Phase Transformation and Dynamic Recrystallization Behavior of Forged Beta Gamma Tial Alloy in Variable Thermomechanical Conditions

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 strain and holding time. 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