Hot working and geometric dynamic recrystallisation behaviour of a near-α titanium alloy with acicular microstructure

The hot working behaviour of near-α titanium alloy – TITAN 29A (equivalent to IMI 834) with an acicular starting microstructure was evaluated by carrying out hot compression tests over a range of temperatures (850–1060 °C) and strain rates (3×10−4–100/s). Using the flow curves, processing maps were generated to identify the safe processing window for the material. The material exhibits a deterministic domain between 920 and 1030 °C at low strain rates of 3×10−4–10−3/s where it undergoes geometric dynamic recrystallisation (GDRX) or globularisation of α lamellae. The initiation and evolution of globularisation was investigated using the flow curve analysis method. The work hardening rate (θ)–flow stress (σ) curve was used to estimate the critical strain (εc) required for initiation of globularisation and the saturation stress (σsat) for dynamic recovery (DRV). The recrystallised or globularised volume fraction (X) was estimated from the difference between the calculated DRV and experimental DRX curves. The estimated globularised volume fraction modelled using Avrami equation was found to match with the microstructural observations.