The adhesion of Al_2O_3 scales on commercial grade alloys that do not contain a reactive element is usually poor due to the presence of 10-50 wppm of sulfur impurity, and/or of pores that formed at the scale/alloy interface. Sulfur is usually believed to segregate to the interface to weaken the interfacial bonding and to stabilize interfacial pores. By using field emission scanning Auger microscopy, the distribution of sulfur on pores and on oxide imprinted areas at Al_2O_3/FeAl interfaces was precisely determined. Interfacial pore growth as a function of oxidation time was obtained from scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses. The effects of sulfur segregation, surface impurity and reactive elements on pore nucleation and growth are discussed.
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