Sequential oxidation experiments at 1200-degrees-C and 1500-degrees-C
using O-16 and >95% O-18-enriched environments were conducted on undop
ed and Y- and Zr-doped beta-NiAl and FeCrAl alloys. After oxidation, s
amples were analyzed by SIMS sputter depth profiling. At 1200-degrees-
C, a clear pattern was established where the undoped alpha-Al2O3 was f
ound to grow by the simultaneous transport of both Al and O. Zr-doped
alpha-Al2O3 was found to grow mainly by the inward transport of oxygen
. The profiles in all cases indicate O diffusion primarily by short-ci
rcuit pathways. Results at 1500-degrees-C (only on beta-NiAl) indicate
d a similar behavior but were less conclusive. Y and Zr were found to
segregate to the oxide grain boundaries at 1200-degrees-C and 1500-deg
rees-C The segregation of these dopants is believed to impede the cati
on transport in the alpha-Al2O3 scale and thereby change the oxidation
mechanism.