High-temperature oxidation behavior of ODS-Fe3Al

The high-temperature oxidation behavior of an oxide dispersion-strengthened (ODS) Fe3Al alloy has been studied during isothermal and cyclic exposures in oxygen and air over the temperature range 1000 to 1300 degreesC. Compare d to commercially available ODS-FeCrAl alloys, it exhibited very similar sh ortterm rates of oxidation at 1000 and 1100 degreesC, but at higher tempera tures the oxidation rate increased because of increased scale spallation. O ver the entire temperature range, the oxide scale formed was alpha -Al2O3, with the morphological features typical of reactive-element doping and was similar to those formed on the ODS-FeCrAl alloys. Although initially this s cale appeared to be extremely adherent to the Fe3Al substrate, an undulatin g metal-oxide interface formed with increasing lime and temperature, which led to cracking of the scale in the vicinity of surface undulations accompa nied bl, a loss of small fragments of the full-scale thickness. In some ins tances, the surface undulations appeared to have resulted from guess outwar d local extrusion of the alloy substrate. Similar features developed on the FeCrAl alloys, hut they were typically much smaller after a given oxidatio n exposure. The ODS-Fe3Al alloy has a significantly larger coefficient of t hermal expansion (CTE) than typical FeCrAl alloys (approximately 1.5 times at 900 degreesC) and this appears to be the major reason for the greater te ndency,for scale spallation. The stress generated by the CTE mismatch,vas a pparently sufficient to lead to buckling and limited loss of scale at tempe ratures up to 1100 degreesC, with an increasing amount of substrate deforma tion at 1200 degreesC and above. This deformation led to increased scale sp allation by producing an out-of-plane stress distribution, resulting in cra cking or shearing of the oxide.