Method for manufacturing a timepiece or jewellery component, and said timepiece or jewellery component

Abstract

The present invention relates to a method for manufacturing a timepiece or jewellery component comprising at least one part made from a metal alloy based on gold and copper and containing, by weight, at least 58% gold, said method comprising at least the step a) of providing a workpiece comprising at least one solid part made of said metal alloy, and the step b) of applying various manufacturing operations to the workpiece in order to obtain the timepiece or jewellery component. Said method comprises at least a step c) of applying to the workpiece a heat treatment that is performed for the purpose of controlling the dimensional variations of the workpiece during the course of the manufacturing method, said treatment comprising a first increase in temperature to a temperature TR comprised between the (AuCu)α / AuCuⅠⅠ phase transition temperature and the melting point of the alloy, followed by a first soak at the temperature TR for at least 1 minute, followed by a decrease in temperature down to 25°C comprising, immediately after the first soak at the temperature TR, a first lowering of temperature at a rate comprised between 0.1°C / min and 6000°C / min, preferably between 1°C / min and 10°C / min, and more preferably between 2°C / min and 5°C / min, at least down to a temperature TP comprised between 100°C and the (AuCu)α / AuCuⅠⅠ phase transition temperature, a second soak at the temperature TP for a duration comprised between 0 and 48h and chosen so as to allow the alloy to convert into a state in which it possesses at least 25% of AuCuⅠ ordered phase, followed by a second lowering of temperature down to the ambient temperature of 25°C, the alloy of the workpiece obtained at step c) being in a state in which it possesses at least 25% of AuCuⅠ ordered phase and the workpiece obtained at step c) having a geometry that is maintained and dimensional variations that are controlled during the course of the manufacturing method, the step c) being performed before the step b) and / or during the step b). The invention also relates to a timepiece or jewellery component obtained according to said manufacturing method.

Description

[0001] METHOD FOR MANUFACTURING A WATCH OR JEWELRY COMPONENT AND SAID WATCH OR JEWELRY COMPONENT

[0002] Technical field

[0003] The present invention relates to a method for manufacturing a watch or jewelry component comprising at least one part made of at least a binary metal alloy based on gold and copper comprising at least 58% gold by weight relative to the total weight of the alloy.

[0004] The present invention also relates to said watch or jewelry component obtained by said manufacturing method.

[0005] State of the art

[0006] Gold alloys containing at least 14K gold (i.e., at least 58% gold by weight relative to the total weight of the alloy) and a high copper content are widely used in watchmaking, jewelry, and jewelry. Dimensional and aesthetic control is necessary to ensure a quality product.

[0007] For clothing, 18K 2N / 3N / 4N / 5N / 6N alloys and any other alloy with a very similar chemical composition to which other elements, often metallic, have been added in order to modify the color or resistance to color change, are generally delivered to watchmakers or jewelers in the form of a raw part or rough part, in the austenitic a phase which has been obtained by rapid cooling after high temperature annealing, such as annealing at 650°C followed by quenching in water at room temperature of 25°C.

[0008] It was observed that the hardness of the parts increased during their storage at room temperature (25°C) and that the said parts deformed, with also significant dimensional variations compared to the precisions sought in the fields of watchmaking and jewelry. This evolution would be linked to the transformation of the a phase which is unstable at room temperature. These 18K 2N / 3N / 4N / 5N / 6N alloys and any other alloy with a very similar chemical composition all have the particularity of being hardenable by heat treatment. This hardening occurs by a change of the disordered austenitic (AuCu)a phase, in which the alloy supplied by the refiner is found, towards the AuCuII phase, then towards the ordered martensitic AuCuI phase which is stable below the AuCuII / AuCuI phase transition temperature which is around 350°C.This phase transformation occurs in alloys with contents between 14K and 22K, including 18K.

[0009] However, when watchmakers or jewelers wish to harden the gold and copper-based alloy using a conventional tempering technique at 300°C, for example, the formation of the AuCuI phase during hardening often causes distortions that can lead to cracking and fracture of the parts. A large part of the literature teaches those skilled in the art that the phase change from (AuCu)a to AuCuI creates internal stresses that are responsible for these uncontrolled deformations. Recent discoveries show that these deformations are due to stresses already present before the start of the transformation.

[0010] In addition, the deformations generated during the manufacturing of components make it difficult to meet the dimensional tolerances required in the watchmaking and jewelry industries. These deformations are in the order of 0.1 to 0.5% and are unpredictable due to an uncontrolled phase change in the alloy. They cannot therefore be anticipated. These deformations result in components outside manufacturing tolerances and lead to a high quantity of waste, significant reworking of parts, i.e. adjustment, modification or retouching operations. This has the disadvantage of lengthening manufacturing times.

[0011] Furthermore, a part undergoing long exposure to room temperature and various manufacturing processes involving low heating has most likely already significantly initiated the phase transformation in the alloy but in an uncontrolled manner. This can result in a lack of control of the geometry during manufacturing, particularly if it involves heat treatment during brazing, for example.

[0012] The present invention aims to overcome these drawbacks by proposing a method for manufacturing a watch or jewelry component comprising at least one part made of at least a binary metal alloy based on gold and copper comprising at least 58% gold by weight relative to the total weight of the alloy, making it possible to obtain at least 25% of AuCuI phase by aiming to relax the internal stresses before carrying out the phase change from (AuCu)a to AuCuI in order not to generate uncontrolled deformation, which makes it possible to guarantee compliance with the manufacturing tolerances imposed in the fields of watchmaking and jewelry. The internal stresses responsible for the deformations are often residual stresses of mechanical or thermal origin.

[0013] Another aim of the present invention is to propose a method for manufacturing a watch or jewelry component comprising at least one part made of at least binary metal alloy based on gold and copper comprising at least 58% gold by weight having improved mechanical properties.

[0014] Disclosure of the invention

[0015] To this end, the invention relates to a method for manufacturing a watch or jewelry component comprising at least one part made of at least a binary metal alloy based on gold and copper comprising at least 58% gold by weight, said method comprising at least the following steps: a) providing a part comprising at least one solid part composed of said metal alloy; b) applying different manufacturing operations to the part to obtain the watch or jewelry component.

[0016] According to the invention, said method comprises at least one step c) of applying to said part a heat treatment implemented to control the dimensional variations of the part during the manufacturing process, said heat treatment comprising a first temperature rise to a temperature TR between the phase transition temperature (AuCu)a / AuCuII and the melting temperature of the alloy, directly followed by a first maintenance at the temperature TR for a period of at least 1 minute, preferably between 5 minutes and 48 hours, preferably between 10 minutes and 300 minutes, and more preferably between 30 minutes and 90 minutes, directly followed by a temperature reduction to the ambient temperature of 25°C, said temperature reduction comprising, immediately after the first maintenance at the temperature TR, a first temperature reduction at a rate between 0.1°C / min and 6,000°C / min,preferably between 1°C / min and 10°C / min, more preferably between 2°C / min and 5°C / min, at least up to a temperature TP of between 100°C and the AuCuI / AuCuII phase transition temperature, as well as a second holding at the temperature TP for a period of between 0 and 48 hours chosen to allow the alloy to transform into a state in which it has at least 25% of ordered AuCuI phase, said second holding at the temperature TP being directly followed by a second temperature reduction to room temperature of 25°C at a rate greater than or equal to that of the first reduction, preferably between 20°C / min and 100°C / min, the alloy of the part obtained in step c) being in a state in which it has at least 25% of ordered AuCuI phase, and the part obtained in step c) having a geometry preserved and controlled dimensional variations during the manufacturing process,step c) being implemented before step b) and / or during step b).,

[0017] Such a process advantageously makes it possible to obtain a watch or jewelry component made of at least 14K gold / copper alloy which comprises at least 25% of AuCuI phase without creating internal stress during the phase transformation from (AuCu)a to AuCuI, in order not to generate uncontrolled deformation. This allows dimensional control during the phase transformation from (AuCu)a to AuCuI which occurs either voluntarily or involuntarily (spontaneously) during the manufacturing operations of the watch or jewelry component and time.

[0018] Such a process advantageously makes it possible to obtain a watch or jewelry component in at least 14K gold / copper alloy that meets manufacturing tolerances. The process of the invention advantageously makes it possible to improve the dimensional control of the parts and thus reduce the number of defective components and retouching operations.

[0019] In addition, the method according to the invention makes it possible to improve the mechanical properties of the alloy such as the elastic limit while maintaining a very acceptable ductility, as well as an advantageous increase in hardness.

[0020] The present invention also relates to a watch or jewelry component obtained by the manufacturing method as defined above.

[0021] The present invention also relates to a method for controlling the dimensional variations of a part made of at least a binary metal alloy based on gold and copper comprising at least 58% gold by weight during a manufacturing process for a watch or jewelry component from said part, said manufacturing process comprising at least one manufacturing operation for which uncontrolled dimensional variations are normally observed, by applying a heat treatment comprising a first temperature rise to a temperature TR between the phase transition temperature (AuCu)a / AuCuII and the melting temperature of the alloy, directly followed by a first maintenance at the temperature TR for a period of at least 1 minute, preferably between 5 minutes and 48 hours, preferably between 10 minutes and 300 minutes, and more preferably between 30 minutes and 90 minutes,directly followed by a temperature reduction to room temperature of 25°C comprising, immediately after the first maintenance at temperature TR, a first temperature reduction at a rate of between 0.1°C / min and 6,000°C / min, preferably between 1°C / min and 10°C / min, more preferably between 2°C / min and 5°C / min, at least to a temperature TP of between 100°C and the AuCuI / AuCuII phase transition temperature, a second maintenance at temperature TP for a period of between 0 and 48 hours chosen to allow the alloy to transform into a state in which it has at least 25% of ordered AuCuI phase, said second maintenance at temperature TP being directly followed by a second temperature reduction to room temperature of 25°C at a rate greater than or equal to that of the first reduction, preferably between 20°C / min and 100°C / min,the alloy of the treated part being in a state in which it has at least 25% of ordered AuCuI phase, said heat treatment being applied to the part at least before or during said manufacturing operation.,

[0022] Brief description of the drawings

[0023] Other characteristics and advantages of the present invention will appear on reading the following detailed description of different embodiments of the invention, given as non-limiting examples, and made with reference to the appended drawings in which:

[0024] - figure 1 schematically represents the steps of the manufacturing process according to the invention;

[0025] - figures 2 to 4 represent the temperature curves for different variants of heat treatment applied in step c) of the manufacturing method according to the invention;

[0026] - figure 5 represents the thermal sequences for a manufacturing method according to the invention comprising brazing;

[0027] - figures 6, 7 and 8 respectively represent the measurements of the external diameter, flatness and circularity of three same parts, as a function of each heat treatment according to the temperature curves of figure 5;

[0028] - Figures 9, 10 and 11 respectively represent the measurements of the external diameter, flatness and circularity of three same parts as a function of different heat treatments applied, including a TM stabilization heat treatment according to the temperature curves of Figure 3, the duration of the second holding at temperature TP being 0; - Figure 12 represents the measurements of the external diameter of three same parts as a function of different heat treatments applied, including a TMM maximized stabilization heat treatment according to the temperature curves of Figure 3, the duration of the second holding at temperature TP being 60 minutes;

[0029] - Figures 13, 14 and 15 respectively represent the measurements of the external diameter, flatness and circularity of three same parts according to different heat treatments applied, including a standard 300°C TD hardening heat treatment from a part annealed at 650°C and quenched in water at room temperature;

[0030] - figure 16 represents the relative reduction in the external diameter of four parts of different geometries as a function of different heat treatments applied, including a stabilization heat treatment TM according to the temperature curves of figure 3, the duration of the second maintenance at temperature TP being 0;

[0031] - Figure 17 represents the stress as a function of elongation for specimens having undergone different heat treatments;

[0032] - Figure 18 is an optical image of the microstructure after electrochemical attack of the alloy obtained after traditional hardening; and

[0033] - figure 19 is an optical image of the microstructure after electrochemical attack of the microstructure of the alloy obtained after hardening according to a heat treatment applied according to the method of the invention.

[0034] Embodiments of the invention The present invention relates to a method for manufacturing a watch or jewelry component comprising at least one part made of at least a binary metal alloy based on gold and copper comprising at least 58% gold by weight, and for example 34% copper and 8% silver, which corresponds to a 14K alloy. The metal alloy may comprise up to 92% gold by weight, with 8% copper, which corresponds to a 22K alloy.

[0035] Preferably, said alloy comprises by weight 75% gold, and between 9% and 25% copper, the remainder to reach 100% by weight being one or more elements chosen from the group comprising for example silver, palladium, platinum, indium, zinc, etc. However, these elements are added in small quantities so that the gold and copper remain sufficiently concentrated in terms of mass proportions and in particular atomic proportions. This includes the 2N / 3N / 4N / 5N / 6N alloys which each correspond to a color for which there are several compositions to obtain them. The ternary alloys used may for example have the compositions defined in Table I below, given in mass percentages:

[0036] Table I Preferably, the alloy used is the 5N alloy comprising by weight 75% gold, 20.5% copper and 4.5% silver.

[0037] With reference to Figure 1, the method according to the invention comprises at least one step a) consisting of providing a part comprising at least one solid part composed of the metal alloy defined above. These alloys are very generally supplied to watchmaking and jeweler users prepared by refiners in an annealed state (for example at 650°C) then quenched in water at 25°C, so that said alloys are in the (AuCu)a phase which is soft (approximately 165 HV for a 5N alloy as defined above) when the parts arrive at the watchmaking and jeweler users.

[0038] Said part can be supplied in the form of a solid raw part 1, directly obtained after the manufacture of the alloy, as shown in Figure 1. The solid raw part 1 can be for example in the form of a strip or a profile. It is obvious that the part used in the method of the invention can be supplied already in the form of a blank 2 or in the form of a partially produced semi-finished product 4 which must still undergo other manufacturing operations before obtaining the watch or jewelry component 6 in its finished state. In Figure 1, the watch or jewelry component is shown in the form of a watch case as an example.It is obvious that the watch or jewelry component manufactured according to the method of the invention can be any watch, jewelry or jewelry component made at least partially from the metal alloy defined above, such as an element of the exterior or of a movement of a watch, such as a wheel or a bridge, or a piece of jewelry.

[0039] The method according to the invention also comprises a step b) consisting of applying to the part different manufacturing operations to obtain the watch or jewelry component in its finished state. These manufacturing operations for producing the watch or jewelry component 6 according to step b) comprise all the production operations necessary to obtain a finished product. They can be chosen for example from the group comprising storage, stamping, machining, such as machining by turning or milling, sintering, heat treatment, engraving, such as laser engraving, punching, 3D printing, setting, bonding, polishing, diamond plating, washing and brazing, different operations being able to be used in combination.

[0040] According to the invention, the method comprises at least one step c) of applying to said part a heat treatment implemented to control the dimensional variations of the part during the manufacturing process, in a repeatable manner.

[0041] Said heat treatment comprises at least a first temperature rise, according to the temperature curve AB, to a temperature TR between the phase transition temperature (AuCu)a / AuCuII TTP and the melting temperature of the alloy, directly and immediately followed by a first maintenance, according to the temperature curve BC, at the temperature TR for a period of at least 1 minute, preferably between 5 minutes and 48 hours, preferably between 10 minutes and 300 minutes, and more preferably between 30 minutes and 90 minutes, directly followed by a temperature reduction, according to the temperature curve CD, to the ambient temperature of 25°C, said temperature reduction according to the curve CD comprising, immediately after the first maintenance BC at the temperature TR, a first temperature reduction at a rate between 0.1°C / min and 6,000°C / min, preferably between 1°C / min and 10°C / min,more preferably between 2°C / min and 5°C / min, at least up to a temperature TP of between 100°C and the AuCuII / AuCuI phase transition temperature, for example 250°C, as well as a second hold at temperature TP, according to the temperature curve EF shown in Figures 3 and 4, for a duration of between 0 and 48 hours chosen as a function of the speed of the first temperature reduction to allow the alloy to transform into a state in which it has at least 25% of ordered AuCuI phase for less than 75% of (AuCu)a phase, said second hold at temperature TP immediately following or subsequently said first reduction and being directly and immediately followed by a second reduction in temperature to room temperature of 25°C at a speed greater than or equal to that of the first reduction, for example between 20°C / min and 100°C / min,the alloy of the part obtained in step c) being in a state in which it has at least 25% of ordered AuCuI phase, and the part obtained in step c) having a geometry preserved and dimensional variations controlled during the manufacturing process, step c) being carried out before step b) and / or during step b), for example as an intermediate sub-step during step b), or as the last sub-step of step b).,

[0042] In practice, the appearance of the AuCuII phase is not necessarily observed, contrary to what theoretical binary diagrams predict. The phase transformation then occurs directly from (AuCu)a to AuCuI with hysteresis between the rise and fall, so that the TTP temperature is most often considered to be the phase transition temperature from (AuCu)a to AuCuI.

[0043] In the present description, however, the theoretical presence of the AuCuII phase has been considered based on the phase transition temperatures AuCuI to AuCuII and AuCuII to (AuCu)a which give an indication of the temperatures to be used in the implementation of the manufacturing process of the invention.

[0044] In practice, the theoretical phase transition temperatures AuCuI to AuCuII and AuCuII to (AuCu)a are close to each other (generally 20°C difference, with the alloy elements being able to increase or decrease this difference), said temperatures being quite close to the actual phase transition temperature AuCuI to (AuCu)a.

[0045] The parameters of the heat treatment implemented in step c) can be chosen to allow the alloy to transform into a state in which it has at least 60% of ordered AuCuI phase for less than 40% of (AuCu)a phase.

[0046] The parameters of the heat treatment implemented in step c) can be chosen to allow the alloy to transform into a state in which it more preferably has at least 95% of ordered AuCuI phase for less than 5% of (AuCu)a phase, and more preferably at least 99% of ordered AuCuI phase for less than 1% of (AuCu)a phase. The (AuCu)a / AuCuI phase transformation rate tends towards 100% asymptotically. But in practice, the (AuCu)a / AuCuI phase transformation rate is around 99% when trying to maximize this transformation rate.

[0047] The duration of the second hold at temperature TP according to the temperature curve EF different or not from 0, and therefore the presence or not of said second hold at temperature TP, depends on the speed of the first temperature drop and the desired phase transformation rate (AuCu)a / AuCuI.

[0048] Thus, according to an embodiment in which the duration of the second holding at temperature TP is equal to 0 (therefore no second holding at temperature TP), the temperature reduction to the ambient temperature of 25°C of step c) is a temperature reduction immediately after the first holding BC at temperature TR, said reduction being carried out continuously at a rate of between 0.1°C / min and 2°C / min, preferably between 0.5°C / min and 2°C / min, more preferably between 0.5°C / min and 1°C / min, down to the ambient temperature of 25°C, without a temperature increase, according to the temperature curve CD shown in Figure 2. Such an embodiment makes it possible to obtain at least 95% of ordered phase AuCuI without it being necessary to apply a second holding at temperature TP.

[0049] According to another embodiment in which the duration of the second maintenance at temperature TP is non-zero (therefore presence of a second maintenance at temperature TP), the first temperature reduction takes place at a speed between 0.1 °C / min and 6,000°C / min, preferably between 1 °C / min and 10°C / min, preferably between 2°C / min and 10°C / min, the duration of the second holding at temperature TP being between 1 minute and 48 hours, preferably between 10 minutes and 300 minutes, preferably between 30 minutes and 90 minutes, said duration being chosen to allow the alloy to transform into a state in which it has at least 25% of ordered phase AuCuI for less than 75% of phase (AuCu)a, preferably at least 60% of ordered phase AuCuI for less than 40% of phase (AuCu)a, preferably at least 95% of ordered phase AuCuI for less than 5% of phase (AuCu)a, and more preferably at least 99% of ordered phase AuCuI for less than 1% of phase (AuCu)a. The speed of the second temperature reduction can be equal to or greater than that of the first temperature reduction, preferably between 20°C / min and 6000°C / min.

[0050] According to a first variant, the first reduction is immediately followed by the second holding at temperature TP as shown in Figure 3, the first temperature reduction taking place from temperature TR to temperature TP, according to the temperature curve CE, directly and immediately followed by the second holding at temperature TP according to the curve EF directly and immediately followed by the second temperature reduction according to the curve FD. The speed of the second temperature reduction may be equal to or greater than that of the first temperature reduction, preferably between 20°C / min and 6000°C / min, preferably between 20°C / min and 100°C / min. The heat treatment does not include any temperature increase between C and D before reaching the temperature of 25°C and in particular after the second holding at temperature TP according to the curve EF.

[0051] According to another variant, the first decrease is subsequently followed by the second holding at temperature TP as shown in Figure 4, the part being able to remain for a certain time at 25°C before subsequently applying the second holding at temperature TP according to the curve EF, the first decrease in temperature taking place from temperature TR to the ambient temperature of 25°C, according to the temperature curve CG, a second increase in temperature up to temperature TP then being provided according to the curve HE, followed directly and immediately by the second holding at temperature TP directly and immediately followed by the second decrease in temperature. The heat treatment does not include any increase in temperature between C and G before reaching the temperature of 25°C for the first time.The speed of the second temperature reduction may be equal to or greater than that of the first temperature reduction, for example between 20°C / min and 100°C / min.

[0052] It is specified that whatever the method of implementing the heat treatment used, the heat treatment does not include any temperature increase until the ambient temperature of 25°C has been reached for the first time. After the first maintenance at the temperature TR, the temperature drops uninterruptedly from the temperature TR until the ambient temperature of 25°C is reached for the first time, although it may be constant over a certain period as described above in relation to Figure 3, but without any temperature increase until the ambient temperature of 25°C has been reached for the first time.

[0053] Regardless of the method of implementing the heat treatment used, the first temperature rise to temperature TR according to temperature curve AB is preferably carried out at a rate greater than 20°C / min, and more preferably at a rate greater than or equal to 30°C / min. Preferably, the first temperature rise to temperature TR according to temperature curve AB is carried out at a rate of 30°C / min.

[0054] Similarly, the second temperature rise to temperature TP according to the temperature curve HE is preferably carried out at a rate greater than 20°C / min, and more preferably at a rate greater than or equal to 30°C / min. Preferably, the second temperature rise to temperature TP according to the temperature curve HE is carried out at a rate of 30°C / min.

[0055] Regardless of the method of implementing the heat treatment used, the temperature TR is at least 1°C higher, preferably at least 10°C, preferably at least 50°C, than the phase transition temperature (AuCu)a / AuCuII, and at least 1°C lower, preferably at least 10°C, preferably at least 50°C lower than the melting temperature of the alloy. For example, for 2N / 3N / 4N / 5N / 6N alloys comprising 75% by weight of gold, copper and silver as defined in Table I, the phase transition temperature (AuCu)a / AuCuII TTP is generally around 350°C (between 340°C and 360°C) depending on the silver content, and the melting temperature is approximately 890°C. Therefore, for this type of alloy, the TR temperature can be between 400°C and 840°C. Preferably for this type of alloy, the TR temperature is in the order of 450°C to 500°C.It is obvious that the person skilled in the art will adapt the temperature range TR according to the composition of the alloy used. For example, for an alloy comprising 75% by weight of gold, copper and platinum, such as the Au750 / Cu225 / Pt25 alloy, the phase transition temperature is approximately 420°C, and the melting temperature is approximately 900°C, so that the temperature TR can be between 470°C and 850°C.

[0056] The duration of the first hold at temperature TR according to the temperature curve BC is chosen to allow the relaxation of residual stresses in the (AuCu)a phase in which the alloy is found at this temperature, in particular after the manufacture of the solid part by a refiner. This relaxation phase must however not be too long so as not to cause an increase in the grain size. It is therefore a question of finding a compromise between this harmful effect and the relaxation of the stress. The duration of the first hold at temperature TR according to the temperature curve BC is preferably 60 minutes. For a 5N alloy as defined above, the duration of the first hold BC is preferably 60 minutes at a temperature of 450°C.

[0057] The alloy in which the residual stresses are fully relaxed is then cooled according to the CD temperature curve at a sufficiently slow and homogeneous rate, less than 6,000°C / min, so as not to induce a thermal gradient inside the part likely to recreate stresses and cause deformation during the phase transformation (AuCu)a into the AuCuI phase. During this phase transformation, the hardness of the alloy increases progressively until it reaches its maximum which is approximately 300 HV for a 5N alloy as defined above. Vickers hardness test methods are defined according to ISO 6507.

[0058] The duration of holding at temperature TP is chosen to allow the alloy to transform according to the desired transformation rate. For the same temperature TP, holding at temperature TP for a longer time makes it possible to increase the transformation rate of the (AuCu)a phase into the AuCuI phase. Those skilled in the art also know that the choice of temperature TP also makes it possible to obtain the desired transformation rate of the (AuCu)a phase into the AuCuI phase.

[0059] In particular, a person skilled in the art knows that the higher the TP temperature, the higher the transformation rate of the (AuCu)a phase into the AuCuI phase for an equivalent heat treatment time. A person skilled in the art also knows that a larger grain size promotes phase transformation, so that it will therefore be necessary to reduce the TP temperature to obtain an alloy having an ordered AuCuI phase rate of approximately 25%. Furthermore, since a higher work hardening rate promotes phase transformation, it will therefore be necessary to reduce the TP temperature to obtain an alloy having an ordered AuCuI phase rate of approximately 25%.

[0060] For example, for a 5N gold and copper-based alloy as defined above, having an initial grain size of 30 pm and a work hardening rate of 0% (annealed state), the temperature TP is approximately between 100°C and 120°C to allow the alloy to transform into a state in which it has an AuCuI ordered phase rate of approximately 25%, approximately between 125°C and 150°C to allow the alloy to transform into a state in which it has an AuCuI ordered phase rate of approximately between 30% and 60%, and approximately between 250°C and the AuCuII / AuCuI phase transition temperature to allow the alloy to transform into a state in which it has an AuCuI ordered phase rate of at least 95%, or even 99%.

[0061] The TR and TP temperatures must be adapted according to the alloying elements which can influence the phase transition temperatures.

[0062] Step c) advantageously makes it possible to stabilize, that is to say to preserve, the geometry that the part has at the time of implementation of step c). In particular, the flatness and circularity of the part are preserved during the implementation of step c).

[0063] In addition, during the transformation of the (AuCu)a phase into the AuCuI phase, a reduction in the dimensions of the part occurs, but this reduction, probably linked to the change in volume of the crystallographic mesh, occurs very advantageously in a controlled manner, being very repeatable and reproducible, whatever the shape of the part for a given alloy, as will be detailed in the examples below.

[0064] For this purpose, the heat treatment implemented in step c) of the process of the invention is chosen to obtain a transformation of at least 25%, preferably at least 60%, more preferably at least 95%, and more preferably at least 99%, of the disordered (AuCu)a phase into an ordered AuCuI phase, perfectly thermodynamically stable below the phase transition temperature TTP, in order to obtain dimensional variations during the manufacturing process that are controlled and acceptable in the watchmaking and jewelry fields.

[0065] Thus, for example, the part whose 18K gold and copper-based alloy comprises at least 95% AuCuI phase for less than 5% (AuCu)a phase obtained after the implementation of step c), is the homothetic of the part under the (AuCu)a phase before the implementation of step c), the homothetic ratio being repeatable and only linked to the gold / copper alloy used and the chosen transformation rate. For example, for a 5N gold / copper alloy as defined above, the shrinkage is approximately 0.18% for a 95% transformation, this shrinkage being constant for a 95% transformation rate and therefore repeatable regardless of the shape of the part.In this state, even if the dimensions continue to decrease slightly when the part is re-exposed once or twice to a temperature below the AuCuII / AuCuI phase transition temperature TTP, while maintaining its geometry, these last dimensional variations are of the order of a few microns, which are very acceptable variation values ​​in the watchmaking and jewelry fields.

[0066] For example, a heat treatment consisting of a temperature rise to 30°C / min followed by a hold at 450°C for 60 minutes, followed by a continuous temperature decrease at a rate of 2°C / min to room temperature of 25°C, as shown in Figure 2, makes it possible to obtain a part in a 5N gold and copper-based alloy as defined above comprising at least 95% of stable AuCuI ordered phase for less than 5% of disordered phase (AuCu)a. In this state, once the dimensions have been modified following the phase change (AuCu)a / AuCuI, a slight reduction (a few microns) in the dimensions of the part is observed when it is re-exposed for the first time to a temperature lower than the AuCuII / AuCuI phase transition temperature TTP, then a further reduction of a lesser value in the dimensions when the part is re-exposed a second time to a temperature lower than the TTP temperature.However, these reductions in dimensions are suitable for the field of watchmaking and jewelry, the geometry of the piece being preserved.

[0067] A similar heat treatment but with a continuous temperature decrease at a rate lower than 1 °C / min, for example 0.5 °C / min, down to room temperature of 25 °C, as shown in Figure 2, makes it possible to obtain a part in a 5N gold and copper-based alloy as defined above comprising 99% stable ordered phase AuCuI for 1% disordered phase (AuCu)a. In this state, as will be described in more detail below, the geometry and dimensions of the part treated according to step c) are perfectly stable, once the dimensions have been modified following the phase change (AuCu)a / AuCuI, no variation in dimensions being observed when the part is re-exposed to a temperature lower than the TTP temperature.

[0068] For the methods of implementing the heat treatment with a first temperature reduction at a rate of between 2°C / min and 6,000°C / min with a second maintenance at the temperature TP according to figures 3 or 4, the duration of said second maintenance at the temperature TP according to the curve EF will be increased as the first reduction is rapid in order to obtain a transformation of at least 25%, preferably at least 60%, more preferably at least 95%, and more preferably at least 99%, of the phase (AuCu)a into AuCuI.

[0069] For example, for a 5N gold and copper-based alloy as defined above, having an initial grain size of 30 μm, a work-hardening rate of 0% (annealed state), a heat treatment consisting of a temperature rise AB at 30°C / min followed by the first hold BC at the temperature TR equal to 450°C for 60 minutes, followed by the first temperature reduction CE at a rate of 2°C / min to the temperature TP of 250°C, followed by the second hold EF at 250°C for 60 minutes, followed by the second temperature reduction FD to room temperature of 25°C at a rate of 20°C / min, as shown in Figure 3. This heat treatment makes it possible to obtain a part in an alloy comprising 99% of ordered phase AuCuI for 1% of disordered phase (AuCu)a.

[0070] For a 5N gold and copper-based alloy as defined above, it is also possible, for example, to apply a heat treatment consisting of a temperature rise AB at 30°C / min followed by the first hold BC at the temperature TR equal to 650°C for 30 minutes, followed by the first temperature drop CG at a rate of 1200°C / min to the ambient temperature of 25°C (non-critical), followed subsequently by the second temperature rise HE at 30°C / min, followed by the second hold EF at the temperature TP of 120°C for 60 minutes, followed by the second temperature drop FD to the ambient temperature of 25°C at a rate of 30°C / min, non-critical, as shown in Figure 4. This heat treatment makes it possible to obtain a part in an alloy comprising 25% of ordered phase AuCuI for 75% of disordered phase (AuCu)a.

[0071] For a 5N gold and copper-based alloy as defined above, it is also possible, for example, to apply a heat treatment consisting of a temperature rise AB at 30°C / min followed by the first hold BC at the temperature TR equal to 650°C for 30 minutes, followed by the first temperature drop CG at a rate of 1200°C / min to the ambient temperature of 25°C (non-critical), followed subsequently by the second temperature rise HE at 30°C / min, followed by the second hold EF at 150°C for 60 minutes, followed by the second temperature drop FD to the ambient temperature of 25°C at a rate of 30°C / min, non-critical as shown in Figure 4. This heat treatment makes it possible to obtain a part in an alloy comprising 60% of ordered phase AuCuI for 40% of disordered phase (AuCu)a.

[0072] For a 5N gold and copper-based alloy as defined above, it is also possible, for example, to apply a heat treatment consisting of a temperature rise AB at 30°C / min followed by the first hold BC at the temperature TR equal to 450°C for 60 minutes, followed by the first temperature drop CG at a rate of 20°C / min to the ambient temperature of 25°C, subsequently followed by the second temperature rise HE at 30°C / min, followed by the second hold EF at 250°C for 60 minutes, followed by the second temperature drop FD to the ambient temperature of 25°C at a rate of 20°C / min, as shown in Figure 4. This heat treatment makes it possible to obtain a part in an alloy comprising 95% of ordered phase AuCuI for 5% of disordered phase (AuCu)a.

[0073] In addition, in a particularly advantageous manner, the heat treatment implemented in step c) of the method of the invention is chosen to obtain a part in an alloy based on 18K gold and copper in a state in which it preferably has at least 99% of stable ordered phase AuCuI, for less than 1% of disordered phase (AuCu)a, in order to stabilize the dimensions of the part, once its dimensions have been modified following the phase change (AuCu)a / AuCuI, when the part is exposed to a temperature below the AuCuII / AuCuI phase transition temperature TTP. For example, for a 5N gold / copper alloy as defined above, the shrinkage is approximately 0.19% for a 99% transformation, this shrinkage being constant for a transformation rate of 99% and therefore repeatable whatever the shape of the part.For the gold / copper alloys defined in Table I, we observe that the shrinkage is all the more significant when the ratio of atomic concentration of gold / atomic concentration of copper is close to 1.

[0074] Furthermore, this shrinkage remains fixed, the dimensions of said alloy part in a state in which it has at least 99% of ordered AuCuI phase no longer undergoing any modification even if the part is re-exposed several times to a temperature lower than the AuCuII / AuCuI phase transition temperature TTP.

[0075] This heat treatment allowing maximized stabilization of the AuCuI phase (i.e. stable dimensions of the part once its dimensions have been modified following the phase change (AuCu)a / AuCuI) can be applied according to the different modes of implementation of the heat treatment described more specifically above in relation to their respective figures 2 to 4. The temperature range for which stable dimensions of the part are obtained, once its dimensions have been modified following the phase change (AuCu)a / AuCuI, depends on the transformation rate of the phase (AuCu)a into the AuCuI phase.

[0076] Thus, for a 5N alloy as defined above, the heat treatment of step c) can be implemented to allow the alloy to transform into a state in which it has an ordered phase rate AuCuI of approximately 25% (with for example a temperature TP of approximately 120°C), so that the part obtained has controlled dimensional variations and a stabilized percentage of dimensional variation (i.e. stable dimensions) when a manufacturing operation is applied to it at a temperature of between 25°C and approximately 110°C (such as storage at room temperature or washing at 110°C), said part having controlled dimensional variations if it is subjected to a temperature above 110°C.

[0077] Similarly, for a 5N alloy as defined above, the heat treatment of step c) can be implemented to allow the alloy to transform into a state in which it has an ordered phase rate AuCuI of approximately 60% (with for example a temperature TP of approximately 150°C), so that the part has controlled dimensional variations and a stabilized percentage of dimensional variation (i.e. stable dimensions) when a manufacturing operation is applied to it at a temperature of between 25°C and approximately 140°C, said part having controlled dimensional variations if it is subjected to a temperature above 140°C.

[0078] Similarly, for a 5N alloy as defined above, the heat treatment of step c) may be implemented to allow the alloy to transform into a state in which it has an ordered AuCuI phase rate greater than approximately 99% (with, for example, a TP temperature of approximately between 250°C and the AuCuII / AuCuI phase transition temperature), such that the part has controlled dimensional variations and a stabilized dimensional variation percentage (i.e., stable dimensions) when a manufacturing operation is applied to it at a temperature of between 25°C and the AuCuII / AuCuI phase transition temperature, said part having controlled dimensional variations if it is subjected to a temperature greater than the AuCuII / AuCuI phase transition temperature.

[0079] Thus, the phase transformation rate (AuCu)a to AuCuI phase can be advantageously chosen according to the temperature of the manufacturing operation for which the stability of the dimensions of the part is sought. For example, a phase transformation rate (AuCu)a to AuCuI phase of 25% will be sufficient if the temperature of all the manufacturing operations of the watch or jewelry component is lower than 110°C if one wishes to have a part with stable dimensions throughout the manufacturing process. A phase transformation rate (AuCu)a to AuCuI phase of 99% will be necessary if one wishes to have a part with stable dimensions for any manufacturing operation at a temperature lower than the TTP temperature.Different heat treatments according to the method of the invention can be used during the manufacturing process, to obtain the phase transformation rate (AuCu)a into AuCuI phase depending on the temperature of the manufacturing operation for which stabilization of the dimensions is sought.

[0080] For example, a heat treatment with a continuous temperature decrease at a rate of the order of 0.1 °C / min to 1 °C / min down to the ambient temperature of 25 °C, as shown in Figure 2, and a heat treatment comprising a first temperature decrease of between 2 °C / min and 6,000 °C / min, in a homogeneous manner, and a second maintenance at the temperature TP for a sufficient time as shown in Figures 3 and 4, make it possible to very advantageously obtain a maximized stabilization of the AuCuI phase, the part, in particular in a 5N gold and copper-based alloy as defined above, obtained then comprising at least 99% of stable ordered AuCuI phase for less than 1% of disordered phase (AuCu)a.In this state, the geometry and dimensions of the part treated according to step c) are perfectly stable, once the dimensions have been modified following the phase change (AuCu)a / AuCuI, no variation in dimensions being observed when the part is re-exposed to a temperature below the TTP temperature. Thus, regardless of the method of implementing the heat treatment used, the maximized stabilization of the AuCuI phase makes it possible to guarantee excellent stability of the dimensions of the part obtained after the reduction in dimensions linked to the phase change, when the part is exposed to a temperature below the AuCuII / AuCuI phase transition temperature TTP, in particular for a rate of transformation of phase (AuCu)a into AuCuI phase of 99%, this exposure temperature of the part for which the dimensions are stable being a function of the rate of transformation of phase (AuCu)a into AuCuI phase.

[0081] Since the AuCuI phase is perfectly stable at a temperature below the phase transition temperature which is below 350°C for the 5N alloy as defined above, the part will retain intact geometry, properties, microstructure and aesthetics during short or prolonged exposure to a temperature below this value.

[0082] In addition, the AuCuI phase has a hardness of about 300HV compared to that of the (AuCu)a phase which is 165HV. This therefore helps to improve the life of the manufactured component by increasing its scratch resistance.

[0083] The hardness of the part obtained in step c) increases as a function of the transformation rate of the (AuCu)a phase into the AuCuI phase, the increase in hardness for a transformation rate Tx being substantially equal to (hardness of the alloy at the transformation rate of the (AuCu)a phase into the AuCuI phase of 100% - hardness of the alloy at the transformation rate of the (AuCu)a phase into the AuCuI phase of 0%) x (transformation rate Tx / 100).

[0084] In addition, the implementation of step c) of the method of the invention makes it possible to improve the mechanical properties of the material, such as the yield strength which is very significantly increased compared to standard hardening at 300°C, while retaining a very acceptable ductility, as will be demonstrated in the examples below. Without being bound by theory, this can be explained by the fact that the alloy treated according to step c) has a finer microstructure which seems to better accommodate deformation. Thus, the method of the invention makes it possible to guarantee hardening of the 18K gold / copper alloy without deformation of the geometry that the part had before the implementation of step c), while controlling the dimensional variants of the part which are specific to an alloy, independently of the shape of the part, in particular during re-exposure at a temperature below the AuCuII / AuCuI phase transition temperature TTP.The manufacturing process according to the invention therefore advantageously makes it possible to harden parts and improve the mechanical properties of the alloy, such as the elastic limit, while maintaining very acceptable ductility, without causing uncontrolled deformations.

[0085] Consequently, for a given alloy, it is easy to anticipate the dimensional variations of the part after the implementation of step c) by giving the part, before the implementation of step c), the necessary oversizes to obtain a hardened part that is not deformed and has the correct dimensions, which makes it possible to guarantee compliance with the manufacturing tolerances imposed in the fields of watchmaking and jewelry.

[0086] To this end, the method of the invention may comprise a preliminary step of measuring the dimensional variations of a sample made from the metal alloy used, said sample being subjected to a heat treatment according to step c), the part provided in step a) being sized to take into account said dimensional variations measured in the preliminary step relative to the dimensions of the watch or jewelry component to be manufactured.

[0087] In a particularly advantageous manner, the preliminary stage comprises the following sub-stages:

[0088] 1) provide a sample of said alloy;

[0089] 2) if said sample of the alloy is likely to have more than 0% of ordered AuCuI phase, returning the alloy sample to a state in which it has 100% of (AuCu)a phase and 0% of ordered AuCuI phase, preferably by an annealing operation followed by quenching in water at the temperature recommended for this alloy; ) determining the percentage of stabilized dimensional variation VDstabilisée corresponding to the percentage of variation in the dimensions of the alloy sample between the initial dimensions of the alloy sample obtained according to sub-step 2) until stable dimensions are obtained when the alloy sample obtained according to sub-step 2) is subjected to a temperature corresponding to the temperature of the manufacturing operation according to step b) for which the stability of the dimensions of the part is sought; ) applying to the alloy sample obtained according to sub-step b) the heat treatment of step c),said heat treatment making it possible to obtain control of the dimensional variations of the sample (no loss of geometry), the parameters being further chosen to obtain a transformed alloy sample in a state in which it has a maximized (AuCu)aZAuCuI phase transformation rate, closest to 100% of ordered AuCuI phase, ) measuring the percentage of maximum dimensional variation VDmax of the alloy sample treated according to sub-step 4), said maximum dimensional variation VDmax being defined as corresponding to a transformation rate of the (AuCu)a phase into the AuCuI phase of 100%, the initial dimensions of the alloy sample obtained according to sub-step 2) corresponding to an initial transformation rate of the (AuCu)a phase into the AuCuI phase of 0%,the percentage of intermediate dimensional variation then being equal to the percentage of maximum dimensional variation VDmax x (intermediate transformation rate / 100); ) determine the transformation rate of the phase (AuCu)a into the phase AuCuI Tx that the alloy of the part must have to obtain a part having controlled dimensional variations and a percentage of dimensional variation stabilized at the temperature of the manufacturing operation according to step b) for which dimensional stability is sought, said transformation rate Tx being equal to 100 x (percentage of dimensional variation VDstabilized determined in sub-step 3) / percentage of maximum dimensional variation VDmax determined in sub-step 4)).,

[0090] In addition, the part provided in step a) is such that the alloy of said part has been brought back to a state in which it has 100% of (AuCu)a phase and 0% of ordered AuCuI phases if said alloy was likely to have more than 0% of ordered AuCuI phase, said part provided in step a) being further dimensioned by adding oversizes to take into account the percentage of dimensional variation VDstabilised determined in sub-step 3) relative to the dimensions of the watch or jewellery component to be manufactured.

[0091] Step c) consists of applying to the part the heat treatment for which the parameters are chosen to allow the alloy to transform according to the transformation rate of the (AuCu)a phase into the AuCuI Tx phase determined in sub-step 6), said heat treatment making it possible to obtain control of the dimensional variations of the part (therefore no loss of geometry), the part obtained in step c) having stable dimensions when exposed to the temperature of the manufacturing operation according to step b) for which dimensional stability is sought, and said part having controlled dimensional variations according to the formula defined in sub-step 5) for the percentage of intermediate dimensional variation if it is subjected to a temperature higher than the temperature for which the dimensions of the part are stable.

[0092] A manufacturing process will preferably be used in which the heat treatment is implemented to transform at least 99% of the (AuCu)a phase into AuCuI in order to guarantee hardening of the 18K gold / copper alloy without deformation of the geometry that the part had before the implementation of step c), while having perfect dimensional stability to guarantee stability of the dimensions during a next heat treatment at a temperature lower than the AuCuII / AuCuI phase transition temperature TTP. Therefore, only the reduction in dimensions linked to the (AuCu)a / AuCuI phase change is to be taken into consideration for oversizes. Furthermore, exposure of the part treated according to step c) to a temperature higher than the (AuCu)a / AuCuII phase transition temperature TTP causes the formation of the (AuCu)a phase, the part then recovering its dimensions before stabilization.A new exposure to the stabilization heat treatment according to step c) with the same parameters as those of the first step c) makes it possible to recover the dimensions of the part after the first stabilization, without ever degrading its geometry. This shows that the transformation is perfectly reversible. The method of the invention therefore advantageously makes it possible to guarantee that, after a heat treatment at a temperature above the phase transition temperature TTP (AuCu)a / AuCuII followed by exposure to a second stabilization heat treatment according to step c) with the same parameters as those of the first step c), the part recovers the dimensions previously given to it after the first exposure to the stabilization heat treatment according to step c).

[0093] Here again, a manufacturing process will preferably be used in which heat treatment is carried out to transform at least 99% of the (AuCu)a phase into AuCuI in order to guarantee perfect dimensional stability, thereby ensuring stability of the dimensions over the widest possible temperature range. Therefore, only the reduction in dimensions linked to the change from (AuCu)a to AuCuI phase is to be taken into consideration for oversizes.

[0094] More generally, if the part is subjected to a temperature higher than the maximum temperature for which the dimensions of the part are stable, the dimensions of the part will be modified but with controlled variations. Re-exposing the part to the same heat treatment as that used to obtain the transformation rate for which the dimensions of the part were stable according to step c) makes it possible to recover the dimensions of the part after the first stabilization, without ever degrading its geometry.

[0095] One or more steps c), carried out in their entirety, as described above may be implemented during the manufacturing process of the watch or jewelry component, in particular depending on the nature of the part supplied in step a), depending on the manufacturing operations implemented during step b) and depending on the moment at which stabilization of the alloy is sought during the manufacturing process.

[0096] Advantageously, step c) can be implemented before step b), for example if it is desired to have a stabilized alloy for storing the parts in the form of solid parts or to stabilize the part as early as possible, in particular when it is already delivered in the form of a blank, before starting the manufacturing operations according to step b). This makes it possible to have parts made of an alloy based on 18K gold and copper whose dimensions remain stable during storage of the parts, for example. As described above, a phase transformation rate (AuCu)a to AuCuI phase of 25% is sufficient for the part to maintain stable dimensions during its storage.

[0097] Advantageously, at least one step c) may be carried out during step b). Step c) may generally be carried out at any time during step b). Preferably, step c) is carried out after having carried out all the manufacturing operations which require low hardness.

[0098] In particular, a step c) may be implemented during step b) before subjecting the part to a manufacturing operation carried out at a temperature below the AuCuII / AuCuI phase transition temperature, such as washing or bonding. If all the manufacturing operations are carried out at a temperature below the AuCuII / AuCuI phase transition temperature, then it is sufficient to implement a single step c) at the earliest of step b).

[0099] The phase transition strongly modifies the surface state so that if it is polished before transformation, a surface roughness in the form of an orange peel will appear due to the lifting of the microstructure during the formation of martensite in the austenitic grains. Performing the polishing on a material stabilized according to step c) allows for no modification of the surface state during a temperature increase. In particular, no orange peel effect is observed during ironing in an oven below the AuCuII / AuCuI phase transition temperature, given that the microstructure has been stabilized beforehand. Similarly, during hot bonding (180°C) for example, a roughness clearly appears on the surface of the unstabilized part while the problems of deformation and orange peel during bonding are avoided with a part stabilized according to step c).

[0100] Depending on the manufacturing operations, a first step c) is implemented before step b), and step b) comprises, for example after machining operations, a manufacturing operation carried out at a temperature higher than the phase transition temperature (AuCu)a / AuCuII, then a second step c) with the same parameters as those of the first step c) is implemented directly after said manufacturing operation. Such an embodiment can be used when the manufacturing operation is crimping or brazing.

[0101] More particularly, with reference to Figure 5, a first step c) is implemented before step b), for example after receiving a part supplied according to step a) in the annealed state at 650°C then quenched in water according to the temperature curve R, and having a given geometry, the first step c) carried out according to the temperature curve TMM making it possible to obtain a maximized controlled transformation of the alloy to give a stabilized part which is a controlled and known homothetic reduction of the part supplied, and step b) comprises, for example after machining operations of the stabilized part, a brazing operation carried out according to the temperature curve B, which detransforms the material, the part being in a shape close to the received shape, then a second step c) with the same parameters as those of the first step c) carried out according to the temperature curve TMM is implemented directly after the brazing operation.The second stabilization heat treatment according to step c) allows the part to be rehardened and to recover, after brazing, the dimensions of the part stabilized by the first stabilization heat treatment according to step c) before brazing. It should be noted that the chemical compositions of the brazes are very close to those of the alloy to approximate its color. Thus, the braze behaves in a very similar way to that of the part and undergoes the same volume changes, which ensures that the transformation will not create local constraints. The other manufacturing operations can be implemented to obtain the finished component. For a brazed part, it is therefore possible to carry out a sequence of operations in order to guarantee perfect dimensional control without calculating any phase transformation oversize compared to the dimensions of the part stabilized by the first stabilization heat treatment according to step c).

[0102] For a crimped part, a first step c) is implemented before step b), for example after receiving a part having a given geometry, the first step c) making it possible to obtain a controlled transformation of the alloy to give a stabilized part which is a controlled and known homothetic reduction of the part supplied, and step b) comprises, for example after machining operations of the stabilized part, a heat treatment at a temperature above the phase transition temperature (AuCu)a / AuCuII to soften the alloy, such as annealing followed by water quenching, which detransforms the material, the part being in a shape close to the received shape, followed by a crimping operation carried out on a soft material, then a second step c) with the same parameters as those of the first step c) is implemented directly after the crimping operation.The second stabilization heat treatment according to step c) makes it possible to reharden the part and to recover, after crimping, the dimensions of the part stabilized by the first stabilization heat treatment according to step c) before the softening heat treatment. It is therefore possible to carry out crimping without calculating any phase transformation oversize compared to the dimensions of the part stabilized by the first stabilization heat treatment according to step c).

[0103] The invention also relates to a watch or jewelry component comprising at least one part made of at least binary metal alloy based on gold and copper comprising at least 58% gold by weight obtained according to the manufacturing method described above. This component differs from hardened components obtained by conventional hardening for 60 min at 300°C from a state annealed at 650°C then quenched in water, for example, by a different microstructure. The microstructure is significantly modified by the phase transformation. In this transformation, the austenitic α phase is transformed into the martensitic AuCuI phase, inducing a modification of the parent intra-grain structure.Depending on the heat treatment applied, i.e. between a conventional hardening of 60 min at 300°C and a stabilization heat treatment according to step c) (e.g. 60 min at 450°C + slow cooling at 2°C / min), a slightly different microstructure is observed as shown in Figures 18 and 19. Figure 18 shows an austenitic microstructure obtained after conventional hardening and Figure 19 shows that the austenitic microstructure obtained after a stabilization heat treatment according to step c) is finer.

[0104] The invention also relates to a method for controlling the dimensional variations of a part made of at least a binary metal alloy based on gold and copper comprising at least 58% gold by weight during a method for manufacturing a watch or jewelry component from said part, said manufacturing method comprising at least one manufacturing operation for which uncontrolled dimensional variations are normally observed, by applying a heat treatment comprising a first temperature rise to a temperature TR between the phase transition temperature (AuCu)a / AuCuII and the melting temperature of the alloy, directly followed by a first maintenance at the temperature TR for a period of at least 1 minute, preferably between 5 minutes and 48 hours, preferably between 10 minutes and 300 minutes, and more preferably between 30 minutes and 90 minutes,directly followed by a temperature decrease to room temperature of 25°C comprising, immediately after the first hold at temperature TR, a first temperature decrease at a rate of between 0.1°C / min and 6,000°C / min, preferably between 1°C / min and 10°C / min, more preferably between 2°C / min and 5°C / min, at least to a temperature TP of between 100°C and the AuCuII / AuCuI phase transition temperature, a second hold at temperature TP for a period of between 0 and 48 hours chosen to allow the alloy to transform into a state in which it has at least 25% of ordered AuCuI phase, said second hold at temperature TP being directly followed by a second temperature decrease to room temperature of 25°C at a rate greater than or equal to that of the first decrease, preferably between 20°C / min and 100°C / min,the alloy of the treated part being in a state in which it has at least 25% of ordered AuCuI phase, said heat treatment being applied to the part at least before or during said manufacturing operation.,

[0105] The following examples illustrate the present invention without, however, limiting its scope.

[0106] Examples

[0107] 1) Stability of the 5N alloy at temperatures below the AuCull / AuCul phase transition temperature

[0108] Thick rings are provided in 18k gold / 5N copper alloy as defined above having dimensions similar to a watch case for example, with an outside diameter of 43 mm, an inside diameter of 28 mm and a thickness of 7 mm. The rings are first all treated according to heat treatment R consisting of annealing at 650°C and quenching in water at room temperature. For all the rings provided according to step a) of the process of the invention, the alloy is therefore in its (AuCu)a phase. The hardness is 165 HV.

[0109] Then, three rings A1, A2, A3 are prepared according to step c) of the process of the invention and hardened at 300 HV by applying the stabilization heat treatment TM defined by a temperature rise at a rate of 30°C / min, a first maintenance at the temperature TR of 450°C for 60 minutes, a first reduction in temperature to the temperature TP of 250°C at a rate of 2°C / min followed by the second reduction in temperature at a rate of 20°C / min, as shown in Figure 3, the duration of the second maintenance at the temperature TP being 0. This TM heat treatment for stabilizing the alloy allows a transformation of 95% of the (AuCu)a phase into the AuCul phase.

[0110] The hardened rings A1, A2, A3 are subsequently subjected to two temperings RV1, RV2 at 300°C for 60 minutes, simulating re-exposures of the rings treated according to the method of the invention to a manufacturing operation at a temperature lower than the phase transition temperature AuCull / AuCul. Three other rings A4, A5, A6 are prepared according to step c) of the process of the invention and hardened at 300 HV by applying the maximized stabilization heat treatment TMM defined by a temperature rise at a rate of 30°C / min, a first maintenance at the temperature TR of 450°C for 60 minutes, a first reduction in temperature to the temperature TP of 250°C at a rate of 2°C / min followed by the second maintenance at the temperature TP for 60 minutes followed by the second reduction in temperature at a rate of 20°C / min, as shown in Figure 3, the duration of the second maintenance at the temperature TP being non-zero.This TMM heat treatment for maximized stabilization of the alloy allows a transformation of 99% of the (AuCu)a phase into the AuCuI phase.

[0111] The hardened rings are subsequently subjected to RV1 tempering at 300°C for 60 minutes, corresponding to re-exposures of the rings treated according to the process of the invention to a temperature below the AuCuII / AuCuI phase transition temperature.

[0112] For comparison, three rings A7, A8, A9 supplied in the annealed state (at 650°C) then quenched in water at room temperature are hardened to 300 HV in the traditional way by exposing them to a temperature of 300°C for 60 min according to the TD heat treatment.

[0113] The hardened rings are subsequently tempered at 300°C RV1 for 60 minutes, simulating re-exposure of the rings to a temperature below the AuCuII / AuCuI phase transition temperature.

[0114] For each ring, the outer diameter, as well as the circularity and flatness, are measured after each heat treatment applied.

[0115] The transformation rate is calculated by considering an equivalence between the phase transformation rate, the hardness and the dimensional evolution (shrinkage rate).

[0116] Thus, a transformation rate of the (AuCu)a phase into the AuCuI phase of 100% is assigned when the percentage of dimensional variation is maximum, equal to VDmax (i.e. a maximum shrinkage rate). The transformation rate Tx corresponding to a percentage of dimensional variation VDx is defined by Tx=(VDx / VDmax) x 100.

[0117] The increase in hardness for a transformation rate Tx being substantially equal to (hardness of the alloy at the transformation rate of the (AuCu)a phase into the AuCuI phase of 100% - hardness of the alloy at the transformation rate of the (AuCu)a phase into the AuCuI phase of 0%) x (transformation rate Tx / 100).

[0118] It is observed that during a transformation, the increase in hardness and the percentage of dimensional variation are equivalent and correspond to the same transformation rate.

[0119] Indeed, for example, for a 5N alloy ring treated according to the method of the invention for a complete transformation, a percentage of dimensional variation VDmax equal to approximately 0.19% and an increase in hardness from 160 HV to 300 HV are measured. A ring comprising 100% of (AuCu)a phase is left to age at room temperature for 220 days. A shrinkage of approximately 0.05% and an increase in hardness of 35 HV are observed. The same ring comprising 100% of (AuCu)a phase is exposed to three washes at 110°C. A shrinkage of approximately 0.05% is observed.

[0120] The transformation rate (AuCu)a in AuCuI phase at room temperature and at 110°C corresponding to a shrinkage of 0.05% is equal to (0.05 / 0.19) x 100, or approximately 25%.

[0121] The transformation rate (AuCu)a into the AuCuI phase at room temperature corresponding to an increase in hardness of 35 HV is equal to (35 / (300 - 160)) x 100, or approximately 25%.

[0122] The same transformation rate is obtained for the increase in hardness as that observed for the percentage of dimensional variation in a similar time at room temperature, as well as at 110°C. We therefore have an equivalence between the transformation rate of phase (AuCu)a into AuCuI phase, hardness and dimensional evolution.

[0123] To determine the transformation rate, we can therefore take as a measure either the percentage of dimensional variation or the increase in hardness. However, we will prefer to take as a measure the percentage of dimensional variation which can be determined with more precision than the increase in hardness.

[0124] This means that by applying the method of the invention to a part to have a transformation rate of the (AuCu)a phase into the AuCuI phase of 25%, the dimensions of said part thus treated will be stable when the part is exposed to a temperature between 25°C and 110°C.

[0125] The results obtained for the rings A1, A2, A3 treated according to the method of the invention with a 95% transformation of the (AuCu)a phase into the AuCuI phase are shown in Figures 9, 10 and 11, which respectively represent the measurements of the circumscribed external diameter, the flatness measurements and the circularity measurements as a function of each heat treatment R, TM, RV1 and RV2 on each ring A1, A2, A3.

[0126] The results obtained for the rings A4, A5, A6 treated according to the process of the invention with a transformation of 99% of the (AuCu)a phase into the AuCuI phase are shown in Figure 12 which represents the measurements of the circumscribed external diameter as a function of each heat treatment R, TMM, and RV1 on each ring A4, A5, A6.

[0127] The results obtained for rings A7, A8, A9 for comparison are shown in Figures 13, 14 and 15, which respectively represent the measurements of the circumscribed external diameter, the flatness measurements and the circularity measurements as a function of each heat treatment R, TD, and RV1 on each ring A7, A8, A9. These results show that the parts A1, A2, A3 treated according to the method of the invention with a 95% transformation of the (AuCu)a phase into the AuCuI phase retain an excellent geometry in terms of flatness and circularity (Fig. 10 and 11), even after exposure to the two tempers. Figure 9 shows for the three rings A1, A2, A3 the same first decrease in the average diameter of the part of approximately 70 μm after the implementation of the TM stabilization heat treatment. This first decrease in diameter is therefore carried out in a very repeatable manner, being linked to the change in volume of the mesh.Then we observe a slight decrease in the average diameter of the part after exposure to the tempering (6 pm after RV1 tempering and 2 pm after RV2 tempering) until reaching a state of equilibrium. These last variations are very acceptable in the watchmaking and jewelry fields.

[0128] For parts A4, A5, A6 treated according to the method of the invention with a 99% transformation of the (AuCu)a phase into the AuCuI phase, Figure 12 shows a single decrease in the average diameter of the part of approximately 76 μm after the implementation of the TMM stabilization heat treatment, but in a very repeatable manner, being linked to the change in volume of the mesh. This dimension is stable, since practically no decrease in the average diameter of the part is then observed after exposure to tempering. It is specified that the parts also retain an excellent geometry in terms of flatness and circularity, even after exposure to tempering.

[0129] For the comparative parts A7, A8, A9, the phase transformation caused colossal deformations of the parts, in particular on the geometry. At the end of the transformation, a flatness and circularity defect (see figures 14 and 15) can be observed which can exceed one tenth whereas it was originally less than two hundredths.

[0130] Similar tests are carried out but replacing the re-exposure to tempering at 300°C with re-exposures of the rings hardened at 300 HV according to the TM stabilization heat treatment defined above to washing in production washing baths at 70°C, the rings then being dried in hot air at 110°C. For comparison, annealed and water-quenched rings are also subjected to the same washing and drying. The parts are measured immediately after their last respective heat treatment and are washed three times in the production washing baths. The parts are remeasured between each passage in the washing baths. Identical results are obtained in terms of conservation of the ring geometry and dimensional stability after the implementation of the stabilization heat treatment for the rings treated according to the TM treatment.On the contrary, it is observed that the annealed parts undergo dimensional variations of almost 20 pm in a very repeatable manner after three passages in the washing bath. The hardness of these parts also increased slightly.

[0131] The parts that have been heat treated by the TM heat treatment are not at all affected by passages in the washing baths. This shows that the material has been well stabilized and is insensitive to temperature exposures below 350°C unlike the (AuCu)a phase which is unstable at these temperatures.

[0132] 2) Independence of withdrawal

[0133] Four pieces of different geometry are provided in 18k gold / 5N copper alloy as defined above, piece P1 being a thick ring with an outer diameter of 48 mm, an inner diameter of 28 mm and a thickness of 7 mm, piece P2 being a thin ring with an outer diameter of 38 mm, an inner diameter of 35 mm and a thickness of 5 mm, piece P3 being a flat cylinder with a diameter of 30 mm and a thickness of 10 mm, piece P4 being a flat cylinder with a diameter of 23 mm and a thickness of 7 mm.

[0134] The four parts are treated in the same way and are first treated according to heat treatment R consisting of annealing at 650°C and quenching in water at room temperature. For all the parts supplied according to step a) of the process of the invention, the alloy is therefore in its (AuCu)a phase. The hardness is 165 HV.

[0135] Then, the four parts P1, P2, P3 and P4 are prepared according to step c) of the method of the invention and hardened at 300 HV by applying the stabilization heat treatment TM of the alloy described in the example above allowing a transformation of 95% of the (AuCu)a phase into the AuCuI phase (rise at 30°C / min, first hold at 450°C for 60 minutes, first temperature reduction to 250°C at 2°C / min followed by the second temperature reduction at a rate of 20°C / min, as shown in Figure 3, the duration of the second hold at temperature TP being 0).

[0136] The four hardened parts P1, P2, P3 and P4 are subsequently subjected to the two temperings RV1, RV2 at 300°C for 60 minutes, corresponding to re-exposures of the rings treated according to the process of the invention at a temperature lower than the AuCuII / AuCuI phase transition temperature.

[0137] For each part P1, P2, P3 and P4, the external diameter, as well as the circularity and flatness, are measured after each heat treatment applied.

[0138] The results obtained for the parts P1, P2, P3 and P4 treated according to the method of the invention with a transformation of 95% of the phase (AuCu)a are shown in Figure 16, which represents the relative reduction of the external diameter, i.e. the relative shrinkage, as a function of each heat treatment R, TM, RV1 and RV2 for each part P1, P2, P3 and P4.

[0139] Figure 16 shows that the total shrinkage after RV2 is very similar for all parts P1, P2, P3 and P4. It is on average 0.180 ±0.01%.

[0140] Since these pieces P1, P2, P3 and P4 have very different geometries and come from different batches of material, we can conclude that the material shrinkage is independent of the geometry and the microstructure, it depends only on the alloy, here 5N red gold Au750 / Cu205 / Ag45.

[0141] Similar tests were reproduced but with a TMM stabilization heat treatment as described in the example above. The shrinkage, always independent of the geometry, is approximately 0.19% for 5N red gold for 99% transformation as defined above. For a 4N gold / copper alloy as defined above, the shrinkage, always independent of the geometry, is approximately 0.13%. Furthermore, it was observed that, for all parts P1, P2, P3 and P4, the flatness and circularity of parts P1, P2, P3 and P4 were preserved during the TM or TMM stabilization heat treatment.

[0142] For comparison, similar tests were reproduced but with a TD heat treatment (hardening at 300°C for 60 min from the annealed state at 650°C and quenched in water) as described in the example above. The same orders of magnitude of deformations are observed on the different geometries. The solid parts deform almost as much as the thin parts.

[0143] 3) Mechanical properties

[0144] Mechanical tests were conducted on 5N gold tensile specimens as defined above.

[0145] Test specimens E1, E2, and E3 were exposed to the heat treatments defined in Table II below:

[0146] Test piece E1 is simply treated according to heat treatment R consisting of annealing at 650°C and quenching in water at room temperature.

[0147] Test specimen E2 was hardened by the TM stabilization heat treatment according to step c) as described in the example above.

[0148] For comparison, specimen E3 was hardened by the standard TD treatment at 300°C for 60 minutes.

[0149] For each test piece, the hardness (ISO 6507 standard), the conventional elastic limit (Rpo.2), the tensile strength limit o are measured. m ax and elongation £ (ISO 6892-1 standard). Ductility is calculated by integrating the area under the tensile curve.

[0150] The results are shown in Table II below and represented in Figure 17 which represents the stress as a function of the elongation for the specimen having undergone simple annealing (curve E1), the TM treatment (curve E2) and the TD treatment (curve E3). Table II

[0151] It can be seen in Table II above and in Figure 17 that the TM stabilization heat treatment according to step c) of the invention gives the material very interesting mechanical properties. The yield strength is very significantly increased and the material retains a very acceptable ductility with an area under the curve very close between the annealed state and the hardened state by the TM stabilization heat treatment according to step c) of the invention. It can be seen that the elastic and breaking stresses are higher with the TM treatment than with the TD treatment but the elongation at break is also increased, which results in almost a factor of two on the ductility.

[0152] Despite identical hardness, the mechanical properties with hardening by the TM stabilization heat treatment according to step c) of the invention are more interesting than with hardening at 300°C for 60 min according to the TD heat treatment. This can be explained by a finer microstructure of the alloy which accommodates deformation better.

[0153] 4) Stability of the 5N alloy at temperatures above the phase transition temperature (AuCu)a / AuCuII

[0154] Three thick rings A10, A11, A12 are provided in 18k gold / 5N copper alloy as defined above, having dimensions similar to a watch case for example, with an outside diameter of 43 mm, an inside diameter of 28 mm and a thickness of 7 mm. The rings are treated according to the thermal sequence shown in Figure 5:

[0155] - heat treatment according to curve R consisting of annealing at 650°C and quenching in water at room temperature giving the ring shape 1;

[0156] - the maximized stabilization heat treatment according to the TMM curve, defined by a temperature rise at a rate of 30°C / min, a first maintenance at the TR temperature of 450°C for 60 minutes, a first temperature reduction to the TP temperature of 250°C at a rate of 2°C / min followed by the second maintenance at the TP temperature for 60 minutes followed by the second temperature reduction at a rate of 20°C / min, as shown in Figure 3, the duration of the second maintenance at the TP temperature being non-zero. This maximized TMM stabilization heat treatment of the alloy allows a transformation of 99% of the (AuCu)a phase into the AuCuI phase, giving the rings A10, A11, A12 form 2, which is a reduction homothety of form 1;

[0157] - a brazing heat treatment according to curve B at 780°C; rings A10, A11, A12 are found in form 1;

[0158] - a second heat treatment according to the TMM curve as defined above, directly after brazing, the rings A10, A11, A12 cover shape 2.

[0159] Machining operations of the A10, A11, A12 rings stabilized after the first TMM heat treatment can be carried out.

[0160] For each ring A10, A11, A12, the outer diameter, as well as the circularity and flatness are measured after each heat treatment applied.

[0161] The results are shown in Figures 6, 7 and 8, which respectively represent the outer diameter measurements, the flatness measurements and the roundness measurements as a function of each heat treatment R, 1 er TMM, B and 2 èmeTMM on each ring A10, A11, A12. The line at 0.02 mm indicates the acceptable tolerance in the watchmaking and jewelry industry.

[0162] Figure 6 shows the decrease in the average diameter of the rings A10, A11, A12 expected after the implementation of the TMM stabilization heat treatment, but in a very repeatable manner, being linked to the change in volume of the mesh.

[0163] It is observed that during brazing, the rings A10, A11, A12 recover their initial dimensions, after the annealing R. During the cycle, the geometry of the rings A10, A11, A12 is always preserved, as shown in figures 7 and 8. In a particularly advantageous manner, the rings A10, A11, A12 recover the same dimension, to the nearest pm, by carrying out the second hardening according to the second TMM stabilization thermal treatment as during the first hardening according to the first TMM stabilization thermal treatment. The method according to the invention therefore very advantageously makes it possible to “detransform” the alloy of a part while keeping the possibility of recovering the same geometry of the part later.

Claims

Demands 1. A method for manufacturing a watch or jewelry component comprising at least one part made of at least a binary metal alloy based on gold and copper comprising at least 58% gold by weight, said method comprising at least the following steps: a) providing a part comprising at least one solid part composed of said metal alloy; b) applying various manufacturing operations to the part to obtain the watch or jewelry component; characterized in that said method comprises at least one step c) of applying to said part a heat treatment implemented to control the dimensional variations of the part during the manufacturing process, said heat treatment comprising an initial temperature increase to a temperature TR between the phase transition temperature (AuCu)a / AuCuII and the melting temperature of the alloy,directly followed by a first holding at temperature TR for a period of at least 1 minute, preferably between 5 minutes and 48 hours, preferably between 10 minutes and 300 minutes, and more preferably between 30 minutes and 90 minutes, directly followed by a temperature decrease to ambient temperature of 25°C comprising, immediately after the first holding at temperature TR, a first temperature decrease at a rate between 0.1°C / min and 6,000°C / min, preferably between 1°C / min and 10°C / min, more preferably between 2°C / min and 5°C / min, at least to a temperature TP between 100°C and the AuCuII / AuCuI phase transition temperature, a second holding at temperature TP for a duration between 0 and 48 hours chosen to allow the alloy to transform into a state in which it has at least 25% ordered phase None,said second holding at temperature TP being directly followed by a second temperature decrease to ambient temperature of 25°C at a rate greater than or equal to that of the first decrease, preferably, between 20°C / min and 100°C / min, the alloy of the part obtained in step c) being in a state in which it has at least 25% AuCuI ordered phase, and the part obtained in step c) having a conserved geometry and controlled dimensional variations during the manufacturing process, step c) being carried out before step b) and / or during step b). Manufacturing process of a watch or jewelry component according to claim 1, characterized in that the parameters of the heat treatment carried out in step c) are chosen to allow the alloy to transform into a state in which it has at least 60% AuCuI ordered phase.A method for manufacturing a watch or jewelry component according to claim 1, characterized in that the parameters of the heat treatment implemented in step c) are chosen to allow the alloy to transform into a state in which it possesses at least 95%, and more preferably at least 99%, of the ordered AuCuI phase. A method for manufacturing a watch or jewelry component according to claim 3, characterized in that the temperature decrease to the ambient temperature of 25°C in step c) is a continuous temperature decrease at a rate between 0.1°C / min and 2°C / min, preferably between 0.5°C / min and 2°C / min, down to the ambient temperature of 25°C. A method for manufacturing a watch or jewelry component according to claim 1, characterized in that the first temperature decrease is carried out at a rate between 0.1 °C / min and 6,000°C / min, preferably between 1 °C / min and 10 °C / min, in that the duration of the second holding at temperature TP is between 1 minute and 48 hours, preferably between 10 minutes and 300 minutes, preferably between 30 minutes and 90 minutes, said duration being chosen to allow the alloy to transform into a state in which it has at least 25% of ordered AuCuI phase. A method for manufacturing a watch or jewelry component according to claim 5, characterized in that the first temperature decrease is carried out to temperature TP, directly followed by a second holding period at temperature TP, directly followed by a second temperature decrease. A method for manufacturing a watch or jewelry component according to claim 5, characterized in that the first temperature decrease is carried out to an ambient temperature of 25°C, a second temperature increase to temperature TP then being carried out, directly followed by a second holding period at temperature TP, the second holding period at temperature TP being directly followed by a second temperature decrease.A method for manufacturing a watch or jewelry component according to any one of the preceding claims, characterized in that the temperature TR is at least 1°C higher, preferably at least 10°C, preferably at least 50°C, than the phase transition temperature of (AuCu)a / AuCuII, and at least 1°C lower, preferably at least 10°C, preferably at least 50°C, than the melting temperature of the alloy. A method for manufacturing a watch or jewelry component according to any one of the preceding claims, characterized in that the part supplied in step a) is a solid blank, a rough blank, or a semi-finished product.Method of manufacturing a watch or jewelry component according to one of the preceding claims, characterized in that the manufacturing operations to produce the watch or jewelry component according to step b) are selected from the group comprising storage, stamping, machining, sintering, heat treatment, engraving, punching, 3D printing, crimping, gluing, polishing, diamond cutting, washing and brazing. A method for manufacturing a watch or jewelry component according to any one of the preceding claims, characterized in that step c) is carried out before step b). A method for manufacturing a watch or jewelry component according to any one of the preceding claims, characterized in that at least one step c) is carried out during step b). A method for manufacturing a watch or jewelry component according to claim 12, characterized in that one step c) is carried out during step b), said step c) being carried out before subjecting the part to a manufacturing operation performed at a temperature below the AuCuII / AuCuI phase transition temperature if all manufacturing operations are carried out at a temperature below the AuCuII / AuCuI phase transition temperature.A method for manufacturing a watch or jewelry component according to claim 12, characterized in that a first step c) is carried out before step b), in that step b) comprises a manufacturing operation performed at a temperature above the phase transition temperature of (AuCu)a / AuCuII, and in that a second step c) is carried out after said manufacturing operation with the same parameters as those of the first step c). A method for manufacturing a watch or jewelry component according to claim 14, characterized in that a first step c) is carried out before step b), in that step b) comprises a brazing operation, and in that a second step c) is carried out after the brazing operation with the same parameters as those of the first step c).Method of manufacturing a watch or jewelry component according to claim 14, characterized in that a first step c) is carried out before step b), in that step b) includes a heat treatment at a temperature above the phase transition temperature (AuCu). a I AuCuII to soften the alloy, followed by a crimping operation, and in that a second step c) is carried out after the crimping operation with the same parameters as those of the first step c). Method for manufacturing a watch or jewelry component according to any one of the preceding claims, characterized in that it comprises a preliminary step of measuring the dimensional variations of a sample made from said metal alloy subjected to heat treatment according to step c), and in that the part supplied in step a) is dimensioned to take into account said dimensional variations measured in the preliminary step with respect to the dimensions of the watch or jewelry component to be manufactured. Method for manufacturing a watch or jewelry component according to the preceding claim, characterized in that the preliminary step comprises the following substeps: 1) provide a sample of said alloy; 2) if said alloy sample is likely to possess more than 0% of ordered AuCuI phase, bring the alloy sample back to a state in which it possesses 100% of (AuCu)a phase and 0% of ordered AuCuI phase; 3) determine the percentage of stabilized dimensional variation VDstabilisée corresponding to the percentage of variation of the dimensions of the alloy sample between the initial dimensions of the alloy sample obtained according to sub-step 2) until stable dimensions are obtained when the alloy sample obtained according to sub-step 2) is subjected to a temperature corresponding to the temperature of the manufacturing operation according to step b) for which the stability of the dimensions of the part is sought; 4) Apply to the alloy sample obtained according to substep b) the heat treatment of step c), said heat treatment enabling control of the dimensional variations of the sample, the parameters being further chosen to obtain a transformed alloy sample in a state in which it has a transformation rate of phase (AuCu)aZAuCuI maximized, closest to 100% of ordered phase AuCuI, 5) measure the percentage of maximum dimensional variation VDmax of the alloy sample treated according to substep 4), said maximum dimensional variation VDmax being defined as corresponding to a transformation rate of the (AuCu)a phase into the AuCuI phase of 100%, the initial dimensions of the alloy sample obtained according to substep 2) corresponding to a transformation rate of the (AuCu)a phase into the initial AuCuI phase of 0%, the percentage of intermediate dimensional variation then being equal to the percentage of maximum dimensional variation VDmax x (intermediate transformation rate / 100); 6) determine the transformation rate of the (AuCu)a phase into the AuCuI phase Tx that the alloy of the part must exhibit to obtain a part with controlled dimensional variations and a percentage of dimensional variation stabilized at the temperature of the manufacturing operation according to step b) for which dimensional stability is sought, said transformation rate Tx being equal to 100 x (percentage of dimensional variation VDstabilized determined in sub-step 3) / percentage of maximum dimensional variation VDmax determined in sub-step 4)), in that the part supplied in step a) is such that the alloy of said part has been brought back to a state in which it has 100% of the (AuCu)a phase and 0% of the ordered AuCuI phase if said alloy were likely to have more than 0% of the ordered AuCuI phase,said part supplied in step a) being dimensioned by adding allowances to take into account the percentage of dimensional variation VDstabilized determined in sub-step 3) relative to the dimensions of the watch or jewelry component to be manufactured; in that step c) consists of applying to the part the heat treatment for which the parameters are chosen to allow the alloy to transform according to the transformation rate of the (AuCu)a phase to the AuCuI Tx phase determined in sub-step 6), said heat treatment allowing, to obtain control of the dimensional variations of the part, the part obtained in step c) exhibiting stable dimensions when exposed to the temperature of the manufacturing operation according to step b) for which dimensional stability is sought, and said part exhibiting controlled dimensional variations according to the formula defined in sub-step 5) for the intermediate percentage of dimensional variation if it is subjected to a temperature higher than the temperature for which the dimensions of the part are stable.A method for manufacturing a watch or jewelry component according to any one of the preceding claims, characterized in that the temperature TP varies according to the degree of transformation of the (AuCu)a phase into the AuCuI phase, wherein the temperature TP is preferably between approximately 100°C and 120°C to allow the alloy to transform into a state in which it has an ordered phase AuCuI content of approximately 25%, or the temperature TP is preferably between approximately 125°C and 150°C to allow the alloy to transform into a state in which it has an ordered phase AuCuI content of approximately 30% to 60%, or the temperature TP is preferably between 250°C and the AuCuII / AuCuI phase transition temperature to allow the alloy to transform into a state in which it has an ordered phase AuCuI content of at least 95%, and preferably at least 99%.A method for manufacturing a watch or jewelry component according to any one of the preceding claims, characterized in that the alloy is a 5N alloy, and in that the heat treatment of step c) was implemented to enable the alloy to transform into a state in which it has an ordered phase AuCuI ratio of about 25%, so that the part exhibits controlled dimensional variations and a stabilized percentage of dimensional variation when a manufacturing operation is applied to it at a temperature between 25°C and about 110°C, said part exhibiting controlled dimensional variations if it is subjected to a temperature above 110°C.

21. A method for manufacturing a watch or jewelry component according to any one of claims 1 to 19, characterized in that the alloy is a 5N alloy, and in that the heat treatment of step c) was implemented to enable the alloy to transform into a state in which it has an ordered phase AuCuI ratio of about 60% so that the part exhibits controlled dimensional variations and a stabilized percentage of dimensional variation when a manufacturing operation is applied to it at a temperature between 25°C and about 140°C, said part exhibiting controlled dimensional variations if it is subjected to a temperature above 140°C.

22. A method for manufacturing a watch or jewelry component according to any one of claims 1 to 19, characterized in that the alloy is a 5N alloy, and in that the heat treatment of step c) was implemented to enable the alloy to transform into a state in which it has an ordered phase AuCuI content greater than about 99% such that the part exhibits controlled dimensional variations and a stabilized percentage of dimensional variation when a manufacturing operation is applied to it at a temperature between 25°C and the AuCuII / AuCuI phase transition temperature, said part exhibiting controlled dimensional variations if it is subjected to a temperature above the AuCuII / AuCuI phase transition temperature.

23. A method for manufacturing a watch or jewelry component according to one of the preceding claims, characterized in that the part obtained in step c) has an increased hardness depending on the rate of transformation of the (AuCu)a phase into the AuCuI phase, the increase in hardness being substantially equal to (hardness of the alloy at the rate of transformation of the (AuCu)a phase into the AuCuI phase of 100% - hardness of the alloy at the rate of transformation of the (AuCu)a phase into the AuCuI phase of 0%) x (rate of transformation Tx / 100).

24. A watch or jewelry component comprising at least one part made of a metallic alloy, at least binary in number, based on gold and copper, comprising at least less than 58% gold by weight obtained according to the manufacturing process according to claims 1 to 23. Watch or jewelry component according to claim 23, characterized in that it consists of a watch case element, a watch movement element, or a piece of jewelry. Method for controlling dimensional variations of a part made of at least binary gold-copper-based metal alloy comprising at least 58% gold by weight during a manufacturing process of a watch or jewelry component from said part, said manufacturing process comprising at least one manufacturing operation for which uncontrolled dimensional variations are normally observed, by applying a heat treatment comprising a first temperature increase to a temperature TR between the phase transition temperature (AuCu) a / AuCuII and the melting temperature of the alloy,directly followed by a first holding at temperature TR for a period of at least 1 minute, preferably between 5 minutes and 48 hours, preferably between 10 minutes and 300 minutes, and more preferably between 30 minutes and 90 minutes, directly followed by a temperature decrease to ambient temperature of 25°C comprising, immediately after the first holding at temperature TR, a first temperature decrease at a rate between 0.1 °C / min and 6,000 °C / min, preferably between 1 °C / min and 10 °C / min, more preferably between 2 °C / min and 5 °C / min, at least to a temperature TP between 100 °C and the AuCuII / AuCuI phase transition temperature, a second holding at temperature TP for a duration between 0 and 48 hours chosen to allow the alloy to transform into a state in which it has at least 25% ordered phase None,said second holding at temperature TP being directly followed by a second temperature decrease to ambient temperature of 25°C at a rate greater than or equal to that of the first decrease, preferably between 20°C / min and 100°C / min, the alloy of the treated part being in a state in which it possesses at least, 25% ordered phase AuCuI, said heat treatment being applied to the part at least before or during said manufacturing operation.

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