Feasibility of ceramic coating to guard stainless steels against intergranular corrosion

Abstract

The aim of this study is to examine the corrosion behaviour of yttria stabilised zirconia (YSZ) coated 304LN stainless steel, with or without bond coat, in order to assess the potential of the coatings to protect stainless steels against intergranular corrosion (IGC). The coatings have been prepared by plasma spraying technique, and their effectiveness in providing corrosion resistance has been examined by carrying out double loop electrochemical potentiokinetic reactivation test, anodic polarisation studies and boiling nitric acid tests. Characterisations of the steel, the coating and the interfaces, supplement the primary corrosion tests. The effectiveness of the coatings has been mainly assessed using the nature of spelling of the coated material subjected to boiling nitric acid tests, and the results have been discussed using the porosity in the coatings and their nature of the interfaces. It can be inferred from the obtained results that the developed plasma sprayed YSZ coatings, with or without bond coat, are unable to act as protective environmental barrier to prevent IGC of the stainless steel substrate primarily due to inappropriate plasma spray processing which leads to considerable amount of interconnected porosity. However, these results provide some interesting guidelines to develop corrosion resistant ceramic coatings. © 2008 Institute of Materials, Minerals and Mining.