Hot deformation physical mechanisms and a unified constitutive model of a solid solution Ti55511 alloy deformed in the two-phase region

Abstract

In this work, the flow behaviors and microstructure evolution of a solid solution Ti55511 alloy deformed in the two-phase region are investigated by hot compression experiments. Subsequently, The spheroidization mechanisms of α phases and the refinement mechanism of β matrix are analyzed. The alloy exhibits obvious work hardening (WH) and flow softening characteristics. The secondary α phases gradually precipitate and spheroidize, while the primary α phases dissolute above the solution temperature or coarsen when the alloy is deformed below the solution temperature. Meanwhile, the β matrix undergoes continuous dynamic recrystallization (CDRX) behavior. The increase of deformation amounts promotes the simultaneous precipitation and spheroidization of lamellar α phases. Raising deformation temperature inhibits the precipitation and spheroidization of lamellar α phases. However, the maximum values of precipitated and spheroidized lamellar α phase occur at 0.01 s−1. Higher strain rate can promote CDRX of β matrix between 1003 and 1033 K, but inhibit it between 1063 and 1123 K, indicating differences in the dynamic recrystallization (DRX) mechanism at different temperature regions. A unified constitutive model based on physical mechanisms is proposed. The model takes into account both WH and grain boundary strengthening effects by coupling all parts of phases. Furthermore, the dynamic softening, including dynamic recovery (DRV), spheroidization of lamellar α phases, and CDRX of the β matrix, are also considered. Material constants are determined using a genetic algorithm (GA), and the experimental data align well with the predicted data. Finally, process parameters are optimized based on the model to achieve favorable microstructures.

Keywords

• Ti alloy
• Hot deformation
• Model
• Continuous dynamic recrystallization
• Spheroidization