Microstructure, texture, and superplastic properties of an intermetallic Ti-45.2Al-3.5(Nb,Cr,B) alloy subjected to deformation and rolling below the eutectoid temperature

The effect of two-stage hot deformation by compression at temperatures first above and then below the eutectoid temperature (T_e ≈ 1125°C) and by subsequent rolling below the eutectoid temperature on the evolution of the microstructure and texture of the as-cast intermetallic Ti-45.2Al-3.5(Nb,Cr,B) alloy was studied. Owing to the development of recrystallization and spheroidization, this treatment leads to the formation of a uniform fine-grained microstructure in a sheet; the disappearance of the sharp casting-induced texture; and the formation of a weakly pronounced axial texture, which transforms into a rather sharp {010}«100» texture after rolling. Tensile tests of samples cut along and perpendicular to the rolling direction exhibit a high ductility of the sheet material at temperatures of 900-1100°C; however, at 1000-1100°C, the superplastic characteristics of the sheet are found to be isotropic. These results suggest a new approach to choosing the composition and working of intermetallic γ-Ti Al + α₂-Ti₃Al-based alloys. This approach includes the use of alloys completely solidified with the formation of the β phase and two-stage working, first, in the α + γ field and, then, in the α₂ + γ phase field. This working provides the most effective refining of the ingot structure and the possibility of rolling at temperatures below the eutectoid temperature.