Enhanced anti-corrosion performance of copper doped diamond-like carbon thin films

Abstract

This work evaluated the microstructural, electrochemical and anti-corrosion properties of Cu-doped diamond-like carbon (DLC) coatings deposited using the plasma-enhanced chemical vapor deposition (PECVD) technique. The coatings were synthesized with varying Cu concentrations (0.68, 2.25,10.28, 22.32, and 40.1 at.%) to investigate their effect on film characteristics. The structural and chemical composition of the coatings was analysed using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and X-ray diffraction (XRD). The electrochemical performance was evaluated using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and potentio dynamic polarization (PP) tests in a 3.5 wt% NaCl solution. The XPS and Raman analysis revealed that Cu incorporation altered the sp²/sp³ hybridization ratio, increasing graphitization at higher concentrations. The results demonstrated that DLC-Cu₂.₂₅ exhibited the lowest surface roughness (Ra = 7 nm), enhancing its corrosion resistance due to its dense, uniform structure and passivating CuO layer. The electrochemical results showed that the corrosion potential shifted towards a more noble direction (-640 mV), and the corrosion rate decreased to 0.003 mm/year, confirming improved stability. However, at higher Cu concentrations, Cu segregation led to increased roughness (Ra = 30 nm) and localized corrosion due to the formation of Cu-rich clusters. Incorporation of Cu improves the corrosion resistance of DLC coatings, although at higher Cu levels some corrosion still occurs. These findings highlight that moderate Cu incorporation optimally enhances protective performance, whereas excessive Cu content compromises corrosion resistance. A mechanistic description of the corrosion-resistance behaviour of Cu-DLC coatings is proposed.