Trifunctionally strengthening, ductilizing and toughening of TB18 metastable β-titanium alloy through heterogeneous α precipitation

Advanced high-performance titanium (Ti) alloys are progressively demanded in aerospace applications, yet enhancing strength through α precipitation typically compromise ductility and toughness, known as the ‘strength-ductility-toughness’ trade-off. In this study, we exploit a counterintuitive strategy based on unsaturated precipitation to construct a heterogeneous α microstructure, enabling trifunctionally strengthening, ductilizing and toughening of industrial TB18 large-scale alloy bars by simply shortening aging duration during conventional heat treatment. Mechanical testing reveals that this heterogeneous structure achieves an exceptional combination of high strength of ∼1346 MPa, decent ductility of ∼8.3 %, and Charpy impact toughness of ∼19.3 J, not only matching the strength of its homogeneous counterpart, but also exhibiting a 22.1% increase in ductility and a 30% improvement in Charpy impact energy. The coexistence of precipitation zones (PZs) and precipitation-free zones (PFZs) generates significant back stress during tension, which enhances the strength of the alloy by compensating for its inferior precipitation strengthening. Concurrently, the soft PFZs undergo substantial plastic deformation, leading to the formation of high-density deformation bands (DBs) that suppress strain localization and promote deformation within the PZs, thereby sustaining a high work hardening rate and improving ductility. Furthermore, the PFZs effectively absorb plastic deformation and expend the plastic affected zones (PAZs), which delays crack initiation near the V-notch and thus improves impact toughness of the TB18 alloy. These findings present an industrially feasible strategy for age-hardening structural materials to achieve synergetic high mechanical performance.