Microstructural evolution during hot working of ti aluminide alloys: Influence of phase constitution and initial casting texture

The hot-working behavior of γ(TiAl)-based alloys was investigated in order to understand fundamental aspects of the evolution of the microstructure and to establish guidelines for advanced alloy design and processing. The investigations involved a wide range of Al compositions and are based on metallographic investigations of the deformed samples. Particular emphasis was placed on the effects of phase composition and casting texture. It was found that the behavior of dynamic recrystallization was significantly influenced by the Al content of the alloys. Under the same deformation conditions. dynamic recrystallization was fastest for alloys with nearly stoichiometric composition, whereas the recrystallization kinetics decreased for lower or higher Al contents. This result can be attributed to the effect of the Al concentration on the micromechanisms of deformation and diffusion as well as on the initial cast microstructure, which changed from fully lamellar to equiaxed near-γ microstructures by raising the Al content from 45 to 50 at. pct. Further, it was observed that the casting texture, i.e., the orientation of lamellae with respect to the deformation axis, significantly influenced the recrystallization behavior. In this respect, the development of shear bands due to kinking and bending of lamellae is concluded to play an important role in the recrystallization behavior and seems in general, to be a particular feature of the microstructural evolution of lamellar alloys on hot working. R.M. IMAYEV and V.M. IMAYEV, Senior Scientists, formerly with the GKSS Research Centre, Institute for Materials Research