GB2562703A

GB2562703A - Titanium Alloys

Info

Publication number: GB2562703A
Application number: GB1703886.0A
Authority: GB
Inventors: Cooper Audrey; Yakolev Sergey; Kaur Ranjit; Carpy Thomas; Todd Iain
Original assignee: University of Sheffield; Ilika Technologies Ltd
Current assignee: Llika Technologies Ltd; University of Sheffield
Priority date: 2017-03-10
Filing date: 2017-03-10
Publication date: 2018-11-28
Also published as: WO2018162919A1; GB201703886D0

Abstract

A titanium alloy which comprises (in atomic %): 76-89 % titanium, 3-18 % of niobium, 0.5-4.8 % hafnium, 0.05-3 % chromium, 0-5 % tantalum, 0-2 % zirconium and 0-1 % iron. The alloy is superelastic and has high elastic recovery and increased Young's modulus. It can be used to make thin film microelectromechanical systems, an actuator, a sensor, a bearing, a damper an antenna, a bearing, a gear or a spring. The alloy can be made by vapour deposition of the component elements of the alloy onto a substrate. The alloy can also be in powder form which can then be processed by die compaction or additive layer manufacturing or it can be cast into a mould.

Description

(71) Applicant(s):

ILIKA TECHNOLOGIES LIMITED (Incorporated in the United Kingdom) Kenneth Dibben House, Enterprise Road, University of Southampton Science Park, Chilworth, Southampton, Hampshire, SO16 7NS, United Kingdom

University of Sheffield Firth Court, Western Bank, Sheffield, South Yorkshire, S10 2TN, United Kingdom (72) Inventor(s):

Audrey Cooper Sergey Yakolev

Ranjit Kaur

Thomas Carpy lain Todd (74) Agent and/or Address for Service:

D Young & Co LLP

120 Holborn, LONDON, EC1N 2DY, United Kingdom (51) INT CL:

C22C 14/00 (2006.01) C22C 1/00 (2006.01)	B33Y 70/00 (2015.01) C23C 30/00 (2006.01)
(56) Documents Cited: JP 2009097064 A	JP 2004204245 A
US 20160151610 A1	US 20140338795 A
(58) Field of Search: INT CL C22C Other: Online: ALLOYS,	INSPEC

(54) Title of the Invention: Titanium Alloys

Abstract Title: Atitanium-niobium-hafnium-chromium alloy (57) A titanium alloy which comprises (in atomic %): 76-89 % titanium, 3-18 % of niobium, 0.5-4.8 % hafnium, 0.05-3 % chromium, 0-5 % tantalum, 0-2 % zirconium and 0-1 % iron. The alloy is superelastic and has high elastic recovery and increased Young's modulus. It can be used to make thin film microelectromechanical systems, an actuator, a sensor, a bearing, a damper an antenna, a bearing, a gear or a spring. The alloy can be made by vapour deposition of the component elements of the alloy onto a substrate. The alloy can also be in powder form which can then be processed by die compaction or additive layer manufacturing or it can be cast into a mould.

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Titanium Alloys

Background of the Invention [0001] Some metal alloys are known to demonstrate “superelastic” behaviour which is the stress-induced formation of the martensite phase on loading and the reverse transformation from the stress-induced martensite phase to the austenite phase on unloading. Superelasticity is responsible for significant reversible elastic deformation and high Young’s modulus compared to known metals and alloys which undergo an elasticplastic type deformation. These characteristics make these alloys suitable for applications in the aerospace and automotive industries, for example, as actuators, sensors, dampers, antennas, bearings, valves, gears and springs.

[0002] An example of a superelastic alloy is a titanium hafnium niobium zirconium alloy. See e.g., Gonzalez eta/JMEPEG (2009) 18: 506-510 and Gonzalez eta/JMEPEG (2009) 18: 490-494. These titanium alloys were designed to be highly elastic with low Young’s moduli between approximately 44 GPa and 90 GPa. There is however a need to design new titanium alloys which are highly elastic and have high Young's moduli which would make them suitable for applications where components undergo large amounts of repetitive stress, for example in the automotive and aerospace industries.

[0003] Traditionally the discovery of new titanium alloys has been an iterative process, wherein each new alloy is made in bulk and its properties tested, which is a time consuming and expensive process. Guerin and Hayden in J. Comb. Chem. 2006, 8, 6673 disclose a method for the high throughput synthesis of solid-state material libraries which is advantageous over methods which rely on sequential synthesis to produce new material compositions.

[0004] The present invention provides new superelastic alloys with high elastic recovery and a large Young’s modulus using a combination of high-throughput synthesis and screening.

Summary of the Invention [0005] The present invention provides for titanium alloys with superelastic properties, wherein said titanium alloy comprises titanium, niobium, hafnium and chromium. 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.

[0006] According to a first aspect, the invention provides a titanium alloy comprising: 76 at.% to 89 at.% titanium;

at.% to 18 at.% niobium;

0.5 at.% to 4.8 at.% hafnium; and

0.05 at.% to 3 at.% chromium.

[0007] In one embodiment, the invention provides a titanium alloy comprising:

at.% to 89 at.% titanium;

at.% to 18 at.% niobium;

at.% to 4.8 at.% hafnium; and,

0.1 at.% to 3 at.% chromium.

In one embodiment, said titanium alloy has a Young's modulus that is at least 92 GPa. In another embodiment, said titanium alloy has a work recovery ratio that is at least 0.20. [0008] According to a second aspect, the invention provides an article of manufacture comprising a titanium alloy, wherein said titanium alloy is according to the first aspect of the invention.

[0009] In one embodiment, said titanium alloy comprises:

at.% to 89 at.% titanium;

at.% to 18 at.% niobium;

at.% to 4.8 at.% hafnium; and,

0.1 at.% to 3 at.% chromium.

In one embodiment, said titanium alloy has a Young's modulus that is at least 92 GPa. In another embodiment, said titanium alloy has a work recovery ratio that is at least 0.20. [0010] In a further embodiment, the article of manufacture is selected from the group consisting of: a microelectromechanical system (MEMS), a gear an actuator, a sensor, a damper, an antenna, a bearing, a valve and a spring.

[0011] According to a third aspect, the invention provides, methods of making said titanium alloy according to the first aspect of the invention. In some embodiments said 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.

[0012] 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, niobium, hafnium and chromium; 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.

[0013] 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.

[0014] 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 is 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.

[0015] 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.

[0016] In one embodiment, provides for a method of making the article of manufacture of the second aspect as 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, niobium, hafnium and chromium; and, (b) depositing said titanium alloy or said component elements thereof onto a substrate.

[0017] In a further embodiment, the article of manufacture formed by the vapour deposition process is a microelectromechanical system (MEMS).

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] In another embodiment, there is 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.

[0023] 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 [0024] Figure 1: Load displacement curve from the nanoindentation of a TiNbHfCr alloy, showing the loading curve (black circles) and the unload curve (open circles) The residual displacement is typical of a superelastic material.

[0025] Figure 2(a): X-ray diffraction pattern obtained from titanium alloy, Ti92.04Nb1.66Hf5.13Cr1.17 (at.%) showing the formation of the hexagonal close packed structure at low doping levels.

[0026] Figure 2(b): X-ray diffraction pattern obtained from titanium alloy Ti80.92Nb14.46Hf2.28Cr1.80 (at.%) showing that the addition of niobium to the alloy affects the stabilisation of the beta-type structure. Peaks (110) and (200) represent the formation of the alpha + beta type structure.

[0027] Figure 2(c): X-ray diffraction patterns which show the evolution of the beta-phase with increasing niobium content resulting in the increase in intensity of the cubic (110) peak and a decrease in intensity of the hexagonal close packed (102) and (200) peaks.

[0028] Figure 3(a): Trend plot of work recovery ratio vs titanium content. A maximum at around 83 at.% titanium is observed.

[0029] Figure 3(b): Trend plot of work recovery ratio vs niobium content. A maximum at around 12 at.% niobium is observed.

[0030] Figure 3(c): Trend plot of work recovery ratio vs hafnium content. A maximum at around 4 at.% hafnium is observed.

[0031] Figure 3(d): Trend plot of work recovery ratio vs chromium content. No maximum is observed due to the relatively small concentration of chromium used compared to the other elements.

[0032] Figure 4(a): pseudo-ternary plot obtained by combining chromium and niobium showing the entire compositional range of the TiNbHfCr alloy. The boundary between the alpha and alpha + beta phases is shown.

[0033] Figure 4(b): pseudo-ternary plot obtained by combining chromium and niobium showing the compositions of the TiNbHfCr alloy where work recovery ratio was at least 0.24 [0034] Figure 4(c): pseudo-ternary plot obtained by combining titanium and hafnium showing the entire compositional range of the TiNbHfCr alloy. The boundary between the alpha and alpha + beta phases is shown.

[0035] Figure 4(d): pseudo-ternary plot obtained by combining titanium and hafnium showing the compositions of the TiNbHfCr alloy where work recovery ratio was at least 0.24

Detailed Description [0036] 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.

[0037] 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.

[0038] 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 [0039] 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.

[0040] High-throughput synthesis methods are used to rapidly synthesise libraries of new materials. High-throughput synthesis may be combined with high-throughput screening methods to identify new materials which are suitable for the desired purpose. [0041] New libraries of titanium alloys are synthesized using a vapour deposition method, wherein the individual elements are vapour deposited onto a substrate to form a titanium alloy comprising titanium, niobium, hafnium and chromium. Each source is 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 is varied by, for example, placing a wedge shutter between each vapour source and the substrate, such that the wedge shutter partially interrupts the flow of the vapour source, resulting in each vapour source being deposited onto the substrate with a gradient distribution. Such methodology allows a large number of titanium alloys with a large compositional range to be deposited simultaneously onto a single substrate. This is advantageous for material discovery because it substantially decreases the amount of time required to prepare new titanium alloys fortesting.

[0042] 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, niobium, hafnium and chromium;

(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.

[0043] Examples of vapour sources may include electron beam evaporators and Knudsen cells (K-cells). For example, the titanium, niobium 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.

[0044] 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.

[0045] 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.

[0046] 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, 2012008,770-774.

[0047] Nanoindentation may be used for thin-film samples with a thickness between 50 nm and 2000 nm.

[0048] 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.

[0049] 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 (Wt) 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).

M/_t = f_o ^hmaxPd/r (1)

M4 = ^^axPdh (2) wherein, W_t is the total work done during loading;

W_e is the total reversible work obtained during unloading;

hmax is the indentation depth at maximum load;

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

P is the load.

[0050] The work recovery ratio, q_wis 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.

=| <³>

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

Wt is the total work done during loading.

[0051] 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 0.196 and more preferably a work recovery ratio of at least 0.24.

[0052] The Young’s modulus, (E) is calculated using equation (4):

E = (4) ^£rep wherein, a_rep is the representative stress; and, s_rep is the representative strain.

[0053] The representative stress, a_rep is calculated using equation (5):

= (5) wherein, P is the load and A_G 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, ht is the total displacement into the surface,

P is the load; and,

S is the harmonic contact stiffness.

[0054] The representative strain e_rep is obtained from equation (8):

o.2a ^rep ~ _R (θ) wherein a is the contact depth radius; and,

R is the radius of the indenter.

[0055] 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).

[0056] 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.

[0057] The present inventors surprisingly found that doping titanium with low amounts of niobium, hafnium and chromium increased 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. The high Young's modulus means that the titanium alloys 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. The titanium alloys may be used in military, automotive and aerospace applications where the materials are desired that have a high flexibility and are also relatively rigid.

[0058] According to a first aspect of the invention, there is provided a titanium alloy wherein said titanium alloy comprises:

at.% to 89 at.% titanium;

at.% to 18 at.% niobium;

at.% to 4.8 at.% hafnium; and,

0.1 at.% to 3 at.% chromium.

[0059] In one embodiment, there is provided a titanium alloy wherein said titanium alloy consists essentially of:

at.% to 89 at.% titanium;

at.% to 18 at.% niobium;

at.% to 4.8 at.% hafnium; and,

0.1 at.% to 3 at.% chromium.

[0060] In this specification the term ‘consists essentially of means that the total amount of titanium, niobium, hafnium and chromium, 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, niobium, hafnium and chromium 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: niobium, hafnium and chromium.

[0061] Tantalum may substitute for a portion of niobium in the alloy. Tantalum may substitute for niobium 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 tantalum.

[0062] Zirconium may substitute for a portion of hafnium in the alloy. Zirconium may substitute for hafnium in concentration up to 2 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.%, or up to 2 at.%, (expressed as an atomic percentage of the total amount of metal atoms in the alloy) of the alloy may be zirconium.

[0063] Iron may substitute for a portion of chromium in the alloy. Iron 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 iron.

[0064] In one embodiment, there is provided a titanium alloy wherein said titanium alloy comprises:

at.% to 89 at.% titanium;

at.% to 18 at.% niobium;

0.5 at.% to 4.8 at.% hafnium;

0.05 at.% to 3 at.% chromium;

at.% to 5 at.% tantalum;

at.% to 2 at.% zirconium; and, at.% to 1 at.% iron.

[0065] In one embodiment, there is provided a titanium alloy wherein said titanium alloy comprises:

at.% to 89 at.% titanium;

at.% to 18 at.% niobium;

at.% to 4.8 at.% hafnium;

0.1 at.% to 3 at.% chromium; and, at.% to 5 at.% tantalum.

[0066] In one embodiment, there is provided a titanium alloy wherein said titanium alloy comprises:

at.% to 89 at.% titanium;

at.% to 18 at.% niobium;

0.5 at.% to 4.8 at.% hafnium;

0.1 at.% to 3 at.% chromium; and, at.% to 2 at.% zirconium.

[0067] In one embodiment, there is provided a titanium alloy wherein said titanium alloy comprises:

at.% to 89 at.% titanium;

at.% to 18 at.% niobium;

at.% to 4.8 at.% hafnium;

0.05 at.% to 3 at.% chromium; and, at.% to 1 at.% iron.

[0068] In one embodiment, the titanium alloy comprises 80 at.% to 87 at.% titanium. In one embodiment, the titanium alloy comprises 81 at.% to 86 at.% titanium. In one embodiment, the titanium alloy comprises 82 at.% to 85 at.% titanium. In one embodiment, the titanium alloy comprises 83 at.% to 85 at.% titanium.

[0069] In one embodiment, the titanium alloy comprises 7 at.% to 16 at.% niobium. In one embodiment, the titanium alloy comprises 8 at.% to 14 at.% niobium. In one embodiment, the titanium alloy comprises 9 at.% to 13 at.% niobium. In one embodiment, the titanium alloy comprises 10 at.% to 12 at.% niobium.

[0070] In one embodiment, the titanium alloy comprises 1 at.% to 4.8 at.% hafnium. In one embodiment, the titanium alloy comprises 2 at.% to 4 at.% hafnium. In one embodiment, the titanium alloy comprises 2 at.% to 3.5 at.% hafnium. In one embodiment, the titanium alloy comprises 2.5 at.% to 3.5 at.% hafnium.

[0071] In one embodiment, the titanium alloy comprises 0.2 at.% to 2.8 at.% chromium. In one embodiment, the titanium alloy comprises 0.5 at.% to 2.6 at.% chromium. In one embodiment, the titanium alloy comprises 1 at.% to 2.4 at.% chromium. In one embodiment, the titanium alloy comprises 1.5 at.% to 2.2 at.% chromium.

[0072] In another embodiment, the titanium alloy comprises 84.01 at.% titanium, 11.28 at.% niobium, 3.00 at.% hafnium and 1.71 at.% chromium.

[0073] In one embodiment, said titanium alloy has a Young's modulus that is at least 92 GPa. In one embodiment, said titanium alloy has a Young's modulus that is between 92 GPa and 120 GPa. In a further embodiment, said titanium alloy has a Young's modulus that is at least 100 GPa. In a further embodiment, said titanium alloy has a Young's modulus that is at least 110 GPa. In a further embodiment, said titanium alloy has a Young's modulus that is between 110 GPa and 120 GPa.

[0074] In one embodiment, said titanium alloy 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 0.22. In a further embodiment, said titanium alloy has a work recovery ratio that is at least 0.24. In a further embodiment, said titanium alloy has a work recovery ratio that is between 0.2 and 0.3. In a further embodiment, said titanium alloy has a work recovery ratio that is between 0.2 and 0.24. in a further embodiment, said titanium alloy has a work recovery ratio that is between 0.24 and 0.30.

[0075] In one embodiment, there is provided a titanium alloy wherein said titanium alloy comprises:

at.% to 87 at.% titanium;

at.% to 16 at.% niobium;

1.5 at.% to 4.5 at.% hafnium; and,

0.1 at.% to 3 at.% chromium.

In one embodiment, said titanium alloy has a work recovery ratio that is at least 0.2 and a Young's modulus that is at least 92 GPa. In one embodiment, said titanium alloy has a work recovery ratio that is at least 0.22 and a Young's modulus that is at least 100 GPa. In a further embodiment, said titanium alloy has work recovery ratio that is at least 0.24 and a Young's modulus that is at least 110 GPa. In a further embodiment, said titanium alloy has a work recovery ratio that is between 0.2 and 0.3 and a Young's modulus that is between 92 GPa and 120 GPa. In a further embodiment, said titanium alloy has a Young's modulus that is between 110 GPa and 120 GPa and a work recovery ratio that is between 0.24 and 0.30.

[0076] In another embodiment, said titanium alloy comprises:

at.% to 86 at.% titanium;

at.% to 14 at.% niobium;

at.% to 4 at.% hafnium; and,

0.1 at.% to 3 at.% chromium.

[0077] In another embodiment, said titanium alloy comprises:

at.% to 85 at.% titanium;

at.% to 13 at.% niobium;

at.% to 3.5 at.% hafnium; and,

0.1 at.% to 3 at.% chromium.

In one embodiment, said titanium alloy has a work recovery ratio that is at least 0.2 and a Young's modulus that is at least 92 GPa. In one embodiment, said titanium alloy has a work recovery ratio that is at least 0.22 and a Young's modulus that is at least 100 GPa. In a further embodiment, said titanium alloy has work recovery ratio that is at least 0.24 and a Young's modulus that is at least 110 GPa. In a further embodiment, said titanium alloy has a work recovery ratio that is between 0.2 and 0.3 and a Young’s modulus that is between 92 GPa and 120 GPa. In a further embodiment, said titanium alloy has a Young's modulus that is between 110 GPa and 120 GPa and a work recovery ratio that is between 0.24 and 0.30.

[0078] In another embodiment, said titanium alloy comprises:

at.% to 85 at.% titanium;

at.% to 12 at.% niobium;

at.% to 3.5 at.% hafnium; and,

0.1 at.% to 3 at.% chromium.

[0079] In another embodiment, said titanium alloy comprises, 84.01 at.% titanium, 11.28 at.% niobium, 3.0 at.% hafnium and 1.71 at.% chromium, wherein, said titanium alloy has a work recovery ratio that is at least 0.2 and a Young's modulus that is at least 92 GPa. In one embodiment, said titanium alloy has a work recovery ratio that is at least 0.22 and a Young's modulus that is at least 100 GPa. In a further embodiment, said titanium alloy has work recovery ratio that is at least 0.24 and a Young's modulus that is at least 110 GPa. In a further embodiment, said titanium alloy has a work recovery ratio that is between 0.2 and 0.3 and a Young's modulus that is between 92 GPa and 120 GPa. In a further embodiment, said titanium alloy has a Young's modulus that is between 110 GPa and 120 GPa and a work recovery ratio that is between 0.24 and 0.30.

[0080] According to a second aspect of the invention, the invention provides an article of manufacture comprising the titanium alloy of the first aspect [0081] In one embodiment, the invention provides an article of manufacture comprising a titanium alloy with superelastic properties wherein said titanium alloy comprises:

at.% to 89 at.% titanium;

at.% to 18 at.% niobium;

at.% to 4.8 at.% hafnium; and,

0.1 at.% to 3 at.% chromium.

In one embodiment, said titanium alloy has a work recovery ratio that is at least 0.22 and a Young's modulus that is at least 100 GPa. In a further embodiment, said titanium alloy has work recovery ratio that is at least 0.24 and a Young's modulus that is at least 110 GPa. In a further embodiment, said titanium alloy has a work recovery ratio that is between 0.2 and 0.3 and a Young's modulus that is between 92 GPa and 120 GPa. In a further embodiment, said titanium alloy has a Young's modulus that is between 110 GPa and 120 GPa and a work recovery ratio that is between 0.24 and 0.30.

[0082] In another embodiment, said article of manufacture comprises a titanium alloy, wherein said titanium alloy comprises:

at.% to 87 at.% titanium;

at.% to 16 at.% niobium;

1.5 at.% to 4.5 at.% hafnium; and.

0.1 at.% to 3 at.% chromium.

[0083] In another embodiment, said article of manufacture comprises a titanium alloy, wherein said titanium alloy comprises:

at.% to 86 at.% titanium;

at.% to 14 at.% niobium;

2at.% to 4 at.% hafnium; and,

O.lat.% to 3 at.% chromium.

[0084] In another embodiment, said article of manufacture comprises a titanium alloy, wherein said titanium alloy comprises:

at.% to 85 at.% titanium;

at.% to 13 at.% niobium;

at.% to 3.5 at.% hafnium; and,

0.1 at.% to 3 at.% chromium.

[0085] In another embodiment, said article of manufacture comprises a titanium alloy, wherein said titanium alloy comprises:

at.% to 85 at.% titanium;

at.% to 12 at.% niobium;

at.% to 3.5 at.% hafnium; and,

0.1 at.% to 3 at.% chromium.

In another embodiment, said article of manufacture comprises, 84.01 at.% titanium, 11.28 at.% niobium, 3.0 at.% hafnium and 1.71 at.% chromium, wherein, said titanium alloy has a work recovery ratio that is at least 0.2 and a Young's modulus that is at least 92 GPa. In one embodiment, said titanium alloy has a work recovery ratio that is at least 0.22 and a Young's modulus that is at least 100 GPa. In a further embodiment, said titanium alloy has work recovery ratio that is at least 0.24 and a Young's modulus that is at least 110 GPa. In a further embodiment, said titanium alloy has a work recovery ratio that is between 0.2 and 0.3 and a Young's modulus that is between 92 GPa and 120 GPa. In a further embodiment, said titanium alloy has a Young's modulus that is between 110 GPa and 120 GPa and a work recovery ratio that is between 0.24 and 0.30.

[0086] 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 microelectromechanical system (MEMS), an actuator, a sensor, a damper, an antenna, a bearing, a gear, a valve and a spring.

[0087] 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.

[0088] 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, niobium, hafnium and chromium; 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.

[0089] Examples of vapour sources may include electron beam evaporators and Knudsen cells (K-cells). For example, the titanium, niobium 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.

[0090] 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.

[0091] 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.

[0092] In another embodiment, the invention provides for making a power 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.

[0093] The bar or ingot may be further processed prior to 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.

[0094] 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.

[0095] 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, niobium, hafnium and chromium; and, (b) depositing said titanium alloy or said component elements thereof, onto a substrate to form a titanium alloy thin-film.

[0096] Examples of vapour sources include electron beam evaporators and Knudsen cells (K-cells). For example, titanium niobium 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.

[0097] 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, wet etching, isotropic etching, plasma etching and reactive ion etching to form the article of manufacture. [0098] In a further embodiment, the article of manufacture formed by a vapour deposition method is a microelectromechanical system (MEMS).

[0099] 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.

[0100] 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;

(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 steps (f) and (g) until the article is formed.

[0101] The powder may be fused for example, using a laser or an electron beam.

[0102] 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.

[0103] 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 titanium alloy powder 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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

1. High-Throughput Synthesis of Ti-Nb-Hf-Cr Library [0108] The depositions were carried out within an ultra-high vacuum (UHV) system using the arrangement described in Guerin, S; Hayden, B. E., J. Comb Chem., 2006, 8, 66 and WO 2005/035820, incorporated by reference in their entirety. The thin-film were deposited onto Si(100)/Si3N4 (150 nm) substrates from Nova Electronic Materials.

[0109] Titanium-niobium-hafnium-chromium thin-films were deposited from the individual elemental sources. Titanium (99.995% purity), niobium (99.95% purity) and hafnium (99.99% purity) were evaporated from electron beam sources, and chromium (99.99% purity) was evaporated from a Knudsen cell. Each source had an associated wedge shutter, which allowed continuous thin-films with a broad compositional gradient to be deposited across the substrate. The wedge shutter positions and deposition rates were optimised during the processing of the films using a series of test samples to obtain thin-film materials where the compositions were within the desired range. The compositional range of the deposited Ti-Nb-Hf-Cr thin-films is shown in Table 1.

[0110]

Element	Lower limit, At. %	Upper limit, At. %
Ti	Balanced
Nb	0.9	24.2
Hf	0.3	5.5
Cr	0.0	3.4

Table 1: Composition range of studied Ti-Nb-Hf-Cr thin-film material library [0111] The Ti-Nb-Hf-Cr gradient thin-films were processed by in-situ heating at 450 °C. The thickness of the films was determined usinga Veeco MYKO NT1100 optical profilometry system. All films were found to have 20-30 % thickness gradient due to composition non-uniformity. The deposition time was selected to attain minimum thickness of the films of 1 μπΊ.

[0112] Elemental analysis was performed for a 14x14 array of locations on the materials libraries using scanning electron microscope equipped with X-Max energydispersive X-ray spectroscopy (EDX) detector from Oxford Instruments.

[0113] Phase composition of the films was analysed for the same matrix of locations using a 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 a conical diamond tip, radius 5μηι. 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 μπι pitch. The depth of penetration was 100 nm and 200 nm. Fused silica was used as a calibration reference material and the maximum indentation depth was 2000 nm.

2. XRD Results [0114] Figures 2(a) and 2(b) show representative X-ray diffractograms (XRD) obtained from the Ti-Nb-Hf-Cr thin-film materials library. The optimised deposition conditions resulted in the formation of alpha- (hexagonal close packing, hep) and beta- (body centred cubic, bcc) types of crystal structure. No other phases indicating intermetallic compounds or the products of chemical interaction with the substrate material were detected. At low doping levels, (Figure 2(a)) only the hexagonal close packing crystal structure was observed and the peaks ((100), (002), (101), (102) and (110)) can be assigned according to the P63/mmc (194) space group.

[0115] Niobium was found to have the most pronounced effect on the stabilisation of the beta-type structure. Figure 2(b) shows an X-ray diffraction pattern obtained for the alloy with ca. 14 at. % of niobium. For this composition, both alpha- and beta-type (Im3m, (229) body centred cubic, peaks shown in underlined italic typeface) of structures were observed. No region of pure beta-type structure was found within the composition range covered by this materials library. Figure 2(c) shows the evolution of the beta-phase with increasing niobium content. High-angle fragments of the patterns show appearance and progressive increase of the intensity of the cubic (110) peak with simultaneous decreasing of both (102) and (200) hep peaks.

[0116] XRD therefore demonstrates how co-doping the titanium alloy with different amounts of niobium, hafnium and chromium affects the overall crystal structure of the alloy.

3. Nanoindentation [0117] From the load-unload nanoindentation curve, the work recovery ratio η was calculated using equation 3;

W_e (3) wherein W_t is the total work done during loading and is calculated using equation (1) W/_e is the reversible work and is calculated using equation (2);

W_{t =} ^rna_{Xpdh (±)}

W_e = S^PdhP) hmax is the indentation depth at maximum load;

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

P is the load.

[0118] The work recovery ratio was plotted as a function of titanium, hafnium, niobium and chromium content allowing trends in the elastic properties of the alloy to be observed as a function of composition.

[0119] Figures 3(a-d) show the depth recovery data plotted as a function of: titanium, figure 3(a); hafnium; figure 3(b); niobium, figure 3(c); and chromium, figure 3(d). The plots show compositional dependencies with maxima at around 83 at.% titanium, 4 at.% hafnium and 12 at.% niobium. No maximum was observed for chromium due to the low concentration and the relatively uniform distribution across the sample.

[0120] Elastic recovery was found to be very sensitive to the niobium content and a high elastic recovery was observed for a specific combination of concentrations of doping elements. To identify an accurate compositional range of interest more accurately, a cutoff value for the work recovery ratio of 0.24 was selected (shown as a dashed line in Figures 3(a-d)).

[0121] The results of this analysis are summarised in Figure 4 (a-d) which show the compositional spread of the quaternary materials library in a pseudo-ternary space obtained by combining two of the elements in the system. Figures 4 (a) and 4(b) show the pseudo-ternary space obtained when chromium and niobium are combined and figures 4(c) and 4(d) show the pseudo-ternary space obtained when titanium and hafnium are combined. Separately, Figures 4(b) and 4(d) show the composition range with the work recovery ratios higher than 0.24. Additionally, Figures 4 (a) and (c) show position of the alpha/alpha + beta phase boundary, observed for the system. Lower and upper limits for the elements where the work recovery ratio is higher than 0.24 are shown in Table 2.

[0122]

Element	Lower limit, At. %	Upper limit, At. %
Ti	77.7	89.0
Nb	6.4	17.6
Hf	1.1	4.6
Cr	0.3	2.9

Table 2: Lower and upper limits of Ti, Nb, Hfand Cr contents for the composition area with high work recovery ratio.

[0123] One titanium alloy was identified as having a particularly high work recovery ratio:

ΤΪ84.01Ν bll.28Hf3.00Cr1.7i [0124] It was possible to identify this new superelastic compositional range using:

1. The continuous nature of composition gradients formed via HT-PVD technique;

2. Controlled cleanness of the experiment (high purity of the elements with reduced undesired impurities and ultra-high vacuum); and,

3. Systematic screening of trends in nanomechanical properties vs. composition.

[0125] 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.

Claims

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

76 at.% to 89 at.% titanium;

3 at.% to 18 at.% niobium;

0.5 at.% to 4.8 at.% hafnium and;

0.05 at.% to 3 at.% chromium.

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

76 at.% to 89 at.% titanium;

3 at.% to 18 at.% niobium;

0.5 at.% to 4.8 at.% hafnium;

0.05 at.% to 3 at.% chromium;

0 at.% to 5 at.% tantalum;

0 at.% to 2 at.% zirconium; and,

0 at.% to 1 at.% iron.

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

76 at.% to 89 at.% titanium;

3 at.% to 18 at.% niobium;

1 at.% to 4.8 at.% hafnium;

0.1 at.% to 3 at.% chromium; and,

0 at.% to 5 at.% tantalum.

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

76 at.% to 89 at.% titanium;

6 at.% to 18 at.% niobium;

0.5 at.% to 4.8 at.% hafnium;

0.1 at.% to 3 at.% chromium; and,

0 at.% to 2 at.% zirconium.

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

76 at.% to 89 at.% titanium;

6 at.% to 18 at.% niobium;

1 at.% to 4.8 at.% hafnium;

0.05 at.% to 3 at.% chromium; and,

0 at.% to 1 at.% iron.

6. The titanium alloy according to claim 1, wherein said titanium alloy consists essentially of:

76 at.% to 89 at.% titanium;

6 at.% to 18 at.% niobium;

1 at.% to 4.8 at.% hafnium and;

0.1 at.% to 3 at.% chromium;

wherein said titanium, niobium, hafnium and chromium has a combined atomic percentage of at least 94%.

7. The titanium alloy according to claim 6, wherein said titanium, niobium, hafnium and chromium have a combined atomic percent of at least 95%.

8. The titanium alloy according to claim 6, wherein said titanium, niobium, hafnium and chromium have a combined atomic percent of at least 97%.

9. The titanium alloy according to claim 6, wherein said titanium, niobium, hafnium and chromium have a combined atomic percent of at least 99%.

10. The titanium alloy according to claim 6, wherein said titanium, niobium, hafnium and chromium have a combined atomic percent of at least 99.5%.

11. The titanium alloy according to claim 6, wherein said titanium, niobium, hafnium and chromium have a combined atomic percent of at least 99.9%.

12. The titanium alloy according to claim 6, wherein said titanium, niobium, hafnium and chromium have a combined atomic percent of at least 99.95%.

13. The titanium alloy of claim of any one of claims 1-5, wherein the titanium alloy comprises:

80 at.% to 87 at.% titanium;

7 at.% to 16 at.% niobium;

1 at.% to 4.8 at.% hafnium and;

0.1 at.% to 3 at.% chromium.

14. The titanium alloy of claim of any one of claims 1-5, wherein the titanium alloy comprises:

81 at.% to 86 at.% titanium;

8 at.% to 14 at.% niobium;

2 at.% to 4 at.% hafnium and;

0.1 at.% to 3 at.% chromium.

15. The titanium alloy of claim of any one of claims 1-5, wherein the titanium alloy comprises:

82 at.% to 85 at.% titanium;

9 at.% to 13 at.% niobium;

2 at.% to 3.5 at.% hafnium; and,

0.1 at.% to 3 at.% chromium.

16. The titanium alloy of claim of any one of claims 1-5, wherein the titanium alloy comprises;

83 at.% to 85 at.% titanium;

10 at.% to 12 at.% niobium;

2 at.% to 3.5 at.% hafnium; and,

0.1 at.% to 3 at.% chromium.

17. The titanium alloy of any one of claims 1-16, wherein said titanium alloy has a Young's modulus that is at least 92 GPa.

18. The titanium alloy of any one of claims 1-16, wherein said titanium alloy has a work recovery ratio that is at least 0.2.

19. The titanium alloy of any one of claims 1-16, wherein said titanium alloy has a work recovery ratio that is at least 0.2 and a Young's modulus that is at least 92 GPa.

20. The titanium alloy of any one of claims 1-16, wherein said titanium alloy has a Young’s modulus that is from 92 GPa to 120 GPa and a work recovery ratio that is between 0.2 and 0.3.

21. The titanium alloy of any one of claims 1-20, wherein the titanium alloy has a Young’s modulus that is at least 100 GPa and a work recovery ratio that is at least 0.22.

22. A titanium alloy of any one of claims 1-20, wherein the titanium alloy has a Young's modulus that is at least 110 GPa and a work recovery ratio that is at least 0.24.

23. The titanium alloy of any one of claims 1-20, wherein the titanium alloy has a Young's modulus that is between 110 GPa and 120 GPa and a work recovery ratio that is between 0.24 and 0.30.

24. An article of manufacture comprising a titanium alloy, wherein said titanium alloy is as defined in any one of claims 1-23.

25. The article of manufacture of anyone of claim 24, wherein the article of manufacture is a thin-film material, wherein the thin-film material comprises a microelectromechanical system (MEMS).

26. The article of manufacture of claim 24, 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.

27. A method of making the titanium alloy of claim 1-23, 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, niobium, hafnium and chromium; and, (b) depositing said titanium alloy or said component elements thereof on a substrate.

28. A method of making the titanium alloy of any one of claims 1-23, 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.

29. A method of making the article of manufacture of claim 24, 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, niobium, hafnium and chromium;

(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.

30. A method of making the article of manufacture of claim 24, 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;

(c) filling the powder reservoir with a titanium alloy powder of any one of claims 1-23;

31. A method of making the article of manufacture of claim 24, 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.

32. A method of making the article of manufacture of claim 24, 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.

Intellectual

Property Office

Application No: GB1703886.0 Examiner: Matthew Lawson