Influence of carbon content on the structure and tribocorrosion properties of TiAlCN/TiAlN/TiAl multilayer composite coatings

To improve the tribocorrosion performance of protective coatings in a real running environment under the synergistic action of friction and corrosion, the development of advanced coatings with excellent properties and research on the tribocorrosion mechanism are important. Based on the design principle of functional gradients/ multilayers, TiAlCN/TiAlN/TiAl multilayer composite coatings were prepared by the filter cathodic vacuum arc (FCVA) technique. The effects of carbon contents on the structure, friction, corrosion and tribocorrosion properties were studied. With increasing carbon content, the composite structure of crystalline TiAlCN/amorphous carbon significantly improves the corrosion and wear resistance of the coatings. The TiAlCN/TiAlN/TiAl coating with the highest carbon content of 22.1 at.% has the best resistance to corrosion and wear but shows the worst tribocorrosion resistance under the synergistic action of friction and corrosion. The TiAlCN/TiAlN/TiAl coating with a carbon content of 12.4 at.% exhibits the best tribocorrosion resistance with the minimum values of the cathodic shift of open circuit potential (AOCP), coefficient of friction(COF) and wear rate. The results indicate that an overall optimized TiAlCN/TiAlN/TiAl multilayer composite coating with appropriate amounts of amorphous carbon phase and the strongest crystallized form of TiAlCN has excellent performance in terms of ultrahigh hardness (44.36 GPa), high H/E, the dense structure and stable passivation layer to achieve good tribocorrosion resistance.