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The present work investigates the thermal stability and mechanical properties of a Co–20Cr–15W–10Ni (wt%) alloy with a bimodal grain (BG) structure. The BG structure consisting of fine grains (FGs) and coarse grains (CGs) is thermally stable under high-temperature exposure treatments of 760 °C for 100 h and 870 °C for 100–1000 h. The size of both FGs and CGs remains no significant changes after thermal exposure treatments. The microstructural stability is associated with the slow kinetics of grain growth and the pinning of carbides. The thermal stability enables to maintain the BG structures, leading to the same mechanical properties as the sample without thermal exposure treatment. In particular, the BG alloy samples after thermal exposure treatment exhibit superior mechanical properties of both high strength and high ductility compared to the unimodal grain (UG) structured ones. The BG structure of the alloy samples after thermal exposure is capable of avoiding severe loss of ductility and retaining high strength. More specifically, the ductility of the BG alloy samples after thermal exposure treatments of 870 °C for 500–1000 h is ten times higher (44.6% vs. 3.5% and 52.6% vs. 5.0%) than that of the UG ones. The finding in the present work may give new insights into high-temperature applications of the Co–20Cr–15W–10Ni alloy and other metallic materials with a BG structure.

A nearly fully dense β stabilized γ-TiAl alloy was additively manufactured by electron beam melting. The as-fabricated specimen exhibited a fine structure consisting of α2/γ colonies ( 50%) in the sample at 800 °C. Annealing and subsequent stabilization treatments resulted in α2/γ colonies (

A bimodal grain structure consisting of fine grains (d ~ 1–2 µm) and coarse grains (d ~ 10–20 µm) was achieved in the biomedical Co–20Cr–15W–10Ni alloy via medium cold rolling (area reduction of 50%) followed by short-term annealing (15 min) at relatively low temperatures (950–1100 °C). The medium cold rolling induced a heterogeneous microstructure featuring the coexistence of severely deformed regions and weakly deformed domains. With short-term annealing at low temperatures, fine and coarse grains were preferentially recrystallized in severely deformed regions and weakly deformed domains, respectively, resulting a bimodal grain size distribution. During tension, dislocations were more rapidly generated in the fine grains, thus increasing the strain hardening, while they glided longer on the {111} planes in the coarse grains, contributing a high ductility. The combination of these two factors provided well-balanced strength–ductility behavior with an ultimate tensile strength of 1278 MPa, a yield strength of 787 MPa, and an elongation to fracture of 53%, making the alloy suitable for surgical implant and stent applications where the strength and ductility are both important to ensure mechanical reliability in a human body.

We have performed quantitative analysis of {332}〈113〉 twinning in a β-Ti-15Mo (wt.%) alloy by in situ scanning electron microscopy and electron backscattering diffraction (EBSD). Microstructure-twinning relations were evaluated by statistical analysis of the evolving twin structure upon deformation at room temperature. Our analysis reveals that at the early stages of deformation (ε < 1.5 to 2.0%), primary twinning is mainly determined by the applied macroscopic stress resolved on the twin system. Most of the primary twins (~70–80% of the analyzed twins) follow Schmid’s law with respect to the macroscopic stress, and most of the growth twins (~ 85% of the analyzed twins) correspond to the higher stressed variant. In the grain size range studied here (40–120 μm), we find that several twin parameters such as number of twins per grain and number of twins per grain boundary area exhibit grain size dependence. We ascribe these effects to the grain size dependence of twin nucleation stress and apparent critical resolved shear stress for twinning, respectively.

We have studied {332} detwinning mechanism in a bcc-Ti–10Mo–xFe (x = 1–3 wt%) multilayered alloy upon annealing treatment at 900 °C by electron backscatter diffraction and electron channeling contrast imaging. Our analysis reveals that in the present material the detwinning process consists of two independent detwinning events that occur at two different microstructural regions, namely twin tips located at grain interiors and grain boundaries. Boundary dissociation reactions and mobilities were analyzed by tracking the evolution of the twin structure upon thermal annealing. We find that the first detwinning process is characterized by the evolution of incoherent twin boundaries into a Σ3 boundary and its subsequent migration. The second detwinning event is characterized by the detachment of the twin crystal from a grain boundary by the formation and migration of Σ11 {113} incoherent twin boundaries. Both detwinning modes can be explained from a thermodynamic standpoint where the boundary dissociation processes minimize the boundary free energy.

In order to develop a new titanium alloy with a good combination of strength–ductility–toughness, a near-beta titanium alloy was designed based on the already widely used Ti-1023 alloy. To avoid beta fleck occurring in the microstructure, the new Ti–Al–Fe–V (Cr, Zr) alloy has been made through decreasing the content of Fe, based on molybdenum equivalency and Bo–Md molecular orbital method (a method for new alloy designing based on the molecular orbital calculating). After primary design computation, Ti–Al–Fe–V (Cr, Zr) alloy was optimized as Ti–3Al–4.5Cr–1Fe–4V–1Zr finally. The microstructure and tensile properties of this alloy subjected to several commonly used heat treatments were investigated. The results show that the tensile strength of the alloy after solution treated below the β-transus temperature comes between 850 and 1100 MPa, with elongation in the range of 12.5 %–17.0 %. In solution-treated and solution-aged samples, a low-temperature aging at 500 °C results in the precipitation of finer α phase. With the increase in aging temperature, the secondary α phase becomes coarser and decreases in amount. Thus, it will lead to the increase in tensile ductility, but reduction in strength. Eventually, after modulated aging treatment, the alloy can obtain high-strength level with acceptable ductility. The tensile strength of the alloy can achieve 1273 MPa, with an elongation of 11.0 %. At the same time, the fracture toughness (K IC) of the alloy achieves 83.8 MPa·m1/2. It is obvious that the newly designed alloy has achieved a good blend of strength–ductility–toughness.

The effect of Al addition on ω precipitation and age-hardening behavior of Ti-9.2Mo-2Fe and Ti-2Al-9.2Mo-2Fe alloy during aging treatment was investigated. The results showed that athermal and isothermal ω phase formation in Ti-2Al-9.2Mo-2Fe alloy was suppressed to a certain extent due to Al addition. In addition, a small amount of athermal ω phase was observed in the β matrix with a size of about ~5 nm during water quenching from above the β transus temperature for both alloys. Isothermal ω formation was also found during aging at temperatures ranging from 573 K to 773 K (300 °C to 500 °C) in both alloys, although it had a limited time of stability at 773 K (500 °C). The hardening due to isothermal ω precipitation exhibited no over-aging as long as ω phase existed in both alloys, and ω phase played a more important role in hardening than α phase. And the ω phase in 50 to 100 nm size exhibited the best hardening effect in Ti-9.2Mo-2Fe alloy. Similarly, α phase with 100 to 200 nm in length showed better hardening effects in Ti-2Al-9.2Mo-2Fe alloy. Both the alloys showed stronger age hardening at an intermediate temperature of 673 K (400 °C) and in the first aging stage at a higher temperature of 773 K (500 °C) due to the sufficiently fine size (50 nm), while they exhibited weaker age hardening at a lower temperature of 573 K (300 °C) and long period aging at a higher temperature of 773 K (500 °C) due to incomplete ω formation and/or coarsening of α phase. No over or peak aging stage was found at 573 K and 673 K (300 °C and 400 °C) during the aging for 72 hours, while the peak hardness values of both alloys aged at 773 K (500 °C) were obtained in the first stage of aging. The hardness of the alloys was very sensitive to size and volume fraction of ω phase, which depends on aging temperature, time, and composition of the involved alloys.

The use of selective laser melting (SLM) has become more common with regard to the fabrication of high-strength Ti-6Al-4V components. However, the as-SLMed Ti-6Al-4V alloy parts typically exhibit low ductility because of the formation of acicular and brittle α′ martensites. It is essential to use post-heat treatment to change their microstructures to achieve superior mechanical properties. In this study, a particular multi-step heat treatment (MSHT) was applied to the Ti-6Al-4V alloy samples fabricated via SLM. Conventional post-heat treatments were conducted for comparison. The microstructures and tensile properties of the as-SLMed and heat-treated samples were investigated. The as-SLMed Ti-6Al-4V sample is dominated by plate and acicular α′ martensites, which exhibit high strength (1280 MPa) and low ductility (9.0%). The conventional solution plus aging or stress-relieving treatment cannot result in a good combination of strength and ductility. A single step annealing process at 700 °C for 2 h changes the martensitic structure to a fine lamellar α+β structure, which provides a strong and ductile Ti-6Al-4V with an ultimate tensile strength of 1108 MPa and a total elongation of 17.6%. In contrast, the MSHT process facilitates the globularization of α and, thereby generates a nearly equiaxed structure, resulting in superior ductility (21.8% of total elongation), while maintaining a moderate ultimate tensile strength of 953 MPa.

The present work investigates the microstructural evolution of a biomedical Co-20Cr-15W-10Ni alloy during multi-pass thermomechanical processing (TMP) and clarifies its effect on the tensile properties. The results indicate that multi-pass TMP consisting of repetitive cold groove-rolling followed by annealing is attractive for fabricating the alloy rod for fine wire and mini-tube making. The multi-pass TMP provided significant grain refinement from 100 to 4 μm via five repetition and, can create bimodal grain structures consisting of fine (≈3 μm) and coarse grains (4−16 μm). The bimodal grain structure provided a superior strength-ductility combination, a yield strength of 593−738 MPa and ultimate strength of 1197−1304 MPa with a uniform elongation of 54.7−61.1%. Changing the annealing condition in the final TMP step enables to further refine the grains to 2 μm and also modify the grain size distribution and, the dispersion and fraction of nano-carbides. Thus, the mechanical properties of the Co-20Cr-15W-10Ni alloy can be further optimized, leading to a yield strength of 795−890 MPa and ultimate strength of 1328−1363 MPa with a uniform elongation of 49.4−64.0%.

We have investigated the propagation of {332} twins in a multilayered Ti-10Mo-xFe (x = 1–3) alloy fabricated by multi-pass hot rolling. The material contains a macroscopic Fe-graded structure (about 130 μm width) between 1 and 3 wt% Fe in the direction perpendicular to rolling. We observe strong influence of the Fe-graded structure in the twin propagation behavior. The propagation of {332} twins that are nucleated in Fe-lean regions (~1 wt% Fe) is interrupted in the grain interiors at a specific Fe content, namely, about 2 wt% Fe. We ascribe this effect to the role of Fe content in solid solution on the stress for twin propagation. The interruption of twins in the grain interiors results in the development of characteristic dislocation configurations such as highly dense dislocation walls (HDDWs) associated to strain localization phenomena. The nucleation and propagation of these dislocation configurations is ascribed to the underlying plastic accommodation mechanisms of the stress field...

A study on microstructural evolution and age hardening behavior of a new metastable beta titanium alloy Ti–2Al–9.2Mo–2Fe was undertaken by microscopic observation, Vickers hardness and tensile tests in this research. The result showed that the athermal ω phase was formed in the beta matrix after solution treatment and followed by water quench, but it seemed that the athermal ω phase did not result in a considerable hardening (300 HV in hardness and 670 MPa in YS in ST condition). However, the isothermal ω phases with 10–40 nm and nano-scaled α platelets with 30–100 nm were observed in the alloy aged at lower temperatures (300–450 °C). The nano-scaled ω and α phase led to an attractive hardening effect (400–500 HV in hardness and above 1500 MPa in YS). However, micro-scaled α phase with 0.5–3 μm obtained in the samples aged at temperatures (500–600 °C) showed a moderate hardening (350–450 HV in hardness and 1100–1500 MPa in YS). The hardening went through an under-aging, peak-aging and over-aging due to the continuation of nucleation and growth of the α phases and subsequent coarsening. The coarsen α phases (3–5 μm) and grain boundary α layers (0.1–0.5 μm in thickness) obtained at high temperatures aging (650–750 °C) showed a poor hardening or even a softening (around 300 HV in hardness and below 1000 MPa in YS). The Ti–2Al–9.2Mo–2Fe alloy had a fast aging response, and can be age hardened to high hardness above 400 HV within 30 min at a broad aging temperature region. The age hardening curves can also provide a basic criterion for selecting aging treatment for a given stress level.

The influence of solution and aging parameters on the microstructures and mechanical properties of Ti–8V–1.5Mo–2Fe–3Al alloy was studied through microstructural observation and mechanical property test. It is a newly designed near beta titanium alloy for high strength and toughness on the basis of Ti–10V–2Fe–3Al alloy. According to microstructural observation, the shape and volume fraction of primary α phase is found to be determined by the solution treatment, while aging parameters control the precipitation behavior of secondary α platelets. Moreover, the effect of aging time on tensile properties is slighter compared with that of aging temperature. Tensile test reveals the dependence of mechanical properties on the heat treatment parameters, according to which the tensile strength and elongation can be controlled in a range of 1230–1435 MPa and 9–13%. It is a little superior to the Ti-1023 alloy, the alloy solution treated at 800–820 °C for 1 h and aged at 550–600 °C for 2–8 h has well balanced combination of strength and ductility. At the same strength level, the Ti–8V–1.5Mo–2Fe–3Al alloy has higher toughness and higher ductility than the Ti-1023 alloy, the reason is unknown and should be studied further. Morphological features of the fracture surfaces are consistent with the tensile test result and provide further information on the intragranular fracture behavior when solution treated above the β-transus.

Grain growth behaviors of a beta titanium alloy (Ti–2Al–9.2Mo–2Fe) have been systematically investigated for various temperatures. Quantitative evaluations of the grain growth kinetics over a wide range of temperatures from 820 °C to 1000 °C have been performed. The results showed that the isothermal grain growth kinetics followed the normal growth behavior. The solution-treated alloy at lower temperatures (820–900 °C) exhibited a good uniformity of the grain size. It showed a poor uniformity of the grain size due to the abnormal grain growth at higher temperatures (950–1000 °C). The grain growth exponent values ( n ) were at the range of 0.1–0.2, about 0.1 at lower temperatures and about 0.2 at higher temperatures. They were lower than other beta titanium alloys. The lower exponent values ( n ) and the higher activation energy ( Q ) can be attributed to the solute drag effect and the high Mo content with low diffusivity in Ti matrix.

The present study describes the influence of β stabilizers (namely Fe and Cr) on the microstructural evolution and mechanical behavior of Ti–6Al–4V alloy fabricated by direct energy deposition. As the β stabilizer content increases from 1 to 4 wt%, the coarse columnar-grained morphology typical of additively manufactured Ti–6Al–4V is significantly refined, with a columnar-to-equiaxed transition. Furthermore, reheating of the deposited layers by the deposition of overlaying layers during fabrication induces an element partitioning effect, resulting in the formation of fine-grained α and isothermal ω. Hence, the heat profile during direct energy deposition resembles conventional solution and aging treatments. In addition, increasing the amount of β stabilizer steadily increases the room temperature strength of the Ti–6Al–4V alloy. The alloy with 4 wt% Fe showed the maximum strength, of ∼1.5 GPa.

Unfortunately, the acknowledgements were incomplete in the original version of this article.

A series of Ti–Al–V titanium alloy bars with nominal composition Ti–7Al–5V ELI, Ti–5Al–3V ELI, commercial Ti–6Al–4V ELI and commercial Ti–6Al–4V were prepared. These alloys were then heat treated to obtain bimodal or equiaxed microstructures with various contents of primary α phase. Dynamic compression properties of the alloys above were studied by split Hopkinson pressure bar system at strain rates from 2,000 to 4,000 s−1. The results show that Ti–6Al–4V alloy with equiaxed primary α (αp) volume fraction of 45 vol% or 67 vol% exhibits good dynamic properties with high dynamic strength and absorbed energy, as well as an acceptable dynamic plasticity. However, all the Ti53ELI specimens and Ti64ELI specimens with αp of 65 vol% were not fractured at a strain rate of 4,000 s−1. It appears that the undamaged specimens still have load-bearing capability. Dynamic strength of Ti–Al–V alloy can be improved as the contents of elements Al, V, Fe, and O increase, while dynamic strain is not sensitive to the composition in the appropriate range. The effects of primary alpha volume fraction on the dynamic properties are dependent on the compositions of Ti–Al–V alloys.

An investigation is given on the influence of heat treatment by the microstructural characteristics and tensile properties of a new high strength alloy Ti–2Al–9.2Mo–2Fe. Both of the α/β and β solution treatment (α/β-ST and β-ST), then aged at temperatures ranging from 400 °C to 600 °C, were prepared. The primary α phases having 2–5 μm are formed during the α/β-ST, and restrain the size of β grains below 10 μm. As a result of the fine β grains, the α/β-ST contributes a higher strength than the β-ST. The co-existence of α″ and athermal ω phase is found in the β-ST and water quenched samples. However, these have little influence on the alloy hardening. After aging, the alloys in the α/β-ST and β-ST condition reveal the phase transformation of β to isothermal ω, and β to α depending on the aging temperature. Although the primary α phase formed during the α/β-ST increases the stability in the β matrix, and the isothermal ω phase also appears to occur during aging at 400 °C and 450 °C for 2 h. These phenomena are less common in beta titanium alloys, when treated in the α/β-ST and aged at lower temperatures. The isothermal ω phase formed in both conditions results in high strength levels (1600 MPa of ultimate strength) with much ductility loss (2.5–4.5% of elongation) as a result of the superior hardening effect and brittleness of ω phase. However, the secondary α phase with the size of 1–3 μm leads to attractive combinations of strength and ductility (1200–1400 MPa of ultimate strength with 7.5–12.5% of elongation). The reason for that is too fine α phase below 1 μm tends to result in ultra-high strength with much ductility loss. As a whole, the alloy can be heat treated to obtain excellent balances of strength and ductility, and provided abundant stress levels with optional ductility as a usable material.

The effect of solution treatment on microstructural characteristics and tensile properties of a new high strength Ti–6Cr–5Mo–5V–4Al alloy was studied. The microstructure–mechanical property relationship is also discussed. The results show that, the Ti–6Cr–5Mo–5V–4Al alloy in solution treated condition has moderate strength levels (800–1000 MPa) with an excellent ductility (−22% of the elongation and 50–60% of the reduction of area). The alloy in the α/β-solution and aged (α/β-STA) condition shows a more attractive combination of strength and ductility than the alloy in the β-solution and aged condition (β-STA). The α/β-STA results in the occurrence of mixed α precipitates at nano-scale (−100 nm) and at micron-scale (1 μm), which contributes to the high ultimate strength levels (1400–1600 MPa). However, the fine β grains below 10 μm and the primary α phase contribute to good ductility (6–13.5% of the elongation and 22–52% of the reduction of area). The β-ST leads to equiaxed and coarsen β grains (40–100 μm), and subsequent aging contributes to the α phase with the size of 1–5 μm. The β-STA microstructure contributes to 1200–1400 MPa of the ultimate strength with 7–10% of the elongation and 22–28% of the reduction of area, which shows less attractive behavior on the properties than that of the α/β-STA.

Ti-Al-Mo-Fe alloys were developed as low cost beta Ti alloys for automotive springs, and designed based on Molybdenum equivalency and Bo-Md molecular orbital method. Low priced Mo-Fe master alloys were introduced as alloying elements for the cost and elastic modulus reduction. Eight Ti-Al-Mo-Fe alloy candidates were pre-designed according to the Bo-Md method. Primary laboratory scale ingots were thus melted by ISM (Induction Skull Melting). After primary property evaluation, the Ti-2Al-9.2Mo-2Fe alloy was optimized finally and large scale ingot was made by VAR for further property evaluation. Resultantly, it shows that the alloy has lower elastic modulus (60-70 GPa) and good tensile properties in the solution condition, and compares well with the other developed commercial beta alloys.

The effect of aging treatment on the microstructures and hardening behavior of a metastable beta Ti–9.2Mo–2Fe alloy, which is new designed on the basis of Bo–Md molecular orbital method (Bo, the bond order; Md, the metal d-orbital energy level), has been investigated using hardness measurement, X-ray diffraction, optical microscopy and TEM characterization. The results reveal that, the athermal ω phase with the size of 2–5 nm is found in Ti–9.2Mo–2Fe alloy when solution-treated at 860 °C followed by water quench. The isothermal ω phase is also found when Ti–9.2Mo–2Fe alloy aged at temperatures from 300 °C to 500 °C, although the ω phase has a limited time of stability at 400 °C and 500 °C. The athermal ω phase does not lead to attractive hardening due to its too small size and volume fraction, so the hardness of the solution-treated alloy is about 370 Hv. However, the isothermal ω phase with the size of 5–10 nm shows a moderate hardening (470 Hv), while the ω phase with the size of 50–100 nm contributes the best hardening (∼500 Hv). As well, the hardening due to isothermal ω phase precipitation hardly exhibits over-aging response as long as ω phase exists.

A study on the microstructural characteristics and tensile properties of a new high strength Ti–6Cr–5Mo–5V–4Al alloy were investigated. Both the α/β and β solution treatment and subsequent aging at temperatures ranging from 460 °C to 560 °C were introduced to investigate the microstructural characteristics and microstructure–property relationships. The results show that the primary α phase formed during the α/β solution treatment can increase the stability of the β matrix and then restrain the size of secondary α phase during subsequent aging. In the α/β solution plus aging condition, the secondary α phase with the size of about 1 μm results in a high strength above 1500 MPa with −6% of elongation. The β solution treatment leads to the least stable β matrix and the greatest driving force for secondary α phase, so coarser α phases tend to form during aging. The β solution plus aging does not lead to attractive high strength because of the coarser and non-uniform α phase. And it also leads to a poorer combination of strength and ductility than the α/β solution plus aging. Direct aging exhibits the best strengthening. The ultimate strength of the alloy is about 1600 MPa with acceptable elongations of 6.5–7.5% when direct aged at 500 °C for 2–8 h. It benefits from the mixed microstructure with nano-scale and micron-scale α phases. However, more detailed investigations are needed to improve the ductility. As a whole, the alloy can be heat treatable to obtain an excellent balance of strength and ductility, and provide abundant stress levels with optional ductility (900–1600 MPa in ultimate strength and 6–20% in elongation).

Microstructure characterization and hardening behavior of a new designed Ti-12.1Mo-1Fe alloy during solution and aging treatment was investigated in the present study by OM, Vickers hardness. The results showed that the beta transus temperature of new Ti-12.1Mo-1Fe alloy was about 780°C. Further observation of ω phase should be performed by TEM later. It is also found that ω phase played a more important role than α phase in hardening. The hardening due to ω phase can lead to a high hardness about 470 Hv but the coarse α phases result in a hardness below 300 Hv.

A study on effect of boron addition on microstructure and property of low cost beta Ti-Al-Cr-Fe-B alloys are undertaken in the present. The Ti-Al-Cr-Fe alloys were developed as low cost beta Ti alloys for automotive springs, based on Molybdenum equivalency. Low priced Cr-Fe master alloys were introduced as beta stabilizing alloying elements for lowering cost, and elastic modulus. The boron addition is introduced in to refine the ingot microstructure and thus simplify hot working, which should lead to a cost reduction. On the other hand, the Ti-B compositions are able to restrict beta grain growth during heat treatments. So it can increase strength and microstructural stability. The mechanical tests show that the boron modified alloy has good tensile properties in solution condition. Moreover, the alloy can obtain well-balanced high strength levels with acceptable ductility after modulated aging treatment.

The microstructure evolution of a new designed metastable beta Ti-9.2Mo-2Fe alloy during aging treatment was investigated by TEM. The results revealed that athermal ω phases were observed in SAD pattern during water quenching from above the β transus temperature for the alloy. As well, isothermal ω phases were found during aging at 500 °C even though they have a limited time of stability. The coexistence of ω and α phase was found in the early aging time and the pre-formed ω phase during aging undergoes coarsening and act as uniformly distributed nucleation sites for α precipitation during subsequent isothermal aging treatment. A consequence of such ω- assisted nucleation is that relatively large amount of α precipitations are formed and fine distributed in β matrix. In addition, the α precipitations are of a relatively finer size scale (nanometers to sub micrometers).

Ageing behaviors and microstructural characterization by aging condition of Ti-Al-Mo-Fe alloy was investigated. Due to the formation of ω phase, it occurs a drastic change in mechanical properties of β alloys. There is large increasing in hardness and yield strength, accompanied with serious ductility reduction. However, it has been proved that proper control of ω phase volume fraction can bring to improve strength with a reasonable ductility. In this work new beta titanium alloy was designed and developed in Ti-Al-Mo-Fe alloy to investigate the hardening behavior of ω and α precipitation during aging. The results showed that a small amount of athermal ω was observed in the β matrix during water quenching from above the β transus temperature. Isothermal ω formation was also found during aged at temperatures ranging from 573 K to 773 K although it has a limited time of stability at 773 K. The hardening due to isothermal ω precipitation exhibits no over-aging effect as long as ω phase exists inside the matrix. The hardness of this alloy is very sensitive to size and volume fraction of ω phase and its existence, which depends on aging temperature, time and alloy compositions.

Ti-1023 alloy has been widely used in aerospace field as a typical titanium alloy with high strength and toughness. The relatively high content of Fe causes beta fleck which will make uneven microstructure and less plasticity. The new Ti-Al-Fe-V (Cr, Zr) alloys have been designed, based on Molybdenum equivalency and Bo-Md molecular orbital method, to aim at developing a new type of titanium alloy with high strength and fracture toughness. After primary design computation, Ti-Al-Fe-V (Cr, Zr) alloy was optimized finally. A large scale ingot was made by vacuum arc re-melting (VAR) for further property evaluation. Resultantly, it shows that athermal ω phase forms in Ti-Al-Cr-Fe-V-Zr alloy when solution treated at a temperature above the β-transus. Micro-hardness of alloy conducted to different aging conditions decreases with the aging temperature and time increasing respectively. Moreover, the new alloy has got a more sluggish age hardening response relating to the aging time. Additionally, after modulated aging treatment, the alloy can obtain high strength levels with acceptable ductility. When the alloy solution treated at 770 °C for 1h, followed by aging at 500 °C for 2h, the tensile strength of the alloy can achieve 1268 MPa, with an elongation of 11.5%, at the same time, the reduction of area has surpassed 30%. As a result, the newly designed alloy can achieve a good combination of tensile strength and plasticity through appropriate heat treatment.

We have investigated {332} twinning and detwinning mechanisms in a multilayered Ti-10Mo-xFe (x =1−3) alloy fabricated by multi-pass hot rolling. A strong influence of the Fe-graded structure on both phenomena is observed. The propagation of twins that are nucleated in Fe-lean regions (~1 wt.% Fe) is interrupted in the grain interiors at about 2 wt% Fe. We ascribe this effect to the role of the Fe content on the stress for twin propagation. The unusual twin structure determines the subsequent detwinning process upon thermal annealing. This process consists of two independent detwinning events that occur at two different microstructural regions, namely at twin tips located at grain interiors and at grain boundaries. Both detwinning modes can be explained from a thermodynamic standpoint whereby the boundary dissociation processes minimize the boundary free energy.

Ti-Mo-Fe alloy was developed as low cost beta Ti alloys for automotive springs, and designed based on Molybdenum equivalency and Bo-Md molecular orbital method. Low priced Mo-Fe master alloys were introduced as alloying elements for the cost and elastic modulus reduction. A laboratory scale ingot was melted by ISM (Induction Skull Melting). Then, microstructure characterization and hardening behavior of a new designed Ti-12.1Mo-1Fe alloy during solution and aging treatment were investigated in the present study by microscopy, X-ray diffraction and hardness test. The results showed that ω phase played a more important role than a phase in hardening. The hardening due to ω phase can lead to high hardness about 470 Hv. However, the coarse a phase resulted in hardness below 300 Hv. On the other hand, the alloy exhibited fast aging response due to high diffusion rate of Fe element in the Ti matrix.