The effect of yttrium and sulfur on the oxidation of FeCrAl

In order to examine the influence of Y and S on the oxidation process of FeCrAl, isothermal oxidation experiments with a set of 4 high purity FeCrAl alloys with well defined Y and/or S content were carried out between 1100 degrees C and 1400 degrees C. The experiments showed convolution, void formation and spallation for the oxide on the undoped FeCrAl with 45 ppm S content, whereas the undoped alloy with 2 ppm S, as well as the Y doped alloys, exhibited a flat and adherent scale. TEM studies revealed an equiaxed oxide grain structure for the undoped materials and a columnar structure for the Y doped FeCrAl. This indicates a change in the oxide growth process due to the presence of Y. The segregation of Y to the oxide grain boundaries and the metal/oxide interface could be detected with STEM-EDS. The characterization of the microstructure was combined with mechanical stress measurements of the oxide using optical fluorescence spectroscopy.