Understanding the effect of Al/Ti ratio on the tribocorrosion performance of Al/Ti co-doped diamond-like carbon films for marine applications

Al and Ti co-doped diamond-like carbon (DLC) films (Al/Ti-DLC) were prepared through hybrid ion beam deposition technique, in which the Al/Ti ratio was tailored from 6.6 to 2.0. The dependence of tribocorrosion performance of Al/Ti-DLC film on the Al/Ti ratio in 3.5 wt% NaCl solution was systematically explored. Results indicated that the existing states of Al and Ti dopants in the film were independent on the Al/Ti ratio, where Al existed in the form of oxidized state, while Ti mainly bonded with C and thus formed the titanium carbide following the presence of titanium oxide, leading to the increase of hardness and elastic modulus with the decrease of Al/Ti ratio. In particular, with reducing the Al/Ti ratio from 6.6 to 2.0, the tribocorrosion resistance was improved, mainly originating from the reduction of pure mechanical wear. However, EIS analysis further revealed that although the mechanical wear accelerated the electrochemical corrosion of Al/Ti-DLC films, the contribution of the synergistic effect between mechanical wear and corrosion attack to materials loss increased following the drop of Al/Ti ratio, due to the corrosion-induced wear rather than wear-induced corrosion. These outcomes not only shed light on the effect of Al/Ti ratio in the film on the tribocorrosion property but also guide the design of DLC films for marine applications.