Evaluation of corrosion resistance and surface film analysis after corrosion testing of materials coated by chemical densified coating method under boiling sulfuric acid environment

Hirota, Noriaki   ; Funamoto, Kodai*; Tachibana, Yukio 

For the purpose of developing metallic materials with excellent corrosion resistance under boiling sulfuric acid environment, the coated materials were evaluated for their corrosion resistance and the differences in surface morphology were investigated. As a result, the corrosion resistance of SUS304 coated and sintered eight times by chemical densified coating method (S-ZAC) was maintained at the point after 12h corrosion test, but the corrosion rate rapidly increased after 100h corrosion test. The cross-sectional microstructural analysis of the specimens showed that only a small amount of SiO remained on the surface, while CrO completely disappeared. The mechanism of film delamination in S-ZAC is assumed to be due to the thermal expansion caused by heating, which resulted in curvature of the thick film and cracks at the CrO and SiO interfaces. On the other hand, SUS304 coated with higher density of CrO by repeating the coating and sintering eleven times (MS-ZAC) showed excellent corrosion resistance as well as SiC even after 100h corrosion test. The results of cross-sectional microstructuCrO particle layer, in addition to the thinning of the entire film.