Extended post-uniform elongation during warm tensile deformation of Ti–6Al–4V: roles of deformation-assisted martensite reversion and lamellar β continuity/refinement

Two α′-containing microstructures, a fully martensitic (α′) structure and a dual-phase α+α′ structure (≈45–50% α′), were generated in Ti-6Al-4V by solution-treatment above and below the β-transus, followed by water quenching. Their tensile responses at 600°C/0.001s -1 were subsequently evaluated, showing extremely low post-UTS softening rate and substantial post-uniform elongation (18.4±1.5% for the dual-phase α+α′ microstructure and 16.5±1.2% for the fully α′ condition), which is attributed to deformation-assisted reverse transformation of α′ during warm tension. In the α+α′ starting condition, reversion manifested as α intergrowth within α′-laths and β formation that coarsened from discrete particles to rods and, locally, continuous layers, yielding a refined bimodal α/β architecture. The greater extent and continuity of β in the α+α′ condition, relative to the fully α′ state, correlate with its superior post-uniform elongation under identical thermomechanical loading. The observed reversion kinetics and β morphology are consistent with differences in the starting-state α′ chemistry. This work reveals, for the first time, how the initial α′ chemistry (Al/V partitioning) directly controls the kinetics, morphology, and continuity of deformation-assisted reverse transformation during warm tension. We further demonstrate that applied stress substantially lowers the effective α′ to α+β transformation temperature, enabling extensive martensite decomposition at 600°C, far below the stress-free reversion temperature. These mechanistic insights establish a direct link between α′ chemistry, β-phase topology, and post-uniform ductility in Ti-6Al-4V. Accordingly, the α+α′ condition shows more extensive reversion and greater β continuity, correlating with its higher post-uniform elongation, whereas the fully α′ condition exhibits limited reversion with discrete/rod-like β.