THE EFFECT OF YTTRIUM ON THE GROWTH-PROCESS AND MICROSTRUCTURE OF ALPHA-AL2O3 ON FECRAL

The oxidation behavior of undoped and Y-doped high-purity FeCrAl at 12 00 degrees C was investigated. The scale-growth processes were studied using two-stage O-16/O-18 experiments and high-resolution imaging SIM S. SEM, TEM, and scanning transmission electron microscopy-electron-di spersive X-ray spectrometry (STEM-EDS) studies were performed in order to determine the microstructure of the oxide and the chemistry of the metal-oxide interface. An equiaxed alpha-Al2O3 scale was found to gro w by simultaneous outward Al and inward oxygen diffusion on the undope d FeCrAl. In contrast, a columnar alpha-Al2O3 grain structure on the Y -doped FeCrAl was produced by inward oxygen diffusion; outward Al diff usion was suppressed. Y was shown to segregate to alpha-A(2)O(3) grain boundaries and to the metal-oxide interface.