Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C5/00—Alloys based on noble metals
  • C22C5/02—Alloys based on gold
• • A—HUMAN NECESSITIES
  • A44—HABERDASHERY; JEWELLERY
  • A44C—PERSONAL ADORNMENTS, e.g. JEWELLERY; COINS
  • A44C27/00—Making jewellery or other personal adornments
  • A44C27/001—Materials for manufacturing jewellery
  • A44C27/002—Metallic materials
  • A44C27/003—Metallic alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C28/00—Alloys based on a metal not provided for in groups C22C5/00 - C22C27/00
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/14—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of noble metals or alloys based thereon

Definitions

• the present invention relates to a method of manufacturing a solid gold alloy by sintering.
• gold alloys There are different types of gold alloys depending on the metals or elements that are mixed with the gold. Depending on the desired use of these alloys, different properties can be sought such as solidity, shine or even the ease of forming the alloy. The metals and/or elements mixed with the gold are thus chosen to obtain the desired properties.
• gold alloys are more or less resistant to corrosion.
• the resistance of gold alloys to corrosion can depend on their composition, the way they are made and the roughness of their surface, among other things.
• Some gold alloys cannot be used in jewelry or watchmaking because their resistance to corrosion is insufficient. This is the case, for example, of the alloy of gold and aluminum (AuAl 2 ), or of the alloy of gold and indium (Auln 2 ) which are conventionally prepared by casting the alloy melted in a mould.
• the alloys of gold and aluminum, on the one hand, and of gold and indium, on the other hand have interesting properties, and in particular a good resistance to shocks and also an attractive violet color, and it would therefore be interesting to be able to use them in jewelry or watchmaking.
• the object of the present invention is thus to improve the resistance of gold alloys to corrosion, in particular so that they can be used in jewelery or watchmaking.
• the method according to the invention in which the step of sintering the powder is carried out at a temperature depending on the melting temperature of the alloy, makes it possible to obtain a solid gold alloy having optimized mechanical properties.
• the solid gold alloy obtained has improved corrosion resistance compared to the corresponding solid alloys obtained by methods of the prior art, in particular by casting the molten alloy in a mold.
• the solid gold alloys obtained by the process according to the invention can thus advantageously be used in jewelry or watchmaking.
• the gold alloy of the invention comprises 37.5% gold, it is 9 carat (cts) gold.
• the gold alloy may comprise at least 44% gold (Au) by mass relative to the total mass of said alloy.
• the second metal can be aluminum and the gold alloy (or alloy) can have the formula AuAl 2 .
• the alloy comprises a quantity of gold ranging from 58.5% to 95% by mass, preferably ranging from 70% to 90% by mass, and more preferentially ranging from 75% to 85% by mass, relative to the total mass of the alloy.
• the gold alloy of the invention comprises 58.5% gold by mass relative to the total mass of the alloy, it is 14 ct gold. Moreover, when the gold alloy has 75% gold by mass relative to the total mass of the alloy, it is 18 ct gold.
• the alloy comprises at least 75% gold by mass relative to the total mass of the alloy. According to another preferred variant of this embodiment, the alloy comprises at most 77% gold by mass relative to the total mass of the alloy.
• the alloy comprises an amount of aluminum ranging from 10% to 35%, preferably ranging from 15% to 27%, plus preferentially ranging from 15% to 24%, and even more preferentially ranging from 16 to 22%, by mass relative to the total mass of the alloy.
• the alloy may also comprise at least one additional element chosen from silicon (Si), palladium (Pd), platinum (Pt), tin (Sn), silver ( Ag), copper (Cu), manganese (Mn), and a mixture thereof.
• additional elements make it possible to improve the properties of the alloy, in particular the mechanical properties such as the hardness, the resistance to corrosion, or even to facilitate the manufacturing process and/or the shaping of the alloy.
• the total quantity of additional element(s) in the alloy can range from 0% to 10% by mass, preferably from 0.2 to 10% by mass, preferably from 1% to 9 % by mass, preferably from 3.5% to 8.5% by mass, relative to the total mass of the alloy.
• the alloy when the alloy comprises gold and aluminium, the alloy can preferably comprise at least two additional elements, preferably chosen from Si and Pd; Si and Pt; Sn and Pt; Si and Sn; Si and Ag; and Si and Cu. According to this embodiment, the alloy may comprise at least a third additional element, or a third and a fourth additional elements chosen from among the aforementioned additional elements.
• the alloy may also comprise modifying elements which are present in smaller quantities than the additional elements and which make it possible to modulate the properties of the alloy, in particular the mechanical properties such as the resistance to corrosion or the hardness, or else facilitate the manufacturing process and/or the shaping of the alloy. These elements can be present in an amount of at most 1% by mass, preferably at most 0.5% by mass, and more preferably at most 0.1% by mass, relative to the total mass. Golden.
• the modifying elements can be selected from iron (Fe), nickel (Ni), zinc (Zn), titanium (Ti), cobalt (Co), zirconium (Zr), rhenium (Re), l iridium (Ir), vanadium (V), molybdenum (Mo), yttrium (Y), and a mixture thereof.
• rhenium (Re), iridium (Ir), vanadium (V), molybdenum (Mo) and yttrium (Y) are in particular grain refiners which make it possible to prevent the grains grow during the manufacturing process and thereby to obtain a solid gold alloy having improved corrosion resistance.
• These grain refiners may be present in amounts ranging from 0.01% ⁇ to 2% ⁇ by mass, and preferably ranging from 0.02% ⁇ to 0.5% ⁇ by mass, relative to the total mass of the alloy.
• an amount of gold when an amount of gold (and not of gold alloy) is indicated, it is pure gold which may contain at most 1% of impurities by mass, preferably at most 0 .5% impurities by mass, and more preferably at most 0.1% impurities by mass, relative to the total mass of gold.
• the small amount of these impurities is such that they do not modify the mechanical properties of the alloy.
• the second metal can be indium and the gold alloy (or alloy) can have the formula AuIn 2 .
• the alloy comprises a quantity of gold ranging from 30% to 60% by mass, preferably ranging from 40% to 60% by mass, and more preferentially ranging from 42% to 50% by mass , with respect to the total mass of the alloy.
• the alloy comprises at least 30% gold by mass relative to the total mass of the alloy. According to another preferred variant of this embodiment, the alloy comprises at most 60% gold by mass relative to the total mass of the alloy.
• the alloy comprises a quantity of indium ranging from 40% to 65% by mass, preferably 45% to 60% by mass, and more preferentially ranging from 50% to 56% by mass, by relative to the total mass of the alloy.
• the gold and indium alloy may further comprise additional elements, modifying elements and/or impurities, such as those described for the first embodiment.
• the second metal can be gallium and the gold alloy (or alloy) can have the formula AuGa 2 .
• the alloy comprises a quantity of gold ranging from 40% to 65% by mass, preferably ranging from 50% to 62% by mass, and more preferably ranging from 56% to 60% by mass , with respect to the total mass of the alloy.
• the alloy may comprise at least 55% gold by mass relative to the total mass of the alloy. According to another preferred variant of this embodiment, the alloy comprises at most 60% gold by mass relative to the total mass of the alloy.
• the alloy comprises a quantity of gallium ranging from 35% to 60% by mass, preferably 37% to 50% by mass, and more preferentially ranging from 39% to 44% by mass, compared to the total mass of the alloy.
• the alloy of gold and gallium can also comprise additional elements, modifying elements and/or impurities, such as those described for the first embodiment.
• the process for manufacturing the solid gold alloy firstly comprises a step of powdering the alloy in the form of particles.
• the powdering can be carried out by atomization under gas, in particular under argon, nitrogen or helium, or under water, of an initial material according to a method well known to those skilled in the art.
• the initial material may be one of the additional metals/elements of the alloy.
• the various metals/elements of the alloy are powdered separately by atomization and then are mixed to form the desired alloy in powder form.
• the initial material may be the desired alloy (pre-alloyed material) and the powdering may be carried out by atomization of this initial material.
• the powdering can be carried out by mechanosynthesis and in particular by grinding techniques well known to those skilled in the art, for example by using a planetary grinder.
• the initial material may be in solid and pre-alloyed form, and in particular from casting in an induction or arc furnace, for example.
• the powder can be formed of particles having a size ranging from 100 nm to 500 ⁇ m and preferably ranging from 1 ⁇ m to 500 ⁇ m, which means that at least one of the dimensions of said particles has a value ranging from 200 nm to 500 ⁇ m and preferably ranging from 1 ⁇ m to 500 ⁇ m.
• dimension is understood to mean the number-average dimension of all the particles of a given population, this dimension being conventionally determined by methods well known to those skilled in the art. Mention may be made, for example, of laser diffraction, otherwise known as laser granulometer.
• the size of the particles according to the invention can also be determined by microscopy, in particular by transmission electron microscope (TEM).
• TEM transmission electron microscope
• the aforementioned particle size ranges, or even particle size ranges, can be obtained either directly by the powdering step according to the first or second embodiment, or by an additional step of sorting the particles obtained following the powdering step.
• This sorting step can be carried out by sieving or classification techniques well known to those skilled in the art.
• the sintering can be carried out by SPS sintering (“Spark Plasma Sintering”), also called flash sintering, by hot pressing, or by hot isostatic pressing (CIC) also known as “hot isostatic pressing” (HIP).
• SPS sintering Spark Plasma Sintering
• CIC hot isostatic pressing
• HIP hot isostatic pressing
• the sintering can be carried out by SPS sintering.
• the alloy in powder form is then placed in a mold (or matrix) in a vacuum chamber, for example at a pressure of 5 Pa, and a uniaxial pressure is applied.
• the uniaxial pressure applied during the sintering step can have a value ranging from 10 to 150 MPa, preferably from 20 to 120 MPa, and even more preferably from 30 to 90 MPa. . These pressure ranges are notably applied when the mold (also called matrix) containing the powder is made of graphite.
• any pressure below 1050 MPa can be used.
• this type of mold is preferably used at high pressures, in particular between 700 MPa and 1050 MPa, which makes it possible to lower the temperature applied during the sintering step.
• the sintering can be carried out in one or more cycles.
• a cycle corresponds in particular to the application of pressure on the powder then to an increase in temperature while maintaining the powder under pressure.
• the duration of the cycles can be between 2 min and 20 min.
• the cycles can include the same temperature and pressure conditions or different temperature and pressure conditions.
• a change in temperature may take place between two cycles. This temperature change can be a cooling to then carry out another cycle or on the contrary a temperature increase.
• the temperature applied to the alloy during the sintering step can have a value ranging from 40% to 99%, preferably from 60% to 97%, and preferably ranging from 85% to 95%, of the melting temperature of the alloy.
• the temperature applied to the alloy during the sintering step can have a value ranging from 40% to 90%, and preferably ranging from 70% to 80%, of the melting temperature.
• the method can then include a sintering post-treatment step under isostatic charge (CIC or HIP) well known to those skilled in the art.
• the sintering process makes it possible to densify the powder at a lower temperature, which avoids increasing the grain size and which allows the final solid to retain or improve its mechanical properties.
• the temperature is adjusted according to the alloy produced and the solid alloy obtained at the end of the manufacturing process has an improved resistance to corrosion.
• the second metal is aluminum and the temperature applied during the sintering step can have a value ranging from 400°C to 1050°C, preferably ranging from 600 to 1000°C.
• the second metal is indium and the temperature applied during the sintering step can have a value ranging from 300°C to 500°C.
• the solid gold alloy may have a porosity rate of at most 2% and preferably of at most 0.5%.
• the porosity rate can be obtained by techniques well known to those skilled in the art such as, for example, making one or more longitudinal or transverse sections of the solid prepared then analyzing the surface of the section, in particular by optical microscopy, so as to be able to evaluate, or even count, the number of pores and thus determine the porosity rate.
• pellets in the shape of a cylinder and having a diameter of 20mm (millimeter) and a height of 10mm are obtained.
• the alloy comprises 78.5% by weight gold, 21.5% by weight aluminum.
• the term “mass” means by mass relative to the total mass of the alloy.
• the size of the particles after powdering was obtained by laser diffraction using a Malvern Mastersizer device and is between 4 ⁇ m and 58 ⁇ m.
• the sintering process is carried out at a temperature of 600° C., under a pressure of 40 MPa and for a duration of 7 minutes.
• the alloy comprises 46.1% by mass of gold, 53.9% by mass of indium.
• the particle size after powdering is between 3 ⁇ m and 35 ⁇ mm.
• the sintering process is carried out at a temperature of 500° C., under a pressure of 40 MPa and for a duration of 7 minutes.
• Two solid gold alloys were prepared using a process cast in an induction furnace and cast in a copper mold. At the end of the process, a the piece is obtained and is cut into pellets having a dimension of 20mm diameter and 10mm height.
• the alloy comprises 78.5% by weight of gold, 21.5% by weight of aluminum
• the casting process is carried out at a temperature of 1200°C under primary vacuum
• the alloy comprises 46.1% by mass of gold, 53.9% by mass of indium
• the corrosion resistance of the examples according to the invention E1 to E3 and of the comparative examples C1 to C3 was evaluated by means of the synthetic sweat test (test 1) according to standard EN1811 under neutral pH conditions and by means of tests salt spray (test 2) according to NIHS 96-50.
• the time from which signs of corrosion begin to appear was measured.
• the signs of corrosion observed include changes visible to the naked eye, with a magnifying glass and/or under a microscope. These modifications are in particular pinholes (or holes) and/or areas of discoloration.

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• 2021
  • 2021-03-01 EP EP21305245.9A patent/EP4053299A1/de active Pending
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  • 2022-02-25 EP EP22159005.2A patent/EP4053300A1/de active Pending

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