Abstract
Iron-based mechanical alloys containing 3.2–6.6 Al, 16.0–24.7 Cr, 0.5 Ti, and 0.5 Y2O3 (mass%) were preoxidized in air at 1373 K for 10–180 min. Alumina scales were formed. Scales were isolated and examined in a high-voltage transmission electron microscope. Specimen sections were examined in a scanning electron microscope. Specimens were exposed to atmospheres exhibiting oxygen activities from 1.5×10−13 to 1.4×10−14 and sulfur activities from 7.4×10−7 to 3.6×10−5 at 1123, 1223, and 1323 K. Alumina, chromia, and iron sulfide are thermodynamically stable under these conditions. Sulfidation did not occur at 1223 or 1323 K. Specimens exposed at 1123 K were sulfidized and formed a scale containing iron, chromium, and sulfur. The period before the onset of sulfidation was dependent on the preoxidation time. A model is developed to account for the temperature dependence of the sulfidation in terms of the alloy-interdiffusion rate of aluminum and the activity of the sulfidizing species at the scale-gas interface.
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Richard Weber, J.K., Hocking, M.G. Effects of preformed alumina scales on the behavior of FeCrAl alloys in simulated coal-gasifier atmospheres. Oxid Met 32, 1–12 (1989). https://doi.org/10.1007/BF00665266
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DOI: https://doi.org/10.1007/BF00665266