Metal Matrix Composites for Watch Parts

Abstract

2. A metal matrix composite for a watch component, comprising: a metal alloy based on gold, the composite comprising at least 75% by weight of gold; or a metal alloy based on platinum, the composite comprising at least 95% by weight of platinum; or a metal alloy based on palladium, the composite comprising at least 95% by weight of palladium; in which the metal alloy further comprises between 0.1% and 2% by weight of at least one hardening element, or between 0.5% and 2% by weight of at least one hardening element, or between 0.5% and 1.5% by weight, or between 0.5% and 1.25% by weight, or between 0.5% and 1% by weight; and a reinforcing material comprising ceramic particles, in a weight percentage between 1% and 10%, or between 1% and 5%,

Description

[Technical field]

[0001] The present invention relates to a material, including a metal alloy, that is particularly suitable for forming all or part of a component of a timepiece item, such as a component of the external part of a watch, in particular. The present invention also relates to a timepiece component, timepiece, jewellery or fine jewellery itself, such as a wristwatch, that includes the material. The present invention also relates to a method for producing the material. [Background technology]

[0002] It is known to use metal alloys to form watch components, in particular external parts of small watches, in order to meet the many demands that are made on the components, in particular in terms of obtaining a desired color on the one hand and high mechanical strength on the other hand.

[0003] Certain alloys, such as the alloy Au75Ag25, have the advantage of an attractive color and therefore meet the color requirements of watch components. However, such alloys have a low hardness, below 40HV, which prevents them from being used in the manufacture of watch components, despite the importance of their color. In other words, the hardness requirements of watch components deprive design experts in the manufacture of watch components of the possibility of obtaining certain interesting colors that certain alloys can provide.

[0004] Apart from the two requirements regarding colour and hardness, the materials used for the manufacture of watch components must satisfy other requirements, including sufficient stability against modification of their colour over time despite external stresses, for example the effect of weakly aggressive aqueous media such as tap water, sea water, swimming pool water, salt water or soapy water, as well as a robustness enabling them to maintain their mechanical properties over time. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] "CIE15:2004 report", published by the Commission Internationale de l'Eclairage (International Commission on Illumination) Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, one of the aims of the invention is to propose a material for watches, jewellery or fine jewellery components, which has a desired colour and sufficient hardness.

[0007] Another object of the invention is to propose a material that is resistant to modification of its color and / or mechanical properties over time.

[0008] Another object of the invention is to propose a method for the manufacture of said material, which is sufficiently simple and can be expected to be well reproducible, in order to obtain a given color, identical in each cycle of manufacture. [Means for solving the problem]

[0009] For this reason, the present invention provides a metal-based composite material for a watch part, comprising: a gold-based metal alloy, said composite material comprising at least 75% by weight of gold; or a platinum-based metal alloy, said composite material comprising at least 95% by weight of platinum, or A palladium-based metal alloy, the composite material comprising at least 95% by weight of palladium; In metal alloys, The composite material further comprises a metal alloy comprising between 0.1% and 2% by weight of at least one hardening element, or between 0.5% and 2% by weight of at least one hardening element, or between 0.5% and 1.5% by weight, or between 0.5% and 1.25% by weight, or between 0.5% and 1% by weight; a reinforcing material, the reinforcing material including ceramic particles, in a weight percentage of 1% to 10%, or 1% to 5%, The present invention relates to a metal matrix composite material comprising:

[0010] The present invention also provides a method for producing a metal-based composite material for a watch component, comprising the steps of: a gold-based metal alloy, such that the composite material contains at least 75% by weight of gold; or a platinum-based metal alloy, such that the composite material contains at least 95% by weight of platinum; or providing a metal alloy based on palladium, such that the composite material contains at least 95% by weight of palladium; providing a metal alloy comprising a hardening element such that the composite material comprises between 0.1% and 2% by weight of at least one hardening element, or between 0.5% and 2% by weight of at least one hardening element, or between 0.5% and 1.5% by weight, or between 0.5% and 1.25% by weight, or between 0.5% and 1% by weight of at least one hardening element; producing a metal powder from said metal alloy; mixing said metal powder with a reinforcing powder comprising ceramic particles to obtain a powdered composite material, said reinforcing powder exhibiting a weight percentage between 1% and 10%, or between 1% and 5%, densifying the powdered composite material; The present invention relates to a method for producing a metal-based composite material for watch parts, comprising the steps of:

[0011] The invention is more particularly defined in the claims.

[0012] The objects, features and advantages of the present invention will be explained in more detail in the following description of particular embodiments, given as non-limiting examples, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0013] [Figure 1]FIG. 1 shows the hardness obtained by adding 1% by weight of each of the hardening elements Ti, Zr, Al, and Y to a metal alloy, compared to the hardness of a similar metal alloy without the hardening element. [Diagram 2] FIG. 2 is a metallographic cross-section illustrating the effect of adding the hardening element Ti for a selected metal alloy, AuAg22Ti1. [Diagram 3] FIG. 3 shows colorimetric measurements of different metal alloys according to an illustrative embodiment of the present invention. [Figure 4] 4a and 4b are diagrams illustrating the color and brightness changes, respectively, of different metal alloys according to illustrative embodiments of the present invention within salt spray exposure aging tests over periods ranging from 1 to 200 days. [Diagram 5] 5a and 5b show the microstructures of densified samples of a metal alloy without hardening elements mixed with ceramic reinforcement and the same mixture but with the metal alloy containing hardening elements, respectively. [Figure 6] FIG. 6 is a diagram illustrating a flow chart of a method for producing a composite material according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] To simplify the explanation, the following convention is used hereafter for the designation of alloys: The amount of an element is indicated as weight % after the sign of the element. Example: Au75Ag25 corresponds to an alloy containing 75% gold (18 carat) and 25% silver. As a variant, the "75" after the element Au may be omitted, in which case the weight % of Au is the complement to 100% of the proportions of the other elements and / or components of the composite.

[0015] The inventive concept consists in the use of a determined metal alloy to obtain a given color, which is reinforced with a reinforcing material including ceramic particles to form a metal matrix composite. With this approach, the reinforcement used makes metal alloys of insufficient hardness suitable for watch use, which leads to a significant increase in the number of available metal alloys, and in particular the number of available colors.

[0016] A method for producing a composite material according to an embodiment of the invention is explained in detail below. In this embodiment, a metal alloy based on gold and silver is used. In particular, the invention is suitable for metal alloys in which the resulting composite material contains at least 75% by weight of gold and between 15% and 24% by weight or between 20% and 24% by weight of silver. As explained below, the invention makes it possible to use metal alloys that, as mentioned above, could not be used in watch applications before because of their insufficient hardness.

[0017] More generally, the method described is - containing at least 75% by weight of gold, based on gold, or - containing at least 95% by weight of platinum, based on platinum, or - based on palladium, containing at least 95% by weight of palladium; This is particularly suitable when a metal alloy is selected. It is noted that the percentages by weight indicated correspond to the percentages by weight of the resulting material, in particular of the resulting composite material. In the case of gold-based alloys, the percentage of gold is preferably lower than 95% by weight, or lower than 90% by weight, or lower than 80% by weight. Above this, but not excluded, the gold-based alloy becomes very soft and very difficult to handle with the present invention. Advantageously, the gold-based alloy is an 18 carat alloy, which contains 75% by weight of gold.

[0018] In addition, the described method is also particularly suitable when a metal alloy is selected with a hardness of 70HV or less, or 50HV or less, or 40HV or less.

[0019] The first step E1 of the method consists of the selection of a metal alloy that forms the basis of the composite matrix. In the embodiment shown, said alloy is based on gold and silver. It is noted that by virtue of the invention it is possible to select said metal alloy from a large choice of metal alloys, including alloys that are known to have insufficient hardness. Thus, for example, a design expert can select a metal alloy according to its color, without having to consider its hardness.

[0020] To produce the composite material from the selected metal alloy, a method according to an embodiment of the invention advantageously employs powder metallurgy.

[0021] The second step of the method, E2, comprises adding at least one hardening element to the selected metal alloy to produce a hardened metal alloy.

[0022] For this purpose, a hardened metal alloy is prepared by incorporating said hardening element into the selected metal alloy. Advantageously, the composite material comprises between 0.05% and 2% by weight of at least one hardening element, or between 0.075% and 1.75% by weight of at least one hardening element, or between 0.1% and 1.5% by weight of at least one hardening element, or between 0.5% and 1.5% by weight, or between 0.5% and 1.25% by weight, or between 0.5% and 1% by weight. It is noted that these percentages by weight correspond to the percentages by weight of the resulting composite material.

[0023] Depending on the embodiment, at least one hardening element of the metal alloy is selected from elements that form precipitates in low concentrations, in other words elements that are sparingly soluble in the alloy, in particular titanium (Ti), zirconium (Zr), aluminum (Al), yttrium (Y), calcium (Ca) or lanthanides. For this reason, one or more of these hardening elements are incorporated in the selected metal alloy in very small proportions to form a microalloy, here called hardened metal alloy. Alternatively or additionally, at least one hardening element of the metal alloy is selected from elements capable of reacting with the material selected to reinforce and / or elements capable of forming a reinforcement in situ during densification, in particular boron (B), carbon (C), nitrogen (N) or oxygen (O). It is noted that the hardening element is therefore an element in the sense of a chemical element, i.e. a simple element and not a compound. On the other hand, the hardening element is integrated and incorporated into the structure of the alloy itself to form a hardened metal alloy. Thus, hardening elements, as opposed to reinforcing elements, as described below, are not elements that are left out of the alloy.

[0024] According to an exemplary embodiment of the present invention, the hardened metal alloy has a composition of AuAg22X1, where X=Ti, Zr, Al or Y. These four hardened metal alloys are produced by vacuum melting. FIG. 1 shows the HV0.5 hardness obtained by adding each of the four hardening elements Ti, Zr, Al and Y, compared to the hardness of the metal alloy AuAg25 without the hardening element. It can be clearly seen that each of the hardening elements can significantly increase the hardness of the metal alloy, almost up to 4 times for Ti. Thus, the hardness of the alloy increases up to 135 Hv by adding 1 wt.% of element Zr and up to 150 Hv by adding 1 wt.% of element Ti.

[0025] It is noted that advantageously, the hardening element is added to the selected metal alloy in a very low concentration, close to its solubility limit in the liquid phase. This means that during cooling and transition to the solid phase during the production of the hardened metal alloy, precipitates can form in the solid phase, which increase the hardness of the hardened metal alloy. X-ray diffraction measurements show that the addition of the hardening element Ti causes the formation of intermetallic precipitates that induce hardening of the alloy. Figure 2 illustrates the effect of the addition of the hardening element Ti on the microstructure of a bulk sample of the hardened metal alloy, obtained by casting, highlighting the intermetallic precipitates, which are not easily visible in the atomized powder described below due to the small size of the precipitates.

[0026] It is noted that the selected hardening elements, according to the exemplary embodiment in a proportion of 1% by weight, may also have an interesting effect on color and may form hardened metal alloys that are endowed with sufficient color stability over time, even when exposed to stress.

[0027] Colors are defined in the conventional way by points on the CIELAB space formed by the green-red axis along the abscissa, the blue-yellow axis on the ordinate and the axis showing contrast (see non-patent document 1). All measurements were made using the following conventions: D65 illuminant and standard observer at a 10° angle (CIE 1964).

[0028] FIG. 3 shows colorimetric measurements of different hardened metal alloys according to exemplary embodiments of the present invention compared to alloys AuAg22 and AuAg25 without hardening elements. In summary, the addition of hardening elements enhances the red of the color of Au-Ag based alloys, on the one hand, with a ΔE*ab separation of +1 to +3, and on the other hand, reduces the yellow component to various degrees. At the same weight percentage, yttrium has the least effect on the color variation, followed by the elements Zr, Al, and Ti, in that order, with a ΔE*ab separation between 1 and 10. In all cases, the color of hardened AuAg22X1 type metal alloys remains comparable to the base alloys AuAg22 or AuAg25.

[0029] Figures 4a and 4b respectively illustrate the evolution of colour (Figure 4a, a*(D65) plotted against b*(D65)) and lightness (Figure 4b, L*(D65) as a function of time) within a salt spray exposure ageing test over a period of 1 to 200 days for different alloys based on gold and silver, with or without the hardening elements mentioned above. In Figures 4a and 4b, curve 13 illustrates the behaviour of a metal alloy hardened by the hardening element Ti. The figure shows that the behaviour is comparable to that of the base metal alloys without the hardening element Ti, in particular the metal alloys AuAg22 illustrated by curve 11 and AuAg25 illustrated by curve 12. Curves 14 to 16 illustrate the behaviour of hardened metal alloys with hardening elements Al, Zr and Y, respectively.

[0030] The method then carries out a third step E3 of preparing a powdered composite material.

[0031] For this reason, the method according to an embodiment comprises a first sub-step E31 of producing a hardened metal alloy powder. Any milling or atomization process may be carried out in the step E31 of producing the hardened metal alloy powder. Preferably, the sub-step E31 is carried out by atomization, more particularly by gas atomization or ultrasonic atomization. Advantageously, the step E31 of producing the metal powder is such that the resulting metal powder has particles with an average size of less than or equal to 200 μm, or less than or equal to 100 μm, or less than or equal to 50 μm.

[0032] The method then carries out a second substep E32 of mixing the metal powder previously obtained with a reinforcing powder comprising ceramic particles, the function of which is to reinforce the selected metal alloy whose hardness, and more generally its mechanical properties, may be insufficient for the desired horological application.

[0033] The ceramic particles may be produced from aluminum oxide (Al2O3), zirconium oxide (ZrO2), titanium oxide (TiO2), titanium nitride (TiN), silicon oxide (particularly SiO or SiO2), silicon carbide (SiC), diamond, boron nitride (BN), boron carbide (B4C), silicon nitride (Si3N4), or aluminum titanate (Al2TiO5). Single or multiple ceramics from the above list may be used. Alternatively, other ceramics may be used.

[0034] Thus, the reinforcing powder may comprise ceramic particles of a single material or may comprise a mixture of ceramic particles of two, three or more different materials. In addition, the reinforcing powder may be completely composed of ceramic particles. Alternatively, the reinforcing powder may be ceramic-based, i.e., contain at least 50% by weight of ceramic, and may comprise reinforcing particles of other nature.

[0035] The term "ceramic" refers to technical ceramics, which are distinguished in their composition from traditional ceramics, since they are obtained from refined synthetic powders, and not from natural mineral powders, such as feldspar or kaolin. In general, technical ceramic materials have a certain number of properties that make them suitable for a range of different applications. More specifically, these properties are, among others, hardness, physical stability, extreme heat resistance, and chemical inertia. Suitable technical ceramic materials are materials such as alumina, aluminum nitride, aluminum silicate; zirconium silicate, boron carbide, boron nitride; nitrides, carbides and carbonitrides of zirconium, titanium, hafnium, niobium, and / or silicon; barium titanate, magnesium, titanium, and zirconium oxide (zirconia). In the context of the present invention, alumina and / or zirconia are preferred.

[0036] Advantageously, the proportion of reinforcing powder corresponds to a proportion by weight of between 0.5% and 10%, or between 1% and 5%, relative to the total composition by weight of the composite material, said proportion being chosen so as to be high enough to obtain an adequate hardness of the composite material, but low enough to avoid altering the base color of the selected metal alloy.

[0037] On the other hand, advantageously, the ceramic particles of the reinforcing powder have an average size of less than or equal to 1 μm, or less than or equal to 0.5 μm, or less than or equal to 0.2 μm, or less than or equal to 0.1 μm. Small particle size means, on the one hand, that the particles cannot be seen, and, on the other hand, that for a given proportion by weight, the number of reinforcing particles can be maximized.

[0038] Another important factor is the distribution of the reinforcing particles within the composite: in fact, it is advantageous for the reinforcing particles to be dispersed within the metal matrix of the final composite in a uniform or substantially uniform manner, rather than forming a continuous network, which is preferred in the milling of hardened metal alloys, as explained below.

[0039] According to an advantageous embodiment of the invention, the simple mixing of the two powders is complemented by milling. The composite powder may be obtained, for example, by milling in a mill of the standard planetary ball mill type. The milling speed is advantageously in the range of 200 rpm to 800 rpm, or 100 to 1200 rpm. In addition, the milling time is selected to be between 3 and 12 hours. The milling time may vary between 1 and 48 hours, depending on the metal alloy and the milling speed. The purpose of complementing the mixing of the two powders with milling is to incorporate reinforcing particles (of submicron dimensions) into the particles of the powdered metal alloy. In this case, the reinforcing particles are located in the metal grains after sintering and act as obstacles for the movement of dislocations, thus optimizing the hardening. In addition, it is advantageous to obtain a homogeneous distribution of the reinforcing particles in the metal matrix of the composite material to promote said result. For this reason, a proper milling is optimal, whereby the particles of the metal powder are deformed, work-hardened and crushed under the action of the mill balls in order to re-agglomerate and be incorporated into the reinforcing particles. A metal alloy that is too soft will not be work-hardened sufficiently to be crushable, which will reduce the efficiency of the method and result in an inhomogeneous mixture. For this reason, at least one hardening element exerts the effect of increasing the hardness of the metal alloy, which makes it suitable for a proper milling and has the additional advantage of obtaining a homogeneous distribution of the reinforcing particles. It is noted that at least one hardening element of the metal alloy is essentially involved in the intermediate milling stage of the method, in order to promote an optimal mixing of the reinforcing particles with the metal alloy, thereby optimizing the positioning of the metal alloy and the reinforcing particles, respectively, in the final composite. For the vast majority of anticipated applications, at least one hardening element cannot be used to form a hardened metal alloy with sufficient properties to make it possible to omit the use of said reinforcing particles. In particular, without the steps of producing a metal powder and adding a strengthening agent, at least one hardening element will form precipitates at the grain boundaries during solidification, resulting in a rough and inhomogeneous microstructure that is not suitable for producing a properly finished surface, especially by polishing.

[0040] According to a variant embodiment, the step of preparing the metal powder or mixing said metal powder with the reinforcing powder comprises the addition of oxygen, boron, carbon and / or nitrogen, pure or in the form of their oxides, borides, nitrides or carbides, in a weight percentage of less than 2% and preferably more than 0.05%. This variant embodiment has the effect of promoting the formation of precipitates that act as reinforcing particles in the final composite material, in situ, during the final step of densification and / or during heat treatment and / or potentially during milling. More specifically, the reinforcing powder added in E32 may act as precursors of the final reinforcing particles present in the composite material, formed during the final step of densification and / or during heat treatment. As an example, boron and / or carbon and / or nitrogen and / or oxygen added as components of the reinforcing powder may react with Ti, or Zr, or Al, or Y, or Nb, or Hf, or V, or Ta, or Cr, or M, or W present in the alloy in the form of a solid solution to form reinforcing particles during the final step of densification and / or during subsequent heat treatment.

[0041] It is noted that the reinforcing material is therefore in the form of particles distributed within the composite material within the metal matrix formed by the hardened metal alloy. In contrast to hardening elements positioned within the structure of the metal alloy itself, the reinforcing material acts in the form of particles positioned outside the metal alloy itself in a juxtaposed manner to the hardened metal alloy to form a monolithic composite material in which the reinforcing material particles are interwoven with the assembly formed by the hardened metal alloy forming the metal matrix of the composite material. Thus, the reinforcing material particles strengthen the hardened metal alloy compared to the hardened metal alloy used alone without the reinforcing material.

[0042] The method then carries out a fourth step E4 of densification of the composite powder obtained in the preceding step. According to this embodiment, the densification is carried out by sintering, using a technique of the Spark Plasma Sintering (SPS) type, also known as flash sintering. The mixed and compressed powder is placed in a crucible, for example a cylindrical crucible, and heated by the Joule effect by placing the crucible between two electrodes and passing a pulsed or non-pulsed direct current, typically with a strength of a few kA. The method is carried out under an inert or reactive atmosphere or under vacuum, and under a pressure, typically of the order of a few MPa.

[0043] The advantage of heating using the Joule effect is that the heating and cooling rates are very high, thus allowing the total duration of the heat treatment to be reduced, thus limiting the growth of grains and any precipitates in the metal alloy. The resulting microstructure largely reflects the microstructure of the starting powder, hence the value of using powders with small grain sizes. Mechanical properties suitable for horological applications, especially hardness, are promoted by the fine microstructure of the composite material.

[0044] In an exemplary embodiment, the heating and cooling rates are at least 1 K / min, preferably greater than 50 K / min, typically 100 K / min, with a preferred range of 50 to 200 K / min. The sintering temperature is advantageously between 800° C. and 900° C., more broadly between 600° C. and 1000° C. These values ​​must potentially be adapted to the type and size of the powder. The processing is carried out under vacuum or under an inert gas such as Ar or Formiergaz (a mixture of N2 and H2). It is noted that the melting temperature of the reinforcing material is advantageously higher than the sintering temperature used.

[0045] As variants, other densification methods are foreseeable, such as hot pressing, hot isostatic pressing (HIP), conventional sintering or sintering with pulsed current or electric sintering forging (ESF). Optionally, the densification step may comprise an additional heat treatment under vacuum or in a neutral or reactive atmosphere.

[0046] 5a and 5b show the microstructures of samples sintered according to the above-mentioned method, respectively showing a 2% AuAg22-Al2O3 composite obtained from an Au-Ag metal alloy without hardening elements mixed with an Al2O3 ceramic reinforcement, and on the other hand the same Au-Ag metal alloy with hardening element Ti mixed with an Al2O3 ceramic reinforcement according to the above-mentioned exemplary embodiment of the invention. From FIG. 5b it can be seen that the composite of the invention comprises a metal matrix forming a continuous network with a substantially uniform and / or discontinuous distribution of ceramic-based reinforcement within the matrix. It is noted that due to the very small dimensions of the ceramic particles, they are not directly visible to the naked eye and are therefore difficult to detect on the metallographic cross section of FIG. 5b. The hardness measured for the 2% AuAg22Ti1-Al2O3 composite of FIG. 5b is 202 HV0.5. In contrast, the composite of FIG. 5a contains clear areas 20, which correspond to insufficiently milled pieces of metal alloy remaining due to the low hardness of the Au-Ag metal alloy. The black spots 21 correspond to alumina agglomerates. Thus, the structure of the composite is significantly different from that of the composite of the present invention and is much less optimized. The measured hardness of the AuAg22-Al2O32% composite of FIG. 5a is substantially lower, only 91 HV0.5. Thus, these figures provide a good illustration of the effect of adding hardening elements to the metal alloy. As mentioned above, the hardening elements can be used to improve the milling of the metal alloy and to obtain a composite without unmilled areas and without agglomerates. Thus, the reinforcing particles are uniformly distributed in the powder and then in the final composite.

[0047] The embodiments of the present invention have been described with respect to a manufacturing method based on powder metallurgy techniques, in particular with densification by sintering. According to alternative embodiments, the hardened metal alloy powder or composite powder may be modified to be adapted for densification by additive laser manufacturing techniques or by adding a binder for deposition, for example using a "binder jet" type printer.

[0048] It is noted that the method according to the invention can be used to form highly advantageous composite materials, including structures that are ideally suited to the desired horological application and that endow the mechanical properties well adapted to the desired purpose. It is noted that the method according to the invention can thus be used to define composite materials that are substantially improved with respect to metallic materials, the structure of which is simply reinforced by infiltration of reinforcing elements, or with respect to ceramic materials that have a continuous ceramic phase that is to be infiltrated by a metallic material. In particular, the method according to the invention can be used to define composite materials with a continuous metallic network, making it possible to obtain substantially improved mechanical strength and toughness.

[0049] The present invention also relates to a metal matrix composite material for watch components as such. According to an embodiment, this type of composite material comprises: a gold-based metal alloy, the composite material comprising at least 75% by weight of gold, or a platinum-based metal alloy, the composite material comprising at least 95% by weight of platinum, or A palladium-based metal alloy, the composite material containing at least 95% by weight of palladium; A metal alloy comprising: The composite material further comprises a metal alloy comprising between 0.1% and 2% by weight of at least one hardening element for the metal alloy, or between 0.5% and 2% by weight of at least one hardening element for the metal alloy, or between 0.5% and 1.5% by weight, or between 0.5% and 1.25% by weight, or between 0.5% and 1% by weight; A reinforcing material, including ceramic powder, in a weight percentage of 0.5% to 10%, or 1% to 5%, It is a composite material composed of

[0050] The bond between the reinforcement and the metal alloy appears to be improved by the presence of hardening elements in the metal alloy.

[0051] Advantageously, the metal alloy selected in the embodiment of the present invention is free of copper and / or iron or contains less than 0.5% copper and / or iron.

[0052] Alternatively, the composite material comprises at least 75% by weight gold, less than 99.9%, or less than 99%, or less than 95%, or preferably less than 90%, or less than 80% by weight gold.

[0053] Metal matrix composites advantageously include a structure in which the hardened metal alloy forms a continuous network that forms the metal matrix of the composite. In addition, the ceramic particles of the reinforcement are advantageously substantially uniformly and / or discontinuously distributed within the composite.

[0054] The present invention can be implemented to produce metal matrix composites having a hardness of 135HV or greater, or 150HV or greater, or 200HV or greater.

[0055] The low reinforcement content has little effect on the color of the composite, i.e., the color of the composite is close to that of the metal alloy originally selected, so that the metal alloy can be chosen specifically for its color as a function of the desired aesthetic effect.

[0056] The invention also relates to a timepiece component, characterized in that it contains a composite material as described above. In fact, said composite material is particularly suitable for manufacturing all or part of a timepiece component, in particular a watch casing or glasses, or an external part of a small watch, such as a bracelet element or a bracelet clasp element. The invention can also be used in the manufacture of jewellery or fine jewellery components.

[0057] Of course, the manufacture of watch parts, jewellery or fine jewellery does not mean merely a surface coating, but rather the manufacture of all or a significant part of the thickness of said watch parts. For this reason, the parts under consideration contain a composite material, advantageously in the form of solid components, in large quantities, in particular at least a part of a thickness of 0.1 mm or more. Of course, nothing prevents the addition of a coating to all or part of the composite material under consideration, although this is not a preferred embodiment.

[0058] The invention also relates to a watch item, characterized in that it includes at least one watch part as defined above.

Claims

1. A metal matrix composite material for a watch part, comprising: The composite material comprises: the composite material comprises at least 75% gold by weight, based on gold; or the composite material comprises at least 95% by weight platinum, based on platinum; or Based on palladium, the composite material comprises at least 95% by weight palladium; A metal alloy; at least one hardening element, wherein the composite material comprises between 0.1% and 2% by weight of the at least one hardening element; a reinforcing material, wherein the composite material comprises a reinforcing material in a weight percentage of 1% or more and 10% or less; Including, The reinforcing material includes ceramic particles. Metal matrix composite material.

2. The metal matrix of the composite material comprises the metal alloy hardened by the at least one hardening element. The metal matrix composite material according to claim 1.

3. The ceramic particles have an average size of 1 μm or less. The metal matrix composite material according to claim 1.

4. The ceramic particles are oxides and / or carbides and / or nitrides and / or borides. The metal matrix composite material according to claim 1.

5. the at least one hardening element of the metal alloy is selected from the group consisting of titanium (Ti), zirconium (Zr), aluminum (Al), yttrium (Y), calcium (Ca), and lanthanides; The metal matrix composite material according to claim 1.

6. the metal alloy is a gold-based alloy containing silver, and the composite material contains between 15% and 24% silver by weight; The metal matrix composite material according to claim 1.

7. The metal alloy, which does not contain the at least one hardening element, has a hardness of 70 HV or less. The metal matrix composite material according to claim 1.

8. the metal alloy forms a continuous network in the metal matrix of the composite material; and / or The ceramic particles of the reinforcement are substantially uniformly and / or discontinuously distributed within the composite material. The metal matrix composite material according to claim 1.

9. The composite material has a hardness of 135 HV or more. The metal matrix composite material according to claim 1.

10. Comprising the composite material of claim 1 . Watch parts.

11. An external part of a watch, or a component of glasses, or a bracelet element, or a bracelet clasp element, The timepiece component according to claim 10.

12. A timepiece item comprising the timepiece component according to claim 10.

13. A method for producing a metal matrix composite material for a watch part, comprising: The method comprises: a gold-based metal alloy, such that the composite material contains at least 75% gold by weight; or a platinum-based metal alloy, such that the composite material contains at least 95% by weight of platinum; or a palladium-based metal alloy, such that the composite material contains at least 95% by weight of palladium; and (E2) preparing a metal alloy comprising a hardening element, such that the composite material comprises between 0.1% and 2% by weight of the at least one hardening element. a step (E31) of producing a metal powder from said metal alloy; a step (E32) of mixing said metal powder with a reinforcing powder comprising ceramic particles to obtain a powdered composite material, said composite material comprising said reinforcing powder in a proportion by weight of 1% to 10%; a step (E4) of densifying the powdered composite material; A method for producing a metal matrix composite material for a watch part, comprising:

14. the ceramic particles of the reinforcing powder have an average size of 1 μm or less; The method of claim 13.

15. The metal powder has particles with an average size of 200 μm or less. The method of claim 13.

16. the densification step (E4) is a rapid sintering step using spark plasma sintering (SPS), hot pressing, hot isostatic pressing (HIP), conventional sintering or sintering with pulsed current or microwave sintering, or electric sinter forging, or a material addition step; The method of claim 13.

17. the step of producing the metal powder and the step of mixing the metal alloy with the reinforcing powder comprise the addition of oxygen, carbon and / or nitrogen and / or boron in the pure form or in the form of oxides, nitrides, borides or carbides in a weight percentage of less than 2%; The method of claim 13.

18. The metal alloy is based on gold, and the composite material comprises at least 75% by weight and less than 95% by weight of gold, between 0.5% and 1.5% by weight of the at least one hardening element, and a weight percentage of the reinforcing material of between 1% and 10%. The metal matrix composite material according to claim 1.

19. The ceramic particles are selected from the group consisting of aluminum oxide (Al2O3), zirconium oxide (ZrO2), titanium oxide (TiO2), silicon oxide, silicon carbide (SiC), titanium carbide (TiC), diamond, boron nitride (BN), boron carbide (B4C), silicon nitride (Si3N4), and / or aluminum titanate (Al2TiO5), and titanium nitride (TiN), The metal matrix composite material according to claim 1.

20. The ceramic particles are made from technical ceramics. The metal matrix composite material according to claim 1.

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