Unlocking High Ductility in a High-Strength Titanium Alloy via Cooling-Rate-Controlled Dual-Phase Connectivity

The strength–ductility trade-off limits the wider application of high-strength titanium alloys in aerospace. Here, a new Ti-3.7Al-3V-3Fe-1.7Mo-0.5Cr alloy is designed based on d-electron alloy design theory and molybdenum equivalence, and the dual-phase microstructure is tailored by varying the cooling rate after solution treatment, which governs both the phase fraction and the spatial connectivity of the primary α (αp) and β phases. In the furnace-cooled (FC) condition, the αp phase exhibits the highest fraction (76%) and a continuous network with isolated β islands, whereas higher cooling rates (AC and WQ) yield lower fractions (50% and 38%) and a continuous β matrix, confirming that decreasing cooling rate promotes αp connectivity and β isolation. Consequently, the FC sample achieves a tensile strength of 1250 MPa and a total elongation of 18.4%, significantly higher than those of the AC (14.0%) and WQ (10.0%) samples. This interconnected architecture enhances dislocation storage and work hardening, while enabling effective load transfer and strain compatibility between phases, thereby suppressing strain localization and interface debonding. In situ SEM observations further confirm that high-density αp/β interfaces, crack deflection, and deformation twinning also play a key role in enhancing damage tolerance. These findings identify phase connectivity as a key microstructural parameter for overcoming the strength–ductility trade-off in α/β titanium alloys.