Abstract
Present authors have investigated the corrosion characteristics of plasma-spray ceramic coated stainless steel by various electrochemical corrosion testings methods. It was indicated that microcracks and micropores in ZrO2 top coated layer play important role as the path through which aqueous solution comes into inner layers. And, intense corrosion was recognized on the interface regions between ZrO2 top coat and NiCrAlY undercoated layer. In some cases, these corrosion brought about peeling off the top coated layer. Therefore in this paper, to improve corrosion resistance of plasma-sprayed ceramic coating in an aqueous solution environment, sealing treatment and microstructural grading were conducted employing NiCrAlY and ZrO2 system. Then, several investigations concerning corrosion characteristics of these plasma-sprayed ceramic coating system, were conducted from electrochemical view points. As a result, it was recognized that microstructurally graded coating shows little improvements in the corrosion properties. On the contrary, sealing treatment shows much improvements in corrosion resistance especially in the case when heat treatment was employed at 300°C for the period of 2 hours. Then, some evaluations of defect ratio in plasma-spray ceramic coatings were conducted.
