FR3063675A1 - MATERIAL COMPRISING A THIN LAYER OF AN ALLOY COMPRISING TITANIUM AND GOLD, AND PROCESS FOR OBTAINING SUCH MATERIAL - Google Patents

Abstract

The present invention relates to a material comprising a base substrate and a thin layer of an alloy comprising titanium and gold. The present invention also relates to a process for obtaining such an alloy, said process comprising in particular, after having deposited a substrate to be coated, two target substrates made of pure titanium and a target substrate made of pure gold in a deposition chamber; - adjusting the pressure in the deposition chamber; injecting an inert gas into the deposition chamber; the bombardment of the first target substrate of pure titanium by a first magnetron; - the bombardment of said target substrate in pure gold by a second magnetron; bombarding the second target substrate of pure titanium with a third magnetron; so as to cause the formation of a plasma comprising titanium ions and gold ions in determined stoichiometric proportions; - the deposition of a thin layer of the alloy comprising titanium and gold on the substrate to be covered.

Description

Field of Invention

The invention relates to an alloy comprising titanium and gold, and relates in particular to a material comprising a base substrate and a thin layer of such an alloy comprising titanium and gold, as well as a process for manufacturing such a material.

State of the art

The context is that of the design of materials resistant to scratches and abrasion. In the field of watchmaking in particular, as in the field of jewelry, eyewear or fashion accessories, these fields being given by way of nonlimiting examples, the person skilled in the art seeks to develop new materials with such properties.

A general problem resides in the development of materials having a hardness greater than that of materials conventionally used in these fields, such as titanium or steel for example. To this end, developments are being carried out in particular to design new alloys having improved hardness characteristics.

A particularly hard alloy has also been recently developed, based on titanium and gold. This new alloy is of particular interest to biomedical research because it is a very hard biocompatible alloy very resistant to abrasion. This alloy has the atomic formula Ti ₃ Au and has been able to be synthesized in the β phase. This discovery was the subject of a published study: E. Svanidze et al., "High hardness in the biocompatible intermetallic compound p-Ti ₃ Au".

As part of this study, exceptional hardness qualities of the P-Ti ₃ Au alloy, reaching 800 HV, were highlighted. The publication thus shows that βTi ₃ Au is four times harder than titanium and eight times harder than gold.

For the authors, the intrinsic qualities of bio-integrability of titanium and gold make this alloy an interesting candidate for the production of prostheses.

In this context, researchers are encouraged to explore methods of producing such an alloy in the mass, that is to say in "bulk" according to the term in English known to those skilled in the art.

However, on the one hand, the production of this bulk p-Ti ₃ Au alloy turns out to be tricky because this compound in particular has relative instability. Exploitation of the intrinsic properties of a titanium-gold alloy in one of the abovementioned applications is therefore not obvious, in particular because of the difficulty in obtaining parts formed in bulk in such an alloy, having an acceptable solidity and ensuring the integrity of said parts.

On the other hand, economically, the production of such a bulk alloy would be expensive.

The proposed solution consists in depositing a thin layer of an alloy comprising titanium and gold, in particular p-Ti ₃ Au, on a substrate, in particular a titanium, steel, brass or ceramic substrate. .

The present invention also relates to a method relating to the manufacture of such a material, in particular formed of β-ThAu deposited in a thin layer on a substrate.

Statement of the invention

More specifically, the invention relates to a material comprising a base substrate and a thin layer made of an alloy comprising titanium and gold.

Thanks to the material according to the invention, it is possible to design particularly hard and / or abrasion resistant parts.

According to one embodiment, said alloy has the atomic formula Ti ₍ i- _X y) Au ( _X ) M (y), where M is a chemical element or a combination of chemical elements, with 0.15 <x <0 , 40; 0.00 <y <0.15.

According to one embodiment, y is equal to 0.

According to one embodiment, M comprises one of the metals or a combination of several of the following metals: Ag, Cu, Zn, Pt, Pd, Ni, Zn, Cd, Fe, Al, Ga, ln.

According to one embodiment, M is a non-metallic chemical element or a combination of non-metallic chemical elements. For example M includes nitrogen (N). In another example, M may include nitrogen and a metallic element such as copper.

The presence of the chemical element or the combination of chemical elements M allows an adjustment of the coloring of the alloy.

According to one embodiment, said alloy has a crystalline shape.

Advantageously, said alloy has the atomic formula Ti ₃ Au.

In particular, said alloy can be Ti ₃ Au in the β phase.

According to another embodiment, said alloy has an amorphous shape.

Advantageously, the thin layer has a thickness less than or equal to 50 μm.

According to one embodiment, the base substrate consists of titanium, for example grade 2 titanium, or steel, or brass or ceramic.

The present invention also relates to a timepiece movement part comprising the material briefly described above. This example of use should not be interpreted in a limiting manner.

The present invention also relates to a watch case comprising the material briefly described above. This example of use should not be interpreted in a limiting manner.

Furthermore, the present invention relates to a method of depositing a thin layer of an alloy comprising titanium and gold on a substrate, said method comprising the following steps:

placing a substrate to be covered, at least one target substrate made of pure titanium and at least one target substrate made of pure gold in a deposition chamber;

adjusting the pressure in the deposition chamber;

injecting an inert gas to allow the formation of a plasma, said inert gas possibly being argon, in the deposition chamber;

bombarding said at least one target substrate made of pure titanium with a first magnetron;

bombarding said at least one pure gold target substrate with a second magnetron;

so as to cause the formation of a plasma comprising titanium ions and gold ions in determined stoichiometric proportions;

depositing a thin layer of the alloy comprising titanium and gold on the substrate to be covered.

Thanks to this process, it is possible to deposit a thin layer of an alloy comprising titanium and gold on a base substrate.

According to one embodiment, the method also comprises heating the substrate to be covered, for depositing the alloy in the crystalline phase.

Advantageously, the adjustment of the pressure in the deposition chamber consists in placing under pseudo-vacuum at a pressure between 1.10 ^-4 and 10.10 ⁴ Pa.

Advantageously, the power of each of said magnetrons is configured independently to obtain the deposition of said thin layer of the alloy comprising titanium and gold on the substrate to be covered.

According to one embodiment, a first and a second target substrate made of pure titanium and a target substrate made of pure gold being placed in the deposition chamber, three independent magnetrons are used, the first magnetron using a power included between 20.3 and 61.2 kW / m ² to bombard the first target substrate made of pure titanium connected to a radiofrequency source, the second magnetron using a power of between 0.5 and 20.4 kW / m ² to bombard the pure gold target substrate connected to a direct current source and a third magnetron using a power of between 20.3 and 61.2 kW / m ² to bombard the second pure titanium target substrate connected to a current source pulsed.

According to one embodiment, the power used by each of said magnetrons is configured to deposit a layer of Ti ₃ Au in β phase on said substrate to be covered.

Other characteristics and advantages of the invention will become apparent from the following description given with reference to the appended figures given by way of nonlimiting examples.

Brief description of the drawings

Figure 1 illustrates a phase balance diagram of Ti-Au compounds.

FIG. 2 shows a transverse view of p-Ti ₃ Au under the scanning electron microscope.

Figures 3 and 4 show the comparison between a raw surface of a substrate covered with a thin layer of p-Ti ₃ Au (FIG. 3) and a polished surface of the same substrate also covered with a thin layer of p-Ti ₃ Au polished (FIG. 4).

Figure 5 shows the hardness of the alloy obtained as a function of the percentage of gold in the thin layer deposited.

Figure 6 shows the Young's modulus of the alloy obtained as a function of the percentage of gold in the thin layer deposited.

Detailed description of embodiments of the invention

The material according to the invention and the process for obtaining this material can be used in any field, for the manufacture of parts having high hardness and / or abrasion resistance.

With regard to producing an alloy of titanium and gold, it must first be noted that titanium (Ti) and gold (Au) have an almost identical atomic size, but have crystalline structures, electronegativities and different electronic structures. Titanium is a transition metal with a lower number of d electrons compared to the noble metal of gold, which has a higher number of d electrons. Therefore, when forming an alloy of these two elements, significant redistribution and overlap of charges is expected, which can result in a wide variety of structures and physical properties.

With reference to FIG. 1, the equilibrium phase diagram of the Ti-Au compounds thus gives an overview of the stoichiometric structures which can be formed.

The phase diagram of the Ti-Au alloy thus reveals four equilibrium compounds: Ti ₃ Au, of cubic crystal structure, TiAu, orthorhombic, TiAu ₂ , tetragonal and TiAu ₄ , otherwise tetragonal.

Among these four compounds, the aforementioned study (E. Svanidze et al.) Showed that Ti ₃ Au, in the β phase, exhibited the highest hardness, exceeding 800 HV (or approximately 7.85 GPa), which constitutes, as already mentioned, a hardness four times that of pure titanium and eight times that of pure gold.

To explain the reasons for such a high hardness of the Ti ₃ Au compound, it was hypothesized that this came either from the intermetallic character of the crystal structure which requires a unique arrangement of atoms, or from its particular electronic structure, which is characterized by a high valence electron density, a reduced bond length and the formation of pseudo-gaps.

The Ti ₃ Au compound is formed in two distinct phases, a and β, both in a cubic lattice structure.

The β phase preferably forms at high temperature and, like other intermetallic compounds of molecular formula A ₃ B, crystallizes in the form of a cubic network of type A15, space group No. 223, in which two atoms d 'gold occupy the atomic positions (0, 0, 0; ¹ />, ¹ />, Vz) and six titanium atoms occupy the atomic positions (%, 0, ¹ /> 0, 0, ¹ />, ¹ / >,%, 0, ¹ />,%, 0, 0, ¹ />,%, 0, ¹ />,%). The particular arrangement of the titanium atoms on the sites positioned at (%, 0,%) generates orthogonal non-interactive chains with gold atoms located at the corner and in the center of the unit cells of the cubic network, but form linear chains mutually orthogonal which run through the crystal lattice.

Phase a, which is favored at lower temperatures, develops in the form of a cubic network of type L12, space group n ° 221, where the gold atoms occupy the positioned sites (0, 0 , 0) and the titanium atoms occupy the positioned sites (0, ¹ />, 1/2).

Therefore, the two phases a and β differ in the atomic environment of titanium and gold, respectively, and it can be expected that Ti ₃ Au in β phase has a higher hardness than Ti ₃ Au in a phase, on the one hand because the titanium is coordinated 14 times in the β phase against 12 times in the phase a, and on the other hand because the length of the titanium-gold bond is shorter in the β phase than in the phase at.

In practice, in the following detailed description, reference is often made to the particular alloy Ti ₃ Au, in particular in the β phase. However, even when reference is made to Ti ₃ Au, and unless it is explicitly indicated that only this alloy is targeted in a particular embodiment, it should be understood that any alloy of atomic formula Ti 1. xAu _x is adapted. In particular, for x = 0.25, the alloy obtained is Ti ₃ Au, in phase a or β. For other values of x, different atomic formulas can be obtained, including TiAu, TiAu ₂ , TiAu ₄ or mixed phases composed of alloys comprising Ti ₃ Au and / or TiAu and / or TiAu ₂ and / or TiAu ₄ .

The traditional preparation Tii- _{x x} melt stoichiometric amounts of the components requires high temperatures for melting and possible annealing of the samples.

As mentioned in the preamble, the formation of Ti ₃ Au, in particular in the β phase, by mass, in other words in bulk, is complicated by the great brittleness of this material.

However, growth from the vapor phase, using plasma, can be achieved at significantly lower temperatures.

In this context, it is proposed here the development of an alloy based on titanium and gold, applied in a thin layer on a substrate, by a method of mixing ions under energetic plasma. Thus, it is proposed to form a plasma of titanium and gold, in stoichiometric proportions and shape desired conditions, in particular to form a thin Au layer Tii- _{x x} deposited on a substrate to be coated.

Description of the process for depositing a thin layer of Tii- _x Au _x on a substrate:

To deposit a thin layer of Tii- _x Au _x , and in particular Ti ₃ Au in the β phase, a specific reactor and specific shaping conditions can be used.

As regards the deposition reactor used, according to one embodiment, the latter consists of a cylindrical stainless steel chamber 400 mm in diameter and 500 mm in height. It is understood that other shapes of deposition chambers and other dimensions may be entirely suitable, in particular as a function of the shape and the amount of the substrate to be covered and / or of the target substrates.

Three spray sources, namely magnetrons, are preferably used. The number of magnetrons used can however be adapted as a function of the number of target substrates.

The three magnetrons typically have flexible heads, are fitted with flaps and are mounted symmetrically at 120 ° each relative to the base plane of the deposition chamber.

In practice, the flexibility of the magnetron heads makes it possible either to co-spray under confocal positions, or to form multilayer coatings by rotating the substrate to be covered alternately in front of each target. Target substrates of magnetrons can be connected to a direct current source, a radio frequency source or a pulsed energy source.

According to one embodiment, the substrate to be covered can for example be introduced into the reactor chamber from an upper plate, as well as crosspieces for the electrical supply intended to heat and polarize as well as to measure the temperature of the substrate to be covered. Preferably, the presence of a linear displacement and alignment unit allows precise adjustment of the distance between the target substrates, consisting respectively of pure titanium and pure gold, and the surface of the substrate to be covered. According to one embodiment, in the chosen reactor, the substrate can be heated to 850 ° C and rotate at a speed of 1 to 60 revolutions per minute.

Consequently, various experiments have made it possible to deposit thin layers of Ti _x Au _x on a substrate, such as a substrate made of silicon, titanium or steel in particular. It should be noted that the substrate to be covered can also be ceramic for example. In the case where the base substrate is ceramic, this material already having a very high hardness, the deposition of a thin layer of Tii- _x Au _x has the advantage of improving the visual appearance of the material obtained .

In particular, thin layers of Tii- _x Au _x were obtained from 50 mm target substrates made of pure titanium (99.995%) and pure gold (99.997%). As already indicated, the dimensions of these target substrates can of course be adapted. The deposition chamber is placed, according to one embodiment, at a pressure between 1.10 ^-4 and 2.10 ⁴ Pa. Then, an inert gas, such as argon, is introduced into the chamber, as plasma for atomizing and ionizing titanium and gold atoms.

According to a preferred embodiment, two target substrates made of pure titanium and a target substrate made of pure gold are arranged in the chamber. According to this embodiment, a titanium target substrate is connected to a radio frequency source while the other titanium target substrate is connected to a pulsed current source at a frequency between 10 kHz and 100 kHz, with a pulse duration from 2 to 5 microseconds, each target titanium substrate also being each bombarded by means of a magnetron, each magnetron applying a power of between 20.3 and 61.2 kW / m ² . According to this embodiment, the target substrate in gold is in turn connected to a direct current source with an applied power of between 0.5 and 20.4 kW / m ² .

According to one embodiment, by maintaining constant the power applied to the target substrates in titanium and by varying the power applied to the target substrate in gold, the stoichiometric composition of the compound Tii- _x Au _x varies, x evolving between 0.15 and 0 , 40.

Furthermore, according to the proposed embodiment, the temperature of the substrate to be covered has been adjusted between ambient temperature and 650 ° C., measured on the rear face of the substrate to be covered, with a view to forming in particular the Ti ₃ Au compound under quasiamorphic or totally crystalline form in β phase.

According to one embodiment, the target substrates are moreover arranged at a distance of between 40 and 200 mm from the substrate to be covered in order to promote the formation of β phase and to optimize the deposition rate and the adhesion of the thin layer. of Tii- _x Au _x on the substrate to be covered.

The thickness of the Tiix _x Au _x deposit produced on the substrate to be covered was measured using a Tencor alpha step D500 type profilometer, at a value between 2 and 10 μm, depending on the substrate to be covered. It is understood that the thickness of the thin layer can be adapted as required.

It should be noted that by "thin" layer is meant a layer whose thickness is less than or equal to 50 μm.

Previously, a method has been described according to the invention for obtaining an alloy formed from a thin layer of titanium and gold deposited on a substrate to be covered.

In the following, certain experimental results obtained will be presented.

Experimental results observed on alloys produced by the process described above:

The results given below were obtained on the basis of tests carried out on a material produced in accordance with the method according to the invention in the particular configuration given by way of example above.

The hardness and Young's modulus of the samples obtained were determined from loading-unloading curves, carried out by nanoindentation, using a three-sided Berkovich diamond tip and operating in continuous stiffness measurement mode. For each sample, a set of four times four indentations was applied at 35 µm intervals and for a depth of 1 µm. Hardness like Young's modulus were calculated as a function of penetration depth or applied load using the method described by Oliver and Pharr in WC Oliver, GM Pharr, "Measurement of hardness and elastic modulus by instrumented indentation: Advances in understanding and refinements to methodology >>, J. Mater. Res. 19 (2004) 320. The range of indentation depths used was chosen so as not to exceed approximately 10% of the thickness of the deposited thin layer, in order to minimize the effects of the substrate. For example, for a thin layer deposited around 2 μm thick, the indentations used did not exceed, in the tests carried out, approximately 200 nm.

In transverse view, the morphology of the different titanium-gold compounds is variable. In particular, according to the preferred embodiment, in which gold represents 25 at.% Of the thin layer in stoichiometric proportions, the compound therefore being Ti ₃ Au, the columnar structures are clearly pronounced, as shown in FIG. 2 Furthermore, said columns seem to extend over the entire thickness of the thin layer.

The morphology of the surface after the deposition of the thin layers and the roughness obtained are important parameters of the thin layers because they link the growth mechanisms (random or preferred orientation, shading effects, atom mobility, ion flux , surface diffusion, etc.) with functional properties (mechanical, optical, etc.). For a given thin layer, for example Ti ₃ Au, the surface morphology and the roughness depend on the deposition speed of said thin layer, on the growth texture, on the type of ion bombardment, on the thickness of the layer. profile of the underlying substrate. These parameters can be adjusted, according to the invention, to produce the desired material, consisting of a thin layer of Tii_ xAu _x deposited on a substrate.

FIGS. 3 and 4 respectively show a view carried out under the scanning electron microscope of a material formed from a base substrate of grade 2 titanium covered with a thin layer of Ti ₃ Au in the β phase deposited at a temperature above 350 ° C. In the case of FIG. 4, the base substrate was polished before the deposition of the thin layer, unlike that of FIG. 3. The sample obtained has crystallites having a certain localization, because the deposition of the thin layer is done first to fill the holes and porosities of the sanded surface to finally generate a smoother surface than the original surface.

Thus, as shown in FIG. 4 in particular, by depositing a thin layer of Ti ₃ Au on a substrate such as a grade 2 titanium substrate, it is possible to obtain a polished effect. At a minimum, the deposition of such a thin layer significantly decreases the surface roughness of a grade 2 titanium substrate, a material known to be difficult to polish.

According to a preferred embodiment, the present invention provides the production of a material consisting of the deposition of a thin layer of Ti ₃ Au in β phase (βTi ₃ Au) on a base substrate, such as a titanium substrate. , steel, brass or ceramic for example.

To achieve such a deposition of a thin layer of β-Τί ₃ Αυ in a stable manner, the method according to the invention can in particular comprise, on the one hand, the adjustment of the deposition parameters, essentially of the powers applied to each of the three magnetrons, in order to obtain the ratio between titanium ions and gold ions in the plasma which is 75 at.% of titanium ions per 25 at.% of gold, required to obtain the composition Ti ₃ Au , and, on the other hand, the optimization of the entirely crystalline β phase by adjusting the deposition temperature of the thin layer.

Advantageously, it is also possible to optimize the conditions for depositing the thin layer in order to obtain strongly adherent thin layers, without cracks, and hard.

In particular, the deposition temperature was determined to be greater than 350 ° C to obtain the deposition of a thin layer of totally crystalline fi-Ti ₃ Au.

It should be noted that, as already mentioned, according to the preferred embodiment, three magnetrons are actually used, two magnetrons being used to bombard two target substrates of pure titanium respectively, the third magnetron being used to bombard a single target substrate in pure gold.

In order to obtain the deposition of a thin layer of Tii- _x Au _x adhering optimally to the substrate to be covered, the configuration of said three magnetrons can be optimized. In particular, the third magnetron is configured to allow the production of high energy gold ions and this makes it possible to reduce the distance between the target substrates and the substrate to be covered. The rotation of the substrate to be covered also promotes the reduction of the distance between the target substrates and the substrate to be covered, compared to confocal spraying. Furthermore, the use of a radio frequency energy source on a first titanium target substrate, and the use of a pulsed energy source on the second titanium target substrate makes it possible to adjust the energy of the titanium ions. This also ensures proportionality between the titanium ions and the gold ions since the atomization rate of gold is significantly higher than that of titanium. In addition, the application of a negative polarization on the substrate to be covered also promotes the deposition of a thin layer of desired Ti _x Au _x , as a function of all the above parameters.

Finally, the negative polarization of the substrate to be covered can also be optimized to minimize the risk of cracking of the alloy obtained. By adjusting this negative polarization of the substrate, the adhesion of the thin layer to the substrate is also reinforced.

To measure the hardness of the materials obtained by the method described above, different types of indentation have been implemented, based respectively on a constant load, a constant relative depth and the measurement of continuous stiffness.

Depending on the indentation mode at constant load or at constant relative depth, several loads were applied to measure the hardness and Young's modulus, in particular in order to highlight possible effects of the substrate and the probable modification of the hardness in depending on the thickness of the thin layer. These measurements are averaged over four times four indentation tests for each set of measurements.

As shown in FIGS. 5 and 6, the hardness and Young's modulus values measured present a maximum for the p-Ti ₃ Au compound, going in particular up to more than 12 GPa for the hardness.

In summary, the present invention relates to the production of a material comprising a thin layer of an alloy comprising titanium and gold, in particular of atomic formula of Ti- _x Au _x , in particular of formula Ti ₃ Au, in particular in β phase, deposited on a base substrate, in particular a titanium, steel, brass, or ceramic substrate.

Experimental results have shown that such a material has exceptional hardness, well above 8 GPa, and up to more than 12 GPa according to the tests carried out. Such a material can in particular be used in the field of watchmaking, either to manufacture particularly solid watch cases, with a titanium base substrate for example, or to manufacture parts of watch movements particularly resistant to abrasion, such as gears or bearings, with a basic brass substrate for example. The preceding examples are of course given by way of illustration and should not be considered as limiting.

In other fields, where the production of parts resistant to scratches or abrasion is sought, such as in jewelry, eyewear or for fashion accessories for example, the material according to the invention can indeed also be advantageously exploited .

Furthermore, it should be noted that, in the context of the present invention, the alloy deposited in a thin layer on a substrate can comprise, in addition to titanium and gold, a metal or a combination of metals whose addition allows in particular to adjust the color of the alloy, or even, more generally, a chemical element or a combination of metallic and / or non-metallic chemical elements.

According to the invention, the alloy deposited as a thin layer on a substrate consequently has the atomic formula Ti (i- _x - _y ) Au ( _X ) M ( _y ), with 0.15 <x <0.40; 0.00 <y <0.15.

As noted, M is a chemical element or a combination of chemical elements. More precisely, M is Ag, Cu, Zn, or a combination of these metals, in particular to obtain a yellow tint of the alloy, M is Cu, in particular to obtain a red tint of the alloy, M is Ag, Cu, or a combination of these metals, in particular to obtain pink and hot pink hues of the alloy, M is Pt, Pd, Ni, Zn, or a combination of these metals, in particular to obtain a white hue of l alloy, M is Ag, Cu, Cd, or a combination of these metals, in particular to obtain a green tint of the alloy, and M is Fe, Al, Ga, ln, or a combination of these metals, in particular to get blue and purple hues of the alloy.

M can also include a chemical element which is not necessarily metallic: M can for example include nitrogen (N), making it possible to obtain more vivid colors. M can also be a combination of nitrogen and a metallic element. For example M can be a combination of nitrogen and copper, to obtain a bright red hue.

It is further specified that the present invention is not limited to the examples described above and is susceptible to variants accessible to those skilled in the art.

Claims (15)

1. Material comprising a base substrate and a thin layer made of an alloy comprising titanium and gold. 2. Material according to claim 1, said alloy having the atomic formula Ti (i- _x -y) Au (x) M (y), where M is a chemical element or a combination of chemical elements, with 0.15 < x <0.40; 0.00 <y <0.15. 3. Material according to claim 2, wherein M comprises one of the metals or a combination of several of the following metals: Ag, Cu, Zn, Pt, Pd, Ni, Zn, Cd, Fe, Al, Ga, ln. 4. Material according to claim 2 or 3, wherein M comprises nitrogen. 5. Material according to claim 1, said alloy being of atomic formula Ti ₃ Au. 6. Material according to the preceding claim, wherein said alloy is Ti ₃ Au in β phase. 7. Material according to one of the preceding claims, in which the thin layer has a thickness less than or equal to 50 μm. 8. Material according to one of the preceding claims, in which the base substrate consists of titanium, for example grade 2 titanium, or steel, or brass or ceramic. 9. Timepiece movement part comprising the material according to one of the preceding claims. 10. Watch case comprising the material according to one of claims 1 to 8. 11. A method of depositing a thin layer of an alloy comprising titanium and gold on a substrate, comprising the following steps: placing a substrate to be covered, at least one target substrate made of pure titanium and at least one target substrate made of pure gold in a deposition chamber; adjusting the pressure in the deposition chamber; injecting an inert gas to allow the formation of a plasma, said inert gas possibly being argon, in the deposition chamber; bombarding said at least one target substrate made of pure titanium with a first magnetron; bombarding said at least one pure gold target substrate with a second magnetron; so as to cause the formation of a plasma comprising titanium ions and gold ions in determined stoichiometric proportions; depositing a thin layer of the alloy comprising titanium and gold on the substrate to be covered. 12. Method according to the preceding claim, further comprising heating the substrate to be covered, for the deposition of the alloy in the crystalline phase. 13. Method according to one of claims 11 to 12, wherein the adjustment of the pressure in the deposition chamber consists of placing under pseudo-vacuum at a pressure between 1.10 ^-4 and 10.10 ⁴ Pa. 14. Method according to one of claims 11 to 13, wherein the power of each of said magnetrons is configured independently to obtain the deposition of said thin layer of the alloy comprising titanium and gold on the substrate to cover. 15. Method according to one of claims 11 to 14, in which, a first and a second target substrates made of pure titanium and a target substrate made of pure gold being placed in the deposition chamber, three independent magnetrons are used , the first magnetron using a power of between 20.3 and 61.2 kW / m ² to bombard the first target substrate made of pure titanium connected to a radio frequency source, the second magnetron using a power of between 0.5 and 20.4 kW / m ² for bombarding the target substrate in pure gold connected to a direct current source and a third magnetron using a power of between 20.3 and 61.2 kW / m ² for bombarding the second substrate pure titanium target connected to a pulsed current source. 1/3 Temperature [° C] Mass percentage Au [wt.%] 0 20 30 40 50 1800 ....., - U 100 Atomic percentage Au [at.% 100