric acid-free Ni-based nanocomposite coatings as safer, sustainable alternatives to HC. Environment-friendly electrolytes were developed by replacing boric acid in traditional Watts-type Ni baths with safer organic acids. Candidate acids were screened, and optimized formulations were developed incorporating ceramic (e.g., SiC) and two-dimensional (2D) nanomaterials (e.g., graphene, WS) as reinforcing agents. Dispersion stability was ensured via the application of ultrasonication (U/S) and validated by dynamic light scattering (DLS). The Ni composite coatings were electrodeposited using both direct current (DC) and pulse current (PC) regimes under varied conditions. The structural, morphological, and mechanical properties of the coatings were evaluated using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), Vickers microhardness testing, and water contact angle measurements. Corrosion resistance was assessed via Tafel polarization and electrochemical impedance spectroscopy (EIS). Results revealed that Ni/SiC and Ni/WS composite coatings exhibit excellent mechanical and corrosion-resistant properties, surpassing 1,100 HV in microhardness and achieving a CR below 14.5 μm/year under certain plating conditions. A real-life example of Ni/SiC coatings in forged piston rods used in the automotive industry demonstrated strong potential for a viable and eco-friendly replacement of HC coatings.