Patent Application
20210302914
This application claims priority to European Patent Application No. 20165964.6 filed Mar. 26, 2020, the entire contents of which are incorporated herein by reference.
The invention relates to a non-magnetic watch component intended for the movement or external watch parts and to the method for manufacturing the same.
Hard and non-ferromagnetic metal alloys find application in numerous fields, mainly for components subjected to high mechanical and/or tribological stresses and required to remain insensitive to magnetic fields. This is notably the case for numerous watch components, such as, for example, wheels, pinions, arbors or springs in the movement. For the external watch parts, it is also advantageous to obtain high hardnesses, for example for the case middle, the bezel, the case back or the crown. Indeed, a high hardness generally makes it possible to obtain improved scratch and wear resistance and therefore good durability of these components exposed to the external environment.
In metallurgy, various mechanisms make it possible to harden alloys, depending on their chemical compositions and their thermomechanical histories. Thus, the following are known: solid solution hardening, structural hardening, strain hardening, martensitic transformation in steels, spinodal decomposition, and grain-boundary strengthening (Hall-Petch). In the most remarkable alloys, several of these hardening mechanisms are used simultaneously. However, non-ferromagnetic alloys which have hardnesses of more than 500 HV are rare. Further, such alloys are difficult to machine and almost impossible to deform, due to their very high hardness and their very low ductility.
There is known from EP Patent No. 3273304 a watch component, and more particularly a pivot arbor, comprising at least one part made of a non-magnetic copper alloy containing between 10 and 20% by weight of Ni and between 6 and 12% of Sn. This alloy has a low intrinsic hardness of around 350 HV. In order to increase hardness, the external surface of the component is hardened by the diffusion of atoms or by depositing a layer of TiN, of diamond, etc., or by an ion implantation process.
To date, there is still a need for new non-magnetic watch components having improved wear resistance, and, depending on the type of component, if appropriate, also better tribological properties.
It is an object of the present invention to propose a watch component which makes it possible both to limit sensitivity to magnetic fields and to obtain an improve hardness compatible with the wear and shock resistance requirements in the watchmaking field while offering better tribological properties for components such as pivot arbors, wheels, etc.
To this end, the invention relates to a watch component intended for the movement or external watch parts comprising a substrate made of a copper alloy, with at least one part of the substrate having a surface layer of CuxTiy intermetallics. This component combines the advantages of the non-magnetic copper alloy and the hardness of the outer intermetallic layer for the most used parts with the result that wear resistance is improved. Further, the presence of the intermetallic surface layer reduces the friction coefficient during use.
The present invention also relates to the method of manufacturing said component, which includes the following steps:
a) Providing a substrate made of a copper alloy, wherein at least one part of said substrate already substantially has the final shape of the non-magnetic watch component,
b) Depositing a titanium layer on said part of the substrate,
c) Heat treating to diffuse the titanium in the copper alloy to form a layer of CuxTiy intermetallics on said part,
This diffusion treatment makes it possible to obtain a hard outer layer which adheres perfectly to the substrate. Indeed, the intermetallic layer forms a layer which is continuous with the substrate owing to the diffusion of titanium in the copper alloy of the substrate.
Other features and advantages will appear clearly from the following description, given by way of non-limiting illustration, with reference to the annexed drawings, in which:
In the present description, the term “non-magnetic” alloy means a paramagnetic or diamagnetic or antiferromagnetic alloy, whose magnetic permeability is less than or equal to 1.01.
The invention relates to a watch component intended for the movement or the external watch parts. Thus, it may be an external component chosen from the non-exhaustive list including a case middle, a case back, a bezel, a pusher, a bracelet link, a bracelet or strap, a buckle and a crown. For the movement, the non-exhaustive list may include a pallet plate, a wheel plate, a gear train, an arbor, a pallet-staff and a pinion. More specifically, the watch component can be a pivot arbor with at least one part of said arbor, such as a pivot, a screw, a winding stem or a balance spring stud having improved wear resistance and tribological properties owing to the method of the invention.
The invention will be described below in the context of application to a non-magnetic balance staff, generally referenced 1 for a watch component, as represented in
Referring to
According to the invention and as represented in
According to the invention, the intermetallic layer has a hardness HV0.01 (10 g load) greater than 400 HV0.01 and preferably greater than 500 HV0.01. The substrate itself has a hardness less than or equal to 400 HV0.01.
The method of manufacturing the watch component of the invention includes the following steps:
According to the invention, the substrate can be made by any suitable technique: casting, rolling, powder metallurgy, additive manufacturing, etc., followed, if required for sizing, by a machining operation. It can be fully sized before the titanium layer is deposited, It is also possible for only one part of the substrate to be sized prior to the deposition of the titanium layer and for the rest of the component to be sized after the diffusion heat treatment. More specifically for a balance staff, at least the pivot is sized by bar turning or any other chip removal machining technique from copper alloy bars with a diameter of less than 3 mm and preferably less than 2 mm prior to the deposition of the titanium layer.
The titanium layer can be added around the substrate by galvanic means, PVD, CVD, ALD, or any other suitable process. The deposited layer has a thickness comprised between 20 nm and 10 μm, and preferably between 500 nm and 2.5 μm. The diffusion heat treatment is carried out in a range of temperatures comprised between 600 and 900° C. for a time comprised between 30 minutes and 10 hours, and preferably between 1 and 6 hours. According to a variant of the invention, the whole titanium layer is transformed to intermetallics. According to another variant of the invention, the titanium layer is only partially transformed to intermetallics, with a layer of titanium thus remaining around the intermetallic layer. This residual titanium layer has a thickness comprised between 1 nm and 5 μm. It may be kept on the final product or removed by selective chemical etching or polishing.
The method may also include a heat treatment for volume hardening of the substrate, such as, for example, spinodal decomposition hardening for CuNiSn family alloys or structural hardening for CuBe family alloys, in a range of temperatures comprised between 300 and 500° C., preferably between 320° C. and 450° C., for a time comprised between 30 minutes and 3 hours, more particularly between 30 minutes and 1 hour 30 minutes. The hardening heat treatment first requires high temperature dissolution of the elements involved in the hardening, Ni and Sn for a CuNiSn alloy or Be for a CuBe or CuBePb alloy, followed by quenching to maintain in solution the elements before carrying out the hardening heat treatment. According to the invention, the diffusion heat treatment between 600 and 900° can be used to carry out the dissolution. By way of example, for a CuBe2Pb alloy, the Ti diffusion and Be dissolution treatment is carried out at 800° C., the substrate is then rapidly cooled to a temperature below 200° C. before being treated at 325° C. for 3 hours for the precipitation of CuBe2. Generally, the manufacturing method thus includes, after the titanium layer deposition step, the steps of:
The manufacturing method can be finalised after the surface diffusion heat treatment or volume hardening treatment as appropriate, by a surface finish step such as polishing or rolling.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20165964.6 | Mar 2020 | EP | regional |
