阅读说明：本技术 用于钟表机芯的摆轮游丝 (Balance spring for a timepiece movement ) 是由 C·查尔邦 M·维拉多 L·米什莱 于 2020-09-18 设计创作，主要内容包括：本发明公开了用于钟表机芯的摆轮游丝。本发明涉及意在为钟表机芯的摆轮而配备的摆轮游丝(1),其特征在于所述摆轮游丝(1)由铌和钛的合金制成,所述合金含有：-铌:补足至100wt%；-钛,重量百分比大于或等于1wt%且小于40wt%；-选自O、H、C、Fe、Ta、N、Ni、Si、Cu和Al的痕量的其它元素,各所述元素在总重量的0至1,600 ppm的范围内,且所述痕量元素的总和小于或等于0.3wt%。本发明进一步涉及其制造方法。(The invention discloses a balance spring for a timepiece movement. The invention relates to a balance spring (1) intended to be provided for a balance of a timepiece movement, characterized in that said balance spring (1) is made of an alloy of niobium and titanium, said alloy containing: niobium, up to 100 wt%; -titanium, in a weight percentage greater than or equal to 1wt% and less than 40 wt%; -other elements selected from traces of O, H, C, Fe, Ta, N, Ni, Si, Cu and Al, each of said elements being in the range of 0 to 1,600 ppm of the total weight, and the sum of said trace elements being less than or equal to 0.3 wt%. The invention further relates to a method for the production thereof.)

1. Balance spring (1) intended to be equipped for a balance of a timepiece movement, characterized in that said balance spring (1) is made of an alloy of niobium and titanium, said alloy containing:

niobium, up to 100 wt%;

-titanium, in a weight percentage greater than or equal to 1wt% and less than 40 wt%;

-other elements selected from traces of O, H, C, Fe, Ta, N, Ni, Si, Cu and/or Al, each of said elements being in the range of 0 to 1,600 ppm of the total weight, and the sum of said trace elements being less than or equal to 0.3 wt%.

2. Balance spring (1) according to claim 1, characterized in that said alloy comprises titanium in a percentage by weight lying in the range 5 to 35 wt%.

3. Balance spring (1) according to claim 1, characterized in that said alloy comprises titanium in a percentage by weight lying in the range 15 to 35 wt%.

4. Balance spring (1) according to claim 1, characterized in that said alloy comprises titanium in a percentage by weight lying in the range 27 to 33 wt%.

5. Balance spring (1) according to one of the preceding claims, characterized in that it has a two-phase microstructure comprising niobium in the form of the β phase and titanium in the form of the α phase.

6. Balance spring (1) according to one of the preceding claims, characterized in that it has a yield strength greater than or equal to 500 MPa and an elastic modulus less than or equal to 120 GPa, preferably less than or equal to 110 GPa.

7. Method for manufacturing a balance spring (1) intended to equip a balance of a timepiece movement, characterized in that it comprises in succession:

-a step of producing a billet made of an alloy of niobium and titanium, said alloy containing:

niobium, up to 100 wt%;

-titanium, in a weight percentage greater than or equal to 1wt% and less than 40 wt%;

-other elements selected from traces of O, H, C, Fe, Ta, N, Ni, Si, Cu and/or Al, each of said elements being in the range of 0 to 1,600 ppm of the total weight, and the sum of said trace elements being less than or equal to 0.3 wt%;

-a step of quenching the blank in beta form, so that the titanium of the alloy is substantially in the form of a solid solution with beta-phase niobium,

-a sequence of steps of deformation-followed by intermediate heat treatment of the alloy,

-a winding step for forming said balance spring (1),

-a final heat treatment step.

8. Method for manufacturing a balance spring (1) according to claim 7, characterized in that the deformation during each process is performed by drawing and/or rolling.

9. Method for manufacturing a balance spring (1) according to claim 8, characterized in that the deformation of the last process step is performed by plate rolling.

10. Method for manufacturing a balance spring (1) according to one of claims 7 to 9, characterized in that the deformations of the various processes are carried out with a given deformation ratio lying in the range 1 to 5, the total accumulated deformation through the whole of said series of processes producing a total deformation ratio lying in the range 1 to 14.

11. Method for manufacturing a balance spring (1) according to one of claims 7 to 10, characterized in that said type β quenching is a dissolution treatment in vacuum at a temperature lying in the range 700 ℃ to 1,000 ℃ for a duration lying in the range 5 minutes to 2 hours, followed by cooling in a gas.

12. Method for manufacturing a balance spring (1) according to one of claims 7 to 11, characterized in that said β -type quenching is a dissolution treatment at 800 ℃ for 1 hour in vacuum, followed by cooling in a gas.

13. Method for manufacturing a balance spring (1) according to one of claims 7 to 12, characterized in that the final heat treatment, in addition to the intermediate heat treatment of each process, is also an alpha phase Ti precipitation treatment at a temperature lying in the range 300 ℃ to 700 ℃, the duration of which lies in the range 1 hour to 200 hours.

14. Method for manufacturing a balance spring (1) according to one of claims 7 to 13, characterized in that the final heat treatment, in addition to the intermediate heat treatment of each process, is also an alpha phase Ti precipitation treatment at a temperature lying in the range 400 ℃ to 600 ℃, the duration of which lies in the range 5 hours to 30 hours.

15. Method for manufacturing a balance spring (1) according to one of claims 7 to 14, characterized in that it comprises from 1 to 5 said steps of deformation followed by an intermediate heat treatment.

16. Method for manufacturing a balance spring (1) according to one of claims 7 to 15, characterized in that a first of said processes of deformation followed by an intermediate heat treatment comprises a first deformation with a cross-sectional reduction of at least 30%.

17. Method for manufacturing a balance spring (1) according to claim 16, characterized in that said sequence of deformations followed by an intermediate heat treatment, in addition to the first, comprises a deformation with a cross-sectional reduction of at least 25% between two intermediate heat treatments.

18. Method for manufacturing a balance spring (1) according to one of claims 7 to 17, characterized in that after the step of manufacturing an alloy blank and before the step of applying a series of working steps, a surface layer of a ductile material selected from copper, nickel, copper-nickel alloy, copper-manganese alloy, gold, silver, nickel-phosphorus Ni-P and nickel-boron Ni-B is added on said blank to ease the wire forming operation, and in that before or after the winding step, said layer of ductile material is removed from said wire by etching.

Technical Field

The present invention relates to a balance spring intended to be provided for a balance of a timepiece movement. It further relates to a method for manufacturing such a balance spring.

Background

The manufacture of balance springs for timepieces is limited by what generally seems to be incongruous at first sight:

the need to obtain a high yield strength,

easy to manufacture, in particular to perform drawing and rolling operations,

-a superior fatigue strength, and a superior fatigue strength,

-a level of stability over time of the performance,

-a small cross section.

The manufacture of balance springs also focuses on temperature compensation to ensure a consistent level of timing performance. This requires that a thermoelastic coefficient close to 0 be obtained.

Any improvement in at least one of these points, and in particular in the mechanical strength of the alloys used, therefore represents a significant advance.

Disclosure of Invention

The invention proposes to determine a new timepiece balance spring based on the selection of a specific material and to develop a suitable manufacturing method.

To this end, the invention relates to a timepiece balance spring made of an alloy of niobium and titanium. According to the invention, the titanium content is in the range of 1wt% (inclusive) to 40wt% (exclusive). Advantageously, it lies in the range from 5% by weight (inclusive) to 35% by weight (inclusive), preferably in the range from 15% by weight (inclusive) to 35% by weight (inclusive), and more preferably in the range from 27% by weight (inclusive) to 33% by weight (inclusive). The balance consisting of niobium and impurities including interstitial elements such as H, C, N and/or O, the percentage of impurities being less than or equal to 0.3 wt%.

The invention further relates to a method for manufacturing such a timepiece balance spring as claimed in the appended claims.

Drawings

Other features and advantages of the present invention will be better understood upon reading the following detailed description, given with reference to the accompanying drawings, in which:

figure 1 shows diagrammatically a balance spring made of Nb-Ti alloy according to the invention;

figure 2 shows the evolution of young's modulus as a function of temperature calculated on the basis of young's modulus at 20 c for pure Nb and for Nb-Ti alloys according to the invention containing 30wt% Ti, respectively.

Detailed Description

The invention relates to a timepiece balance spring made of a binary alloy containing niobium and titanium.

According to the invention, this alloy comprises:

niobium, up to 100 wt%;

-titanium, in a weight percentage greater than or equal to 1wt% and less than 40 wt%. More particularly, this alloy comprises a proportion by weight of titanium lying in the range 5 to 35 wt.%, preferably in the range 15 to 35 wt.% and more preferably in the range 27 to 33 wt.%;

-other elements selected from traces of O, H, C, Fe, Ta, N, Ni, Si, Cu and/or Al, each of said elements being in the range of 0 to 1,600 ppm of the total weight, and the sum of these trace elements being less than or equal to 0.3 wt%. In other words, the total weight percent of titanium and niobium is in the range of 99.7wt% to 100wt% of the total.

The weight percentage of oxygen is less than or equal to 0.10wt% of the total amount, or even less than or equal to 0.085wt% of the total amount.

The weight percent of tantalum is less than or equal to 0.10wt% of the total.

The percentage by weight of carbon is less than or equal to 0.04% by weight of the total, in particular less than or equal to 0.020% by weight of the total, or even less than or equal to 0.0175% by weight of the total.

The weight percentage of iron is less than or equal to 0.03wt% of the total, in particular less than or equal to 0.025wt% of the total, or even less than or equal to 0.020wt% of the total.

The weight percentage of nitrogen is less than or equal to 0.02wt% of the total, in particular less than or equal to 0.015wt% of the total, or even less than or equal to 0.0075wt% of the total.

The weight percentage of hydrogen is less than or equal to 0.01wt% of the total, in particular less than or equal to 0.0035wt% of the total, or even less than or equal to 0.0005wt% of the total.

The weight percentage of nickel is less than or equal to 0.01wt% of the total.

The weight percentage of silicon is less than or equal to 0.01wt% of the total.

The weight percentage of nickel is less than or equal to 0.01wt% of the total, in particular less than or equal to 0.16wt% of the total.

The weight percentage of copper is less than or equal to 0.01wt% of the total amount, or even less than or equal to 0.005wt% of the total amount.

The weight percentage of aluminum is less than or equal to 0.01wt% of the total.

Advantageously, this balance spring has a two-phase microstructure comprising niobium in the form of a body-centred cubic β phase and titanium in the form of a close-packed hexagonal α phase.

In order to obtain such a microstructure, and depending on the manufacture of the balance spring, it is necessary to precipitate a portion of the alpha phase by heat treatment.

The higher the titanium content, the higher the maximum proportion of alpha phase that can be precipitated by heat treatment, which encourages the pursuit of a high titanium proportion. However, conversely, the higher the titanium content, the more difficult it is to obtain the precipitation of the α phase at the grain boundaries. The presence of precipitates of the α -Ti type within the widcast ä tten crystal grain or of the ω -phase within the crystal grain makes the deformation of the material difficult or even impossible and is therefore not suitable for the manufacture of balance springs, which means that the incorporation of too much titanium in the alloy should be avoided. Furthermore, the application of this alloy to a balance spring requires the property of ensuring the maintenance of the chronograph performance even if the temperature of use of the watch incorporating this balance spring varies. The thermal elastic coefficient or TEC of the alloy is therefore very important. In order to form a timing oscillator with a wobbler made of CuBe or nickel-silver, a TEC of +/-10 ppm/deg.C must be achieved. The following provides a formula relating the TEC of the alloy to the expansion coefficients of the balance spring and balance:

the variables M and T are rate and temperature, respectively. E is the Young's modulus of the balance spring, and in this formula E, β and α are in C^-1To represent。

CT is the thermal coefficient of the oscillator, (1/e. dE/dT) is the TEC of the balance spring alloy, β is the expansion coefficient of the balance, and α is the expansion coefficient of the balance spring. Cold rolling beta-phase alloys with high positive TEC and precipitation of alpha phase with high negative TEC enables two-phase alloys to reach a TEC close to 0, which is particularly beneficial. However, as mentioned above, too high a titanium percentage results in the formation of brittle phases. A titanium percentage of less than 40wt% achieves a good compromise between different properties that are favoured. Furthermore, it is believed that the interaction between C, H, N, O interstitial elements present in the alloy and dislocations, as well as the interaction between alpha-titanium precipitates and dislocations, also play a beneficial role for TEC. The setting of the dislocations in motion as a function of temperature reduces the young's modulus of the balance spring, which is opposed to the positive anomaly of the beta phase.

A balance spring made using this alloy has a yield strength greater than or equal to 500 MPa, and more particularly in the range 500 to 1,000 MPa. Advantageously, it has an elastic modulus of less than or equal to 120 GPa, and preferably less than or equal to 110 GPa.

The invention further relates to a method for manufacturing a timepiece balance spring, characterized in that it comprises the successive implementation of the following steps:

-making a billet made of an alloy comprising niobium and titanium, and more particularly:

niobium, up to 100 wt%;

-the weight percentage of titanium is greater than or equal to 1wt% and less than 40wt% of the total;

-trace amounts of other elements selected from O, H, C, Fe, Ta, N, Ni, Si, Cu and Al, each of said elements being in the range of 0 to 1,600 ppm of the total weight, and the sum of said trace elements being less than or equal to 0.3 wt%;

-beta quenching of the billet, so that the titanium of the alloy is substantially in solid solution with beta-phase niobium;

-a step of applying a deformation to said alloy followed by a heat treatment. The term "deformation" is understood herein to mean deformation by wire drawing and/or rolling. Drawing may require the use of one or more die plates, if desired, in the same or different processes. Drawing was performed until a wire having a circular cross section was obtained. The rolling may be performed during the same deformation process as the wire drawing or in another process. Advantageously, the last step of the alloy application is a rolling operation, preferably with a rectangular profile compatible with the inlet cross section of the winder spindle. These procedures allow the production of a two-phase microstructure comprising a beta-phase niobium and an alpha-phase titanium, having a yield strength greater than or equal to 500 MPa and an elastic modulus less than or equal to 120 GPa, and preferably 110 GPa;

winding to form a balance spring, followed by a final heat treatment.

In these paired (couppled) deformation-heat treatment processes, each deformation is carried out at a given deformation ratio in the range of 1 to 5, which satisfies the conventional formula 2ln (d0/d), where d0 is the diameter of the final beta quench, and where d is the diameter of the cold rolled wire rod. The total cumulative deformation through this series of processes results in a total deformation ratio in the range of 1 to 14. Each pair of deformation-heat treatment processes comprises in each case an alpha-phase Ti precipitation heat treatment.

The beta quenching before the deformation and heat treatment process is a dissolution treatment at a temperature in the range of 700 ℃ to 1,000 ℃ in vacuum for a duration in the range of 5 minutes to 2 hours, followed by cooling in a gas.

Even more particularly, this beta quenching is a dissolution treatment at 800 ℃ for 1 hour in vacuum, followed by cooling in a gas.

Referring back to the paired deformation-heat treatment process, the heat treatment is a precipitation treatment at a temperature lying in the range 300 ℃ to 700 ℃, with a duration lying in the range 1 hour to 200 hours. More particularly, the duration lies in the range from 5 hours to 30 hours at a temperature lying in the range from 400 ℃ to 600 ℃.

More particularly, the method comprises from 1 to 5 paired deformation-heat treatment processes.

More particularly, the first paired deformation-heat treatment process comprises a first deformation with a cross-sectional reduction of at least 30%.

More particularly, each paired deformation-heat treatment process, except the first, comprises a deformation with at least a 25% cross-sectional reduction between two heat treatments.

More particularly, after the alloy billet is thus produced, and before the deformation-heat treatment process, in an additional step, a surface layer of a ductile material selected from the group consisting of copper, nickel, copper-nickel alloy, copper-manganese alloy, gold, silver, nickel-phosphorus Ni-P and nickel-boron Ni-B or the like is added to the billet to facilitate the wire forming operation during deformation. Furthermore, after the deformation-heat treatment process or after the winding step, the layer of ductile material is removed from the wire rod, in particular by etching.

In an alternative embodiment, a surface layer of ductile material is deposited to form a balance spring, the pitch of which is not a multiple of the thickness of the band. In another alternative embodiment, a surface layer of ductile material is deposited to form a balance spring, the pitch of which may be varied.

In one particular horological application, ductile material or copper is therefore added at a given moment to facilitate the wire forming operation, leaving a thickness of 10 to 500 microns on the wire with a final diameter of 0.3 to 1 mm. The layer of ductile material or copper is removed from the wire, in particular by etching, and said wire is then rolled flat before the actual production of the balance spring itself by winding.

The addition of ductile material or copper may be electroplating or mechanical; in this case a sleeve or tube of ductile material or copper, which is adjusted onto a niobium-titanium alloy rod with a large diameter and then thinned during the deformation step of the composite rod.

A diffusion barrier layer, for example nb, may be added between nb-Ti and Cu to prevent the formation of intermetallic compounds that are detrimental to the deformability of the material. The thickness of this layer is chosen so that it corresponds to a thickness of 100 nm to 1 μm on a wire of diameter 0.1 mm.

The removal of this layer can be carried out in particular by etching with cyanide-based or acid-based solutions, for example nitric acid.

By a suitable combination of deformation and heat treatment procedures, ultra-thin layered two-phase microstructures, in particular nano-microstructures, can be obtained, comprising or consisting of beta-phase niobium and alpha-phase titanium. This alloy combines a very high yield strength of greater than at least 500 MPa with a very low modulus of elasticity of about 80 GPa to 120 GPa. This combination of properties is very suitable for a balance spring. After the deformation-heat treatment process, the alloy has a texture <110 >. Furthermore, such niobium-titanium alloys according to the invention are easily covered by ductile materials or copper, which makes them very easy to deform by wire drawing.

The binary alloy containing niobium and titanium of the type chosen above for implementing the invention also has an effect similar to "Elinvar", has a thermoelastic coefficient of almost 0 in the range of normal operating temperatures of the watch, and is suitable for making self-compensating balance springs.

More specifically, when comparing Young's moduli (E (T)/E) for pure Nb and Nb-Ti alloys containing 30wt% Ti according to the invention in FIG. 2₂₀C) as a function of temperature, the two curves are seen to be sigmoidal, with the obvious difference that the presence of Ti significantly reduces the difference between the minimum and maximum values of the curve along both the X-and Y-axes. More specifically, the presence of Ti in the alloy and the manufacturing method according to the invention tend to smooth the curve by reducing the maximum value of the curve. This positive effect of the alloy according to the invention on reducing the maximum is the result of a number of factors:

crystallographic texture of the alloy, which is affected by the deformation rate from beta quenching,

dislocation density adjusted by a thermal treatment inducing a reversion or even a recrystallization phenomenon,

-the concentration of interstitial elements that will interact with dislocations,

-the percentage of alpha-phase Ti,

density of precipitates in the alloy (number of alpha phase Ti precipitates per unit volume).