LAUSR

Abstract Powder metallurgy (PM) Ti–22Al–25Nb (at.%) alloy was prepared by spark plasma sintering under the conditions of 950 °C/80 MPa/10 min. Isothermal unidirectional compression experiments of the PM Ti–22Al–25Nb alloy were completed on the Gleeble-3500 thermal–mechanical simulator at temperature and strain rate ranges of 920 °C–1100 °C and 0.001–10s−1, respectively, and a total height reduction of 50%. The flow characteristics were described by the establishment of constitutive models belonging to the (α2+β/B2+O) three-phase (920 °C–980 °C) and (α2+B2) two-phase (1010 °C–1070 °C) regions. The three-dimensional (3D) hot processing maps regarding temperatures, strain rates and strains were obtained. The optimum processing parameters (temperature and strain rate) were determined. The microstructures of the deformed specimens under various conditions were analyzed to characterize the corresponding deformation mechanisms. Moreover, electron backscattered diffraction (EBSD) measurements were employed to study the mechanisms of DRX. It was determined that the deformation activation energies of the PM alloy corresponding to the (α2+β/B2+O) phase and (α2+B2) phase regions were 763.969 and 685.587 kJ mol−1, respectively. In addition, the results proved that the proposed 3D hot processing maps could reveal the deformation mechanism and microstructural evolution of the PM Ti–22Al–25Nb alloy during hot processing. The main softening mechanisms in the stability regions were dynamic recrystallization (DRX) and lamellar dynamic globularization. The deformation mechanisms of the unstable domains identified from the 3D instability maps were adiabatic shear bands and flow localization.