The effect of fluorine doping on the corrosion resistance of diamond-like carbon thin films applied on the surface of cobalt-chromium-molybdenum alloy

In this study, the effects of F-doped diamond-like carbon (F-DLC) thin films on corrosion resistance of the cobalt-chromiummolybdenum (CoCrMo) alloy substrate were investigated. For this purpose, deposition of F-DLC thin film on CoCrMo substrates was carried out through radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) method. Methane, argon and CF4 gases were used to deposition of F-DLC thin film. TiN intermediate layer was used to improve the adhesion of F-DLC thin film on CoCrMo substrate. Corrosion behavior of the samples have been determined using electrochemical impedance and polarization tests. Electrochemical measurements indicated that the corrosion resistance of CoCrMo substrates increases to a great extent by deposition of F-DLC thin film, so that the corrosion potential and corrosion current decreased from -0.396 volt to -0.057volt and from 5.55×10-6 to 1.288×10-7 µA, respectively. Raman spectroscopy, as a nondestructive method to characterize carbon-based materials, was used for the structural characterization of DLC and F-DLC films. The results demonstrated that higher concentration of sp2 bonding and more graphitic structure in the F-DLC films, which could lead to lower intrinsic stress in these films, compared to those of the DLC coatings.