Effect of rare-earth elements on high-temperature oxidation resistance of Fe-20Cr-5Al alloy foils

The oxidation behavior of 50 mu m thick Fe-20 mass% Cr-5 mass% Al alloy foils containing small amounts of Y, La, Ce, Pr, Nd or Sm was examined by a cyclic oxidation test at 1373 and 1473 K in air. The addition of rare-earth elements decreased the growth rates of both the Al2O3 scale, which grew until Al in the foil had been depleted, and the Cr2O3 scale, which formed between the Al2O3 scale and the substrate after the depletion of Al. The segregation of the rare-earth elements to the Al2O3 grain boundaries was observed with a transmission electron microscope equipped with an energy-dispersive X-ray spectrometer. The reduction in the growth rate of the Cr2O3 scale indicates that the oxygen diffusion rate in the Al2O3 scare is reduced. Therefore, we infer that the segregation of rare-earth elements suppress oxygen diffusion via the Al2O3 grain boundaries, resulting in the decreased growth rate of the Al2O3 scale.