披覆在不同金屬基材上之類鑽碳膜於3.5 wt%氯化鈉水溶液中之靜態及動態電化學行為研究

Abstract

Diamond-like carbon (DLC) coatings have been deposited onto 316SS, titanium, brass and carbon steel by plasma-enhanced chemical vapor deposition, respectively. Atomic arrangement, chemical structure, surface morphology and cross-section microstructure of the DLC coatings were examined by X-ray diffraction, Raman scattering spectroscopy and scanning electron microscopy. The electrochemical behaviors of the DLC coatings in 3.5 wt% NaCl solution were investigated by performing open circuit potential (OCP) measurement and potentiodynamic polarization test. The experimental results showed that properly deposited DLC coatings could cause an increase of OCP by hundreds of millivolts and a reduction of anodic current density by several orders of magnitude as compared to that of the substrate. The results also demonstrated that electrochemical techniques could be used as tools to detect the soundness of the DLC coating by examining OCP and polarization curve, which varied with the form of defect and depended on the type of substrate. After that, we have investigated effect of hydrodynamic flow condition at rotation speed 2500rpm using rotating disk electrode (RDE) on the electrochemical corrosion behavior of DLC-Coated specimens. The electrochemical behaviors of the DLC coatings in 3.5 wt% NaCl solution were investigated by performing open circuit potential (OCP) measurement, electrochemical impedance resistance analysis and potentiodynamic polarization curves determination, same condition with under static condition. The experimental results showed that corrosion current density was increased for either bare or coated substrates under hydrodynamic condition. The effects of enhanced mass transport and flow stress on corrosion behavior of various metallic materials were demonstrated. We also investigated the influence of hydrodynamic conditions on the corrosion of bare substrates (316SS, brass, carbon steel, and Titanium) in 3.5 wt% NaCl solution at different rotation speeds using rotating disk electrode (RDE). It was found that the corrosion potential, Ecorr, shifted toward more positive potential, corrosion current density, icorr , increased and charge transfer resistance decreased as the rotation speed increased, indicating a decrease in corrosion resistance of material. The increase of rotation rate, causing the relatively high rate of oxygen mass transport to the RDE is due to thinner Nernst boundary layer. This behavior could be attributed to the enhanced the mass transport from bulk to the metal surface in high rotation rates.