Evolution of microstructure and texture during recrystallization of the cold-swaged Ti-Nb-Ta-Zr-O alloy

The deformed microstructure and evolution of microstructure and texture during recrystallization of the cold-swaged multifunctional Ti-23Nb-0.7Ta-2Zr-1.2O (TNTZO, at. pct) alloy were investigated by optical microscope, electron backscatter diffraction, and transmission electron microscope. This alloy has been reported, by Saito et al., to possess a specific dislocation-free plastic deformation mechanism. In this study, the results show a curly grain or swirled structure and a pronounced fibrous < 110 > texture along the swaging axis in the cold-swaged TNTZO alloy. The normal to the swirled grain surface is near < 001 > in the cross section of the rod. This characteristic microstructure can be considered to arise from the plane strain deformation of the grains under applied stress, which is similar to that in ordinary bcc metals after heavily drawing or swaging. It is also shown that recovery involves the redistribution and partial annihilation of dislocations within the deformation bands, and recrystallization proceeds by a typical new grain nucleation-growth mechanism during annealing of the TNTZO alloy. The fibrous < 110 > deformation texture is gradually replaced by random orientations with increasing annealing time. Thus, it could be concluded that the TNTZO alloy deforms by the traditional dislocation glide on < 111 >{110}, {112}, or {123} slip systems, rather than the dislocation-free mechanism.