Establishment of Ceramic Coating System for Improving Resisting Function of Thin Film Coating from the Environmental Attack

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Thin film coatings toward various types of materials such as metal and organic compound have been used for protecting substrate surface from harsh environment or adding a lot of functions to them. However, nanometric defects and cracks were always existed in coated thin film from the initial stage. In actual environment, degradation was generated as a result of the corrosive solution going into substrate through the nanometric defect of coating. Therefore, various investigations were conducted from the view points of (a) improvement of corrosion resistance of substrate metal through N^+ ion implantation, (b) Improvement of adhesion strength by optimizing thin film formation condition by Dynamic Ion Mixing (DIM) method and (c) protection of thin film coated specimen from corrosion by photo-catalytic effect of coated TiO_2 film.Results obtained are summarized as follows ;(1) The adhesion characteristic of TiN films, which was coated by plasma CVD, was investigated by the scratch test. Th … More en, through investigating the relationship between temperature condition of TiN film formation and critical load of Lc obtained by scratch test, the adhesive strength between TiN film and substrate was evaluated. Also, through evaluating the substrate materials dependency upon adhesive strength, the applicable range of the CPCD test was made clear for the defect ratio evaluation of TiN films with various film thickness and adhesion strength. In addition, some improvements in CPCD test method for avoiding the overestimation of defect in film were discussed.(2) Because of the better understanding of correlation between localized corrosion progress and defect morphology of thin film coating, in situ observation in aqueous solution together with electrochemical measurement was needed. Therefore, in situ observation of defect morphology and nm or μm orders localized corrosion generated in 3% NaCl aqueous solution was conducted by Electrochemical Atomic Force Microscopy (EAFM) newly established by present authors.(3) Formation and characterization of TiO_2 thin film made on 304 stainless steel by Ion-beam-mixing method were conducted. Therefore, TiO_2 thin film made by Ion-beam-mixing method have superior adhesive characteristics and graded microstructure. Then, examination of the compositions and crystal structure of deposited thin films were conducted by XRD and ESCA.And also, it was confirmed that the 0.15mm thick TiO_2 thin film could have cathodic protection performance in 0.3wt% NaCl aqueous solution at room temperature. Less