Characterization of the breakaway al content in alumina-forming alloys

Residual Al contents were measured in Fe- and Ni-base alloys in order to improve lifetime prediction models based on the consumption of the Al reservoir. Measurements were made using electron probe microanalysis (EPMA) on both foil (50-125 mum thickness) and plate (0.5-2mm) material. For FeCrAl, NiCrAl and Fe3Al plate specimens, significant Al concentration gradients were measured. An Al gradient is not considered in current reservoir type models. Residual Al contents at the onset of breakaway oxidation were somewhat lower than previously reported for several FeCrAl alloys and significantly higher (much greater than10at.%) for Fe3Al and Fe-Al alloys. The implications of these results for performance and lifetime predictions are discussed.