Despite very low surface roughness values of steel substrates (Ra = 0.06 mu m), plasma sprayed coatings of Al2O3 exhibited an excellent adhesion (> 60 MPa) when the substrate was preliminary oxidized before coating. Investigation in the interfacial zone, mainly by TEM study, showed a cry stallographic continuity through the different heterophase interfaces present from the inner steel substrate up to the outer alumina coating: steel/iron (alpha-Fe)/wilstite (Fe1-xO)/magnetite (Fe3O4)/metastable alumina (gamma-Al2O3). No chemical reaction occurred between iron oxides and alumina, but strong crystallographic relationships linked every phase through the different interfaces. Such a structural continuity explained the solidity of this alloy/ceramic bonding. (c) 2007 Elsevier B.V. All rights reserved.