436, San Francisco, CA, 1996. Fundamental Aspects of High Temperature Corrosion, Vol. Cr 2 O 3 on more conventional stainless steels, provides a self-healing barrier that inhibits oxidation of the base metal. The a -Al 2 O 3 protective scales extend the temperature range of operation of these alloys and substantially increase operating lifetimes. Nonetheless, after extended periods of operation, or after operation at excessively high temperatures, the scale eventually loses adherence to the substrate and debonds.
Failure often occurs as a result of the stress that builds up between the oxide and the alloy.
Because the stress depends on thermal expansion mismatch, growth strains, surface morphology, and creep in the alloy-scale system, materials scientists have not be able to accurately predict these stresses. Therefore, measuring these stresses is important in evaluating the performance of corrosion-resistant alloys. To solve this problem, we have developed a unique application of a luminescence technique to determine stresses in aluminum oxide scales. Correspondingly, for the scales, we measure spectral shifts of the fluorescence to determine stresses. In Figure 1, we show ruby luminescence spectra obtained from an Al-containing alloy treated, in air, at various temperatures, and measured at room temperature.