Lamellar Colony Size Research Articles

Lamellar orientation control of TiAl-based alloy by uniaxial compressive deformation at high-temperature in (α+β) two-phase region

In this study, the orientation of (α+γ) lamellar structure in the TNM alloy (Ti-43.7Al-4 Nb-1Mo-0.1B) is controlled by high-temperature uniaxial compression conducted in the (α+β) two-phase region. The control of the lamellar orientation is focused on a control of α phase orientation because of being decisive for lamellar γ orientation. All true stress-true strain curves indicated the work softening due to dynamic recrystallization. The stress-strain curve behaviors were consistent with microstructure observation. The peak stress increased with a decrease in lamellar colony size. After deformation in the (α + β) two-phase region at 1543 K and 1573 K, where the content of α phase was dominant, a fiber texture with the (0001)α2 plane tilted 35° away from the compression plane was formed by the deformation mechanism of α phase. On the other hand, at 1623 K where the content of β phase was dominant, a double (0001)α2 fiber texture tilted at 35°- 45° and 80°- 90° away from the compression plane was observed. The double (0001)α2 fiber texture is considered to be caused by β→α phase transformation during cooling according to Burgers orientation relationship. Single-step uniaxial compressions conducted at the (α + β) two-phase region at different temperature (1543 K−1623 K) led to an inclination of (0001)α2to compression plane and subsequently lamellar interfaces of one colony unparallel to those of other colonies.

Effect of trace boron addition on the microstructural evolution and mechanical properties in Ti45Al8Nb2Cr-B alloys

High Nb-containing TiAl alloys have been deemed ideal candidates for demanding structural applications under high temperatures due to their appealing mechanical qualities and low density. Nonetheless, its inherent brittleness at room temperature remains a significant impediment to its processability. Herein, different concentrations of boron were added into the Ti45Al8Nb2Cr (Ti4582) alloy by vacuum arc melting to tailor the microstructure and corresponding mechanical properties. The coarse lamellar colonies were significantly refined via boron addition, while excessive boron addition did harm to the mechanical properties. The different morphologies of the borides (Bf or B27) profoundly influenced the microstructure and mechanical properties of as-prepared alloys. Further elemental distribution, phase constitution, lamellar colony size, and mechanical properties were systematically investigated. Noteworthily, trace boron additions effectively improved the mechanical properties of Ti4582-xB alloys with an optimal adjustment in Ti4582–0.2B, showing 673 MPa for room temperature ultimate tensile strength (UTS) with elongation of 1.3 % and 1623 MPa for ultimate compressive strength (UCS) with compressive strain of 32.5 %. The improved mechanical properties of Ti4582-xB were mainly attributed to grain refining and second phase strengthening. Moreover, the hindrance and accommodation for dislocations by deformed twins and reinforcements effectively enhanced the mechanical properties.

Multiple ceramic particles help to improve oxidation resistance of TiAl alloy

A novel microstructural regulation strategy was utilized to improve the oxidation resistance of TiAl alloy by the controllable multiple ceramic particles. TiAl composites were prepared using spark plasma sintering (SPS) by introducing SiC and graphene oxide (GO). TiAl composites showed nearly full lamellar microstructure, and the Ti5Si3 particles in-situ precipitated at the lamellar colony boundaries and Ti2AlC in-situ precipitated at the α2/γ interfaces. Grain refinement of TiAl composite was obvious, displaying a decrease of lamellar colony size from 259 to 81 μm after addition 0.3 wt% SiC and 0.5 wt% GO. The isothermal oxidation results showed that the mass gain of TiAl composite was decreased by 56% compared to TiAl alloy after oxidation at 950 ℃ for 100 h. This was mainly attributed to the in-situ precipitated Ti2AlC and Ti5Si3 ceramic particles inhabiting the interior diffusion of O atoms and the outward diffusion of Ti and Al atoms, then the activity of O and Ti was decreased. Furthermore, the Ti2AlC and Ti5Si3 ceramic particles contributed to release the internal stress between the oxide layer and matrix, strengthening the bondability between the oxide layer and matrix.

Refinement and enhancement of high-Nb TiAl alloy via in-situ precipitation of Ti2AlC and TiB2 nanoparticles

An in-situ dual morphology of Ti2AlC/TiB2 nanoparticles was refined and enhanced to fabricate Ti-47.7Al-7.1Nb-2.3V-1.1Cr composites via induction hot-pressing sintering with nano-B4C addition. The generation process of nanoparticles, lamellar refinement mechanism, and effect of nanoparticles on the microstructure evolution/mechanical properties were meticulously analysed. With 0.2 at% nano-B4C addition, Ti2AlC/TiB2 nanoparticles were uniformly distributed in the matrix following sintering. In addition, upon sintering at 1425 °C for 10 min under a pressure of 50 MPa, the lamellar colony size decreased from 280 ± 145 μm to 55 ± 16 μm, and the ultimate tensile strength (UTS) increased by 116 MPa, 142 MPa, and 176 MPa, when tested at room temperature, 800 °C, and 900 °C, respectively. The enhanced mechanical properties were attributed to the synergistic effects of grain refinement strengthening, solid solution strengthening, the Orowan mechanism, and twinning strengthening.

In-situ synthesized multi-component particle reinforced TiAl composite with excellent mechanical properties

In order to overcome the inherent trade-off between strength and ductility of TiAl alloys, the BN nanosheets were added in Ti-48Al-2Cr-2Nb alloy. Ti-48Al-2Cr-2Nb-xBN (x = 0, 0.1, 0.5, 1, 2 wt%) alloys were prepared by vacuum arc melting (VAR), and the microstructures displayed a fully lamellar structure accompanied by simultaneous precipitation of Ti2AlN and TiB2 phases. The reaction of BN nanosheets with the Ti and Al elements resulted in formation of Ti2AlN and TiB2 phases. The lamellar colony size of TiAl composites was refined from 276.7 to 29.4 µm with BN content increasing from 0 to 2 wt%. While the lamellar spacing displayed an initial decrease followed by an increase, which was attributed to the synergistic effect of Ti2AlN and TiB2. Room temperature compression results showed that the compressive strength surged from 1653 to 2272 MPa as BN content rose from 0 to 0.5 wt%, with the highest compression strain of 34.7 % at 0.5 wt% BN. The high temperature compression results showed that the compressive strength increased from 887 to 1399 MPa as the BN content increasing from 0 to 1 wt%. Crack extension took the form of both trans-granular and inter-granular modes. The strengthening effect of TiAl composites was attributed to grain refinement strengthening and secondary phase strengthening via Ti2AlN and TiB2.

The columnar dendrite and equiaxed dendrite transformation of high Nb-TiAl alloy by laser-directed energy deposition

Laser-directed energy deposition (LDED) is a significant method for shaping high Nb-TiAl alloys. The dendrite type has an impact on the mechanical properties of parts fabricated with LDED. This study establishes a dendrite transformation model for the alloy. The refinement mechanism of microstructure and the strengthening mechanism of high-temperature mechanical properties are analyzed through experiment and simulation. The results show that the scanning rate has a significant influence on the dendrite type. Modifying the scanning rate brings about a gradual decrease in the G/R (where G denotes temperature gradient and R is the growth rate) value of the molten pool, and a concurrent gradual increase in the value of G×R. These changes facilitate the transformation of columnar dendrites into equiaxed dendrites. Furthermore, the lamellar colony size is reduced by 72.8% and the tensile strength at 900 °C is increased by 16.2%. Microstructure refinement is the primary reason for the enhancement of high-temperature tensile characteristics, with dislocations and deformation twins also contributing to crack propagation resistance.

Improving mechanisms of lamellar microstructure and mechanical properties by Y and in-situ Y2O3: Modification of carbides particles and complete transformation of Ti2AlC particles

To reveal the modification mechanism of carbides particles by in-situ Y2O3, and then the improvement mechanisms for Ti42Al6Nb2.6C-xY alloys, the microstructures were observed by SEM, XRD and TEM, and the mechanical properties were examined. Results show that the flaky TiC transformed completely into Ti2AlC, and the morphology of Ti2AlC turned fine-needle shaped into short-rod shaped. The content of Ti2AlC with the aspect ratio of 1–5 increased from 24.2 to 81.4%, and the average aspect ratio decreased from 7.9 to 3.7 as Y increased from 0 to 0.08 at. %. The average lamellar colony size and lamellar spacing decreased from 24.054 to 17.500 μm and 0.531 to 0.304 μm, respectively. The growth of TiC phase was constrained by in-situ Y2O3, which alleviated agglomeration distribution of TiC and provided a fine TiC substrate for the nucleation of Ti2AlC. The interfacial interaction between in-situ Y2O3 and Ti2AlC restricted the longitudinal and transverse growth of Ti2AlC. The modified Ti2AlC and in-situ Y2O3 particles as nucleation sites for β grains were the basis for obtaining fine lamellar structure. For mechanical properties, the compressive strength increased from 1388 to 1781 MPa, the yield strength increased from 1265 to 1544 MPa, and the Vickers hardness increased from 495 to 609 HV. The refinement of lamellar colony by modified Ti2AlC and in-situ Y2O3, and the load strengthening of Ti2AlC particle contributed to the mechanical properties.

Improvement in compressive creep resistance of Ti-43.5Al–4Nb–1Mo-0.1B alloy via micro-alloying with C and Si

In the present work, the effects of the addition of C and Si on the compressive creep behavior of Ti-43.5Al–4Nb–1Mo-0.1B (TNM) alloy at 850 °C and 900 °C under 260 MPa were investigated. The results show that micro-alloying with C and Si can significantly strengthen the compressive creep resistance of TNM alloy. During compressive creep, obvious dynamic recrystallization occurs in TNM alloy, including major discontinuous dynamic recrystallization and minor continuous dynamic recrystallization. The development of dynamic recrystallization greatly softens the alloy, which leads to large creep deformation. Meanwhile, with the increase of creep strain, the bearing area increases and the actual stress decreases, which eventually results in the secondary creep behavior. In addition, the content of α2 phase increases during compressive creep, which can be attributed to two phase transformations. After adding C and Si, the B2 phase content is decreased and the lamellar colony size is increased, which contributes to the improvement of creep resistance. In addition, fine and dispersed Ti3AlC and Ti5Si3 particles precipitate in α2 lamellae during compressive creep, and maintain definite orientation relationships with α2 and γ phases. This will delay the decomposition of α2 lamellae and greatly improve the lamellar stability. Then, the excellent lamellar stability will inhibit the development of dynamic recrystallization, thus effectively reducing the creep rate.

Simultaneously enhancing strength and ductility of high-Nb-containing TiAl alloy via extrusion-assisted microstructure tailoring

In most metallic materials, the strength-ductility trade-off serves as an inevitable scenario. Therefore, improving the room/high-temperature strength/ductility of high Nb-TiAl alloys based on a lamellar microstructure is important for practical applications. In this work, a novel microstructure with fine lamellar colonies and a certain number of residual γ grains was developed through hot extrusion in the near α phase region. The results indicated that the lamellar colony size and spacing of the as-cast alloy were significantly refined by hot extrusion. The as-extruded Ti-45Al-8Nb-(W, B, Y) alloy demonstrated a good combination of high strength and ductility. The tensile strength and ductility were 1129 MPa and 2.04% at room temperature (RT), respectively, and 744 MPa and 51.20%, respectively, at 850 °C. A simultaneous improvement in strength and ductility below ductile-brittle transition temperature (DBTT) could be attributed to the abundant deformation twins and their intersections, as well as prominent strain working caused by high-density dislocations in the γ phase. Due to dynamic recrystallization, the ductility was significantly enhanced when stretched over DBTT. This extrusion-assisted microstructure tailoring strategy could be extended to other TiAl systems and may serve as a useful solution for addressing the significant engineering constraints posed by the low RT ductility and poor hot-working capabilities of high Nb-TiAl alloys.

Effect of Microstructure Change on Mechanical Properties after High Temperature Forming of Ti-6Al-4V Alloy

Ti-6Al-4V alloy is not easy to machine complicated shapes due to its low thermal conductivity, so high-temperature forming techniques such as ring-rolling are being applied. When this high-temperature forming technology is applied, the microstructure is greatly changed by process variables, and the mechanical properties of the forming product are also different accordingly. In particular, in the case of the Widmanst tten structure, α lamellar spacing and colony size have a great influence on mechanical properties. Therefore, in this study, the most suitable process conditions were selected by performing a high-temperature compression test to apply the ring-rolling process to the Ti-6Al-4V alloy used as an aerospace material. After that, the microstructure of the forming product was observed, the effects of α lamellar spacing and colony size on the mechanical properties were confirmed, and the correlation between mechanical properties and microstructure was evaluated based on this.

Improvement of microstructure and acquirement of excellent mechanical properties of high-Nb Ti2AlC/TiAl alloy by Ta under ultrasonic action in solid-liquid zone

To promote element diffusion in the solid-liquid two-phase region, optimize solidification microstructure, and improve the matching degree of strength and toughness, Ti–46Al–8Nb-2.6C-xTa (at. %) alloys were prepared by arc melting under the action of ultrasound. The lamellar colony, precipitate phase, elements distribution, and related mechanisms were analyzed. Results show that the relative content of the γ phase decreases, while the relative content of the α2 phase and Ti2AlC phase increases as the addition of Ta increases. The coarse long rod-shaped Ti2AlC transforms into short rod-shaped particles. The lamellar colony size reduces from 32.1 to 18.6 μm, the lamellar spacing reduces from 1.4 to 0.7 μm, and the aspect ratio of Ti2AlC reduces from 5.8 to 2.5 as the addition of Ta increases from 0 to 1.0 at. %. The acoustic streaming effect of ultrasound promotes the diffusion of tantalum in the solid-liquid two-phase region for a certain ultrasonic processing time. Tantalum is a heterogeneous nucleation particle of Ti2AlC particles and causes composition supercooling at the forefront of the solidification interface, which is the main reason for refining the microstructure. Compressive strength increases from 1996 to 2596 MPa and the strain increases from 25.4 to 29.3% as the addition of Ta increases from 0 to 0.6 at. %. The main reasons for improving the properties of alloy are the refinement of the microstructure and the formation of a large number of dislocations.

Influence of section thickness of casting on the microstructure characteristics and creep rupture properties of Ti-45Al-2Nb-2Mn-1B

Ti-45Al-2Nb-2Mn-1B (atomic percent, 4522XD) cast step plate with different thicknesses was prepared by investment casting, and the variations of microstructure and creep rupture properties with thickness were examined. With decreasing thickness, lamellar colony size, lamellar thickness, and the size of equiaxed γ grains at the colony boundaries decreased, and the colony boundaries varied from smooth to serrated. Boride particles are mainly long flat needles in the region with 12 mm thickness, curvy flakes with considerable length and width in the region with 8 mm thickness, and curvy ribbons with small length in the region with 4 mm thickness. B27-TiB particles were observed in all the thicknesses, Ti3B4+ TiB2 lamellar particles were observed in the region with 8 mm and 12 mm thicknesses, and Bf-TiB+ TiB2 lamellar particles were observed in the region with 4 mm thickness. The smallest creep rupture elongation is obtained in samples taken from the plate with 12 mm thickness, while the shortest creep rupture life is obtained in samples taken from the region with 8 mm thickness. The former is attributed to the smooth colony boundaries which have weaker resistance to grain rotation, while the latter is attributed to the curvy boride particles that tend to nucleate cracks at the corner with small curve radius, providing a fast track for crack propagation along the boride/matrix interfaces, their considerable size makes the crack reach the critical size for fracture more easily. Weak creep rupture properties of some samples are mainly attributed to the aggregation of colonies whose lamellar interfaces are nearly perpendicular to the loading direction.

In situ synthesis of nano/micron Ti2AlC reinforced high-Nb TiAl composites: Microstructure and mechanical properties

Induction hot-pressing sintering, as an effective sintering technique, has been rarely investigated and reported in the sintering of TiAl alloys. In this paper, in-situ nano/micron Ti2AlC reinforced high-Nb TiAl composites were fabricated via induction hot-pressing sintering, and the effect of nano-C addition on the microstructure and tensile properties was investigated. With 0.75 at% nano-C addition, the lamellar colony size decreased from 406 ± 151 μm to 141 ± 62 μm, and the Ti2AlC particles were mainly distributed at the γ/α2 lamellar interface. At 800 °C and 900 °C, the ultimate tensile strength and the elongation of the TiAl alloy were 436 MPa and 437 MPa, 0.84%, and 1.12%, respectively. However, with 0.75 at% addition (after heat treatment 900 °C/48 h), the ultimate tensile strength increases by 129 MPa and 78 MPa, and the elongation increases by 0.27% and 0.64%, respectively. The significant improvement in tensile property is mainly attributed to the precipitation phase enhancement and grain refinement.

In-situ synthesized nano/micron carbide and boride reinforced high-Nb TiAl alloy via nano-B4C addition

An in-situ dual morphology carbide and boride reinforced Ti-47.7Al-7.1Nb-2.3 V-1.1Cr (at%) alloys were fabricated with nano-B4C addition by spark plasma sintering (SPS), and the effect on the microstructure and tensile property of high Nb-TiAl alloys were studied. Compared with Ti-47.7Al-7.1Nb-(V, Cr) matrix, the lamellar colony size has been significantly refined from 126 ± 45 μm to 45 ± 15 μm and the ultimate tensile strength (UTS) improved 105 MPa with 0.2 at% nano-B4C addition. Multiple strengthening induced by the Ti2AlC micron/nanoparticles and TiB2 nanoparticles is the reason for the improvement of the tensile property.

Twinning behavior and strengthening mechanism in a microalloyed TiAl alloy

The tensile properties and deformation behavior of a newly developed TNM-based alloy after microalloying with W, C, and Y have been systematically investigated by scanning electron microscopy and transmission electron microscopy. The T435-WCY alloy with a fine and uniform microstructure was obtained by one-step alpha-extrusion processing. Meanwhile, high-density dislocations, deformation twins, and twin intersections were found in the γ lamellae near the tensile fracture. The results showed that compared with the T445 alloy, the addition of trace microalloying elements significantly refined the lamellar colony size and spacing of the T435-WCY. T435-WCY alloy had a good combination of high strength and ductility. The tensile strength and ductility were 964 MPa and 1.60% at room temperature, respectively, and 748 MPa and 9.28% at 850 °C, which was because the grain refinement, high-density deformation twins, and twin intersections were beneficial for improving the strength and plasticity of the TiAl alloy. The dislocation dissociation could promote the formation of deformation twins, and three types of intersecting twins were observed in the γ phase. The twin intersection could hinder the movement of dislocations and relieve stress concentration in the intersection region by lattice distortion, which was beneficial for enhancing the tensile performance of the TiAl alloy.

A study on the hot workability of a novel TNM-RE alloy (RE = Y, La, Ce)

The hot deformation behavior of a novel TNM-RE alloy (RE = Y, La, Ce) was studied using a hot simulation machine (Gleeble-3800), and microstructural evolution was also characterized. Finally, 3D forging was carried out on isothermal forging equipment. It is shown that the as-cast lamellar colony size is about 20 ∼ 30 μm, which is refined by the formation of rare Earth oxides and borides at grain boundaries inhibiting grain growth. The peak stress of the TNM-RE alloy deformed at 1200 °C/0.01 s−1 is about 97 MPa, which is governed by the lamellar colony size and the B2 phase. Based on microstructure observation, it is found that the lamellar is bent and elongated to coordinate plastic deformation, where dynamic recrystallization nucleates preferentially, and full dynamic recrystallization is obtained at 1220 °C/0.01 s−1. The TNM-RE alloy was forged by 3D isothermal forging method, and fine grains with a size of 10 ∼ 20 μm were obtained by controlling the process parameters. The novel TNM-RE alloy shows an excellent hot workability.

Exploration of homologous substitution element on phase ratio and high temperature properties in high Nb-containing TiAl alloy

To reveal homologous substitution and refined mechanisms, and improve mechanical properties, Ti42Al6Nb 2.5 CxTa alloys were prepared by arc melting. Element distribution, lamellar colony size, length-diameter radio of Ti2AlC phase, tensile properties, and the corresponding influence mechanism were studied. Results show that the relative contents of γ and Ti2AlC phase increase, the content of α2 phase decreases, when Ta content increases from 0 to 2.0 at%. The relative content of B2 phase increases among the lamellar colonies and the length-diameter ratio of Ti2AlC particle decreases. Lamellar colony size decreases from 24.9 to 10.6 µm. With the increase of Ta content, the supercooling at the front of the solid-liquid interface increases and the β phase is refined. The increase of the precipitated phase content leads to the increase of the number of α phase heterogeneous nucleation particles, which will refine the lamellar colony. Tensile results show that the strength increases from 238 to 513 MPa and strain increases from 2.7 % to 11.1 % of Ti42Al6Nb 2.5 C1.6Ta alloy when the tested temperature increases from 750 to 950 ℃. The high temperature tensile properties of the alloy with more Ta content are relatively higher. Ta forms large lattice distortion after solid solution into the matrix due to its large atomic size, and Ta makes more Nb dissolve into the collective to increase the effect of solid solution strengthening. Another reason is the refinement of microstructure.

Microstructural factors governing the significant strengthening of Al/Al2Cu mille-feuille structured alloys accompanied by kink-band formation

Development of high-strength Al alloys that can be used at temperatures above 150 °C is strongly desired. To achieve this, Al/Al2Cu mille-feuille structured alloys, in which soft (Al) layer and hard (Al2Cu) layer are alternatively stacked in lamellar form, is recently focused, via inducing kink-band formation as a novel strategy for controlling the mechanical properties. However, the localized formation of large kink bands reduces the yield stress and degrades the ductility of the alloy. There was little information to derive a "general law" for quantitatively predicting an increase in yield stress in mille-feuille structured alloys from a microstructure perspective. In this study, we successfully distinguished the effects of lamellar thickness and colony size on the strength. The results demonstrated that the yield stress governed by kink-band formation is less related to the lamellar thickness in the Al/Al2Cu alloys but it highly depends on the colony size. The decrease in lamellar colony size obtained by increasing the growth rate during the directional solidification of the Al/Al2Cu eutectic alloy can induce the homogeneous formation of tiny kink bands in the alloy, leading to a drastic increment of the yield stress accompanied by ductility. In addition, the formation of tiny kink bands was demonstrated to contribute to tensile deformation. That is, the control of the morphology of kink band changes its role from a fracture mode to a deformation mode. Furthermore, such microstructure control can induce “kink-band strengthening” in the alloys. These experimental results demonstrate that controlling the colony size while maintaining the alignment of lamellae is the key factor for inducing superior mechanical properties of the mille-feuille structured alloy via tiny kink-band formation.

The influence of micro-nano Ti2AlC on the hot deformation behavior of TiAl alloys

To strengthen TiAl alloys, micro-nano Ti2AlC precipitates were fabricated in situ by spark plasma sintering using Ti–48Al–2Nb–2Cr pre-alloyed powder and multilayer graphene oxide. The effect of micro-nano Ti2AlC precipitation on the hot deformation behavior of Ti–48Al–2Nb–2Cr alloy was systematically studied at 1100, 1150, and 1200 °C under strain rates of 0.01, 0.1, and 1 s−1. The fully lamellar structure was transformed to a nearly lamellar structure when the graphene content was increased. In addition, the lamellar colony size significantly decreased and the number of Ti2AlC particles increased with increasing graphene content. The hot deformation results show that the flow stress of the Ti2AlC–TiAl composites first increased and then decreased with increasing graphene content, reaching the maximum with the addition of 0.3 wt% graphene. Micro-nano Ti2AlC particles hindered dislocation slip, leading to a strengthening effect. However, Ti2AlC particles promoted dynamic recrystallization through grain refinement and dislocation pile-up, resulting in a softening effect. The strengthening and softening effects of the Ti2AlC–TiAl composites depend on the Ti2AlC particle content.

Microstructure and mechanical properties of a novel PM Ti–2Al–1.3V alloy in different heat treatment conditions

ABSTRACT A novel Ti–2Al–1.3V (wt.%) alloy was prepared by thermomechanical consolidation of a composite powder produced by high-energy ball milling of a mixture of TiH2 granules with a low oxygen content (0.1wt.%) and Ti–6Al–4V machining chips with a high oxygen content (0.8wt.%) at a mass ratio of 2:1. The microstructures and mechanical properties of the alloy in as-extruded state and after different heat treatments were investigated. The as-extruded alloy exhibits a martensite microstructure consisting of ultrafine and nanometer sized α’ laths and aciculae and domains of layered structure containing δ(TiH) layers. The alloy in this state is brittle and fractures prematurely before yielding due to the ultrafine martensitic microstructure and hydrogen embrittlement associated with the high hydrogen content of the alloy. After vacuum annealing at 700°C for 6 h followed by furnace cooling, the alloy is further dehydrogenated with the hydrogen content being reduced to 0.008wt.%, the microstructure of the alloy changes into a full α/β lamellar microstructure with the continuous and discontinuous β layers being only 80–90 nm thick and the lamellar colony sizes being 10–30μm. The fine structured alloy in this heat treatment condition shows an excellent combination of high tensile yield strength of 996 MPa and ductility of 13.9%. After a further heat treatment of 980°C for 1 h followed by air cooling, the microstructure of the alloy consists of equiaxed α grains and α/βt lamellar structured domains (βt = β transformed structure), and unfortunately, this microstructure leads to a significant decrease of both the tensile yield strength (to 876 MPa) and the tensile ductility (to 7.4%). The fracture behavior of the alloy in different states is also studied, and the correlation between the microstructure and mechanical properties is discussed.