Superplasticity in large-grained iron aluminides

The superplastic behavior has been found in Fe3Al and FeAl alloys with large grains. The large-grained Fe3Al and FeAl alloys exhibit all deformation characteristics of conventionally fine-grained superplastic alloys. The values of strain rate sensitivity index (m) are all larger than 0.3 at a temperature range and a strain rate range, at which the superplastic deformation proceeds. The maximum elongation to fracture of 620% with m value of 0.4 for Fe-28Al-2Ti alloy at 850 degrees C under an initial strain rate of 1.25 x 10(-2) s(-1) and 297% with m value of 0.34 for Fe-36.5Al-2Ti alloy at 1000 degrees C under an initial strain rate of 2.08 x 10(-2) s(-1) were obtained. The optical microscope and TEM observations have shown that during superplastic deformation grains become finer and an unstable subgrain boundary network forms, in which the subboundaries are absorbing gliding dislocations and transformed into low and high angle grain boundaries. The observed superplastic phenomenon is attributed to continuous recovery and recrystallization.