Corrosion Resistance of TiN Coatings Prepared by Filtered Cathodic Vacuum Arc Process
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Corrosion Resistance of TiN Coatings Prepared by Filtered Cathodic Vacuum Arc Process Jin-Bao Wu ; Yin-Wen Tsai ; Chin-Te Shih ; Mei-Yi Li1; Ming-Sheng Leu ; Chiou-Chu Lai . Materials Research Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan. 1
National Nano Device Laboratories, Hsinchu, Taiwan
ABSTRACT For the purpose of developing the corrosion-resistant and low-cost metallic bipolar plates for direct methanol fuel cell (DMFC), Ti mesh, stainless steel and Si(100) were coated with TiN by using the filtered cathodic vacuum arc system (FCVA). These TiN films have received considerable attention because of its high anti-corrosion behavior and low contact-resistance. In order to improve the corrosion protective ability of TiN films and decrease pinholes of coating, growth modifications such as thickness of the coatings and bias applied to substrates have also been carried out. The microstructures and composition of TiN film were identified by the instrumental analyses such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The corrosion behavior of TiN coatings was studied in 0.5 M H2SO4 solutions by using potentiodynamic polarization method. The DC bias of –150 V was applied to the substrates to achieve a dense structure of approximately 400 nm coating of TiN, so that good corrosion protection of the Ti mesh and stainless steel substrates can be achieved. The TiN coating on stainless steel exhibited excellent corrosion behavior especially in lower corrosion current than 2×10-7 A/cm2. INTRODUCTION Owing to the extreme hardness, high thermal and chemical stability, and low electrical resistance, titanium nitride (TiN) has been widely applied as a coating material, which can be used in hard and protective coatings on mechanical tools, decorative coatings and anti-corrosion materials. The technologies of preparing TiN films are generally divided into physical vapor deposition (PVD) and chemical vapor deposition (CVD). Among the various methods used for growing TiN film, filtered cathodic vacuum arc (FCVA) deposition has attracted considerable attention for its industrial applications compared to other methods. FCVA has good adhesion and great potential for large-area production with high growth rates at relatively low temperature. TiN coatings produced by FCVA system have the following advantages: low internal stress, good adhesion, and good anti-corrosion[1]. The approach is demonstrated for the highly coating-defect sensitive problem of protecting metallic separator for direct methanol fuel cell
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(DMFC). Coatings for metal separators need to be not only corrosion resistant in a cell environment but also electrically conductive as electrode material [2]. From the viewpoint of corrosion, a key-parameter is thus the rate of forming microporosities [3]. Several ways for reducing the pinhole rate and pinhole area per unit coating area have been proposed such as: increasing the coating thickness [5]; controlling th
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