High-temperature stress measurements during the oxidation of NiAl

The growth stresses in a-alumina scales growing on stoichiometric NiAl duri ng oxidation in air at 1100 degrees C have been measured by two X-ray diffr action techniques. the classic rocking technique and a newly developed fixe d-incidence multiplane (FIM) technique. The growth stresses were found to b e within the experimental uncertainty of the measurements, ie., near zero. Measurement of the residual stresses using an optical-fluorescence spectros copy (OFS) technique in adherent regions of the scale, after cooling to roo m temperature, were consistent with the growth stresses having been negligi bly small. These measurements contrast with previous measurements of growth stresses in alpha-alumina growing on Fe-Cr-Al alloys, using the FIM techni que, which indicated compressive growth stresses on the order of 1 GPa. Pos sible reasons for these differences are discussed.