Corrosion Protection of C90300 Bronze by Diamond-like Carbon Coatings: Suppression of Cathodic Oxygen Reduction

This study investigates the corrosion protection of amorphous hydrogenated diamond-like carbon (DLC) films over C90300 bronze alloy (Cu-Sn-Zn) in chloride-rich environments. To overcome poor adhesion between copper and carbon, we used an amorphous hydrogenated silicon (a-Si:H) interlayer via modified pulsed DC PECVD. Raman spectroscopy and spectroscopic ellipsometry characterized the DLC layer, revealing a thickness of approximately 177 nm and an estimated hydrogen content of 35.2 at%. Electrochemical evaluation in a 3.5% NaCl solution over 30 days showed that the DLC coating provides a strong barrier effect, achieving an initial protection efficiency of 97% and polarization resistance (Rp) up to 122 times higher than the bare alloy. Cathodic polarization measurements demonstrated reduced cathodic current densities for the DLC-coated bronze, consistent with suppression of oxygen reduction under aerated conditions. Mott–Schottky analysis suggested that the electronic properties of the multilayer coating may contribute to restricted interfacial electron transfer, in addition to its physical barrier effect. Tribological tests indicated that the DLC coating reduced and stabilized the coefficient of friction (~0.50), although the coated system exhibited more extensive wear-track damage, potentially involving coating rupture, material transfer, and third-body abrasion. These findings demonstrate the potential of DLC coatings to enhance the corrosion resistance of bronze, although the progressive decrease in electrochemical protection during prolonged immersion highlights the need for further optimization of coating durability.