SEGREGATION STUDIES OF OXIDIZED Y AND ZR DOPED NIAL

Conventional electron microscopy, analytical electron microscopy, high resolution electron microscopy and high resolution SIMS have been used to investigate the effect of the reactive elements, Y and Zr, on the oxide scale formation on NiAl. Polycrystalline NiAl samples, doped with either 0.1 wt% Y or 0.2 wt% Zr, were oxidized in air at 1200 degrees C. O-18 tracer experiments in conjunction with high resolution SIMS suggest that the reactive elements reduce the outward diffusion of cations. Energy dispersive X-ray spectroscopy on a dedicated STEM showed that the reactive elements seg regate to the grain boundaries in the oxide scale and to the metal/oxide interface. The amount at the oxide scale grain boundaries was calculated to be 0.2 monolayers for both Zr and Y doped NiAl. The amounts of segregation were calculated to be 0.15 monolayers (Zr-doped) and 0.07 monolayers (Y-doped) at the metal/oxide interface. The presence of sulfur was detected in Y-rich particles in the NiAl close to the interface.