Effect of reactive element oxide coating on the high temperature oxidation behaviour of FeCrAl alloys

The influence of yttrium oxide coating (processed by the sol–gel method) on the oxidation behaviour of a commercial FeCrAl alloy (Kanthal A1) has been investigated during isothermal exposures in air at 1373 K. The scale growth kinetics of the uncoated alloy obey a parabolic rate law during the whole oxidation test, whereas the kinetic curves of the Y-coated specimen exhibit an initial transient stage for the first few hours, followed by a parabolic regime. The yttrium sol–gel coating deposited on the bare alloy does not provide the beneficial effect usually ascribed to reactive elements. No oxidation rate improvement of the coated alloy is observed, the parabolic rate constant values are strictly identical for 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-coated specimen comprised, in addition to a-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. # 2004 Published by Elsevier B.V.