Research on flow stress behavior, constitutive modeling, processing mapping and microstructure evolution of as-cast Ti-6Mo-4Al-4Zr-3Nb-2Cr-1Fe alloy during hot deformation in (α+β) region

To investigate the hot deformation behavior and the microstructure evolution of Ti644321 alloy in α+β region, the hot compression tests were conducted within the temperature range from 720 to 810 °C and strain rate from 0.001 to 1 s⁻¹. The as-cast Ti alloy mainly consists of coarse equiaxed β phases. During the thermal deformation of alloys in the (α+β) region, lots of α phase precipitates. At lower strain rates, the microstructure consists of fine spherical or short rod-shaped α phase embedded within the β matrix. This indicates that under thermal deformation conditions, the α phase undergoes spheroidization, which is caused by the wedging of β phase. At high strain rates, dynamic recrystallization is difficult to occur due to insufficient time consumption or sustained generation of dislocations. With the increase of deformation temperature, the number of primary α phases decreases, and the size also slightly increases. The relationship between microstructural characteristics and power dissipation efficiency (η) is established through the analysis of the hot processing map and corroborated by microstructural observations. Flow localizations and lamellar kinking of α phase appear in the instability region. The optimal processing parameters for Ti644321 alloy are in the medium temperature (740–770 °C) and the low strain rate (0.001–0.03 s⁻¹). The dynamic recovery of β phase and the spheroidization of α phase are the main softening mechanisms in this area.