Preparation and characterisation of an electrolytically deposited ceramic coating on stainless steel

Ceramic coatings are widely used to protect metals against oxidation at high temperatures. In order to obtain ceramic layers with strong metal substrate adhesion, an original method has been developed. It involves pretreatment of the metal surface that leads to the formation of a functional conversion coating, characterised by strong interfacial adhesion with the substrate and by a particular morphology. Its particular texture allows the cathodic deposition of alumina and/or zirconia during electrolysis of aluminium and/or zirconium salt solutions. After heating, the coating presents a continuous composition gradient with refractory compounds at the surface. This electrochemical method offers a relatively easy way to establish coating composition and enables the preparation of a mixed ceramic layer. Results for alumina-zirconia coating preparation are presented. The electrochemical behaviour and chemical composition are analysed. Electrolytic bath composition, electrochemical parameters and coating composition are correlated.