Crrosion Characteristics of Thermal Sprayed Coating of Stainless Alloys in Chloride Solution
Tsuguo Suzuki, Kazuo Ishikawa, Yoshiharu Kitamura
Corrosion behavior of thermal sprayed coating of SUS 304, 316, and Hastelloy C was studied in 3.5% NaCl solution by anodic and cathodic polarization measurements, and by SEM and EPMA. It was found that anodic dissolution occurs along the crevices between the deposited particles. The anodic process is thought to be essentially the same as that of crevice corrosion, It was also found that the corrosion resistance of the sprayed alloys is considerably less than that of their solid wire counterparts. This was attributed not only to the accelerated anodic process but also to the increase of cathodic reactivity. The latter was suggested by the existence of diffusion controlled cathodic current observed from the onset of cathodic polarization measurements. Such behavior is not observed usually for the stainless steels in neutral solutions. Sealing of the micro-crevices in the spray deposited alloy layers is essential to improve their corrosion resistance in chloride solutions. The thermal sprayed Hastelloy C, with a lower crevice corrosion susceptibility, coated with the epoxy resin exhibited the highest corrosion resistance.