High-temperature Corrosion Behavior of Iron Aluminide Alloys and Coatings

A multi-year effort has been focused on optimizing the long-term oxidation performance of ingot-processed (IP) and oxide-dispersion strengthened (ODS) Fe3Al and iron aluminidebased coatings. Based on results from several composition iterations, a Hf-doped alloy (Fe28Al-2Cr-0.05at.%Hf) has been developed with significantly better high temperature oxidation resistance than other iron aluminides. The scale adhesion is not significantly better; however, the α-Al2O3scale grows at a slower rate, approximately a factor of 10 less than undoped iron aluminide. The benefit of Hf is greatest at 1100°-1200°C. Long-term oxidation resistance of commercially fabricated ODS Fe3Al has been determined and compared to commercially available ODS FeCrAl. Scale spallation rates for ODS Fe3Al are higher than for ODS FeCrAl. To complement studies of iron-aluminide weld-overlay coatings, carbon steel was coated with Fe-Al-Cr by thermal spraying. These specimens were then exposed in air at 900 and 1000°C and in air-1%SO2 at 800°C. Most likely due to an inadequate aluminum concentration in the coatings, continuous protective Al2O3could not be maintained and, consequently, the corrosion performance was significantly worse than what is normally observed for Fe3Al.