Competition between dynamic softening and hardening of Ti-6Al-4V alloy during hot deformation: Multi-mechanism coupling

Thermomechanical processing (TMP) is an effective approach for precisely tailoring high-performance titanium alloy components for aerospace applications. The theoretical construction of the complex correlation between microstructure evolution and deformation mechanisms of the TC4-DT alloy under thermos-mechanical coupling in the (α+β) dual-phase region still needs to be perfected. In this study, the thermal deformation behavior of TC4-DT alloy is deeply analyzed, a correlation framework linking multi-morphological microstructure evolution with microscopic deformation mechanisms is constructed under the influence of deformation parameters. The gradients of deformation temperature and strain rate modulate the competition and balance between softening and hardening mechanisms, thereby significantly affecting microstructural morphology and homogeneity. The α phase dominates the hot deformation mechanism in the (α+β) phase region, while the microstructural evolution of the β phase proceeds passively in response to the microstructural regulation of the α phase. A correlation network is established through the synergistic operation of multiple dynamic softening processes, work hardening, α→β dynamic phase transformation (DPT), dynamic dislocation evolution, and non-equilibrium transformation of β phase based on the multi-morphological α phase and deformation characteristics. The differences in grain boundary (GB) evolution pathways are manifested in the role of GB migration during dynamic spheroidization (DS), continuous dynamic recrystallization (CDRX), and discontinuous dynamic recrystallization (DDRX). In the upper part of the (α+β) dual-phase region, an “α interface transition phase” exhibiting characteristic crystallographic orientation and elemental distribution is formed through the interaction between the DPT and DRX mechanisms. The comprehensive analysis of the thermal deformation behavior of the as-cast TC4-DT alloy in the (α+β) dual-phase region and the elucidation of microstructure evolution rules are of great value for the synergistic optimization of microstructure and mechanical properties during hot processing.