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Direct aging of water-quenched metastable β-titanium alloys usually follows the sequence: rapid growth of ωiso and then slow transformation into α. To inhibit ωiso growth and promote α nucleation, 6% pre-deformation was introduced in Ti-10V-6Cu alloy before 500°C/60s aging. An ultrafast α-formation and a few α-free kink-bands are observed, indicating the alteration of the precipitation sequence. For α-nucleation without ωiso as the sites, it shows that O' nanodomains induced by stress accumulation around slip bands mediate the ultrafast nucleation of hcp-α structure, while dislocation pipe diffusion accelerates the necessary phase separation. This provides new insights into regulating precipitation kinetics of age-hardenable β-titanium alloys. [ABSTRACT FROM AUTHOR]

The Ti-7Al-1Mo-0.5V-0.1C alloy exhibits low density and good mechanical properties, and has potential applications in aerospace industries. The microstructure features of titanium alloys, such as the morphology and volume fraction of the primary α phase (αp) and the precipitation of the secondary α phase (αs), are sensitive to heat treatment parameters, especially the cooling rate from the two-phase region. In this work, we have characterized the precipitation of the secondary α phase and ordered α2 phase in Ti-7Al-1Mo-0.5V-0.1C alloy under water quenching, air cooling, and furnace cooling, and have investigated their effects on the mechanical properties of the Ti-7Al-1Mo-0.5V-0.1C alloy. The results show that the secondary α phase is significantly coarsened in the air-cooled alloy and leads to an increase in the strength but decrease in the ductility of the alloy, while the equiaxed microstructure generated in the furnace-cooled alloy, with no precipitation of the secondary α phase and an increase in size of the ordered α2 precipitation phase within the primary α phase, contributes to a further increase in ductility. [ABSTRACT FROM AUTHOR]

contraction twins that are commonly activated in α-titanium interact to each other and form three types of twin-twin junctions (, , TTJs) corresponding to the crystallography of six twin variants (i = 1,2, …, 6). We detected 243 TTJs in rolled pure α-titanium sheets. Electron backscatter diffraction analysis reveals that TTJs are profuse, 79.8% among three types while and TTJs take up 17.7 and 2.5%. Twin transmission does not occur. Consequently, boundaries associated with twin-twin interactions block twin propagation and influence twin growth. We explain structural features of TTJs according to the Schmid factor analysis and the reaction mechanism of twinning dislocations. The knowledge regarding TTJs provides insight for improving the predictive capability of meso/macro-scale crystal plasticity models for hexagonal metals. [ABSTRACT FROM AUTHOR]

By compression along the normal direction of rolled pure titanium sheet, primary { 11 2 ¯ 2 } type compression twins were observed, followed by secondary { 10 1 ¯ 2 } extension twins. The latter can be classified into three groups according to their misorientation with respect to the parent matrix grains: 41.34° around < 5 143 ¯ > (Group I), 48.44° around < 5 ¯ 50 3 ¯ > (Group II), and 87.85° around < 7 43 ¯ 0 > (Group III). The experimental observations revealed the following activity frequency of these groups: Group II is the most frequent followed by Group I, and only a few secondary twins can be seen for Group III. When the classical Schmid factor (SF) analysis is applied, the smallest activity is predicted for Group III, in agreement with the experimental observations. However, the SF based criterion fails to distinguish between Group I and Group II variants. Similarly, the twin-shear accommodation based variant selection model proposed earlier for titanium [Qin and Jonas, Acta Mater. 75 (2014) 198–211] is not effective because the easiest accommodation by prismatic slips favors Group III variants which are nearly absent in the experiment. A possible explanation can be based on the smallest inclination angle of the secondary twinning habit plane with respect to the primary one, proposed by Barnett et al. [Acta Mater. 56 (2008) 5–15] which clearly favors Group II. It cannot make distinction between variants of the same group but can predict the right variants if complemented with the SF criterion. In the present work a new approach is proposed in order to disclose the preference for Group II variant over Group I. It is based on the special twinning geometry that applies to Group II; the intersection line of the primary and secondary twin planes lies in an active prismatic plane in the primary twin. Consequently, dislocation reactions are possible for the selection of secondary twin variant in Group II. Namely, prismatic < a > type dislocations in the primary twin can produce partial dislocations that activate the corresponding secondary twin variant. Nevertheless, a further selection rule has to be applied to choose one out of the two possible Group II variants; this is based on the higher Schmid factor of the two secondary variants. By contrast, pyramidal dislocations would be required for the formation of Group I twins, which is less likely due to their relatively high critical resolved shear stress. [ABSTRACT FROM AUTHOR]

The accumulated dislocations are widely reported to be easily transmitted at low angle grain boundaries (GBs), while the associated mechanism at high angle GB needs further investigation. In this paper, the mechanisms associated with the interaction between GBs and 〈111〉 dislocations are investigated in Ti-5553 alloy with body-centered cubic structure. Slip traces transmitted into the neighboring grain or blocked by GBs are observed on the surface of the sample via secondary electron imaging. The corresponding slip system is determined with the combined use of EBSD-detected grain orientation and slip traces. The experimental results indicate that most slips can transfer at low angle GBs, while some slips can also transmit into the neighbor at high angle GBs. The misorientation angle of GBs is invalid to evaluate the mechanism induced by the interaction of dislocations with GBs. Crystallographic alignment-based analysis shows that slip transfer happens at GBs with favorable parameters of high geometric alignment (m ′) and low residual Burgers vector magnitude (|∆ b |). The general relation of GB misorientation angle with m ′ and |∆ b | is established. The results indicate that low angle GBs always possess high m ′ and low ∆ b , while only some high angle GBs meet the requirement of large alignment parameters. This difference contributes to their preference of slip transfer. Finally, the orientations of best neighboring grains that are favorable for slip transfer are calculated, which is in agreement with the experimentally detected examples. [Display omitted] • Dislocations can transmit at some high-angle grain boundaries with special orientations. • General effect of grain boundary misorientation angle on slip transmission is studied. • The best orientations of neighboring grains favorable for slip transmission are established for low- and high-angle GBs. [ABSTRACT FROM AUTHOR]

In this work, ultra-high hardness of 598 HV of Ti–3Si-1.5Fe–1Mo alloy was manufactured via tailoring the in-situ Ti 5 Si 3 phases. The manipulation of solution and precipitation as well as the regulation of morphology and distribution of the in-situ Ti 5 Si 3 phases were achieved by solution heat treatment and subsequent aging. The average size of Ti 5 Si 3 in titanium alloy was reduced from 3.13 μm to 2.39 μm, and the tiny Ti 5 Si 3 was dispersed in the grain interior, while the residual rod-like and particle Ti 5 Si 3 were distributed at the grain boundaries. The hardness and ultimate compressive strength of the alloys were remarkably increased by 151 HV and 373 MPa, respectively. The improvement of mechanical properties by Ti 5 Si 3 evolution was mainly ascribed to the unique regulation of morphology and distribution of Ti 5 Si 3 and Si-involved variation in solute. Moreover, the degree of solid solution strengthening of Si element produced by the evolution of Ti 5 Si 3 was quantitatively obtained by theoretical calculation of phase diagram. • Ultra-high hardness (598 HV) of Ti–3Si-1.5Fe–1Mo alloy is achieved. • The solid solubility of Si is elaborately controlled based on the phase diagram. • The intra-grain dispersion of tiny Ti 5 Si 3 precipitates is tailored by aging treatment. • Effect of Ti 5 Si 3 evolution on the mechanical properties is quantitatively revealed. [ABSTRACT FROM AUTHOR]

To realize strength-ductility balance in a novel titanium alloy Ti–6Mo-3.5Cr–1Zr, the microstructure transition of stress-induced β→ω was intendedly retarded by design of α-β hybrid structure. The outstanding quasi-static tensile properties with yield strength of ∼825 MPa, true tensile strength of ∼1171 MPa and total elongation of ∼29.7% was obtained via microstructure optimization. [Display omitted] • α" phase transformation is suppressed for improving yield strength in the material. • The SIω transformation is intendedly retarded by design of α-β hybrid structure. • Excellent strength-ductility balance is achieved via microstructure optimization. [ABSTRACT FROM AUTHOR]

Taking advantage of high strength of a titanium alloy and high ductility of the other one is performed to manufacture titanium laminated composite that is promisingly applied in high strain rate environments, but the challenge of fabricating high bonding interface of the two titanium alloys still needs to be overcome. In this work, the TB9/TC4 titanium laminated composite was successfully prepared by hot rolling. A strong bonding interface was constructed between the layers of TB9 and TC4 titanium alloys, achieving a high shear strength of up to 770 MPa. The dynamic compression of the TB9/TC4 titanium laminated composite under Split Hopkinson Pressure Bar (SHPB) showed that the stress-strain curve of the composite presented a unique dual-peak feature, indicative of an excellent strain hardening capability. The TB9/TC4 interface, characterized by coherent and low interface formation energy, facilitated deformation accommodation between TC4 and TB9 layers. Concurrently, the TB9/TC4 interface hindered the ASBs and triggered dislocation strengthening due to stress concentration, leading to high dynamic strength of the laminated composite. [ABSTRACT FROM AUTHOR]

The dual-hardness titanium alloy laminated composites exhibit high hardness and toughness, making it an ideal material for applications in ballistic protection, wear-resistant and other fields. However, the substantial difference in hardness poses a challenge in effectively bonding these alloys, potentially resulting in the emergence of cracks and a decrease in bonding strength. In this study, a new Ti 5 Si 3 -reinforced high-hardness Ti311 (475 HV) and TC4 (352 HV) titanium alloys were successfully combined by hot-pressing diffusion bonding. The synergy effects of hot-pressing temperature and deformation on the microstructural evolution and mechanical properties of the Ti311/TC4 interface were systematically studied. The metallurgical bonding interface was formed at 850 °C under 25 MPa of 15.9% deformation, with the maximum shear strength value of 606 MPa. Moreover, a continuous and discontinuous coupled dynamic recrystallization mechanism was revealed. Deformed α grains were transformed to fine recrystallized grains, and gradually grew with the help of continuous dynamic recrystallization to eliminate the original flat interface. In addition, with the occurrence of element diffusion, the interface between Ti311 and TC4 is ultimately successfully bonded. Notably, the Ti 5 Si 3 phase played a double-edge sword effect on bonding the Ti311/TC4 interface, promoting the occurrence of continuous dynamic recrystallization of adjacent α phase in TC4, but having negative effects on element diffusion. • Ti311/TC4 laminated composites with significant hardness difference but high shear strength were fabricated. • The synergy effects of temperature and deformation on the T311/TC4 interface were elaborated. • Continuous and discontinuous recrystallization were found to jointly promote the interface bonding. • Ti 5 Si 3 on the interface promotes dynamic recrystallization but hinders element diffusion. [ABSTRACT FROM AUTHOR]

Opinions regarding the relationship between impact toughness and quasi-static properties of titanium alloys remain divided to this day. In this paper, quasi-static tensile property parameters were introduced into the classical model of elastic-plastic fracture toughness. Utilizing the absorbed energy during the elastic and plastic stages, as conveyed by the integral of the quasi-static tensile stress-strain curve, the description of elastic and plastic work within the fracture toughness model was provided. Additionally, for the first time, a quantitative model relating impact toughness to quasi-static tensile property parameters in high-strength titanium alloys was proposed and applied to the high-strength Ti-652 titanium alloy. Decoupling the elastic and plastic segments of stress-strain curve, it was found that plasticity contributes more to impact toughness than strength, especially for high-strength metallic materials. Comparing the mechanical properties of Ti-652 titanium alloy with 9 kinds of microstructure, M9 was found to have the highest impact toughness (53.713 J/cm2) which features a duplex microstructure and underwent more severe plastic deformation during the test of samples, leaving shear bands and "ripple-like" patterns on the quasi-static tensile and impact fractures. Besides, statistics of dislocation density assisted by TEM images demonstrate that the dislocation density ( ρ ̅ GND =4.82 ×1014 m−2) of high-impact toughness specimens are apparently higher than that ( ρ ̅ GND =3.86 ×1014 m−2) of low-impact toughness specimens. Severe plastic deformation increased the energy consumption during the fracture process, resulting in high impact toughness of specimen. [Display omitted] • Quantitative model of impact toughness and tensile properties of high-strength titanium alloys was first proposed. • Validity of the model was confirmed through the application to Ti-652 high-strength titanium alloy. • Plasticity contributes more to impact toughness than strength, which was identified mathematically and experimentally. [ABSTRACT FROM AUTHOR]

[Display omitted] • The correlation between dynamic and basic mechanical properties is mined by machine learning. • Random Forest models of dynamic performance are established, with the accuracy over 86.11%. • Excellent dynamic performance and tensile properties are rapidly screened in Quantitative Maps. • Micro-scale secondary α-phase is found to contribute to excellent dynamic performance. The dynamic compression performance of titanium alloys is important for material design under shock, but the intrinsic relationship between them and basic mechanical properties is still unclear. In this work, based on the mechanical-property data set of Ti20C sheet (4788 pieces of data), the correlation between them was constructed through data-driven and machine-learning methods. Through the trained random-forest regression models, the Quantitative Maps were constructed, and the dynamic compression strength σ D , critical fracture strain ε f , as well as impact absorption energy E D , were effectively predicted, with the accuracy rates all over 86.11%. Accordingly, the zone of excellent dynamic performance and corresponding quasi-static tensile properties in Maps can be rapidly screened. Furthermore, combined with microstructure observation, it was found that nano-scale acicular secondary α-phase significantly increased σ D , micro-scale secondary α-phase resulted in excellent dynamic strength and plasticity, while the equiaxed, bimodal and mixture microstructure without secondary α-phase corresponded to the high value of ε f. Meanwhile, both nano-scale and micro-scale secondary α-phase contributed to the high value of E D. Finally, the generalization capabilities of models were validated. By comparing predicted values with experimental values, it was found the models realized the relatively accurate prediction of dynamic compression performance on other titanium alloys. [ABSTRACT FROM AUTHOR]

The stress-induced α" phase transformation in titanium alloys has received extensive attention due to its significant effect on mechanical properties. In this work, by adjusting the heat treatment process, the stress-induced α" phase transformation is activated in Ti-5Al-2.5Cr-5Mo-1Sn. The quasi-static tensile mechanical properties of the alloy under air-cooled and as-quenched states have been compared. Further, the morphology and orientation of the stress-induced α" phase and its interaction with dislocations are investigated by X-ray diffraction (XRD), optical microscope (OM), electron backscattered diffraction (EBSD) and transmission electron microscope (TEM) experiments. The value of average misorientation at the stress-induced α" bands region is larger than that in the β matrix, which indicates that the degree of plastic deformation in the stress-induced phase transformation region is higher. Therefore, the stress-induced α" phase exhibits a strong strain partitioning effect during the stretching process and improves the ductility of the material. The β/α" interface has a weak effect to hinder the dislocations, which results in low tensile strength of the alloy. This work can provide insight into the influence of stress-induced α" phase transformation on the mechanical properties of transformation induced plasticity (TRIP) type titanium alloys. • The Ti-5Al-2.5Cr-5Mo-1Sn alloy is elaborately regulated to produce TRIP effect. • Average misorientation of α" band region is generally larger than that of β matrix. • α" phase exhibits a strong strain partitioning effect to increase alloy ductility. • The β/α" interface is semi-coherent and has a weak effect to hinder dislocations. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel metastable β titanium alloy Ti-6Mo-3.5Cr-1Zr with stress-induced ω phase transformation is designed. • The alloy exhibits strain hardening during dynamic compression because of the stress-induced phase transformation. • The stress-induced structures hinder the formation and propagation of adiabatic shear bands (ASB). • The microstructural evolution along outer edge → transition zone → center of the ASB region corresponds to (β + ω)→(β + α)→(β). Metastable β titanium alloys are attracting great interest due to their intricate plastic deformation mechanisms. In this work, a novel metastable β titanium alloy Ti-6Mo-3.5Cr-1Zr is developed by controlling the phase stability. The alloy exhibits a compressive strength of ∼ 1152 MPa with large malleability (∼34 %) during dynamic compressions. The microstructural evolution and adiabatic shearing behavior of the alloy are investigated by applying stop rings to control the compressive strains. Microstructural characterizations and differential scanning calorimetry show that the content of stress-induced ω (SIω) phase increases with the accumulation of strain, resulting in strain hardening of the material. The formation of adiabatic shear band (ASB) is observed in samples with 30% strain, whilst the formation and expansion of ASB are hindered by stress-induced structures. The microstructural evolution along outer edge → transition zone → center of the ASB region corresponds to (β + ω)→(β + α)→(β), which is caused by the temperature increasement in ASB. In addition, the average grain sizes in ASB region are gradually refined under the action of dynamic recrystallization. These results provide insights into the dynamic deformation mechanism and adiabatic shearing behavior of metastable β titanium alloys. [ABSTRACT FROM AUTHOR]

A novel metastable β-type Ti–6Mo-3.5Cr–1Zr alloy is designed using d-electrons theory to introduce diverse phase transformations. Stress-induced ω (SIω) phase transformation dominates the initial deformation, while the SIω bands are transformed to α+β phase as the strain increases. The sequential mechanism associated with β→SIω→α+β is first reported in titanium alloys. • A novel metastable β alloy Ti–6Mo-3.5Cr–1Zr is designed using d-electrons theory. • The stress-induced β.→ω→(β+α) phase transformation is firstly reported • Localized growth and combination of the single athermal ω variant form the SIω. • Elemental redistribution occurs during the stress-induced ω.→(β+α) process • The covalent bond gradually dominates during the β.→ω→α transformation [ABSTRACT FROM AUTHOR]