The Effects of Reactive Element Oxide Coatings on the High Temperature Oxidation of FeCrAl Alloy
The effect of reactive element additions (external doping as an yttrium-oxide coating on the metal) on the oxidation behaviour of a commercial FeCrAl alloy (Kanthal A1) has been investigated during isothermal exposures in air at 1373K. The scale growth kinetics of the bare alloy obey a parabolic rate law during the whole oxidation test whereas the kinetic curves of the yttrium-bearing specimen exhibit an initial transient stage during the first hours, followed by a parabolic regime. The yttrium addition to the bare alloy does not give the beneficial effect usually ascribed to the reactive elements. No significant oxidation rate improvement of the alloy is observed, the parabolic rate constants values obtained are roughly similar for the both specimens. In situ X-ray diffraction reveals a marked influence of the reactive element on the composition of the oxide scale. The oxide layer formed on the yttrium-bearing specimen revealed, in addition to α- alumina which is the main oxide also identified on the bare specimen, the presence of yttrium aluminates (YAlO3, Y3Al5O12) located in the outermost part of the layer.
Pierre Steinmetz, Ian G. Wright, Alain Galerie, Daniel Monceau and Stéphane Mathieu
R. Cueff et al., "The Effects of Reactive Element Oxide Coatings on the High Temperature Oxidation of FeCrAl Alloy", Materials Science Forum, Vols. 595-598, pp. 933-940, 2008