The Effect of Thermal Expansion on Spallation Behavior of Fe-Base Alumina-Forming Alloys

Long-term cyclic oxidation behavior was compared for commercial FeCrAl alloys and mode. Fe-Al and FeCrAl alloys, and their coefficients of thermal expansion (CTE) were measured. For single-phase disordered (ferritic) Fe(Al) alloys, the CTE increased only slightly with Al content and was similar to that of FeCrAl alloys. More significant CTE increases were observed at >= 20%Al, as intermetallic phases, Fe(3)Al and FeAl, formed. As expected, the intermetallic compositions showed increased oxide spallation rates during cyclic oxidation at 1100 degrees and 1200 degrees C. However, after extensive spallation and loss of Al from the substrate, the compositions of Fe(3)Al and FeAl specimens entered the ferritic phase field, and the amount of scale spallation decreased. Among commercial oxide dispersion strengthened (ODS) FeCrAl alloys, a composition containing Mo (ODM751) exhibited the lowest thermal expansion and showed the slowest degradation rate in long-term testing at 1100 degrees C. The concept of minimizing CTE as a route for alloy development was investigated.