Failure analysis and corrosion resistance study of tetrahedral amorphous carbon (ta-C) coated copper in 3.5 % sodium chloride

The early failure and corrosion perforation of the heat exchange copper tubes of the refrigeration unit led to leakage accidents. In this paper, the test and analysis were carried out by means of macromorphological observation, XRF, UTM, SEM and EDS, the results show that the failure corrosion begins on the outer wall of the copper tube, under the action of chloride ions, CuCl, Cu₂O and CuCO₃·Cu(OH)₂ are predominantly corrosion products with anthill-like microcrack propagation. which eventually leads to perforation. The surface treatment of copper tubes was carried out by ion plating ta-C film and ferrous sulfate film-forming process, moreover, it innovatively uses a Ti transition layer to address the adhesion problems in ta-C coatings. Then, the corrosion resistance of the two samples was compared and analyzed by electrochemical corrosion experiments. The results show that the ta-C film specimen has the maximum potential and the smallest corrosion current density, indicating that it has the best corrosion resistance.