The precipitation behavior and microstructural evolution of α phase in a novel metastable β-type Ti alloy, Ti-10Mo-6Zr-4Sn-3Nb (wt.%), during isothermal compression are investigated in this study through the use of SEM (scanning electron microscope), TEM (transmission electron microscope) (HRTEM) (high-resolution transmission electron microscopy) and EBSD techniques. The results show that some finer α precipitates are randomly distributed within the β matrix during hot deformation. The morphological characteristics of α precipitates are distinctly different from those of α precipitates during the same solution-plus-aging treatment. The volume fraction of α precipitate gradually increases with increased true strain. A large proportion of precipitated α phases are prone to be precipitated at HAGBs (high-angle grain boundaries) and LAGBs (low-angle grain boundaries) during isothermal deformation. On the contrary, only a small amount of spherical α phases is precipitated within the β grain. The crystallographic orientation relationships for most spherical α precipitates formed at LAGBs and within the β grains are similar, whereas the crystallographic orientation relationships for α precipitates at grain boundaries are significantly different. The precipitation behavior of α phase in the Ti-B12 alloy during hot compression is considerably influenced by the density of dislocations.

The dynamic spheroidization mechanism and its orientation dependence in Ti-6Al-2Mo-2V-1Fe alloys during subtransus hot deformation were studied in this work. For this purpose, hot compression tests were carried out at temperatures of 780–880 °C, with strain rates of 0.001–0.1 s⁻¹. Based on SEM, EBSD and TEM characterization, the results showed that the aspect ratio of the α phase decreased with increasing deformation temperatures and decreasing strain rates. At 880 °C/0.001 s⁻¹, the aspect ratio of the α phase was the smallest at 2.05. The proportion of HAGBs decreased with increasing temperatures and strain rates, which was different from the trend of the spheroidization; this indicated that the formation of HAGBs was not necessary for the spheroidization process. Furthermore, the formation of the α/α interface was related to the evolution of dislocations and twin boundaries at high (880 °C) and low temperatures (780 °C), respectively. Moreover, the dependence of lamellar spheroidization on the crystallographic orientation tilt from the compression direction (θ) was clarified: when θ was between 45° and 60°, both the prism slip and basal slip systems were activated together, which was more favorable for spheroidization. This study could provide guidance for titanium alloy process designs and microstructure regulation.

The α variant selection and microstructure evolution in a new metastable β titanium alloy TB17 were studied in depth by DTA, microhardness, XRD, SEM, and EBSD characterization methods. Under the rapid cooling rate conditions (150 °C/min–400 °C/min), only a very small amount of granular α_WM (α Widmanstatten precipitates within the grains) precipitated within the grains. The secondary α phase precipitated in the alloy changed from granular to fine needle-like at moderate cooling rates (15 °C/min–20 °C/min). When continuing to slow down the cooling rates (10 °C/min and 1 °C/min), the α_GB (α precipitates along the β grain boundaries), α_WGB (α Widmanstatten precipitates that developed from β grain boundaries or α_GB) and α_WM grew rapidly. Moreover, the continuous cooling transformation (CCT) diagram illustrated the effect of cooling rate on the β/α phase transition. EBSD analysis revealed that the variants selection of α near the original β grain boundary is mainly divided into three categories. (i) The double-BOR (Burgers orientation relationship) α_WGB colonies within neighboring β grains grow in different directions but have the same crystallographic orientation. (ii) The double-BOR α_WGB colonies within neighboring β grains have different growth directions and different crystallographic orientations. (iii) The double-BOR α_WGB colonies within the same grain have the same growth direction, but different crystallographic directions. And these double-BOR α_WGB colonies correspond to two variants of the given {0001}α//{110}β.

Three types of solution treatment and aging were designed to reveal the α’ decomposition and its effect on the mechanical properties of near-α Ti-80 alloy, as follows: solution at 970 °C then quenching (ST), ST + aging at 600 °C for 5 h (STA-1), and ST + aging 600 °C for 24 h (STA-2). The results show that the microstructures of the ST samples were mainly composed of equiaxed α_p and acicular α’, with a large number of dislocations confirmed by the KAM results. After subsequent aging for 5 h, α’ decomposed into acicular fine α_s and nano-β (intergranular β, intragranular β) in the STA-1 specimen, which obstructed dislocation motion during deformation, resulting in the STA-1 specimen exhibiting the most excellent yield strength (1012 MPa) and maintaining sufficient elongation (8.1%) compared with the ST (898 MPa) and STA-2 (871 MPa) samples. By further extending the aging time to 24 h, the size of acicular α_s and nano-β gradually increased while the density of dislocations decreased, which resulted in a decrease in strength and an increase in plasticity. Based on this, a microstructures–properties correlation model was proposed. This study provides a new method for strength–plasticity matching of near-α titanium alloys through α’ decomposition to acicular α_s+nano-β.

In this paper, the dependence of dynamic recrystallization (DRX) and post-dynamic recrystallization (PDRX) of TC18 alloy on strain rate within the range of 0.001 s⁻¹~1 s⁻¹ was investigated through isothermal compression and subsequent annealing in the single-phase region. Electron backscatter diffraction (EBSD) characterization was employed to quantify microstructure evolution and to reveal the recrystallization mechanism. At the thermo-deformation stage, the DRX fraction does not exceed 10% at different strain rates, due to the high stacking fault energy of the β phase. During the subsequent annealing process, the total recrystallization fraction increases from 10.5% to 79.6% with the strain rate increasing from 0.001 s⁻¹ to 1 s⁻¹. The variations in the geometrically necessary dislocation (GND) density before and after annealing exhibit a significant discrepancy with the increasing strain rate, indicating that the GND density is a key factor affecting the PDRX rate. The PDRX mechanisms, namely meta-dynamic recrystallization (MDRX), continuous static recrystallization (CSRX) and discontinuous static recrystallization (DSRX), were also revealed during the annealing process. A new kinetic model coupling DRX and PDRX was proposed to further describe the correlation between recrystallization and the strain rate during continuous deformation and annealing. This new model facilitates the prediction of recrystallization fraction during isothermal deformation and annealing of titanium alloys.

The β grain size in titanium alloys during industrial forging is critical for balancing toughness, cost-effectiveness, and processability. To address the industrial challenge of high cost and difficulty in refining β grains to the tens of micrometers scale, this study investigates the feasibility of achieving a superior strength–ductility balance in TC18 alloy with near-industrial coarse β grains (296~857 μm) under room temperature tension. A pronounced inverse correlation is observed between β grain size and both strength and ductility. The yield strength–grain size relationship follows the Hall–Petch effect, while the anomalous increase in ductility for fine-grained specimens is attributed to three factors. First, smaller grains provide a higher grain boundary density, promoting stress redistribution and mitigating stress concentrations. Second, more uniform stress distribution induces thinner, denser kink bands that enhance plasticity. Third, strain-induced martensite evolves from discrete nanoscale particles to discontinuous lines and ultimately coalesces into continuous planar bands along the (112)β and (110)β planes. This phase transformation, which initiates below a critical grain size of ~500 μm, further alleviates stress concentrations towards slip bands and contributes to dynamic work hardening. The findings demonstrate that coordinated deformation mechanisms enable excellent mechanical performance even in coarse-grained microstructures, providing a practical pathway for optimizing industrial-grade titanium alloys.