Effect of thermomechanical treatments on the room-temperature mechanical behavior of iron aluminide Fe3Al

The room-temperature hydrogen embrittlement (HE) problem in iron aluminides has restricted their use as high-temperature structural materials. The role of thermomechanical treatments (TMT), i.e., rolling at 500 degrees C, 800 degrees C, and 1000 degrees C, and post-TMT heat treatments, i.e., recrystallization at 750 degrees C and ordering at 500 degrees C, in affecting the room-temperature mechanical properties of Fe-25Al intermetallic alloy has been studied from a processing-structure-properties correlation viewpoint. It was found that when this alloy is rolled at higher temperature, it exhibits a higher fracture strength. This has been attributed to fine subgrain size (28 mu) due to dynamic recrystallization occurring at the higher rolling temperature of 1000 degrees C. However, when this alloy is rolled at 1000 degrees C and then recrystallized, it shows the highest ductility but poor fracture strength. This behavior has been ascribed to the partially recrystallized microstructure, which prevents hydrogen ingress through grain boundaries and minimizes hydrogen embrittlement. When the alloy is rolled at 1000 degrees C and then ordered at 500 degrees C for 100 hours, it shows the highest fracture strength, due to its finer grain size. The alloy rolled at 500 degrees C and then ordered undergoes grain growth. Hence, it exhibits a lower fracture strength of 360 MPa. Fracture morphologies of the alloy were found to be typical of brittle fracture, i.e., cleavage-type fracture in all the cases.