Temperature dependent dynamic restoration mechanisms in Ti-6Al-4V during isothermal deformation across α + β phase regions

Optimizing the α + β microstructure of Ti-6Al-4V alloy through thermomechanical processing is challenging due to the heterogeneity between the crystallographic differences of the two phases, and the bimodal characteristics of α. This study investigates the intricate microstructural evolution and formation of equiaxed α and β phases during isothermal compression of Ti-6Al-4V alloy across near-α (850 °C), α + β (900 and 925 °C), and near-β (950 °C) temperature regimes. Through systematic analysis, the dominant dynamic restoration mechanisms at varying deformation temperatures and strain levels were comprehensively analyzed. The findings reveal that deformation temperature and strain level significantly influence restoration mechanisms: α grain dynamic recrystallization (DRX) dominates flow softening at near-α, while dynamic phase transformation (DPT) occurs up to a critical strain, and the β grain undergoes a transition from dominant dynamic recovery (DRV) and coarsening to continuous DRX (CDRX), promoting grain refinement and reducing flow softening at near-β. In α+β regions, restoration mechanisms depend on proximity to near-α or near-β conditions, with slip system activation playing a key role in dislocation movement and reverse DPT. These findings provide new insights into the interplay of DPT, DRX, and DRV, as well as the influence of temperature and strain on phase stability and slip system activation, offering a framework for designing thermomechanical processing parameters to achieve tailored microstructures and enhanced mechanical properties in Ti-6Al-4V.