Behavior of iron aluminides in oxidizing and oxidizing/sulfidizing environments

Abstract Fe 3 Al alloys have potential as structural materials and coatings for use in hostile environments because they form protective scales at very low oxygen partial pressures at elevated temperatures. Weight gains and parabolic rate constants were small for exposures to dry air at 800 and 900°C. Chromium additions to Fe 3 Al resulted in higher initial rates of oxidation in dry air at 800 and 900°C and substantially increased overall reaction rates in a very aggressive oxidizing/sulfidizing mixed gas when greater than 2 at.%. There was some evidence that an α-alumina layer formed during extended air exposure at 900°C. The ability to rapidly form an oxide layer appeared to limit damage caused by any loss of scale during thermal cycling. Preoxidation reduced the corrosion of Fe 3 Al5%Cr in the oxidizing/sulfidizing gas, but aluminizing this alloy to form an FeAl coating appeared to be the best way to assure long-term protection in sulfidizing environments.