Factors affecting aluminum depletion during cyclic oxidation of Fe-base alumina-forming alloys

In order to develop an improved oxidation-limited lifetime model, experiments are being conducted to assess the critical factors that affect the rate of Al loss from Fe-base alumina-forming alloys during cyclic oxidation. Both wrought and dispersion strengthened ferritic and intermetallic Fe-Al +/- Cr alloys are being investigated at exposure temperatures from 1100-1300 degrees C. Higher temperatures, thinner specimens and cycle frequency are used to accelerate degradation during oxidation. However, the effects of these experimental choices often have not been critically assessed in prior work. Electron probe microanalysis has been used to measure the residual Al Content under various conditions and at various stages of life. For 0.5-2 mm thick specimens, lifetime repeatedly showed a linear relationship to thickness. Increasing the oxidation temperature appears to be the most viable strategy to accelerate the evaluation of oxidation resistance for comparing and developing alloys.