Phase transformation and dynamic recrystallization behavior of forged beta gamma TiAl alloy in variable thermomechanical conditions
Tengfei Ma, Siying Li, Yupeng Wang, Xiaohong Wang, Duo Dong, Dongdong Zhu
Abstract
Hot workability of a forged beta gamma Ti–44Al–6Nb–1Mo-0.3 (B, Y, La, Ce) alloy was studied on a Gleeble-3800 thermal simulation machine under variable conditions. The flow stress and microstructural evolution were analyzed carefully after deformed at variable conditions (deformed to different strains holding 30s then continue to deform to ε = 0.6; deformed to ε = 0.2 holding 5s, 10s, 60s, 120s respectively, and then continue to deform to ε = 0.6). All true stress–strain curves showed typical work hardening and flow softening features indicating that dynamic recrystallization (DRX) was the dominating softening mechanism under variable hot deformation conditions. Lamellar colonies transformed into γ phase through DRX under normal continuous deformation conditions, which was because that the γ-DRX and B2-DRX were triggered at all stage. However, the γ→α phase transformation (PT) was observed when the discontinuous two-step deformation was carried out. The deformation residual stress was significantly reduced with the appearance and growth of α phase. The results show that uniform equiaxed DRX grains can be obtained by increasing of strain and holding time at the first stage during two-step hot deformation.