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The influence of slow cooling rate and the isothermal holding temperature in isothermal solution treatment on microstructure evolution and tensile properties of near-β Ti alloy was investigated in this work. The results showed that plenty of colonies consisting of parallel α needles were formed during the slow cooling and the isothermal holding stages. In comparison with the primary α developed during solutionizing, the secondary α precipitates formed during aging were more effective in strengthening the alloy. The hardness difference observed due to the cooling rate changes was reduced as the isothermal solutionizing temperature was increased. With the isothermal holding temperature decreasing, the volume fraction of primary α was gradually increased, and the volume fraction of secondary α precipitates dropped accordingly. When held below 750 °C, basketweave microstructures could be obtained after aging treatment, because most of α phase had been formed upon solution stage with plate-like shape. These α plates could accommodate larger degree of local strain than secondary α precipitates, resulting in higher fracture elongation of alloy. A balanced combination of strength and ductility was achieved under the cooling rate of 10 °C/min and isothermal holding temperature of 800 °C, and the yield strength, ultimate tensile strength, elongation and area reduction were 1470, 1497 MPa, 4 and 5.8%, respectively. [ABSTRACT FROM AUTHOR]

We investigated the phase transformation sequence, kinetics, and microstructural evolutions during heating, isothermal treatment, and continuous cooling of the metastable Ti-B19 alloy. On the basis of these results, we summarized the phase transformation characteristics of this kind of alloys, especially the metastable β-Ti alloy. We also analyzed and discussed the possibility of describing the size, morphology, and distribution of precipitates as well as the possibility of and complications in establishing relationships among the chemical composition, microstructure, processing parameters, and properties of the metastable Ti-B19 alloy. [ABSTRACT FROM AUTHOR]

Abstract: TC21 alloy is a new alpha–beta damage tolerance titanium alloy with high strength and high toughness. Little work has been done in the field of microstructure and phase analysis since this alloy was developed. The phase and microstructure of TC21 alloy under different heat-treatment were investigated in this paper. Different experiment methods such as OM, SEM, TEM and XRD were adopted to investigate the microstructure and phase of TC21. The result showed that heat-treatment parameters (solution temperature, cooling rate and cooling mode) had influence on the feature of α phase, β phase and secondary α phase. Two precipitated phases (α2-Ti3Al and B2-Ti2AlNb) were discovered by XRD analysis. [Copyright &y& Elsevier]

The isothermal hot compression behavior of new Ti–Fe–B (named as TF400) alloy was investigated in the temperature range of 750–950 °C and strain rate range from 0.01 to 10 s−1 with the maximum height reduction of 60% by using a Gleeble 3800 thermal simulator. By considering the effect of strain via variable material parameters, a modified constitutive model was proposed to accurately predict the flow stress. The predicted results demonstrate that the flow stress decreases with the increase of temperature while it increases as the strain rate increases, in good agreement with the present experimental results. A mechanistic understanding of plastic deformation behavior in the TF400 alloys was developed by inspecting the microstructural characteristics prior to and after deformations. Dynamic recrystallization and dynamic transformation were found to be the dominant restoration mechanism during the hot deformation process. [ABSTRACT FROM AUTHOR]

The atomic mobility in BCC Ti-Mn and Ti-Al-Mn alloys was assessed by using the DICTRA software after critically evaluating all available experimental diffusion data. Good agreements were obtained from the comprehensive comparisons between the calculated and experimental diffusion coefficients. The interdiffusion behaviour was further well predicted, confirming the reliability of the present mobility parameters. [ABSTRACT FROM AUTHOR]

Friction stir additive manufacturing (FSAM) is a promising and cost-effective technology that has found extensive applications in the fabrication of lightweight alloy components, particularly aluminum and magnesium. However, the exploration of FSAM for titanium alloys is still at an early stage. In this study, the microstructure evolution and mechanical properties of the dual-phase Ti6Al4V alloy fabricated by FSAM were investigated. The microstructural characteristics under various process parameters were determined using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The experimental findings revealed that the stir zone (SZ) exhibited a refined and equiaxial grain structure with a gradient microstructure when the tool rotation speed was set at 150 rpm and the travel speed at 50 mm/min, which was attributed to the combined effects of mechanical fragmentation and dynamic recrystallization (DRX) behavior. Moreover, upon employing a tool rotation speed of 300 rpm and a travel speed of 100 mm/min, acicular products were observed in conjunction with lamellar (α+β) structures located at both the top and center regions within the SZ. The microhardness and tensile properties were improved after FSAM treatment (150 rpm-50 mm/min). Furthermore, the dominant mechanisms of microstructure evolution as well as mechanical property enhancement in friction stir additive manufactured (FSAMed) Ti6Al4V were revealed, thereby providing valuable insights for titanium alloy additive manufacturing processes. [Display omitted] • Friction stirring additive manufacturing (FSAM) can regulate the precipitated phase. • FSAM can change the texture characteristics. • FSAM can significantly improve the mechanical properties. • FSAM process promotes grain refinement and equiaxed grain formation. [ABSTRACT FROM AUTHOR]

Abstract The influences of up-quenching aging (UQA) and step-quenching aging (SQA) on the microstructure development and mechanical properties of near β-Ti alloy Ti-5Al-3Mo-3V-2Cr-2Zr-1Nb-1Fe have been comparatively studied. The results showed that a large number of fine α precipitates were uniformly formed in UQA sample via ω-assisted nucleation, resulting in a higher aging hardening effect. Whereas under SQA treatment, the α precipitates had lower number density and became coarser in addition to inhomogeneous size distribution, in which plenty of α precipitates with large aspect ratio (>50) could be observed. With increasing the aging temperature from 480 °C to 650 °C, the number density of α precipitates with large aspect ratio was gradually reduced, and the hardness interval between UQA and SQA samples was decreased from 90 HV to 20 HV. When aged at high temperature (600 °C), a large number of ultrafine α precipitates were obtained in the UQA sample within 30 min, the number density, thickness and length of α precipitates were ~20 ppt/μm2, 40 nm and 180 nm, respectively, resulting in very high peak hardness (473 HV), but a rapid over-aging occurred due to the ripeness of α precipitates. The SQA treatment showed no evident over-aging tendency, and could yield a good combination of ultimate tensile strength (1284 MPa) and elongation (8%) with the existence of multiscale α precipitates. Highlights • Step quenching aging and up quenching aging treatments were comparatively studied. • Peak hardness of UQA condition was ~100 HV higher than that of SQA. • Fine and uniform α precipitates were formed by UQA due to ω-assisted nucleation. • Large aspect ratio (>50) of α precipitates were formed by SQA treatment. [ABSTRACT FROM AUTHOR]

Abstract An integrated experimental-numerical method combining a realistic microstructure-based isotropic crystal-plasticity (CP) model and fracture surface analysis was adapted to analyze the fracture behavior of the titanium alloy Ti-6Al-4V. A hybrid fracture mode consisting of cleavage facets and elongated dimples was observed and analyzed. With the help of numerical simulations and post-mortem SEM, the micro-mechanism of the hybrid fracture mode was revealed. The results show that ruptured α lamellae can be linked to cleavage facets induced by the development of voids. Simultaneously, hard β lath can function as walls that separate two neighboring arrays of voids or micro-cracks within the α lamellae. The origin of this behavior can be associated with a heterogeneous stress/strain distribution in the α/β phases, which was revealed via numerical simulations. Further, the influence of the α grain orientation on the void evolution was investigated by varying the Schmid factor of the grains in simulations. Graphical abstract fx1 Highlights • A realistic microstructure-based RVE was created and implemented in an isotropic Crystal Plasticity Model. • The model revealed the origin of distinct damage behaviors of α lamellae and β laths. • A hybrid fracture behavior was observed and analyzed by simulations and SEM observations. • The study revealed the role of β phase in plastic deformation and damage development. • The influence of the α grain orientation on the void evolution was investigated. [ABSTRACT FROM AUTHOR]

A multi-alloyed near β-Ti alloy Ti-6Cr-4Mo-2Al-2Sn-1Zr (Ti-64221) with high strength and high ductility was designed utilizing the d -electron theory combined with molybdenum equivalence approaches. Mechanical properties and microstructural evolution of the β-solution treated alloy were investigated. The results show that Ti-64221 alloy exhibits excellent tensile strength, ultra-high total elongation and high ability of strain hardening. The product of strength and elongation is as high as 42.6 GPa% exceeded those achieved earlier in β-Ti alloys. Mechanical activation of {332}〈113〉 and {112}〈111〉 twinning and the stress-induced phase transformation during the process of plastic deformation are benefited for enhanced strength and ductility. [ABSTRACT FROM AUTHOR]

Abstract This paper presents the results of studies on the microstructure and mechanical properties of a near β-Ti alloy processed with different ageing approaches. Influences of intragranular ultrafine α precipitates and grain boundary α layer on mechanical properties in Ti-55531 alloy were analyzed. The results indicate that the precipitation microstructure of the duplex aged alloy exhibits a uniform size and acicular α precipitated orientation shows an angle of approximately 60°. While the morphology of secondary α precipitates in single-step aged samples appear the irregular distribution and heterogeneous size. With the final ageing time increasing, the morphology of intragranular α precipitates and grain boundary α phase brings out a distinct coarsening. The single-step aged alloy can yield a better combination of the ultimate tensile strength (1265 MPa) and ductility (9%). However, the ultimate tensile strength of the duplex aged alloy even reaches 1368 MPa but it breaks at the stage of elastic deformation. The fracture mode of Ti-55531 alloy changes from predominantly dimple fracture in single-step aged samples to predominantly faceted and cleavage type fracture in duplex aged samples causing by the differences of intragranular α precipitates and the interface between grain boundary α layer and intragranular microstructure. Highlights • High strength β-Ti alloys are widely used for their excellent properties. • To reach an excellent combination of strength and ductility, it is attractive to explore the right heat treatment system. • While compared to the conventional single-step ageing process, duplex ageing could change the development and refinement of secondary α precipitations in near/metastable β-Ti alloys resulting varying in performance. • Therefore it is of scientific significance and engineering value to understand the influence of duplex ageing on the formation of secondary α precipitates and mechanical properties for this type of alloy. [ABSTRACT FROM AUTHOR]

A new near β-Ti alloy Ti-5Al-3Mo-3V-2Cr-2Zr-1Nb-1Fe (Ti-5321) with a unique combination of high strength and good fracture toughness was designed. The microstructure was tailored by changing the solution and ageing conditions, and the influences of microstructural evolution on tensile properties and fracture toughness of the alloy were investigated. The results showed that the volume fraction and size of primary α phase were decreased with increasing the solution temperature, while the morphology of secondary α precipitates was related to ageing temperature. The ultimate tensile strength (UTS), total elongation (EL) and fracture toughness can be achieved in a range of 1147–1439 MPa, 3–26% and 57–76 MPa m 1/2 , respectively, depending on the heat treatment parameters. An excellent balance of high strength and good ductility was realized after the solution treatment at 830 °C and ageing at 620 °C for 480 min, in which the UTS, EL and fracture toughness were 1238 MPa, 20% and 73 MPa m 1/2 , respectively. Morphological features of the fractography were discussed against the different microstructural morphologies, and this provided further information on the fracture behavior of the alloy. [ABSTRACT FROM AUTHOR]

• The hierarchical micro-nano porous structure preparation via dealloying. • The micro-groove was 2.42 ± 0.83 μm in length and 0.58 ± 0.12 μm in width, the size of the nanopores was 14.6 ± 0.57 nm. • The hierarchical micro-nano porous structure guided the elongated morphology of MSCs cells. • Elongated cell morphology favored osteogenic differentiation in vitro. • The hierarchical micro-nano porous structure was beneficial to the early osseointegration in vivo. The hierarchical micro-nano porous structure in this study was prepared on the surface of Ti-3Zr-2Sn-3Mo-25Nb (TLM) titanium alloy by electrochemical dealloying process, in which the size of the micro-grooves was 2.42 ± 0.83 μm in length and 0.58 ± 0.12 μm in width, and the size of the nanopores was 14.6 ± 0.57 nm. The hierarchical porous structure was detected to significantly reduce the surface roughness and enhance wettability, which is beneficial for the adhesion and spreading of cells. Notably, the hierarchical porous structure remarkably up-regulated osteogenic differentiation and inhibited adipogenic differentiation. The relevant mechanism can be explained as micro-scale grooves induced cell morphology and then guided differentiation behavior. In addition, the hierarchical porous structure also increased the contact area between the bone and the implant, and induced more new bone formation. [ABSTRACT FROM AUTHOR]

In this paper, we investigated the tensile embrittlement of lamellar Ti-5553 alloy by analyzing its deformation mechanism, damage behavior and tensile fractography. The lamellar alloys were prepared by solution at 900 °C and ageing at 500 °C, 600 °C, 700 °C and 800 °C respectively. Although the lamellar alloys are different in the dimension and volume fraction of Alpha precipitation, they exhibit the same deformation, damage and fracture feature. The deformation of the alloy is dominated by the shearing of the Alpha precipitation and the simultaneous straining of the Beta matrix inside the lamellar unit, and the strain localization of lamellar unit may lead to the formation of the deformation band. The damage of the alloy initiates at the intrinsic ruptured Alpha precipitation. As the strain increases, the micro-crack may propagate inside the deformation band by the coalescence of the micro-void inside the lamellar unit. Once the crack reaches the critical length, the trans-granular shearing fracture takes place, leading to the final failure. In summary, the tensile embrittlement of lamellar Ti-5553 alloy is mainly caused by the strain localization of lamellar unit and the trans-granular shearing fracture. [ABSTRACT FROM AUTHOR]

In this paper, porous Ti6Al4V alloys for biomedical applications were fabricated by diffusion bonding of alloy meshes. The compression–compression fatigue behavior was studied. It results that porous Ti6Al4V alloys show enhanced normalized fatigue strength which is in the range of 0.5–0.55 at 10 6 cycles. The porosity has some effect on the absolute S – N curves but minor effect on the normalized S – N curves. The relationship between strain per cycle and number of cycles shows three distinct stages and the value of strain per cycle is constant in stage II. The reasons for the higher normalized fatigue strength of porous Ti6Al4V alloys are discussed based on the fatigue crack initiation and propagation. [ABSTRACT FROM AUTHOR]

The formation of intermediate phases ω and O′ during low-temperature aging at 200 °C and its effect on plastic deformation in a new-developed near β-Ti alloy Ti–5Al–3Mo–3V–2Cr–2Zr–1Nb–1Fe (wt %) have been studied in this work. The results showed that the ω and O′ phases were continuously transformed upon aging, and larger amount of O′ precipitates was developed in air-cooled sample than water-quenched one. Upon early aging the yield strength and ductility of alloy were simultaneously improved until 60 min. The trade-off relationship of strength and ductility was overcome by the simultaneous precipitation of ω and O′ phases. It was suggested that the ω and O′ precipitation changed the deformation mechanisms, leading to this alloy exhibited different deformation behaviors and mechanical properties. With the quantities of ω and O′ increasing, the strain-induced α′′ martensite transformation was gradually suppressed, and the primary deformation mechanism changed into a mixture of strain-induced ω transformation, mechanical twining and dislocation slipping. These findings would provide an insight to achieve better combinations of strength and ductility in near β-Ti alloys through tailoring the ω and O′ phase transformations. [ABSTRACT FROM AUTHOR]

A nanostructured surface layer was successfully performed on a biomedical β-type TiNbZrFe alloy by surface mechanical attrition treatment (SMAT). The results reveal that the surface layer along the depth from treated surface to strain-free matrix could be divided into an outer nanocrystalline layer (0–30 μm), a high-density dislocation region (30–200 μm) and an inner region with low-density dislocations and twins (200–700 μm) when the surface was treated for 60 min. The microhardness of the surface layer is enhanced and increases with increasing treatment time. Although the {1 1 2} 〈1 1 1〉 twin coordinates the deformations with dislocations, this coordination only occurs in the low strain area and cannot affect the nanocrystalline formation. The self-nanocrystallization of TiNbZrFe alloy is mainly attributed to dislocation movements. First, the dislocations start to move and easily form dislocation bands along certain crystal directions; then, multiple slips of dislocations gradually form dislocation tangles; after that, high-density dislocation tangles increases, which divides primary grains into many small domain areas. As high strain energies accumulate on the interfaces among these areas, the lattice rotation can be driven between the adjacent small domain areas, finally resulting in a large number of nanocrystalline regions with low or large angle grain boundaries. [ABSTRACT FROM AUTHOR]

The role of the forging temperature, forging strain and solution temperature on the preparation of bimodal Ti-5553s alloy has been studied in this paper. The initial full lamellar Ti-5553s alloy could be forged within a wide temperature scope of 600–800°C by a high compression strain (0.88), demonstrating the excellent thermal processing ability in the α+β field. The sub-transus forging is essential to the preparation of the bimodal alloy, and the recommended forging temperature and the critical forging strain for the lamellar Ti-5553 alloy are 780°C and 0.3, respectively. To prevent the coarsening of the β grain, the recommended solution temperature for bimodal alloy lies in 790–820°C. The decrease in the forging temperature or the increase in the solution temperature may lead to the increase in the Vickers hardness of the bimodal alloy. The relationship between the forging factors, the microstructure and the mechanical performance of Ti-5553s alloy has been developed, and these laboratory results provide a guideline for the preparation of the large-scale Ti-5553s alloy component with the homogeneous bimodal microstructure. [ABSTRACT FROM AUTHOR]

Abstract: A combination of transmission electron microscopy, scanning electron microscopy and x-ray diffractometer is used to analyse the deformation mechanism and the fracture behavior of bi-model structure Ti–5Al–5V–5Mo–3Cr–1.5Zr–0.5Fe alloy during uniaxial tensile test. In the uniform deformation region, the strain of the primary α particles is dominated by the planar slipping and the dislocation tangling, and the deformation of the β matrix is accompanied by the dislocation tangling. In the necking region, the additional deformation twinning is found in the primary α particle, and the β phase is still strained by the dislocation tangling. The local shearing occurs in the necking region and results in the micro-twinning dominated deformation in secondary α precipitation and the 〈110〉β fiber texture. The room temperature tensile fracture of Ti-55531 alloy is extremely sensitive to the formation of the voids, and the critical dimension of the crack is the diameter of the primary α particles. [Copyright &y& Elsevier]

Highlights: [•] We examine the effects of aging temperature and time on the microstructure of the new near-β titanium alloy (Ti-7333 alloy). [•] We discuss the distinctions and similarities between the new near-β titanium alloy and the traditional β titanium alloys. [•] The diffraction pattern from the [111] β zone axis show reflections consistent with the α variants obeying the Burgers relationship. [ABSTRACT FROM AUTHOR]

Abstract: Grain boundary character distribution and texture evolution of Ti–45Nb wires were investigated during the cold-drawn process. The results revealed that the fiber microstructure formed along drawing direction after cold-drawn process. The <110> fiber texture formed and the intensity enhanced by increasing the strain from 90% to 98% during the cold-drawn process. A large amount of high angle grain boundaries (HAGB) occurred at a large strain state of 90%, which was resulted from the rotation of the initial β grains. By increasing the strain to 98%, the fraction of low angle grain boundaries (LAGB) increased remarkably by the formation of the subdivided grains. [Copyright &y& Elsevier]

Abstract: X-ray photoelectron spectroscopy was used to investigate the ω phase in water quenched Ti-5553 alloy with a nominal composition of Ti–5Al–5V–5Mo–3Cr (wt.%), and the ω and the β phase were distinguished by deconvoluting the XPS spectra of Al2p, V2p and Cr2p core level regions. In addition, it is found that the binding energy of core level electron of alloying elements shifts comparing with that of pure metals, and the fact was interpreted by charge redistribution model. X-ray photoelectron spectroscopy technique could be used to characterize the nano-scale ω phase in β alloys. [Copyright &y& Elsevier]

Abstract: The initial microstructure of Ti40Zr25Ni8Cu9Be18 metallic glass is sensitive to preparation condition. The Ti40Zr25Ni8Cu9Be18 metallic glasses, prepared at different liquid temperature by copper mold casting, would possess different first crystallization product because of difference in initial microstructure. During first crystallization, Crystallization product is mainly metastable icosahedral phase for metallic glass prepared at relative low liquid temperature. However, the mixture of α-Ti + icosahedral + unknown phase precipitates from metallic glass prepared at relative high liquid temperature. Moreover, the difference in initial microstructure also has a significant influence on compressive properties. Ti40Zr25Ni8Cu9Be18 metallic glasses prepared at relative low temperature exhibit better plasticity. One of important reasons is that dominant icosahedral short range order (SRO) increases shear viscosity of shear band, and the possibility of catastrophic failure caused by fast and continuous slide of shear band is depressed. [Copyright &y& Elsevier]

Abstract: The ω phase transformation kinetics of TB-13 titanium alloy has been analyzed by non-isothermal dilatometry. The average value of local activation energy determined is about 91.7kJ/mol. The nucleation and growth mechanism of the ω phase has been investigated by the non-isothermal local Avrami exponent. Both the local Avrami exponent and the local activation energy during the ω phase transformation process change significantly with the transformed volume fraction, indicating that the ω phase transformation mechanism in this alloy varies at different stages. The local Avrami exponent lies between 1 and 2 in a wide transformed volume fraction range of 0.17–0.95, indicating that the dominating mechanism of ω phase transformation in TB-13 titanium alloy is the three-dimensional growth with a near-zero nucleation rate. [Copyright &y& Elsevier]

Abstract: In TC21 alloy, the influence of solution treatment temperature on phase transformation has been investigated. When solution treatment was conducted at temperature above 840°C, orthorhombic α″ martensite was formed. Moreover, the α2 phase was observed after solution treatment between 1000°C and 920°C for 1h. Below 840°C, the β phase was stable, no martensitic occurred. Crystallographic analysis suggests that the principal strains of martensitic transformation decrease with the solution treatment temperature decreasing. The microhardness of TC21 alloys on examination increased with the solution treatment temperature decreasing firstly, and then decreased, below 840°C, the microhardness increased again with the solution treatment temperature. [Copyright &y& Elsevier]

Abstract: A dilatometry for investigating phase transformation in TC21 alloy was observed at constant heating rate. These experiments were conducted at a computer-controlled horizontal pushrod dilatometer to monitor the thermal expansion caused by the transformation as a function of heating time under different heating rates. Microstructures at different stages of the transformation had been observed by scanning electron microscopy. Results showed that phase transformation in TC21 alloy during continuous heating included three stages, retained β→acicular α, acicular α→β and equiaxed α→β. The rates of the alloy expansion decreased after an increase, and then increased intensively, and finally, it decreased to a constant. Moreover, the activation energy value related to the α→β transformation in TC21 alloy was evaluated based on the JMA equation. [Copyright &y& Elsevier]

Abstract: Compressive deformation behavior of the Ti40Zr25Ni8Cu9Be18 bulk metallic glass was investigated over a wide strain rate ranging from 10−4 to 103 s−1 at room temperature. Fracture stress was found to increase and fracture strain decrease with increasing applied strain rate, which were due to the decrease of the density of shear bands. Serrated flow was observed at lower strain rate. The appearance of a large number of shear bands was probably associated with flow serration observed during compression. At high strain rates, the rate of shear band nucleation was not sufficient to accommodate the applied strain rate and thus caused an early fracture of the test sample. The positive strain rate dependence of compressive strength might be associated with the different microstructure on the atomic scale in the Ti-based amorphous matrix. [Copyright &y& Elsevier]

• The cyclic behavior and microstructure evolution of TC4F alloy were investigated. • Phase transformations and α dynamic recrystallization contributed to great changes in the microstructure of TC4F alloy. • The evolution of substructure played an important role in the dwell-fatigue of TC4F alloy. The cyclic behavior and microstructure evolution of Ti-6Al-4V-0.55Fe alloy were investigated with three different total strain amplitudes. A slight softening was occurred with Δ ε t /2 = 1.20%, and the alloy mainly suffered α recrystallization. Besides, a gentle softening can be observed with Δ ε t /2 = 1.60%, which led to more substructure deformation. Furthermore, a sudden drop of the stress amplitude was occurred with Δ ε t /2 = 4.00% which resulted in more plastic deformation. The phase transformation and α recrystallization were observed. Cracks were propagated along the α grain boundaries and the α/β lamellar interfaces due to the concentrated dislocations at the α/β lamellar interfaces. [ABSTRACT FROM AUTHOR]

In this work, damage/fracture development of Ti-6Al-4V alloy was analyzed with the help of in situ tensile test by synchrotron X-ray tomography. The result shows that during the whole damage/fracture procedure for Ti-6Al-4V alloy, the value of stress triaxiality (T) seems to maintain as a constant (T = 0.472–0.510) and to be adjacent with the critical value (T c = 0.49). This can result in the fracture of the alloy in the way of Mix mode (component induced by cleavage component and ductile component). With the help of X-CT scanning, voids evolution were clearly realized and characterized during damage development. On the basis of void tracking results, Rice-Tracey damage model and Huang damage model were adapted to depict and predict the voids growing behavior by calibrating the material parameter. Finally, the micro-mechanism of the mix damage mode was revealed, which can be attributed to local internal shear stress. The significant act of microstructure morphology on the component from mix damage mode was also determined and discussed. [Display omitted] • 3 damage stages were clearly characterized by using In situ X-CT. • Both Rice-Tracey model and Huang model were implemented to schematize voids growing behavior. • Mix damage mode was intensively analyzed during the whole damage development. • The influence of microstructure morphology on the mix damage mode was deeply discussed. [ABSTRACT FROM AUTHOR]

Titanium alloys manufactured via additive manufacturing are suffering from coarse columnar grains due to the insufficient spontaneous nucleation rate during solidification. In this study, a newly designed Ti–2Fe-0.1B alloy with higher nucleating agent were introduced and manufactured by laser melting deposition method. The manufactured part is presenting a fully equiaxed grain morphology with 779 MPa on ultimate tensile strength. In order to reveal the mechanism of equiaxed grain formation and its influence on mechanical properties, a comprehensive study of microstructure evolution was carried out on Ti–2Fe-0.1B alloy manufactured via casting, forging and laser melting deposition. The results indicate that cooling speed are playing an important role on TiB morphology and Ti–2Fe-0.1B grain size simultaneously. The TiB formed from fast cooling speed are presenting a 3D quasi-network structure and improves the ultimate tensile strength of laser melting deposited part by 1.7 and 1.5 times when compared with casting and forging parts correspondingly. The study reveals that B addition is a sufficient method to control equiaxed grain formation in additive manufacturing of Ti–Fe alloy and promotes B addition as grain morphology controlling method in other additive manufactured titanium alloys in future. [ABSTRACT FROM AUTHOR]

To achieve preferable impact performance of a newly designed high strength Ti-5321 alloy, samples with three kinds of microstructures, i.e., bimodal microstructure (BM), tri-modal microstructure (TM) and lamellar microstructure (LM) were prepared for instrument Charpy tests at room temperature. Results of impact tests indicated that LM presented the higher impact toughness of 37.5 J/cm2 than that of BM (11.25 J/cm2) and TM (25 J/cm2). Moreover, both crack initiation energy and crack propagation energy of LM were obviously raised. Further analysis containing fracture surfaces and the cross-sectional microstructures of the impact samples by the usage of SEM and EBSD provided insights into the influence of microstructure on crack initiation and propagation during impact process. The largely plastic deformation of primary α near the V-notch tip impeded crack initiation and enhanced the crack initiation energy. The interweaved α colonies with high angle boundaries deflected the crack propagation direction and thus increased the crack propagation energy. Besides, TEM analysis showed that the typical deformation characteristic under impact test with high strain rate. Except for dislocation lines, the pile-up of highly dense dislocations, twinning, dislocation cells, sub-grains, shear bands and fragmentation of α phase can be found. These approaches presented in this study could provide certain insights into fabricating typical microstructure in the high strength titanium alloys to ameliorate impact properties. • Lamellar microstructure shows the superior combination of strength, ductility and impact toughness. • Effective crack deflection and compatible deformation of lamellar microstructure can improve the impact toughness. • Dislocation slip, twinning, dislocation cells, shear belts and fragmentation of α phase can be found in the impact samples. [ABSTRACT FROM AUTHOR]

A comprehensive study of Fe alloying influence on as-cast titanium alloys, including microstructure, mechanical properties, bio-corrosion behavior and in-vitro cell response have been carried out to evaluate the biological application potential of Ti-Fe binary alloys. The results indicate that grain sizes of as-cast Ti-Fe alloys are remarkably refined with Fe addition and the mechanical strength is increased tremendously. For instance, Ti-2Fe alloy presents excellent mechanical properties by elevating the tensile strength to 566 MPa, or 1.5 times over pure Ti, while maintaining a relative high plasticity. All Ti-Fe alloys carried in this study show a higher corrosion resistance in Hank's solution than pure Ti due to the grain refine enhancement and higher oxide film growth kinetics. Ti-2Fe alloy presents the best corrosion resistance among them and higher Fe content could bring more Fe 2 O 3 to the oxidation films that decrease the corrosion resistance accordingly. All Ti-Fe alloys are holding a similar osteoblast cell viability and response to pure Ti which ensure their biocompatibility. The combination of mechanical properties, corrosion resistance and in-vitro response of Ti-2Fe promised its application as dental implants in a near future. Unlabelled Image • The Fe amount could affect titanium grain size tremendously and thus influence its mechanical and corrosion behavior • Corrosion resistance of Ti-Fe alloys are varied with oxidation film thickness and composition difference. • Ti-Fe alloys exhibit an excellent biocompatibility attributed to increasement of corrosion resistance and cell response. • Ti-2Fe presents a good combination between mechanical and corrosion performance thus promotes its potential application. [ABSTRACT FROM AUTHOR]

A series of ternary Ti–6Zr-xFe (x = 4, 5, 6, 7 wt %) biomedical titanium alloy was designed to develop potential biomedical materials. The effect of the Fe content on microstructure, mechanical properties, Young's modulus, and electrochemical behavior was studied in depth. The developed Ti–6Zr-xFe (x = 4, 5, 6, 7 wt %) alloys are mainly composed of α and β phases. The results indicated that the grain size of the β phase in Ti–6Zr-xFe alloys decreased with the increase of Fe element. The increase of Fe content also caused the decrease of α phase fraction, increase of β phase fraction and formation of ω phase. Besides, the increase of Fe content improved the microhardness (264, 300, 328, and 348 HV) and ultimate tensile strengths (748, 829, 917, and 994 MPa) of Ti–6Zr-xFe alloys due to the contribution of solid-solution strengthening effect for higher Fe contents, the refined strength of the β phase and the dispersion strength of ω phase. Young's modulus of Ti–6Zr-xFe alloys was 90, 93, 93, and 94 GPa, which was lower than that of Ti–6Al–4V alloy. Moreover, the Ti–6Zr-xFe alloy with the addition of 4 and 5 wt % Fe displayed excellent corrosion resistance. These results show that Ti–6Zr-xFe alloys are potential biomedical materials. • A series of novel Ti–6Zr-xFe biomedical titanium alloys was designed. • β grain size is refined with increasing Fe content. • Microhardness, tensile strength, and Young's modulus increase with increasing Fe. • Ti–6Zr-xFe alloys display excellent corrosion resistance at 4 and 5 wt % Fe. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) process belongs to a layer-by-layer additive manufacturing technology, which has different temperature gradients, cooling rates, and reheating treatment in different regions due to the variation of the thermal histories for different layers during SLM process. This work aims to study the microstructural homogeneity evolution of β phases, such as size, morphology, distribution, crystallographic orientation, and phase composition in different regions of the SLM Ti-6Zr-5Fe near β titanium alloy. The results indicate that the microstructure in different regions of SLM Ti-6Zr-5Fe alloy sample is quite different. The β phase in the bottom area had the smallest size about 7.25 μm, the β phase in the side-top area had the largest size about 20.56 μm. The β phase in the side-middle and middle part had a lower aspect ratio of 1.52 and 1.59, the β phase in the side-bottom and top part had a larger aspect ratio of 1.93 and 1.92. Most of the β phase in the side-bottom and top part had the 〈001〉 crystal orientation towards build direction and laser moving direction, the texture type in other regions was random. The α phase in the top of the SLM Ti-6Zr-5Fe sample had a smaller size than that in the middle and bottom of the sample. Meanwhile, the microhardness in the top of SLM Ti-6Zr-5Fe sample was higher than that in the middle and bottom of the sample. The temperature gradients, cooling rates, and reheating treatment play different leading roles in different regions of the SLM Ti-6Zr-5Fe alloy sample. • β phase size, morphology, crystallographic orientation are not entirely the same. • α phase size in middle and bottom is larger than that in the top. • Microhardness in the top is higher than that in the middle and bottom. • Temperature gradients, cooling rates, reheating treatment play different roles. [ABSTRACT FROM AUTHOR]

The microstructure evolution and selection of α variants in a new near β titanium alloy Ti-5321 (Ti–5Al–3Mo–3V–2Cr–2Zr–1Nb–1Fe) were thoroughly investigated by dilatometry under continuous cooling conditions accompanied with OM, XRD, SEM, EBSD and TEM. Cooling rates from β region to room temperature significantly influenced the microstructure based on the competitive growth of α GB , α WGB and α WI. The low (0.01 °C/s and 0.1 °C/s), intermediate (0.5 °C/s and 1 °C/s) and high (2 °C/s, 4 °C/s and 5 °C/s) cooling rates resulted in bi-lamellar, basket-weave and single metastable-β microstructures, respectively. Moreover, the transformed microtexture was also found in the cooling process at low cooling rate. In addition, a continuous cooling transformation (CCT) diagram obtained by the dilatometric analysis revealed the sensibility of the β→α phase transformation temperature range to the cooling rate. EBSD analysis revealed that microtexture formed by α colonies with the similar orientations, occurred in the adjacent β grains and maintained Burgers orientation relationship (OR) with at least one of the adjacent β grains. Two typical cases, i.e. the single-BOR α colonies (the colonies which maintain Burgers OR with β grain only on one side) and the double-BOR α colonies (α colonies which maintain Burgers OR with both the adjacent β grains) were studied. The single-BOR α colonies corresponded to the different α variants from the parent β grain. The double-BOR α colonies occurred in which the adjacent β grains shared nearly common {110} β plane, moreover, the double-BOR α colonies could possess the identical orientation in the adjacent β grains which have a 60° rotation about a common <111> β direction. The cooling rate significantly affects the final microstructure of Ti-5321 alloy and the corresponding continuous cooling transformation (CCT) diagram is obtained. The variant selection of α colonies can be divided into single-BOR and double-BOR variant selection in the adjacent β grains. Image 1 • Low, intermediate and high cooling rates resulted in bi-lamellar, basket-weave and single metastable-β microstructures, respectively. • CCT diagram reveals the sensibility of the β.→α phase transformation temperature range to the cooling rate. • Variant selection of α colonies can be divided into single-BOR and double-BOR. [ABSTRACT FROM AUTHOR]

• Role of nanosized O′ and ω phases on α precipitation in near βTi alloy is studied. • O′ and ω are both formed by air cooling but only O′ is developed by quenching. • The O′ promoting α precipitation is activated and the ω dissolves during aging. • Finer α precipitates are obtained in the aged AC alloy due to the greater O′ amount. Two types of intermediate phases, O′ and ω, were observed in a β-solutionized Ti-5Al-3Mo-3V-2Cr-2Zr-1Nb-1Fe alloy depending on the cooling rate. During heating the as-solutionized sample to aging temperature, the isothermal ω precipitated from β, but then decomposed before α precipitation. While the O′ was continuously formed and eventually assisted α precipitation. The air cooling sample had a greater amount of O′ domains, therefore produced finer microstructure and higher strength in the aged sample. [ABSTRACT FROM AUTHOR]

The influences of heating rate to aging temperature on intermediate phase transformation and final microstructures of near βTi alloy Ti–5Al–3Mo–3V–2Cr–2Zr–1Nb–1Fe (wt.%) have been studied in this work. The results showed that three nano-scaled intermediate phases, i. e. O′, ω iso and O″ phases, were subsequently formed before α precipitation when heating by slow (10 °C/min) and fast (~100 °C/min) rates, depending on heating rate. The ω iso and O″ phases become unstable and will dissolve before arriving the aging temperature, while plenty of O′ domains can always be observed accompanying with the precipitation of needle-like α phase. Whereas upon rapid heating (~400 °C/min), only O′ phase can be observed during continuous heating to target aging temperature. We suggest that the uniform and dense distribution of fine α precipitates formed even at fast heating rate ascribes for the precipitation of a large number of O′ precursors assist α nucleation. The slow and fast heating rates result in similar yield strength of the aged samples, however, the slow heating rate can obtain better ductility due to the formation of discontinuous grain boundary α colonies instead of continuous α layers. • Intermediate phases O′, ω iso and O″ can form subsequently during continuous heating. • The O′ domains can form at a wide heating rate range and promote α precipitation. • Only O′ phase formation can be observed during the rapid heating (~400 °C/min). • Fast heating rate (~100 °C/min) can also produce fine α precipitates. [ABSTRACT FROM AUTHOR]

The widely used Ti–6Al–4V (TC4) titanium alloy has been modified through the micro-alloying of Fe. The microstructural features and mechanical properties of the designed alloy, TC4F, are compared with other alloys in Ti–6Al–4V class by combining experimental characterizations and thermodynamic calculations. TC4F alloy not only maintains strength, hardness, and elongation similar to baseline TC4 but also exhibits improved fracture toughness comparable to TC4_ELI and even superior to TC4_DT under the heat-treated condition. It opens up a new cost-reducing way to enhance fracture toughness in place of controlling interstitial contents, showing potential in engineering applications. The discerned mechanisms indicate that the trace addition of Fe gives rise to composition redistribution between V and Fe in the β phase, boosts the lattice distortion and vibration, thereafter enhances Young's modulus and fracture toughness. It has been validated and verified by experiments, thermodynamic calculations, and Hahn-Rosenfield empirical research. The enhanced fracture toughness also benefits from the kinked β+α lamellar microstructure at crack tip as well as the improved fracture surface due to the Fe addition. The enlarged plastic zone, redirected crack propagation, and more dimples with even-distributed size additionally contribute to the improvement of fracture toughness. Image 1 • The microalloying of Fe in Ti–6Al–4V can effectively improve the fracture toughness. • The Fe-alloyed Ti–6Al–4V shows comparable mechanical properties to TC4ELI and TC4DT. • The interaction between Fe and V leads to enhanced modulus and increases fracture toughness of TC4F. • The kinked β+α lamellae are found nearby the crack of TC4F in contrast with bent α lamellae in TC4. [ABSTRACT FROM AUTHOR]