The effect of yttrium on the growth process and microstructure of α-Al2O3 on FeCrAl

The oxidation behavior of undoped and Y-dopedhigh-purity FeCrAl at 1200°C was investigated. Thescale-growth processes were studied using two-stage16O/18O experiments andhigh-resolution imaging SIMS. SEM, TEM, and scanning transmission electronmicroscopy-electron-dispersive X-ray spectrometry(STEM-EDS) studies were performed in order to determinethe microstructure of the oxide and the chemistry of the metal-oxide interface. An equiaxedα-Al2O3 scale was found togrow by simultaneous outward Al and inward oxygendiffusion on the undoped FeCrAl. In contrast, a columnarα-Al2O3 grain structure on the Y-doped FeCrAl was produced by inwardoxygen diffusion; outward Al diffusion was suppressed.Y was shown to segregate toα-Al2O3 grain boundaries andto the metal-oxide interface.