CH710389B1 - Palladium-based alloy. - Google Patents

Abstract

The invention relates to a palladium-based alloy comprising, expressed by weight: between 50 and 55% palladium, between 45% and 50% rhodium; a quantity ≤R≤5%. The invention also relates to a piece of timepiece, jewelry or jewelry comprising at least one component made of such an alloy.

Description

Field of the invention

[0001] The invention relates to a palladium alloy. The invention also relates to a piece of timepiece, jewelry or jewelry comprising at least one component made with such an alloy.

Background of the invention

[0002] In the fields of watchmaking and jewelry, three types of precious alloys are white: platinum alloys, palladium alloys and gold alloys. Currently, the majority of manufacturers of precious metal alloys for these fields have the same objective: to find a very white alloy, close to the color of rhodium which is a reference in the field, having the following characteristics: massive , legally marked with a punch, resistant to corrosion and particularly tarnishing, easy to cast, easy to deform, resistant to scratches (minimum 160 HV in the annealed state) and easy to machine, economical and which meets the European standard EN1811 on the release of nickel. This objective is difficult to achieve using known traditional techniques. The 18 carat white gold and silver alloys are mostly rhodium plated, the 950% platinum alloys are very white but very expensive, due to the high platinum content and the high cost thereof. The palladium alloys known to date have a color that is too gray, not white enough, and pure rhodium, in its massive state, is difficult to deform when cold, its melting point being high.

[0003] The Platinum Metal Journal (2013, 57, (3), 202-213) describes the main colorimetric characteristics of the precious alloys presented in Table 1, according to the L*a*b chromatic model (C.I.E. 1976). Platinum alloys and platinum group alloys 85 0 4.5 Pure silver 95 -0.5 4.2 18-karat white gold 84 0 9.5 14-karat white gold 84 -0.5 9

Table 1: Colorimetric values of precious metal alloys. Platinum Metal Journal (2013, 57, (3), 202-213)

[0004] Various research studies have been carried out to propose very white alloys. Thus, patent application WO 2010/127458 describes a nickel-free and copper-free gray gold alloy, based on gold, and comprising palladium as well as a certain number of addition elements used to improve various properties alloys. The alloys obtained advantageously have colorimetric values whose chromaticity (a*; b*) is slightly lower than the 18-carat binary gold-palladium alloy, but while remaining gray (L > 81).

[0005] Patent application EP 2 546 371 describes a gray gold alloy based on gold and comprising chromium as well as a certain number of addition elements used to improve various properties of the alloys. The alloys obtained present colorimetric values, exceptional with regard to chromaticity, and interesting for the L value (> 83). But in these two cases, the addition elements used are relatively reactive to the processes used by traditional jewelry, in particular the blowtorch, by producing oxides which obscure the much sought-after shine, indicated by the high L value.

[0006] Patent application EP 2 420 583 opened a new path in the world of very white precious metals. It describes in particular an alloy made up by weight of 50% platinum and 50% Rhodium, massive, very white, very resistant to corrosion, close to the color of rhodium using high temperature deformation techniques to avoid spinodal decomposition above 800°C existing between the two elements, inducing poor deformability of the alloy when cold due to the heterogeneity of the alloy. This technique therefore makes this alloy particularly attractive for the watchmaking/jewellery sector with the exception of two major, significant disadvantages for the end consumer: its price remains high due to the presence of platinum; and platinum 500 or rhodium 500 titles are not legally recognized by international and national organizations. A product without a guarantee mark is difficult to accept for consumers, leaving doubt about the real composition of the precious metals contained in the alloy. In addition to these two disadvantages, the melting temperature of the alloy is relatively high (~ 1900°C) making it particularly difficult to cast for jewelry applications.

Summary of the invention

[0007] The invention aims in particular to overcome the various disadvantages of known alloys.

[0008] More precisely, an objective of the invention is to provide very white alloys, close to the color of rhodium, economical, capable of being marked with a legal hallmark, with a lower melting temperature (~ 1750°C ), and resistance to oxidation allowing the use of classic jewelry techniques.

[0009] The invention also aims to provide nickel-free precious metal alloys which therefore respond favorably to the regulations on the release of nickel.

[0010] For this purpose, the present invention relates to a palladium-based alloy consisting, expressed by weight: of palladium between 50 and 55%, of rhodium between 45% and 50%; a quantity x of silver, where 0%≤x≤5%, and a quantity R of a residue consisting of at least one element chosen from iridium, ruthenium, platinum, titanium, zirconium and rhenium, and their combinations, where 0%≤R≤5%.

[0011] According to an alternative embodiment, x is less than or equal to 2%.

[0012] According to a preferred embodiment, the alloy consists, expressed by weight: of palladium between 50 and 53%, of rhodium between 47% and 50%; a quantity x of silver, where 0%≤x≤2%, and a quantity R of a residue consisting of at least one element chosen from iridium, ruthenium, platinum, titanium, zirconium and rhenium, and their combinations, where 0%≤R≤3%.

According to another preferred embodiment, x is equal to 0.

[0014] According to an alternative embodiment, R is less than or equal to 1%, preferably less than or equal to 0.5%, and more preferably less than or equal to 0.1%.

According to a preferred embodiment, R is equal to 0.

According to a preferred embodiment, x and R are equal to 0.

The alloys according to the invention are very white, can be marked with a legal hallmark, and have the appropriate properties authorizing use in the field of watchmaking, jewelry or jewelry.

[0018] The present invention also relates to a piece of timepiece, jewelry or jewelry comprising at least one component made of an alloy as defined above.

[0019] The present invention also relates to the use of an alloy as defined above in a timepiece, piece of jewelry or jewelry.

Detailed description of preferred embodiments

The present invention relates to a palladium-based alloy comprising, expressed by weight: between 50 and 55% palladium, between 45% and 50% rhodium; a quantity x of silver, where 0%≤x≤5%, preferably 0%≤x≤4%, and more preferably 0%≤x≤2%, and a quantity R of a remainder comprising at least one element chosen from iridium, ruthenium, platinum, titanium, zirconium and rhenium, and combinations thereof, where 0%≤R≤5%, preferably 0%≤R≤3%, preferably 0%≤R≤1%, and more preferably 0%≤R≤0.1%.

[0021] The alloys obtained have, after polishing, colorimetric values according to the chromatic model L*a*b (C.I.E. 1976) such that L* is between 84 and 91, a* is less than or equal to 1 and b* is less than or equal to 4.5. Preferably, L* is between 88 and 90, a* is less than or equal to 0.8 and b* is less than or equal to 3.

[0022] Additional elements such as iridium, ruthenium, platinum, titanium, zirconium and rhenium can optionally be used to improve, for example, the metallurgical properties, such as casting, to avoid porosity, or to improve the properties of the alloy such as as the deformation or its shine.

[0023] The alloys meeting the above-mentioned definition are precious metal alloys meeting all the criteria required for alloys intended for use in the watchmaking, jewelry or jewelry fields, particularly in terms of their color, their luster, the title hallmark, their reasonable price, their better castability, massive alloys with good corrosion resistance, nickel-free, scratch-resistant (minimum 160 HV in the annealed state) and easy to machine.

According to a first embodiment, the alloy comprises a quantity of silver x less than or equal to 2%.

[0025] According to a first variant, the palladium alloy comprises, expressed by weight: from 50 to 53% palladium, from 47% to 50% rhodium, from 0 to 2% silver, the remainder comprising at least one of the elements Ir, Ru, Pt, Ti, Zr and Re.

According to another variant, the palladium alloy comprises, expressed by weight of 50 to 55% palladium, 45% to 50% rhodium, and 0 to 2% silver, the quantity R of additional elements (remainder) being preferably equal to 0.

According to a second embodiment, x is equal to 0 so that the alloy of the invention does not contain silver. The palladium alloy can then comprise, expressed by weight: from 50 to 55% palladium, from 45% to 50% rhodium, the remainder comprising at least one of the elements Ir, Ru, Pt, Ti, Zr and Re, for a total value of the remainder as defined above, and preferably less than 0.1.

According to another embodiment, x is different from 0 so that the alloy of the invention contains silver. The palladium alloy can then comprise, expressed by weight: between 50 and 55% palladium, between 45% and 50% rhodium; a quantity x of silver, where 0% ≤ ≤R≤5%, preferably 0%≤R≤3%, preferably 0%≤R≤1%, and more preferably 0%≤R≤0.1%. The quantity x of silver can then be such that 0.1%≤x≤5%, preferably such that 0.1%≤x≤4%, and more preferably 0.1%≤x≤2%.

According to another embodiment, x and R are equal to 0 so that the alloy of the invention contains neither silver nor additional element (remainder) as defined in the remainder above. In this case, the palladium alloy comprises, expressed by weight, 50% to 55% palladium, and 45% to 50% rhodium.

[0030] According to a preferred embodiment, the palladium-based alloy is a Pd500 alloy and comprises, expressed by weight, 50% palladium, minimum 49% rhodium, the remainder comprising at least one of the elements Ir, Ru , Pt, Ti, Zr.

[0031] According to another preferred embodiment, the palladium alloy is a Pd500 alloy and comprises, expressed by weight, 50% palladium, 45% rhodium and a maximum of 4% silver, the remainder comprising at least one of the elements Ir, Ru, Pt, Ti, Zr.

According to another preferred embodiment, the palladium alloy is a Pd500 alloy and comprises, expressed by weight, 50% palladium, 45% rhodium and 5% silver.

According to another preferred embodiment, the palladium alloy comprises, expressed by weight, 50% palladium and 50% rhodium.

[0034] To prepare the palladium alloy according to the invention, we proceed as follows: The main elements entering into the composition of the alloy have a purity of at least 999% and are deoxidized. The elements of the alloy composition are placed in a crucible which is heated until the elements melt. Heating is carried out in a sealed induction furnace under partial nitrogen pressure. The molten alloy is poured into an ingot mold. After solidification, the ingot is quenched in water. The quenched ingot is then hot deformed at 1000°C and then annealed. The work hardening rate between each annealing is 60 to 80%. Each annealing lasts between 20 to 30 minutes and is done at 1000 °C under a reducing atmosphere composed of N2 and H2. Cooling between annealing is done by water quenching.

The following examples illustrate the present invention without limiting its scope.

[0036] Table 2 below indicates the composition of different “very white” materials tested. The proportions indicated are expressed as a percentage by weight. Comparative Example 1 is an alloy consisting of 95% platinum and 5% ruthenium. This alloy is the color reference for platinum alloys in the world of jewelry. Comparative example 2 relates to the alloy consisting of 50% platinum and 50% rhodium described in application EP 2 420 583. Comparative example 3 is pure rhodium.

[0037] Two examples according to the invention (examples 4 and 5) were produced, namely an alloy consisting of 50% palladium and 50% rhodium and an alloy consisting of 50% palladium, 45% rhodium and 5% money. 1 (comp.) Pt95Ru 2 (comp.) Pt50Rh50 3 (comp.) Pure Rh 4 (inv.) Pd50Rh50 5 (inv.) Pd50Rh45Ag5

Table 2

[0038] For these materials, the colorimetric values are measured, according to the L*a*b chromatic model (C.I.E. 1976) (measured after polishing, the samples having been polished down to 1 micron), the density, the Vickers hardness at l annealed state and melting temperature.

[0039] The colorimetric values are measured with a MINOLTA CM 3610 d device under the following conditions: Illuminant: D65 Tilt: 10° Measurement: SCI + SCE (specular included + excluded) UV: 100% Measuring focal length: 4 mm Calibration: black body and white body

[0040] The measured values are indicated in Table 3 below: 1 (comp.) 88.5 0.2 4.1 20.7 140 1850 2 (comp.) 89.5 0.60 2.8 15.7 150 1900 3 (comp.) 90.4 0.93 2.0 12.4 100 196 3 4 (inv.) 89.2 0.75 2.6 12.2 160 1750 5 (inv.) 88.7 0.79 2.9 12.1 180 1735

Table 3

The results in Table 3 show that the alloys according to the invention (examples 4 and 5) have colorimetric values very close to pure rhodium (example 3) while offering densities and melting temperatures much lower than the alloys of comparative examples 1 and 2, and therefore suitable for jewelry applications. The alloys according to the invention meet the hardness criterion after annealing and have sufficient scratch resistance.

Claims (8)

1. Palladium-based alloy consisting, expressed by weight: of palladium between 50 and 55%, of rhodium between 45% and 50%; a quantity x of silver, where 0%≤x≤5%, and a quantity R of a residue consisting of at least one element chosen from iridium, ruthenium, platinum, titanium, zirconium and rhenium, and their combinations, where 0%≤R≤5%. 2. Alloy according to claim 1, characterized in that x is less than or equal to 2%. 3. Alloy according to one of the preceding claims, consisting, expressed by weight: of palladium between 50 and 53%, of rhodium between 47% and 50%; a quantity x of silver, where 0%≤x≤2%, and a quantity R of a residue consisting of at least one element chosen from iridium, ruthenium, platinum, titanium, zirconium and rhenium, and their combinations, where 0%≤R≤3%. 4. Alloy according to one of the preceding claims, characterized in that x is equal to 0. 5. Alloy according to one of the preceding claims, characterized in that R is less than or equal to 1%, preferably less than or equal to 0.5%, and more preferably less than or equal to 0.1%. 6. Alloy according to one of the preceding claims, characterized in that R is equal to 0. 7. Alloy according to one of the preceding claims, characterized in that x and R are equal to 0. 8. Timepiece, piece of jewelry or jewelry comprising at least one component made of an alloy according to one of claims 1 to 7.