Effect of Fe-Al substrate mechanical properties on alumina scale morphology

The alumina scale formed on undoped iron aluminides (Fe-40Al and Fe-28Al-2Cr) was studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM). For cast alloys, a convoluted scale was observed after exposures at 950° and 1000 °C. However, oxide dispersed Fe-28Al-2Cr formed a flat oxide after similar exposures. To clarify the role of the substrate, the high temperature mechanical properties of these materials were studied in tension and/or compression. The largest scale convolutions were observed on the material with the lowest 1000 °C yield stress, wrought Fe-28Al-2Cr, suggesting that substrate mechanical properties can explain the observed differences in scale morphology.