Fe-25wt%Cr, Fe-25wt%Cr-20wt%Ni and Fe-25wt%Cr-6wt%Al alloys have been exposed to H2/H2O/H2S/Ar gas mixtures at 700°C. The mechanisms of formation and degradation of oxide scales on these alloys have been investigated using electron microscopy and surface analytical techniques. The Fe-25Cr-6Al alloy is attacked the least as a result of the formation of a γ-Al2O3 scale, whereas the Fe-25Cr-20Ni alloy is attacked the most, through rapid formation of Fe and Ni sulfides. The Fe-25Cr alloy, forms a Cr2O3 scale initially, followed by formation of CrS1.17 precipitates, which allow Fe to diffuse out rapidly.

Subject
Sulfur, Metal surfaces, Precipitates, Nickel based alloys, Oxide formation, Nodules, Corrosion scales, Oxide scales, Interfaces, Scale formation, Scale, Sulfides, Alloys
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1989
Association for Materials Protection and Performance (AMPP)
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