The present study focuses on the development of a novel Zr-12Nb-3Sn alloy displaying a body-centered tetragonal (BCT) / beta dual-phase microstructure and engineered to achieve a superior combination of high strength and low elastic modulus. The BCT phase is shown to play a critical role in enhancing strength without increasing elastic modulus. Comprehensive analyses using in situ straining electron backscatter diffraction (EBSD) experiment and transmission electron microscopy (TEM) were conducted to characterize the microstructure of the BCT phase and the associated deformation mechanisms, including dislocation slip, stress-induced reversion from BCT to beta transformation, and mechanical twinning. The present findings reveal that the BCT phase and mechanical twinning both contribute to material strengthening, whereas the stress-induced reversion of the BCT phase to beta acts as a mechanism for stress relaxation. As a result, the alloy demonstrates exceptional mechanical performance, achieving a yield strength exceeding 1200 MPa, an elastic modulus of approximately 70 GPa, and an elongation of similar to 13%.

The microstructure-mechanical property relationships of alpha+alpha ' dual phase microstructures are studied in Ti-6Al4V. Various annealing temperatures in the alpha+(3 field are analyzed and the decomposition of the metastable martensite phase is also investigated. Low annealing temperatures lead to large work-hardening that is attributed to the occurrence of the concurrent deformation of a composite structure where the martensite is the softer phase and the occurrence of Reorientation Induced Plasticity in the martensite (RIP effect). This is studied by Electron Backscattered Diffraction (EBSD) and in-situ tensile testing combined with Digital Image Correlation (DIC). High annealing temperatures lead to a large decrease in work hardening due to the disappearance of RIP and of the mechanical contrast between alpha and alpha'. Further annealing of the alpha+alpha' microstructures goes along with the disappearance of RIP associated with the decomposition of the metastable martensite. The decomposition mechanism is shown to be a reversion phenomenon with the (3 phase precipitating within the martensite and at interfaces while retrieving its high temperature orientation. The precipitation of the (3 phase is shown to largely increase the strain to fracture of the samples annealed at high temperatures. The precipitates act as reinforcement of the larger laths that form within the large (3 grains associated with the high annealing temperatures.

Compositional boundaries of transformation-induced plasticity and mechanical twinning (TRIP/TWIP) activity in the Ti–Nb system are determined using a chemically graded sample containing 18–30 at. pct Nb, prepared via diffusion couple. Deformation mechanisms triggered by a single tensile test are analyzed by EBSD and EDX. TRIP activity is resolved in the range 22–25 at. pct Nb and TWIP activity in the range 23–28 at. pct Nb, showing the possibility to chemically map deformation mechanisms with a single tensile test.

Though metastable beta titanium alloys, such as the Ti-10V-2Fe-3Al (Ti-10-2-3), in their single beta phase condition (solution treated and quenched), can exhibit relatively high strain hardening rates arising from transformation induced plasticity (TRIP) and/or twinning induced plasticity (TWIP) effects, these alloys suffer from relatively poor yield strengths (YS). We demonstrate that processing Ti-10-2-3 via additive manufacturing (AM), followed by a simple heat-treatment in the alpha+beta region, leads to a high YS (similar to 820 - 1130 MPa) while preserving the TRIP effect, resulting in reasonable strain hardening rates while maintain uniform tensile elongation similar to 7-10%. This promising combination of properties results from homogeneously distributed nanoscale Al-rich clusters within the beta matrix of the AM processed alloy, acting as intragranular heterogeneous alpha nucleation sites, leading to a unique distribution of refined alpha precipitates, typically not observed in the conventionally processed condition of the same alloy. This optimal distribution of refined alpha precipitates confines the volume of the retained beta matrix into small pockets, thus increasing the triggering stress for alpha" formation and constraining the length of the martensite plates. Thus, AM opens up a new pathway to design and develop beta Ti alloys exhibiting high yield strengths, coupled with reasonable strain hardening rates, and good uniform tensile elongation.

Dislocation loops are critical defects inducing detrimental effects like embrittlement and swelling in materials under irradiation. Distinguishing their nature (interstitial- or vacancy-type) is a long-standing challenge with great implications for understanding radiation damage. Here, we demonstrate that the morphology of radiation-induced Frank loops can unveil their nature in face-centered cubic (fcc) structure: Circular loops are interstitial-type in all fcc materials, while segmented loops are vacancy-type in high stacking fault energy (SFE) alloys but varied-type in low SFE and high-entropy alloys. The polygonal shape is attributed to the dissociation of an a0/3<111> dislocation into an a0/6<112> Shockley partial and an a0/6<110> stair-rod dislocation. The dissociation of vacancy loops is energetically favorable, whereas interstitial loops require external stimuli to promote dislocation propagation. This "morphology-nature" correlation not only highlights the asymmetry of vacancy/interstitial loops but also offers an efficient way to distinguish loop nature for a wide range of materials.

In recent years, (0001) twist grain boundaries (BTGBs) located in primary α grain clusters were identified as fatigue crack nucleation sites in different Ti alloys. In the present study, crack initiation was investigated in a bimodal Ti-5Al-4V alloy subjected to low-cycle fatigue and dwell-fatigue loadings at room temperature. The low fraction of primary α grains was not associated with a lack of sensitivity to BTGB cracking. Transmission electron microscopy and electron back-scattered diffraction were used to characterize BTGBs in the initial microstructure. The fatigue mechanisms were then analyzed with a focus on dislocation activity. αp grains adjacent to cracked BTGBs contained a high dislocation density. It was primarily composed of planar slip bands of dislocations. In addition, dislocations were noticed in the vicinity of cracked BTGBs. They supposedly pertain to crack tip plasticity during growth, and no evidence of a role of an incoming slip event in crack nucleation was obtained. Also, basal slip bands extending across adjacent grains were found to emerge from BTGBs. This feature provides an easier path for crack extension when growth along the grain boundary becomes difficult owing to a deviation from the basal plane. Atom probe tomography analyses evidenced V and Fe segregation at a grain boundary with a significant deviation from the BTGB configuration. This suggests a possible contribution of local solute segregation to the high cracking resistance of general αp / αp grain boundaries. This work provides new insights into the mechanisms involved in cracking of BTGB in Ti alloys subjected to cyclic loadings.

While work-hardening is typically considered in Ti as a prerogative of the 13 -metastable alloys, this paper introduces a novel perspective, presenting a set of alloy design rules to develop solute lean alpha + 13 titanium alloys exhibiting increased work-hardening capabilities. More specifically, reaching this goal is made possible through the development of alpha + alpha ' microstructures exhibiting Reorientation Induced Plasticity (RIP) within the alpha ' martensitic phase. The microstructural requirements for activating RIP and maximizing mechanical properties (i. e., combining high work-hardening, yield strength and ductility levels) are derived from an analysis of the microstructures/mechanical property relationships of various alpha + alpha ' samples. A set of design rules is provided. Emphasis is laid on the pivotal role of the chemistry of the alpha ' martensitic phase in RIP activation and a Molybdenum equivalent chemical criterion is proposed. The alpha phase is here suggested as a mean to reduce the prior 13 grain size and the resulting size of the martensite plates. This approach reveals that the versatile thermal treatments leading to alpha+alpha' structures broaden the mechanical property landscape, achieving large work hardening capabilities (typically over 500 MPa) that can be combined with high yield strength (over 800 MPa).

This study proposes a novel strategy for the design of a new family of metastable Zr alloys. These alloys offer improved mechanical properties for implants, particularly in applications where conventional stainless steels and Co-Cr alloys are currently used but lack suitability. The design approach is based on the controlled twinning-induced plasticity (TWIP) effect, significantly enhancing the ductility and strain-hardenability of the Zr alloys. In order to draw a "blueprint" for the compositional design of biomedical TWIP (Bio-TWIP) Zr alloys-using only non-toxic elements, the study combines d-electron phase stability calculations (specifically bond order (B-o) and mean d-orbital energy (M-d)) with a systematic experimental screening of active deformation mechanisms within the Zr-Nb-Sn alloy system. This research aids in accurately identifying the TWIP line, which signifies the mechanism shift between TWIP and classic slip as the primary deformation mechanism. To demonstrate the efficacy of the TWIP mechanism in enhancing mechanical properties, Zr-12Nb-2Sn, Zr-13Nb-1Sn, and Zr-14Nb-3Sn alloys are selected. Results indicate that the TWIP mechanism leads to a significant improvement of strain-hardening rate and a uniform elongation of similar to 20% in Zr-12Nb-2Sn, which displays both {332}<113> mechanical twinning and dislocation slip as the primary deformation mechanisms. Conversely, Zr-14Nb-3Sn exhibits the typical mechanical properties found in stable body-centered cubic (BCC) alloys, characterized by the sole occurrence of dislocation slip. Cell viability tests confirm the superior biocompatibility of Zr-Nb-based alloys with deformation twins on the surface, in line with existing literature. Based on the whole set of results, a comprehensive design diagram is proposed.(c) 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Recent experiments identified a new type of stress induced structural transformation allowing to combine high strength, great work hardening and good ductility in multiphase Ti alloys. These properties are achieved through reorientation of the alpha' martensite plates being in specific self accommodating < 5 (4) over bar(1) over bar3 > type II twin relation, i.e. under applied load one martensite variant reconfigure to its twinned configuration with visible motion of the {13 (4) over bar1} twin boundary. This mechanism of plastic deformation was never observed before thus, its current understanding is fragmentary. In this article we present the results of experimental observations and ab initio calculations of < 5 (4) over bar(1) over bar3 > type II twins determining the crystallography of twin formation, structure and energy of the {13 (4) over bar1} interface as well as mobility of the corresponding twinning disconnections. It was found that the investigated boundary has one of the lowest energies among known twinning modes in hexagonal Ti. Moreover, the < 5 (4) over bar(1) over bar3 >{13 (4) over bar1} disconnections have the smallest Burgers vector and step height in comparison to other active twinning systems. As a result, these disconnections are highly mobile which rationalize migration of the {13 (4) over bar1} twin boundaries at straining. Furthermore, energy of the twin boundary and mobility of disconnections can be adjusted by particular alloying elements enabling the conscious development of new alloys exhibiting reorientation induced plasticity.

Compositional boundaries of activity regarding transformation-induced plasticity and mechanical twinning (TRIP/TWIP) in Ti-Nb alloying system is determined by a novel methodology using chemically graded samples prepared by Spark Plasma Sintering. Presented methods of characterization include nanoindentation and microindentation testing complemented by EBSD analyses. The link between composition, microstructure, deformation mechanisms and mechanical properties can be established. Applied to the Ti-Nb system for a proof of concept, both the identification of local mechanical properties with respect to composition, and the refinement of the compositional ranges within which the different deformation mechanisms occur can be obtained. The graded sample ranging from 14 at.% to 34 at.% Nb is studied. TRIP/TWIP activity is resolved by EBSD in range 17 to 24 at.% of Nb, which is significantly lower than the results from the literature. This difference is attributed to the presence of interstitial oxygen (2470 +/- 60 weight ppm).

Variations with oxygen concentration of titanium lattice parameters are obtained by means of ab initio calculations, considering the impact of oxygen ordering. The quasiharmonic approximation is used to take into account the thermal expansion at finite temperature. Results show that lattice parameters depend mainly on oxygen concentration and, to a lesser extent, on the ordering state. Knowing these theoretical variations, one can get insights into the composition of ordered compounds existing in Ti-O binary alloys from their lattice mismatch measured experimentally by x-ray diffraction. The approach is used in a binary alloy containing 6000 ppm in weight of oxygen. It is concluded that the ordered compounds, which are observed after a recrystallization heat treatment, do not have the expected Ti6O stoichiometry but have a composition close to the nominal concentration. Oxygen ordering proceeds, therefore, before oxygen partitioning in titanium.

This study delved into exploring microstructural states in a Ti–7Ag alloy to achieve targeted functional and structural properties. Specifically, the focus was on attaining a homogeneously precipitated state and a solid solution, known for their potential to combine functional traits like corrosion resistance and antibacterial activity with structural properties such as mechanical strength. However, obtaining these optimized microstructures presents challenges due to kinetic considerations. A key finding of this study was the crucial role of a pre-deformation stage, prior to heat treatment, to create an even distribution of fine Ti2Ag precipitates. Moreover, we demonstrated that starting from this precipitated state, a controlled dissolution step could yield a single-phase solid solution with similar grain size. Therefore, a tailored set of thermomechanical treatments was developed to achieve both microstructures, and these metallurgical states were fully characterized combining SEM (BSE imaging and EDS analysis), TEM, and XRD. Associated mechanical properties were also assessed by tensile testing. In addition, the process was proven to be robust enough to overcome potential industrial problems, such as slow cooling rates when water-quenching large ingots. Considering the limited existing documentation on microstructural features in Ti–Ag alloys, this work on this model alloy significantly advanced our current understanding of the broader Ti–Ag alloy system by providing new data and showcasing a tailored approach involving thermomechanical treatments.

Micro-alloying strongly affects the incubation period of void swelling in irradiated face-centered cubic materials. However, the underlying mechanism, which relates to the formation of dislocation loops, is still unclear. Here, we investigate pure Ni, Ni-0.4wt.%Cr and Ni-0.4/0.8/1.2wt.%Ti as model materials, to gain insight into the solute effects on the loops evolution in the early stage of irradiation. The dislocation loop characteristics (mobility, Burgers vector, nature) are studied using in-situ transmission electron microscopy and ex-situ irradiation with Ni+ ions at 450°C and 510°C for doses from 0.06 to 0.7 dpa. It appears that a tiny amount of Ti effectively increases the loop density, reduces the loop mobility and the stacking fault energy. It leads to an equal distribution among a/2<110> perfect loop families. It also stabilizes self-interstitial loops against vacancy loops depending on Ti content and temperature. Our modeling of radiation-induced segregation, based on experiments and recent ab initio calculations of flux couplings, predicts a Cr enrichment and a Ti depletion nearby dislocation loops. It is in good agreement with our observations by X-ray spectroscopy in TEM and by atom probe tomography. However, the lowered loop mobility must be the signature of a thermal segregation rather than the impact of radiation-induced depletion. Indeed, oversized Ti atoms subsequently trapped at strained lattice sites around the dislocation line of the loop due to thermal segregation would inhibit its diffusion. This opens new perspectives for future experimental investigations and radiation-effect modeling.

The present paper aims at providing a fine-scale analysis of the Ti-4.5Al-2.5Fe-0.25Si α+α'+βretained microstructures to give insight into the link between the microstructural characteristics of the alloy (phase fraction and chemistry, grain size, etc.) and the deformation mechanisms at play. These microstructures were found to exhibit outstanding work-hardening capabilities that have the great potential to be obtained simultaneously with a high yield strength when the microstructural features are carefully optimized. Ex-situ analyses coupled with TEM revealed the simultaneous occurrence of Reorientation Induced Plasticity (RIP) into the self-accommodated Fe-enriched α' martensite, TRansformation Induced Plasticity (TRIP) of the βretained phase and TWinning Induced Plasticity (TWIP) of the α phase that add to dislocation glide. The Fe-enriched martensite has the remarkable capability to induce reorientation through two distinctive mechanisms: by the motion upon deformation of the intervariant boundary associated to the [45¯13¯]α′ Type II twin, a rather classical mechanism although not often reported into α'; but more surprisingly into such a fine phase, by the creation and growth upon deformation of {101¯2}1¯011α′ twins. A 3-scale mechanical contrast is proposed to explain the remarkable work-hardening rates achieved. Reorientation is shown to be a key microstructural feature for the development of Ti alloys with superior mechanical properties.

Defect-tolerant materials are good candidates to be produced by additive manufacturing as parts often suffer from the presence of various kinds of defects: internal (pores) and especially surface defects (roughness). A β-metastable binary Ti-14Mo alloy exhibiting a TWIP effect with a composition adapted to take into account constraints of powder bed additive manufacturing processes was fabricated by electron powder bed fusion (E-PBF). The processing window was identified and dense samples with a relative density > 99.9% measured by X-ray computed tomography were fabricated. Microstructures were examined using metallography, X-ray diffraction, and electron microscopy. The mechanical properties were determined using monotonous and cyclic loading-unloading tensile testing. The as-built microstructure shows a two-phase α + β microstructure with a gradient in size of the α phase along the building direction. Post-fabrication heat treatment is therefore required to achieve a β-metastable microstructure. The peculiarities and similarities with other β-metastable binary Ti-Mo alloys fabricated by the more traditional cast and wrought processing route are highlighted. The possibility to tailor the mechanical response by low-temperature ageing via precipitation of the ωiso phase is also investigated. Such Ti-alloy could be used to improve the energy absorption capacity of architected materials for which the surface-to-volume ratio is very high and thus defect tolerance is of utmost importance.

Since its discovery in 1954, the omega (ω) phase in titanium and its alloys has attracted substantial attention from researchers. The β-to-ω and ω-to-α phase transformations are central to β-titanium alloy design, but the transformation mechanisms have been a subject of debate. With new generations of aberration-corrected transmission electron microscopy and atom probe tomography, both the spatial resolution and compositional sensitivity of phase transformation analysis have been rapidly improving. This review provides a detailed assessment of the new understanding gained and related debates in this field enabled by advanced characterization methods. Specifically, new insights into the possibility of a coupled diffusional-displacive component in the β-to-ω transformation and key nucleation driving forces for the ω-assisted α phase formation are discussed. Additionally, the influence of ω phase on the mechanical properties of β-titanium alloys is also reviewed. Finally, a perspective on open questions and future direction for research is discussed.

Oxygen content has always been limited in commercial titanium and titanium alloys due to its propensity to induce a severe ductility loss. Yet, its effect on the macroscopical behavior has never been clearly understood and is still rather unclear considering the wide variability in the literature results. Here, we investigate the tensile properties of alpha-titanium with oxygen contents ranging from 0.15 to 0.80 weight percent (wt%). While the strain-hardening ability of oxygen is maintained, no ductility drop is observed up to 0.60 wt% of oxygen, thus allowing exceptional combinations of mechanical properties with an ultimate tensile strength (UTS) of 800 MPa and 29% of elongation at fracture for the Ti-0.6O alloy. Both high strength and ductility of these alloys result from the dislocations/precipitate's interactions. It is proposed that these interactions induce an important cross-slip ac-tivity responsible for a dislocation multiplication and a high work-hardening rate. With the addition of Zr, alloys exhibit an even more promising combination of mechanical properties, achieving 1,075 MPa of UTS and 28% of elongation at fracture for the Ti-4.5Zr-0.8O alloy. The mechanical properties of TiO and TiZrO alloys brought out in this study surpass those of Ti-6Al-4V alloy and open significant prospects for developing a new generation of oxygen-tolerant titanium alloys.

(0001) twist grain boundaries (BTGB) have been identified as critical microstructure configurations regarding fatigue crack initiation in titanium alloys. In the presently reported study, Ti-Al-V based alloys with different microstructures were tested in the low-cycle fatigue regime. Early cracking occurred at BTGB for all investigated alloys and microstructures. Microstructural statistics collected at crack initiation sites revealed a weak sensitivity to moderate differences in & alpha; and & beta; stabilizers content and microstructural features. Criteria for the identification of crack initiation sites were then defined using this dataset. An automatic processing routine was applied on large-scale electron back-scattered diffraction maps to analyze the spatial distribution of BTGB susceptible to cracking. The low associated density implies that large microstructural regions, i.e., typically > 1 mm2, must be considered to include microstructural configurations prone to crack nucleation. It is likely to play a critical role in the high lifetime variability of Ti alloys.

In this work, the dual phase titanium alloy Ti–5Al-7.5V was subjected to low-cycle fatigue at room temperature to reveal the deformation mechanisms of fatigue and crack initiation. Transmission electron microscope analysis showed that planar dislocation slip, most of them localized at the basal and prismatic planes of α phase, is the primary deformation mode of low-cycle fatigue. Multiple slips operate concurrently in the high Schmid factor planes within a single grain. Moreover, a limited number of observed microcracks were formed along the basal slip bands. Electron back-scattered diffraction analysis evidenced that numerous microcracks were formed along basal planes. And, the microcracks were confined in primary α grains without propagation to surrounding transformed β matrix, indicating that the alloy exhibits a high tolerance to microcrack propagation. The α grain aggregate oriented for basal slip is a fatigue-critical microstructure configuration, which provides a high Schmid factor path by linking adjacent grains and potentially lead to internal crack initiation with the formation of a field of facets in the cycling process. While the silicides were observed in contact with the microcracks and slip bands, no evidence of crack initiation from silicides was detected. Given that the microcracks were formed along the pre-existing slip bands, it remains an open question whether the silicides can act as the dislocation sources for planar slips and facilitate crack nucleation from these silicides.

Processing heterogeneous microstructures, especially the so-called harmonic structures consisting of soft core and hard shell regions, is an efficient way to achieve a strength-ductility trade-off in classical metallurgy. In this study, two harmonic samples with the same composition of Ti-24Nb-4Zr-8Sn but different microstructures were processed to exhibit different grain size heterogeneities between the core and the shell. Both samples were consolidated from a ball-milled powder using Spark Plasma Sintering (SPS) but applying two different sintering times, 1 and 60 min. The grain size heterogeneities were higher for the longer SPS sintering time due to the enhanced grain dimension in the core for 60 min consolidation time. The mechanical behavior of the two materials was studied via a monotonic quasi-static compression test. For both harmonic-structured Ti-24Nb-4Zr-8Sn alloys, a high compressive proof stress of about 1 GPa was detected. The strain-hardening rate was higher for the longer SPS time due to the higher grain size differ-ences between the core and shell. A high dislocation density was detected in both mate-rials after compression deformation (several tens of 1014 m-2). The dislocations tend to form cells and LAGBs during compression. The dislocation pile-ups at the core-shell in-terfaces caused a back stress of about 640 MPa after compression at 2-5% strains. The contributions of the different features of the microstructure (grain size, a phase pre-cipitates, and oxygen concentration) to the proof stress were determined. & COPY; 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).