High Temperature Corrosion Behavior of Iron Aluminide Alloys andCoatings

摘要

A multi-year effort has been focused an optimizing the large-term oxidation performance of ingot-processed (IP) and oxide-dispersion strengthened (ODS) Fe3A1 and iron aluminide-based coatings. Based on results from several composition iterations, a Hf-doped alloy (Fe-28A1-2Cr-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 oc-A1203 scale 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 CDSFe3A1 has been determined and compared to commercially available CSD FeCrA1. Scale spallation rates for CDS Fe3A1 are higher than for CDS FeCrA1. 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 the air at 900 and 1000 C and in air - 1%SO2at 800 C. Most likely due to an inadequate aluminum concentration in the coatings, continuous protective A12O3 could not be maintained and, consequently, the corrosion performance was significantly worse than what is normally observed for Fe3A1.