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 Youngs modulus compared to known metals and alloys which undergo an elastic- plastic 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] A common superelastic alloy is Ti-Ni, which may be additionally alloyed with other metals to alter the superelastic properties.

[0003] In many applications, it is desirable that a device with superelastic

characteristics has the largest possible recoverable elasticity range and low rigidity (low Young's modulus) and many superelastic alloys display these characteristics. For example, in the biomedical industry, it is desirable that stents have a large elastic recovery, whilst being very flexible for insertion into the body. For many applications, however, where components undergo large amounts of repetitive stress, for example in the automotive and aerospace industries, these material characteristics are not suitable. There is therefore a need for superelastic materials which have a large recoverable elasticity range and high rigidity (high Young's modulus).

[0004] M. Abdel-Hady et al. Scripta Materialia 55 (2006), 477-480, describes generally β-type titanium alloys and the general correlation between the phase stability and elastic properties (e.g. the Young's modulus, the superelasticity and the shape memory effect) of the alloys. The maximum Young's modulus of Ti-V alloys is stated to be 72 GPa.

However, the paper does not disclose alloys having the atomic percentage of iron specified herein, nor does it disclose that such alloys would exhibit both high elastic recovery and high Young's modulus.

[0005] Furuhara et al, J. Mat. Eng. and Pert. 14 (2005) 761. discovered that the introduction of nitrogen to an alloy of Ti-10V-2Fe-3AI (wt%) up to 0.2% mass a shape recovery of up to 90% is achieved after heating. They also reported Ti-10V-2Fe-3AI (wt%) alloy without the inclusion of nitrogen has an elastic recovery of up to 60% by unloading after bending. The Young's modulus reported in this paper was low (between 50 to 60GPa) for the alloys with the inclusion of nitrogen. However, the paper does not disclose alloys having the atomic percentage of iron specified herein, nor does it disclose that such alloys would exhibit both high elastic recovery and high Young's modulus.

[0006] US2014/0338795 describes titanium alloys and methods for manufacturing them. The alloys are stated to have superelastic properties and/or shape memory. The composition of the alloys generally range: titanium 30-98 at.%; niobium 0-40 at.%;

molybdenum 0-15 at.%; chromium 0-15 at.%; iron 0-15 at.%; zirconium 0-40

at.%;hafnium 0-40 at.%; tantalum 0-60 at.%; 0 0-2 at.%; nitrogen 0-2 at.%; silicon 0-2 at.%; boron 0-2 at.%; carbon 0-2 at.%; vanadium 0-15 at.%; tungsten 0-10 at.%;

aluminium 0-10 at.%; tin 0-10 at.%; gallium 0-10 at.%. However, there is no disclosure of a specific alloy containing titanium, vanadium, iron and aluminium, nor does it disclose that such alloys would exhibit both high elastic recovery and high Young's modulus.

[0007] The present invention provides new superelastic alloys with high elastic recovery and a large Young's modulus.

Summary of the Invention

[0008] The present invention provides for titanium alloys with superelastic properties, wherein said titanium alloy comprises titanium, vanadium, iron and aluminium. 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.

[0009] According to a first aspect, the invention provides a titanium alloy comprising:

70 at.% to 85 at.% titanium;

3.0 at.% to 23 at.% of vanadium;

1.8 at.% to 5 at.% iron; and

0.5 at.% to 3 at.% aluminium.

[0010] In one embodiment, the invention provides a titanium alloy comprising:

70 at.% to 85 at.% titanium;

7 at.% to 23 at.% vanadium;

4.3 at.% to 5 at.% iron; and,

0.5 at.% to 3 at.% aluminium.

In one embodiment, said titanium alloy has a Young's modulus that is at least 113 GPa. In another embodiment, said titanium alloy has a depth recovery ratio that is at least 0.60. [0011] 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.

[0012] In one embodiment, said titanium alloy comprises:

70 at.% to 85 at.% titanium;

7 at.% to 23 at.% vanadium;

4.3 at.% to 5 at.% iron; and,

0.5 at.% to 3 at.% aluminium.

In one embodiment, said titanium alloy has a Young's modulus that is at least 113 GPa. In another embodiment, said titanium alloy has a depth recovery that is at least 0.60.

[0013] In a further embodiment, 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.

[0014] 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.

[0015] 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, vanadium, iron and aluminium; and,

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

[0016] 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 an ingot.

[0017] 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 the component elements of the titanium alloy;

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

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

[0018] 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.

[0019] In one embodiment, the invention 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 the titanium alloy or vapour sources of

component elements of the titanium alloy, wherein the component elements comprise titanium, vanadium, iron and aluminium;

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

[0020] In a further embodiment, the article of manufacture formed by the vapour deposition process is a microelectromechanical system (MEMS).

[0021] In another embodiment, the invention provides an additive manufacturing process for making the article of manufacture of the second aspect, wherein said additive 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 to a bottom surface, wherein the bottom surface is in contact with 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.

[0022] 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.

[0023] In another embodiment, the invention provides for a method of making the article of manufacture of the second aspect, wherein said method is a powder metallurgy process 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.

[0024] 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.

[0025] In another embodiment, there is provided a method of making the article of manufacture of the second aspect, wherein said method is casting process 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 titanium alloy.

[0026] 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

[0027] Figure 1: Load displacement curve (solid black line) from the nanoindentation of a TiVFeAI alloy showing the deviation from the elastic Hertzian curve (dashed grey line) which is attributed to the superelastic effect. [0028] Figure 2(a): X-ray diffraction patterns obtained from a titanium alloy sample showing the formation and progressive increase in concentration of the beta-phase (β) ( A representing crystal structures (110) and (200)) with increasing vanadium content a phase (♦ representing crystal structures (100), (002), (101), (102) and (110)).

[0029] Figure 2(b): an expanded view of the top three patterns, corresponding to the inset box of Figure 2(a), showing the formation of the beta-phase (β) (▲ , peak (110)), and the decrease in the alpha phase (a) (♦, peak (101)) which begins to form at 17 at.% vanadium.

[0030] Figure 3(a): Trend plot of depth recovery ratio vs vanadium content. A maximum at around 17 at.% vanadium is observed.

[0031] Figure 3(b): Trend plot of depth recovery ratio vs titanium content. A maximum at around 78 at.% titanium is observed.

[0032] Figure 3(c): Trend plot of depth recovery ratio vs iron content. A maximum at around 4.4 at.% iron is observed.

[0033] Figure 4: Load displacement curve showing the deviation from the elastic Hertzian curve attributing to the superelastic effect for the material Ti ₇ 9 _. 8Vi4.9Fe4.5Alo. ₉ with an elastic recovery of 0.74 and a Young's modulus of 134GPa. Four different phases are represented by the areas separated by the vertical dashed lines, labelled 1- 4. Phase 1 shows the linear elastic deformation of the beta-phase (β). Phase 2 shows the forward phase transformation of the beta-phase (β) to the martensitic phase. The inset circle shows a "pop-in" which represents a sudden displacement burst in the loading part of the load-unload curve. Phase 3 shows the linear elastic deformation of the martensite phase and phase 4 shows the elastic-plastic deformation of the material before unloading.

[0034] Figure 5: Representative stress strain curves for (a) (Ti ₇ 9 _.8 Vi4.9Fe4.5Alo _. 9) (in accordance with the invention) and (b) (Ti63 _. 56V0.88AI32.38Fe3 _. i8) (not in accordance with the invention), with a maximum depth limit from the surface of the thin-film set to lOOnm.

Detailed Description

[0035] 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. [0036] 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.

[0037] 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.

[0038] During repetitive load-unload cycles, strain will be accommodated by the martensitic transformation rather than forming microcracks as in typical fatigue failure mechanisms. See, e.g., Shape Memory Materials, K. Otsuka and CM. Wayman, 1999, Chapter 1 and Engineering Aspects of Shape Memory Alloys, Duerig et al, 1990, Chapter 1.

[0039] 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.

[0040] 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, 770-77 ^' 4.

[0041] Nanoindentation may be used for thin-film samples with a thickness between 50 nm and 2000 nm.

[0042] 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. [0043] The results obtained from nanoindentation can be represented by a load/unload curve as shown by the solid black line in Figure 1. The dashed grey line depicts the load/unload profile of a purely elastic material. This is calculated using the Hertz contact theory, and describes the purely-elastic contact problem under the limits of small deformation using equation (1):

P = -^ E ^* R ¹ ' ² h ³ ' ² (1)

wherein: P is the applied load;

R is the radius of the indenter;

h is the indentation depth; and,

E ^* is the contact modulus between the indenter and the sample and is defined in equation 2: i_ _ (i-v ² ) i-v' ^z ,^.

E* E E' ^ ' wherein; E' is the elastic modulus of the indentor;

v' is the Poisson's ratio of the indenter;

E is the elastic modulus of the sample; and,

v is the Poisson's ratio of the sample.

[0044] Elastic and superelastic materials can be identified from their load/unload curves by comparing the load/unload curves with the Hertzian curve. A material is elastic if the load/unload curve follows the Hertzian curve. Deviation from the Hertzian curve in the elastic region of the measured loading curve (see e.g., Figure 1) indicates the material is superelastic. The deviation can be characterised by the depth recovery ratio whereby a superelastic material has as at least a doubling of the depth recovery ratio compared to the depth recovery ratio of the Hertzian curve.

[0045] The depth recovery ratio describes the ability of a material to recover after deformation. "Depth recovery ratio" (η _Η ) is calculated from the stress-strain curve using equation (3): wherein, hmax is the indentation depth at maximum load; and, h _r is the residual indentation depth at zero load on unloading.

[0046] Herein, a titanium alloy is classed as superelastic if the load/unload curve deviates from the load/unload curve of the Hertzian curve and the calculated depth recovery ratio is at least double the depth ratio of the Hertzian curve.

[0047] The Young's modulus, (E) is calculated using equation (4): wherein, o _rep is the representative stress; and,

e _rep is the representative strain.

[0048] The representative stress, sigma o _rep , is calculated using equation (5): wherein, P is the load and A ₀ 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 ₀ 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.

[0049] The representative strain, e _rep , is obtained from equation (8):

0.2a

ε- rep (8)

R wherein a is the contact depth radius; and,

R is the radius of the indenter.

[0050] 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).

[0051] 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., US2014/0338795.

[0052] The present inventors surprisingly found that doping a titanium alloy with iron increased the Young's modulus whilst maintaining a high elastic recovery. It would be expected that doping a titanium alloy with iron would increase the Young's modulus whilst making the alloy brittle rather than superelastic. 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.

[0053] According to a first aspect, there is provided a titanium alloy wherein said titanium alloy comprises:

70 at.% to 85 at.% titanium;

7 at.% to 23 at.% vanadium;

4.2 at.% to 5 at.% iron; and,

0.5 at.% to 3 at.% aluminium.

[0054] In one embodiment, there is provided a titanium alloy wherein said titanium alloy consists essentially of:

70 at.% to 85 at.% titanium; 7 at.% to 23 at.% vanadium;

4.2 at.% to 5 at.% iron; and,

0.5 at.% to 3 at.% aluminium.

[0055] In this specification the term 'consists essentially of means that the total amount of titanium, vanadium, iron and aluminium, 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, vanadium, iron and aluminium 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 vanadium, iron and aluminium.

[0056] Metals that may substitute for a portion of vanadium in the alloy are selected from the group consisting of chromium, cobalt and manganese. Any one of these metals, or a combination of any two or all three of these metals, may substitute for vanadium in concentrations of: up to 2 at% of chromium; up to 1 at% cobalt; and/or up to 1 at % manganese; wherein the atomic percent of the substituting metal(s) is 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.%, or up to 4 at.%, (expressed as an atomic percentage of the total amount of metal atoms in the alloy) of the alloy may be chromium, cobalt and/or manganese.

[0057] Metals that may substitute for a portion of iron in the alloy are selected from the group consisting of chromium, cobalt and manganese. Any one of these metals, or a combination of any two or all three of these metals, may substitute for iron in concentrations up to 2.5 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.%, or up to 2.5 at.% (expressed as an atomic percentage of the total amount of metal atoms in the alloy) of the alloy may be chromium, cobalt and/or manganese.

[0058] Tin may substitute for a portion of aluminium in the alloy. Tin may substitute for aluminium in concentration of up to 0.5 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.% (expressed as an atomic percentage of the total amount of metal atoms in the alloy) of the alloy may be tin.

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

70 at.% to 85 at.% titanium;

3 at.% to 23 at.% vanadium;

1.8 at.% to 5 at.% iron;

0.5 at.% to 3 at.% aluminium;

0 at.% to 3 at.% chromium;

0 at.% to 2 at.% cobalt;

0 at.% to 1.5 at.% manganese; and,

0 at.% to 0.5% tin.

[0060] In one embodiment, there is provided a titanium alloy wherein said titanium alloy comprises:

70 at.% to 85 at.% titanium;

7 at.% to 23 at.% vanadium;

4.2 at.% to 5 at.% iron;

0.5 at.% to 3 at.% aluminium;

0 at.% to 3 at.% chromium;

0 at.% to 2 at.% cobalt;

0 at.% to 1.5 at.% manganese; and,

0 at.% to 0.5% tin. [0061] In one embodiment, there is provided a titanium alloy wherein said titanium alloy comprises:

70 at.% to 85 at.% titanium;

3 at.% to 23 at.% vanadium;

4.2 at.% to 5 at.% iron;

0.5 at.% to 3 at.% aluminium;

0 at.% to 2 at.% chromium;

0 at.% to 1 at.% cobalt; and,

0 at.% to 1 at.% manganese.

[0062] In one embodiment, there is provided a titanium alloy wherein said titanium alloy comprises:

70 at.% to 85 at.% titanium;

7 at.% to 23 at.% vanadium;

4.2 at.% to 5 at.% iron;

0.5 at.% to 3 at.% aluminium;

0 at.% to 2 at.% chromium;

0 at.% to 1 at.% cobalt; and,

0 at.% to 1 at.% manganese.

[0063] In one embodiment, there is provided a titanium alloy wherein said titanium alloy comprises:

70 at.% to 85 at.% titanium;

7 at.% to 23 at.% vanadium;

1.8 at.% to 5 at.% iron;

0.5 at.% to 3 at.% aluminium;

0 at.% to 1 at.% chromium;

0 at.% to 1 at.% cobalt; and,

0 at.% to 0.5 at.% manganese.

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

70 at.% to 85 at.% titanium;

7 at.% to 23 at.% vanadium;

4.2 at.% to 5 at.% iron;

0.5 at.% to 3 at.% aluminium;

0 at.% to 1 at.% chromium; 0 at.% to 1 at.% cobalt; and,

0 at.% to 0.5 at.% manganese.

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

70 at.% to 85 at.% titanium;

7 at.% to 23 at.% vanadium;

4.2 at.% to 5 at.% iron;

0.5 at.% to 3 at.% aluminium; and,

0 at.% to 0.5 at.% tin.

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

70 at.% to 85 at.% titanium;

7 at.% to 23 at.% vanadium;

4.2 at.% to 5 at.% iron; and,

0.5 at.% to 3 at.% aluminium.

[0067] In one embodiment, the titanium alloy comprises 72 at.% to 84 at.% titanium. In one embodiment, the titanium alloy comprises 75 at.% to 83 at.% titanium. In one embodiment, the titanium alloy comprises 76 at.% to 82 at.% titanium. In one embodiment, the titanium alloy comprises 77 at.% to 81 at.% titanium. In one embodiment, the titanium alloy comprises 77 at.% to 79 at.% titanium.

[0068] In one embodiment, the titanium alloy comprises 7 at.% to 23 at.% vanadium. In one embodiment, the titanium alloy comprises 9 at.% to 22 at.% vanadium. In one embodiment, the titanium alloy comprises 12 at.% to 20 at.% vanadium. In one embodiment, the titanium alloy comprises 14 at.% to 18 at.% vanadium. In one embodiment, the titanium alloy comprises 14.5 at.% to 17.5 at.% vanadium. In one embodiment, the titanium alloy comprises 16.5 at.% to 17.5 at.% vanadium.

[0069] In one embodiment, the titanium alloy comprises 4.2 at.% to 4.9 at.% iron. In one embodiment, the titanium alloy comprises 4.2 at.% to 4.7 at.% iron. In one embodiment, the titanium alloy comprises 4.2 at.% to 4.4 at.% iron. In one embodiment, the titanium alloy comprises 4.25 at.% to 4.5 at.% iron. In one embodiment, the titanium alloy comprises 4.2 at.% to 4.55 at.% iron.

[0070] In one embodiment, the titanium alloy comprises 0.6 at.% to 2.5 at.%

aluminium. In one embodiment, the titanium alloy comprises 0.7 at.% to 2 at.% aluminium. In one embodiment, the titanium alloy comprises 0.7 at.% to 1.5 at.% aluminium. In one embodiment, the titanium alloy comprises 0.75 at.% to 1.25 at.% aluminium. In one embodiment, the titanium alloy comprises 0.77 at.% to 1 at.% aluminium.

[0071] In another embodiment, the titanium alloy comprises 77.8 at.% titanium, 17.0 at.% vanadium, 4.3 at.% iron and 0.8 at.% aluminium.

[0072] In a further embodiment, the titanium alloy comprises 79.8 at.% titanium, 14.9 at.% vanadium, 4.5 at.% iron and 0.9 at.% aluminium.

[0073] In one embodiment, said titanium alloy has a Young's modulus that is at least 113 GPa. In one embodiment, said titanium alloy has a Young's modulus that is between 113 GPa and 140 GPa. In a further embodiment, said titanium alloy has a Young's modulus that is at least 125 GPa. In a further embodiment, said titanium alloy has a Young's modulus that is at least 130 GPa. In a further embodiment, said titanium alloy has a Young's modulus that is between 130 GPa and 140 GPa.

[0074] In one embodiment, said titanium alloy has a depth recovery ratio that is at least 0.6. In a further embodiment, said titanium alloy has a depth recovery ratio that is at least 0.65. In a further embodiment, said titanium alloy has a depth recovery ratio that is at least 0.70. In a further embodiment, said titanium alloy has a depth recovery ratio that is between 0.60 and 0.75. In a further embodiment, said titanium alloy has a depth recovery ratio that is between 0.60 and 0.70. In a further embodiment, said titanium alloy has a depth recovery ratio that is between 0.65 and 0.75.

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

70 at.% to 85 at.% titanium;

7 at.% to 23 at.% vanadium;

4.3 at.% to 5 at.% iron; and,

0.5 at.% to 3 at.% aluminium.

In one embodiment, said titanium alloy has a Young's modulus that is at least 113 GPa and a depth recovery ratio that is at least 0.6. In one embodiment, said titanium alloy has a Young's modulus that is at least 125 GPa and a depth recovery ratio that is at least 0.65. In a further embodiment, said titanium alloy has a Young's modulus that is at least 130 GPa and a depth recovery ratio that is at least 0.70. In a further embodiment, said titanium alloy has a Young's modulus that is between 113 GPa and 140 GPa and a depth recovery ratio that is between 0.60 and 0.75. In a further embodiment, said titanium alloy has a Young's modulus that is between 130 GPa and 140 GPa and a depth recovery ratio that is between 0.65 and 0.75.

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

75 at.% to 83 at.% titanium;

12 at.% to 20 at.% vanadium;

4.2 at.% to 4.7 at.% iron; and,

0.5 at.% to 3 at.% aluminium.

In one embodiment, said titanium alloy has a Young's modulus that is at least 113 GPa and a depth recovery ratio that is at least 0.6. In a further embodiment, said titanium alloy has a Young's modulus that is at least 125 GPa and a depth recovery ratio that is at least 0.65. In a further embodiment, said titanium alloy has a Young's modulus that is at least 130 GPa and a depth recovery ratio that is at least 0.70. In a further embodiment, said titanium alloy has a Young's modulus that is between 113 GPa and 140 GPa and a depth recovery ratio that is between 0.60 and 0.75. In a further embodiment, said titanium alloy has a Young's modulus that is between 130 GPa and 140 GPa and a depth recovery ratio that is between 0.65 and 0.75.

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

76 at.% to 82 at.% titanium;

14.0 at.% to 18.0 at.% vanadium;

4.2 at.% to 4.4 at.% iron; and.

0.5 at.% to 3 at.% aluminium.

In one embodiment, said titanium alloy has a Young's modulus that is at least 113 GPa and a depth recovery ratio that is at least 0.6. In a further embodiment, said titanium alloy has a Young's modulus that is at least 125 GPa and a depth recovery ratio that is at least 0.65. In a further embodiment, said titanium alloy has a Young's modulus that is at least 130 GPa and a depth recovery ratio that is at least 0.70. In a further embodiment, said titanium alloy has a Young's modulus that is between 113 GPa and 140 GPa and a depth recovery ratio that is between 0.60 and 0.75. In a further embodiment, said titanium alloy has a Young's modulus that is between 130 GPa and 140 GPa and a depth recovery ratio that is between 0.65 and 0.75.

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

77 at.% to 81 at.% titanium;

14.5 at.% to 17.5 at.% vanadium;

4.25 at.% to 4.55 at.% iron: and. 0.5 at.% to 3 at.% aluminium.

In one embodiment, said titanium alloy has a Young's modulus that is at least 113 GPa and a depth recovery ratio that is at least 0.6. In a further embodiment, said titanium alloy has a Young's modulus that is at least 125 GPa and a depth recovery ratio that is at least 0.65. In a further embodiment, said titanium alloy has a Young's modulus that is at least 130 GPa and a depth recovery ratio that is at least 0.70. In a further embodiment, said titanium alloy has a Young's modulus that is between 113 GPa and 140 GPa and a depth recovery ratio that is between 0.60 and 0.75. In a further embodiment, said titanium alloy has a Young's modulus that is between 130 GPa and 140 GPa and a depth recovery ratio that is between 0.65 and 0.75.

[0079] In another embodiment, said titanium alloy comprises:

77 at.% to 79 at.% titanium;

16.5 at.% to 17.5 at.% vanadium;

4.25 at.% to 4.55 at.% iron; and,

0.5 at.% to 3 at.% aluminium.

In one embodiment, said titanium alloy has a Young's modulus that is at least 113 GPa and a depth recovery ratio that is at least 0.6. In a further embodiment, said titanium alloy has a Young's modulus that is at least 125 GPa and a depth recovery ratio that is at least 0.65. In a further embodiment, said titanium alloy has a Young's modulus that is at least 130 GPa and a depth recovery ratio that is at least 0.70. In a further embodiment, said titanium alloy has a Young's modulus that is between 113 GPa and 140 GPa and a depth recovery ratio that is between 0.60 and 0.75. In a further embodiment, said titanium alloy has a Young's modulus that is between 130 GPa and 140 GPa and a depth recovery ratio that is between 0.65 and 0.75.

[0080] In another embodiment, said titanium alloy comprises, 77.8 at.% titanium, 17.0 at.% vanadium, 4.3 at.% iron and 0.8 at.% aluminium, wherein, said titanium alloy has a Young's modulus that is at least 113 GPa and a depth recovery ratio that is at least 0.60. In a further embodiment, said titanium alloy has a Young's modulus that is at least 125 GPa and a depth recovery ratio that is at least 0.65. In a further embodiment, said titanium alloy has a Young's modulus that is at least 130 GPa and a depth recovery ratio that is at least 0.70. In a further embodiment, said titanium alloy has a Young's modulus that is between 113 GPa and 140 GPa and a depth recovery ratio that is between 0.60 and 0.75. In a further embodiment, said titanium has a Young's modulus that is between 130 GPa and 140 GPa and a depth recovery ratio that is between 0.65 and 0.75. In a further embodiment, said titanium alloy has a Young's modulus of 134 GPa and a depth recovery ratio of 0.72.

[0081] In a further embodiment, said titanium alloy comprises 79.8 at.% titanium, 14.9 at.% vanadium, 4.5 at.% iron and 0.9 at.% aluminium, wherein, said titanium alloy has a Young's modulus that is at least 113 GPa and a depth recovery ratio that is at least 0.6. In a further embodiment, said titanium alloy has a Young's modulus that is at least 125 GPa and a depth recovery ratio that is at least 0.65. In a further embodiment, said titanium alloy has a Young's modulus that is at least 130 GPa and a depth recovery ratio that is at least 0.70. In a further embodiment, said titanium alloy has a Young's modulus that is between 113 GPa and 140 GPa and a depth recovery ratio that is between 0.60 and 0.75. In a further embodiment, said titanium alloy has a Young's modulus that is between 130 GPa and 140 GPa and a depth recovery ratio that is between 0.65 and 0.75. In a further embodiment, said titanium alloy has a Young's modulus of 134 GPa and a depth recovery ratio of 0.72.

[0082] In further embodiment, the aluminium present in said titanium alloy may be 0.7 at.% to 2.5 at.%, 0.7 at.% to 2 at.%, 0.7 at.% to 1.5 at.% and 0.7 at.% to 1 at.%.

[0083] According to a second aspect of the invention, the invention provides an article of manufacture comprising a titanium alloy of the first aspect.

[0084] In one embodiment, the invention provides an article of manufacture comprising a titanium alloy with superelastic properties wherein said titanium alloy comprises:

70 at.% to 85 at.% titanium;

7 at.% to 23 at.% vanadium;

4.3 at.% to 5 at.% iron; and,

0.5 at.% to 3 at.% aluminium.

In one embodiment, said titanium alloy has a Young's modulus that is at least 113 GPa and a depth recovery ratio that is at least 0.6. In one embodiment, said titanium alloy has a Young's modulus that is at least 125 GPa and a depth recovery ratio that is at least 0.65. In a further embodiment, said titanium alloy has a Young's modulus that is at least 130 GPa and a depth recovery ratio that is at least 0.70. In a further embodiment, said titanium alloy has a Young's modulus that is between 113 GPa and 140 GPa and a depth recovery ratio that is between 0.60 and 0.75. In a further embodiment, said titanium alloy has a Young's modulus that is between 130 GPa and 140 GPa and a depth recovery ratio that is between 0.65 and 0.75. [0085] In another embodiment, said article of manufacture comprises a titanium alloy, wherein said titanium alloy comprises:

75 at.% to 83 at.% titanium;

12 at.% to 20 at.% vanadium;

4.2 at.% to 4.7 at.% iron; and,

0.5 at.% to 3 at.% aluminium.

In one embodiment, said titanium alloy has a Young's modulus that is at least 113 GPa and a depth recovery ratio that is at least 0.6. In a further embodiment, said titanium alloy has a Young's modulus that is at least 125 GPa and a depth recovery ratio that is at least 0.65. In a further embodiment, said titanium alloy has a Young's modulus that is at least 130 GPa and a depth recovery ratio that is at least 0.70. In a further embodiment, said titanium alloy has a Young's modulus that is between 113 GPa and 140 GPa and a depth recovery ratio that is between 0.60 and 0.75. In a further embodiment, said titanium alloy has a Young's modulus that is between 130 GPa and 140 GPa and a depth recovery ratio that is between 0.65 and 0.75.

[0086] In another embodiment, said article of manufacture comprises a titanium alloy, wherein said titanium alloy comprises:

76 at.% to 82 at.% titanium;

14.0 at.% to 18.0 at.% vanadium;

4.2 at.% to 4.4 at.% iron; and.

0.5 at.% to 3 at.% aluminium.

In one embodiment, said titanium alloy has a Young's modulus that is at least 113 GPa and a depth recovery ratio that is at least 0.6. In a further embodiment, said titanium alloy has a Young's modulus that is at least 125 GPa and a depth recovery ratio that is at least 0.65. In a further embodiment, said titanium alloy has a Young's modulus that is at least 130 GPa and a depth recovery ratio that is at least 0.70. In a further embodiment, said titanium alloy has a Young's modulus that is between 113 GPa and 140 GPa and a depth recovery ratio that is between 0.60 and 0.75. In a further embodiment, said titanium alloy has a Young's modulus that is between 130 GPa and 140 GPa and a depth recovery ratio that is between 0.65 and 0.75.

[0087] In another embodiment, said article of manufacture comprises a titanium alloy, wherein said titanium alloy comprises:

77 at.% to 81 at.% titanium;

14.5 at.% to 17.5 at.% vanadium; 4.25 at.% to 4.55 at.% iron; and,

0.5 at.% to 3 at.% aluminium.

In one embodiment, said titanium alloy has a Young's modulus that is at least 113 GPa and a depth recovery ratio that is at least 0.6. In a further embodiment, said titanium alloy has a Young's modulus that is at least 125 GPa and a depth recovery ratio that is at least 0.65. In a further embodiment, said titanium alloy has a Young's modulus that is at least 130 GPa and a depth recovery ratio that is at least 0.70. In a further embodiment, said titanium alloy has a Young's modulus that is between 113 GPa and 140 GPa and a depth recovery ratio that is between 0.60 and 0.75. In a further embodiment, said titanium alloy has a Young's modulus that is between 130 GPa and 140 GPa and a depth recovery ratio that is between 0.65 and 0.75.

[0088] In another embodiment, said article of manufacture comprises a titanium alloy, wherein said titanium alloy comprises:

77 at.% to 79 at.% titanium;

16.5 at.% to 17.5 at.% vanadium;

4.25 at.% to 4.55 at.% iron; and,

0.5 at.% to 3 at.% aluminium.

In one embodiment, said titanium alloy has a Young's modulus that is at least 113 GPa and a depth recovery ratio that is at least 0.6. In a further embodiment, said titanium alloy has a Young's modulus that is at least 125 GPa and a depth recovery ratio that is at least 0.65. In a further embodiment, said titanium alloy has a Young's modulus that is at least 130 GPa and a depth recovery ratio that is at least 0.70. In a further embodiment, said titanium alloy has a Young's modulus that is between 113 GPa and 140 GPa and a depth recovery ratio that is between 0.60 and 0.75. In a further embodiment, said titanium alloy has a Young's modulus that is between 130 GPa and 140 GPa and a depth recovery ratio that is between 0.65 and 0.75.

[0089] In another embodiment, said article of manufacture comprises a titanium alloy, wherein said titanium alloy comprises, 77.8 at.% titanium, 17.0 at.% vanadium, 4.3 at.% iron and 0.8 at.% aluminium, wherein, said titanium alloy has a Young's modulus that is at least 113 GPa and a depth recovery ratio that is at least 0.60. In a further

embodiment, said titanium alloy has a Young's modulus that is at least 125 GPa and a depth recovery ratio that is at least 0.65. In a further embodiment, said titanium alloy has a Young's modulus that is at least 130 GPa and a depth recovery ratio that is at least 0.70. In a further embodiment, said titanium alloy has a Young's modulus that is between 130 GPa and 140 GPa and a depth recovery ratio that is between 0.65 and 0.75. In a further embodiment, said titanium alloy has a Young's modulus of 134 GPa and a depth recovery ratio of 0.72. In a further embodiment, said article of manufacture comprises a titanium alloy, wherein said titanium alloy comprises 79.8 at.% titanium, 14.9 at.% vanadium, 4.5 at.% iron and 0.9 at.% aluminium, wherein, said titanium alloy has a Young's modulus that is at least 113 GPa and a depth recovery ratio that is at least 0.6. In a further embodiment, said titanium alloy has a Young's modulus that is at least 125 GPa and a depth recovery ratio that is at least 0.65. In a further embodiment, said titanium alloy has a Young's modulus that is at least 130 GPa and a depth recovery ratio that is at least 0.70. In a further embodiment, said titanium alloy has a Young's modulus that is between 113 GPa and 140 GPa and a depth recovery ratio that is between 0.60 and 0.75. In a further embodiment, said titanium alloy has a Young's modulus that is between 130 GPa and 140 GPa and a depth recovery ratio that is between 0.65 and 0.75. In a further embodiment, said titanium alloy has a Young's modulus of 134 GPa and a depth recovery ratio of 0.72.

[0090] In further embodiment, the aluminium present in the article of manufacture comprising said titanium alloy may be 0.7 at.% to 2.5 at.%, 0.7 at.% to 2 at.%, 0.7 at.% to 1.5 at.% and 0.7 at.% to 1 at.%.

[0091] The article of manufacture of the present invention is particularly well-suited to applications where the article undergoes repetitive stress is 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.

[0092] 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 alloy powder, or titanium alloy ingot.

[0093] 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, vanadium, iron and aluminium; 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.

[0094] Examples of vapour sources may include electron beam evaporators and Knudsen cells (K-cells). For example, vanadium and iron may be evaporated using electron beam evaporators and titanium and aluminium 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 alloy to be controlled to obtain a specific composition.

[0095] 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.

[0096] In one embodiment, the invention provides for making a method of making the titanium alloy, 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 in to a mould; and,

(e) cooling the melted components elements to form the titanium alloy, for example, as a solid bar or ingot.

[0097] 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 a titanium alloy of the first aspect as a bar or ingot; and,

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

[0098] 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 alloy. 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.

[0099] 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.

[0100] 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,

(b) wherein the component elements comprise titanium, vanadium, iron and aluminium;

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

[0101] Examples of vapour sources include electron beam evaporators and Knudsen cells (K-cells). For example, vanadium and iron may be evaporated using electron beam evaporators and titanium and aluminium 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.

[0102] 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.

[0103] In a further embodiment, the article of manufacture formed by a vapour deposition method is a microelectromechanical system (MEMS).

[0104] In another embodiment, the invention provides an additive manufacturing process for making the article of manufacture of the second aspect. 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;

(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 to a bottom surface, wherein the bottom surface is in contact with 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.

The powder may be fused, e.g., using a laser or an electron beam. 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.

[0105] 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.

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. The titanium alloy powder in the powder metallurgy process generally comprises particles of titanium alloy that are between 2 microns to 100 microns in diameter.

[0106] In a further embodiment, the invention provides for 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. [0107] The titanium alloy material may be provided, e.g., 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.

[0108] 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-V-Fe-AI Library

[0109] 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)/Si3N (150 nm) substrates from Nova Electronic Materials.

[0110] Titanium-vanadium-iron-aluminium thin-films were deposited from the individual elemental sources. Vanadium and iron were evaporated from electron beam sources, and titanium and aluminium were evaporated from Knudsen cells. 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-V-Fe-AI thin-films is shown in Table 1.

[0111]

Table liComposition range of studied Ti-V-Fe-AI thin-film materials library

[0112] The Ti-V-Fe-AI thin-films were processed with in-situ heating at 450 °C. The thickness of the films was determined using a scanning electron microscope equipped with X-Max energy-dispersive X-ray spectroscopy (EDX) detector from Oxford Instruments and LayerProbe software to fit the experimental data. 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 μιη.

[0113] 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.

[0114] Phase composition of the films was analysed for the same matrix of locations using a Bruker D8 Discover X-ray Diffracto meter system incorporating a H I 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 5μιη. 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 μιη pitch. The depth of indentation was lOOnm. Fused silica was used as a calibration reference material.

2. XRD results.

[0115] Figure 2(a) shows representative X-ray diffractograms (XRD) obtained from the Ti-V-Fe-AI thin-film materials library. The optimised deposition conditions resulted in the formation of alpha-hexagonal close packing, (hep denoted by♦) and beta-body centred cubic, (bec denoted by A) types of crystal structure. Intermetallic compounds were detected in regions with high aluminium content. Peaks were also observed due to the chemical interaction of titanium with the substrate to form TiN peaks. Both hep and bee structures were observed in titanium alloys with low concentrations of vanadium and aluminium and high concentrations of iron.

[0116] Vanadium was found to have the most pronounced effect on the stabilisation of the beta-type structure. Figure 2(b), shows an expanded view of the top three patterns of Figure 2(a) (boxed area) and shows the evolution of the beta-phase with increasing vanadium content in the Ti-alloy. High-angle fragments of the patterns show the appearance and progressive increase of the intensity of the beta-phase cubic (110) peak with simultaneous decreasing of the alpha-phase (101) hep peak intensity.

[0117] XRD therefore demonstrates how co-doping the titanium alloy with different amounts of vanadium, iron and aluminium affects the overall crystal structure of the alloy.

3. Nanoindentation

[0118] From the load-unload nanoindentation curve, the depth recovery ratio (η _¾ ) was calculated using equation 3;

„ h _max —h _r

¾ - ~~ z W

" ^■ max wherein hmax is the indentation depth at maximum load; and,

h _r is the residual indentation depth at zero load on unloading.

[0119] The depth recovery ratio was plotted as a function of vanadium, titanium and iron content allowing trends in the elastic properties of the alloy to be observed as a function of composition.

[0120] Figures 3(a), 3(b) and 3(c), show the depth recovery data plotted as a function of vanadium 3(a), titanium 3(b) and iron 3(c). The plots show composition dependencies with maxima at around 17 at.% vanadium, 78 at.% titanium and 4.4 at.% iron. No maxima were observed for aluminium (not shown).

[0121] The load-displacement curve obtained for Ti ₇ 9 _. 8Vi4.9Fe4.5Alo. ₉ is shown in Figure 4 (solid line). The loading part of the curve was acquired in contact stiffness mode (CSM) where the elastic stiffness of the contact, S was measured at any point. The

representative stress was calculated from the loading section of the curve. The dashed grey line shows pure elastic (Hertzian) response. Deviation of the experimental data from this line and the associated increase in the depth recovery ratio was used as an indicator of superelastic behaviour for each composition of the titanium alloy. [0122] The load-unload curves for superelastic materials demonstrated up to four different phases (shown by the vertical dashed lines on Figure 4 and labelled 1-4), which may be summarised as follows:

1. The linear elastic deformation of the beta-phase.

2. The forward phase transformation of the beta-phase to the martensitic phase. In the example shown in Figure 4, this was indicated by a "pop-in" (see, inset circle) which represents a sudden displacement burst in the loading part of the load-unload curve. A pop-in was not observed for all superelastic materials.

3. The linear elastic deformation of the martensite phase.

4. The elastic-plastic deformation which occurred before unloading.

[0123] The reverse transformation from the martensitic phase to the parent phase was not observed due to the onset of irreversible elastic-to-plastic deformation in phase 4.

[0124] Figure 5 compares the representative stress-strain curves for a titanium alloy with high iron content Figure 5(a) according to the invention (Ti79.8Vi4.9Fe4.5Alo. ₉ ) and a titanium alloy with high aluminium content Figure 5(b) (Ti63.56V0.88AI32.38Fe3.i8) not in accordance with the invention. The representative stress and strain values were calculated from the loading section of the curve. In figure 5(a), there is a sudden increase in the gradient at point σ^. This represents the forward phase transformation from the parent to the martensite phase and is characteristic of a superelastic material. Following the sudden increase in gradient at point O the gradient of the curve changes again as the strain is increased. This represents the elastic deformation of the martensite phase and may also represent the strain hardening effect of the martensite phase. A comparison of the Young's modulus of the martensite phase (E _m ,) with the Young's modulus of the parent phase (Ε _β ), shows that phase transformation results in an approximate doubling of the Young's modulus. In figure 5(b), no such peak is observed. This alloy only shows elastic deformation and it is not superelastic.

[0125] In summary, Ti-V-Fe-AI thin films with various combinations of compositions were investigated. Using the Nanoindentation technique the following criteria were established to identify superelasticity in the Ti-V-Fe-AI alloys:

1. High elastic recovery (depth recovery ratio) greater than 60%; and

2. Deviation from the elastic Hertzian curve, showing an increase in the depth recovery ratio. Some, but not all, superelastic Ti-V-Fe-AI alloys further demonstrated a plateau or peak due to pop-in in the stress-strain curve indicating the forward transformation of beta to alpha" martensitic phase. [0126] The high-throughput synthesis and screening methods were used to define criteria to identify superelastic compositions. This allowed a range of compositions to be identified. The samples with the highest elastic recoveries and mechanical (high

Young's modulus, 134 GPa) properties identified were:

Ti79.8Vl4.9Fe4.5Alo.9

Ti ₇ 7 _. 8Vi7 _. oFe4 _. 3Alo. ₈ (at.%)

[0127] 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.