Optimization of Black Nickel Coatings’ Electrodeposit onto Steel

Coatings can be created using various technologies and serve different roles, including protection, functionality, and decorative purposes. Among these technologies, electrodeposition has emerged as a low-cost, versatile, and straightforward process with remarkable scalability and manufacturability. Nickel, extensively studied in the context of electrodeposition, has many applications ranging from decorative to functional. The main objective of the present work is the electrodeposition of double-layer nickel coatings, consisting of a bright nickel pre-coating followed by a black nickel layer with enhanced properties, onto steel substrates. The influence of deposition parameters on colour, morphology, adhesion, roughness, and coefficient of friction was studied. The effects of cetyltrimethylammonium bromide (CTAB) and WS2 nanoparticles on the coatings’ properties and performance were also investigated. Additionally, the influence of the steel substrate’s pre-treatment, consisting of immersion in an HCl solution, prior to the electrodeposition, to etch the surface and activate it, was evaluated and optimized. The characterization of the pre-coating revealed a homogeneous surface with a medium superficial feature of 2.56 μm. Energy dispersive X-ray spectroscopy (EDS) results showed a high content of Ni, and X-ray diffraction (XRD) confirmed its crystallinity. In contrast, the black films’ characterization revealed their amorphous nature. The BN10 sample, which corresponds to a black nickel layer with a deposition time of 10 min, showed the best results for colour and roughness, presenting the lowest brightness (L*) value (closest to absolute black) and the most homogeneous roughness. EDS analysis confirmed the incorporation of WS2, but all samples with CTAB exhibited signs of corrosion and cracks, along with higher coefficient of friction (COF) values.