Improvement of DLC electrochemical corrosion resistance by addiction of fluorine

Abstract

The combination of chemical and mechanical properties of diamond-like carbon (DLC) films opens the possibilities for its use in electrochemical applications. DLC electrochemical corrosion behavior is heavily dependent on deposition techniques and precursor gas. Fluorinated-DLC combines the superlative properties of diamond and teflon and becomes one of the most suitable coating for tribological applications. F-DLC was grown over 316L stainless steel using plasma enhanced chemical vapor deposition by varying the ratio of carbon tetrafluoride and methane. The influence of fluorine content on deposition rate, composition, bonding structure, surface energy, hardness, stress, and surface roughness was investigated. Emphasis was placed on the investigation of F-DLC electrochemical corrosion behavior, which was tested by potentiodynamic method. As F content increased, F-DLC films presented lower stress, hardness values and surface free energy. In addition, Raman G-band peak position shifted to higher frequency. The corrosion potential becomes more negative and the anodic and cathodic current densities decreased with the increase of F content, as compared to the pure DLC and the substrates. These results were confirmed by Nyquist plot, which shows a stronger ohmic behavior for F-DLC and Bode plots with different corrosion behaviors. The electrochemical analysis indicated F-DLC films present superior impedance, polarization resistance and breakdown potential as compared to the pure DLC, which indicate they are promising corrosion protective coating in aggressive solutions.