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[Display omitted] High specific-strength lightweight titanium (Ti) alloys, in the absence of interstitial strengthening of oxygen (O) atoms to avoid O-embrittlement, are mainly strengthened via densely semi-coherent nanoprecipitates in the β-matrix that act as dislocation obstacles and often result in high-stress concentrations, contributing to their strength-ductility trade-off. Here, using a low cost Ti-2.8Cr-4.5Zr-5.2Al duplex alloy as a model material, we present a counterintuitive O-doping strategy to create topologically coherent, interstitial-O α′ nanotwinned nanomartensites (NTNMs) with good interfacial strain compatibilities. The interstitial atoms tailor the stress field of edge dislocation cores from planar to non-planar, facilitating multiple variants nucleate simultaneously along O-rich edge dislocations to construct interstitial-O NTNMs. The interstitial-O NTNMs endow our duplex Ti alloys with superior strength of 1.64 gigapascals and large uniform elongation of 11.5%, surpassing all previously reported bulk Ti alloys. This unprecedented combination of mechanical properties is conferred mainly by the interstitial NTNMs, which serve as a sustainable ductility source via a self-hardening deformation mechanism and utilize the pronounced interstitial strengthening of concentrated O atoms. As such, the coherent interstitial NTNMs engineering strategy efficiently combines interstitial solid solution strengthening, and coherent interface strengthening mechanisms, that provides new insights into designing high-strength and large ductility O-tolerant alloys for cost-effective and lightweight applications. [ABSTRACT FROM AUTHOR]

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]

Precipitates in alloys are traditionally considered as dislocation obstacles that often lead to high stress concentration and even microcracks owing to the strain incompatibility of semi-coherent interfaces, a cause of progressive strain localization and the origin of the strength-toughness conflict in engineering materials, such as titanium (Ti) alloys. Based on the metastability engineering, here we architect hierarchically ordered coherent interfaces for strength-toughness optimization through densely dispersed nanomartensites in a ductile Ti-Cr-Zr-Al alloy with ultrahigh specific-strength and superior fracture toughness. It is unveiled that these ordered coherent interfaces simultaneously serve as dislocation obstacles and sources, leading to a sustainable and self-hardening deformation mechanism via hierarchical nanomartensite-dislocation interactions for ultra-high strength and toughness of Ti alloys. These nanomartensites are thermally stable at elevated temperature less than 400 °C, above which tempering-induced ductile-to-brittle transition occurs due to the decomposition of hierarchically ordered nanomartensites and the spheroidization of prior β lamellae. The design strategy of hierarchically ordered coherent interfaces confers our cost-effective nanomartensite Ti alloys an unprecedented combination of strength, ductility and toughness, which provides a new pathway in the microstructural design for strong and ductile structural materials with superior fracture resistance. [Display omitted] [ABSTRACT FROM AUTHOR]