Microstructure and mechanical property correlation and property optimization of a near β titanium alloy Ti-7333

As a newly developed near β titanium alloy, knowledge on heat treatment associated microstructural evolution and its influence on mechanical properties has not yet been established for Ti-7333. Thus mechanical property potential of this alloy is not fully explored. In view of such a situation, a detailed study on heat treatment dependent mechanical property evolution and its correlation with microstructure was made in the present work with an aim to explore the optimum strength-ductility combination. The results show that the optimal combination of strength and ductility of Ti-7333 is realized with a mixed microstructure possessing globular/ellipsoidal α_p (about 3% in volume fraction and about 1 μm in average particle size) and fine lenticular/acicular α_s (about 30 nm in width and about 500 nm in length) distributed dispersedly in the β matrix (about several microns in average grain size). With such a microstructure, an ultrahigh tensile strength (over 1400 MPa) with a reasonable ductility (over 10% in elongation) can be achieved. The corresponding heat treatment procedure is composed of a subtransus solution treatment at 820 °C for 50 min with air cooling plus an aging at 520 °C/540 °C for 6 h with air cooling. Compared with some other high strength Ti alloys (Ti-5553, Ti-1023, VT22, etc.), the newly developed Ti-7333 exhibits not only a more excellent strength-ductility combination but a more flexible heat treatment operation, rendering it more competitive. The results of the present work provide practical information for process optimization and to enrich the database of Ti alloys.