Corrosion performance of diamond-like carbon (DLC)-coated Ti alloy in the simulated body fluid environment

DLC coatings have been deposited onto substrate of Ti alloy (Ti-6Al-4V) using r.f. PACVD (plasma-assisted chemical vapor deposition) with C₆H₆, and mixture of C₆H₆ and SiH₄ as the process gases. Three kinds of DLC coatings were prepared as a function of diverse bias voltage and Si incorporation. Corrosion performance of DLC coatings was investigated by electrochemical techniques (potentiodynamic polarization test and electrochemical impedance spectroscopy) and surface analyses (atomic force microscopy and scanning electron microscopy). The electrolyte used in this test was a 0.89% NaCl solution of pH 7.4 at temperature 37°C. The porosity and protective efficiency of DLC coatings were obtained using potentiodynamic polarization test. Moreover, the delamination area and volume fraction of water uptake of DLC coatings as a function of immersion time were calculated using electrochemical impedance spectroscopy. This study provides the reliable and quantitative data for assessment of the effect of Si incorporation and an increase of bias voltage on corrosion performance. In conclusion, electrochemical measurements showed that DLC coatings with Si addition and an increase of bias voltage could improve corrosion resistance in the simulated corrosive environment of the body fluid by a 0.89% NaCl solution. This could be attributed to the formation of a dense and low-porosity coating, which impede the penetration of water and ions.