Residual stresses in convoluted oxide scales

Alumina scales that grow during oxidation of FeCrAl alloys can develop a co nvoluted morphology. Although convolution relieves the overall growth stres s, high thermal stresses develop locally and can he detrimental to the scal e or interface integrity. Ruby fluorescence measurements and finite element simulations are used to examine residual thermal stresses and strains that result when the convoluted scales are cooled to room temperature. Unlike a flat scale that is in biaxial compression, a convoluted scale contains sig nificant gradients, with tensile stress components along the outside and ne ar the interface of the convoluted peaks. The experimental results are in g ood agreement with model calculations and provide much needed verification of the model assumptions. Because the ruby fluorescence technique provides only the hydrostatic stress averaged over an excited volume that includes t he entire alumina scale thickness, modeling provides derail and insight to the experimental measurements. (C) 1999 Elsevier Science S.A. All rights re served.