Microstructure evolution in a large-grained TiAl alloy

Microstructure evolution during superplastic deformation of a large-grained TiAl alloy with near-γ microstructure was characterized by orientation imaging microscopy (OIM) and transmission electron microscopy (TEM). In OIM, significant grain refinement is observed at different strain levels with an increase in the density of low angle and high angle grain boundaries. A direct evidence of dynamic formation of grain boundaries with misorientation of 15°-30° during deformation is found, which is a result of subboundary evolution. The formation of subboundaries by intersecting dislocations, and the evidence of dislocation glide in the interior of grains are revealed by TEM. A continuous recovery and recrystallization process similar to that in FeAl and Fe3Al was proposed as superplastic deformation mechanism in the large-grained TiAl alloy.