Wrinkling behavior of alumina scales formed during isothermal oxidation of Fe-Al binary alloys

The morphological development of Al2O3 scales formed on Fe-24, 28, 32, 36 and 40 at% Al alloys during isothermal oxidation at 900-1100 °C in pure oxygen was studied by SEM, and the extent of surface undulation was quantified by AFM. In all cases, the initially formed scale was flat with a macroscopically planar scale/alloy interface. With further oxidation, the scale and the alloy undulated together, developing a convoluted interface that was often strongly depended upon alloy grain orientations. Eventually, the scale detached and buckled. Convolution was found to develop much earlier at higher oxidation temperatures and on alloys with aluminum concentrations in the disordered bcc phase field (A2) than those with the ordered bcc structure (B2), which suggests that diffusivity in the alloy is the dominating factor for Al2O3/alloy interface convolution during scale growth.