In this study, isothermal compression tests of TB18 titanium alloy were conducted using a Gleeble 3800 thermomechanical simulator for temperatures ranging from 650 to 880 °C and strain rates ranging from 0.001 to 10 s−1, with a constant height reduction of 60%, to investigate the dynamic softening mechanisms and hot workability of TB18 alloy. The results showed that the flow stress significantly decreased with an increasing deformation temperature and decreasing strain rate, which was affected by the competition between work hardening and dynamic softening. The hyperbolic sine Arrhenius-type constitutive equation was established, and the deformation activation energy was calculated to be 303.91 kJ·mol−1 in the (α + β) phase zone and 212.813 kJ·mol−1 in the β phase zone. The processing map constructed at a true strain of 0.9 exhibited stability and instability regions under the tested deformation conditions. The microstructure characteristics demonstrated that in the stability region, the dominant restoration and flow-softening mechanisms were the dynamic recovery of β phase and dynamic globularization of α grains below transus temperature, as well as the dynamic recovery and continuous dynamic recrystallization of β grains above transus temperature. In the instability region, the dynamic softening mechanism was flow localization in the form of a shear band and a deformation band caused by adiabatic heating.

In the present work, the hot deformation behavior of TB18 titanium alloy was investigated by isothermal hot compression tests with temperatures from 650 to 880°C and strain rates from 0.001 to 10 s−1. The flow curves after friction and temperature correction show that the peak stress decreased with the temperature increase and the strain rate decrease. Three typical characteristics of flow behavior indicate the dynamic softening behavior during hot deformation. At a strain rate of 0.001∼0.01 s−1, the flow stress continues to decrease as the strain rate increases after the flow stress reaches the peak stress; the flow softening mechanism is dynamic recovery and dynamic recrystallization at a lower temperature and dynamic recrystallization at a higher temperature. The discontinuous yielding phenomenon could be seen at a strain rate of 1 s−1, dynamic recrystallization took place in the β single-phase zone, and flow localization bands were observed in the α + β two-phase zone. At a higher strain rate of 10 s−1, the flow instabilities were referred to as the occurrence of flow localization by adiabatic heat. Constitutive equation considering the compensation of strain was also established, and the results show high accuracy to predict the flow stress with the correlation coefficient of 99.2% and the AARE of 6.1%, respectively.

In the present study, microstructure characteristic and texture evolution of TB18 titanium alloy were studied by isothermal hot compression under different strain with strain rate of 0.001 s ¹1 and 0.1 s ¹1 in the ¢ phase zone. Electron Back-Scattered Diffraction (EBSD) and XRD were used to characterize the microstructure and macrotexture. Microstructure characteristic demonstrated that coarse ¢ grains flatten and elongated to the compression direction as strain increased. The dynamic recrystallization mechanism is continuous dynamic recrystallization (CDRX) at lower strain rate, while discontinuous dynamic recrystallization (DDRX) at higher strain rate. The deformation is strongly dependent on the dislocation density, geometrically necessary dislocations density increased with strain at different strain rate. The limited faction of dynamic recrystallization has little effect on texture evolution, and the texture evolution is ascribed to the strain induced boundary migration and activity of slip system. At lower strain rate, the lower activity of {110}©111ª slip system and higher activity of {123}©111ª enhanced the ©110ª texture and weakened the ©111ª texture; at higher strain rate, the higher activity of {123}©111ª slip system modified the ©111ª ¢ texture intensity and enhances the ©110ª texture.