A study of microstructural and electrochemical properties of ultra-thin DLC coatings on altic substrates deposited using the ion beam technique
1999; Elsevier BV; Volume: 8; Issue: 1 Linguagem: Inglês
10.1016/s0925-9635(98)00364-1
ISSN1879-0062
AutoresZhi Hui Liu, Jun Zhao, James McLaughlin,
Tópico(s)Metal and Thin Film Mechanics
ResumoMicrostructural and electrochemical characterization of diamond like carbon (DLC) ion beam-deposited on AlTiC (70 wt% Al2O3+30 wt% TiC) substrate has been carried out. Tapping mode atomic force microscopy (AFM) imaging showed that the island-like topography of DLC-coated substrates is similar to the un-coated one, indicating the uniform coverage of DLC without visible pinholes. Confocal micro-Raman analysis demonstrated that the total Raman intensity, as well as the ID/IG ratio, increases with the coating thickness. Electrochemical impedance spectra showed that with the increasing DLC coating thickness, a transition from one-time constant response to two-time constant response occurred when the coating thickness equals 5 nm (IS2), indicating the existence of micro-defects in the coatings which are invisible for AFM. More detailed analysis using the equivalent circuit model revealed that the charge transfer resistance (Rct) at electrolyte/substrate interface and the resistance (Rp) related to DLC coatings increase significantly with the coating thickness, while the double-layer capacitance (Cdl) and the capacitance (Cco) of DLC coatings decrease dramatically. All these phenomena can be interpreted in terms of the evolution of the subsurface diamond-like phase (sp3-bond) and the reduction of micro-defects in the DLC coatings with the growing film. As a result, an increase in the corrosion potential (Ec) with the DLC coating thickness was also detected using the Tafel technique. In consequence, the DLC coatings can improve significantly the anti-corrosion properties of AlTiC substrates when the coating thickness is more than a few tens of nanometres.
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