Creep of binary Fe-Al alloys with ultrafine lamellar microstructures. (November 2017) - Schmitt, A.
Abstract: On the Al-rich side of the Fe-Al binary system, the eutectoid decomposition of Fe5 Al8 into B2-ordered FeAl and triclinic FeAl2 in the composition range of 55–65 at.% Al produces an ultrafine lamellar microstructure. The compression creep behavior of such two-phase intermetallic materials was investigated in the temperature range 600–800 °C under constant stress. In addition to the fully lamellar Fe-61Al alloy, Fe-58Al and Fe-62Al that included, pro-eutectoid FeAl and FeAl2, respectively, were characterized in terms of their microstructure and creep response. For all microstructures, the strain rate as a function of time and strain exhibits a distinct minimum instead of a steady state creep regime. Microstructure instability, primarily in the vicinity of colony boundaries, is identified as the main reason for the increase in strain rate beyond the minimum. In contrast, lamellar coarsening is shown to be only a secondary factor influencing creep response for the conditions investigated. In comparison to single phase FeAl, the fully lamellar FeAl-FeAl2 shows enhanced creep resistance while the presence of either pro-eutectoid phase leads to a relative deterioration of the creep resistance. Highlights: Lamellar Fe-Al eutectoid alloys exhibit a minimum in creep rate versus strain. The creep rate is controlled by FeAl2. Lamellar structure breaks down near colony boundaries beyond the minimum creep rate. Lamellar coarsening only has a secondary effect on creep response. The fully lamellar material shows better creep resistance than off-eutectoid alloys.