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Titanium (Ti) alloys, which are highly promising as structural materials in critical industrial applications, generally require high strength and ductility, particularly high fracture toughness. However, the conventional approach of enhancing strength through mechanical processing to induce dislocations often leads to a compromised ductility known as the strength-ductility trade-off. Here, we develop a new strategy of the nanocrystallized kinks to overcome this issue in Ti-11V metastable β -Ti alloys via combining industrially used cold forging (CF) and cold rolling (CR) processes. Deformation kinks are firstly activated by CF, and subsequently they are fragmented into nanograins during CR, architecting nanocrystallized kinks in the coarse-grained matrix. This unique microstructure effectively balances the strength-ductility conflict, endowing this Ti-V binary alloy with high yield strength ∼1200 MPa, appreciable ductility ∼17 % and high fracture toughness ∼ 52.0 MPa·m½, which is superior to numerous multielement engineering Ti alloys. This design strategy of nanocrystallized kinks can be extended to other engineering materials, e.g. , Mg and Zr alloys, for advanced performance at large industrial scales. [Display omitted] [ABSTRACT FROM AUTHOR]

Metastable β -titanium (Ti) alloys have always attracted great attention due to the available ultra-high strength via precipitation strengthening, while they often succumb to a strength-ductility trade-off known as improving strength but degrading ductility. In this study, we exploit a novel strategy to address the issue in Ti–6Cr–5Mo–5V–4Al (Ti6554) high-strength metastable β -Ti alloy through the trace boron addition. It is found that an ultra-high strength ∼1600 MPa with elongation of ∼9 % is synchronously achieved with the addition of minor boron, corresponding to a ∼7 % increase in strength and ∼70 % improvement in ductility compared to the boron-free counterpart. Microstructural characterizations manifest that boron addition promotes almost complete transformation from abnormal β -grain region to normal β -grain region, which possesses better deformation accommodation capacity at the aged state. Meanwhile, TiB whiskers are produced and adhered by a layer of α s -film, creating a sandwiched structure architected by TiB whisker/ α s -film/the aged β -matrix. This unique structure not only effectively retards the deteriorative development of highly localized deformation propagating from the aged β -matrix, but also sufficiently activates dislocation slip within TiB whiskers. These findings demonstrate a counterintuitive result that TiB intermetallic compound well-known as the susceptive brittleness can be harnessed in ductilizing materials, and also provide a practical strategy for enhancing plasticity of high-strength Ti alloys by microalloying design. [ABSTRACT FROM AUTHOR]

A metastable β-titanium Ti–Al–Mo–V–Cr–Nb alloy exhibits a synergistic increasing in strength and ductility via coupling thermomechanical processing and heat treatment in present work. Synergistic effect of the thermomechanical processing and heat treatment on microstructure evolution and mechanical properties of the metastable β-Ti alloy was systematically investigated. α+β rolled sample sheet consumes less time to finish recrystallization, and leads to more uniformly distribution and smaller size of β grains than β rolled sample after same solution treatment. Primary α phase in α+β rolled sample hinders the growth of β grains during solution treatment and the spacing distance of α lamella in α+β rolled sample is smaller than β rolled sample after aging treatment, enhancing the strength significantly. The small spacing distance of α lamella is due to an increase in precipitation density. The small size and homogeneous distribution of β grains provides moderate ductility. After solution treatment at 770 °C for 2 h and aging treatment at 525 °C for 6 h, α+β rolled samples exhibit higher ultimate tensile strength (1550 MPa) and better ductility (6.5 %) than β rolled sample. The relationship between the average grain size of β grains, the average spacing distance of α lamella, and the yield strength of the alloy is quantitatively calculated using mathematical methods. The mechanisms of synergistic enhancement of strength and ductility in the alloy is qualitatively analyzed. These findings facilitate manufacturing high-performance metastable β-Ti alloys at an industry scale using commercially available thermomechanical processing. [ABSTRACT FROM AUTHOR]

In conventional duplex titanium (Ti) alloys, the soft primary α-precipitates (α p) are beneficial to ductility with the loss of high yield strength, while the continuous α-precipitates at grain boundaries (GBs, α GBs) often accompanied with α precipitate-free zones (α-PFZs) renders the strain incompatibility for limited ductility. Here, to overcome this longstanding issue, we utilize interstitial (O and N) atoms to notably strengthen the α-phase, and simultaneously architect the multi-morphologic secondary α-precipitates (α s) so as to improve the strain compatibility nearby GBs, thus develop a Ti-4.1Al-2.5Zr-2.5Cr-6.8Mo (wt.%) alloy with ultra-high yield strength of ∼1580 MPa and good ductility of ∼8.2%. The phase boundaries between the hard α-precipitates and the soft β-matrix not only act as dislocation barriers for strengthening, but also as sustainable dislocation sources for ductilizing to achieve a good combination of strength and ductility in our Ti alloys. This strategy not only sheds light on the understanding of the strength-ductility synergy of duplex Ti alloys, but also offers an available pathway to design ultra-strong and ductile alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

The microstructure evolution, mechanical property and deformation behavior of α lamella structure in a novel metastable β alloy Ti–5Al–4Zr–8Mo–7V were studied in this paper. Via different heat treatments, large differences in size, morphology and volume fraction of α lamella were obtained. Tensile tests show that high strength with low ductility is represented after low temperature aging. Tensile brittleness at low temperature aging is originated from precipitation of high fraction nano-scaled α lamella, which induced intensive stress concentration along α/β interface where local shear and plastic instability takes place. The alloy exhibits improved strength-ductility combination after BASCA (β annealing slow cooling plus aging) treatment and high temperature aging. High resolution-TEM results suggest that highly defected substructure and local distortion of (10 1 ‾ 0) planes are exhibited in α lamella. Both the highly defected substructure and finely dispersed α lamella could effectively strengthen the alloy. Improvement of ductility is on account of the increase of free slip length in β matrix where a large amount of dislocation accumulated and compatible deformation between coarse α lamella and β matrix. In addition, deformation twining is generated in coarse α lamella which will increase the ductility as well. • The α lamella spacing length determines the slip in β phase which in turn dominant the mechanical properties of the alloy. • The tensile brittleness at low temperature aging (490–550 °C) is attributed to the intense strain localization in shear bands of β grains. • Improved ductility of 680°C aging and BASCA samples is attributed to compatible deformation between β matrix and α lamella. [ABSTRACT FROM AUTHOR]

As a novel high strength metastable β alloy, Ti–5Al–4Zr–8Mo–7V, it is essential to establish the correlation between its microstructure and mechanical property. In this paper, the microstructure evolution, mechanical properties and work hardening behavior with Bi-modal structure were studied in detail. With the increase of solution treatment (ST) temperature, the volume fraction of primary α phase (α p) decreases, and α platelets (α s) increases during subsequent aging treatment. Aging temperature directly determines the size and volume fraction of α s which significantly influences the strength of the alloy. Low temperature aging (510 °C) treatment produces a high density nano-scale distribution of α s precipitates which induces an extremely high ultimate tensile strength (UTS~1630 MPa) together with considerable total elongation (El~6%). As the ageing temperature increases to 630 °C, the UTS reduces to ~1208 MPa but the El dramatically improves to ~13%. The alloy exhibits a good strength-ductility combination with UTS~1390 MPa and El~10% after ST at 800 °C followed by aging at 570 °C. A Hall-Petch like equation is used to calculate the strengthening effect of α s , which shows a good agreement with the experimental results. It's concluded that the α s spacing length (λ) dominates the free slip length in β matrix, and determines the alloy strength. The ductility evolution is explained by work hardening behavior. Limited elongation of samples aged at 510 °C is attributed to the rapid decrease of work hardening rate after yielding. A slow decrease of working hardening rate of the samples aged at 630 °C results from the slightly dynamic recovery which could effectively postpone the occurrence of necking and increase the alloy's ductility. [ABSTRACT FROM AUTHOR]

Abstract A novel high-strength metastable β -Ti alloy Ti-5Al-4Zr-8Mo-7V has been successfully designed utilizing the " d -electron theory" combined with the semi-empirical element-hardening criteria. The excellent combination of strength σ b ~ 1460 MPa and ductility ɛ f ~ 10% is achieved by tailoring hierarchical distribution of α -phase in β -matrix. This hierarchical microstructure consisting of elongated primary α -phase (α p), sub-micro α -rods (α r) and nano-scale α -platelets (α s) was produced by β -transus forging together with heat treatment. Detailed TEM analysis shows that both the α p and α r could deform plastically, resulting in dense tangled dislocations. Furthermore, dislocation features of α p show that the α p /β interface is effectively hardened whilst the entire α p presents prominent deformation capability. Meanwhile, the plastic strain is partitioned among α p , α r and β -matrix compatibly, which is beneficial to improve the ductility. As for the α s , HRTEM observation shows highly defected substructure and local lattice rotation. This highly defected substructure and nano-scale α -distribution effectively block dislocation motion and ultimately strengthen the alloy. The approach presented in this study provides a guideline for the design and fabrication of other β -Ti alloys with hierarchical structure and superior mechanical properties. Graphical abstract Unlabelled Image Highlights • A novel β -titanium alloy, Ti-5Al-4Zr-8Mo-7V, was successfully designed using the 'd-electron theory'. • Hierarchical distribution α-phase in β-matrix was developed by proper β -transus forging and heat treatment. • The novel alloy possesses superior combination of strength and ductility. [ABSTRACT FROM AUTHOR]