Conventional electron microscopy, analytical electron microscopy, high
resolution electron microscopy and high resolution SIMS have been use
d to investigate the effect of the reactive elements, Y and Zr, on the
oxide scale formation on NiAl. Polycrystalline NiAl samples, doped wi
th either 0.1 wt% Y or 0.2 wt% Zr, were oxidized in air at 1200 degree
s C. O-18 tracer experiments in conjunction with high resolution SIMS
suggest that the reactive elements reduce the outward diffusion of cat
ions. Energy dispersive X-ray spectroscopy on a dedicated STEM showed
that the reactive elements seg regate to the grain boundaries in the o
xide scale and to the metal/oxide interface. The amount at the oxide s
cale grain boundaries was calculated to be 0.2 monolayers for both Zr
and Y doped NiAl. The amounts of segregation were calculated to be 0.1
5 monolayers (Zr-doped) and 0.07 monolayers (Y-doped) at the metal/oxi
de interface. The presence of sulfur was detected in Y-rich particles
in the NiAl close to the interface.