Microstructural Evolution during Superplastic Deformation in Large-Grained Iron Aluminides

Abstract

The superplastic behavior has been found in Fe 3 Al and FeAl alloys with grain sizes of 100-600μm The large-grained Fe 3 Al and FeAl alloys exhibit all deformation characteristics of conventional fine size superplastic alloys. However, superplastic behavior was found in large-grained iron aluminides without the usual pre-requisites for the superplasticity of a fine grain size and grain boundary sliding. The metallographic examinations have shown that average grain size of large-grained iron aluminides decreased during superplastic deformation. Transmission electron microscopy (TEM) observation has shown that there were great number of subgrain boundaries which formed a network and among which the proportion of low and high angle boundaries increased with the increase of strain The observed superplastic phenomenon is explained by continuous recovery and recrystallization. During superplastic deformation, an unstable subgrain network forms and these subboundaries are absorbing gliding dislocations and transformed into low and high angle grain boundaries. A dislocation gliding and climbing process accommodated by subboundary sliding, migration and rotation, enables the superplastic flow to proceed.