EP3527678B1 - Alloy of gold and copper, method for preparing same and use thereof - Google Patents

Description

FIELD OF THE INVENTION

The present invention relates to an alloy based on gold and copper. This alloy, pink (4N) or red (5N and 6N), can be used in particular in the fields of jewelry and watchmaking.

PRIOR STATE OF THE ART

Historically, gold has been mixed with other metals in order to modify its properties. Depending on the nature of the metal (s) introduced and their quantities, it is in particular possible to modulate the rigidity or the color of the gold.

Thus, an alloy comprising 75% by mass of gold, 12.5% of copper and 12.5% of silver corresponds to yellow gold. An alloy comprising 75% gold, 20% copper and 5% agent corresponds to rose gold. Finally, an alloy (Au750 Pd125 Ag30 Cu95) comprising for example 75% gold, 30% silver, 125% palladium and 95% copper corresponds to gray gold.

The color of the alloy can be determined using the CIE L * a * b * color space, the CIE being the International Commission on Illumination. In general, conventional rose or red gold alloys (gold, silver and copper) correspond to zones 4N, 5N and 6N of the figure 2 .

The rose gold conventionally used in the fields of watchmaking or jewelry meets the formula Au750Cu205Ag45 (L * = 86.3; a * = 8.8; b * = 18.5). However, this alloy is subject to a phenomenon of discoloration over time by yellowing. This phenomenon corresponds to the corrosion of copper and to the increase in the concentration of gold metal on the surface of the alloy.

Alloys have been developed to remedy this problem.

For example, the document JP 10 245646 describes an 18-carat rose gold alloy, comprising between 15.0 and 23.0% by mass of copper and between 0.3 and 5.0% of palladium.

• 75 à 77,5 % d'or,
• 1,35 et 1,45 % de palladium,
• 20,1 et 23,8 % de cuivre.

The document EP 2,776,597 describes an 18 karat red gold alloy devoid of nickel, chromium and silver. The composition of this alloy includes:

• 75 to 77.5% gold,
• 1.35 and 1.45% palladium,
• 20.1 and 23.8% copper.

The document WO 2015/038636 describes an alloy not containing tin. This alloy comprises 12.7 to 14.7% silver, 9.3 to 11.3% copper, 0.5 to 2% palladium, the remainder being gold.

The document GB 2447620 describes an alloy comprising gold and tin.

Even though the alloys of the prior art have the desired properties in the field of jewelry, there is still a need to have an alloy of pink (4N) or red (5N and 6N) color, the color of which can be maintained over time, with little change under normal conditions of use.

The present invention presents an alternative thanks to the development of a gold-based alloy limiting or eliminating corrosion of copper, and therefore the phenomenon of discoloration over time.

DISCLOSURE OF THE INVENTION

The Applicant has developed a gold-based alloy making it possible to solve the problems of discoloration of the alloys of the prior art thanks to the presence of specific amounts of several metals.

This alloy is non-tarnishing and non-bleaching over time, which provides an undeniable advantage in fields such as jewelry and watchmaking by avoiding the return of items related to this problem. The invention is defined in the appended claims.

• 75 % à 77,5 % d'or,
• 10 % à 24,0 % de cuivre,
• 0,1 % à 10,0 % d'argent,
• 0,1 % à 1,1 % de palladium,
• 0,1 % à 2,0 % d'étain,
• 2 % ou moins de titane,
• 0,2 % ou moins d'au moins un élément choisi parmi le ruthénium, le rhénium, le fer, l'iridium, le cobalt, le vanadium, le molybdène et leurs mélanges et d'éventuelles impuretés.

More precisely, the alloy according to the invention has a composition consisting of, by mass relative to the mass of the alloy:

• 75% to 77.5% gold,
• 10% to 24.0% copper,
• 0.1% to 10.0% silver,
• 0.1% to 1.1% palladium,
• 0.1% to 2.0% tin,
• 2% or less of titanium,
• 0.2% or less of at least one element selected from ruthenium, rhenium, iron, iridium, cobalt, vanadium, molybdenum and their mixtures and possible impurities.

It is an 18 carat gold alloy, it comprises between 18 and 18.6 parts by mass of gold for 24 parts by mass of alloy.

• la composante L* correspond à la clarté, elle est comprise entre 0 (noir) et 100 (blanc),
• la composante a* représente une gamme de 600 niveaux entre le rouge (+299), le gris (0) et le vert (-300),
• la composante b* représente une gamme de 600 niveaux entre le jaune (+299), le gris (0) et le bleu (-300).

In general, the color of a material can be defined by its CIE L * a * b * coordinates:

• the L * component corresponds to the clarity, it is between 0 (black) and 100 (white),
• component a * represents a range of 600 levels between red (+299), gray (0) and green (-300),
• component b * represents a range of 600 levels between yellow (+299), gray (0) and blue (-300).

The CIE L * a * b * coordinates can in particular be obtained by means of a conventional spectrophotometer, by measuring the reflectance properties as a function of the illumination wavelength.

The alloy according to the invention is pink (4N) or red (5N and 6N). It is preferably located in one of zones 4N, 5N or 6N of the CIE L * a * b * color space, or in an intermediate zone between zones 4N, 5N or 6N ( figure 2 ). Advantageously, the alloy according to the invention corresponds to zone 5N.

The zones 4N 5N and 6N are advantageously defined according to the ISO 8654 standard and this, in accordance with the practice of a person skilled in the art.

• Au752Cu158Ag78Pd4Sn8 : zone 4N : L* = 90,41 ; a* = 5,72 ; b* = 20,07 ;
• Au752Cu210Ag22Pd5Sn11 : zone 5N : L* = 87,24 ; a* = 8,23 ; b* = 17,07 ;
• Au752Cu233Ag2Pd10Sn3 : zone 6N : L* = 86,76 ; a* = 9,6 ; b* = 15,7.

By way of example, the alloy according to the invention can have the following CIE L * a * b * coordinates:

• Au752Cu158Ag78Pd4Sn8: zone 4N: L * = 90.41; a * = 5.72; b * = 20.07;
• Au752Cu210Ag22Pd5Sn11: zone 5N: L * = 87.24; a * = 8.23; b * = 17.07;
• Au752Cu233Ag2Pd10Sn3: 6N zone: L * = 86.76; a * = 9.6; b * = 15.7.

The Au752Cu158Ag78Pd4Sn8, Au752Cu210Ag22Pd5Sn11 and Au752Cu233Ag2Pd10Sn3 alloys correspond to particular embodiments of the invention. The quantity of each element is expressed in tenths of a percentage by mass. The Au752Cu158Ag78Pd4Sn8 alloy therefore consists of 752 ‰ of gold, 158% o of copper, 78 ‰ of silver, 4 ‰ of palladium and 8 ‰ of tin.

Thus, in addition to possible minute amounts that can be assimilated to impurities, the alloy according to the invention is devoid of nickel, chromium, niobium, hafnium and yttrium.

The alloy according to the invention can consist of gold, copper, silver, palladium, and tin. In this case, in addition to any impurities, the sum of the percentages of the metals gold, copper, silver, palladium and tin is equal to 100.

The alloy according to the invention comprises 2% or less of titanium. In other words, it comprises between 0% and 2% titanium.

According to a particular embodiment, the alloy according to the invention can comprise titanium, advantageously between 0.05% and 2% by mass relative to the mass of the alloy, more advantageously between 0.1% and 2% , and even more advantageously between 0.8 and 1.5%.

The alloy according to the invention can thus consist of gold, copper, silver, palladium, tin, and titanium. In this case, in addition to any impurities, the sum of the percentages of the metals gold, copper, silver, palladium, tin and titanium is equal to 100.

The mass percentage of gold in the alloy is between 75% and 77.5%, advantageously between 75% and 75.5%.

Unless otherwise indicated, the quantities of elements are expressed as a percentage by mass or as a part per million by mass (ppm) relative to the mass of the alloy. In other words, 75% gold means that for 100 parts by mass of alloy, the alloy includes 75 parts by mass of gold.

The value ranges include the limits. For example, the range of values "between 75% and 77.5%" includes the values 75% and 77.5%. On the other hand, the description discloses all the possible combinations between the limits of the different ranges of values. For example, with regard to the quantity of copper, the disclosure of the ranges 10% to 24%, advantageously 15% to 22% includes in particular the ranges 10% to 15%, 10% to 22%, 15% to 24% or 22% to 24%.

The alloy according to the invention has a homogeneous composition. Indeed, its various elements are distributed homogeneously within the alloy. This alloy necessarily comprises the following five elements: gold, copper, silver, palladium and tin. It can include a total of 13 elements: gold, copper, silver, palladium, tin, titanium, ruthenium, rhenium, iron, iridium, cobalt, vanadium and molybdenum.

Copper makes it possible to obtain the pink (4N) or red (5N and 6N) color of the alloy. However, as already indicated, the corrosion of the copper in the alloy over time causes a change in color, the alloy gradually passing from the pink / red color to the yellow color.

The percentage by mass of copper in the alloy is between 10% and 24%, advantageously between 15% and 22%.

The silver fixes the copper within the alloy. However, silver has the disadvantage of whitening the alloy, moving it away from the color areas of interest.

The percentage by weight of silver in the alloy is between 0.1% and 10.0%, advantageously between 1% and 4%.

In general, palladium makes it possible to limit or stop the discoloration by acting on the corrosion of the copper. However, it also has a whitening effect of the alloy. Thus, too much palladium can be detrimental to obtaining a pink (4N) or red (5N and 6N) colored alloy. It is therefore important to limit the amount of palladium (1.1%) so as not to deviate from the color zones of interest.

The percentage by mass of palladium in the alloy is between 0.1% and 1.1%, advantageously between 0.3% and 0.8%.

Tin reduces corrosion of copper but to a lesser extent than palladium. In addition, synergistic effects between tin and palladium appear to exist in terms of optimization of corrosion resistance. Finally, tin does not exhibit the undesirable whitening effect of palladium.

The percentage by mass of tin in the alloy is between 0.1% and 2.0%, advantageously between 0.5% and 1.5%.

Thus, the alloy according to the invention presents a compromise between silver, palladium and tin in order to obtain the properties required not only in terms of color but also for use in watchmaking or jewelry.

The optional presence of titanium also makes it possible to reduce the phenomenon of discoloration while having a negligible impact on the color of the alloy. This effect is observed when the titanium represents between 0.05% and 2% by weight of the alloy, more particularly when the titanium advantageously represents 0.05 to 0.5% by weight of the alloy.

Titanium makes it possible to slow down the kinetics of ordering in the alloy according to the invention, in order to optimize the stability of the alloy during the various stages of the manufacturing process (deformation, heat treatments, brazing, etc. .). This effect is particularly observed when the titanium represents between 0.05% and 2% by mass of the alloy, more particularly when the titanium advantageously represents 1.5 to 2% by mass of the alloy.

Also, advantageously, titanium partly replaces palladium.

The Applicant has noted that titanium, in combination with palladium and tin, significantly slows down the ordering transformation of the alloy according to the invention.

In general, the elements titanium, tin, indium and germanium slow down the phenomenon of discoloration / desalloying (selective dissolution of certain elements) existing in 18-carat pink and red gold.

• entre 15 et 22 % de cuivre,
• entre 1 et 4 % d'argent,
• entre 0,3 et 0,8 % de palladium,
• entre 0,5 et 1,5 % d'étain.

Thus, according to a particular embodiment, the alloy according to the invention comprises, by mass relative to the mass of the alloy:

• between 15 and 22% copper,
• between 1 and 4% silver,
• between 0.3 and 0.8% palladium,
• between 0.5 and 1.5% tin.

The alloy according to the invention comprises 0.2% or less of at least one grain refiner element (Ru, Re, Fe, Ir, Co, V, Mo). In other words, it includes between 0% and 0.2% of at least one grain refiner.

Thus, according to a particular embodiment, the alloy according to the invention can also comprise at least one grain refiner element. The grain refiner is 0.2% or less based on the weight of the alloy, more preferably 0.1% or less. In general, when it is present, the grain refiner represents at least 0.001% by mass relative to the mass of the alloy (ie 10 ppm). It is an element chosen from the group comprising ruthenium, rhenium, iron, iridium, cobalt, vanadium, molybdenum and their mixtures. Elements such as ruthenium, rhenium or iron make it possible to guarantee the fineness of the grain, without appreciably modifying the hardness or affecting the color.

Thus, the alloy according to the invention consists of 97.8% by mass or more of the elements gold, copper, silver, palladium and tin. In other words, the alloy according to the invention comprises between 97.8% and 100% by mass of the elements gold, copper, silver, palladium and tin.

1. a) on prépare un mélange constituée en masse par rapport à la masse totale des métaux :
   • entre 75 % et 77,5 % d'or,
   • entre 10 % et 24,0 % de cuivre,
   • entre 0,1 % et 10,0 % d'argent,
   • entre 0,1 % et 1,1 % de palladium,
   • entre 0,1 % et 2,0 % d'étain,
   • 2 % ou moins de titane, avantageusement entre 0,05 % et 2 %,
   • 0,2 % ou moins d'au moins un élément choisi parmi le ruthénium, le rhénium, le fer, l'iridium, le cobalt, le vanadium, le molybdène et leurs mélanges et d'éventuelles impuretés,
2. b) on met en alliage ce mélange, avantageusement par une mise en température entre 750°C et 1500°C, avantageusement entre 1050°C et 1300°C,
3. c) on refroidit le mélange mis en solution lors de l'étape b), par exemple par trempe thermique.

The present invention also relates to a process for preparing the gold alloy described above. This process comprises at least the following steps:

1. a) a mixture is prepared consisting of mass relative to the total mass of metals:
   • between 75% and 77.5% gold,
   • between 10% and 24.0% copper,
   • between 0.1% and 10.0% silver,
   • between 0.1% and 1.1% palladium,
   • between 0.1% and 2.0% tin,
   • 2% or less of titanium, advantageously between 0.05% and 2%,
   • 0.2% or less of at least one element chosen from ruthenium, rhenium, iron, iridium, cobalt, vanadium, molybdenum and their mixtures and possible impurities,
2. b) this mixture is placed in an alloy, advantageously by heating between 750 ° C and 1500 ° C, advantageously between 1050 ° C and 1300 ° C,
3. c) the mixture dissolved in step b) is cooled, for example by thermal quenching.

During step a), the respective percentages of the metals correspond to the percentages of the final alloy. This step is carried out conventionally, according to techniques known to those skilled in the art.

Step b) consists in melting the different metals so as to form a homogeneous mixture. This step is advantageously carried out by heating the mixture until the desired temperature is reached. Since the temperature rise kinetics (° C./minute) are generally not important, the alloying is advantageously carried out in a crucible, for example with induction heating.

The cooling step c) makes it possible to set the structure of the alloy. It advantageously consists in carrying out thermal quenching in air or in water.

Even though the air quenching is much slower than the water quenching, the alloys obtained by these two routes exhibit similar hardness properties, which provides an additional advantage. Thus, the alloy according to the invention can be implemented (deformation, heat treatment, brazing, etc.) without its mechanical properties and its color being altered.

The alloy thus obtained can then be shaped. Advantageously, the shaping is carried out by cold or hot deformation, then by machining, for example by means of a cutting tool or by electro erosion or by means of a laser.

According to another embodiment, the shaping can be carried out by additive manufacturing. For this, the alloy is previously transformed into powder form.

Also part of the present invention is the use of this gold alloy in the field of jewelry; the use of this gold alloy in the field of watchmaking; articles of jewelry comprising or consisting of this gold alloy; horological articles comprising or consisting of this gold alloy.

The invention and the advantages which result therefrom will emerge more clearly from the following figures and examples given in order to illustrate the invention and not in a limiting manner.

DESCRIPTION OF FIGURES

• The figure 1 illustrates the change in color of gold alloys over time in a synthetic sweat test.
• The figure 2 illustrates the color of gold alloys in CIE L * a * b * space.
• The figure 3 illustrates the change in color of gold alloys as a function of time during synthetic sweat test
• The figure 4 illustrates the evolution over time of the hardness deviation over time after water quenching and air quenching for gold alloys.
• The figure 5 illustrates the change in color of gold alloys (invention + prior art) as a function of time during a salt spray test and a synthetic sweat test.

EXAMPLES OF EMBODIMENT OF THE INVENTION

Eight examples of alloys according to the invention were prepared. Table 1 groups together the compositions of these examples.

Table 1: Examples of alloys according to the invention, in tenths of a percentage by mass (‰). Alloy Color At ‰ Cu ‰ Ag ‰ Pd ‰ Sn ‰ INV-1 4N 752 170 63 5 10 INV-2 4N 752 158 78 4 8 INV-3 5N 752 210 22 5 11 INV-4 6N 752 235 4 5 4 INV-5 6N 752 233 2 10 3 INV-6 5N 752 210 13 5 20 INV-7 5N 752 210 23.48 4.55 10.02 INV-8 5N 752 210 30 5 2.5

The hardness (measured on the as-cast structures) of these alloys according to the invention is similar, whether they have been obtained after thermal quenching or after air quenching, which is not always the case with alloys not corresponding to the composition according to the invention. The figure 4 shows the difference in hardness (Δ hardness) between alloys which have undergone water quenching and alloys which have undergone air quenching, and this as a function of time.

These tests made it possible to demonstrate that, unlike titanium, palladium, tin and their combinations, metals of the niobium, hafnium and yttrium type favor the ordering of the alloys. In other words, the introduction into the alloy according to the invention of titanium and / or palladium and / or tin makes it possible to slow down the kinetics of organization of the metals of the alloy during its cooling. This therefore makes it possible to have a stable alloy, in particular for deformation, heat treatment or brazing operations, etc.

These alloys were subjected to aging tests listed in Table 2. These corrosion tests comply with the normal conditions of use of a piece of jewelry or a timepiece. They were carried out on the as-cast structures.

For this, pellets having a diameter of 15 mm and a thickness of 2 mm were prepared. For color testing, the diameter is at least 10mm, which is the size of the sensor. Table 2: Aging tests of the alloys according to the invention. Humid heat Thioacetamide Sulfur flower Synthetic sweat Salt bath or mist Standard NIHS 96-50: 2017 NIHS 96-50: 2017 SN EN ISO 4538: 1978 NIHS 96-50: 2017 EN1811 NIHS 96-50: 2013 SN EN ISO 9227: 2006 HR 93 ± 5% 75% ≥ 95% immersion 100% Temperature 40 ± 2 ° C 20 ± 5 ° C 40 ± 2 ° C 37 ± 0.5 ° C 35 ± 2 ° C Duration 7 days 48 hours 48 hours (*) 15 days Other conditions Sulfur agents: sulfur flower without buffer pH = 3.5-4 Mist: NaCl (50 ± 5 g / L) Observations after 1, 3 and 7 days after 24 and 48 hours after 24 and 48 hours after 5, 15 and 50 days after 1, 4, 8, 11 and 15 days (*) The sample is placed in a wheel allowing it to be immersed in synthetic sweat for 30 seconds, then to dry for 30 seconds in the open air. This immersion / drying cycle is maintained for the duration of the aging test.

In general, very small color changes were observed under the conditions of Table 2, these changes remaining significantly lower than those observed for the 5N alloys (Au750Ag45Cu205) of the prior art. Thus, the alloy according to the invention makes it possible to solve the problems associated with the discoloration of the alloy under normal conditions of use.

dans laquelle, ${\mathrm{L}}_1^{\ast },$

${\mathrm{a}}_1^{\ast }$

et ${\mathrm{b}}_1^{\ast }$

sont les coordonnées initiales de l'alliage (t = 0), et ${\mathrm{L}}_2^{\ast },$

${\mathrm{a}}_2^{\ast }$

et ${\mathrm{b}}_2^{\ast }$

sont les coordonnées de l'alliage au moment de l'observation après vieillissement.The figure 5 shows that the INV-3 alloy of Table 1 exhibits a slight change in color over time, compared with a conventional alloy of the formula Au750Ag45Cu205 after aging for several days (synthetic sweat; salt bath or mist). The color change ΔE is obtained from the following formula: $$\mathrm{\Delta }\mathrm{E}={\left[{\left({\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">L</figure-callout>}}_2^{\ast }-{\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">L</figure-callout>}}_1^{\ast }\right)}^2+{\left({\mathrm{at}}_2^{\ast }-{\mathrm{at}}_1^{\ast }\right)}^2+{\left({\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">b</figure-callout>}}_2^{\ast }-{\mathrm{<figure-callout\; id="1"\; label="b"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">b</figure-callout>}}_1^{\ast }\right)}^2\right]}^{1/2}$$

in which, ${\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">L</figure-callout>}}_1^{\ast },$

${\mathrm{at}}_1^{\ast }$

and ${\mathrm{<figure-callout\; id="1"\; label="b"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">b</figure-callout>}}_1^{\ast }$

are the initial coordinates of the alloy (t = 0), and ${\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">L</figure-callout>}}_2^{\ast },$

${\mathrm{at}}_2^{\ast }$

and ${\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">b</figure-callout>}}_2^{\ast }$

are the coordinates of the alloy at the time of observation after aging.

The figures 1 and 3 show the color change for alloys not forming part of the invention.

The figure 1 highlights the decrease in the discoloration phenomenon over time when part of the copper is substituted by palladium. The whitening effect of palladium is highlighted by the figure 2 . Indeed, the more the alloy contains palladium, the more it moves away from the color zone 6N.

The figure 3 highlights the reduction in the phenomenon of discoloration over time in the presence of palladium and of an element chosen from germanium, indium, tin and titanium compared to an alloy of the Au750Cu205Ag45 type.

Claims (15)

1. An alloy having a composition consisting of, by mass relative to the mass of the alloy:

   - from 75% to 77.5% of gold,

   - from 10% to 24.0% of copper,

   - from 0.1% to 10.0% of silver,

   - from 0.1% to 1.1% of palladium,

   - from 0.1% to 2.0% of tin,

   - 2% or less of titanium,

   - 0,2% or less of at least one element selected from ruthenium, rhenium, iron, iridium, cobalt, vanadium, molybdenum and mixtures thereof; and

   - any possible impurities.
2. The alloy according to claim 1, characterized in that it comprises between 75% and 75.5% of gold.
3. The alloy according to claim 1 or claim 2, characterized in that it comprises between 15% and 22% of copper.
4. The alloy according to any one of claims 1 to 3, characterized in that it comprises between 1% and 4% of silver.
5. The alloy according to any one of claims 1 to 4, characterized in that it comprises between 0.3% and 0.8% of palladium.
6. The alloy according to any one of claims 1 to 5, characterized in that it comprises between 0.5% and 1.5% of tin.
7. The alloy according to any one of claims 1 to 6, characterized in that it comprises between 0.05% and 2% of titanium.
8. The alloy according to any one of claims 1 to 6, characterized in that the alloy consists of gold, copper, silver, palladium, and tin.
9. The alloy according to any one of claims 1 to 7, characterized in that the alloy consists of gold, copper, silver, palladium, tin, and titanium.
10. A method for the production of an alloy according to any one of claims 1 to 9, comprising at least the following steps:

    (a) preparing a mixture consisting of, by mass relative to the total mass of the metals:

    - between 75% and 77.5% of gold,

    - between 10% and 24.0% of copper,

    - between 0.1% and 10.0% of silver,

    - between 0.1% and 1.1% of palladium,

    - between 0.1% and 2.0% of tin,

    - 2% or less of titanium,

    - 0,2% or less of at least one element selected from ruthenium, rhenium, iron, iridium, cobalt, vanadium, molybdenum and mixtures thereof, and any possible impurities;

    b) alloying this mixture,

    c) cooling the mixture dissolved in step b).
11. The method according to claim 10, characterised in that step b) is carried out at a temperature between 750°C and 1500°C, advantageously between 1050°C and 1300°C.
12. The method according to claim 10 or 11, characterized in that the mixture of step a) comprises between 0.05% and 2% of titanium, by mass relative to the total mass of the metals.
13. The method according to any one of claims 10 to 12, characterized in that step c) consists in carrying out a thermal quenching in air or water.
14. An use of the alloy according to any one of claims 1 to 9, in the field of watchmaking or jewellery.
15. A watchmaking or jewellery article comprising or consisting of the alloy according to any one of claims 1 to 9.

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