Crystallographic orientation related dynamic recrystallization behavior and its impact on texture development of high-temperature α phase in TiAl alloy

Profound and comprehensive knowledge on deformation behavior of the parent high-temperature α phase in TiAl alloys during thermomechanical processing will provide a guidance for microstructural and mechanical property improvement of the resultant (α2+γ) lamellar structure. In this work, the deformation characteristics and continuous dynamic recrystallization (CDRX) process, as well as microstructure and texture development of the high-temperature α phase are thoroughly studied. It is demonstrated that the crystallographic orientations of the initial α grains play an important role in deformation mechanism and CDRX progress. For soft α grains, CDRX is completed at a relatively small macroscopic strain by intragranular dislocation slip. The hard α grains demonstrate two ways: (ⅰ) grains with < 0001 > //LD, in which dislocation accumulation is only assisted by local strain accommodation with the neighboring α grains from boundary regions; (ⅱ) grains with < 11̅0 > //LD, in which dislocation accumulation is achieved by kinking through basal slip and dislocation slip near boundary regions from incompatible local strain. These hard α grains require relatively large strain to accumulate sufficient dislocations for CDRX. The strain-resolved contribution of deformation (hardening) and CDRX (softening) result in the specific flow stress state composed of a slow work hardening stage, a long work softening stage and a belated steady stage. The texture evolution is mainly induced by dislocation slip. The crystallographic orientations of newly CDRXed grains are largely inherited from those of the parents. With the deformation, the typical tilted basal fiber texture is developed in both the retained coarse α and the formed CDRXed α grains.