Mesures des contraintes, influence de la vapeur d'eau. Étude de la structure et caractérisation de l'interface métal/oxyde de l'alliage FeCrAl(Ce)

Abstract

The behaviour of the FeCrAl(Ce) alloy in oxidation at high temperature made it possible to confirm the beneficial effect of the addition of rare earth, the role of the additions of zirconium on the stability of carbides, nitrides and the intermetallic phases. The microstructure of the interface, precipitation, the morphology and the kinetics of the oxide coatings formed were studied. The study was carried out on alloy, strip iron thin of 50 μm thickness. It was noted that the nature of oxide and its morphology depend on the temperature of the test and the oxidizing atmosphere. The precipitates are present in various forms. The examination of the transverse sections and the interface shows that the layers formed during isothermal oxidation are compact, seem well to adhere to the substrate, appreciably variable thicknesses. The kinetic mode is parabolic, some is the oxidizing medium. The kinetics was followed by thermogravimetric method. Isothermal oxidation in dry oxygen generates constraints of tension at temperature 900 °C and compressive stresses to 1 000 °C. The level of the constraints is almost the same one, some is the temperature and the oxidizing atmosphere. Nevertheless, its evolution is much more important in an oxide coating formed in an atmosphere made up of oxygen plus steam than in made up atmosphere an only out of dry oxygen. In all the cases the samples were observed by electronic scanning microscopy (MEB) in combination with dispersive analysis X in energy (EDS) or electronic microscopy with transmission (MET). The stress measurements were carried out by the method of deflection.