WO2019193312A1

WO2019193312A1 - Titanium alloy comprising tantalum, chromium and optionally hafnium

Info

Publication number: WO2019193312A1
Application number: PCT/GB2019/050765
Authority: WO
Inventors: Sergey Yakovlev; Audrey COOPER; Ranjit KAUR; Thomas CARPY
Original assignee: Ilika Technologies Limited
Priority date: 2018-04-03
Filing date: 2019-03-19
Publication date: 2019-10-10
Also published as: GB2572609A

Abstract

The invention relates to a titanium alloy comprising: 65 at.% to 95 at.% titanium; 2 at.% to 21 at.% tantalum; 1 at.% to 10 at.% chromium; and, 0 at.% to 4 at.% total amount of one or more additional elements selected from hafnium, vanadium, zirconium, molybdenum, tungsten, or rhenium. The invention further relates to articles of manufacture comprising the titanium alloy, as well as methods of making the titanium alloy, article of manufacture and methods of using the same.

Description

TITANIUM ALLOY COMPRISING TANTALUM, CHROMIUM AND OPTIONALLY HAFNIUM

Background of the Invention

[1] Titanium alloys containing high amount of beta stabilising elements form a class of metastable beta (b) alloys with significantly improved mechanical properties and ductility. They can be solution treated and aged to further increase the strength.¹ V, Zr, Nb, Mo, Hf, Ta and Re are the iso-morphous-type beta stabilising elements while Cr, Mn, Fe, Co, Ni,

Cu, Pd, Ag, W, Pt, Au, Be, Si, Sn, Pb, Bi and U belong to the eutectoid-type beta stabilisers.^{1 2} Of the particular interest are the beta titanium alloys stabilised by Zr, Nb, Hf, Au, Ta and Sn due to the complete biocompatibility of these elements (³ and references cited therein). Less biocompatible in a pure form but currently accepted as the dopants in biomedical alloys are, e.g., Co, Cr, Mn, Mo, Fe and Ni.⁴

[2] In general, mechanical properties of titanium alloys strongly correlate with the chemical composition and electronic structure of the doping elements.⁵ Therefore, alloy design for a specific application usually involves preparation of a large number of samples and is being time- and labour-consuming.

[3] In the present invention, the inventors used a combinatorial materials synthesis and screening approach for accelerated alloy design based on high throughput physical vapour deposition (HT-PVD) method. Combinatorial screening using various techniques has been proven to be an indispensable tool for accelerated materials discovery.⁶ The HT-PVD method employed in this work uses off-axis molecular beam epitaxy, MBE, sources, (e- beam evaporators and Knudsen cells) for simultaneous deposition of individual elements in ultra-high vacuum environment. The composition gradients of the elements across a substrate are controllable and are achieved by an adjustable "wedge" shutter on each source.⁷

[4] The inventors synthesised high-throughput materials libraries of Ta-, Hf- and Cr- doped Ti with a broad variation of Ta and Cr and near-uniform distribution of Hf. As mentioned earlier, Ta and Hf have excellent biocompatibility. Cr in the oxidation state other than +6 has no adverse effect. Furthermore, Ti-Cr alloys are considered for dental prostheses applications due to improved strength and elongation.¹⁹ The aim of the work was (i) systematic screening of their structural and mechanical properties, and (ii) identifying alloy(s) with the highest elasticity suitable, for example, for biomedical applications.

Summary of the Invention

[5] The present invention provides fortitanium alloys comprising titanium, tantalum, chromium, and, optionally, an element selected from the group consisting of hafnium, vanadium, zirconium, molybdenum, tungsten, and rhenium. The invention further provides for articles of manufacture made of these titanium alloys, as well as methods of

manufacturing and methods of using the same.

[6] According to a first aspect, the invention provides a titanium alloy comprising:

65 at.% to 95 at.% titanium;

2 at.% to 21 at.% tantalum;

1 at.% to 10 at.% chromium; and,

0 at.% to 4 at.% total amount of one or more additional elements selected from hafnium, vanadium, zirconium, molybdenum, tungsten, or rhenium.

[7] In one embodiment, said titanium alloy has a Young's modulus that is at least 40,

50, 60, 70, 80, or 90 GPa. In another embodiment, said titanium alloy has a work recovery ratio that is at least 0.3, 0.4, 0.5, 0.6, or 0.7. [8] According to a second aspect, the invention provides an article of manufacture comprising a titanium alloy of the first aspect.

[9] According to a third aspect, the invention provides for a method of making the titanium alloy of the first aspect. In some embodiments the titanium alloy is made by a method selected from the group consisting of sputtering, vapour deposition, chemical vapour deposition, molecular beam epitaxy, atomisation, powder metallurgy and casting.

In one embodiment, the method produces a thin-film, a powder, or an ingot of the titanium alloy.

[10] In one embodiment, the invention provides for a method of making a thin-film of the titanium alloy of the first aspect. In one embodiment, said method is a vapour deposition process comprising the steps of:

(a) providing a vapour source of the titanium alloy or vapour sources of component elements of the titanium alloy;

(b) wherein the component elements comprise titanium, tantalum, chromium and, optionally, one or more elements selected from hafnium, vanadium, zirconium, molybdenum, tungsten, or rhenium; and,

(c) depositing said titanium alloy onto a substrate or depositing said component elements thereof onto a substrate to form the titanium alloy thin-film.

[11] In another embodiment, the invention provides for a method of making an ingot of the titanium alloy of the first aspect, said method comprising the steps of:

(a) providing component elements of the titanium alloy;

(b) melting the component elements to form a melted titanium alloy;

(c) pouring the melted titanium alloy into a mould that forms a shape of an

ingot; and,

(d) cooling the melted titanium alloy to form a solid titanium alloy in the shape of the ingot.

[12] In another embodiment, the invention provides for a method of making a powder of the titanium alloy of the first aspect. In one embodiment, said method comprises an atomisation process comprising the steps of:

(a) providing component elements of the titanium alloy; (b) combining the component elements to form the titanium alloy in the form of a bar or ingot; and,

(c) atomising the bar or ingot to form a powder.

[13] According to a fourth aspect, the invention provides a method of making the article of manufacture according to the second aspect of the invention. In one

embodiment, said method is selected from the group consisting of vapour deposition, additive manufacturing, powder metallurgy, and casting. In another embodiment, the article of manufacture is a thin-film material. In one embodiment, said method is a vapour deposition process comprising the steps of:

(a) providing a vapour source of a titanium alloy or vapour sources of component elements of the titanium alloy, wherein the component elements comprise titanium, tantalum, chromium and, optionally, one or more additional elements selected from hafnium, vanadium, zirconium, molybdenum, tungsten, or rhenium; and,

(b) depositing said titanium alloy or said component elements thereof onto a substrate.

[14] In a further embodiment, the article of manufacture formed by the vapour deposition process is a microelectromechanical system (MEMS).

[15] In a further embodiment, the invention provides an additive manufacturing process for making the article of manufacture of the second aspect, wherein said manufacturing process comprises the steps of:

(a) providing a powder bed fusion chamber comprising a work surface;

(b) providing a powder reservoir adjacent to said powder bed fusion chamber;

(c) filling the powder reservoir with a titanium alloy powder of the first aspect;

(d) taking a portion of the powder from the reservoir and forming a first

powder layer on the work surface of the powder bed fusion chamber;

(e) fusing the first powder layer to form a first structure layer with a top surface opposite a bottom surface, wherein the bottom surface is in contact with the work surface of the powder bed fusion chamber;

(f) taking a portion of the powder from the reservoir and forming a second layer of powder on the top surface of the structure; (g) fusing the second layer of powder to the top surface of the first structure layer to form a second structure layer; and,

(h) adding and fusing successive powder layers to form successive structure layers according to the steps (f) and (g) until the article is formed.

[16] In one embodiment, the article of manufacture formed by the additive

manufacturing process is selected from the group consisting of: an actuator, a sensor, a damper, an antenna, a bearing, a gear, a valve and a spring.

[17] In another embodiment, the invention provides a powder metallurgy process for making the article of manufacture of the second aspect, wherein said powder metallurgy process comprises the steps of;

(a) providing a titanium alloy material in the form of a powder;

(b) placing the powder into a die with a desired shape; and,

(c) compacting the powder into the desired shape.

[18] In a further embodiment, the article of manufacture formed by the powder metallurgy process is selected from the group consisting of: an actuator, a sensor, a damper, an antenna, a bearing, a gear, a valve and a spring.

[19] In another embodiment, the invention provides a method of making the article of manufacture of the second aspect, wherein said method is a casting process comprising the steps of:

(a) providing a titanium alloy;

(b) melting the titanium alloy;

(c) pouring the melted titanium alloy into a mould; and,

(d)cooling the melted titanium alloy in the mould to form a solid.

[20] In a further embodiment, the article of manufacture formed by the casting process is selected from the group consisting of: an actuator, a sensor, a damper, an antenna, a bearing, a gear, a valve and a spring.

Description of the figures

[21] Figure 1. Composition range and relative gradients of elements in synthesised Ti- Ta-Cr-Hf high-throughput materials library. [22] Figure 2. Typical load-unload nanoindentation curve obtained for Ti-Ta-Cr-Hf thin- film materials library.

[23] Figure 3. X-ray diffraction patterns obtained for representative compositions within characterised Ti-Ta-Cr-Hf high-throughput materials library: Ti_93.2Ta _.9Cr_1.1Hf_3.8 (a), Ti_73.oTa_2o.7Cr_3.3Hf_3.7 (b), Ti_87.oTa _.gCr_7.3Hf_3.8 (c), Ti_8o.5Ta_7. Cr_7. Hf_3.7 (d), Tis ^Ta _o.iCr_g.oHfg_.g (e).

[24] Figure 4. Phase composition of studied Ti-Ta-Cr-Hf high throughput materials library as a function of Ta (a), Cr (b) and Hf (c) contents.

Detailed Description

[25] As used herein, ranges of values set forth herein as "X to Y" or "between X and Y" are inclusive of the end values X and Y.

[26] As used herein, the term "superelasticity" or "superelastic" refers to materials which exhibit a stress-induced formation of the martensite phase on loading and the reverse transformation from the stress-induced martensite phase to the parent phase on unloading.

[27] The martensitic transformation is understood to be a diffusionless phase transformation in solids, in which atoms move cooperatively. The parent phase is generally cubic, whilst the martensite phase is known to have a lower symmetry. When the material is subjected to stress, martensitic transformation begins by a shear-like mechanism. If the stress is subsequently removed, the martensite phase becomes unstable and the reverse transformation occurs, whereby the martensite reverts to the parent phase. The relative atomic displacements are small, but a macroscopic shape change is associated with the martensitic transformation

[28] During repetitive load-unload cycles, strain will be accommodated by the martensitic transformation rather than forming microcracks as in classical fatigue failure. See, e.g., Shape Memory Materials, K. Otsuka and C.M. Wayman, 1999, Chapter 1 and Engineering Aspects of Shape Memory Alloys, Duerig et al, 1990, Chapter 1. [29] High-throughput synthesis methods can be used to rapidly synthesise libraries of new materials. High-throughput synthesis can be combined with high-throughput screening methods to identify new materials which are suitable for a desired purpose.

[30] The inventors of the present invention synthesized new libraries of titanium alloys using a vapour deposition method, wherein the individual elements were vapour deposited onto a substrate to form a titanium alloy comprising titanium, tantalum, chromium and hafnium. Each source was deposited in relative amounts across the surface of the substrate, so that they vary in at least one direction across the surface of the substrate. The deposition of each vapour source was varied, for example, by placing a wedge shutter between each vapour source and the substrate, so that the wedge shutter partially interrupted the flow of the vapour source. This resulted in each vapour source being deposited onto the substrate with a gradient distribution. Such methodology allowed a large number of titanium alloys with a large compositional range to be deposited simultaneously onto a single substrate. This method is advantageous for material discovery because it substantially decreases the amount of time required to prepare new titanium alloys for testing.

[31] Materials made by a high-throughput synthesis method are preferably made as thin-film materials, and are preferably made by a vapour deposition process comprising the steps of:

(a) providing a vapour source of a titanium alloy or vapour sources of

component elements of the titanium alloy, wherein, the component elements comprise titanium, tantalum, chromium and, optionally, one or more additional elements selected from hafnium, vanadium, zirconium, molybdenum, tungsten, or rhenium;

(b) depositing said titanium alloy or component elements thereof onto a substrate;

(c) interrupting the vapour sources of the component elements such that each vapour source is deposited onto a substrate with a gradient distribution, wherein the component elements form a titanium alloy, and wherein the titanium alloy has a compositional gradient across the substrate. [32] Examples of vapour sources may include electron beam evaporators and Knudsen cells (K-cells). For example, the titanium, tantalum and hafnium may be evaporated using electron beam evaporators and chromium may be evaporated using Knudsen cells. The rate of deposition of each component element may be independently controlled to allow the stoichiometry of the deposited compound to be controlled to obtain a specific composition.

[33] The vapour source may be interrupted using any suitable method, for example, each component vapour source may be equipped with an individual wedge shutter which is placed between the source and the substrate.

[34] Nanoindentation is a preferred method of screening thin-film samples of titanium alloys to identify superelastic materials. For bulk materials, other well-known methods of analysis may be used, including bending, compression and tensile testing to screen for superelastic materials.

[35] The nanoindentation method uses a nanoindenter to measure the mechanical properties of thin-films. During testing, an indenter presses into the sample, causing elastic and plastic deformations to occur. This results in an imprint which conforms to the shape of the indenter. During indenter withdraw, the elastic portion of the deformation is recovered. See e.g., J Mats Process Tech, 201 2008,770-774.

[36] Nanoindentation may be used for thin-film samples with a thickness between 50 nm and 2000 nm.

[37] Different geometries may be used for the shape of the indenter, for example, three sided pyramids, four sided pyramids, wedges, cones, cylinders or spheres. The tip end of the indenter may be sharp, flat, or rounded to a cylindrical shape. The nanoindenter may be made from diamond, sapphire, quartz, silicon, tungsten, steel, tungsten carbide or any other suitable metal or ceramic. The indenter is preferentially a cone and is preferentially made from diamond.

[38] The results obtained from nanoindentation are represented by a load/unload curve as depicted in Figure 1, wherein the loading curve is represented by the black circles and the unload curve is represented by the open circles. The total work done during loading (W_t) is calculated by integrating the area under the loading curve (Equation 1) and the total work done during unloading (W_e) is calculated by integrating the area under the unload displacement curve (Equation 2). w_t = /₀ ^hmax P d/i (1)

wherein, W_t is the total work done during loading;

W_e is the total reversible work obtained during unloading;

h_max is the indentation depth at maximum load;

h_r is the residual indentation depth at zero load on unloading; and,

P is the load.

[39] The work recovery ratio, r\_w\s calculated by taking the ratio of the work done during unloading and the work done during loading (Equation 3) and describes the ability of a material to recover after deformation.

wherein, W_e is the reversible work obtained during unloading; and,

W_t is the total work done during loading.

[40] A fully elastic material will have a work recovery ratio of one, because the load and unload curves will be the same. Conversely, a fully plastic material will have a work recovery ratio of zero, because when the load is removed, the unload curve will have an integral value of zero. A superelastic material will have an absolute value of the work recovery ratio because its behaviour is somewhere in between that of a fully elastic and fully plastic material. Pure titanium has a work recovery ratio of between 0.14 and 0.16, and copper which is not considered to be a superelastic material has a work recovery ratio of 0.14. The titanium alloys of the present invention have a work recovery ratio of at least 0.4 and more preferably a work recovery ratio of at least 0.3, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, or 0.7.

[41] The Young's modulus, (E) is calculated using equation (4):

wherein, a_rep is the representative stress; and,

e_rep is the representative strain.

[42] The representative stress, a_rep is calculated using equation (5):

wherein, P is the load and A_c is the contact area function given by equation (6); A_c = 2nRh_c (6) wherein, R is the radius of the conical tip; and h_c is given by equation (7); h_c— h_t 0.75 ^ (7) wherein, h_t is the total displacement into the surface,

P is the load; and,

S is the harmonic contact stiffness.

[43] The representative strain e_rep is obtained from equation (8):

0.2a

-rep _R (8)

wherein a is the contact depth radius; and,

R is the radius of the indenter.

[44] The representative stress and representative strain are obtained from

nanoindentation and are plotted as a stress/strain curve. The Young's modulus is therefore calculated by measuring the gradient of the stress/strain curve which corresponds to equation (4).

[45] The Young's modulus is a measure of the stiffness of a material. A high Young's modulus means that the material is stiff and potentially brittle. Known titanium alloys are characterised by a low Young's modulus and a high elastic recovery, which is typical of elastic and superelastic materials. These characteristics are particularly suited to the biomedical field where for example, a relatively low Young's modulus of 10 GPa to 70 GPa is close to that of cortical bone, making the titanium alloys suitable for implants. This has led to the development of superelastic materials which are highly elastic and flexible. See e.g., US20140338795.

[46] Doping titanium with low amounts of tantalum, chromium and, optionally, hafnium may increase the Young's modulus whilst maintaining a high elastic recovery. High-throughput synthesis and screening methods have accelerated the discovery of new titanium alloy compositions. The disclosed titanium alloys were found to be particularly well-suited for applications where the titanium alloys undergo repetitive stress and in environments where the alloy is not easily accessible. Titanium alloys with a high Young's modulus can withstand higher loads before elastic-plastic or plastic deformation occurs than other known superelastic materials with equivalent elastic recoveries but lower Young's modulus.

[47] The titanium alloys of the present invention may be used, e.g., in military, automotive and aerospace applications.

[48] According to a first aspect of the invention, there is provided a titanium alloy wherein said titanium alloy comprises:

65 at.% to 95 at.% titanium;

2 at.% to 21 at.% tantalum;

1 at.% to 10 at.% chromium; and,

[49] In one embodiment, said one or more additional elements comprises 0 at.% to 4 at.% hafnium. In another embodiment, said one or more additional elements is 3 at.% to 4 at.% hafnium. In another embodiment, said titanium alloy has a Young's modulus that is at least 40, 50, 6o, 70, 8o, or 90 GPa. In another embodiment, said titanium alloy has a work recovery ratio that is at least 0.3, 0.4, 0.5, 0.6, or 0.7. In a further embodiment, the work recovery ratio is at least 0.6, or 0.7.

[50] In another embodiment, said titanium alloy comprises

78 at.% to 83.5 at.% titanium;

6 at.% to 12.5 at.% tantalum;

4 at.% to 8.5 at.% chromium; and,

0 at.% to 3.75 at.% combined amount of one or more additional elements selected from hafnium, vanadium, zirconium, molybdenum, tungsten, or rhenium.

[51] In one embodiment, said one or more additional elements comprises 0 at.% to 3.75 at.% hafnium. In another embodiment, said one or more additional elements is 3.4 at.% to 3.7 at.% hafnium. In another embodiment, said titanium alloy has a Young's modulus that is at least 40, 50, 60, 70, 80, or 90 GPa. In another embodiment, said titanium alloy has a work recovery ratio that is at least 0.3, 0.4, 0.5, 0.6, or 0.7. In a further embodiment, the work recovery ratio is at least 0.5 or 0.6.

[52] In another embodiment, said titanium alloy comprises:

77 at.% to 84 at.% titanium;

6 at.% to 14.5 at.% tantalum;

3.5 at.% to 8.5 at.% chromium; and,

0 at.% to 3.75 at.% total amount of one or more additional elements selected from hafnium, vanadium, zirconium, molybdenum, tungsten, or rhenium.

[53] In one embodiment, said one or more additional elements comprises 0 at.% to 3.75 at.% hafnium. In another embodiment, said one or more additional elements is 3.0 at.% to 3.75 at.% hafnium. In another embodiment, said titanium alloy has a Young's modulus that is at least 40, 50, 60, 70, 80, or 90 GPa. In another embodiment, said titanium alloy has a work recovery ratio that is at least 0.3, 0.4, 0.5, 0.6, or 0.7. In a further embodiment, the work recovery ratio is at least 0.5 or 0.6.

[54] In another embodiment, said titanium alloy comprises:

73.5 at.% to 88 at.% titanium;

2 at.% to 20 at.% tantalum;

2 at.% to 9 at.% chromium; and, 0 at.% to 3.9 at.% total amount of one or more additional elements selected from hafnium, vanadium, zirconium, molybdenum, tungsten, or rhenium.

[55] In one embodiment, said one or more additional elements comprises 0 at.% to 3.9 at.% hafnium. In another embodiment, said one or more additional elements is 3.0 at.% to

3.9 at.% hafnium. In another embodiment, said titanium alloy has a Young's modulus that is at least 40, 50, 60, 70, 80, or 90 GPa. In another embodiment, said titanium alloy has a work recovery ratio that is at least 0.3, 0.4, 0.5, 0.6, or 0.7. In a further embodiment, the work recovery ratio is at least 0.5 or 0.6.

[56] In another embodiment, said titanium alloy comprises:

67 at.% to 90 at.% titanium;

2 at.% to 20.5 at.% tantalum;

2 at.% to 20.5 at.% chromium; and,

0 at.% to 3.9 at.% total amount of one or more additional elements selected from hafnium, vanadium, zirconium, molybdenum, tungsten, or rhenium.

[57] In one embodiment, said one or more additional elements comprises 0 at.% to 3.9 at.% hafnium. In another embodiment, said one or more additional elements is 3.4 at.% to

3.9 at.% hafnium. In another embodiment, said titanium alloy has a Young's modulus that is at least 40, 50, 60, 70, 80, or 90 GPa. In another embodiment, said titanium alloy has a work recovery ratio that is at least 0.3, 0.4, 0.5, 0.6, or 0.7.

[58] In another embodiment, said titanium alloy has a Young's modulus that is at least 40, 50, 60, 70, 80, or 90 GPa. In another embodiment, said titanium alloy has a work recovery ratio that is at least 0.3, 0.4, 0.5, 0.6, or 0.7.

[59] In one embodiment, said titanium alloy comprises:

79.5 at.% to 81.5 at.% titanium;

6.9 at.% to 8.9 at.% tantalum;

6.9 at.% to 8.9 at.% chromium; and

0.0 at.% to 4 at.% total amount of one or more additional elements selected from hafnium, vanadium, zirconium, molybdenum, tungsten, rhenium, or a combination thereof.

[60] In one embodiment, said one or more additional elements comprises 0 at.% to 4.0 at.% hafnium. In another embodiment, said one or more additional elements is 3.5 at.% to 4.0 at.% hafnium. In another embodiment, said titanium alloy has a Young's modulus that is at least 40, 50, 6o, 70, 8o, or 90 GPa. In another embodiment, said titanium alloy has a work recovery ratio that is at least 0.3, 0.4, 0.5, 0.6, or 0.7.

[61] In one embodiment, said titanium alloy comprises:

79.5 at.% to 81.5 at.% titanium;

6.5 at.% to 8.5 at.% tantalum;

6.5 at.% to 8.5 at.% chromium; and

[62] In one embodiment, said one or more additional elements comprises 0 at.% to 4.0 at.% hafnium. In another embodiment, said one or more additional elements is 2 at.% to 4.0 at.% hafnium. In another embodiment, said titanium alloy has a Young's modulus that is at least 40, 50, 60, 70, 80, or 90 GPa. In another embodiment, said titanium alloy has a work recovery ratio that is at least 0.3, 0.4, 0.5, 0.6, or 0.7.

[63] In one embodiment, said titanium alloy is Ti8o_.5Ta_7.9Cr_7.9Hf_3.7 (at. %) or

Ti8o.₅Ta8.oCr8.oHf_4.o. (at. %).

[64] As used herein the term 'consists essentially of means that the total amount of titanium, tantalum, chromium and hafnium, expressed as an atomic percentage of the total amount of metal and non-metal atoms in the alloy, is at least 94%, preferably at least 95%, preferably at least 97%, more preferably at least 98%, even more preferably at least 99%, still more preferably at least 99.5%, even more preferably at least 99.7%, still more preferably at least 99.8%, even more preferably at least 99.9%, still more preferably at least 99.95%, even more preferably at least 99.97%, still more preferably at least 99.98%, even more preferably at least 99.99%, still more preferably at least 99.995%, even more preferably at least 99.997%, still more preferably at least 99.998%, even more preferably at least 99.999%, still more preferably at least 99.9995%, even more preferably at least 99.9997%, still more preferably at least 99.9998%, even more preferably at least

99.9999%, and most preferably 100%. Where the combined total of titanium, tantalum, chromium and hafnium is less than 100%, the remaining atomic percentage may result from impurities, e.g., nitrogen, hydrogen or oxygen or may result from substitutions for one or more of the elements: tantalum, chromium and hafnium.

[65] Vanadium, zirconium, molybdenum, tungsten, rhenium, or a combination thereof, may substitute for a portion of tantalum in the alloy. Vanadium, zirconium, molybdenum, tungsten, rhenium, or a combination thereof, may substitute for tantalum in concentration up to 5 at.% of the atomic percentage of the total amount of metal atoms in the alloy. In one embodiment, up to 0.0001 at.%, up to 0.0002 at.%, up to 0.0005 at.%, up to 0.001 at.%, up to 0.002 at.%, up to 0.005 at.%, up to 0.01 at.%, up to 0.02 at.%, up to 0.05 at.%, up to 0.1 at.%, up to 0.2 at.%, up to 0.5 at.%, up to 1 at.%, up to 1.5 at.%, up to 2 at.%, up to 2.5 at.%, up to 3 at.%, up to 3.5 at.%, up to 4 at.%, up to 4.5 at.%, or up to 5 at.% (expressed as an atomic percentage of the total amount of metal atoms in the alloy) of the alloy may be vanadium, zirconium, molybdenum, tungsten, rhenium, or a combination thereof.

[66] Vanadium, zirconium, molybdenum, tungsten, rhenium, or a combination thereof, may also substitute for all or a portion of hafnium in the alloy. Vanadium, zirconium, molybdenum, tungsten, rhenium, or a combination thereof, may substitute for hafnium in concentration up to 3.9 at.% of the atomic percentage of the total amount of metal atoms in the alloy. In one embodiment, up to 0.0001 at.%, up to 0.0002 at.%, up to 0.0005 at.%, up to 0.001 at.%, up to 0.002 at.%, up to 0.005 at.%, up to 0.01 at.%, up to 0.02 at.%, up to 0.05 at.%, up to 0.1 at.%, up to 0.2 at.%, up to 0.5 at.%, up to 1 at.%, up to 1.5 at.%, up to 2 at.%, or up to 3.9 at.%, (expressed as an atomic percentage of the total amount of metal atoms in the alloy) of the alloy may be vanadium, zirconium, molybdenum, tungsten, rhenium, or a combination thereof.

[67] Manganese, iron, cobalt, nickel, copper, palladium, gold or silver, or a combination thereof, may substitute for a portion of chromium in the alloy. Manganese, iron, cobalt, nickel, copper, palladium, gold or silver, or a combination thereof, may substitute for chromium in concentration up to 1 at.% of the atomic percentage of the total amount of metal atoms in the alloy. In one embodiment, up to 0.0001 at.%, up to 0.0002 at.%, up to 0.0005 at.%, up to 0.001 at.%, up to 0.002 at.%, up to 0.005 at.%, up to 0.01 at.%, up to 0.02 at.%, up to 0.05 at.%, up to 0.1 at.%, up to 0.2 at.%, up to 0.5 at.%, or up to 1 at.%, (expressed as an atomic percentage of the total amount of metal atoms in the alloy) of the alloy may be manganese, iron, cobalt, nickel, copper, palladium, gold or silver, or a combination thereof.

[68] In some embodiments, the titanium alloy of the invention has a Young's modulus that is at least 50, 60, 70, 80, 90, 100, 110, or 120 GPa. In one embodiment, said titanium alloy has a Young's modulus that is between 50 GPa and 120 GPa.

[69] In one embodiment, said titanium alloy on the invention has a work recovery ratio that is at least 0.2. In a further embodiment, said titanium alloy has a work recovery ratio that is at least 0.3. In a further embodiment, said titanium alloy has a work recovery ratio that is at least 0.4. In a further embodiment, said titanium alloy has a work recovery ratio that is at least 0.4. In a further embodiment, said titanium alloy has a work recovery ratio that is at least 0.5. In a further embodiment, said titanium alloy has a work recovery ratio that is at least 0.55. In a further embodiment, said titanium alloy has a work recovery ratio that is at least 0.6. In a further embodiment, said titanium alloy has a work recovery ratio that is at least 0.65. In a further embodiment, said titanium alloy has a work recovery ratio that is at least 0.7. In a further embodiment, said titanium alloy has a work recovery ratio that is between 0.4 and 0.7. In a further embodiment, said titanium alloy has a work recovery ratio that is between 0.3 and 0.65. in a further embodiment, said titanium alloy has a work recovery ratio that is between 0.25 and 0.55.

[70] According to a second aspect of the invention, the invention provides an article of manufacture comprising the titanium alloy of the first aspect

[71] The article of manufacture of the present invention is particularly well-suited to applications where the article undergoes repetitive stress and in environments where the article is not easily accessible. For example, the article of manufacture is selected from the group consisting of a biomedical device, a microelectromechanical system (MEMS), an actuator, a sensor, a damper, an antenna, a bearing, a gear, a valve and a spring.

[72] According to a third aspect, the invention provides, through some embodiments, methods of making said titanium alloy according to the first aspect of the invention. In one embodiment, said method is selected from the group consisting of sputtering, vapour deposition, chemical vapour deposition, molecular beam epitaxy, atomisation, powder metallurgy and casting. In one embodiment, the method is a process for making a titanium alloy thin-film, a titanium powder, or a titanium alloy ingot.

[73] In one embodiment, the invention provides for a method of making a thin-film of the titanium alloy of the first aspect. In one embodiment, said method is a vapour deposition process comprising the steps of:

(a) providing a vapour source of the titanium alloy or vapour sources of

component elements of the titanium alloy, wherein the component elements comprise titanium, tantalum, chromium and, optionally, an element selected from the group consisting of hafnium, vanadium, zirconium, molybdenum, tungsten, and rhenium; and,

(b) depositing said titanium alloy onto a substrate, or depositing said component elements thereof onto a substrate, to form a thin-film material of the titanium alloy.

[74] Examples of vapour sources may include electron beam evaporators and Knudsen cells (K-cells). For example, the titanium, tantalum and hafnium may be evaporated using electron beam evaporators and chromium may be evaporated using Knudsen cells. The rate of deposition of each component element may be independently controlled if they are provided as separate sources to allow the stoichiometry of the deposited compound to be controlled to obtain a specific composition.

[75] In a further embodiment, a vapour deposition method is used to deposit a titanium alloy onto a substrate so that there is a compositional gradient across the whole of the substrate. A compositional gradient may be obtained by any appropriate method, for example, by placing wedge shutters between one or more of the sources and the substrate.

[76] In one embodiment, the invention provides for making the titanium alloy of the first aspect, said method comprising the steps of:

(a) providing component elements of the titanium alloy of the first aspect;

(b) combining the component elements;

(c) melting the component elements;

(d) pouring the melted component elements into a mould; and,

(e) cooling the melted component elements to form the titanium alloy, as a solid bar or ingot. [77] In another embodiment, the invention provides for making a powder of the titanium alloy of the first aspect. In one embodiment, said method is a powder atomisation process comprising the steps of:

(a) providing the titanium alloy of the first aspect as a bar or ingot; and,

(b) atomising the bar or ingot to form a titanium alloy powder.

[78] The bar or ingot may be further processed priorto atomisation using a suitable process, for example a vacuum arc remelt (VAR) process to produce an ingot of the titanium alloy with increased homogeneity. The vacuum arc remelt process may be repeated multiple times to further increase homogeneity of the titanium atom. The ingot may be converted into powder using any suitable atomisation method, for example, gas atomisation, water atomisation, direct reduction with hydrogen, plasma atomisation, electrode induction melting gas atomisation and centrifugal atomisation.

[79] According to a fourth aspect, the invention provides a method of making the article of manufacture according to the second aspect of the invention. In one

embodiment, said article is made by a method selected from the group consisting of vapour deposition, additive manufacturing, powder metallurgy and casting.

[80] In one embodiment, the invention provides a vapour deposition process for making a thin-film article of manufacture, said method comprising the steps of:

(a) providing a vapour source of the titanium alloy or vapour sources of

component elements of the titanium alloy; wherein the component elements comprise titanium, tantalum, chromium and hafnium; and,

(b) depositing said titanium alloy or said component elements thereof, onto a substrate to form a titanium alloy thin-film.

[81] Examples of vapour sources include electron beam evaporators and Knudsen cells (K-cells). For example, titanium tantalum and hafnium may be evaporated using electron beam evaporators and chromium may be evaporated using Knudsen cells. The rate of deposition of each component element may be independently controlled if they are provided as separate sources to allow the stoichiometry of the deposited compound to be controlled to obtain a specific composition. [82] In a further embodiment, the titanium alloy thin-film may be selectively patterned following vapour deposition using any suitable method, for example, electron beam lithography, ion beam lithography, ion track technology, dry or wet etching, isotropic etching, plasma etching, laser ablation, and reactive ion etching to form the article of manufacture.

[83] In a further embodiment, the article of manufacture formed by a vapour deposition method is a microelectromechanical system (MEMS).

[84] In another embodiment, a method is provided for making the article of

manufacture, wherein said method is an additive manufacturing process. In another embodiment, the invention provides an additive manufacturing process for making the article of manufacture of the second aspect.

[85] In a further embodiment, the process is a powder bed fusion method comprising the steps of;

(a) providing a powder bed fusion chamber comprising a work surface;

(b) providing a powder reservoir adjacent to said powder bed fusion chamber;

(d) taking a portion of the powder from the reservoir and forming a first powder layer on the work surface of the powder bed fusion chamber;

(e) fusing the first powder layer to form a first structure layer with a top surface opposite to a bottom surface, wherein the bottom surface is in contact with the work surface of the powder bed fusion chamber;

(f) taking a portion of the powder from the reservoir and forming a second layer of powder on the top surface of the structure;

(g) fusing the second layer of powder to the top surface of the first structure layer to form a second structure layer; and,

(h) adding and fusing successive powder layers to form successive structure layers according to steps (f) and (g) until the article is formed.

[86] The powder may be fused for example, using a laser or an electron beam.

[87] The titanium alloy powder may be made by any suitable method, for example, as described above. Suitable titanium alloy powder will generally comprise particles of titanium alloy that are between 2 microns and 100 microns in diameter. [88] In another embodiment, the invention provides a powder metallurgy process for making the article of manufacture of the second aspect, said process comprising the steps of:

(a) providing a powder of the titanium alloy of the first aspect;

(b) placing the powder into a die with a desired shape;

(c) compacting the powder in said die; and,

(d) forming a solid titanium alloy.

[89] The powder may be compacted into a desired shape through the application of suitable pressure, for example between, 0.5 MPa to 700 MPa, more preferably between 150 MPa and 700 MPa.

[90] In a further embodiment, the invention provides a casting process for making the article of manufacture of the second aspect, said process comprising the steps of:

(a) providing the titanium alloy of the first aspect;

(b) melting the titanium alloy;

(c) pouring the melted titanium alloy into a mould; and,

(d) cooling the melted titanium alloy to form a solid titanium alloy.

[91] The titanium alloy material may be provided, for example, as a bar, ingot or powder, as provided above. The internal shape of the mould corresponds to the shape of the article of manufacture. Multiple moulds may be required to obtain the article of manufacture.

[92] The article of manufacture of the present invention is particularly well suited for applications where the article undergoes repetitive stress and in environments where the article is not easily accessible. For example, the bulk material may be used in the aerospace or automotive industries. The bulk material may comprise for example, an actuator, a sensor, a damper, an antenna, a bearing, a gear, a valve or a spring.

Experimental

[93] Ti-Ta-Cr-Hf thin-film materials libraries were synthesized in a modified PVD system from DCA. The thin films were fabricated on square 35x35 mm² Si<ioo>/Si₃N₄ (150 nm) substrates from Nova Electronic Materials. Prior to deposition, substrates were washed in acetone and isopropanol absolute and dried in a flow of nitrogen. Deposition of thin films was carried out in cryo-pumped ultra-high vacuum (UHV) environment with the base pressure in the deposition chamber of the order xio ⁸ torr. Individual off-axis sources with associated wedge shutters⁷ were used to deposit continuous thin films with a broad composition gradient across the substrate. Ti (99.995 % purity), Ta (99.95 % purity) and Hf (99.99 % purity) were evaporated using electron beam sources and Cr (99.99 % purity) was deposited using Knudsen cell. Quartz crystal micro-balances were used to monitor the deposition rates of individual elements.

[94] Overall elemental composition of resulting materials library is shown schematically in Figure 1. Thin films were processed with the in-situ heating at 450 °C. The thickness of the films was determined using the Veeco MYKO NT1100 optical profilometry system. All films were found to have 20-30 % thickness gradient due to composition non-uniformity. Suitable deposition time was selected to attain minimum thickness of the films of 1 pm. Elemental analysis was performed for 14x14 array of locations on the materials libraries using scanning electron microscope equipped with X-Max energy-dispersive X-ray spectroscopy (EDX) detector from Oxford Instruments. Phase composition of the films was analysed for the same matrix of locations using Bruker D8 Discover X-ray Diffractometer system incorporating a HI Star area detector, IpS Incoatec Microfocus Cu Ka source with a UMC 150 sample stage. High throughput screening of nanomechanical properties of selected materials libraries of titanium alloys were carried out using Nano Indenter G200 (Keysight Technologies) with conical diamond tips (radius 5 pm). Measurements were conducted on 14x14 arrays of location. For each location on the materials library, load- unload curves were recorded in the continuous stiffness mode (CSM) for 3x3 mini-arrays with 50 pm pitch. Fused silica was used as a calibration reference material. Maximum indentation depth was 100 and 200 nm for the films and 2000 nm for the calibration sample.

[95] In order to systematically study trends in mechanical properties of synthesised materials libraries, universal figure of merit is required. Ni and co-workers^{20 21} used depth and work recovery ratios (r|h and h«, respectively) calculated from nanoindentation data as follows to estimate elastic recovery of Ni-Ti shape memory alloys:

where h_max is the indentation depth at maximum load, h_r is the residual indentation depth at zero load on unloading, W_t is the total work done during loading (obtained by integrating the load-displacement curve), W_e is the reversible work (obtained by integrating the unload displacement curve), and P is the load. Typical load-unload nanoindentation curve obtained forthis materials library is shown in Figure 2. Depth and work recovery parameters describe the same phenomenon, i.e. "ability" of the material to recover after the deformation. Here, we use the work recovery ratio. This parameter relies on the integrating the data over the entire range of loads and displacements and is more accurate compared to the depth recovery. Handling and analysis of high-throughput data were performed using proprietary software package.

[96] XRD phase analysis

[97] Close revision of all 196 X-ray diffractograms (14 X14 macro of locations) obtained for Ti-Ta-Cr-Hf thin-film materials library revealed four types of the phase contents in the composition range investigated. Representative X-ray diffraction patterns are shown in Figure 3. Depending on the composition range and relative concentrations of doping elements, phase content of the alloys can be classified as follows:

i) Pure a phase at low doping level. Typical XRD pattern is shown in Figure 3(a).

The crystal structure belongs to P6₃/mmc hexagonal space group. PDF # 04- 003-2227 was used as a reference for peak indexing. ii) a+b phase mixture at higher Ta content. Example of X-ray diffraction data is shown in Figure 3(b). b phase belongs to the cubic Im3m space group. PDF # 01- 081-9817 was used as a reference. iii) a+"amorphous" phase mixture at higher Cr content. Examples of XRD patterns are shown in Figures 3(c) and 3(d) for two different alloys within the investigated composition space. Presence of amorphous or very poorly crystallized phase (crystallite size at nm scale) results in a broad hump on XRD patterns observed between 37° and 45° 2Q. Also note that main phase (a) in this case is characterised by lower intensity and significant broadening of the peaks (compare Figures (3(c) and 3(d) with 3(a) and 3(b)). This effect can be attributed to finer crystallinity and/or structural disorder and high concentration of structural defects. iv) Three-phase region (maximum number of phases allowed by the Gibbs' phase rule in thermodynamic equilibrium), where a-, b-, and "amorphous"-type phases co-exist. The example of corresponding XRD pattern is shown in Figure 3(e). Similar to the results presented in Figure 3(c) and 3(e), the main phases (a and b in this case) are characterised by peaks of low intensity with significant broadening.

[98] No region of pure b-type structure was found within the composition range covered by this materials library. Due to the systematic nature of high throughput screening and continuous gradients of doping elements, it became possible to map described phase content on the composition space. Figure 4 shows ranges of existence of a, a+b, a+"amorphous" and a+b+''amorphous" structure of alloys as a function of Ta (a), Cr (b), and Hf (c) contents. The narrowest stability window was found for the three-phase region, while a+b alloys exist in much broader composition space with respect to both Ta and Cr.

[99] Nanomechanical screening of elastic properties of Ti-Ta-Cr-Hf high throughput materials library

[100] Nanoindentation screening of mechanical properties of deposited Ti-Ta-Cr-Hf materials library revealed significant correlation of the work recovery ratio with elemental composition of alloys and phase content. The highest work recovery ratio, as high as 0.71, was measured for the alloy with the unique composition Ti_8o.5Ta_8.oCr_8.oHf_4.o. This value is very close to the results reported for superelastic NiTiNol^{20 21} (commercial benchmark alloy, work recovery ratio is in the range 0.70-0.75) and significantly exceeds work recovery ratio of 0.5 measured for a-type Ti_93.2Ta .₉Cr_1.1Hf_3.8 - the alloy with the lowest doping level in this system, close to pure Ti and also 0.2 reported for Cu (typical example of a metal with elastic-plastic-type of deformation).²⁰

[101] Alloys with the work recovery ratios > 0.67 belong to the following composition range: Ti 83.2-78.1 at. %, Ta 6.0-12.3 at. %, Cr 4.0-8.2 at. %, Hf 37-3.4 at. %.

[102] Alloys with the work recovery ratios > 0.65 belong to the following composition range: Ti 83.7-77.4 at. %, Ta: 6.0-14.3 at. %, Cr: 3.5-8.2 at. %, Hf: 37-3.4 at. %.

[103] Alloys with the work recovery ratios > 0.60 belong to the following composition range: Ti 87.6-73.9 at. %, Ta 2.0-20.0 at. %, Cr 2.0-87 at. %, Hf 3.9-3.0 at. %.

[104] Alloys with the work recovery ratios > 0.55 belong to the following composition range: Ti 89.7-67.1 at. %, Ta 2.0-20.5 at. %, Cr 2.0-9.6 at. %, Hf 3.9-3.0 at. %.

[105] Composition ranges are also summarised in Table I together with identified phase contents. [106] Ta and Cr are both b-stabilising elements. However, Ta is the simple isomorphous b-stabilizer, while Cr is eutectoid b-stabilizer. The important finding is that equimolar substitution by Ta and Cr (e.g. Ti_8o.5Ta_8.oCr_8.0Hf_3.5 - composition with the highest elasticity found) results in (i) mixture of a- and amorphous-type phases (corresponding XRD pattern is shown in Figure 3(d)), and (ii) very high work recovery ratio. It is surprising that no b- phase was detected for Ti_8o.5Ta_8.oCr_8.oHf_4.0, considering rather high aggregate content of b- stabilizing elements. Molybdenum equivalence, [Mo]_eq, calculated for the alloy with the highest work recovery ratio, excluding Hf, equals to 15.6, roughly indicating that the alloy may be metastable b. It is therefore surprising to observe no traces of cubic phase for this particular stoichiometry.

[107] It is important to point out a mechanism other than superelasticity is responsible for high elasticity of alloys with the compositions around Ti_8o.5Ta_8.oCr_8.0Hf_3.5. We may speculate that one of the mechanisms, or both, are responsible for high elasticity of the alloys: (i) mechanical instability of a phase due to the specific/unique combination of doping elements and/or: (ii) fine-grain microstructure stabilised by co-doping by Ta and Cr will inhibit plastic deformation via classic dislocation motion mechanism. This discovery could only be made due to (i) the continuous nature of composition gradients formed via HT-PVD technique, (ii) controlled cleanness of the experiment (high purity of the elements with reduced undesired impurities and ultra-high vacuum), and (iii) systematic screening of trends in nanomechanical properties vs. composition.

Table I. Compositions corresponding to various work recovery ratio ranges. Respective phase contents are also described.

[108] All publications mentioned in the above specification are herein incorporated by reference. Various modifications and variations of the described methods and system of the present invention will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. Although the present invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments.

Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in chemistry, physics and materials science or related fields are intended to be within the scope of the following claims.

[109] References

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Claims

1. A titanium alloy, wherein said titanium alloy comprises:

65 at.% to 95 at.% titanium;

2 at.% to 21 at.% tantalum;

1 at.% to 10 at.% chromium; and,

2. The titanium alloy according of claim 1, wherein said titanium alloy comprises 0 at.% to 4 at.% hafnium.

3. The titanium alloy according of claim 1, wherein, said one or more additional

elements is 3 at.% to 4 at.% hafnium.

4. The titanium alloy according of claim 1, wherein said titanium alloy comprises:

78 at.% to 83.5 at.% titanium;

6 at.% to 12.5 at.% tantalum;

4 at.% to 8.5 at.% chromium; and,

5. The titanium alloy according of claim 4, wherein said titanium alloy comprises 0 at.% to 3.75 at.% hafnium.

6. The titanium alloy according of claim 4, wherein, said one or more additional

elements is 3.4 at.% to 3.7 at.% hafnium.

7. The titanium alloy according of claim 1, wherein said titanium alloy comprises:

77 at.% to 84 at.% titanium;

6 at.% to 14.5 at.% tantalum;

3.5 at.% to 8.5 at.% chromium; and,

8. The titanium alloy according of claim 7, wherein said titanium alloy comprises 0 at.% to 3.75 at.% hafnium.

9. The titanium alloy according of claim 7, wherein, said one or more additional

elements is 3.0 at.% to 3.75 at.% hafnium.

10. The titanium alloy according of claim i, wherein said titanium alloy comprises:

73.5 at.% to 88 at.% titanium;

2 at.% to 20 at.% tantalum;

2 at.% to 9 at.% chromium; and,

0 at.% to 3.9 at.% combined amount of one or more additional elements selected from hafnium, vanadium, zirconium, molybdenum, tungsten, or rhenium.

11. The titanium alloy according of claim 10, wherein said titanium alloy comprises 0 at.% to 3.9 at.% hafnium.

12. The titanium alloy according of claim 10, wherein, said one or more additional

elements is 3.0 at.% to 3.9 at.% hafnium.

13. The titanium alloy according of claim 1, wherein said titanium alloy comprises:

67 at.% to 90 at.% titanium;

2 at.% to 20.5 at.% tantalum;

2 at.% to 20.5 at.% chromium; and,

14. The titanium alloy according of claim 13, wherein said titanium alloy comprises 0 at.% to 3.9 at.% hafnium.

15. The titanium alloy according of claim 10, wherein, said one or more additional

elements is 3.4 at.% to 3.9 at.% hafnium.

16. The titanium alloy according to claim 1, wherein said titanium alloy consists

essentially of:

79.5 at.% to 81.5 at.% titanium;

6.9 at.% to 8.9 at.% tantalum;

6.9 at.% to 8.9 at.% chromium; and

0.0 at.% to 4 at.% combined amount of one or more additional elements selected from hafnium, vanadium, zirconium, molybdenum, tungsten, rhenium, or a combination thereof.

17. The titanium alloy according of claim 16, wherein said titanium alloy comprises 0 at.% to 4.0 at.% hafnium.

18. The titanium alloy according of claim 16, wherein, said one or more additional elements is 3.5 at.% to 4.0 at.% hafnium.

19. The titanium alloy according to claim i, wherein said titanium alloy consists

essentially of:

79.5 at.% to 81.5 at.% titanium;

6.5 at.% to 8.5 at.% tantalum;

6.5 at.% to 8.5 at.% chromium; and

20. The titanium alloy according of claim 16, wherein said titanium alloy comprises 0 at.% to 4.0 at.% hafnium.

21. The titanium alloy according of claim 16, wherein, said one or more additional

elements is 2.0 at.% to 4.0 at.% hafnium.

22. The titanium alloy according of claim 1, wherein said titanium alloy comprises:

(a) 78.1 to 83.2-at. % titanium,

6.0 to 12.3 at. % tantalum,

4.0 to 8.2 at. % chromium,

3.7 to 3.4 at. % hafnium;

(b) 77.4 to 83.7 at. % titanium,

6.0 to 14.3 at. % tantalum,

3.5 to 8.2 at. % chromium,

3.7 to 3.4 at. % hafnium;

(c) 87.6 to 73.9 at. % titanium,

2.0 to 20.0 at. % tantalum,

2.0 to 8.7 at. % chromium,

3.9 to 3.0 at. % hafnium; or (d) 89.7 to 67.1 at. % titanium,

2.0 to 20.5 at. % tantalum,

2.0 to 9.6 at. % chromium,

3.9 to 3.0 at. % hafnium.

23. The titanium alloy according to claim 1, wherein said titanium alloy is

Ti_80.5Ta_7.9Cr_7.gHf_3.7 (at. %).

24. The titanium alloy according to claim 1, wherein said titanium alloy is

Ti8o.₅Ta8.oCr8.oHf_4.o. (at. %).

25. The titanium alloy according to any one of the preceding claims, wherein said

titanium, tantalum, chromium and hafnium have a combined atomic percent of at least 95%.

26. The titanium alloy according to claim 25, wherein said titanium, tantalum, chromium and hafnium have a combined atomic percent of at least 97%.

27. The titanium alloy according to claim 25, wherein said titanium, tantalum, chromium and hafnium have a combined atomic percent of at least 99%.

28. The titanium alloy according to claim 25, wherein said titanium, tantalum, chromium and hafnium have a combined atomic percent of at least 99.5%.

29. The titanium alloy according to claim 25, wherein said titanium, tantalum, chromium and hafnium have a combined atomic percent of at least 99.9%.

30. The titanium alloy according to claim 25, wherein said titanium, tantalum, chromium and hafnium have a combined atomic percent of at least 99.95%.

31. The titanium alloy of any one of the preceding claims, wherein said titanium alloy has a Young's modulus that is at least 40 GPa.

32. The titanium alloy of any one ofthe preceding claims, wherein said titanium alloy has a Young's modulus that is at least 50 GPa.

33. The titanium alloy of any one of the preceding claims, wherein said titanium alloy has a Young's modulus that is at least 60 GPa.

34. The titanium alloy of any one ofthe preceding claims, wherein said titanium alloy has a Young's modulus that is at least 70 GPa.

35. The titanium alloy of any one of the preceding claims, wherein said titanium alloy has a Young's modulus that is at least 80 GPa.

36. The titanium alloy of any one ofthe preceding claims, wherein said titanium alloy has a Young's modulus that is at least 90 GPa.

37. The titanium alloy of any one ofthe preceding claims, wherein said titanium alloy has a Young's modulus that is 40-90 GPa.

38. The titanium alloy of any one ofthe preceding claims, wherein said titanium alloy has a Young's modulus that is at least 40-60 GPa.

39. The titanium alloy of any one of the preceding claims, wherein said titanium alloy has a work recovery ratio that is at least 0.2.

40. The titanium alloy of any one ofthe preceding claims, wherein said titanium alloy has a work recovery ratio that is at least 0.3.

41. The titanium alloy of any one of the preceding claims, wherein said titanium alloy has a work recovery ratio that is at least 0.4.

42. The titanium alloy of any one ofthe preceding claims, wherein said titanium alloy has a work recovery ratio that is at least 0.5.

43. The titanium alloy of any one of the preceding claims, wherein said titanium alloy has a work recovery ratio that is at least 0.6.

44. The titanium alloy of any one ofthe preceding claims, wherein said titanium alloy has a work recovery ratio that is at least 0.7.

45. An article of manufacture comprising the titanium alloy of any one of claims 1-43.

46. The article of manufacture of anyone of claim 45, wherein the article of manufacture is a thin-film material, wherein the thin-film material comprises a

microelectromechanical system (MEMS).

47. The article of manufacture of claim 45, wherein the article of manufacture is selected from the group consisting of: actuator, a sensor, a damper, an antenna, a bearing, a valve and a spring.

48. A method of making the titanium alloy of any one of claims 1-44, said method,

comprising the steps of:

(a) providing a vapour source of the titanium alloy or vapour sources of component elements of the titanium alloy, wherein the component elements comprise titanium, tantalum, chromium and, optionally, one or more additional elements selected from hafnium, vanadium, zirconium, molybdenum, tungsten, or rhenium; and,

(b)depositing said titanium alloy or said component elements thereof on a substrate.

49. A method of making the titanium alloy of any one of claims 1-44, said method

comprising the steps of:

(a) providing the titanium alloy as a bar or ingot; and,

(b)atomising the bar or ingot to form a powder.

50. A method of making the article of manufacture of any one of claims 45-47, said

method comprising the steps of:

(a) providing a vapour source of a titanium alloy or vapour sources of component elements of the titanium alloy, wherein the component elements comprise titanium, tantalum, chromium and, optionally, one or more additional elements selected from hafnium, vanadium, zirconium, molybdenum, tungsten, or rhenium;

(b)depositing said titanium alloy or said component elements thereof on to a substrate to form a titanium alloy thin-film; and, optionally,

(c) further processing the thin-film titanium alloy to form a desired shape.

51. A method of making the article of manufacture of any one of claims 45-47, wherein the method is a fusion bed process method, comprising the steps of:

(a) providing a powder bed fusion chamber comprising a work surface;

(b)providing a powder reservoir adjacent to said powder bed fusion chamber;

(d)taking a portion of the powder from the reservoir and forming a first powder layer on the work surface of the powder bed fusion chamber;

(e)fusing the first powder layer to form a first structure layer with a top surface opposite to a bottom surface, wherein the bottom surface is in contact with the work surface of the powder bed fusion chamber;

(g)fusing the second layer of powder to the top surface of the first structure layer to form a second structure layer; and, (h)adding and fusing successive powder layers to form successive structure layers according to the steps (f) and (g) until the article is formed.

52. A method of making the article of manufacture of any one of claims 45-47,

comprising the steps of:

(a) providing the titanium alloy material in the form of a powder;

(b) placing the powder into a die with a desired shape; and,

(c) compacting the powder into a desired shape.

53. A method of making the article of manufacture of any one of claims 45-47,

comprising the steps of:

(a) providing the titanium alloy;

(b)melting the titanium alloy;

(c) pouring the melted titanium alloy into a mould; and,

(d)cooling the melted titanium alloy to form a solid.