Long-Term Oxidation Testing and Lifetime Modeling of Cast and ODS FeCrAl Alloys

Long-term cyclic oxidation testing was conducted on oxide dispersion strengthened (ODS) and cast FeCrAlY alloys at 1100 and 1200 A degrees C with 1 or 100 h hold time in air, O-2, and humid atmospheres. These data were used to optimize four different cyclic oxidation models and calculate the Al consumption rate due to oxidation. The pkp and COSIM-GSA models were able to reproduce accurately the experimental oxidation curves, and lifetime predictions based on these models were in good agreement with experiments. Microstructure characterization revealed that the degradation of the ODS FeCrAlY cyclic oxidation performance was mainly due to the incorporation of Ti carbonitrides in the alumina scale and the formation of tensile cracks. Controlling the levels of C, N, and S in one ODS alloy resulted in oxidation performance only moderately lower than the performance of cast FeCrAlY alloys. A few, very deep, tensile cracks formed at the cast alloy surface upon thermal cycling. Finally, the effect of specimen mechanical strength and the presence of H2O on ODS FeCrAl durability are discussed.