EP2450461B1 - Grey gold alloy with no nickel and no copper - Google Patents

Description

The present invention relates to a nickel-free and copper-free gray gold alloy having a hardness particularly suitable for watchmakers, jewelers and jewelers. The invention also relates to a process for preparing this alloy.

Background of the invention

There are two main types of gray gold alloys on the market, nickel alloys and palladium alloys, in which both are used as whiteners.

Nickel with its allergenic potential tends to be abandoned. In addition, its alloys exhibit reduced hardness and deformability that lend themselves poorly to the fields of jewelery and watchmaking.

So many proposals have been made to replace nickel.

Thus, patent applications EP 1 227 166 (AuCuMn alloy), EP 1 010 768 (AuCuPd alloy) and JP 3130334 (AuPdAgCu alloy), offer alloys containing copper.

The addition of copper makes it possible to harden the alloys but it has drawbacks, in particular, a cooling rate that is too low (during castings in the mold), and during the heat treatment, uncontrollable hardening and a risk of cracking.

In addition, the increase in the copper concentration is to the detriment of other elements having whitening effects.

In addition, copper carries a risk of oxidation.

The Japanese patent application published under the number JP-A-8-003662 discloses white gold alloys of the Au-Pd-In, Au-Pd-Sn or Au-Pd-Bi types. These alloys are intended for the preparation of metal clays, that is to say of clays of precious metals. Metal clays are indeed generally defined as being a raw material for the manufacture of jewelery or works of art and comprising a very fine powder of precious metals, an organic binder and water. After forming, they are dried and burned to remove the organic binder, so that only the sintered metals remain. This Japanese patent application therefore relates to a white gold alloy powder of Au-Pd-In, Au-Pd-Sn or Au-Pd-Bi type to have excellent sinterability. Concretely, by mixing this powder with water, a binder (plasticizer: di-n-butyl phthalate) and a surfactant (ethyl-cellulose), one should obtain a metal clay with a high degree of sintering.

However, with regard to palladium, its alloys without the addition of copper are too soft given the substantial proportion that must be introduced to bleach the gold.

In addition, when choosing an alloy, other important parameters are the color and brightness of the metal. Most alloys containing Pd and / or Cu require galvanic deposition of rhodium to approximate the target color. The thickness of this coating (a few microns) remains sensitive to friction and the color of the substrate reappears punctually, which does not allow to make gold objects to last.

In order not to require rhodium-plating, a gold alloy must guarantee, according to ASTM Method D1925, a YI value: D1925 <19 (YI: "yellowness index"), considered "good white" or "premium" and included in the Grade 1 category (see also http://www.utilisegold.com/jewellery technology / colors / whit e guide and Proceedings of Santa Fe Symposium 2005, pp. 103-120 ).

The value YI can be transposed into the CIELab system, CIE being the acronym of the International Commission on Illumination and Lab the three coordinate axes, the L axis measuring the white-black component (black = 0 and white = 100) , the axis measuring the red-green component (red = positive values, green = negative values) and the b axis measuring the yellow-blue component (yellow = positive values, blue = negative values). (See ISO 7724 standard issued by the International Commission on Illumination).

The colors of the gold alloys are defined in the tri-chromatic space according to the ISO 8654. A YI <19 value corresponds in first approximation to [-2 ≤ a ≤ 2; b ≤ 10].

Summary of the invention

The object of the present invention is to provide a nickel-free and copper-free gray gold alloy having satisfactory mechanical properties as well as a high whiteness (Grade 1) while not requiring rhodium-plating.

• plus de 75% d'Au ;
• de plus de 18% à moins de 24% de Pd ;
• de plus de 1% à moins de 6% d'au moins un élément choisi parmi Mn, Hf, Nb, Pt, Ta, V, Zn et Zr ;
• éventuellement, au plus 0,5% d'au moins un élément choisi parmi Si, Ga et Ti ; et
• éventuellement, au plus 0,2% d'au moins un élément choisi parmi Ru, Ir et Re ;
• la somme de tous ces pourcentages étant bien entendu égale à 100%.

This goal is achieved by an alloy consisting of (in percentages by mass):

• more than 75% Au;
• from more than 18% to less than 24% of Pd;
• from more than 1% to less than 6% of at least one element selected from Mn, Hf, Nb, Pt, Ta, V, Zn and Zr;
• optionally, at most 0.5% of at least one element selected from Si, Ga and Ti; and
• optionally, at most 0.2% of at least one element selected from Ru, Ir and Re;
• the sum of all these percentages being of course equal to 100%.

Indeed, the long and intense research carried out by the inventors allowed them to discover that such an alloy meets all the criteria required for alloys intended for jewelery and watchmaking in particular, both from the the brilliance and color of corrosion resistance and the ability to be worked and polished, while offering a hardness comparable or superior to gray gold containing copper.

• on place les composants de l'alliage d'or gris dans un creuset ;
• on chauffe le creuset jusqu'à fusion des composants ;
• on coule l'alliage fondu ;
• on le laisse se solidifier ;
• on lui fait subir une trempe à l'eau ;
• on lui fait subir au moins un laminage à froid ; et on le recuit sous atmosphère réductrice.

The gray gold alloy according to the invention may be prepared according to a process in which:

• the components of the gray gold alloy are placed in a crucible;
• the crucible is heated until the components have melted;
• casting the molten alloy;
• it is allowed to solidify;
• it is tempered with water;
• it is subjected to at least one cold rolling; and annealing under a reducing atmosphere.

Detailed exposition of the invention

The general composition of the gray gold alloy according to the invention is indicated above.

• plus de 75% d'Au ;
• de 19% à 23,5% de Pd ;
• de 1,4% à 5,9% d'au moins un élément choisi parmi Mn, Hf, Nb, Pt, Ta, V, Zn et Zr ;
• éventuellement, au plus 0,5% d'au moins un élément choisi parmi Si, Ga et Ti ; et
• éventuellement, au plus 0,1% d'au moins un élément choisi parmi Ru, Ir et Re.

The preferred composition of the gray gold alloy according to the invention is the following (expressed in mass percentages):

• more than 75% Au;
• from 19% to 23.5% of Pd;
• from 1.4% to 5.9% of at least one member selected from Mn, Hf, Nb, Pt, Ta, V, Zn and Zr;
• optionally, at most 0.5% of at least one element selected from Si, Ga and Ti; and
• optionally, at most 0.1% of at least one element selected from Ru, Ir and Re.

• l'alliage comprend au moins 20% de Pd ;
• il comprend au moins 1,5% de Zr ou de Nb ;
• il comprend de 0,002% à 0,006% (20 à 60 ppm) de Re ;
• il comprend environ 75,1% d'Au.

Other characteristics of the gray gold alloy according to the invention, which are advantageous individually or in combination, are as follows:

• the alloy comprises at least 20% Pd;
• it comprises at least 1.5% of Zr or Nb;
• it comprises from 0.002% to 0.006% (20 to 60 ppm) of Re;
• it comprises about 75.1% of Au.

Elements such as Si and Ti are known to those skilled in the art to improve, when added in small amounts, the surface condition and brightness and reduce the risk of corrosion, without substantially modifying the hardness or affect the colour.

Elements such as Ir, Re or Ru are known to improve the metallurgical properties, in particular to guarantee the fineness of the grain and to avoid the porosities, without appreciably modifying the hardness or affecting the color.

• -2 ≤ a ≤ 2
• b ≤ 10 et

Whatever its formulation, the alloy according to the invention always meets the following conditions:

• -2 ≤ a ≤ 2
• b ≤ 10 and

HV annealed (Vickers hardness value after annealing)> 85.

These properties are those that must have a gray gold alloy to meet the requirements of watchmakers, jewelers and jewelers.

Preparation of the alloy according to the invention

• les principaux éléments entrant dans la composition de l'alliage ont de préférence une pureté de 99,95% à l'exception de l'or avec 99,99% et du Zr avec 99,8% ;
• l'alliage est obtenu par fusion des éléments dans un creuset (par exemple en ZrO₂). Le chauffage est obtenu par induction dans un four étanche sous pression partielle (par exemple d'argon à 800 mbar). L'alliage en fusion est ensuite coulé dans une lingotière en graphite. Après solidification, la lingotière est sortie du four étanche et le lingot est démoulé, refroidi par une trempe à l'eau et éventuellement écrouté ;
• le lingot est ensuite laminé une ou plusieurs fois à froid, jusqu'à obtention d'un taux d'écrouissage de 75 à 80% ;
• le recuit est réalisé sous atmosphère réductrice (de préférence 80% N₂-20% H₂) durant 30 minutes à 850°C.

The alloys according to the invention are prepared under the following conditions:

• the main components in the alloy composition preferably have a purity of 99.95% with the exception of gold with 99.99% and Zr with 99.8%;
• the alloy is obtained by melting the elements in a crucible (for example in ZrO ₂ ). The heating is obtained by induction in a sealed oven under partial pressure (for example argon at 800 mbar). The molten alloy is then cast in a graphite mold. After solidification, the mold is removed from the sealed oven and the ingot is demolded, cooled by quenching with water and optionally crushed;
• the ingot is then rolled one or more times cold, until a hardening rate of 75 to 80%;
• the annealing is carried out under a reducing atmosphere (preferably 80% N ₂ -20% H ₂ ) for 30 minutes at 850 ° C.

Examples

In the examples that follow, Table I groups together 18-carat white gold alloys of the state of the art that are commercially available.

In addition to the composition of the alloys given in% by mass, this table gives indications relating to the Vickers HV hardness index of the alloy in the cast state (HV cast), hardened to 75% (HV 75%) and annealed ( HV annealing), as well as to the color measured in the CIELab system. TABLE I (State of the art) 18K Gold Gray Commercial (% by weight) The at b HV casting HV 75% HV annealing 1 At 75 Ni 14.5 Cu 5.5 Zn 5 84, 3 -0.8 8, 6 - 320 225 2 At 75 Pd 15 Cu 5 Ni 5 79.8 1.1 8.7 - 250 165 3 At 75 Pd 15 Cu 5 Mn 5 78.1 1.5 8.3 - 290 155 4 At 75 Ni 11 Cu 9.5 Zn 4.5 85.1 0.3 8, 4 223 307 - 5 At 75 Pd 13 Cu 7, 5 Ni 5 Zn 2 82.2 1.43 7.75 - - - 6 At 75 Pd 14.9 Cu 2.6 Ag 7.5 80 1.3 7, 8 70 175 90 7 At 75 Cu 19.9 Mn 4.9 ⁽¹⁾ 86.17 5.03 12.15 135 274 155 8 At 75 Pd 14 Cu 7, 4 In 3.5 ⁽²⁾ 81 2.0 7.63 145 250 188 9 At 75.1 Pd 24.9 79.37 1, 34 4.87 72 150 83 (1): according to EP1277166
(2): according to EP1010768

• -2 ≤ a ≤ 2
• b ≤ 10 et
• HV recuit > 85

ne sont pas toujours cumulativement remplies.It can be seen that the aforementioned conditions:

• -2 ≤ a ≤ 2
• b ≤ 10 and
• HV annealing> 85

are not always cumulatively fulfilled.

In addition, alloy No. 6 has a hardly satisfactory HV value, although it contains copper.

Alloy No. 9, which is composed only of gold and palladium and is therefore free of copper, has a very low annealed HV value.

The following Table II groups together gray gold alloys which are ternary. TABLE II Ternary 18-carat gold (% by weight) The at B HV casting HV 75% HV annealing 10 At 75.1 Pd 21.0 In 3.9 78.79 1.49 5, 68 80 175 115 11 At 75.1 Pd 22.0 V 2.9 81.04 1.33 5.36 115 195 127 12 At 75.1 Pd 20.0 V 4.9 82.15 1.10 5.03 125 230 157 13 At 75.1 Pd 21.0 Ta 3.9 80.15 1.35 5, 14 135 213 164 14 At 75.1 Pd 23.0 V 1.9 79.34 1.38 5.05 90 182 112 15 At 75.1 Pd 22.0 Sn 2.9 79, 54 1.37 5, 14 128 202 118 16 At 75.1 Pd 22.0 Zn 2.9 79.36 1.37 4, 84 80 156 108 17 At 75.1 Pd 23.5 Zr 1.4 80.06 1.30 4.73 87 179 119 18 At 75.1 Pd 23.0 Zr 1.9 79, 72 1, 32 5.10 91 180 127 19 At 75.1 Pd 22.5 Zr 2.4 79.76 1.22 4.83 105 202 136 20 At 75.1 Pd 22.0 Zr 2.9 79, 91 1.19 4, 67 135 220 157 21 At 75.1 Pd 21.5 Zr 3.4 80.14 1.15 4.54 164 249 194 22 At 75.1 Pd 21.0 Zr 3.9 - - - 179 - - 23 At 75.1 Pd 23.0 Mn 1.9 79.10 1.35 5, 12 72 150 100 24 At 75.1 Pd 22.0 Mn 2.9 79.77 1.33 4.86 73 156 105 25 At 75.1 Pd 21.0 Mn 3.9 79,03 1.32 4, 95 90 182 104 26 At 75.1 Pd 20.0 Mn 4.9 78.73 1.28 5.02 135 217 150 27 At 75.1 Pd 23.5 Nb 1.4 80, 34 1.37 5.15 97 173 124 28 At 75.1 Pd 23.0 Nb 1.9 81,28 1.35 4.86 132 200 151 29 At 75.1 Pd 22.5 Nb 2.4 80.76 1.32 4.76 120 192 144 30 At 75.1 Pd 22.0 Number 2.9 81.02 1, 34 5, 17 138 221 168 31 At 75.1 Pd 21.5 Nb 3.4 80, 94 1.34 5.70 138 221 168 32 At 75.1 Pd 21.0 Number 3.9 81,00 1.29 5.15 135 230 208

Each of the ternary alloys 17 to 22 according to the invention therefore has satisfactory L, a, b and HV annealing values.

The following Table III relates to quaternary and quinternal alloys according to the invention. TABLE III (invention) 18 carats quaternary and quinternary (% by weight) The at b HV casting HV 75% HV annealing 33 At 75.1 Pd 21.0 Nb 1.9 Zr 2, 0 80.76 1.18 4.53 167 260 169 34 At 75.1 Pd 21.0 Nb 1.9 Mn 2.0 80.41 1.33 4.79 133 213 147 35 At 75.1 Pd 21.0 Zr 2.0 Mn 1.9 79.95 1.24 4.55 150 237 153 36 At 75.1 Pd 19.0 Nb 2.0 Zr 2.0 Mn 1.9 80.77 1.13 4.16 170 285 255 37 At 75.1 Pd 20.0 Zr 2.0 Pt 2.4 Ga 0.5 79.86 1.20 4.65 185 226 192 38 At 75.1 Pd 20.0 Zr 2.5 Pt 2.4 79.96 1.14 4.31 153 209 188

It is found that Quaternary alloys Nos. 33 to 35 and 38 and Quinternaries Nos. 36 and 37 all have satisfactory L, a, b and HV annealing values.

In the following Table IV are reported the effects of grain refiners commonly employed in 18-carat white gold, on an alloy according to the invention composed of 75.3 Au, 21.7 Pd and 3.0 Zr (in% by weight ).

It can be seen that the values L, a and b of such an alloy are not affected by the addition of the grain refiner.

The grain index is established according to ASTM E 112. TABLE IV (invention) Grain refiner Concentration (ppm) grain index (ASTM E 112) 39 Iridium 500 2 40 Iridium 1000 3 41 Ruthenium 500 4 42 Ruthenium 1000 7 43 Rhenium 20 5 44 Rhenium 50 6

In addition, all the alloys of Table IV have a satisfactory hardness after annealing.

Moreover, the alloys 39 and 40 show a grain structure in columns oriented in the direction of solidification. The other alloys exhibit an equiaxed microstructure. Ruthenium has the most pronounced grain refining effect, however, there are many inclusions that can penalize polishing. Rhenium shows a capacity of refinement of the grain without formation of inclusions. The addition of rhenium at 20 to 60 ppm therefore gives excellent polishing ability.

Claims (13)

1. A nickel-free and copper-free gray gold alloy, constituted of (in percentages by weight):

   - more than 75% of Au;

   - from more than 18% to less than 24% of Pd;

   - from more than 1% to less than 6% of Zr;

   - optionally, from more than 1% to less than 6% of at least one element chosen from Mn, Hf, Nb, Pt, Ta, V, and Zn;

   - optionally, at most 0.5% of at least one element chosen from Si, Ga and Ti; and

   - optionally, at most 0.2% of at least one element chosen from Ru, Ir and Re.
2. The gray gold alloy as claimed in claim 1, constituted of (in percentages by weight):

   - more than 75% of Au;

   - from 19% to 23.5% of Pd;

   - from 1.4% to 5.9% of Zr;

   - optionally, from 1.4% to 5.9% of at least one element chosen from Mn, Hf, Nb, Pt, Ta, V, and Zn;

   - optionally, at most 0.5% of at least one element chosen from Si, Ga and Ti; and

   - optionally, at most 0.1% of at least one element chosen from Ru, Ir and Re.
3. The gray gold alloy as claimed in claim 1 or 2, comprising at least 20% of Pd.
4. The gray gold alloy as claimed in any one of claims 1 to 3, comprising at least 1.5% of Zr or of Nb.
5. The gray gold alloy as claimed in one of claims 1 to 4, comprising from 0.002% to 0.006% (20 to 60 ppm) of Re.
6. The gray gold alloy as claimed in one of claims 1 to 5, comprising around 75.1% of Au.
7. A process for preparing a gray gold alloy as claimed in one of claims 1 to 6, in which:

   - the components of the gray gold alloy are placed in a crucible;

   - the crucible is heated until the components melt;

   - the molten alloy is cast;

   - it is left to solidify;

   - it is subjected to water hardening;

   - it is subjected to at least one cold-rolling operation; and

   - it is annealed in a reducing atmosphere.
8. The process as claimed in claim 7, in which the heating is carried out via induction in a leaktight furnace under a partial pressure of inert gas.
9. The process as claimed in claim 8, in which the inert gas is Ar.
10. The process as claimed in one of claims 7 to 9, in which the annealing is carried out in a reducing atmosphere constituted of a mixture of N₂ and H₂.
11. The process as claimed in claim 10, in which the mixture of N₂ and H₂ is constituted of around 80% of N₂ and 20% of H₂.
12. The process as claimed in one of claims 7 to 11, in which the annealing is carried out over around 30 minutes.
13. The process as claimed in one of claims 7 to 12, in which the annealing is carried out at around 850°C.