Abstract: Traditional titanium alloys with microstructural inhomogeneities presented lower workability due to limited heterogeneous deformation compatibility, particularly the intrinsic α precipitates easily induced the interfacial stress concentration and strain incompatibility, resulting in severe fracture. Good workability remains the hot topic in high-strength titanium alloys. Here, this work deeply reveals the activation of multi-slip systems and dual-functional α phases that enhance the workability, including {110}<111>, {112}<111>, and {123}<111>, and discusses the effect of α phases on the double-softening stages in the novel Ti-1500 G alloy. The dual-functional α phases could synergistically serve both as dislocation barriers and softening agents. The activation of intragranular multiple slips, dominated by dynamic recovery, promote the dynamic softening. This accelerates the orientational transition from sub-grains to continuous dynamic recrystallization (CDRX) grains. The presence of α phases hinders the migration of dislocations and sub-grain boundaries (sub-GBs). This obstruction can lead to the bulging of primary β grain boundaries (β-GBs), facilitating the formation of discontinuous DRX (DDRX) grains separated from the primary β matrix. Furthermore, pinned sub-GBs by α phases promote the development of CDRX. Notably, we demonstrate that these α phases exert a distinctive influence on DRX behavior by activating stress-induced dynamic phase transformation (DPT) from α to β, which enhances DRX grain formation. Additionally, complex interactions between the α phases and dislocation motion mobilize mechanisms such as α spheroidization and particle-stimulated nucleation (PSN), further enhancing the softening effect. These α phases exhibit a dual functional role. Their interaction interfaces transition from coherent α/β boundaries with low lattice misfit to incoherent interfaces characterized by local strain and high-density stacking faults, governed by interface-controlled mechanisms. This new multiple softening integration shows an efficient approach for improving the hot-workability of ultrahigh-strength titanium alloy components at large industrial scales.

Key words: Ultrahigh-strength β titanium alloy, Hot deformation, Dynamic mechanical response, Multiple dislocation slip systems, Stress-induced phase transformation