Synthesis of Nitrogen-Doped Diamond-Like Carbon Films Produced by Plasma-Enhanced Chemical Vapor Deposition and their Tribocorrosion Behavior in Hanks’ Solution

Diamond-like carbon (DLC) films with various nitrogen content were deposited on TC4 titanium (Ti) alloys using a plasma-enhanced chemical vapor deposition (PECVD) technology. The microstructure and mechanical properties of undoped DLC and nitrogen-doped DLC (DLC-N) film were investigated systematically. In addition, the effects of the doped content of nitrogen on the electrochemical behavior and tribocorrosion properties of the DLC-N film in Hanks’ solution were evaluated in detail. The results showed that the doped nitrogen into the carbon network induced the formation of new sp2 sites, which was conducive to the graphitization in the doped DLC film. The doped content of nitrogen greatly affected the mechanical properties of the DLC-N film. The adhesion strength between the DLC-N film and Ti alloy substrate increased with the increase of the doped nitrogen in the film. Unexpectedly, the electrochemical properties of the DLC film became worse as the nitrogen was doped into the film, because of graphitization improving the electron migration speed in the DLC-N film. Interestingly, the tribocorrosion resistance of the doped DLC film was greatly improved as compared to the undoped DLC film. The higher adhesion strength of the DLC-N film resulted in fewer microcracks produced on the film during the tribocorrosion process in Hanks’ solution, which prevented the ionic solution from penetrating through the film and effectively protected the substrate.