HOROLOGICAL COMPONENT FORMED FROM AMAGNETIC BINARY CuNi ALLOY

Abstract

A monolithic horological component comprising a binary amagnetic CuNi alloy, said component being obtained by a process comprising the production of a mold for said component by photolithography and a step for electrodeposition. The fabrication process for the monolithic horological component is selected from UV-LiGA type processes.

Claims

1. A monolithic horological component comprising an amagnetic binary CuNi alloy, said component being obtained by a process comprising the production of a mold for said component by photolithography and a step of electrodeposition.

2. The monolithic horological component according to claim 1, wherein said component is a component of a movement of a timepiece.

3. The monolithic horological component according to claim 1, wherein said component is homogeneous and isotropic.

4. The monolithic horological component according to claim 1, constituted by a binary alloy Cu(x) Ni(100-x), in which 45<x<80, where x designates the atomic percentage of copper.

5. The monolithic horological component according to claim 1, comprising a binary alloy Cu(x) Ni(100-x), in which 55<x<75, where x designates the atomic percentage of copper.

6. The monolithic horological component according to claim 1, wherein said binary CuNi alloy is obtained from an electrodeposition bath solution comprising at least one Ni.sup.2+ salt and one Cu.sup.2+ salt, the Ni.sup.2+ cations being in excess with respect to the Cu.sup.2+ in a manner such that the reduction of Ni.sup.2+ is controlled by kinetics, while the reduction of Cu.sup.2+ is limited by mass transfer.

7. The monolithic horological component according to claim 6, wherein said electrodeposition bath solution comprises a Ni.sup.2+ salt in a concentration of 0.1 M to 0.4 M, and a Cu.sup.2+ salt in a concentration of 0.04 M to 0.1 M, said concentrations being adjusted in a manner such as to obtain a predetermined value for x.

8. The monolithic horological component according to claim 6, wherein said electrodeposition bath solution additionally comprises a chelating agent for Cu.sup.2+ ions, in particular Na citrate, and in that a pH of the bath solution is adjusted to a value of 6.

9. The monolithic horological component according to claim 6, wherein said electrodeposition bath solution additionally comprises additives selected from wetting agents, brightening agents, levelling agents and stress-suppressing agents.

10. The monolithic horological component according to claim 1, obtained by a process selected from processes of a UV-LiGA type.

11. The monolithic horological component according to claim 10, wherein said process of the UV-LiGA type employs an Au/Cr/Si lithography substrate and a photoresistant SU-8 type resin, in that said substrate is exposed to an O.sub.2 plasma before the electrodeposition step and in that said substrate acts as a cathode during the electrodeposition step.

12. The monolithic horological component according to claim 11, wherein the electrodeposition employs an anode comprising a noble metal, disposed parallel to and facing the cathode.

13. The monolithic horological component according to claim 12, wherein a temperature of the electrodeposition bath solution is kept constant during the electrodeposition, in particular adjusted to 40 C., and in that the bath solution is stirred during the electrodeposition.

14. The monolithic horological component according to claim 10, wherein the electrodeposition is carried out using a pulsed current, a duration of cathodic pulses being adjusted to between 5 ms and 2 s, the pulses being separated by pauses with zero current.

15. The monolithic horological component according to claim 14, wherein a current adjusted to a current density in the range 1 mA/cm.sup.2 to 200 mA/cm.sup.2 is applied during the cathodic pulses.

16. The monolithic horological component according to claim 14, wherein a current adjusted to a cathode potential, with respect to an Ag/AgCl electrode, in a range of 0.8V to 1.6 V is applied during the pulses.

17. The monolithic horological component according to claim 14, wherein the electrodeposition process is initiated by a nucleation pulse with a potential adjusted to between 0.8 V and 1.6 V, with respect to an Ag/AgCl electrode, or a current density adjusted to between 1 mA/cm.sup.2 and 200 mA/cm.sup.2.

18. The monolithic horological component according to claim 17, wherein the nucleation pulse is carried out at 1 V, and with respect to an Ag/AgCl electrode, for 11 s.

19. The monolithic horological component according to claim 17, wherein the nucleation pulse is carried out in a galvanostatic mode with a current density which is half of that for the subsequent pulses.

20. The monolithic horological component according to claim 1, comprising a binary alloy Cu(x) Ni(100-x), in which x=55, where x designates the atomic percentage of copper.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings represent embodiments of the invention, by way of examples.

[0026] FIG. 1 shows microphotographs of CuNi alloys of the prior art.

[0027] FIG. 2 shows a microphotograph of a section of a CuNi alloy in accordance with the invention.

[0028] FIG. 3 shows a diffractogram of the alloy of FIG. 2.

[0029] FIG. 4 shows an escape wheel in accordance with the invention.

[0030] FIG. 5 shows a balance spring in accordance with the invention.

[0031] FIG. 6 is a table summarizing the operating conditions for the step for electrodeposition of two CuNi alloys in accordance with the invention.

[0032] FIG. 7 is a table summarizing variations of the composition of the electrodeposition solution baths in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0033] The invention will now be described in detail with reference to the accompanying figures which illustrate several embodiments of the invention by way of example.

[0034] FIG. 1 reproduces microphotographs of five CuNi alloys prepared using a standard metallurgical process, powder compression, followed by sintering in a vacuum furnace. The five alloys were produced by this method with the following compositions: Ni-5% by wt Cu, Ni-10% by wt Cu, Ni-20% by wt Cu, Ni-30% by wt Cu and Ni-50% by wt Cu. The microphotographs shown in FIG. 1 are extracted from the article Metallurgically prepared NiCu alloys as cathode materials for hydrogen evolution reaction by Kunchan Wang and Ming Xia, Materials Chemistry and Physics 186 (2017), pages 61 to 66. They exhibit a heterogeneity in their microstructures, with two phases coexisting in distinct domains.

[0035] FIG. 2 shows a microphotograph of a section of a CuNi alloy produced by ionic milling and ion microscopy of a section of a part obtained by electrodeposition using a LiGA process, in accordance with the invention. In FIG. 2, a microstructure of the alloy is observed which is characterized by a uniform distribution of nanocrystalline grains.

[0036] The alloy shown in FIG. 2 was analyzed by X ray diffractometry (XRD). The XRD diffractogram is shown in FIG. 3; the grain size was evaluated using the Scherrer equation, along with the texture coefficients associated with each crystallographic plane. This diffractogram exhibits a large peak in the (111) orientation, which indicates the formation of textured deposits, with texture along the {111} plane. Such a peak is not visible in the diffractograms of alloys obtained using a standard metallurgical process such as that given above.

[0037] It thus follows that a binary CuNi alloy obtained by an electrodeposition process in accordance with the invention has a metallurgical microstructure which differs from that of a CuNi alloy comprising the components Cu and Ni in the same proportions, but obtained by a standard metallurgical process.

[0038] As a result, a monolithic horological component constituted by or comprising a binary amagnetic CuNi alloy obtained by an electrodeposition process has a metallurgical structure which is different from that which would have a horological component with the same shape and produced by a standard metallurgical process.

[0039] The person skilled in the art is aware that the components Cu and Ni are miscible in all proportions in order to form binary alloys, with the magnetic properties of the alloys being a function of these proportions. These alloys have ferromagnetic type properties when the proportion of Ni is more than approximately 60% by weight.

[0040] In the broadest sense of the present invention, the monolithic components constituted by a binary CuNi alloy obtained by electrodeposition are those which are amagnetic because of the proportions of the components Cu and Ni.

[0041] In particular, the monolithic horological components according to the invention are constituted by a binary alloy Cu(x) Ni(100-x), in which 45<x<80, where x designates the atomic percentage of copper. More specifically, the monolithic horological components according to the invention are constituted by a binary alloy Cu(x) Ni(100-x), in which 55<x<75. In particular, if x is approximately 55, in which x designates the atomic percentage of copper, the alloy exhibits a minimum thermal variation in mechanical properties at the usual ambient temperatures.

[0042] The monolithic horological components according to the invention are preferably obtained from an electrodeposition bath solution comprising at least one Ni.sup.2+ salt and one Cu.sup.2+ salt, the Ni.sup.2+ cations being in excess with respect to the Cu.sup.2+ in a manner such that the reduction of Ni.sup.2+ is controlled by the kinetics, while the reduction of Cu.sup.2+ is limited by mass transfer.

[0043] Said electrodeposition bath solution may in particular comprise a Ni.sup.2+ salt in a concentration of 0.1 M to 0.4 M, and a Cu.sup.2+ salt in a concentration of 0.04 M to 0.1 M, said concentrations being adjusted in a manner such as to obtain a predetermined value for x.

[0044] The bath solution may be produced using Cu sulphate, in particular in a concentration of 0.08 M, and Ni sulphate, in particular in a concentration of 0.2 M or 0.3 M. The bath solution may also be produced using Ni sulphamate, in particular in a concentration of 0.2 M, and a Cu salt selected from the sulphate, the chloride, the citrate or the sulphamate in an appropriate concentration from 0.01 M to 0.1 M. Other Ni and Cu salts may be used without departing from the scope of the invention.

[0045] The electrodeposition bath solution preferably comprises a chelating agent for Cu.sup.2+ ions, in particular Na citrate in a concentration of 0.1 M to 0.2 M, and the pH of the bath solution is adjusted to a value of 6, for example by means of NaOH or H.sub.2SO.sub.4.

[0046] The electrodeposition bath solution preferably comprises additives selected from wetting agents, levelling agents and thickening agents, for example 1 g/L of saccharine, 2 mL/L of PC-3 and 1 mL/L of Wetting W (additives sold by A-GAS International).

[0047] As mentioned above, the process for the fabrication of a monolithic horological component in accordance with the invention is selected from UV-LiGA type processes. Said process employs a lithography substrate, which acts as a cathode during the electrodeposition step, in particular a Au/Cr/Si wafer and a photoresistant resin, for example of the SU-8 type (commercial products). The principle and the general characteristics of LiGA technology are known to the person skilled in the art and thus will not be discussed here. Only the specific characteristics intended for the production of the horological components in accordance with the invention are discussed hereinbelow.

[0048] A number of measures for improving the quality of the deposit, in particular its homogeneity, hence the homogeneity of the horological component, may be taken independently or simultaneously.

[0049] The substrate which has been printed may be exposed to an O.sub.2 plasma before the electrodeposition step.

[0050] The electrodeposition step may employ an anode constituted by a noble metal, for example Pt, disposed parallel to and facing the cathode and, optionally, a reference electrode.

[0051] Preferably, the temperature of the electrodeposition bath solution is kept constant during the electrodeposition, in particular adjusted to 40 C., with its pH adjusted to 6.

[0052] In order to keep the composition of the bath solution constant during the electrochemical process, including in the recesses in the mold, the electrodeposition is carried out using a pulsed current, the duration of the cathodic pulses being adjusted to between 5 ms and 2 s, more particularly to between 0.3 s and 1 s, the pulses being separated by pauses with zero current in order to allow the diffusion layer at the surface of the deposit to relax. In order to reduce the duration of the deposition step, it is preferable to adjust the pauses to a duration of less than 5 s, more particularly 3 s.

[0053] In this embodiment, a current density in the range 1 mA/cm.sup.2 to 200 mA/cm.sup.2 is applied during the cathodic pulses. Or, in fact, a cathode potential, with respect to an Ag/AgCl electrode, in the range 0.8 V to 1.6 V is applied and maintained during the pulses.

[0054] Preferably, the electrodeposition process is initiated by a nucleation pulse with a potential adjusted to between 0.8 V and 1.6 V, with respect to an Ag/AgCl electrode, or a current density adjusted to between 1 mA/cm.sup.2 and 200 mA/cm.sup.2.

[0055] In particular, the nucleation pulse may be carried out at 1 V, with respect to an Ag/AgCl electrode, for 11 s. The nucleation pulse may be carried out in galvanostatic mode with a current density which is half of that for the subsequent pulses.

[0056] In addition, the bath solution is advantageously stirred during electrodeposition. Stirring may be used to increase the current density, thus leading to a faster process. In fact, the inventors have shown that in an experimental device of this type [0057] the current density may be adjusted to approximately 390 mA/cm.sup.2 per mole/L of CO in the absence of stirring, [0058] the current density may be adjusted to approximately 830 mA/cm.sup.2 per mole/L of CO with stirring at 150 rpm, [0059] the current density may be adjusted to approximately 1.3 mA/cm.sup.2 per mole/L of CO with stirring at 300 rpm, [0060] a cathode potential of 1.3 V, with respect to an Ag/AgCl electrode, may be applied with stirring at 300 rpm.

[0061] At the end of the electrodeposition process [0062] the latter is continued until the thickness of the deposit exceeds the thickness of the layer of resin, [0063] the surplus thickness of the deposit with respect to the set thickness of the horological component is eliminated by polishing, [0064] the resin is eliminated by a physico-chemical procedure, for example by means of an O.sub.2 plasma if the resin is of the SU-8 type, [0065] the horological component is detached from the substrate, in particular by dissolving at least the superficial layer thereof, for example with 1.5 M KOH at 80 C.

EXAMPLES

Example 1: Balance Spring

[0066] The balance spring shown in FIG. 5 was produced from a Cu(55)Ni(45) alloy using a LiGA process as described above, with the operating parameters shown in the left hand column in the table of FIG. 6.

[0067] The part obtained had the following mechanical properties:

[0068] Young's modulus: 11010 GPa

[0069] Hardness: 2.400.13 GPa

[0070] Operational frequency: 2 Hz

[0071] Amplitude: 217-268 (mean, at 6 positions).

Example 2: Escape Wheel

[0072] The escape wheel shown in FIG. 4 was produced from a Cu(75)Ni(25) alloy using a LiGA process as described above, with the operating parameters shown in the right hand column in the table of FIG. 6.

Example 3: Electrodeposition Bath Solutions

[0073] FIG. 6 shows the compositions of the bath solutions prepared using Ni and Cu sulphates.

[0074] The table in FIG. 7 shows 3 examples of compositions for bath solutions prepared using Ni sulphamate and, respectively, Cu citrate, sulphate and chloride.

[0075] In view of the above discussions relating to the structure and the process for fabrication of the horological components according to the present invention, it is clear that such a horological component enjoys a number of advantages and allows to achieve the aims defined in the introduction. It should in particular be pointed out that the geometrical two-dimensional shape of such a component may be selected with almost complete freedom by the timepiece designer. The choice of the Ni and Cu components of the binary alloy, which are entirely miscible, means that there is great freedom in selecting the relative concentrations of these two species as a function of the constraints imposed on the finished product.