Corrosion behavior of ternary Fe-15Cu-5Al alloy in pure oxygen at 1000 °C

The corrosion behavior of ternary Fe-15Cu-5Al (mole fraction, %) alloy was studied at 1000 degrees C in 0.1 MPa pure oxygen. The Fe-rich alloy shows two parabolic oxidation stages, with a small increase of the parabolic rate constant from 1.9 x 10(-9) to 4.1 x 10(-9) g(2)/(cm(4).s). The scale grown on the alloy is very complicated, with formation of overgrown nodules interspersed among bulky stratified scales. The nodules and the bulky stratified scales are always composed of an outer layer of CuFe2O4 and of an inner layer containing Fe2O3 and Fe3O4. Beneath the external scale of the nodules, there is an internal oxidation zone where iron oxide is mixed with copper metal. Furthermore, the base of the internal oxidation zone is characterized by a discontinuous aluminum-enriched layer of either Al2O3 or FeAl2O4. For the stratified scales, no internal oxidation zone is present beneath the innermost Al2O3 or FeAl2O4 layer. Aluminum depletion is present in advance of the internal oxidation front, while iron depletion is not observed. The corrosion feature of the ternary Fe-15Cu-5Al alloy is partly associated with that of the corresponding binary Fe-Cu and Fe-Al alloys. The peculiar scale microstructure observed is considered mainly as a consequence of the limited solubility of the iron and copper components in one another and of the monovariant system of the ternary Fe-15Cu-5Al alloy.