High-Temperature Atmospheric Corrosion of Fe-Cr-Si Alloys Studied by Mössbauer Spectroscopy

The high-temperature atmospheric corrosion of iron-based Fe-Cr-Si alloys was studied using ⁵⁷Fe transmission Mössbauer spectroscopy (TMS) and conversion electron Mössbauer spectroscopy (CEMS). The Mössbauer measurements allow one to determine the chemical composition changes as well as the content of iron oxides in 300 nm subsurface layer and the bulk of studied samples during exposure to air at 870 K. The results indicate that the oxidation of iron atoms slows with increasing Si and Cr content in the specimens and as one could expect, the oxidation process in the bulk is much slower than in the 300 nm subsurface layer of studied materials. The parameters of the measured spectra made it possible to compute the iron oxidation kinetics. The comparison of the obtained kinetics for the Fe_0.96Cr_0.03Si_0.01, Fe_0.94Cr_0.03Si_0.03, and Fe_0.90Cr_0.05Si_0.05 samples with corresponding data obtained previously for the binary Fe-Si and Fe-Cr alloys suggests that an addition of a relatively small amount of Cr to the dilute iron-based Fe-Si alloys has a negative effect on high-temperature corrosion resistance of the systems. At the same time, the present investigations show that the iron oxidation process is practically not observed when the alloy that is richer in Cr, Fe_0.85Cr_0.10Si_0.05, is exposed to air at 870 K. Finally, the additional TMS measurements were performed for Fe_0.85Cr_0.10Si_0.05 sample after exposure to air at 1,070 K and 1,270 K.