Evaluation of the Corrosion Resistance of Fe–Al–Cr Alloys in Simulated Low NOx Environments

The first part of this manuscript presented SEM analysis of corrosion products formed on iron–aluminum–chromium alloys that were exposed to a simulated low NOx combustion environments. In Part II, results from electron microprobe analysis (EMPA) and scanning transmission electron microscopy (STEM) analyses of select as-corroded coupons from the long tem tests are discussed. Despite the formation of thick iron sulfide films one of the alloys, EMPA did not detect any measurable depletion of aluminum near the surface of this alloy. STEM analysis revealed that chromium was able to form chromium sulfides only on the higher aluminum content alloys, thereby preventing the formation of deleterious iron sulfides and reducing the overall corrosive attack on this alloy. Also observed in the STEM analysis was the encapsulation of external iron sulfide products with a thin layer of aluminum oxide, which may serve as a secondary layer of corrosion protection in these regions.