Hot deformation and dynamic α-globularization of a Ti-17 alloy: Consistent physical model

Ti-17 is exposed to microstructural modifications during thermomechanical treatment. In this work, we focus on the characterisation, analysis and modelling of the modifications during plastic deformation in the one phase and two phases domain. Hot compression tests are carried out between 810 °C and 970 °C and at 0.001 s⁻¹ to 10 s⁻¹ up to 0.85 strain. Metallographic observations and quantifications are done using SEM-EBSD. A physically-based model is developed to describe the deformation mechanisms: dynamic recovery, followed by continuous dynamic recrystallisation, and dynamic globularization of the α-phase. Flow stresses, dislocation densities, and sizes of both phases are predicted as a function of strain rate and temperature for different starting microstructures. The thickness and aspect ratio of the α-phase is predicted as well as the globularization fraction. The flow softening in the α + β domain is attributed to a change in the load transfer mechanism between α and β-phases from isostrain to isostress due to the dynamic globularization of the α-phase. High strain rates promote the formation of finer subgrains of β and less globularization of α-phase. Moreover, cDRX starts at larger strains in the β-domain and is more advanced already at moderate strains for the deformation in the α + β domain.