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Three types of solution treatment and aging were designed to reveal the α' decomposition and its effect on the mechanical properties of near-α Ti-80 alloy, as follows: solution at 970 °C then quenching (ST), ST + aging at 600 °C for 5 h (STA-1), and ST + aging 600 °C for 24 h (STA-2). The results show that the microstructures of the ST samples were mainly composed of equiaxed αp and acicular α', with a large number of dislocations confirmed by the KAM results. After subsequent aging for 5 h, α' decomposed into acicular fine αs and nano-β (intergranular β, intragranular β) in the STA-1 specimen, which obstructed dislocation motion during deformation, resulting in the STA-1 specimen exhibiting the most excellent yield strength (1012 MPa) and maintaining sufficient elongation (8.1%) compared with the ST (898 MPa) and STA-2 (871 MPa) samples. By further extending the aging time to 24 h, the size of acicular αs and nano-β gradually increased while the density of dislocations decreased, which resulted in a decrease in strength and an increase in plasticity. Based on this, a microstructures–properties correlation model was proposed. This study provides a new method for strength–plasticity matching of near-α titanium alloys through α' decomposition to acicular αs+nano-β. [ABSTRACT FROM AUTHOR]

The dynamic spheroidization mechanism and its orientation dependence in Ti-6Al-2Mo-2V-1Fe alloys during subtransus hot deformation were studied in this work. For this purpose, hot compression tests were carried out at temperatures of 780–880 °C, with strain rates of 0.001–0.1 s−1. Based on SEM, EBSD and TEM characterization, the results showed that the aspect ratio of the α phase decreased with increasing deformation temperatures and decreasing strain rates. At 880 °C/0.001 s−1, the aspect ratio of the α phase was the smallest at 2.05. The proportion of HAGBs decreased with increasing temperatures and strain rates, which was different from the trend of the spheroidization; this indicated that the formation of HAGBs was not necessary for the spheroidization process. Furthermore, the formation of the α/α interface was related to the evolution of dislocations and twin boundaries at high (880 °C) and low temperatures (780 °C), respectively. Moreover, the dependence of lamellar spheroidization on the crystallographic orientation tilt from the compression direction (θ) was clarified: when θ was between 45° and 60°, both the prism slip and basal slip systems were activated together, which was more favorable for spheroidization. This study could provide guidance for titanium alloy process designs and microstructure regulation. [ABSTRACT FROM AUTHOR]

Weight reduction is often considered the primary goal in the development of structure materials. A new Ti-8Al-1Cr-1V-0.5Fe-0.1Si (wt.%) alloy with a low-density and a high-strength was developed in this work. The microstructures and mechanical properties of the alloy were investigated in hot-rolled and solution-aging (STA) treatment conditions. The microstructures of the alloy in both states consist of the spherical αp phase, acicular αs phase, and a small amount of β phase. Attributed to such heterogeneous microstructures, the hot-rolled alloy exhibits an outstanding tensile strength of 1046.1 MPa, a total elongation of ~8.3%, and an impressive low density of 4.23 g/cm3. After heat treatment, the alloy also exhibits a similar strength and ductility. A detailed analysis of the deformation modes shows that the numerous dislocations slippages and deformation twinning in the αp phase are the main reasons for the high ductility, and the acicular αs phase provides the alloy with high strength after heat treatment. This newly developed alloy is a potential material for various structural applications. [ABSTRACT FROM AUTHOR]

The mechanical response and deformation mechanisms of TB17 titanium alloy were studied at room temperature by the split-Hopkinson pressure bar test. The ultimate compression strength increases from 1050 MPa to 1400 MPa, as the strain rate increases from 2000 s−1 to 2800 s−1. The adiabatic shear failure occurred at strain rate 2800 s−1. When the strain rate was 2000 s−1, only {10 9 3}<331>β type II high index deformation twins, a small number of α" martensite, and interfacial ω phase were detected. When the strain rate was 2400 s−1 and above, multiple deformation mechanisms, including the primary {10 9 3}<331>β type II high index deformation twins, secondary {332}<113>β deformation twins, and α" martensite were identified. The deformation mechanism changes from primary deformation twins and α" martensite to multiple deformation mechanisms (primary and secondary deformation structure) with the increase of strain rates. [ABSTRACT FROM AUTHOR]

The two-pass thermal compression behavior of near-β Ti-55511 alloy was investigated. The first-pass restoration mechanisms changed from dynamic recrystallization (DRX) to dynamic recovery (DRV) as the first-pass deformation temperature increased from 700 °C to 850 °C. The occurrence of recrystallization reduced the dislocation density, resulting in a slower grain growth rate in the subsequent process. Because of the static recrystallization (SRX) and β grain growth, the β grain size increased and the morphology became less uniform during the subsequent β holding process, which also changed the restoration mechanism during second-pass compression. The level of continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) become weaker during second-pass deformation. The changes in the restoration mechanism and the microstructures slightly increased the peak stress during the second-pass deformation. [ABSTRACT FROM AUTHOR]

Multi-pass hot rolling was performed on bi-modal Ti-55511 alloy with 50% rolling reduction at 700 °C. Mechanical properties were evaluated by tensile test, and microstructure evolution was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the Ti-55511 alloy with bi-modal microstructure exhibits good strength and high ductility (1102 MPa, 21.7%). Comparatively, after 50% hot rolling, an enhanced strength and decreased ductility were obtained. The refinement of α phases leads to the increased tensile strength, while the fragmentation of the equiaxed α phase results in a decreased ductility. The fragmentation process of equiaxed α phases followed the sequence of: elongation of α phases → formation of grooves and localized shear bands → the final fragmentation accomplished via deepening grooves. [ABSTRACT FROM AUTHOR]

Customized porous titanium alloys have become the emerging materials for orthopaedic implant applications. In this work, diamond and rhombic dodecahedron porous Ti-33Nb-4Sn scaffolds were fabricated by selective laser melting (SLM). The phase, microstructure and defects characteristics were investigated systematically and correlated to the effects of pore structure, unit cell size and processing parameter on the mechanical properties of the scaffolds. Fine β phase dendrites were obtained in Ti-33Nb-4Sn scaffolds due to the fast solidification velocity in SLM process. The compressive and bending strength of the scaffolds decrease with the decrease of strut size and diamond structures showed both higher compressive and bending strength than the dodecahedron structures. Diamond Ti-33Nb-4Sn scaffold with compressive strength of 76 MPa, bending strength of 127 MPa and elastic modulus of 2.3 GPa was achieved by SLM, revealing the potential of Ti-33Nb-4Sn scaffolds for applications on orthopaedic implant. [ABSTRACT FROM AUTHOR]

The influence of various Zr contents (0–45 wt.%) on the microstructure and mechanical properties of Ti6Al4V alloy was investigated through a combinatorial approach. The diffusion multiples of Ti6Al4V–Ti6Al4V20Fe–Ti6Al4V20Cr–Ti6Al4V20Mo–Ti6Al4V45Zr were manufactured and diffusion-annealed to obtain a large composition space. Scanning electron microscopy, electron probe micro-analysis, and a microhardness system were combined to determine the relationships among the composition, microstructure, and hardness of these alloys. The Ti–6Al–4V–30Zr alloy was found to contain the thinnest α lath and showed peak hardness. X-ray diffraction and transmission electron microscope results indicated that after quenching from the β-field, the metastable α″-phase formed; moreover, at the secondary aging stage, the metastable α″-phase acted as precursor nucleation sites for the stable α-phase. The bulk Ti6Al4V30Zr alloy was manufactured. After aging at 550 °C, the alloy showed excellent balance of strength and ductility, and the tensile strength was 1464 MPa with a moderate elongation (8.3%). As the aging temperature increased, the tensile strength and yield strength of the alloys rose, but the total elongation decreased. The lamella thickness and volume fraction of the α-phase were the major factors that had great impacts on the mechanical properties. [ABSTRACT FROM AUTHOR]

Near β titanium alloy Ti-55531 with an acicular starting microstructure was isothermally compressed at 750–825 °C and 10−3−1 s−1. The microstructure evolution and its influence on the flow behavior of yielding and softening were investigated. Discontinuous or continuous yielding depends on the hindrance to the dislocation motion coming from the β grain boundary or α phase. At higher temperatures, the hindrance mainly comes from the β grain boundary. Its discontinuous action, including the piling-up and subsequent loosening of dislocations at the β grain boundary, leads to discontinuous yielding. At lower temperatures, the continuous hindrance to the dislocation motion, which is exerted by the β grain boundary and acicular α, causes continuous yielding. Sequentially, the substructures in acicular α are evolved from high-density dislocations or local shear bands, which depend on the orientation relationship between β and α. Then, the β matrix edges into the acicular α along substructure boundaries. The higher strain rate decreases the deformation time to carry out the fragmentation of acicular α, while the higher temperature decreases the dislocation density due to the recovery of β, which does not benefit the substructure formation and subsequent fragmentation of acicular α. Therefore, the retardation of acicular fragmentation and the as-resulted decreased flow softening rate are observed. [ABSTRACT FROM AUTHOR]

• A novel Ti-xNb-yZr-5Mo-6Sn-0.6O system alloy has been investigated. • Ti-7.8Nb-1.7Zr-5Mo-6Sn-0.6O alloy with excellent mechanical properties was screened. • Rapid development of biomedical titanium alloys has been achieved. Biomedical titanium alloys have been widely used as surgical implant materials, but traditional biomedical titanium alloys no longer meet practical needs, and there is an urgent need to develop new biomedical titanium alloys. In this study, the composition, microstructure, and mechanical properties of novel Ti-xNb-yZr-5Mo-6Sn-0.6O biomedical titanium alloys were investigated based on diffusion multiple high-throughput experiments. The results showed that although the microstructure of the alloys transitioned from β + α″ to β phase with the increase of Nb and Zr content, the β-stabilizing effect of Zr is weaker. The microhardness and elastic modulus of the alloys varied in the range of 2.7∼7.8GPa and 74.3∼130.2GPa, and depended strongly on the Nb content. In the Ti-xNb-yZr-5Mo-6Sn-0.6O system alloy, the Ti-7.8Nb-1.7Zr-5Mo-6Sn-0.6O alloy with the high hardness of 5.5 GPa and low elastic modulus of 74.3 GPa is a promising candidate for orthopedic implants. Moreover, this work indicates that high-throughput experiments are an effective method for rapidly developing high-performance biomedical titanium alloys. [ABSTRACT FROM AUTHOR]

Optimizing performance and reducing costs often exhibit a trade-off relationship, thereby limiting the broader application of Ti alloys. To address the above challenge, this study involves comparative analyses of strength and fracture toughness, for TC18 alloy processed through distinct forging methods—long-period forging (M1) and short-period forging (M2). The results shows that both M1 and M2 present analogous content and dimensions of equiaxed primary α phase (α p) and secondary α phase (α s), as well as comparable values for yield stress (∼1050 MPa), and plasticity (∼7 %). Nevertheless, fracture toughness of the latter (M2) exhibits a notable increase (74.3 MPa∙m1/2) than that of the former (55.1 MPa∙m1/2). This phenomenon is primarily attributed to the heightened compatibility of mechanical properties and superior orientation relationship between α p and β t in M2 as opposed to M1. These characteristics give rise to a homogeneous deformation and an augmentation in void nucleation within the α p phase in the larger plastic deformation zone in M2. Additionally, the translocation of dislocations from α p /β t interfaces into the β t matrix in M2 is also verified by the tensile test at 3 % strain. The findings provide a promising insight for the design of low-cost Ti alloys with attractive strength and damage tolerance. [ABSTRACT FROM AUTHOR]

After 920 °C/120 min → WQ + 780 °C/300 min → air fast cooling heat treatment, a banded ω' phase distributing at interfaces between the β matrix and grain boundary α phase was discovered in a Ti-4.5Al-6.5Mo-2Cr-2.5Nb-2Zr-1Sn (wt%) alloy. The ω' phase shows a P6/mmm hexagonal close packed lattice crystal structure and its lattice parameters are a = 0.399 nm, c = 0.282 nm. The orientation relationship between ω' and adjacent β phase are (110) β1 //(1 1 ¯ 00) ω' , (111) β1 //(0001) ω' , and (112) β1 //(11 2 ¯ 0) ω'. The atom migration path during the β → ω' phase is (121) β plane collapse along the <010> β direction. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Titanium (Ti) and titanium alloys have been increasingly used in fixed and removable prostheses and aerospace bearing materials because of its excellent biocompatibility, corrosion resistance and mechanical properties. Cr element is often added to titanium alloys as a solid solution strengthening element. However, the content of Cr was restricted in the commercial titanium alloy to avoid β-flecks and deterioration of mechanical performance because of the strong segregation of Cr. A series of homogeneous Ti-xCr (x = 6, 8.5, 10, 13.4, 15 wt%) binary alloys near the eutectoid point were manufactured by laser directed energy deposition. The phase composition and morphology, mechanical properties and deformation mechanism were investigated. It was demonstrated that the eutectoid reaction of additive manufacturing Ti–Cr alloy has been suppressed. Hypoeutectoid Ti-xCr alloys (x = 6, 8.5, 10 wt%) obtained microstructures consisting of α and β phase. The Ti-xCr alloy with eutectoid compositions (x = 13.4 wt%) obtained a microstructure mainly composed of ω and β phase. And hypereutectoid Ti-xCr alloy (x = 15 wt%) exhibited a fully β microstructure. For α+β type Ti–Cr alloys, and the average width of α lath decreased from 868 nm to 157 nm with Cr content increased from 6 wt% to 10 wt%. Correspondingly, the α+β type Ti–10Cr alloy presented a good combination of strength (an ultimate tensile strength of 1042 MPa) and ductility (an elongation of 7.1 %). Then, a high density of ω phase was found in the Ti-13.4Cr alloy with eutectoid compositions, which leads to its brittleness. Due to the solid solution of high concentration of Cr, β-type Ti–15Cr alloy obtained a high ultimate tensile strength of 941 MPa. Furthermore, stress-induced ω phase and {112}<111> twinning formed during the deformation, which helps to accommodate stress concentration, thereby the β-type Ti–15Cr alloy can maintain high ductility (20.3 %). [ABSTRACT FROM AUTHOR]

Abstract The deformation mechanisms of lamellar and equiaxed α phases of a Ti–5Al–5Mo–5V–1Cr–1Fe (Ti–55511) alloy with a bi-modal microstructure were investigated. Two types of bi-modal microstructures were introduced though different hot-rolling reductions. Accordingly, the tensile properties, fracture behavior, morphology evolution, and deformation twinning were comparatively analyzed. The results show that the sample with higher rolling reduction exhibits higher strength and better ductility, which are mainly owing to refined grain size and fragmentation of the grain boundary α phase. The deformation behaviors of the lamellar secondary α (α s) phase and equiaxed primary α (α p) phase have similarities as well as differences. During deformation, the { 1 1 ¯ 01 } twinning system is activated in both α p and α s phases. Two twin variants can be found in the lamellar phase, while three twin variants are formed in the equiaxed phase. With an increase in deformation, the twins in the equiaxed α phases extended, and consequently, the microhardness of the α p phases increased. Meanwhile, detailed TEM analyses demonstrated the presence of an α′ martensite phase in the equiaxed α phase, which intersected with the { 1 1 ¯ 01 } twin and is nearly perpendicular to the twin boundary. These findings provide insights into the deformation behaviors of bi-modal near-β Ti alloys, which can help in the optimization of deformation processes to achieve superior mechanical properties of bi-modal Ti alloys. Highlights • Deformation behaviors of lamellar and equiaxed α phases of a Ti–55511 alloy with a bi-modal microstructure were investigated. • The alloy with higher rolling reduction exhibits higher tensile strength and better ductility. • Two twin variants were found in the lamellar phase, while three twin variants were formed in the equiaxed phase. • The formation of martensite α′ phase in equiaxed α phase has been verified. [ABSTRACT FROM AUTHOR]

Customized titanium alloy devices have become the most attractive orthopaedic implants owing to their effects in mitigating the pain and suffering of patients. This work demonstrates the feasible control of the microstructure, i.e., defects, element diffusion, and phase transformation, and the mechanical properties of a biocompatible Ti–37Nb–6Sn alloy obtained by selective laser melting (SLM). Defects such as voids and unmelted Nb particles, as well grains with random orientation or columnar grains with {100} fiber texture in the as-fabricated Ti–37Nb–6Sn alloy can be modulated by varying the solidification rate and aging effects during the deposition process. A high energy density input promotes the diffusion of Sn from the grain boundaries to the β-matrix, resulting in an increase in the lattice constants of the β-matrix, with low elastic modulus of the as-fabricated Ti–37Nb–6Sn alloy. However, reheating effects promotes the formation of nanoscale α-phase precipitates both at the grain boundaries and in the matrix. The combined effects of rapid solidification and aging induced by reheating result in a metastable β-type Ti–37Nb–6Sn alloy with a Young's modulus of 66 GPa, ultimate strength of 891 MPa, and elongation of 27.5%. This method can aid the design of customized titanium devices with low elastic modulus for orthopaedic implants applications. [ABSTRACT FROM AUTHOR]

Enhancing both strength and ductility simultaneously in commercial alloys at an industrial scale remains a challenging task. In this study, we have demonstrated a simple heat treatment method to achieve a heterostructure with coarse and ultra-fine lamellar α precipitates in a common titanium alloy, Ti-5Al-5Mo-5V-3Cr-1Zr. Guided by computer simulations, we successfully attained microscale concentration modulations in the β-phase matrix using up-quenching of a duplex microstructure consisting of a globular primary α phase (α p) and β matrix to dissolve the α p phase rapidly and leave residual concentrations. We subsequently applied aging treatments to create finely dispersed regions of coarse and ultra-fine α precipitates embedded in the β matrix by activating different phase transformation mechanisms. Compared to the commercial alloy that has a homogeneous lamellar structure, the heterostructured alloy we produced exhibits a 6% increase in ultimate tensile strength and a remarkable 130% increase in elongation. The outstanding ductility of the heterostructured alloy is attributable to its unique microstructure design, which prevents strain localization and allows full activation of dislocation and twin deformations in the coarse and ultra-fine α regions. Meanwhile, the high strength of the alloy can be attributed to the enhanced back stress effect induced by strain partitioning of the heterostructure. Our study demonstrates a simple and effective method for creating bulk heterostructures in precipitation-hardened alloys at an industrial scale, leading to substantially improved strength and ductility. [Display omitted] [ABSTRACT FROM AUTHOR]

Stacking faults commonly exist within martensite plates in α + β titanium alloys. However, their structure and formation mechanism remain unclear. In this study, stacking faults within α′′ martensite plates were systematically investigated in an as-quenched Ti-7 wt% Mo alloy using aberration-corrected scanning transmission electron microscopy and first-principles calculations. Two kinds of stacking faults were detected, lying on (001) α′′ and (110) α′′ planes, respectively. Across each of the faults, the arrangement of atoms is 180° rotation symmetrical. The stacking faults are all produced by a specific (112)[ 11 1 ¯ ] β shear and two opposite shuffles on every other (110) β plane during martensitic transformation. First-principles calculated results indicate that the occurrence of the two opposite shuffles is attributed to the decreased stacking fault energies near the Mo solute. Our findings contribute to a deep understanding of structural transformation during bcc-β to orthorhombic-α′′ martensitic transformation. • There are two kinds of stacking faults in α′′ martensite, lying on (001) α′′ and (110) α′′ planes, respectively. • Across each of stacking faults, the structure of α′′ martensite is 180° rotation symmetrical. • Stacking faults are generated by a (112)[ 11 1 ̅ ] β shear and two opposite shuffles on every other (110) β plane. • Two opposite shuffles are driven by the neighboring Mo solute to decrease the total energy. [ABSTRACT FROM AUTHOR]

Heterogeneous precipitation and hence the distribution of α and β phase in α+β titanium alloys can impact strongly on alloy mechanical properties. The β phase is commonly observed to precipitate heterogeneously at boundaries between α′ martensite plates and dislocations inside the martensite, especially in the additively manufactured α+β titanium alloys, with a Burgers orientation relationship with the surrounding matrix phase. Here, we report an interesting phenomenon in a Ti-4wt%Mo alloy where the β phase precipitates heterogeneously on Mo-segregated { 10 1 ¯ 1 } fully coherent twin boundaries (CTBs) within α′ martensite, with an unusual Potter orientation relationship with α′. We find that the CTB has a structure resembling that of the β phase and that Mo segregation in the CTB leads to an unusual out-of-plane shift of the segregated atomic columns that makes the local structure almost identical to the β structure, hence serving as a template for β precipitation with the unique orientation relationship. Our findings reveal a novel mechanism via which the distribution of β precipitates can be manipulated effectively for better mechanical properties and could be extended to a group of Ti alloys including the current workhorse alloy Ti-6Al-4V and more broadly to other engineering alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

Increasing strength and preserving high strain hardening rate are of importance to widen the application of the metastable β titanium alloys. In this study, Ti–4Mo–4Cr–3Al–2Nb–1.2V–1Zr–1Sn (wt.%) alloy with four different primary α phase contents were prepared by solution treatment at different temperatures. The differences in β phase stability, mechanical properties, and deformation modes in these samples were investigated systematically. With the decrease of solution treatment temperature, the volume fraction of α phase, the stability of β matrix, and the tensile strength of the alloy increase, and a high strength and high strain hardening rate can be achieved simultaneously when the content of the primary α phase is less than 20%. When the applied stress exceeds the activated stress of martensitic transformation, martensite plates can be generated at large β domains and caused a dynamic Hall-Petch effect in these samples. With the further increase of strain, substructures are generated within the martensite to accommodate the deformation. Our findings provide a possible route for strengthening the metastable β titanium alloys and are beneficial to the microstructure design of the alloys with a high strength-ductility combination. • The strengthening strategy of changing the content of primary α phase was applied to a new metastable β titanium alloy. • The roles of primary α phase in deformation process and martensite transformation were evaluated. • The deformation mechanism of Ti-4321 alloy as a function of phase stability and deformation strain was proposed. [ABSTRACT FROM AUTHOR]

Isothermal compression tests, electron backscatter diffraction (EBSD) observations and quantitative analysis were performed to investigate high-temperature deformation behavior and recrystallization mechanism of Ti-55511 alloy in β phase region. The stress-strain curves, calculated activation energy and microstructure characterization show that dynamic recovery (DRV) and dynamic recrystallization (DRX) are the main soften mechanisms. DRX becomes more significant with decreasing strain rate and increasing deformation temperature and true strain. Recrystallization grains are identified by calculated grain orientation spread (GOS). It is found that quantitative microstructural characteristics, such as DRX volume fraction and DRX grain size, are strongly dependent on process parameters. The discontinuous dynamic recrystallization (DDRX) by grain boundaries bulging and continuous dynamic recrystallization (CDRX) by progressive sub-grains rotation are observed in the deformed microstructure of Ti55511 alloy. The flow softening rate and kinetics exponent of DDRX are higher than those of CDRX. With increasing deformation temperature, DRX mechanism has transformed from DDRX to CDRX, resulting in the unexpected decrease of DRX kinetics exponent n D and flow softening rate. The η bcc fiber, ε bcc fiber and ξ bcc fiber are the dominant texture component in deformed Ti–55511 alloy. The weakening of the deformation texture is accompanied by the occurrence of DRX, which can be attributed to the random orientation distribution of DRX grains. • DRX grains were identified by calculated GOS, and the effect of deformation parameters on DRX was quantitatively analyzed. • The DDRX by grain boundaries bulging and CDRX by progressive sub-grains rotation were comparative investigated. • With increasing temperature, DRX mechanism has transformed, and DRX kinetics exponent and flow softening rate decrease. • The weakening of deformation texture is accompanied by the occurrence of DRX. [ABSTRACT FROM AUTHOR]

A eutectoid Ti–7Ni (wt.%) alloy was additively manufactured by electron beam powder bed fusion (E-PBF) in this work. The effects of electron beam current and preheating time on the microstructure and mechanical properties of the E-PBF-built Ti–7Ni (wt.%) alloy were investigated. The evolution of the eutectoid microstructure during the in-situ heat treatment of E-PBF was elucidated. The addition of nickel resulted in a microstructure consisting of pre-eutectoid α laths and lamellae of submicron α and Ti 2 Ni. The morphology of the Ti 2 Ni evolved from fine lamellae to discontinued ellipsoids with increasing electron energy density or preheating time. Defects such as pores and lack of fusion were observed in the alloy under insufficient electron energy density. Fine Ti 2 Ni lamellae and pre-eutectoid α laths were obtained in the alloy processed at an electron energy density of 54 J/mm³ and a preheating time of 6 s, contributing to a considerable ultimate tensile strength of 660 MPa and good elongation of 16.8%. In addition, a graded microstructure along the building direction was observed due to the coarsening of Ti 2 Ni during multiple thermal cycles. It was demonstrated that the microstructure of the eutectoid Ti–7Ni alloy can be controlled by the in-situ heat treatment during the layer-by-layer E-PBF process. The findings in this work provide understanding and guidance for microstructure regulation in other additively manufactured eutectoid titanium alloys. [Display omitted] • Electron beam powder bed fusion with in-situ heat treatment was adopted to process Ti–7Ni alloy under 700 °C. • A graded microstructure along the building direction was formed due to the multiple thermal cycles of the in-situ heat treatment. • The growth process of eutectoid microtructure during in-situ heat treatment was demonstrated. [ABSTRACT FROM AUTHOR]

In this study, direct ageing treatments have been employed to improve the strength of selective laser melted near β titanium alloy Ti–5Al–5Mo–5V–1Cr–1Fe (Ti-55511). The microstructure evolution and mechanical behavior of Ti-55511 alloy were systematically investigated. It was demonstrated that the high-density α laths were precipitated with the martensite and the dislocations in as-deposited Ti-55511 as nucleation sites. The alloy aged at or below 600 °C showed the ultimate tensile strength (UTS) as high as 1500 MPa, while the ductility is poor owing to the precipitation of needle-like α laths or isothermal ω phase. With the increase of ageing temperature, the tip curvature of α laths decreased, and all the α laths coarsened, as well as α phase precipitate-free zones (PFZ) are more pronounced, which leads to insufficient strength and ductility of aged Ti-55511. This, therefore, suggests a new duplex ageing treatment to regulating the microstructure and mechanical properties of Ti-55511 alloy. The alloy obtained heterogeneous α laths consist of micron-sized primary α laths and nano-sized secondary α laths, which retain a maximum elongation of 10% with the high UTS of 1264 MPa. The nano-sized secondary α laths are randomly distributed in the β grain and the width of PFZ decreases, which is helpful to improve the ductility of the alloy. In addition, the high density of twinning deformations was observed in the duplex aged Ti-55511, indicating an excellent ability to accommodate the deformation straining under high stress. [ABSTRACT FROM AUTHOR]

In this work, molecular dynamics simulation is performed to investigate the effect of Al element on the crack propagation along the { 10 1 ‾ 1 } twin boundary in Ti alloys with different contents and distribution of Al element during the uniaxial tensile deformation. The results show that increasing Al content obviously promotes the percentage of face-centered cubic (FCC) structure during the deformation process, which hinders the micro-crack propagation and enhances the plasticity and toughness of the Ti–Al alloys. The FCC bands transform from the hexagonal close-packed (HCP) matrix satisfying the basal-type (B-type) orientation relationship (OR) represented by (0001) HCP ||(111) FCC and [ 1 2 ‾ 10 ] HCP ||[ 1 1 ‾ 0 ] FCC. The increase of Al element reduces the basal stacking fault (BSF) energy of the HCP structure and thus contributes to the formation of BSFs, which grow into FCC bands with the B-type orientation by the slip of Shockley partial dislocations. The { 10 1 ‾ 1 } pyramidal SF activated at the crack tip evolves into FCC grains in the Ti–Al alloys following the prismatic-type (P-type) OR with the HCP matrix represented by (10 1 ‾ 0) HCP ||(110) FCC and [ 1 2 ‾ 10 ] HCP ||[ 1 1 ‾ 0 ] FCC , during which atomic shear and shuffle is involved. • The Al element reduces the BSF energy of the HCP structure and thus contributes to the B-type HCP-FCC transformation. • The pyramidal SFs transform into the P-type FCC grains via a shear-shuffle motion. • Adding Al element is effective to restrain crack propagation by promoting the percentage of FCC phase in titanium alloy. [ABSTRACT FROM AUTHOR]

Three alloys with the same molybdenum equivalent (Mo [eq] , Mo [eq] ≈9) were prepared by adjusting the Mo and Cr contents in novel Ti–3Al-1.2V–1Zr–2Nb–1Sn- x Mo- y Cr (x = 6,4,1; y = 2.7,4,5.7, wt.%) alloys. Differences of microstructures, mechanical properties and deformation mechanisms in the three alloys under the same solution and aging treatment conditions were investigated. Effect of Mo on grain refinement during quenching is more notable than Cr in multi-element alloys. The change of elements ratio has little effect on the strengths of these alloys, but a significantly impact on their ductilities. After solution treated at 780°C and aged at 530°C, three alloys show similar strength (UTS~1400 MPa) but the difference of their ductilities is more than 5%. The alloy with the same Mo and Cr contents exhibits the best elongation (El~14.0%). Moreover, detailed analyses of transmission electron microscopy (TEM) results indicate that the dislocation slipping is the main deformation mechanism in β matrix, and the slipping hindered by various boundaries (grain boundaries and α GB , α s /β and α p /β interface) is the main strengthening mechanism. The ductility difference in the three alloys is mainly caused by the deformation ability of α phase. Formation of α-twin, α sub-boundary and other deformation products could accommodate local deformation and relieve stress concentration. This study provides a good guidance for high strength and toughness titanium alloy design. ● The effect of Mo on grain refinement during quenching is more notable than Cr in multi-element alloys ● The change of elements ratio has little effect on the strength of these alloys, but shows a significantly impact on ductility ● The difference of fracture mode and cracks propagation pathway under solution and aging treatment were compared ● The differences of deformation mechanism in three alloys with the same Mo [q] under the same heat treatment conditions were investigated [ABSTRACT FROM AUTHOR]

In addition to the great merits of producing three-dimensional complex components from metallic powders in additive manufactured parts, the microstructural features can be tailored by the intrinsic heat treatment (IHT), i.e., cyclic re-heating without any additional post-treatment of the printed samples. Here we report that the microstructural configurations can be widely manipulated in an additive manufactured Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) near β titanium alloy, with an emphasis on the effect of IHT on the in-situ precipitation of α phase. The typical as-printed samples consist of prior-β grains, coarse primary α (α I) colony and nanoscale secondary α (α II) laths. Based on automatic quantitative image analysis, the increase of substrate temperature has a remarkable impact on accelerating the precipitation of nanoscale α II laths, while suppressing the precipitation kinetics of the primary α colony, and the corresponding volume fraction of α II laths increases from only 2% to more than 40%, resulting in a tensile strength increment from 900 MPa to 1200 MPa. The enhanced strength derives from those extremely fine α II laths in terms of boundary strengthening. The findings in this work provide a strategy of strengthening additively manufactured components by taking advantage of one step intrinsic heat treatment. [ABSTRACT FROM AUTHOR]

Cross rolling (CR) process was successfully applied to solve the grain refinement of the equiaxed microstructure. In this work, microstructural evolution, textural discrepancy, mechanical properties and twin-accommodated mechanisms were studied in the equiaxed near β titanium alloy for different modes of rolling i.e. unidirectional rolling (UR) and cross rolling (CR). The results showed that CR can effectively promote the grain refinement of both the α and β phases as compared to UR, which leads to weaker texture intensities of the CR sample, and results in an elevated ductility. The { 10 1 ‾ 1 } twinning is the major twin-accommodated mechanisms observed in near β-Ti alloys. The { 10 1 ‾ 1 } twinning accommodated the rotation of subgrains and tailored subgrains orientation during the UR process. In comparison, during the CR process, accumulated stress increases the volune fraction of residual activated twins. Furthermore, with the increasing deformation, the α phase was progressively fragmented into fine grains by the thickening and extension of { 10 1 ‾ 1 } twins. The results in the present study can be applided to optimize deformation processes to achieve ultra-fine grained microstructures, and to figure out the refinement of massive-grained microstructures. [ABSTRACT FROM AUTHOR]