Effect of Al and Cr Content on Air and Steam Oxidation of FeCrAl Alloys and Commercial APMT Alloy

To develop the next generation of accident-tolerant fuel cladding for light-water nuclear reactors, wrought FeCrAlY alloys with varying amounts of Cr and Al and commercial Kanthal APMT alloy were evaluated for short-term (4 h) oxidation resistance in steam and air at 1200-1475 A degrees C. Model alloys with lower Cr contents and higher Al contents were evaluated as lower Cr contents are desirable for radiation damage resistance during operation. As expected, a synergistic effect was found between the Cr and Al contents to enable protective Al2O3 formation under these conditions. Characterization of the alumina scales formed in steam found that the scale morphology was affected by the alloy Y content and detailed scanning transmission electron microscopy (STEM) detected Y segregation along scale grain boundaries at 1200 A degrees C. However, after 4 h at 1475 A degrees C, Y and Hf were not segregated to the oxide grain boundaries formed on APMT and the scale had a single layer structure. Compared to oxidation in air, STEM characterization of the outer scale showed differences in the Fe and Cr distributions in steam.