Light-weight and robust timepiece component

Abstract

Component, in particular a timepiece component, characterized in that it comprises at least one porous core, comprising a first material or based on a first material, with a density of less than or equal to 80%, or even less than or equal to 60%, or even less than or equal to 50%, of the density of the first solid material, and in that it comprises a surface coating comprising at least one layer with a density greater than the density of the at least one porous core.

Description

[0001] Lightweight and robust watch component

[0002] The present invention relates to a watch component, in particular a watch component for display purposes, or more generally any other component, even outside the field of watchmaking. It also relates to a timepiece, in particular a wristwatch, comprising at least one such watch component. It also relates to a method for manufacturing such a component, in particular such a watch component.

[0003] A watch component, and more specifically a watch component for exterior use, must achieve numerous mechanical properties, sometimes contradictory. Among these sought-after properties, we can mention:

[0004] - Lightness, which makes wearing a timepiece comfortable;

[0005] - A very attractive appearance, free from defects, compatible with the aesthetic requirements of luxury watchmaking;

[0006] - Robustness, to withstand the external constraints undergone by a timepiece, so that the watch component retains the same appearance over time, and more generally all of its mechanical properties over time.

[0007] In practice, existing solutions represent compromises between these properties. Generally, watch components are thus produced massively from a material that can be both light and hard. These existing solutions, however, have limitations, and there is a need to identify new solutions that optimize the properties and / or appearance of watch components.

[0008] An object of the present invention is therefore to propose a solution for obtaining a component, in particular a watch component, which is light and robust, in an improved manner compared to the state of the art. To this end, the invention is based on a component, in particular a watch component, characterized in that it comprises at least one porous core, comprising a first material or based on a first material, with a density less than or equal to 80%, or even less than or equal to 60%, or even less than or equal to 50%, of the density of the first solid material, and in that it comprises a surface coating comprising at least one layer with a density greater than the density of the at least one porous core.

[0009] The invention is also based on a method of manufacturing a component, in particular a watch component, characterized in that it comprises the following steps:

[0010] - Production of at least one porous core, comprising a first material or based on a first material, with a density less than or equal to 80%, or even less than or equal to 60%, or even less than or equal to 50%, of the density of the first solid material;

[0011] - Deposition of at least one layer of a surface coating of density greater than the density of the at least one porous core.

[0012] The invention is more precisely defined by the claims.

[0013] These objects, characteristics and advantages of the present invention will be explained in detail in the following description of particular embodiments made without limitation in relation to the attached figures among which:

[0014] Figure 1 illustrates elementary lattice structures obtained by a first step of a method of manufacturing a component, in particular a watch component, according to an embodiment of the invention.

[0015] Figure 2 illustrates elementary structures of the TPMS type (for the English name of Triply Periodic Minimal Surface) obtained by the first step of a method of manufacturing a component, in particular a watch component, according to another embodiment of the invention.

[0016] Figures 3a and 3b illustrate the porous cores of a case middle resulting from the first step of the manufacturing process of a watch component respectively according to two variants of the embodiment of the invention.

[0017] Figures 4a and 4b illustrate two views of the porous core of a case blank resulting from the first step of the manufacturing process of a watch component according to a third variant of the embodiment of the invention.

[0018] Figure 5 shows an enlargement of a sectional view of a component according to the embodiment of the invention.

[0019] The concept of the invention consists in proposing a component comprising a porous core, very light, but robust or resistant, covered by a surface coating comprising at least one dense layer, which provides the desired robustness and hardness to the component. The result is thus a component for which no compromise is necessary, since it combines both the maximum possible lightness with the maximum possible robustness and hardness, in particular at the level of its visible and / or exposed and / or external surfaces. In addition, advantageously, the surface condition of the surface coating is such that it has a very attractive appearance, in addition to its hardness. The coating is advantageously arranged directly or indirectly on the surface of the porous core.

[0020] As a note, throughout the text, we will use the expression "based on a material" to designate the fact that said material is the main or majority element. In particular, we will use the expression "based on a material" to designate the fact, for example, of comprising at least 50% by weight of said material. A method of manufacturing a component, in particular a watch component, according to an embodiment of the invention will now be detailed.

[0021] The method first comprises a first step of producing a porous core, made of a first material or based on a first material, with a density less than or equal to 80%, or even less than or equal to 60%, or even less than or equal to 50%, of the density of the first solid material. The density of the porous core is thus particularly low compared to the density of the first solid material. The density considered is the overall or average density of the porous core.

[0022] This first step can be carried out using several variants of the process.

[0023] According to a particular embodiment variant, the step of producing the porous core comprises a step of chemically etching a solid blank formed in the first material. In this first embodiment variant, the first step of the method therefore comprises a first sub-step of producing a solid blank of the core of the watch component, in the first material or based on the first material. The first step of the method then comprises a second sub-step of chemically etching the solid blank formed in the first material, to form a porous core as a result. Such a porous core may then be in the form of a foam, for example a metal foam.

[0024] According to another particular embodiment variant, the step of producing the porous core can be based on the formation of bubbles in a liquid metal which is then solidified in the form of metal foam.

[0025] According to yet another particular embodiment variant, the step of producing the porous core may be based on a technique of infiltrating a liquid metal into a porous body made of a molding material. After solidification of the metal, the molding material forming the porous body is removed. According to yet another particular embodiment variant, the step of producing the porous core comprises an additive manufacturing step, to directly form a porous core in the first material or based on the first material. For example, the laser powder or powder bed fusion technique ("Power Bed Fusion" in English) makes it possible to produce a controlled architecture, with a precise structure and good definition of the pore opening and good control of the anisotropy.

[0026] In all cases, the porous core has a density less than or equal to 80%, or even less than or equal to 60%, or even less than or equal to 50%, of the density of the first solid material. In other words, the porous core has a mass less than or equal to 80%, or even less than or equal to 60%, or even less than or equal to 50%, of that of the mass of a body which would occupy the same volume as that of the porous core of the watch component and which would be entirely in the same first material, in a solid manner.

[0027] The porous core may have a multitude of aspects according to the invention. For example, it may be a porous core having a skeleton shape formed by a regular or irregular porous network, in particular of the lattice type, or the structures known by the acronym TPMS (for the English name of Triply Periodic Minimal Surface), or even alveolar, cellular, or trabecular structures. In particular, the porous core may for example be made of metal foam.

[0028] The porous core may be made of a multitude of materials. For example, it may be a porous core comprising a first material or based on a first material in the form of a metal or a metal alloy, or a metal superalloy, in particular comprising one or more elements from among Fe, Mg, Al, Ti, Au, Pd, Pt, Ni, Si, and / or Co. This first material may also be an amorphous or partially amorphous alloy, or a ceramic, for example a ceramic based on alumina or zirconia. According to an alternative embodiment of the porous core, the latter may be made of several different materials. Preferably, the porous core is based on a first material as described above, that is to say that the structure formed by this first material is that which has the greatest weight in the porous core as a whole, and preferably constitutes at least 50% by weight of the porous core.In a multi-material embodiment variant, the porous core may comprise different materials organized in layers between the center of the porous core and the surface of the porous core. In this particular variant, the porous core is in all cases in a porous structure of several materials, and the density of the porous structure formed by all of said materials is less than or equal to 80%, or even less than or equal to 60%, or even less than or equal to 50%, of the density of the same structure which would be massive and integrally formed in said first material.

[0029] In this document, the density of the porous core corresponds to the average density of the skeleton as a whole formed by the porous core and not to the density of the first material or materials constituting the core. Thus, the density of the porous core is a function of the porosity or porosity rate of the porous core.

[0030] For this purpose, Figure 1 illustrates, as examples, elementary structures representing different lattice structures that can be used in this first step of producing a porous core. Figure 2 also illustrates several elementary structures representing TPMS structures that can be produced as part of the first step of the process.

[0031] According to an exemplary embodiment, the porous core may be a foam having a random structure, i.e. comprising pores whose positions and dimensions are random, in an irregular manner. According to another exemplary embodiment, the porous core may have a regular, non-random structure, for example of the three-dimensional network type (known for example as a “lattice”), having a structure forming a repetitive network. This is the case of the aforementioned lattice structures.

[0032] The structure can thus be chosen to obtain maximum porosity while offering high mechanical resistance.

[0033] According to an alternative embodiment, the porous core is designed not only to minimize the overall weight but also to fulfill one or more other functions. For example, it may be designed to achieve optimal mechanical strength in certain areas intended to undergo the highest stresses or high mechanical stresses. Thus, the structure of the porous core can best respond to these high stresses, by being adapted to withstand these high stresses, for example by a particular non-homogeneous distribution of the first material forming or included in the porous core, so as to form mechanical reinforcements in the areas concerned.Among the other mechanical functions that may be taken into account when designing the structure of the porous core, in particular if the watch component is a case middle or a watch case, it is possible in particular to provide zones shaped to absorb shocks (to isolate a watch movement within a case or case middle, for example), zones dedicated to the assembly of said watch component with other components (to assemble a watch movement within a case or case middle, for example), zones making it possible to reinforce the watertightness of said watch component, or zones allowing the transmission of sound (to transmit a sound coming from a watch movement, for example).Alternatively or additionally, it is also possible to provide flexible zones to allow elastic deformation of the watch component, particularly in the case of a watch component in the form of a blade of a bracelet clasp, for example. These flexible zones can also be dedicated to the assembly of said watch component with other components. In addition, the structure can be designed to optimize the adhesion of the surface coating that will be added, as will be described later. For this, the structure of the porous core can be different near its surface, for example to promote such adhesion.For this purpose, the porous core may comprise pores of smaller dimensions close to its surface relative to its center, so as to have a surface geometry compatible, for example, with the particle size of the particles that may be projected according to an embodiment variant, in order to obtain a compact surface coating with an optimal thickness. It is also possible to produce a denser layer on the surface of the porous core relative to its center, with a given thickness, defined according to the desired properties. More generally, the porous core may therefore have a non-homogeneous structure, in particular having a difference between its center and its surface, in particular a non-homogeneous porosity. This difference may consist of a gradient in the size of the pores, which increases from the surface to the center.In particular, the surface of the porous core or a given layer of the porous core may be devoid of pores, or have very few pores. Additionally or alternatively, a possible layer may be formed on the surface of the core in order to constitute a skin making it possible to seal the pores present on said surface, or even near said surface. All or part of the porous core variants described above may naturally be combined.

[0034] The method then comprises a second step of depositing a surface coating, which may comprise at least one second material different from the first material, with a density greater than the density of the first material. In other words, the first material has a lower density than that of the second material. More generally, the second step comprises the deposit of at least one layer of a surface coating with a density greater than the density of the at least one porous core. This second step makes it possible to obtain a watch component having in particular a high surface hardness, while being very light overall. In particular, this second step makes it possible to obtain a watch component having in particular a high hardness at its visible and / or exposed and / or external surfaces, while being very light overall.

[0035] According to a first embodiment variant, the second step comprises a step of depositing at least one layer of a surface coating produced by thermal spraying, in particular at high temperature, which may be greater than or equal to 800°C. Such a variant, for example, implements the spraying at high temperature, for example at 900°C, of ​​fine particles, such as for example particles of tungsten carbide WC and cobalt-chromium CoCr (the cobalt-chromium CoCr acting, within the coating, as a binder between the WC particles), with WC particles possibly having an average diameter of 40 μm, or even a smaller average diameter. To minimize the porosity of the coating layer, the particle size of the powders is important and must be adjusted for each layer composition and each application, as is known to those skilled in the art. The use of particles with a bimodal or multimodal size distribution is particularly favorable.Alternatively, other binders could be considered such as iron-chromium (Fe-Cr). As a note, in the examples mentioned above, the surface coating layer therefore comprises particles of a second material, such as for example tungsten carbide WC, and particles of a third material, such as for example cobalt-chromium CoCr, which fulfill the function of binder. This third material remains optional, the binder not being essential.Thermal spraying could, for example, be of the plasma type (known by its acronym "VPS" for the English term "Vacuum Plasma Spraying"), which has many advantages, such as allowing adjustment of the chemistry of the material, being able to spray many different materials, such as ceramics, oxides, metals, and allowing a thick layer to be obtained, in particular with a thickness greater than or equal to 20 pm, or even greater than or equal to 100 pm, or even greater than or equal to 250 pm, or even greater than or equal to 300 pm, or even greater than or equal to 350 pm. Alternatively, other spraying or deposition techniques are possible. In particular, electrolytic arc anodizing can be used. Cold dynamic spraying is also possible. The spraying technique will be adapted to the materials used.

[0036] Thermal spraying therefore makes it possible to obtain a thick layer of a coating, for example formed of tungsten carbide WC and cobalt-chromium CoCr. Alternatively, thermal spraying makes it possible to obtain, for example, a thick layer formed among others of TiN or TiC or TiCN, Cr2Os, or even ZrO2. Advantageously, the oxide, carbide, or nitride particles are sprayed within a binder, which makes it possible to obtain a layer of a particularly qualitative surface coating. Alternatively, it is also possible to spray particles devoid of binder, such as for example metallic particles such as titanium or titanium alloy particles. The sprayed particles are advantageously in a semi-pasty state to spread upon impact and form a regular and dense layer.A semi-pasty state is defined as a semi-solid or semi-liquid state, as opposed to solid grains (or "cold grains") which would produce an irregular structure. The resulting coating layer can thus be slightly rough and compact, with low porosity.

[0037] The difference in thermal expansion coefficient between certain materials, such as metals and ceramics for example, induces stresses during temperature changes. The choice of the first material, the geometry and the surface condition of the porous core, advantageously takes this aspect into account. Optionally, it is possible to heat the porous core to a certain temperature to minimize the appearance of stresses during the projection of the surface coating (temperature varies depending on the composition of the porous core, the atmosphere and the pressure of the deposition chamber).

[0038] According to a second embodiment, the second step of depositing at least one surface coating layer can be carried out by at least one additive manufacturing sub-step. According to a third embodiment, the second deposition step comprises a preliminary injection sub-step, for overmolding an intermediate layer of a fourth material at least on the surface of the porous core, upstream of the deposition of the at least one surface coating layer according to, for example, the first or second embodiment. This fourth material can be a resilient material such as a polymer, in particular an elastomer such as a thermoplastic elastomer (TPE) or a fluoroelastomer (FKM, FFKM or FEPM), or a natural rubber (NR) or synthetic rubber (SBR, HNBR, EPDM), or a vinyl methylsilicone (VMQ) or a fluorosilicone (FVMQ). Alternatively, it can be a thermosetting elastomer.

[0039] Thus, the second step of depositing at least one layer of a surface coating makes it possible to form at least one high-hardness layer, which may represent the surface coating alone, or alternatively which may cover a less hard intermediate layer, for example a resilient one. In the latter case, a cold dynamic projection technique to form the high-hardness layer may, for example, be preferred in order to guarantee the integrity of the resilient layer.

[0040] According to a fourth embodiment, the second step of depositing at least one layer of a surface coating comprises a subsequent sub-step of depositing a decorative layer, carried out downstream of the sub-step of depositing said at least one layer of the surface coating according to, for example, the first or second embodiment. It may, for example, be a deposit of a decorative layer intended to produce a particular appearance or color on a layer of high hardness. Such a decorative layer may, for example, be deposited by a physical vapor deposition (PVD) process, or a chemical vapor deposition (CVD) process, or an atomic layer deposition (ALD) process.For example, a first thick layer that provides hardness and protection for the porous core can be deposited, for example with a thickness of 250 μm of tungsten carbide WC and cobalt-chromium CoCr, resulting in a hardness of between 900 and 1200 HV, then a second layer, deposited for example by PVD deposition, intended to produce a particular appearance or color can be added to the first layer, for example with a thickness preferably between 500 nm and 20 μm of a metal or metal alloy, for example of the Au, Ag, Pt, Pd type. An advantage of this surface coating comes from the fact that it makes it possible to form a dense and very hard surface layer, which meets the high requirements of luxury watchmaking.This decorative layer contributes to the overall robustness of the coating, in addition to the at least one layer already applied, while forming a visible and / or exposed and / or exterior surface with an attractive appearance and great hardness.

[0041] Thus, the second step of depositing at least one layer of a surface coating may comprise several sub-steps of producing a deposit of a coating, that is to say it may comprise the production of superimposed layers, resulting in a coating, in particular a surface coating, composed of several distinct layers. In such a case, these layers may be produced by the same embodiment variant among the variants explained above, or by different embodiment variants. In addition, these layers may be in the same material, said second material, or in different materials, said second material, then another material, etc.

[0042] In all cases, the second step makes it possible to form at least one layer of a very hard coating, which can represent the surface coating alone, or alternatively which can cover a less hard intermediate layer, for example resilient, and / or alternatively which can be covered by a thin decorative layer.

[0043] In all cases, the second step makes it possible to produce at least a part of the coating which advantageously achieves high hardness and / or great robustness, such as an inner or upper, or even intermediate, layer of the surface coating in the case of a multi-layer coating. Preferably, the hardest layer of the coating is on the outermost, and therefore most exposed, layer of the surface coating. Alternatively, the hardest layer may be coated with a decorative layer as described above, this decorative layer, preferably also very hard, being very thin and having little or no impact on the surface hardness of the coating.

[0044] Naturally, it is possible to combine the different embodiments described above to enable a component to be obtained, at least one first surface of which achieves a high hardness. For example, a first surface may be coated according to one of these variants and a second surface may be coated according to another of these variants.

[0045] In particular, it is thus possible to obtain a component, in particular a watch component, in particular a case middle or a case, the outer surface of which is coated with at least one relatively dense and advantageously hard layer of a coating, in particular a hard coating obtained for example by thermal spraying, or by any other variant described above, with the aim of making said lightweight component robust and optionally of protecting it.

[0046] Regardless of the embodiment variant, the manufacturing method may also include a step of filling the majority, or even all or almost all, of the pores of the porous core with a material, which may or may not be part of the surface coating. This material may be similar to or identical to the fourth material of the surface coating, mentioned in the third embodiment variant described previously, or be different. In such a case, we continue to define the porous core as the structure considered apart from its filling material.

[0047] In a first case in which the material filling the majority, or even all, or almost all of the pores of the porous core is similar or identical to the fourth material of the surface coating according to the third embodiment variant, the filling step may correspond to or form an initial sub-step of the preliminary sub-step of the second deposition step of the process.

[0048] In the second case in which the material filling the majority, or even all, or almost all of the pores of the porous core is different, the filling step can form a separate intermediate step complementary to the second step of depositing a surface coating.

[0049] Thus, the watch component may, for example, comprise a porous core whose pores are all or almost all filled with a resilient material, and comprise a surface coated with a distinct material, for example dense and hard. Advantageously, such a pore-filling step makes it possible to propose a component according to the invention which is in particular provided with a core comprising a material making it possible to dissipate shocks and thus to best preserve the skeleton formed by the porous core.

[0050] As a note, the adhesion between the porous core and the surface coating is obtained by a natural mechanical adhesion resulting from the manufacturing process. Regardless of the embodiment variant, the manufacturing process advantageously makes it possible to create a transition zone at the interface between the porous core and the surface coating, which comprises the respective materials of the porous core and the surface coating nested together, to optimize the adhesion of the surface coating. Advantageously, this transition zone has a thickness greater than or equal to 50 μm.

[0051] According to an advantageous embodiment variant, the structure of the porous core, in particular at the level of its external surface intended to receive the surface coating, is shaped to optimize this adhesion. For this, it can include pores whose dimensions are substantially the same as those of particles projected during the production of the surface coating, or even have a solid surface, devoid of pores, or having very few pores.

[0052] In this regard, the manufacturing method may implement an optional intermediate step, of mechanical or thermal treatment or intermediate laser, the function of which is to densify the surface of the porous core, in particular by closing at least part of the pores on the surface of the porous core. This may for example be a sandblasting operation or using a laser, in particular a picosecond or femtosecond laser. Another intermediate treatment intended to promote good mechanical adhesion of the surface coating may consist of increasing the surface roughness of the porous core, which will allow the particles of the coating to anchor themselves in the surface irregularities. Yet another intermediate treatment may consist of cleaning or washing or plasma treatment or deposition of an adhesion promoter.More generally, the intermediate step can be provided to improve or control the surface of the porous core, in particular to optimize the adhesion between the porous core and the surface coating.

[0053] The manufacturing process can then include additional, optional treatments.

[0054] In particular, the method may implement an optional finishing step, in particular acting on the surface condition and / or the color of at least one coating layer, to give it a particular aesthetic appearance and optimize its final geometry, for example by erasing any surface defects. Such a step may also confer a particular functionality to the layer or to one of the coating layers. Such a step may be a step of rectification and / or laser texturing and / or polishing and / or micro-blasting and / or termination and / or decoration and / or coloring. It may be implemented mechanically and / or electrochemically and / or by optical means, for example by a picosecond or femtosecond laser. Different techniques may thus be combined in order to implement this finishing step.It thus makes it possible, for example, to obtain a component with a final surface condition such as textured, polished, sandblasted or satin, and / or with a specific color, or a combination of these conditions. This step can be carried out on the last of the deposited layers, but also in an intermediate manner on any of the layers constituting the surface coating, in the case where this surface coating comprises several layers.

[0055] Figures 3a and 3b illustrate the application of the first step of the manufacturing method according to the invention in the context of particular examples of manufacturing a case for a wristwatch. Figures 3a and 3b thus illustrate the porous core of a watch case, resulting from the first step of the method, according to two embodiment variants. In both cases, this porous core is produced by additive manufacturing in a first material which is titanium, in a mesh structure having mesh dimensions of 500 μm (Figure 3a) and 200 μm (Figure 3b) respectively. The corresponding porosity rate is 70% and 48% respectively. The density is 1.6 g / cm respectively. 3 and 2.3 g / cm 3. As a side note, alternatively, the first material used could be magnesium Mg or aluminum Al or an Mg-based alloy or an AI-based alloy or a Ti-based alloy, replacing titanium, so as to obtain a porous core of the same structure even lighter. Indeed, with a Mg alloy with a density of 1.7 g / cm 3 and a porosity of about 50%, it is possible to obtain an apparent density of the porous core of 0.80 - 0.85 g / cm 3 . It is also possible to consider the use of precious alloys based on gold Au, or palladium Pd, or platinum Pt, to obtain a precious metal component with a density significantly lower than that of the solid alloy. In addition, it is also possible to consider the use of a ceramic, such as zirconia, to obtain a ceramic component with a density significantly lower than that of said ceramic.

[0056] Figure 5 illustrates in a sectional view an exemplary embodiment of a watch component according to the invention. In this example, the porous core is made of AISi7Mg alloy foam produced by casting and infiltration of the liquid alloy into a porous substrate which is then removed. The resulting porous core has a density of 1.1 g / cm 3 and a porosity of around 60%, a hardness of 70 HB and a pore size between 0.20 and 0.35 mm in diameter. The surface coating is formed by thermal spraying in a second material which is tungsten carbide WC and cobalt-chromium CoCr. The coating forms a layer of tungsten carbide WC and cobalt-chromium CoCr with a thickness of 500 μm, which is then ground to obtain a continuous surface. The measured surface hardness is 900 HV. The density of the resulting watch component is 1.7 g / cm 3, which is remarkably low considering the strength of the sample and the hardness of the surface. The section shown in Figure 5 illustrates the porous core and the coating well: a typical penetration of the projected particles of the surface coating of the order of a hundred pm is measured in the metal foam forming the porous core, at a transition zone between the two parts of the watch component, and the presence of a continuous and dense layer of tungsten carbide WC and cobalt-chromium CoCr on the surface is clearly observed.

[0057] The invention relates more generally to a component, in particular a watch component, obtained by a manufacturing method according to the invention, which is naturally not limited to the preceding description.

[0058] Thus, the invention makes it possible to form any component, in particular any watch component, comprising a porous core comprising a first material, the porous core having a density less than or equal to 80%, or even less than or equal to 60%, or even less than or equal to 50%, of the density of the first solid material, and comprising a surface coating comprising at least one layer of density greater than the density of the porous core.

[0059] Said at least one layer of the surface coating comprises a second material, which may be identical to or different from the first material. In particular, it is advantageous to choose materials of different densities, the first solid material having, for example, a lower density than that of the second solid material. By density of a solid material, we mean here its bulk volume density, in other words its density.

[0060] The method described above has the advantage of being compatible with a large number of materials. For example, the first material of the porous core may be a metal or a metal alloy or a metal superalloy, in particular comprising one or more elements from among Fe, Mg, Al, Ti, Au, Pd, Pt, Ni, Si, and / or Co. This first material may also be an amorphous or partially amorphous alloy, or be a ceramic, for example an alumina- or zirconia-based ceramic. In addition, the second material of the surface coating may be ceramic-based, i.e. comprise at least 50% by weight of ceramic, or be an oxide, or be a metal or a metal alloy. The ceramic or a ceramic-based material is advantageous in that it makes it possible to achieve high hardness and suitable aesthetics, in particular a particular color.Furthermore, the second material can optionally be loaded with pigments, luminescent material or other functional material.

[0061] The surface coating is advantageously designed in particular to have a high hardness or to include a high hardness layer, as described above. It may thus have a surface hardness greater than or equal to 500HV, or even greater than or equal to 600HV, or even greater than or equal to 900HV. Alternatively or in addition, the surface coating is designed in particular to have an attractive shade, in particular a color or an effect which cannot be achieved by the first material.

[0062] Finally, it may have a high density. Thus, it comprises a layer or consists of a layer of a second material whose density is advantageously greater than or equal to 90%, or even greater than or equal to 99% of the density of the second solid material. In other words, the surface coating comprises at least one layer, that is to say consists of a single layer or comprises several distinct layers superimposed. In addition, the at least one layer comprises a second material, as described above, and preferably consists of this second material.

[0063] Thus, advantageously, the surface coating or a layer of the surface coating may have a porosity rate less than or equal to 0.5%, or even less than or equal to 0.1%, or even less than or equal to 0.05%, or even less than or equal to 0.01%. As a note, the porosity rate has both aesthetic and functional consequences. Depending on the size of the defects resulting from the porosity, a polished surface will, for example, highlight the porosity, which may manifest itself by an irregularity in the reflection of the light fringe. In addition, the porosity may impair the functionality of the deposit and make it permeable, therefore ineffective as a protective barrier (thermal, chemical, etc.). It is therefore advantageous to obtain a surface coating deposit with the lowest possible porosity.

[0064] Furthermore, the surface coating has a sufficient thickness to contribute to the robustness of the finished component or comprises a layer whose thickness is sufficient to contribute to the robustness of the finished component. Advantageously, this thickness is between 20 and 500 pm, or even between 70 and 350 pm, on the finished component after the coating has undergone a possible treatment. The step of depositing the at least one layer of the surface coating may deposit the at least one layer having a thickness greater than or equal to 20 pm, or even greater than 100 pm, or even greater than 250 pm, or even greater than or equal to 300 pm, or even greater than or equal to 350 pm. Advantageously, this thickness is less than or equal to 1.5 mm, so as not to overly complicate the manufacturing process, and to limit the risk of obtaining excessively high porosity of the surface coating. In addition, this surface coating can have a textured, polished, sandblasted or satin surface finish.After such a surface treatment, the resulting thickness of the surface coating is naturally less than that deposited: for example, in the case of a deposit with a thickness of between 150 and 500 μm, polishing by mechanical means or laser texturing treatment can reduce this final thickness to approximately 80 μm. As mentioned, the manufacturing method advantageously makes it possible to create a transition zone at the interface between the porous core and the surface coating which comprises said two interlocking materials, to optimize the adhesion of the surface coating. Advantageously, this transition zone has a thickness greater than or equal to 50 μm.

[0065] The invention is particularly suitable for any component, in particular any watchmaking component, in particular any exterior component, such as a component in the form of a watch case or a bracelet.

[0066] Furthermore, according to a particular variation of the invention, at least one portion or region of the component, in particular of the watch component, could comprise a porous core comprising a surface coating according to the invention, the remainder of the component being able to comprise any other architecture, in particular conventional. Thus, the invention also relates to a watch component which comprises a partially porous core, that is to say a core porous only in certain portions, or several porous cores connected to each other by one or more non-porous portions. Alternatively, the watch component could comprise a core consisting of several different porous portions, by the structure of their porosity and / or by the material(s) thereof. In all cases, the watch component therefore comprises at least one porous core. In other words, the core of the watch component may be wholly or partly composed of said at least one porous core.

[0067] By way of example, Figures 4a and 4b represent a caseband blank 1 provided with portions forming porous cores capable of being coated with a surface coating. These portions may for example prefigure flanks 2 or horns 3 of a caseband. These portions may for example be connected to each other by solid portions 4. These porous cores comprise a first material or are based on a first material, with a density less than or equal to 80%, or even less than or equal to 60%, or even less than or equal to 50%, of the density of the first solid material, and at least one layer of the surface coating, not shown, capable of being deposited or sprayed has a density greater than the density of the porous cores. As a note, the porous cores of these embodiments according to Figures 4a and 4b comprise solid, non-porous edges 5, to form reinforced zones at highly stressed or exposed locations.

[0068] The invention also relates to a timepiece, in particular a wristwatch, which comprises at least one such timepiece component.

[0069] Finally, the invention therefore makes it possible to combine two major objectives for a component, in particular a watch component, which were not achieved until now. It makes it possible to obtain both a lightweight component and a mechanically robust component, having a surface layer that is advantageously hard, resistant and thick, while being aesthetically attractive. By depositing a dense coating, in particular by spraying, a hard and thick surface coating is obtained, having a long-lasting aesthetic, and with great flexibility in the chemistry of the coating. It is also possible to functionalize the coating, for example using laser texturing, and / or to obtain surface conditions and finishes such as sandblasted, satin, or polished. Tests show that it is possible to obtain a watch component, in particular a case middle or a bracelet, with an average or overall density of 2 g / cm 3 and a surface hardness of around 1000 HV.

[0070] The invention has been described in the context of a watch component. However, it appears that it could be implemented in any other field, for example automotive, aeronautics, space, medical, etc., for which it is useful to have light and robust components.

[0071] Alternatively, the invention may consist of providing a component comprising a porous core, very light, but robust or resistant, covered by a surface coating comprising at least one layer comprising a resilient material, which provides it, for example, with an impact resistance property. According to an advantageous variant, the coating provides in particular robustness to the component, in particular with respect to environmental conditions. The result is thus a component for which no compromise is necessary, since it combines both the maximum possible lightness with high impact resistance, and even optionally high resistance to environmental stresses, in particular high resistance to corrosion and / or scratches. In addition, advantageously, the surface condition of the surface coating is such that it has a very attractive appearance.

[0072] In this case, by "resilient material" we mean a material capable of absorbing a given amount of energy when it deforms under the effect of an impact. In other words, a resilient material is capable of overcoming alterations caused by one or more disruptive elements such as one or more impacts, to return to its initial state. Thus, a resilient material has significant impact resistance.

[0073] A manufacturing process according to this variant of a component, in particular a watch component, will now be detailed.

[0074] In this variant, the method comprises a second step of depositing a surface coating comprising at least one layer comprising a resilient material, such as a polymer material, in particular an elastomer such as a thermoplastic elastomer (TPE) or a fluoroelastomer (FKM, FFKM or FEPM), or a natural rubber (NR) or synthetic rubber (SBR, HNBR, EPDM), or a vinyl methylsilicone (VMQ) or a fluorosilicone (FVMQ). Alternatively, it may be a thermosetting elastomer. This resilient material has the advantage of providing the component with an impact resistance property. Furthermore, this material can provide the component with good resistance to environmental stresses. According to a first embodiment variant, the second step comprises a step of depositing at least one layer comprising a resilient material by implementing an overmolding method, to overmold the at least one layer comprising said resilient material onto the porous core.In such an embodiment of at least one layer based on a polymer material, or any resilient material, the at least one surface coating layer may therefore be produced by an overmolding process, to overmold such a material as a polymer, in particular an elastomer such as a thermoplastic elastomer (TPE) or a fluoroelastomer (FKM, FFKM or FEPM), or a natural rubber (NR) or synthetic rubber (SBR, HNBR, EPDM), or a vinyl methylsilicone (VMQ) or a fluorosilicone (FVMQ). Alternatively, it may be a thermosetting elastomer.

[0075] According to other variants, the second step may comprise at least one additional sub-step of depositing another layer of the surface coating made of or comprising a material different from the resilient material.

[0076] Thus, according to a second variant, the second step comprises a preliminary sub-step of depositing a hard layer on the surface of the porous core. Note that this sub-step may only concern part of the surfaces of the porous core.

[0077] In this second embodiment, the second step comprises the prior deposition of at least one other layer by thermal spraying, in particular at high temperature, which may be greater than or equal to 800°C. Such a technique, for example, implements the spraying at high temperature, for example at 900°C, of ​​fine particles, such as for example particles of tungsten carbide WC and cobalt-chromium CoCr (the cobalt-chromium CoCr acting within the coating as a binder between the WC particles), with WC particles which may have an average diameter of 40 μm, or even a smaller average diameter. To minimize the porosity of the coating, the particle size of the powders is important and must be adjusted for each layer composition and each application, as is known to those skilled in the art. The use of particles with a bimodal or multimodal size distribution is particularly favorable.Alternatively, other binders could be considered such as iron-chromium (Fe-Cr). As a note, in the examples mentioned above, the surface coating therefore comprises particles of a given material, such as for example tungsten carbide WC, and particles of another material, such as for example cobalt-chromium CoCr, which fulfill the function of binder. This other material remains optional, the binder not being essential.Thermal projection could for example be of the plasma type (known by its acronym VPS for the English term "Vacuum Plasma Spraying"), which has many advantages, such as allowing adjustment of the chemistry of the material, being able to project many different materials, such as ceramics, oxides, metals, and allowing obtaining a thick layer, in particular with a thickness greater than or equal to 20 pm, or even greater than or equal to 100 pm, or even greater than or equal to 250 pm, or even greater than or equal to 300 pm, or even greater than or equal to 350 pm.

[0078] Alternatively, other spraying or deposition techniques are possible. In particular, electrolytic arc anodizing can be used. Cold spray is also possible. The spraying technique will be adapted to the materials used.

[0079] At the end of the preliminary sub-step of depositing a hard layer on the surface of the porous core, a sub-step implementing an overmolding method for overmolding at least one layer comprising a resilient material can then be implemented. Note that this sub-step makes it possible to coat a hard layer previously deposited on the porous core with a layer comprising a resilient material, or to coat a portion of the surface of the porous core and at least a portion of a hard layer previously deposited on the porous core with a layer comprising a resilient material. This results in a component comprising at least one resilient layer and at least one hard layer. According to a third variant, the second step comprises a subsequent sub-step of depositing a hard layer on the surface of a layer comprising a resilient material. Note that this sub-step may only concern a portion of the surfaces of said layer.

[0080] According to such a third variant, a cold dynamic projection technique could for example be favored in order to guarantee the integrity of the resilient layer previously obtained during the sub-step implementing a process of overmolding a layer comprising a resilient material.

[0081] As a note, this sub-step makes it possible to coat with a hard layer a layer comprising a resilient material previously deposited on the porous core, or to coat with a hard layer a portion of the surface of the porous core and at least a portion of a layer comprising a resilient material previously deposited on the porous core. This results in a component comprising a surface coating comprising at least one resilient layer and at least one hard layer.

[0082] Optionally, a decorative layer may be deposited on such a hard layer so as to produce a particular appearance or color. Such a decorative layer may for example be deposited by a physical vapor deposition PVD, or chemical vapor deposition CVD, or atomic layer deposition ALD process. It may for example be a layer of a metal or a metal alloy, for example of the Au, Ag, Pt, Pd type, with a thickness preferably between 500 nm and 20 μm.

[0083] In all cases, the second step comprises at least one sub-step making it possible to produce at least one layer comprising a resilient material, such as an inner or upper, or even intermediate, layer of the surface coating, in the case of a multi-layer coating. Naturally, it is possible to combine the different embodiment variants described above to make it possible to obtain a watch component of which at least a first surface achieves high resilience, and optionally high resistance to environmental stresses. For example, a first surface, for example an outer or inner surface, can be coated according to one of these variants and a second surface, for example an inner or outer surface, can be coated according to another of these variants.

[0084] In particular, it is thus possible to obtain a watch component, in particular a case middle or a case, one surface of a porous core of which is coated with a resilient layer of a surface coating, with the aim of protecting the component(s) likely to come into interaction with said case middle or case, and another surface of which is formed by a hard layer of the surface coating, with the aim of best preserving said case middle or case from interactions with the external environment, in particular from shocks.Alternatively, it is also possible to obtain a watch component, in particular a case middle or a case, one surface of a porous core of which is coated with a hard layer of a surface coating, with the aim of facilitating the assembly of the component(s) on said case middle or case, and another surface of which is formed by a resilient layer of the surface coating, in order to provide high resistance to environmental stresses and thus to best preserve said case middle or case.

[0085] Regardless of the embodiment variant, the manufacturing method advantageously makes it possible to create a transition zone at the interface between the porous core and the surface coating or a layer of the surface coating, which comprises the respective materials of the porous core and the interlocking surface coating, to optimize the adhesion of the surface coating or a layer of the surface coating. Advantageously, this transition zone has a thickness greater than or equal to 50 μm. Regardless of the embodiment variant, the manufacturing method may also comprise a step of filling the majority, or even all or almost all, of the pores of the porous core with a material, which may or may not belong to the surface coating. This material may advantageously be similar or identical to the resilient material of a layer of the surface coating, or be different.In such a case, we continue to define the porous core as the structure considered outside its filling material.

[0086] In a first case in which the material filling the majority, or even all, or almost all of the pores of the porous core is similar or identical to the material of a layer of the coating formed on the surface of the porous core, the filling step may correspond to or form an initial sub-step of the second step of depositing a surface coating. In particular, the resilient material of a layer deposited on the surface of the porous core may correspond to the material filling the majority, or even all, or almost all of the pores of the porous core.

[0087] In the second case in which the material filling the majority, or even all, or almost all of the pores of the porous core is different from the material of a layer of the coating formed on the surface of the porous core, the filling step may form a separate intermediate step complementary to the second step of depositing a surface coating. The majority of the pores may be filled with a given material, while the pores of the porous core near the coated surface of the porous core are within the transition zone, which may have a thickness greater than or equal to 50 μm.Thus, the watch component may for example comprise a porous core whose pores are all or almost all filled with a resilient material, and comprise a surface coated with at least one layer of the same resilient material or another resilient material, optionally supplemented by another layer comprising or consisting of a dense and hard material. Advantageously, such a pore filling step makes it possible to propose a component which is further provided with a core comprising a material making it possible to dissipate shocks and thus to best preserve the skeleton formed by the porous core.

[0088] Thus, the second step of depositing a surface coating may comprise several sub-steps of producing a deposit of a coating, that is to say it may comprise the production of superimposed layers, resulting in a coating, in particular a surface coating, composed of several distinct layers. In such a case, these layers may be produced by the same embodiment variant among the variants explained above, or by different embodiment variants. In addition, these layers may be in the same material, or in different materials.

[0089] An advantage of this surface coating is that it allows the formation of a resilient surface layer, which meets the high demands of luxury watchmaking.

[0090] Thus, in all cases, the second surface coating step makes it possible to form at least one resilient layer, which may represent the surface coating alone, or alternatively which may be combined with a harder layer, and / or alternatively which may be covered by a thin decorative layer. In the last two variants, the second step of producing the surface coating thus comprises two distinct sub-steps, making it possible to deposit distinct and complementary materials. In all cases, the surface coating has high resilience via a layer comprising or based on or consisting of a resilient material.

[0091] As a note, the adhesion between the porous core and the surface coating is obtained by a natural mechanical adhesion resulting from the manufacturing process. According to an advantageous embodiment variant, the structure of the porous core, in particular at the level of its external surface intended to receive the surface coating, is shaped to optimize this adhesion. For this, it can include small pores, or even can have a solid surface, devoid of pores, or having very few pores.

[0092] With this in mind, the manufacturing method may implement an optional intermediate step of mechanical or thermal treatment or intermediate laser, the function of which is to densify the surface of the porous core, in particular by closing at least part of the pores on the surface of the porous core. This may for example be a sandblasting operation or using a laser, in particular a picosecond or femtosecond laser. Another intermediate treatment intended to promote good mechanical adhesion of the surface coating may consist of increasing the surface roughness of the porous core, which will allow the particles of the coating to anchor themselves in the surface irregularities. Yet another intermediate treatment may consist of cleaning or washing or a plasma treatment or deposition of an adhesion promoter.More generally, the intermediate step can be provided to improve or control the surface of the porous core, in particular to optimize the adhesion between the porous core and the surface coating.

[0093] The manufacturing process can then include additional, optional treatments.

[0094] In particular, the method may implement an optional finishing step, in particular acting on the surface condition and / or the color of at least one layer of the coating, to give it a particular aesthetic appearance and optimize its final geometry, for example by erasing any surface defects. Such a step may also confer a particular functionality to the layer or one of the layers of the coating. Such a step may be a step of rectification and / or laser texturing and / or polishing and / or micro-blasting and / or termination and / or decoration and / or coloring, provided that this step is compatible with the layer or the material forming the layer of the coating. It may be implemented mechanically and / or electrochemically and / or by optical means, for example by a picosecond or femtosecond laser.Different techniques can thus be combined to implement this finishing step. It allows, for example, to obtain a component with a final surface condition such as textured, polished, sandblasted or satin, and / or with a specific color, or a combination of these conditions. This step can be carried out on the last of the deposited layers, but also in an intermediate manner on any of the layers constituting the surface coating, in the case where this surface coating comprises several layers.

[0095] In a particular example of a component, the porous core is made of AISi7Mg alloy foam made by casting and infiltrating the liquid alloy into a porous substrate which is then removed. The resulting porous core has a density of 1.1 g / cm 3and a porosity of around 60%, a hardness of 70 HB and a pore size between 0.20 and 0.35 mm in diameter. The surface coating is formed by overmolding a layer of a 0.5 mm thick surface coating of FKM.

[0096] Thus, this variant makes it possible to form any component, in particular any watch component, comprising a porous core comprising a first material, the porous core showing a density less than or equal to 80%, or even less than or equal to 60%, or even less than or equal to 50%, of the density of the first solid material, and comprising a surface coating, comprising at least one layer comprising a resilient material or consisting of a resilient material, such as a polymer material, at least directly or indirectly arranged on the surface of the porous core.

[0097] The method described above has the advantage of being compatible with a large number of materials. For example, the first material of the porous core may be a metal or a metal alloy or a metal superalloy, in particular comprising one or more elements from Fe, Mg, Al, Ti, Au, Pd, Pt, Ni, Si, and / or Co. This first material may also be an amorphous or partially amorphous alloy, or a ceramic, for example based on alumina or zirconia. In addition, the material of a layer of the surface coating is resilient. This resilient material may be, for example, a polymer, in particular a thermoplastic elastomer (TPE) or a fluoroelastomer (FKM, FFKM or FEPM), or a natural rubber (NR) or synthetic rubber (SBR, HNBR, EPDM), or a vinyl methylsilicone (VMQ) or a fluorosilicone (FVMQ). Alternatively, it can be a thermosetting elastomer.This surface coating may optionally comprise a layer of another ceramic-based material, i.e. comprising at least 50% by weight of ceramic, or being an oxide, or being a metal or a metal alloy. The ceramic or a ceramic-based material is advantageous in that it allows for high hardness and suitable aesthetics, including a particular color. Furthermore, a material of a coating layer may optionally be loaded with pigments, luminescent material or other functional material.

[0098] In particular, the surface coating is intended to have an attractive tint, in particular a color or effect that cannot be achieved by the first material.

[0099] Finally, it may optionally have a high density. Thus, it comprises or consists of a given material, and its density is in particular greater than or equal to 90%, or even greater than or equal to 99% of the density of the given solid material.

[0100] Thus, advantageously, the surface coating or a layer of the surface coating may have a porosity rate of less than or equal to 0.5%, or even less than or equal to 0.1%, or even less than or equal to 0.05%, or even less than or equal to 0.01%. As a note, the porosity rate has both aesthetic and functional consequences. Depending on the size of the defects resulting from the porosity, the porosity may impair the functionality of the deposit and make it permeable, and therefore ineffective as a protective barrier (thermal, chemical, etc.). It is therefore advantageous to obtain a surface coating deposit having the lowest possible porosity. Furthermore, the surface coating has a sufficient thickness to ensure the shock resistance of the finished watch component or comprises a layer whose thickness is sufficient to ensure the shock resistance of the finished watch component.Advantageously, this thickness is between 20 and 500 pm, or even between 70 and 350 pm on the finished watch component after the coating has undergone a possible treatment. The step of depositing at least one layer comprising a resilient material of a surface coating can deposit the at least one layer having a thickness greater than or equal to 20 pm, or even greater than 100 pm, or even greater than 250 pm, or even greater than or equal to 300 pm, or even greater than or equal to 350 pm. Advantageously, this thickness is less than or equal to 1.5 mm. In addition, this surface coating can have a textured, polished, sandblasted or satin surface state.

[0101] Ultimately, this variant therefore makes it possible to combine two major objectives for a component, in particular a watch component for exterior use, which were not previously achieved. It makes it possible to obtain both a lightweight component and a mechanically robust component, with a resilient, shock-resistant surface layer, while being aesthetically attractive and resistant to environmental stresses. It is also possible to functionalize the coating, for example using laser texturing, and / or to obtain surface conditions and finishes such as sandblasted, satin-finished, or polished.

[0102] The variant therefore relates to a component, in particular a watch component, characterized in that it comprises at least one porous core, comprising a first material or based on a first material, with a density less than or equal to 80%, or even less than or equal to 60%, or even less than or equal to 50%, of the density of the first solid material, and in that it comprises a surface coating comprising at least one layer comprising a resilient material, such as a polymer material. The resilient material of the at least one layer of the surface coating may be an elastomer such as a thermoplastic elastomer (TPE) or a fluoroelastomer (FKM, FFKM or FEPM), or a natural rubber (NR) or synthetic rubber (SBR, HNBR, EPDM), or a vinyl methylsilicone (VMQ) or a fluorosilicone (FVMQ).

[0103] The at least one layer of the surface covering or the surface covering may be present entirely in said resilient material.

[0104] The at least one layer of the surface coating may have a porosity rate of less than or equal to 0.5%, or even less than or equal to 0.1%, or even less than or equal to 0.05%, or even less than or equal to 0.01%. The resilient material of the at least one layer of the surface coating may be different from the first material and / or occupies all or part of the pores of the at least one porous core.

[0105] The at least one porous core may be in metallic foam or be a skeleton formed by a regular or irregular porous network, in particular of the lattice, TPMS, alveolar, cellular, or even trabecular type.

[0106] The first material of the at least one porous core may be a metal or a metal alloy or a metal superalloy, in particular comprising elements such as Fe, Mg, Al, Ti, Au, Pd, Pt, Ni, Si, and / or Co, and / or be an amorphous or partially amorphous alloy, or is a ceramic, in particular an alumina or zirconia-based ceramic.

[0107] The surface coating or the at least one layer of the surface coating may have a thickness of between 20 and 500 μm, or even between 70 and 350 μm, and / or may have a textured, polished, sandblasted or satin surface finish. The at least one porous core may have a non-homogeneous porosity, and / or have a porosity at its surface that is less than its porosity towards its center, and / or have pores at its surface that are smaller than the pores towards its center or may comprise a surface free of pores.

[0108] The component may be a watchmaking component, such as a component of a watch case or a bracelet.

[0109] The variant relates to a method of manufacturing a component, in particular a watch component, characterized in that it comprises the following steps:

[0110] Production of at least one porous core, comprising a first material or based on a first material, with a density less than or equal to 80%, or even less than or equal to 60%, or even less than or equal to 50%, of the density of the first solid material;

[0111] Deposition of at least one layer comprising a resilient material of a surface coating on the at least one porous core.

[0112] The step of producing at least one porous core may comprise a step of chemical attack of a solid blank in the first material or based on the first material or an additive manufacturing step, forming at least one porous core in metal foam or in the form of a skeleton formed by a regular or irregular porous network, in particular of the lattice, TPMS, alveolar, cellular, or even trabecular type.

[0113] The step of depositing at least one layer comprising a resilient material of a surface coating can be carried out by overmolding or be carried out by additive manufacturing.

[0114] The step of depositing at least one layer comprising a resilient material of a surface coating may deposit the at least one layer having a thickness greater than or equal to 20 pm, or even greater than 100 pm, or even greater than 250 pm, or even greater than or equal to 300 pm, or even greater than or equal to 350 pm and / or less than or equal to 1.5 mm.

[0115] The manufacturing process of a component may include a final step of texturing and / or grinding and / or polishing and / or micro-blasting and / or decoration, to obtain a final surface condition of the textured, polished, sandblasted or satin type of the surface coating.

Claims

CLAIMS 1. Component, in particular a watch component, characterized in that it comprises at least one porous core, comprising a first material or based on a first material, with a density less than or equal to 80%, or even less than or equal to 60%, or even less than or equal to 50%, of the density of the first solid material, and in that it comprises a surface coating comprising at least one layer of density greater than the density of the at least one porous core, the at least one layer of the surface coating having a surface hardness greater than or equal to 500HV and the at least one layer of the surface coating comprising a second material based on ceramic, or which is an oxide, or which is a combination of a ceramic and a metal or metal alloy.

2. Component according to the preceding claim, characterized in that the at least one layer of the surface coating has a surface hardness greater than or equal to 600HV, or even greater than or equal to 900HV.

3. Component according to one of the preceding claims, characterized in that the at least one layer of the surface coating comprises a second material different from the first material, in particular the first material having a lower density than that of the second material.

4. Component according to the preceding claim, characterized in that the at least one layer of the surface coating has a porosity rate less than or equal to 0.5%, or even less than or equal to 0.1%, or even less than or equal to 0.05%, or even less than or equal to 0.01% and / or a density greater than or equal to 90%, or even greater than or equal to 99% of the density of the second solid material.

5. Component according to one of the preceding claims, characterized in that the surface coating is integrally formed by said at least one layer, which has a hardness greater than or equal to 500HV, or in that said at least one layer covers a less hard intermediate layer, in particular made of resilient material, and / or in that said at least one layer is covered by a thin decorative layer, in particular having a thickness of between 500 nm and 20 pm, of a metal or a metal alloy.

6. Component according to one of the preceding claims, characterized in that the at least one porous core is in metal foam or is a skeleton formed by a regular or irregular porous network, in particular of the lattice, TPMS, alveolar, cellular, or even trabecular type.

7. Component according to the preceding claim, characterized in that the first material of the at least one porous core is a metal or a metal alloy or a metal superalloy, in particular comprising elements such as Fe, Mg, Al, Ti, Au, Pd, Pt, Ni, Si, and / or Co, and / or is an amorphous or partially amorphous alloy, or is a ceramic, in particular a ceramic based on alumina or zirconia.

8. Component according to one of the preceding claims, characterized in that the surface coating or the at least one layer of the surface coating has a thickness of between 20 and 500 pm, or even between 70 and 350 pm, and / or has a textured, polished, sandblasted or satin surface finish.

9. Component according to one of the preceding claims, characterized in that the at least one porous core has a non-homogeneous porosity, and / or has a porosity at its surface less than its porosity towards its center, and / or has pores at its surface of dimensions smaller than those of the pores towards its center or comprises a surface devoid of pores.

10. Component according to one of the preceding claims, characterized in that it is a watch exterior component, such as a component in the form of a watch case or a bracelet.

11. Timepiece, characterized in that it comprises at least one component according to one of the preceding claims.

12. Method of manufacturing a component, in particular a watch component, characterized in that it comprises the following steps: Production of at least one porous core, comprising a first material or based on a first material, with a density less than or equal to 80%, or even less than or equal to 60%, or even less than or equal to 50%, of the density of the first solid material; Deposition of at least one layer of a surface coating of density greater than the density of the at least one porous core, the at least one layer of the surface coating having a surface hardness greater than or equal to 500HV and the at least one layer of the surface coating comprising a second material based on ceramic, or which is an oxide, or which is a combination of a ceramic and a metal or metal alloy.

13. Method of manufacturing a component according to the preceding claim, characterized in that the step of producing at least one porous core comprises a step of chemical attack of a solid blank in the first material or based on the first material or an additive manufacturing step, forming at least one porous core in metal foam or in the form of a skeleton formed by a regular or irregular porous network, in particular of the lattice, TPMS, alveolar, cellular, or even trabecular type.

14. Method of manufacturing a component according to claim 12 or 13, characterized in that the step of depositing the at least one layer of the surface coating is carried out by thermal spraying, in particular at a high temperature greater than or equal to 800°C or at a low temperature.

15. Method for manufacturing a component according to one of claims 12 to 14, characterized in that the step of depositing the at least one layer of the surface coating deposits the at least one layer having a thickness greater than or equal to 20 pm, or even greater than 100 pm, or even greater than 250 pm, or even greater than or equal to 300 pm, or even greater than or equal to 350 pm and / or less than or equal to 1.5 mm.

16. Method of manufacturing a component according to one of claims 12 to 15, characterized in that it comprises a final step of texturing and / or grinding and / or polishing and / or micro-blasting and / or decoration, to obtain a final surface condition of the polished, sandblasted or satin type of the surface coating.

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