Tribological properties and thermal stability of TiAlCN coatings deposited by ICP-assisted sputtering

In this study, the tribological and thermal properties of TiAlCN coatings were investigated to evaluate their feasibility in automobile applications. TiAlCN coatings with carbon compositions between 25 and 65 at.% were prepared by inductively coupled plasma (ICP) assisted sputtering and were annealed at 400, 500, and 600 °C in air. The structures and compositions of the coatings were studied by X-ray diffraction, Raman spectroscopy, transmission electron microscopy, and Auger electron spectroscopy. The hardness and tribological performance were evaluated by micro-indentation and ball-on disk tests. The wear rates were calculated using a non-contact 3D surface profiler. At a carbon composition > 50 at.%, the coatings featured a mixture of amorphous and crystalline phases and exhibited superior tribological performance compared to that of commercialized carbon or nitride coatings. Raman spectroscopy revealed that even when the amorphous carbon phase has a relatively high sp2 to sp3 ratio, there are sufficient amounts of TiAlN grains to support the hardness in the coatings. The coating hardness decreased slightly after high-temperature annealing due to graphitization in the amorphous carbon phase, however, the friction coefficients and wear rates were reduced with the annealing temperature.