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.