CORRELATION BETWEEN INTERFACIAL STATE OF PLASMA CVD COATED TiN FILM/SUBSTRATE AND PINHOLE DEFECT RATIO EVALUATION BY CPCD METHOD

摘要

TiN-coated stainless steel prepared by plasma CVD has some difficulties in using for corrosion resistant film, because TiN films have various defects. From among these various defects in coated thin films, corrosion resistance of TiN film coated specimens was usually governed by pinhole defect. Therefore, for applying TiN film in corrosion surroundings, it is necessary to evaluate the existing state of defects in the film. The Critical Passivation Current Density (CPCD) method had some problems though this method could quantitatively estimate defects as a pinhole defect ratio R(%) through employing the values of the critical passivation current density of TiN thin film coated specimen I{sub}(crit)(Coating/Substrate) and that of non-coated substrate specimen i{sub}(crit) (Substrate). The most serious problem is the overestimation in defect ratio evaluation in the cases when large corrosion pits were generated and some parts of TiN films were exfoliated due to its low adhesion strength. The adhesion characteristic of TiN films, which was coated by plasma CVD, was investigated by the scratch test. Then, 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.