ABSTRACT
The object of this study was to determine the influence of the substrate preparation on the adhesion and corrosion resistance of various ceramic coatings used in seawater.
The adhesion properties of the various coatings were characterised using a four-point bend test or a pull-out test, and the corrosion performance of the coatings was evaluated by electrochemical measurements and exposure tests.
It was shown that substrate sandblasting was without effect both on adhesion and corrosion control. The presence of a sub-layer is not necessary to obtain good adhesion of the three kinds of ceramic coating studied here. The sub-layer/substrate interface is weaker than the ceramic/sub-layer or ceramic/substrate interface. Thus, the risk of decohesion of the multilayer coatings is higher than that of a single ceramic coating. The severity of cracking under mechanical stress depends on the thickness ratio of the ceramic and the sub-layer, and on the nature of this sub-layer.
The electrochemical measurements have confirmed that all the ceramic coatings are porous. For both oxide ceramic coatings, the presence of a sub-layer has a beneficial effect on corrosion control but for the carbide coating it is not possible to conclude whether the presence of a sub-layer is beneficial.
