Microstructural evolution during creep of lamellar eutectoid and off-eutectoid FeAl/FeAl2 alloys.

Abstract The creep behavior of a fully lamellar FeAl/FeAl 2 eutectoid alloy was shown to exhibit a minimum creep rate and the absence of a pronounced steady state regime. To reveal the underlying mechanisms of creep leading to the macroscopic response described above, comprehensive TEM investigation of several crept specimens were performed. In the early stages of creep, the FeAl phase primarily carries creep deformation by dislocation motion, whereas FeAl 2 remains mostly plastically undeformed, except in certain locations near colony boundaries where the lamellar structure is disrupted/absent. Within the colonies, where the lamellae are intact, deformation is accommodated at the FeAl/FeAl 2 interface, resulting in an increase in interface dislocations. This continues to be the case at the minimum creep rate. With further progression in creep, FeAl 2 begins to participate in the process of plastic deformation in a more substantive manner through twinning and slip, while FeAl continues to plastically deform and dynamically recover. Further beyond the minimum, the lamellar structure adjacent to the colony boundaries breaks down, and these areas become the primary contributors to creep and results in a continuous loss in creep resistance. Based on these observations in the fully lamellar material, the creep response of off-eutectoid Fe-58Al and Fe-62Al as well as single-phase FeAl 2 are explained. Highlights • Creep mechanism in a lamellar FeAl/FeAl 2 alloy is examined by electron microscopy. • Initially, FeAl deforms by slip and interface dislocation content increases. • A creep rate minimum then occurs and is associated with slip and twinning in FeAl 2. • Twins nucleate at the FeAl/FeAl 2 interfaces and FeAl 2 twins on the (001) plane. • Increase in creep rate at longer time results from lamellar structure breakdown. [ABSTRACT FROM AUTHOR]