## 冷轧态Ti-35Nb-2Zr-0.3O合金的异常热膨胀行为

1. 南宁师范大学化学与材料学院广西天然高分子化学与物理重点实验室 南宁 530001

2. 东南大学材料科学与工程学院 南京 211189

## Anomalous Thermal Expansion Behavior of Cold-RolledTi-35Nb-2Zr-0.3O Alloy

LAN Chunbo1,2, LIANG Jianeng1, LAO Yuanxia1, TAN Dengfeng1, HUANG Chunyan1, MO Xianzhong1, PANG Jinying,1

1. Guangxi Key Laboratory of Natural Polymer Chemistry and Physics, College of Chemistry and Materials, Nanning Normal University, Nanning 530001, China

2. School of Materials Science and Engineering, Southeast University, Nanjing 211189, China

 基金资助: 广西自然科学基金项目.  Nos.2018GXNSFAA138057广西自然科学基金项目.  2018JJA110055广西大学广西有色金属及特色材料加工重点实验室开放基金项目.  Nos.GXYSOF1802广西大学广西有色金属及特色材料加工重点实验室开放基金项目.  GXYSOF1810

Corresponding authors: PANG Jinying, Tel: (0771)3908065, E-mail: pangjinying@126.com

Received: 2018-07-25   Revised: 2018-10-23   Online: 2019-05-28

 Fund supported: Guangxi Natural Science Foundation.  Nos.2018GXNSFAA138057Guangxi Natural Science Foundation.  2018JJA110055Open Foundation of Guangxi Key Laboratory of Processing for Non-Ferrous Metals and Featured Materials, Guangxi University.  Nos.GXYSOF1802Open Foundation of Guangxi Key Laboratory of Processing for Non-Ferrous Metals and Featured Materials, Guangxi University.  GXYSOF1810

Abstract

Thermal expansion behavior is one of the intrinsic properties of most materials, which is very difficult to control their thermal expansion behavior. Metallic material with ultra-low coefficient of thermal expansion named Invar effect was first found in Fe-Ni alloys. Recently, a multifunctional titanium alloy termed Gum metal (the typical composition is Ti-36Nb-2Ta-3Zr-0.3O, mass fraction, %; three electronic parameters: electron per atom ratio e/a≈4.24, bond order Bo≈2.87 and d electron orbital energy level Md≈2.45 eV) has been developed, and the alloy exhibits Invar effect after severe cold working. It is well known that the Invar effect of Fe-Ni alloys is related to the magnetic transition. However, titanium and its alloys are paramagnetic, and thus this mechanism cannot be used to explain Invar effect of Gum metal. In addition, the Invar effect of Gum metal is related to a dislocation-free plastic deformation mechanism. So far, there is still some controversy about this mechanism. In this study, a new β-type Ti-Nb base alloy Ti-35Nb-2Zr-0.3O (mass fraction, %) was developed whose three electronic parameters are different from those of the above mentioned Gum metal. The alloy was melted under high-purity argon atmosphere in an electric arc furnace, and the effects of cold rolling on microstructures and thermal expansion behaviors were characterized by OM, XRD, SEM, TEM and thermal mechanical analyzer (TMA). Results showed that the stress-induced martensitic α" (SIM α") phase transformation occurs after cold rolling, and the dominant <110> texture forms after severe plastic deformation. The equiaxed grains of Ti-35Nb-2Zr-0.3O alloy exhibit ordinary positive thermal expansion behavior and the thermal expansion rate increases with the increase of temperature. After cold deformation, negative thermal expansion occurs along rolling direction, and normal thermal expansion higher than solution treated sample occurs along transverse direction. The abnormal thermal expansion extent of the alloy increases with the increase of deformation reduction. The 30% cold deformed alloy along rolling direction possesses Invar effect between room temperature to 250 ℃, which is possibly related to SIM α" phase transformation, lattice distortion and <110> texture formation. The anomalous thermal expansion of the cold deformed samples in a temperature range from 25 ℃ to 110 ℃ is attributed to the lattice transition of SIM α" to β phase, while above 110 ℃ is attributed to the precipitation of ω and α phases.

Keywords： Ti-35Nb-2Zr-0.3O alloy ; cold rolling ; microstructure ; anomalous thermal expansion

LAN Chunbo. Anomalous Thermal Expansion Behavior of Cold-RolledTi-35Nb-2Zr-0.3O Alloy. Acta Metallurgica Sinica[J], 2019, 55(6): 701-708 doi:10.11900/0412.1961.2018.00347

2003年起，研究者开发出一种新型β钛合金Ti-36Nb-2Ta-3Zr-0.3O (质量分数，%，下同)，经过约90%的冷塑性变形后具有超高强度、超高弹性极限、超低弹性模量及Invar效应等特性，因而该类合金被命名为橡胶金属(Gum metal)[9,10,11,12]。Saito等[12]认为这些优异性能包括Invar效应的产生与橡胶金属的无位错塑性变形机制有关。这种崭新的观点引起了普遍关注。最近，Xing等[13]在研究轧制态橡胶金属的回复再结晶行为时发现，冷轧形变后的合金组织中未观察到位错存在，但经800 ℃短时退火后就发现了大量的位错，认为冷加工时产生的剧烈变形导致了这些位错的产生，这与普通β钛合金的塑性变形机制相似。因此，关于橡胶金属的塑性变形机制开始出现争议。随后，Talling等[14,15]、Besse等[16]和Yang等[17]相继在形变的橡胶金属中发现应力诱发马氏体α″ (stress-induced martensitic α"，SIM α")相、应力诱发ω相、$12$<111>位错滑移、{112}<111>孪晶和扭结(kinking)等多重塑性变形机制。这表明橡胶金属并不具备无位错塑性变形机制，仍以传统的位错滑移和机械孪生方式进行塑性变形。另外，Kim等[18]和Gutkin等[19]还认为橡胶金属的Invar效应源自纳米扰动。因此，橡胶金属的Invar效应与所谓的无位错塑性变形机制无关。

## 1 实验方法

### 图1

Fig.1   OM images of Ti-35Nb-2Zr-0.3O alloy under ST (a), 30%CR (b), 60%CR (c) and 90%CR (d) (ST—solution treated, CR—cold rolled, RD—rolling direction. Arrows in Figs.1b and c show the deformation bands)

### 图2

Fig.2   Inverse pole figures of Ti-35Nb-2Zr-0.3O alloy under ST (a) and 90%CR (b)

Color online

3为Ti-35Nb-2Zr-0.3O合金在固溶态及不同形变下的XRD谱。可以看出，在固溶态Ti-35Nb-2Zr-0.3O合金的XRD谱中仅存在β相的(110)、(200)和(211)衍射峰，表明固溶态合金为单一的β相。经过30%形变后，开始出现强度较低的α"相(200)衍射峰，表明有SIM α"相产生。随着形变量的增加，α"相(200)峰的强度增加，同时又出现了α"相(002)和(220)衍射峰，表明SIM α"相的含量增多。当形变量达90%时，α"相的(002)、(200)和(220)衍射峰均进一步增强。Hwang等[27]提出，Ti-Nb基合金的e/a值低于4.24和Bo值低于2.87时，合金在形变过程中会产生SIM α"相。另外，Besse等[16]和Wei等[28]均认为，合金中O的加入会抑制SIM α"相的大范围形成。在本工作中，Ti-35Nb-2Zr-0.3O合金的e/a值约为4.22，Bo值约为2.86，因此冷轧会诱发马氏体α"相变[21]

### 图3

Fig.3   XRD spectra of Ti-35Nb-2Zr-0.3O alloy under ST and different CR deformation reductions

### 2.2 热膨胀行为

Saito等[12]和Wang等[29]的研究表明，橡胶金属的Invar效应是由塑性变形引起的。为了揭示这一效应，本工作采用TMA对不同形变量的Ti-35Nb-2Zr-0.3O合金进行表征。图4为Ti-35Nb-2Zr-0.3O合金的热膨胀曲线。可以看出，固溶态Ti-35Nb-2Zr-0.3O合金在室温到350 ℃呈现出正常的膨胀行为。相对于固溶态试样，90%形变Ti-35Nb-2Zr-0.3O合金的膨胀出现了极化现象，轧制方向表现出负膨胀行为，截面方向表现出大于固溶态的正膨胀行为。而对于不同形变合金，轧制方向的负膨胀程度随着形变量的增加而增大，而30%形变的合金试样在室温到250 ℃范围内具有Invar效应。

### 图4

Fig.4   Thermal expansion curves of Ti-35Nb-2Zr-0.3O alloy under ST and different CR deformation reductions (TD—transverse direction)

### 图5

Fig.5   Cyclic thermal expansion curves of 90%CR Ti-35Nb-2Zr-0.3O alloy at 100 ℃ (a), 200 ℃ (b), 300 ℃ (c), 400 ℃ (d) and 500 ℃ (e)

6为90%形变Ti-35Nb-2Zr-0.3O合金在室温到850 ℃的热膨胀曲线和膨胀系数曲线。可以看出，90%形变Ti-35Nb-2Zr-0.3O合金在加热过程中有6个阶段的变化。第I阶段：室温到110 ℃范围内，合金具有恒定的负膨胀系数，为-2.5×10-5-1。在这一阶段内合金主要发生SIM α"相→β母相的晶格转变。众所周知，α"相与β相之间存在[100]α" //[100]β、[010]α" //[011]β和[001]α" //[0$1¯$1]β的晶格对应关系[30]。当发生SIM α"相→β相转变时，轧制方向表现为收缩，即负膨胀。第II阶段：110~190 ℃范围内，膨胀系数减小，在190 ℃达到极小值，为-6.1×10-5-1。这一阶段内合金的应变储能释放，同时SIM α"相也开始分解。第III阶段：190~320 ℃范围内，膨胀系数开始回升，但仍为负值。这一阶段内合金发生SIM α"相→ω相变。第IV阶段：320~450 ℃范围内，膨胀系数继续增加，在450 ℃达到最大，为5×10-5-1。在这一阶段内合金发生ω相→α相转变。第V阶段：450~570 ℃范围内，膨胀系数又开始下降，在570 ℃又出现拐点。在这一阶段内合金发生α相分解，570 ℃也是合金的(α+β)/β转变温度。第VI阶段：570~780 ℃范围内，合金主要发生位错攀移和回复再结晶过程。当温度高于780 ℃时，形变合金再结晶完成，形成等轴晶组织，表现出正常的膨胀行为。

### 图6

Fig.6   Thermal expansion and expansion coefficient curves of 90%CR Ti-35Nb-2Zr-0.3O alloy from room temperature to 850 ℃

7为90%形变Ti-35Nb-2Zr-0.3O合金在300、350和450 ℃时效1 h后显微组织的TEM分析。在300 ℃时效时，如图7a所示，TEM像中可观察到大量的位错存在，这些位错是由于大塑性变形产生。从[110]β晶带轴的选区电子衍射花样(SAED)中发现$23$<211>和$13$<111>位置有ω相的衍射斑点存在，这表明在300 ℃时效过程中SIM α"相分解同时析出ω相。研究[31,32,33,34]表明，ω相为随后的α相析出提供形核质点。升高时效温度，如图7b所示，可观察到大量分布均匀且尺寸为80~100 nm的板条状组织，从[110]β晶带轴的SAED花样(图7b中插图)中可以看出，这些板条状组织为时效析出的α相，另外还发现$23$<211>和$13$<111>位置有ω相的衍射斑点存在，表明350 ℃时效合金中αωβ三相共存。当时效温度达到450 ℃时，如图7c所示，可观察到大量分布均匀且尺寸约为200 nm的板条状组织，从[110]β晶带轴的SAED花样(图7c中插图)中可以看出，这些板条状组织为时效析出的α相，未发现$23$<211>和$13$<111>位置有ω相的衍射斑点存在，表明450 ℃时效合金中的ω相完全转变为α相，合金存在α+β两相。另外，β钛合金具有bcc结构，其晶格常数aβ=0.328 nm，而ω相(aω=0.460 nm，cω=0.282 nm)和α相(aα=0.295 nm，cα=0.469 nm)均为hcp结构。β相、ω相和α相所占的空间体积分别为0.0175、0.0172和0.0177 nm3。可见，若发生SIM α"ω相变或βω相变，则合金的体积会收缩。若发生ωα相变或βα相变，则合金的体积会膨胀[35]

### 图7

Fig.7   TEM images of 90%CR Ti-35Nb-2Zr-0.3O alloy ageing at 300 ℃ (a), 350 ℃ (b), 450 ℃ (c) for 1 h and schematic of SAED patterns of α and ω phases on the [110]β zone axis (d) (Insets in Figs.7a~c show the SAED patterns)

## 3 结论

(1) 在形变过程中，Ti-35Nb-2Zr-0.3O合金产生SIM α"相，并形成平行于应变方向的强<110>织构。SIM α"相的含量随形变量的增加而增多。

(2) 固溶态Ti-35Nb-2Zr-0.3O合金具有正常的膨胀行为。形变后，合金的膨胀行为出现异常现象。随着形变量的增加，合金膨胀行为的异常程度增大。另外，30%形变的合金试样在室温到250 ℃范围内具有Invar效应。

(3) 冷轧态Ti-35Nb-2Zr-0.3O合金在室温到110 ℃的恒定负膨胀归因于SIM α"相到β相的晶格转变，而在高于110 ℃的异常膨胀行为归因于SIM α"相的分解和ωα相的析出。

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Multiple deformation mechanisms of Ti-22.4Nb-0.73Ta-2.0Zr-1.34O alloy

[J]. Appl. Phys. Lett., 2009, 94: 061901

Ti–22.4Nb–0.73Ta–2.0Zr–1.34O(at.%)alloy after cold compression to655.2%strain was investigated. The alloy exhibited multiple plastic deformation mechanisms, including the stress-inducedα″martensitic (SIMα″) andωphase transformations,1/27011171dislocations slipping on the{112}βplanes as well as{332}7011371βand{112}7011171βtwinning, which have not previously been reported to coexist in a titanium alloy. It was also found thatβphase with the {200} planes vertical to the compression direction was almost completely consumed away by aβ→SIMα″transformation, and a (100) texture of SIMα″formed.

Kim H Y, Wei L S, Kobayashi S, et al.

Nanodomain structure and its effect on abnormal thermal expansion behavior of a Ti-23Nb-2Zr-0.7Ta-1.2O alloy

[J]. Acta Mater., 2013, 61: 4874

The microstructure and thermal expansion behavior of a Ti–23Nb–2Zr–0.7Ta–1.2O alloy (Gum metal) were investigated. A systematic diffraction pattern analysis using transmission electron microscopy revealed that a {11040}〈110〉-type transverse lattice modulation is present in the Ti–23Nb–2Zr–0.7Ta–1.2O alloy. Martensite-like nanodomains corresponding to {11040}〈110〉-type lattice modulations were observed in dark-field micrographs. Six variants of lattice modulation were confirmed to be distributed equivalently in the β phase in the annealed condition. Cold rolling resulted in preferential growth of a nanodomain variant which is most suited to releasing the applied stress although the long-range martensitic transformation was prevented by the local stress of the domain structure caused by oxygen atoms. It is suggested that the very small thermal expansion coefficient in the as-rolled specimen is caused by the preferential growth of the nanodomain variant due to residual stress.

Gutkin M Y, Ishizaki T, Kuramoto S, et al.

Nanodisturbances in deformed Gum metal

[J]. Acta Mater., 2006, 54: 2489

Systematic experiments have been performed to characterize defect structures in deformed Gum Metal, a special titanium alloy with high strength, low Young modulus, excellent cold workability and low resistance to shear in certain crystallographic planes. Results from high-resolution transmission electron microscopy characterization reveal nanodisturbances (planar nanoscopic areas of local shear) as typical elements of defect structures in deformed Gum Metal. A theoretical model is suggested describing nanodisturbances as nanoscale dipoles of non-conventional partial dislocations with arbitrary, non-quantized Burgers vectors. It is shown theoretically that the homogeneous generation of nanodisturbances is energetically favorable in Gum Metal, where they effectively carry plastic flow.

Wei L S, Kim H Y, Miyazaki S.

Effects of oxygen concentration and phase stability on nano-domain structure and thermal expansion behavior of Ti-Nb-Zr-Ta-O alloys

[J]. Acta Mater., 2015, 100: 313

In this study, in order to fully elucidate the origin of nano-domain structure and abnormal thermal expansion behavior of Gum metals, the effects of oxygen concentration, β phase stability and cold rolling on the microstructure and thermal expansion properties were investigated in (Ti–xNb–2Zr–0.7Ta)–yO (at.%) (x=21–25;y=0.3–1.8) alloys. Normal thermal expansion behaviors with positive linear thermal expansion coefficients were observed in all the annealed alloys irrespective of oxygen and Nb concentrations. The thermal expansion behavior of as-rolled alloys was strongly affected by the concentration of oxygen and Nb. A negative thermal expansion coefficient was observed in the as-rolled alloys with lower oxygen and Nb concentrations. The thermal expansion coefficient increased with increasing oxygen and Nb concentrations. The amount of nano-domains increased with increasing oxygen concentration while decreased with increasing Nb concentration. The growth of a preferential nano-domain variant was observed in as-rolled alloys and became more prominent with decreasing oxygen and Nb concentrations. The reverse transformation from the nano-domain structure to the β phase occurred with increasing temperature. Thermal expansion behavior of as-rolled alloys resulted from a competing relationship between the contribution of lattice distortion of nano-domain structure and the contribution of lattice vibration of the β phase.

Lan C B, Li G, Wu Y, et al.

Effects of cold deformation on microstructure and mechanical properties of Ti-35Nb-2Zr-0.3O alloy for biomedical applications

[J]. Trans. Nonferrous Met. Soc. China, 2017, 27: 1537

The Ti-35Nb-2Zr-0.3O (mass fraction, %) alloy was melted under a high-purity argon atmosphere in a high vacuum non-consumable arc melting furnace, followed by cold deformation. The effects of cold deformation process on microstructure and mechanical properties were investigated using the OM, XRD, TEM, Vicker hardness tester and universal material testing machine. Results indicated that the alloy showed multiple plastic deformation mechanisms, including stress-induced α" martensite (SIM α") transformation, dislocation slipping and deformation twins. With the increase of cold deformation reduction, the tensile strength and hardness increased owing to the increase of dislocation density and grain refinement, and the elastic modulus slightly increased owing to the increase of SIM α" phase. The 90% cold deformed alloy exhibited a great potential to become a new candidate for biomedical applications since it possessed low elastic modulus (56.2 GPa), high tensile strength (1260 MPa) and high strength-to-modulus ratio (22.4×10), which are superior than those of Ti-6Al-4V alloy.

Lan C B, Wu Y, Chen F.

Effects of cold rolling on microstructure and anomalous thermal expansion behaviors of Ti-35Nb-2Zr-0.3O alloy

[J]. Key Eng. Mater., 2017, 729: 46

Ti-35Nb-2Zr-0.3O (wt.%) alloy was melted under high-purity argon atmosphere in an electric arc furnace, followed by cold rolling. The effects of deformation process on microstructures and thermal expansion behaviors were investigated by OM, XRD and TMA. Results showed that the stress-induced 02±" martensitic transformation occurs after cold rolling. The solution treated sample exhibits normal thermal expansion along the rolling direction, and the thermal expansion rate increases with the increase of temperature. After cold rolling, thermal expansion behavior is polarized (negative thermal expansion occurs along rolling direction and normal thermal expansion higher than solution treated sample occurs along transverse direction). The thermal expansion rate along rolling direction decreases with the increase of reduction. The 40% cold deformed sample along rolling direction possesses Invar effect in a temperature range from 2500°C to 35000°C. The anomalous thermal expansion behaviors of cold rolled samples possibly relate to stress-induced 02±" martensitic transformation and 0205 <110> texture evolution.

Guo W, Quadir M Z, Ferry M.

The mode of deformation in a cold-swaged multifunctional Ti-Nb-Ta-Zr-O alloy

[J]. Metall. Mater. Trans., 2013, 44A: 2307

Multifunctional titanium alloys, termed Gum Metal (TM), are beta-phase Ti alloys first developed in 2003. These alloys exhibit many interesting properties including, for example, low rate of work-hardening and superplasticity during cold deformation. The original report described a new plastic deformation mechanism not involving major dislocation activity to explain such deformation behavior. In the current study, a comparable Ti-36.8Nb-2.7Zr-2.0Ta-0.44O (wt pct) alloy to the original investigators was produced by powder sintering, hot forging, solution treatment, and cold swaging with the aim at investigating the microstructural development during swaging. XRD and TEM showed that the forged/solution-treated alloy was beta-phase with a small amount of omega-phase. After cold swaging by up to 96 pct area reduction, TEM/HRTEM revealed the existence of dislocations, deformation twins, omega-phase, nanodisturbances, and lattice bending, with EBSD showing the grains to be highly elongated in the swaging direction, fragmented, and distorted. Most notably, swaging also generated a strong aOE (c) 110 > fiber texture, even after moderate strains. The foregoing structural analysis provides substantial evidence that dislocations are present in the alloy after cold swaging. The major support of dislocation glide processes acting as the dominant plastic deformation mode in the swaged alloy is the strong aOE (c) 110 > fiber texture that develops, which is a characteristic feature of all cold-drawn/swaged body centered cubic metals and alloys.

J W Jr Morris, Hanlumyuang Y, Sherburne M, et al.

Anomalous transformation-induced deformation in <110> textured Gum metal

[J]. Acta Mater., 2010, 58: 3271

Tensile tests on single crystals of Gum Metal (Ti–36Nb–2Ta–3Zr–0.3O (wt.%)) showed, anomalously, that while a stress-induced β(bcc) → α″(orthorhombic) transformation occurred in a crystal pulled in the 〈1 1 0〉 direction, (1) no transformation was observed in crystals pulled in the 〈1 0 0〉 or 〈1 1 1〉 directions and (2) little or no transformation occurred in severely worked rods, which are polycrystals with very strong 〈1 1 0〉 texture. Analysis of the energetics of the β → α″ transformation offers straightforward explanations: (1) an α″ precipitate has zero elastic energy if it forms as a thin plate with the habit {1 1 1.5}; a 〈1 1 0〉 tensile load significantly decreases the energy of this plate; loading along 〈1 0 0〉 or 〈1 1 1〉 is less effective; (2) while worked rods have a strong 〈1 1 0〉 axial texture, the perpendicular planes are severely distorted, increasing the elastic energy of α″ and inhibiting the transformation.

Lan C B, Wu Y, Guo L L, et al.

Microstructure, texture evolution and mechanical properties of cold rolled Ti-32.5Nb-6.8Zr-2.7Sn biomedical beta titanium alloy

[J]. J. Mater. Sci. Technol., 2018, 34: 788

Ti-32.5 Nb-6.8 Zr-2.7 Sn(TNZS,wt%) alloy was produced by using vacuum arc melting method,followed by solution treatment and cold rolling with the area reductions of 50% and 90%.The effects of cold rolling on the microstructure,texture evolution and mechanical properties of the experimental alloy were investigated by optical microscopy,X-ray diffraction,transmission electron microscopy and universal material testing machine.The results showed that the grains of the alloy were elongated along rolling direction and stress-induced α'' martensite was not detected in the deformed samples.The plastic deformation mechanisms of the alloy were related to {112} 111 type deformation twinning and dislocation slipping.Meanwhile,the transition from γ-fiber texture to α-fiber texture took place during cold rolling and a dominant {001} 110_(α-fiber) texture was obtained after 90% cold deformation.With the increase of cold deformation degree,the strength increased owing to the increase of microstrain,dislocation density and grain refinement,and the elastic modulus decreased owing to the increase of dislocation density as well as an enhanced intensity of {001} 110_(α-fiber)texture and a weakened intensity of {111} 112_(γ-fiber)texture.The 90% cold rolled alloy exhibited a great potential to become a new candidate for biomedical applications,since it possesses low elastic modulus(47.1 GPa),moderate strength(883 MPa) and high elastic admissible strain(1.87%),which are superior than those of Ti-6 Al-4 V alloy.

Lan C B, Wu Y, Guo L L, et al.

Effects of cold rolling on microstructure, texture evolution and mechanical properties of Ti-32.5Nb-6.8Zr-2.7Sn-0.3O alloy for biomedical applications

[J]. Mater. Sci. Eng., 2017, A690: 170

The effects of cold rolling on the microstructure, texture evolution and mechanical properties of Ti-32.5Nb-6.8Zr-2.7Sn-0.3O (TNZSO, wt%) alloy were investigated. The results showed that the TNZSO alloy exhibits multiple plastic deformation mechanisms and excellent workability during cold rolling. The grains of the alloy were refined and no stress-induced α" phase transformation occurred after cold rolling. The dislocation slipping and {112}<111> type twins appeared in the alloy deformed by 25% and 50%. When the deformation reduction was up to 75% and 90%, dislocation slipping became the main mode of deformation accompanying with the formation of nano-sized grains. With the increase of cold deformation reductions, it was found that the strength and hardness increased owing to the increase of dislocation density and grain refinement, and the elastic modulus obviously decreased owing to the increased dislocation density as well as the enhanced orientation density of <110>α-fibertextures (including {001}<110>α-fiberand {111}<110>α-fiber) and the weakened orientation density of {111}<112>γ-fibertexture. The 90% cold deformed alloy exhibited a great potential to become a new candidate for biomedical applications since it possesses low elastic modulus (54.1GPa), high tensile strength (1093MPa) and high strength-to-modulus ratio (20.2×10613), which are superior than those of Ti-6Al-4V alloy.

Hwang J, Kuramoto S, Furuta T, et al.

Phase-stability dependence of plastic deformation behavior in Ti-Nb-Ta-Zr-O alloys

[J]. J. Mater. Eng. Perform., 2005, 14: 747

The authors investigated the effects of alloy content on mechanical properties to make clear a correlation between plastic deformation behavior and β-phase stability in Ti-Nb-Ta-Zr-O alloys. It was realized that there was specific compositional area in which the alloy exhibited little work hardening and minimum Young’s modulus value. The specific area was expressed by the bond order (Bo), based on the DV-X α method, of 2.87 and the averaged electron/atom ratio (e/a) of 4.24, which corresponded to those of a multifunctional β titanium alloy, “Gum Metal.” These electronic conditions also minimized ideal strength required for plastic deformation without any dislocation activity. The deformation behavior of alloys in the specific compositional area revealed that the unique behavior could be characterized by a “giant fault.” It was also confirmed that such a compositional area corresponded to the phase boundary between the α″ martensite and β phases at room temperature.

Wei Q Q, Wang L Q, Fu Y F, et al.

Influence of oxygen content on microstructure and mechanical properties of Ti-Nb-Ta-Zr alloy

[J]. Mater. Des., 2011, 32: 2934

The influence of oxygen content on microstructure and mechanical properties of Ti–22.5Nb–0.7Ta–2Zr (at.%) alloy was investigated in this work. According to experiments, the grains were refined apparently when the oxygen content was between 1.5% and 2.0%. The ultimate tensile strength (UTS) increased and elongation decreased with increasing oxygen content. But at the content of 1.0%, the elongation was nearly the same to that of the original alloy (about 16%). The elastic modulus remained comparatively low (Research highlights? It focused on the influence of oxygen on microstructures and properties of beta titanium alloys. ? Gum Metal has ‘‘superproperties” different with TNTZ alloy, except for the addition of oxygen. ? The change of superelasticity of Ti–Nb–Ta–Zr–O via the addition of oxygen was discussed in the work. ? The comprehensive mechanical properties was improved for Ti–22.5Nb–0.7Ta–2Zr–1.0O alloy.

Wang Y, Gao J H, Wu H J, et al.

Strain glass transition in a multifunctional β-type Ti alloy

[J]. Sci. Rep., 2015, 4: 3995

URL     PMID:24500779

Recently, a class of multifunctional Ti alloys called GUM metals attracts tremendous attentions for their superior mechanical behaviors (high strength, high ductility and superelasticity) and novel physical properties (Invar effect, Elinvar effect and low modulus). The Invar and Elinvar effects are known to originate from structural or magnetic transitions, but none of these transitions were found in the GUM metals. This challenges our fundamental understanding of their physical properties. In this study, we show that the typical GUM metal Ti-23Nb-0.7Ta-2Zr-1.2O (at%) alloy undergoes a strain glass transition, where martensitic nano-domains are frozen gradually over a broad temperature range by random point defects. These nano-domains develop strong texture after cold rolling, which causes the lattice elongation in the rolling direction associated with the transition upon cooling and leads to its Invar effect. Moreover, its Elinvar effect and low modulus can also be explained by the nano-domain structure of strain glass.

Kim H Y, Sasaki T, Okutsu K, et al.

Texture and shape memory behavior of Ti-22Nb-6Ta alloy

[J]. Acta Mater., 2006, 54: 423

Textures of cold-rolled and heat treated plates of Ti-22Nb-6Ta alloy were investigated by X-ray diffraction measurements. A well-developed {0 0 1}lang1 1macr 0rang texture was obtained in the as-rolled specimen and after heat treatment at 873K for 600s. A recrystallization texture of {1 1 2}lang1 1macr 0rang was developed after heat treatment at 1173K for 1.8ks. Anisotropy in the shape recovery strain and Young's modulus was observed in both specimens heat treated at 873 and 1173K. For the specimen heat treated at 873K, a large recovery strain of 3.4% was observed when the loading axis is along the rolling direction (RD) and the transverse direction (TD). On the other hand, recovery strain took the largest value along the RD and the lowest value along the TD for the specimen heat treated at 1173K. The experimental results on orientation dependence of transformation strain were in good agreement with calculated results utilizing the texture information and lattice correspondence between martensite and parent phases. [All rights reserved Elsevier]

Afonso C R M, Ferrandini P L, Ramirez A J, et al.

High resolution transmission electron microscopy study of the hardening mechanism through phase separation in a β-Ti-35Nb-7Zr-5Ta alloy for implant applications

[J]. Acta Biomater., 2010, 6: 1625

Málek J, Hnilica F, Veselý J, et al.

The influence of chemical composition and thermo-mechanical treatment on Ti-Nb-Ta-Zr alloys

[J]. Mater. Des., 2012, 35: 731

Ti–Nb–Ta–Zr quaternary alloying system is very promising for biomedical alloys. It is due to good mechanical properties and corrosion resistance of titanium alloys. Moreover no potentially harmful elements are contained in this system. Mechanical properties were influenced by changing the chemical composition and by various heat-treatment operations. The alloys were prepared by arc melting and then they were hot forged (900–1000°C). After solution treatment 850°C/0.5h/water quenched, cold swaging was carried out with section reduction about 85%. As final heat treatment aging at 450°C/8h/furnace cooling was used. Mechanical properties were measured from tensile tests results at cold swaged and aged specimens. The microstructure was observed by using light microscopy and transmission electron microscopy (TEM)-thin foils method. X-ray diffraction analysis reveals the phase composition. By using these techniques the changes in microstructure caused by precipitation during aging treatment were clarified. After aging, the presence of ω or α phases may occur. Influence of changing Zr and Ta contents on mechanical properties and also on precipitation of secondary phases during aging treatment was observed.

Guo Q H, Zhan Y Z, Mo H L, et al.

Aging response of the Ti-Nb system biomaterials with β-stabilizing elements

[J]. Mater. Des., 2010, 31: 4842

Effects of aging temperature and the contents of β-stabilizing elements on the composition of martensite α′′ in two Ti–Nb alloys and the resulting mechanical properties were investigated for biomedical applications. The microstructures were examined by means of optical microscopy (OM) and X-ray diffraction (XRD). Vickers hardness, compressive elastic modulus and the yield strength have been measured. The results show that the decomposition mode of the martensite α′′ in two studied alloys depends on aging treatment and the contents of β-stabilizing elements. Various microstructures such as α, ( α + β) and ( β + ω) phases were observed to precipitate in the studied alloys after the aging treatments performed at 523 K, 773 K, 883 K and 1023 K for 0.5 h, respectively. Afterwards, the Ti–24Nb–6Zr–7.5Sn–2Fe alloy was aged at 773 K for 1 h. The compressive elastic modulus and mechanical properties of the two alloys are found to be sensitive to the microstructural change caused by aging temperature. For the Ti–24Nb–6Zr–7.5Sn–2Fe alloy, after aging at 773 K for 1 h, its yield strength, compressive elastic modulus and Vickers hardness reach 846 MPa, 26 GPa and 398 HV, respectively. This aged alloy exhibits proper comprehensive mechanical property and strength-to-modulus ratio for biomedical implant applications.

Ferrandini P L, Cardoso F F, Souza S A, et al.

Aging response of the Ti-35Nb-7Zr-5Ta and Ti-35Nb-7Ta alloys

[J]. J. Alloys Compd., 2007, 433: 207

Titanium alloys are the best metallic biomaterials to be used for implant fabrication. However, the Ti–6Al–4V alloy must be replaced because of V and Al toxicity and, non-toxic β-stabilizer elements should be used. This work reports the results found after aging treatments of the alloys Ti–35Nb–7Zr–5Ta and Ti–35Nb–7Ta. The alloys were arc melted, homogenized, hot rolled, solubilized and finally aged at several temperatures, from 200 to 700 °C for 4 h. Afterwards, the alloys were aged at 300 and 400 °C for 90 h. Characterization was mainly performed by X-ray diffraction, which did not indicate the precipitated phases during the 4 h aging, while it showed that during the 90 h aging the precipitated phases were α and ω. The 4 h aging showed that the highest hardness values were found when the alloys were aged at 400 °C. The values found were HV (336 ± 9) for the alloy Ti–35Nb–7Zr–5Ta and HV (317 ± 13) for the alloy Ti–35Nb–7Ta. It was observed that Zr suppresses ω precipitation but also hinders hardness improvement.

Guo W Y, Li J, Sun J.

Thermal expansion behavior of Ti-23Nb-0.7Ta-2Zr-O alloy

[J]. Mater Res. Appl., 2010, 4: 169

(郭文渊, 李 俊, 孙 坚.

Ti-23Nb-0.7Ta-2Zr-O合金的热膨胀行为

[J]. 材料研究与应用, 2010, 4: 169)

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