Micromechanical functional component with a friction coating

Abstract

The invention relates to a micromechanical functional assembly comprising at least one first component, which is formed from a first substrate which is covered on top by a first functional surface, which is intended for frictional contact with a second functional surface, which belongs to the first component or to at least one second component, which is formed from a second substrate which is covered on top by a second functional surface, which, together with the first component, forms the functional assembly, the first functional surface and the second functional surface being formed from a first layer, which is formed integrally with the first substrate and the second substrate or which is different from the first substrate and the second substrate, the first layer comprising ultrananocrystalline diamond, nanocrystalline diamond or microcrystalline diamond and being covered on top by a second layer which comprises S atoms and F atoms. The invention also relates to a method for functionalizing ultrananocrystalline diamond, nanocrystalline diamond or microcrystalline diamond.

Description

Technical Field

[0001] The present invention relates to a micromechanical functional assembly comprising at least one component having a friction contact surface requiring a friction coating. The micromechanical functional assembly more particularly relates to a pair of mechanically cooperating micromechanical timepiece components, such as an escape wheel and a pallet of an anchor escapement. Background Art

[0002] When the technology for producing diamond by chemical vapour deposition (CVD diamond) was first developed, great hopes were placed on tribology due to the intrinsic hardness of diamond. Unfortunately, dry friction between two diamond surfaces is tribologically unfeasible because it would lead to adhesion between the contacting watch parts. This is due to the formation of bonds between the carbon atoms (CC) of the two paired materials of the diamond-diamond pair. In order to minimize this adhesion effect, the diamond-diamond material pair must be exposed to an environment with a relative humidity (%RH) of at least 50%. The threshold of 50% RH makes it possible to provide droplets of water (H2O) on the contact surfaces. This reduces the tangential displacement force F of one surface relative to the other. T These droplets thus act as a local lubricant, thus facilitating the relative movement of the contacting watch parts. Below this threshold, the adhesion phenomenon intensifies and contact instabilities occur within short load times.

[0003] Therefore, under the conditions of moving contact (low normal force and high tangential force), the total friction coefficient CoF of the diamond-diamond pair may be lower than 0.2, such as Figure 1 Unfortunately, these environmental conditions do not guarantee tribological stability of the material pair beyond the 5-minute test period. In fact, tribological instability appears as early as 3.5 minutes into the test.

[0004] The challenge therefore involves using such diamond / diamond pairs in micromechanical functional components while guaranteeing stable tribological properties over extended periods of time in the absence of lubricants. Summary of the Invention

[0005] The present invention aims to overcome these disadvantages by modifying the tribological properties of the diamond layer. As explained above, hydrogen, oxygen, or humid atmospheres are difficult to maintain for extended periods. The present invention aims to replace the atomic OH or H passivation bonds caused by these environments with other molecules. According to the present invention, these extreme surface modifications, which alter the tribological properties, are achieved by functionalizing the diamond layer. More specifically, according to the present invention, the diamond layer is functionalized with sulfur and fluorine compounds.

[0006] The present invention therefore relates to a micromechanical functional assembly comprising at least one first component having a first functional surface intended for frictional contact with a second functional surface, the second functional surface belonging to the first component or to at least one second component, the second component together with the first component constituting the functional assembly, the functional assembly being characterized in that the first and second functional surfaces are formed by a first layer comprising ultrananodiamond, nanodiamond, or microcrystalline diamond, and a second layer covering the first layer, the second layer comprising S atoms and F atoms. It will be understood that the first layer may be made of the same material as the substrate constituting the first and second components, or may be made of a material different from the material constituting the substrate.

[0007] During testing, an improvement in the tribological properties of these functional surfaces was observed. This improvement can be attributed to the sulfur, which prevents the formation of (CC) bonds when the relative humidity is no longer sufficient to prevent this. As a result, watch movements such as the Swiss anchor escapement can function without lubrication of the escape wheel / pallet contact, with performance at least equal to that of a standard reference.

[0008] This improvement in the tribological properties is particularly observed when the two functional surfaces in contact are coated with tribological layers of identical composition.

[0009] The present invention also relates to a method for functionalizing diamond by reactive ion etching. Reactive ion etching is commonly used for deep etching on silicon. The inventors have found that by using very low power (typically in the range of 30W to 70W) reactive ion etching equipment, it is possible to synthesize such S and F compounds on components such as watch components with small dimensions. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The objects, advantages and features will become apparent from the following drawings:

[0011] Figure 1 The total friction coefficient (CoF) of the non-lubricated microcrystalline diamond / microcrystalline diamond pair according to the prior art is shown at a relative humidity of 30%. (总) ) curves that change with time;

[0012] Figure 2 Schematically shows a cross section of a portion of two components of a functional assembly according to the invention;

[0013] Figure 3 is a partial view of a functional assembly comprising two parts, namely an escape wheel and an anchor pallet stone having contact surfaces functionalized according to the invention;

[0014] Figure 4 An electron microscope image showing the morphology of the second layer composed of S and F having a rod-like structure;

[0015] Figure 5a and 5b The friction results of a functional assembly comprising two components over a distance of 25 meters are shown respectively; Figure 5a In order to make a comparison not covered by the present invention, one component is coated with microcrystalline diamond MCD on its functional surface, and the other component is coated with microcrystalline diamond functionalized with SF6; Figure 5b In the embodiment of the present invention, both components are coated with SF6-functionalized microcrystalline diamond on their functional surfaces;

[0016] Figure 6 Shown Figure 5b The friction results of the pair over a longer distance of 2500 meters;

[0017] Figure 7a and 7b The amplitudes of the balance for a reference escape wheel / anchor pair and for an escape wheel / anchor pair according to the invention with a microcrystalline diamond layer functionalized with SF6 are shown, respectively;

[0018] Figure 8 is a schematic diagram of an apparatus for functionalizing diamond. DETAILED DESCRIPTION

[0019] The present invention relates to a functional component comprising at least one component that is subjected to friction on one or more of its surfaces, called functional surfaces or contact surfaces. The functional component according to the invention may comprise a single component having two functional surfaces intended to come into frictional contact. For example, in the field of horology, this may consist of a barrel strip formed by a strip, wherein one face of the strip is intended to come into contact with another face of the strip. Alternatively, the functional component may comprise at least two components, each comprising a functional surface intended to come into friction with a functional surface of the other component. For example, in the field of horology, the functional component 1 may comprise a first component 2 and a second component 3, the first component 2 being a pallet 4 of an anchor escapement fork 5 and the second component 3 being an escape wheel 6, such as Figure 3 As shown. More precisely, pallet 4 has a bearing plane A and an impulse plane B, which mate with a bearing plane C and an impulse plane D of a tooth 7 of escape wheel 6. These planes A, B, C, and D are highly stressed functional surfaces and are subject to high levels of friction and / or contact, which may require a friction layer according to the present invention to reduce friction. In another timepiece application, the first component may be a shaft of a moving part, and the second component may be a bearing. According to another application in this field, the first and second components may be teeth of a gear.

[0020] like Figure 2 As shown, the functional component 1 comprises a first part 2 and a second part 3 formed by a substrate 8, with at least a friction layer 9 on the functional surfaces 2a, 3a of the first and second parts. This layer 9 is formed by a first layer 9a composed of diamond, which can be UNCD (ultra-nano diamond), NCD (nano-diamond) or MCD (microcrystalline diamond). According to the invention, this first layer 9a is functionalized with a sulfur compound, more particularly with S and F, which forms a second layer 9b located on the first layer 9a. Advantageously, the first layer 9a is functionalized with SF6. Other gases such as SF2 and SF4 are also possible, although they are more dangerous and have more limited uses. Usually, as Figure 4 As shown, the S and F functionalized on the surface of the diamond layer are rod-shaped. The second layer composed of S and F generally has a non-constant thickness and is nanometer-sized, typically with an average thickness in the range of 2 to 50 nanometers, more particularly in the range of 5 to 10 nanometers. Suitable techniques for visualizing and chemically analyzing the second layer composed of S and F are, for example, X-ray photoelectron spectroscopy (XPS) or time-of-flight secondary ion mass spectrometry (TOF-SIMS). It should be noted that this layer is very thin and it may be difficult to accurately identify the compounds present. Therefore, reference is made to the layer comprising S and F.

[0021] According to the invention, the surfaces intended to come into contact are each covered with a diamond layer functionalized with S and F. The average thickness of the layer 9 comprising a first layer 9a of diamond and a second layer 9b of S and F is in the range of 800 nm to 1200 nm, preferably in the range of 900 nm to 1200 nm, being MCD, NCD or even UNCD diamond.

[0022] For example, the substrate may be selected from ceramic, silicon, silicon oxide, silicon nitride, carburized silicon and steel. The substrate and diamond layer may also form a single solid material. According to a preferred embodiment, the substrate is silicon with a microcrystalline diamond layer functionalized with S and F.

[0023] The method for functionalizing the diamond layer is as follows. If the substrate is not solid diamond, a diamond layer is previously deposited by chemical vapor deposition (CVD) or hot-filament technology. Sulfur and fluorine are then deposited as a second, ultrafine layer on the diamond layer using a very low-power reactive ion etching method (RIE), enabling deposition rather than etching. Figure 8 An apparatus 10 for functionalizing diamond using a plasma reactor 11 is outlined in . This may be, for example, of the "capacitively coupled" type.

[0024] The parameters of this method are as follows:

[0025] - a reactive gas 12 comprising S and F, such as SF6, SF4 or SF2, with a flow rate in the range of 3 seem (standard cubic centimeter per minute) or cm 3 .min -1 20 seem, preferably in the range of 5 seem to 10 seem,

[0026] - a radio frequency (RF) power in the range of 30 W to 70 W, preferably in the range of 40 W to 60 W,

[0027] - a pressure in the reactor in the range of 30 μbar to 150 μbar, preferably in the range of 80 μbar to 120 μbar,

[0028] - a reaction time in the range of 20 minutes to 120 minutes, preferably in the range of 30 minutes to 70 minutes.

[0029] The second functionalized layer obtained in this way has a very low thickness, of the order of a few nanometers, even if the reaction time is of the order of one hour.

[0030] Tests were carried out to evaluate the friction performance of the functional assembly according to the application.

[0031] The escapement wheel made of silicon and the escapement fork / escapement lever made of silicon are coated with microcrystalline diamond, which is functionalized with S and F and in particular with SF6. Thus, tests are carried out using a functionalized diamond / functionalized diamond pair and are compared with a standard anchor escapement with a ruby contact with lubricated steel. FEMTO-torque tests are used to measure the performance of a Swiss anchor escapement mounted on a workbench. The torque applied is 16 μN.m. Figure 7a and 7b The measurements of the amplitude of the balance (with 3 arms) of a standard anchor escapement and of an anchor escapement treated according to the application are shown respectively. For the standard anchor escapement, the average amplitude for one hour of test is 274°. For the anchor escapement treated according to the application, the average amplitude for one hour of test is 256°, which is 18° lower than for the standard anchor escapement. The regularity of the amplitude is very good, better than the standard reference version, apart from a temporary malfunction at 700 s.

[0032] In parallel, friction tests were also carried out over distances of 25 meters and 2500 meters using a ball / plane tribometer with a 2 mm diameter ball. The 25-meter test was carried out using a ball / plane pair, each of which had a Si substrate with a diamond layer functionalized with SF6 (SF6 / / SF6), and a comparison ball / plane pair, in which the ball was a Si substrate coated with unfunctionalized microcrystalline diamond and the plane was a Si substrate coated with microcrystalline diamond functionalized according to the present invention (MCD / / SF6). The purpose of these tests was to highlight the advantages of functionalizing both contact surfaces. The tests were carried out under a normal force of 10 mN, a sliding speed of 10 mm / s, and an amplitude of 4 mm. Figure 5a and 5b The dynamic friction coefficients of the comparative friction pair and the friction pair according to the invention are shown as a function of distance. It can be seen that the average friction coefficient of the comparative pair is greater than 0.1. It is not very stable and has many peaks. On the other hand, for the friction pair according to the invention, the average friction coefficient is less than 0.1 and stable. A longer test was conducted on the same pair according to the invention over a distance of 2500 meters. The results are shown in Figure 1. Figure 6 The average coefficient of friction was very low, similar to that of the shorter 25-meter test. After a short break-in period, the coefficient of friction remained stable throughout the test.

[0033] Therefore, the femtotorque test and the friction test confirm the good performance of using functionalized diamond on the functionalized diamond pair.

[0034] Reference Signs List

[0035] (1) Functional components

[0036] (2) First component

[0037] a) First contact surface, also called functional surface

[0038] (3) Second component

[0039] a) Second contact surface, also called functional surface

[0040] (4) Pallet fork

[0041] A. Plane of rest

[0042] B. Impact plane

[0043] (5) Anchor Pallet

[0044] (6) Escape wheel

[0045] (7) Teeth

[0046] C. Plane of rest

[0047] D. Impact plane

[0048] (8) Base

[0049] (9) Friction layer

[0050] a) First layer containing diamonds

[0051] b) The second layer containing S and F

[0052] (10) Equipment for functionalization

[0053] (11) Reactor

[0054] (12) Gas

[0055] (13) Plasma

[0056] (14) Electrode

Claims

1. A micromechanical functional component (1), comprising at least one first part (2), the first part being formed by a first substrate topped with a first functional surface (2a), the first functional surface being intended for frictional contact with a second functional surface (3a), the second functional surface belonging to the first part (2) or to at least one second part (3), the second part being formed by a second substrate topped with the second functional surface (3a), the second part (3) together with the first part (2) constituting the functional component (1), the functional component (1) being characterized in that the first functional surface (2a) and the second functional surface (3a) are each formed by a first layer (9a), the first layer (9a) being formed integrally with the first substrate and the second substrate, or the first layer (9a) being different from the first substrate and the second substrate, the first layer (9a) comprising ultrananodiamond, nanodiamond or microcrystalline diamond, and being covered on top of the first layer by a second layer (9b), the second layer comprising S atoms and F atoms, wherein the average thickness of the second layer (9b) is in the range of 2 nm to 50 nm.

2. The functional component (1) according to claim 1, characterized in that The second layer (9b) contains SF6.

3. The functional component (1) according to claim 1 or 2, characterized in that The second layer (9b) is formed of a plurality of rod-shaped members.

4. Functional assembly (1) according to any one of the preceding claims, characterized in that The first component (2) is a pallet (4), and the second component (3) is an escape wheel (6).

5. The functional assembly (1) according to any one of claims 1 to 3, characterized in that The first component (2) is the shaft of the moving part, and the second component (3) is the bearing.

6. The functional assembly (1) according to any one of claims 1 to 3, characterized in that The first component (2) and the second component (3) are teeth of a gear.

7. The functional assembly (1) according to any one of claims 1 to 3, characterized in that The second functional surface belongs to the first component (2), which is a barrel spring formed by a strip, wherein the front surface of the strip forms the first functional surface and the rear surface of the strip forms the second functional surface.

8. Functional assembly (1) according to any one of the preceding claims, characterized in that When the first layer (9a) is different from the first substrate and the second substrate, the first substrate and the second substrate are selected from ceramics, silicon, silicon oxide, silicon nitride, carburized silicon and steel.

9. The functional component (1) according to claim 1, characterized in that The average thickness of the second layer (9b) is in the range of 5 nm to 10 nm.

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