Plasma-jet coating of preoxidized XC38 steel: influence of the nature of the oxide layer

Abstract

Preoxidation of alloy substrates before spraying an oxide powder improves the adhesion of the coating. In the case of a low carbon steel (XC38) coated by plasma sprayed alumina, three preoxidation treatments in a classical furnace have been undertaken, in order to form respectively FeO, Fe₃O₄ and Fe₂O₃ layers. The best adhesion of alumina coating is obtained with FeO interlayers, and the worst with Fe₂O₃. The preliminary thermal treatment giving FeO implies a controlled atmosphere of carbon dioxide, but it points to some interesting prospects for coating complex parts. The origin of the improvement of adhesion may be a diffusion bonding at the FeO/Al₂O₃ interface or more simply it might be due to the increase of the substrate roughness with the time of oxidation. Besides, the epitaxial growth of FeO on steel probably explains the good mechanical resistance of the steel/FeO interface .