The use of a 18 O tracer and Rutherford backscattering spectrometry to study the oxidation mechanism of NiAl.

The oxidation mechanism of NiAl was investigated in the temperature range between 1170 K and 1420 K. Oxidation was performed by alternating exposure of the samples to natural oxygen and oxygen gas enriched with 18O. The 18O tracer was profiled by using the reaction with 800 keV protons, 18O(p,α)15N. Rutherford Backscattering Spectrometry of 2 MeV 4He+ was used to check the position of noble metal markers. The 18O tracer experiments clearly show that up to 1420 K, Al diffusion through the sclae is the major material transport mechanism during oxidation, resulting in outside scale growth. Noble metal “marker” experiments however give misleading results by incorrectly suggesting an inside scale growth mechanism