It is well known that adding elements, especially β-Ti stabilizers, are holding a significant effect on titanium alloy strength due to the solution and precipitate strengthening mechanisms. In order to reveal the Fe strengthening mechanism in titanium, this study investigate the effect of Fe on the stability of β-Ti and the phase transition between α, β and ω phase with first-principle calculations. According to our study, Fe is a strong β-Ti phase stabilizer could owe to the 3d orbital into e_g and t_2g states which results in strong hybridization between Fe-d orbital and Ti-d orbital. The phase transition from ω to β or from α to β becomes easier for Fe-doped Ti compared to pure titanium. Based on our results, it is found that one added Fe atom can lead the phase transition (ω → β) of at least nine titanium atoms, which further proves that Fe has a strong stabilizing effect on β-Ti phase. This result provides a solid guide for the future design of high-strength titanium with the addition of Fe.

A self-designed Ti-35421 (Ti-3Al-5Mo-4Cr-2Zr-1Fe wt%) titanium alloy is a new type of low-cost high strength titanium alloy. In order to understand the hot deformation behavior of Ti-35421 alloy, isothermal compression tests were carried out under a deformation temperature range of 750–930 °C with a strain rate range of 0.01–10 s⁻¹ in this study. Electron backscatter diffraction (EBSD) was used to characterize the microstructure prior to and post hot deformation. The results show that the stress–strain curves have obvious yielding behavior at a high strain rate (>0.1 s⁻¹). As the deformation temperature increases and the strain rate decreases, the α phase content gradually decreases in the α + β phase region. Meanwhile, spheroidization and precipitation of α phase are prone to occur in the α + β phase region. From the EBSD analysis, the volume fraction of recrystallized grains was very low, so dynamic recovery (DRV) is the dominant deformation mechanism of Ti-35421 alloy. In addition to DRV, Ti-35421 alloy is more likely to occur in continuous dynamic recrystallization (CDRX) than discontinuous dynamic recrystallization (DDRX).

In order to discern the effect of rare earth element Er addition on grain refinement of the most widely used titanium alloy Ti6Al4V, new erbium modified Ti6Al4V alloys with compositions of Ti6Al4V-xEr (x = 0, 0.2, 0.4, 0.6 wt %) were developed and investigated for their microstructural characteristics and mechanical properties in comparison with their unmodified baseline alloy. Microstructural examinations revealed that, by adding Er, (1) the microstructure primarily retained a two-phase structure consisting of α and β, (2) remarkable grain refining occurred, and (3) some Er₂O₃ and Al₂Er disperses were formed largely around the β phase and near the grain boundaries. Mechanical property measurements evidenced an overall enhancement under tension and hardness tests. An increase in both strength and plasticity with increasing Er content was obtained but followed by a drop, while a gradual monotonous improvement in hardness was achieved. The Ti6Al4V-0.2Er alloy exhibits optimal mechanical properties.

In order to reduce the cost of titanium alloys, a novel low-cost Ti-3Al-5Mo-4Cr-2Zr-1Fe (Ti-35421) titanium alloy was developed. The influence of heat treatment on the microstructure characteristics and mechanical properties of the new alloy was investigated. The results showed that the microstructure of Ti-35421 alloy consists of a lamina primary α phase and a β phase after the solution treatment at the α + β region. After aging treatment, the secondary α phase precipitates in the β matrix. The precipitation of the secondary α phase is closely related to heat treatment parameters—the volume fraction and size of the secondary α phase increase when increasing the solution temperature or aging time. At the same solution temperature and aging time, the secondary α phase became coarser, and the fraction decreased with increasing aging temperature. When Ti-35421 alloy was solution-treated at the α + β region for 1 h with aging surpassing 8 h, the tensile strength, yield strength, elongation and reduction of the area were achieved in a range of 1172.7–1459.0 MPa, 1135.1–1355.5 MPa, 5.2–11.8%, and 7.5–32.5%, respectively. The novel low-cost Ti-35421 alloy maintains mechanical properties and reduces the cost of materials compared with Ti-3Al-5Mo-5V-4Cr-2Zr (Ti-B19) alloy.

The isothermal hot compression behavior of new Ti–Fe–B (named as TF400) alloy was investigated in the temperature range of 750–950 °C and strain rate range from 0.01 to 10 s⁻¹ with the maximum height reduction of 60% by using a Gleeble 3800 thermal simulator. By considering the effect of strain via variable material parameters, a modified constitutive model was proposed to accurately predict the flow stress. The predicted results demonstrate that the flow stress decreases with the increase of temperature while it increases as the strain rate increases, in good agreement with the present experimental results. A mechanistic understanding of plastic deformation behavior in the TF400 alloys was developed by inspecting the microstructural characteristics prior to and after deformations. Dynamic recrystallization and dynamic transformation were found to be the dominant restoration mechanism during the hot deformation process.