Abstract
The oxidation and hot corrosion behavior of the binary iron aluminide, Fe-25Al (at.%), has been studied at 1100 K, 1225 K and 1330 K. Hot corrosion studies were conducted by coating the specimen surfaces with 2.5 ± 0.2 mg/cm2 of Na2SO4 prior to exposure in pure oxygen. Parabolic rate constants were obtained from weight gain data. The faster kinetics in the initial stages of oxidation have been related to the formation of θ-Al2O3 and the slower kinetics in the later stages of oxidation, to the formation of α-Al2O3. The overall rate of hot corrosion was higher than that of oxidation at all the temperatures. The presence of α-Fe2O3 in addition to alumina was indicated by XRD analysis of the scales present on the surface of the samples after hot corrosion. FTIR spectra from the spalled scales in hot corrosion divulged the presence of α-Al2O3, α-Fe2O3 and sulfate. Cross-sectional microscopy revealed that the metal-scale interfaces were pitted in hot corrosion conditions and the pits contained aluminum sulfide. Sulfides were also identified along the grain boundaries in the intermetallic near the scale-metal interface. The hot corrosion process has been explained based on sulfide formation and its subsequent oxidation.
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