High-resolution SIMS and analytical TEM evaluation of alumina scales on beta-NiAl containing Zr or Y

High-resolution SIMS and TEM have been used to evaluate growth processes and interfacial segregation occurring in alpha-Al2O3 scales grown at 1200 degrees C on beta-NiAl containing zirconium or yttrium. O-18/SIMS shows that the extent of aluminum diffusion occurring during alpha-Al2O3 growth is reduced by the presence of these alloying elements, which are seen by SIMS imaging as oxide particles within the scale, STEM/EDS of the same oxide scales show that zirconium and yttrium also segregated to the oxide-alloy interface to the extent, respectively, of similar to 0.15 and -0.07 of a monolayer and to oxide grain boundaries (similar to 0.2 monolayer). The complementary information provided by SIMS, TEM, and STEM provides a better understanding of the role of ''reactive elements'' in modifying scale-growth processes.