Study on hot deformation behavior of as-cast Ti-5Al-5Mo-5 V-1Cr-1Fe titanium alloy in (α + β) phase region

Hot compression tests were carried out to investigate hot deformation behavior of as-cast Ti-5Al-5Mo-5 V-1Cr-1Fe titanium alloy in (α + β) phase region. A constitutive equation in the form of a power function was established, and the hot activation energy (Q) under different deformation conditions were discussed. The Q is not only affected by dynamic recrystallization (DRX) and dynamic recovery (DRV), but also by deformation conditions and microstructure evolution. The increase of temperature, the buckling of lamellar α phase and the increase of the strain rate cause the decrease of the Q. But the increase of volume fraction of the α phase and dynamic spheroidization of lamellar α phase result in increase of the Q. Therefore, the Q cannot be used to judge the appearance of DRX or DRV for hot deformation of as-cast Ti-5Al-5Mo-5 V-1Cr-1Fe titanium alloy in (α+β) phase region. For hot deformation of as-cast Ti-5Al-5Mo-5 V-1Cr-1Fe titanium alloy, the analysis result of Electron Backscattered Diffraction (EBSD) shows that the softening mechanism are dominated mainly by DRX at 750 °C/0.001 s−1, DRV and DRX at 800 °C/0.001 s−1 and DRV at 850 °C/0.001 s−1, respectively. The analysis result of the misorientation frequency shows that the elevated temperature inhibits the continuous dynamic recrystallization (CDRX) of the β phase but promotes the CDRX of the α phase. The straight separation is a more effective separation mechanism for the dynamic spheroidization of lamellar α phase. A further analysis shows that dynamic spheroidization of lamellar α phase is carried out by CDRX.