Stress relaxation in thermally grown alumina scales on heating and cooling FeCrAl and FeCrAlY alloys

The residual stresses in alpha -Al2O3 scales formed on high-purity, FeCrAl and FeCrAlY during oxidation at 1200 degreesC and subsequent cooling and reheating were studied ruing photostimulated luminescence spectroscopy. Systematic measurements of the stress in the oxide were made as a function of both alloy thickness and cooling rate and the development of stresses in the oxide scale during thermal cycling was investigated as a function of the temperature. Depending on the ratio of the alloy and oxide-scale thicknesses, substantial stress relaxation was observed to occur during cooling at a rate of 8 K/min. Compressive growth stresses of similar to1 GPa were determined by comparing the residual-stress measurements at room temperature e with those calculated based on thermal-expansion mismatch. No significant differences in the growth stresses, the total residual stresses, or the stress relaxation during thermal cycling were observed between the oxides formed on the Y-doped and undoped FeCrAl samples. Stress relaxation is also shown to lead to the development of tensile stresses in the oxide scale under certain conditions, in particular, those associated with slow cooling followed by rapid heating.