High-strength metastable β titanium alloys are promising structural materials to be used in aviation industries. In order to achieve a high strength level, solid solution treatment within β region and subsequent low-temperature aging are usually necessary to obtain fine α precipitates. The selection of the aging temperature is considered critical to the mechanical performance of metastable β titanium alloys. In this work, we investigated the effect of aging temperature on the microscopic structure and mechanical properties of a novel type of titanium alloy TB18 (Ti-4.5Al-5Mo-5V-6Cr-1Nb). A series of aging treatments were conducted on TB18 specimens at 510 °C, 520 °C, 530 °C, and 540 °C after the solid solution treatment at 870 °C. On the basis of the systematic results of scanning electron microscope and transmission electron microscope, the behavior of the α phases affected by the varied aging temperatures were studied. As the aging temperature rose, the grain width of the α phase increased from 60 nm (510 °C) to 140 nm (540 °C). For the TB18 samples aged at 510 °C and 540 °C, the tensile strength/yield strength/impact toughness values were 1365 ± 3 MPa/1260 ± 0.9 MPa/26.5 ± 1.2 J/cm² and 1240 ± 0.9 MPa/1138 ± 0.8 MPa/36.2 ± 1.3 J/cm², respectively. As a result, the tensile performance and the grain width of the α phase agreed well with the Hall–Petch relationship. This work offers valuable support for both theoretical analyses and the heat treatment strategies on the novel TB18 titanium alloy.

TB18 is a newly developed high-strength metastable β-titanium alloy, commonly used in aerospace structural materials, which demands high mechanical performance. By altering the alloy’s microstructure, heat treatment can affect its mechanical characteristics. The alloy was solution treated for one to four hours at 870 °C in order to examine the impact of solution treatment duration. Using X-ray diffraction (XRD) and scanning electron microscopy (SEM), the effects of solution treatment time on the β-phase grain size and its effect on stress distribution during tensile testing were examined. The findings showed that stress concentration during the tensile process was successfully decreased by refining the β-phase grain size. Sample solutions treated for two hours at 870 °C were then aged at various temperatures (510 °C, 520 °C, 530 °C, and 540 °C) to examine the impact of aging temperature. While the mass proportion of the α-phase first climbed and subsequently declined, reaching its maximum at 530 °C, the size of the α-phase increased monotonically as the aging temperature increased. The varies of mass fraction is associated with how the aging temperature affects α-phase nucleation. Tensile studies on TB18 alloy aged at various temperatures showed that while the alloy’s ductility reduced, its strength increased as the aging temperature rose. The Hall-Petch relationship explains this tendency.

High-cycle fatigue (HCF) is a critical property of metastable β Ti alloys in aerospace applications. In this work, the HCF behavior and corresponding microscale deformation mechanisms of a metastable Ti-5Al-5Mo-5V-1Cr-1Fe (Ti55511) alloy with a basket-weave structure were investigated. HCF and its deformation mechanisms of a Ti55511 alloy were systematically studied in the deformed condition by using a scanning electron microscope (SEM), a transmission electron microscope (TEM), and electron backscatter diffraction (EBSD). It was found that the Ti55511 alloy exhibited an excellent HCF strength (10⁷ cycles, K_t = 1, R = 0.06) of 738 MPa. The fractographic investigation demonstrated that fatigue striations and secondary cracks were the main features in the crack initiation zone. Dislocation analyses indicated that the HCF deformation of the basket-weave microstructure was mainly affected by the dislocation slipping of the primary α (α_p) phase. In addition, the dislocation pile-up at the α_p/β_trans interface led to crack initiation. EBSD analyses indicated that the prismatic <a> type slip system of the α_p phase was preferentially activated during the HCF deformation process of the Ti55511 alloy, followed by the basal <a> type and pyramid <a> type systems.

TiAl alloys are characterized by low density, high strength, and excellent mechanical properties at elevated temperatures, making them highly suitable for high-temperature applications. However, their poor workability and limited ductility at ambient temperature restrict their broader use. In this study, a Ti-43Al-9V-0.3Y alloy with a fine-grained duplex microstructure was fabricated via a two-step forging process at 1220 °C. The alloy showed an average room-temperature tensile strength of 822 MPa and an elongation of 1.32%. Importantly, it demonstrated remarkable low-temperature superplasticity, with elongations reaching 151% at 800 °C and 392% at 900 °C. The fine-grained duplex microstructure forms due to the combined effects of discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) of γ grains, as well as the β₀ → γ phase transformation during forging, where γ grains grow by consuming the β0 phase. During tensile deformation at 800 °C, low-temperature superplasticity is achieved through the twinning behavior of γ grains, DDRX, CDRX, and the β₀ → γ phase transformation. This microstructural design and processing strategy provides a novel and promising approach to addressing the significant engineering challenges associated with the poor hot workability of TiAl alloys.