Gold alloy with deformation recovery performance

Abstract

Gold alloy for jewelry or tabulation applications, in particular for the manufacture of jewelry items having at least partial shape and / or dimensional recovery properties upon application of a deformation force, comprising: 700 to 800 per thousand by weight of gold; 25% by weight to 170% by weight of copper; palladium, 50% by weight to 165% by weight; and cobalt, 7% by weight to 40% by weight. And the gold alloy is gray alloy.

Description

Technical Field

[0001] The present invention relates to the field of metallurgy, in particular to the field of gold alloys. In particular, the present invention relates to a gold alloy for jewelry and watchmaking applications.

[0002] The present invention also relates to jewelry and watchmaking articles made at least in part from the gold alloys described herein. Background Art

[0003] Objects made of metal exhibit the property of being deformable. This deformation can be either elastic or plastic. Deformation occurs due to forces acting on the material, such as traction, compression, or bending.

[0004] Elastic deformation is characterized by the ability of an object to return to its original size and / or shape when the deforming force ceases.

[0005] Plastic-type deformation is characterized by the fact that the object can no longer return to its original size and / or shape when the deforming force ceases; in other words, its size and / or shape has been irreversibly changed relative to its original size and / or shape.

[0006] Plastic deformation typically occurs when a force greater than that required to deform an object elastically is applied. Yield strength is the force that, when applied to an object, determines the transition from elastic to plastic behavior.

[0007] The maximum deformation force that an object can withstand is called the breaking load.

[0008] In particular, objects made of gold alloys may also be subject to elastic or plastic type deformations.

[0009] During their service life, certain objects made of gold alloys are subjected to various static or cyclic deformation forces: when objects made of gold alloys are connected to other similar or different objects, or integrated into more complex objects, any plastic deformation will cause play, friction, and misalignment.

[0010] Therefore, objects made from gold alloys may, over time, result in changes in size and / or shape relative to the original object.

[0011] Changing the shape of an article made of gold alloy is inconvenient because the functionality of the article may be impaired due to the difference in size or shape by the application of a force greater than the yield strength.

[0012] Generally, it has been observed that known yellow (according to 3N ISO 8654) and red (according to 5N ISO 8654) gold alloys generally exhibit good mechanical properties, including high yield strength, hardness and elasticity, and are therefore often successfully used in jewelry or watchmaking items that are subject to particularly high stresses during their service life.

[0013] Gray gold alloys are also known to exhibit remarkable mechanical properties, including high yield strength, hardness, and elasticity, with the properties of nickel being used to achieve higher mechanical deformation recovery compared to gold alloys that do not contain nickel.

[0014] Document US Pat. No. 5,173,132 shows a gold alloy 14k in which 1‰ to 7‰ cobalt and 10‰ to 50‰ nickel are present; cobalt and nickel are used for grain refinement in order to further improve the machinability of the alloy.

[0015] However, the use of nickel is strongly discouraged where the alloy is intended for use in articles intended for direct contact with human skin, particularly in the case of gold alloys intended for jewelry applications where objects intended for direct contact with human skin are to be made. In fact, nickel can cause allergic reactions.

[0016] The object of the present invention is to describe a gold alloy that overcomes the above-mentioned drawbacks. The object of the present invention is also to describe a jewellery or watchmaking article comprising a gold alloy that overcomes the above-mentioned drawbacks.

[0017] The object of the present invention is finally to describe a method for producing a gold alloy that overcomes the above-mentioned disadvantages. Summary of the Invention

[0018] Applicants have devised a variety of gold alloys with improved mechanical properties, some of the main aspects of which are described herein. These aspects may be combined with each other or with portions of the specific embodiments or claims.

[0019] According to one aspect of the present disclosure, there is described herein a gold alloy for jewelry applications comprising:

[0020] - Gold, 700 wt‰ to 800 wt‰,

[0021] - copper, 25 wt.‰ to 170 wt.‰,

[0022] - Palladium, 50 wt.‰ to 165 wt.‰,

[0023] - Cobalt, 7% to 40% by weight.

[0024] The Applicant notes that the gold alloy is particularly intended for making jewelry articles having improved mechanical properties, and is characterized in particular by an increase in the yield strength so as to make it comparable to that of the 3N and 5N alloys.

[0025] Applicants note that the yield strength is significantly higher relative to commercial Nickel-free gray Gold alloy.

[0026] According to another non-limiting aspect, the alloy comprises:

[0027] - Gold, 700 wt‰ to 800 wt‰,

[0028] - copper, 25‰ to 95‰ by weight,

[0029] - Palladium, 85 wt.‰ to 165 wt.‰,

[0030] - cobalt, 7 wt‰ to 40 wt‰,

[0031] - Silver, 7‰ to 60‰ by weight.

[0032] According to another non-limiting aspect, the alloy comprises gallium and / or at least one grain refining element, preferably at least one of iridium, rhenium, and ruthenium.

[0033] According to another non-limiting aspect, the at least one grain refining element is present in a pre-alloy comprising:

[0034] - copper, in which the grain refining element is iridium, or

[0035] - Palladium, wherein the grain refining element is rhenium or ruthenium.

[0036] According to another non-limiting aspect, the weight content of gallium and / or the at least one grain refining element (preferably at least one of iridium, rhenium or ruthenium) is determined to be up to 1000 wt%.

[0037] According to another non-limiting aspect, the gold alloy is characterized in that the gold alloy is free of nickel.

[0038] According to another non-limiting aspect, the gold alloy is characterized in that the gold alloy is free of arsenic.

[0039] According to another non-limiting aspect, the gold alloy is characterized in that the gold alloy is free of platinum.

[0040] According to another non-limiting aspect, the gold alloy comprises 1 wt‰ to 10 wt‰, preferably 2 wt‰ to 9 wt‰, more preferably 3 wt‰ to 8 wt‰ of gallium.

[0041] According to another non-limiting aspect, the gallium content is substantially between 4% and 7% by weight.

[0042] According to another non-limiting aspect, the gallium content is 3.5 wt% to 4.5 wt%.

[0043] According to another non-limiting aspect, the alloy comprises at least one grain refining element, preferably at least one of iridium, rhenium, or ruthenium.

[0044] According to another non-limiting aspect, the iridium is pre-alloyed with copper.

[0045] According to another non-limiting aspect, the rhenium and / or ruthenium is pre-alloyed with palladium.

[0046] According to another non-limiting aspect, the at least one grain refining element, in particular at least one of iridium, rhenium or ruthenium, is present in an amount up to 1 wt.%.

[0047] According to another non-limiting aspect, the gold alloy comprises:

[0048] - Gold, 730 wt‰ to 770 wt‰,

[0049] - copper, 40 wt.‰ to 90 wt.‰,

[0050] - Palladium, 100 wt.‰ to 150 wt.‰,

[0051] - cobalt, 8 wt‰ to 30 wt‰,

[0052] - Silver, 8 ‰ to 55 ‰ by weight.

[0053] According to another non-limiting aspect, the gold alloy comprises:

[0054] - Gold, 740 wt‰ to 760 wt‰,

[0055] - copper, 50 wt.‰ to 90 wt.‰,

[0056] - Palladium, 100 wt.‰ to 150 wt.‰,

[0057] - cobalt, 8 wt‰ to 30 wt‰,

[0058] - Silver, 8 ‰ to 55 ‰ by weight.

[0059] According to another non-limiting aspect, the gold alloy comprises:

[0060] - Gold, 740 wt‰ to 760 wt‰,

[0061] - copper, 50 wt.‰ to 90 wt.‰,

[0062] - palladium, 110 to 140 wt. ‰, preferably 115 to 135 wt. ‰,

[0063] - cobalt, 10 wt.‰ to 25 wt.‰,

[0064] - Silver, 8% to 50% by weight.

[0065] According to another non-limiting aspect, the gold alloy comprises:

[0066] - Palladium, 120% to 130% by weight.

[0067] According to another non-limiting aspect, the gold alloy according to one or more of the preceding aspects comprises:

[0068] - a copper content of 45 wt ‰ to 65 wt ‰, preferably 50 wt ‰ to 60 wt ‰, and a silver content of 35 wt ‰ to 52 wt ‰; or

[0069] The copper content is from 75 wt ‰ to 95 wt ‰, preferably from 80 wt ‰ to 90 wt ‰, and the silver content is from 7 wt ‰ to 13 wt ‰, preferably from 8 wt ‰ to 12 wt ‰.

[0070] According to another non-limiting aspect, the gold alloy has a color within the CIELAB 1976 color range and according to the color measurement conditions of CIED65, defined by the following color coordinates:

[0071] L * , between 80 and 84.5, preferably between 81 and 84;

[0072] a * , ranging from 1.2 to 3.7, preferably from 1.5 to 3.5;

[0073] b * , ranging from 6.2 to 10.5, preferably 6.6 to 10.

[0074] According to another non-limiting aspect, the color is gray and / or the gold alloy is a gray gold alloy.

[0075] According to another non-limiting aspect, the gold alloy has a color within the CIELAB 1976 color range and according to the color measurement conditions of CIED65, defined by the following color coordinates:

[0076] L * , between 80 and 84.5, preferably between 81 and 84;

[0077] a * , ranging from 1.2 to 2.4, preferably from 1.5 to 2.1;

[0078] b* , ranging from 6.7 to 8.5, preferably 7 to 8.3.

[0079] For the purposes of the present invention, a color, when placed on the orthogonal axes of a color chart, falls within the aforementioned coordinates, particularly within coordinates a * and b * The gold alloy within the square defined above is considered grey.

[0080] According to another non-limiting aspect, the gold alloy is a gray gold alloy.

[0081] According to another non-limiting aspect, the gold alloy has a color within the CIELAB 1976 color range and according to the color measurement conditions of CIED65, defined by the following color coordinates:

[0082] L * , between 83 and 84.5, preferably between 83.2 and 84.3;

[0083] a * , between 2.7 and 3.7, preferably between 2.9 and 3.5;

[0084] b * , ranging from 8.9 to 9.9, preferably 8.7 to 9.7.

[0085] According to another non-limiting aspect, the gold alloy comprises:

[0086] - gold, 730 to 770 wt.‰, preferably 740 to 760 wt.‰,

[0087] - copper, 150 to 170 wt.%, preferably 155 to 165 wt.%,

[0088] - palladium, 50% to 70% by weight, preferably 55% to 65% by weight,

[0089] - cobalt, 7 wt‰ to 13 wt‰,

[0090] - iron, 10‰ to 30‰ by weight,

[0091] Optionally, at least one grain refining element, preferably at least one of iridium, rhenium or ruthenium, is present in an amount of up to 1 wt. % .

[0092] According to another non-limiting aspect, the sum of gold, copper, palladium, cobalt, iron and optionally at least one grain refining element is up to 1000 wt%.

[0093] According to another non-limiting aspect, the gold alloy consists of:

[0094] - Gold, 700 wt‰ to 800 wt‰,

[0095] - copper, 25‰ to 75‰ by weight,

[0096] - Palladium, 85 wt.‰ to 165 wt.‰,

[0097] - cobalt, 7 wt‰ to 40 wt‰,

[0098] - Silver, 7‰ to 60‰ by weight,

[0099] - gallium, 1 to 10 wt‰, preferably 2 to 9 wt‰, more preferably 3 to 8 wt‰,

[0100] - a content of at least one grain refining element, preferably at least one of iridium, rhenium or ruthenium, of up to 1 wt.‰.

[0101] According to another aspect, a jewelry item comprising the gold alloy according to one or more of the aspects described herein is also described.

[0102] According to another non-limiting aspect, the yield strength of the jewelry article is comparable to the yield strength of a corresponding jewelry article made from a 3N or 5N alloy.

[0103] In particular, the yield strength is greater than the yield strength of a corresponding jewelry item made from a nickel-free, commercially known gray gold alloy.

[0104] According to another non-limiting aspect, the gold alloy is a gray gold alloy.

[0105] According to another non-limiting aspect, an article of jewelry comprises jewelry or a watch or a watch bracelet or a mechanical watch movement or a component of a movement.

[0106] According to another non-limiting aspect, a watch or a mechanical watch movement is configured to be worn or installed in a watch, respectively.

[0107] According to the present invention, a method for producing a gold alloy is also described, comprising a step of mixing gold, copper, palladium and cobalt in at least one or more of the amounts described in the above aspects.

[0108] According to another non-limiting aspect, the method comprises the step of mixing:

[0109] - Gold, 700 wt‰ to 800 wt‰,

[0110] - copper, 9‰ to 79‰ by weight,

[0111] - Palladium, 85 wt.‰ to 165 wt.‰,

[0112] - cobalt, 7 wt‰ to 40 wt‰,

[0113] - Silver, 7‰ to 60‰ by weight,

[0114] The content of the copper iridium (CuIr) pre-alloy is 16 wt‰. BRIEF DESCRIPTION OF THE DRAWINGS

[0115] The alloy article of the present invention will now be described with reference to some preferred embodiments and with reference to the accompanying drawings.A brief description of the drawings is given below.

[0116] Figure 1 A Cartesian diagram illustrating a monotonic tensile test is shown, wherein the abscissa represents the relative deformation (in percentage) to which the specimen is subjected and the ordinate represents the stress to which the specimen is subjected.

[0117] Figure 2 A Cartesian graph is shown in which the abscissa represents the distance corresponding to the displacement of the midpoint of the gold alloy test sample when subjected to bending forces at three points, and in which the ordinate represents the bending forces.

[0118] Figure 3 The coordinates a representing the color range according to CIELAB 1976 are shown. * and b * Cartesian diagram of the color table of , which shows certain compositions that the applicant has studied in particular. Figure 2 The colors detected on the image. DETAILED DESCRIPTION

[0119] The present invention discloses a gold alloy with improved deformation recovery properties. The gold alloy described herein is advantageously and preferably suitable for use in articles subjected to various deformation forces during their service life, and these deformation forces must be maintained below the yield strength. These articles may be articles of fine jewelry or watchmaking and may be connected to other identical or similar articles or integrated into more complex articles. In one non-limiting embodiment, these articles may be bracelets, components of bracelets, or components of watch movements.

[0120] As will be better elucidated in the following description, applicants have focused on embodiments of gold alloys that exhibit distinctly different colors relative to the colors coded according to the 0N-6N standard of ISO 8654. In particular, the family of alloys developed by applicants is a family of gray gold alloys.

[0121] The applicant has developed a family of grey gold alloys with a gold content substantially equal to 18k, having the following characteristics:

[0122] - Gold, 700 wt‰ to 800 wt‰,

[0123] - copper, 25 wt.‰ to 170 wt.‰,

[0124] - Palladium, 50 wt.‰ to 165 wt.‰,

[0125] - Cobalt, 7% to 40% by weight.

[0126] Optionally, the alloy family comprises 7% to 60% by weight of silver.

[0127] Depending on the presence or absence of silver, in a non-limiting embodiment, the sum of the weight contents of gold, copper, palladium, cobalt or the sum of the weight contents of gold, copper, palladium, cobalt and silver is equal to 1000 wt‰. For this reason, it is clear that the present invention shows a special family of gold alloys consisting of the following composition: 700 wt‰ to 800 wt‰ of gold, 25 wt‰ to 170 wt‰ of copper, 50 wt‰ to 165 wt‰ of palladium, 7 wt‰ to 40 wt‰ of cobalt, or a special family of gold alloys consisting of the following composition: 700 wt‰ to 800 wt‰ of gold, 25 wt‰ to 170 wt‰ of copper, 50 wt‰ to 165 wt‰ of palladium, 7 wt‰ to 40 wt‰ of cobalt, 7 wt‰ to 60 wt‰ of silver.

[0128] From this general family of gold alloys, the applicant has defined a more specific family comprising the following elements of the following composition:

[0129] - Gold, 700 wt‰ to 800 wt‰,

[0130] - copper, 25‰ to 95‰ by weight,

[0131] - Palladium, 85 wt.‰ to 165 wt.‰,

[0132] - cobalt, 7 wt‰ to 40 wt‰,

[0133] - Silver, 7‰ to 60‰ by weight.

[0134] Preferably, but not limited thereto, the gold alloy according to the above composition can be made using only the above materials, ie, the amount of gold, copper, palladium, cobalt, and silver reaches 1000 wt‰.

[0135] The family of alloys described herein is nickel-free to ensure compatibility with all those applications in which articles made from gold alloys must come into direct contact with human skin.

[0136] Furthermore, the family of gold alloys described herein are arsenic-free.

[0137] Some embodiments of the alloys of the present invention have improved properties in terms of mechanical properties and further comprise 1 wt‰ to 10 wt‰, preferably 2 wt‰ to 9 wt‰, more preferably 3 wt‰ to 8 wt‰ of gallium.

[0138] In particular, some embodiments have a gallium content of substantially 4% to 7% by weight. The Applicant has studied in particular two main families of gold alloys, either with a gallium content equal to 4% by weight or with a gallium content equal to 7% by weight.

[0139] In particular, cobalt and gallium perform their functions as thermosetting agents through a process of dissolution and precipitation.

[0140] Among the alloys studied by the applicant, some preferred embodiments include iridium as a grain refiner. Other embodiments of the gold alloys disclosed herein include a grain refiner selected from rhenium and / or ruthenium. More grain refiners may be present simultaneously.

[0141] In one embodiment, the weight content of gallium and / or at least one grain refiner (preferably at least one of iridium, rhenium or ruthenium) is determined to be up to 1000 wt‰. The content of grain refiner can be up to 1 wt‰.

[0142] In fact, the applicant has conceived specific embodiments of gold alloys in which the amount of gold, copper, silver, cobalt, palladium and gallium reaches 1000% by weight. These alloys are alloys composed of only six elements.

[0143] Furthermore, the applicant has envisioned specific embodiments of gold alloys in which the amount of gold, copper, silver, cobalt, palladium, gallium and at least one grain refining element (iridium and / or rhenium and / or ruthenium) reaches 1000 wt%.

[0144] However, it is noted that at least one grain refining element, in particular at least one of iridium, rhenium or ruthenium, may be added to the pre-alloy.

[0145] In particular, the alloy that is the subject of the present invention is a platinum-free alloy.

[0146] Starting with the previous general family, applicants have investigated the properties of a family of gold alloys comprising:

[0147] - Gold, 730 wt‰ to 770 wt‰,

[0148] - copper, 40 wt.‰ to 90 wt.‰,

[0149] - Palladium, 100 wt.‰ to 150 wt.‰,

[0150] - cobalt, 8 wt‰ to 30 wt‰,

[0151] - Silver, 8 ‰ to 55 ‰ by weight,

[0152] The focus was then narrowed down to a family of gold alloys comprising 740 to 760 wt‰ gold, 50 to 90 wt‰ copper, and palladium, cobalt and silver within the above ranges, optionally with gallium and grain refining elements as described above.

[0153] Further research was conducted on a family of gold alloys consisting of:

[0154] - Gold, 730 wt‰ to 770 wt‰,

[0155] - copper, 40 wt.‰ to 90 wt.‰,

[0156] - palladium, 110 to 140 wt. ‰, preferably 115 to 135 wt. ‰,

[0157] - cobalt, 10 wt.‰ to 25 wt.‰,

[0158] - Silver, 8% to 50% by weight.

[0159] The applicant has studied two subfamilies of gold alloys, which are concentrated on a copper content equal to 55 wt‰ and a silver content of 40 wt‰ to 50 wt‰, or on a higher copper content, substantially equal to 85 wt‰ and a lower silver content of about 10 wt‰.

[0160] In particular, two subfamilies of alloys have been identified, containing: 45 to 65 wt. ‰, preferably 50 to 60 wt. ‰, of copper, and 35 to 52 wt. ‰; or 75 to 95 wt. ‰, preferably 80 to 90 wt. ‰, of copper, and 7 to 13 wt. ‰, preferably 8 to 12 wt. ‰. These subfamilies have been investigated with combinations of 700 to 800 wt. ‰, gold, 85 to 165 wt. ‰, palladium, and 7 to 40 wt. ‰, cobalt, and further combinations of gallium and / or iridium, as described above. Specific embodiments of gold alloys have been obtained from these two subfamilies, which have been designated with the references 848, 849, and 850.

[0161] The following table shows some specific compositions that have been studied in detail by the applicant. The amounts of gold alloying elements are expressed in ‰ by weight.

[0162]

[0163] Table 1

[0164] In the composition according to Table 1, 1‰ of grain refining elements are added, including at least one of iridium, rhenium or ruthenium, preferably pre-alloyed with copper or palladium, and / or at least one of copper, silver, palladium, cobalt or gallium is added, determined to reach 1000 wt‰ of the alloy.

[0165] Other variants of gold alloys according to compositions 848, 849 and 850 are, for example, those according to the following sub-groups:

[0166] 740 wt‰ to 760 wt‰ of gold, 50 wt‰ to 60 wt‰ of copper, 100 wt‰ to 150 wt‰, preferably 115 wt‰ to 135 wt‰ of palladium, 20 wt‰ to 30 wt‰ of cobalt, 35 wt‰ to 55 wt‰ of silver, 3 wt‰ to 8 wt‰, preferably 3 wt‰ to 5 wt‰ or 6 wt‰ to 8 wt‰ of gallium, and optionally at least one grain refining element, the grain refining element comprising at least one of iridium, rhenium or ruthenium, preferably pre-alloyed with copper or palladium, and / or at least one of copper, silver, palladium, cobalt or gallium, in an amount of up to 1 wt‰, so that the gold alloy is determined to be up to 1000 wt‰.

[0167] Furthermore, other variants of gold alloys according to compositions 848, 849 and 850 are, for example, those according to the following subgroups:

[0168] 740 wt‰ to 760 wt‰ of gold, 50 wt‰ to 60 wt‰ of copper, 100 wt‰ to 150 wt‰, preferably 115 wt‰ to 135 wt‰ of palladium, 20 wt‰ to 30 wt‰ of cobalt, 35 wt‰ to 55 wt‰ of silver, 3 wt‰ to 8 wt‰, preferably 3 wt‰ to 5 wt‰ or 6 wt‰ to 8 wt‰ of gallium, and optionally at least one grain refining element, the grain refining element comprising at least one of iridium, rhenium or ruthenium, preferably pre-alloyed with copper or palladium, wherein the amount of gold, copper, silver, palladium, cobalt, gallium and optionally at least one grain refining element is such that up to 1000 wt‰ is determined.

[0169] Furthermore, other variants of gold alloys according to compositions 848, 849 and 850 are, for example, those according to the following subgroups:

[0170] 740 wt‰ to 760 wt‰ of gold, 70 wt‰ to 95 wt‰ of copper, 100 wt‰ to 150 wt‰, preferably 115 wt‰ to 135 wt‰ of palladium, 20 wt‰ to 30 wt‰ of cobalt, 7 wt‰ to 13 wt‰ of silver, 3 wt‰ to 8 wt‰ of gallium, and optionally at least one grain refining element, the grain refining element comprising at least one of iridium, rhenium or ruthenium, preferably pre-alloyed with copper or palladium, and / or at least one of copper, silver, palladium, cobalt or gallium in an amount of up to 1 wt‰, so that the gold alloy is determined to be up to 1000 wt‰.

[0171] Furthermore, other variants of gold alloys according to compositions 848, 849 and 850 are, for example, those according to the following subgroups:

[0172] 740 wt‰ to 760 wt‰ of gold, 70 wt‰ to 95 wt‰ of copper, 100 wt‰ to 150 wt‰, preferably 115 wt‰ to 135 wt‰ of palladium, 20 wt‰ to 30 wt‰ of cobalt, 7 wt‰ to 13 wt‰ of silver, 3 wt‰ to 8 wt‰ of gallium, and optionally at least one grain refining element comprising iridium, rhenium or ruthenium, wherein the amount of gold, copper, silver, palladium, cobalt, gallium and optionally at least one grain refining element is such that up to 1000 wt‰ is determined.

[0173] Other gold alloy families investigated by the applicant include:

[0174] - gold, 730 to 770 wt.‰, preferably 740 to 760 wt.‰,

[0175] - copper, 150 to 170 wt.%, preferably 155 to 165 wt.%,

[0176] - palladium, 50% to 70% by weight, preferably 55% to 65% by weight,

[0177] - Cobalt, 7% to 13% by weight.

[0178] In particular, a gold alloy has been studied which, in addition to the amounts of elements described in the preceding paragraph, contains 10 wt.‰ to 30 wt.‰ of iron.

[0179] The applicant's research has focused in particular on a family of alloys in which, in addition to iron, iridium may also be present as a grain refiner. From this particular family, component 844 has been extracted, which is shown in the table below.

[0180]

[0181] Table 2

[0182] In composition 844, the 1 wt ‰ missing to complete 1000 wt ‰ can be at least one grain refining element, preferably at least one of iridium, rhenium or ruthenium, and / or can be one of copper, silver, palladium, cobalt, gallium or iron.

[0183] Other variants of gold alloys according to the composition 844 are, for example, the following compositions:

[0184] 740 wt‰ to 760 wt‰ of gold, 150 wt‰ to 170 wt‰ of copper, 40 wt‰ to 80 wt‰, preferably 50 wt‰ to 70 wt‰ of palladium, 5 wt‰ to 15 wt‰ of cobalt, 10 wt‰ to 30 wt‰ of iron, and optionally at least one grain refining element, which preferably includes at least one of iridium, rhenium or ruthenium; the amount of gold, copper, palladium, cobalt, iron and optionally at least one grain refining element (preferably including at least one of iridium, rhenium or ruthenium) is such that 1000 wt‰ is determined.

[0185] The above properties of the gold alloy are compared with the properties of two reference gold alloys as shown below:

[0186]

[0187] Table 3

[0188] like Figure 1 As shown, when tested in the heat-aged (hardened) condition, the alloys of the above family show a tensile yield strength comparable to that of the 5N alloy tested sequentially in the hardened condition. In addition, the yield strength achieved by the alloys of the present invention is higher than the yield strength shown by the 3N alloy and the commercial nickel-free gray alloy subjected to tensile stress in the heat-aged (hardened) condition.

[0189] In particular, Figure 1 The graphs of show stress-strain curves for monotonic tensile tests performed on different alloys, including those that are the subject of the present invention.

[0190] As an indicator of improved mechanical properties, it is considered to be the yield strength value (Rp0.2) measured in MPa and determined according to the ISO 6892 rules for tensile testing of metallic materials, as the point determined by the intersection of the deformation stress curve and a straight line whose slope is equal to the elastic modulus of the material and intersects the abscissa axis corresponding to the value 0.002.

[0191] From the results obtained it is observed that the composition subject of the present invention achieves yield strength values that are substantially at least comparable to those of the 5N alloy tested in the hardened state.

[0192] In particular, for Figure 3 For the composition shown in LRS 848, the yield strength values are higher relative to the yield strength of the corresponding test specimens made with 3N alloy.

[0193] Test specimens made of the alloy according to the invention, in particular of composition LRS 848, showed, after tensile and heat aging, higher yield strength values than corresponding test specimens made of the commercially known alloys Pd125 and Pd60.

[0194] From an application point of view, the mechanical properties obtained with the alloy subject of the invention are improved with respect to those shown by commercial grey gold alloys, so as to ensure an increase in the elastic recovery of the material after deformation.

[0195] The 3N and 5N alloys show good behavior in terms of elastic recovery, whereas the compositions Pd125 and Pd60 show poor behavior. The applicant notes that the Pd125 and Pd60 alloys are used because of their thermosetting properties.

[0196] The applicant has observed that composition 844 shows a limited effect in terms of elastic recovery when compared to the other compositions mentioned in Table 1. It is observed that the 5N alloy is a red gold alloy and that alloys close to the 5N standard, depending on the composition, generally exhibit the best behavior in terms of recovery after deformation. The 3N alloy is a yellow gold alloy.

[0197] The above embodiment shows the colors shown in Table 5.

[0198]

[0199] Table 4

[0200] Figure 3 The alloys in Table 4 are shown in color coordinate a * and b * Colors in the Cartesian diagram above.

[0201] The color of the alloy was measured using a light source with a color temperature of approximately 6500 K according to CIE D65. In particular, the applicant has performed color measurements using a Konica-Minolta CM3610d spectrophotometer module, using a light source conforming to the D65 standard with a color temperature of 6504 K, an observation angle of 2°, and a measurement area of 6 mm.

[0202] Table 5 includes color coordinates expressed according to a particular color scale and according to specific color measurements described below.

[0203] Within the general alloy family described above, we have focused on alloys that exhibit a substantially grey color, within the CIELAB 1976 color range, and according to the color measurement conditions of CIE D65, defined by the following color coordinates:

[0204] L * , between 80 and 84.5, preferably between 81 and 84;

[0205] a * , ranging from 1.2 to 3.7, preferably from 1.5 to 3.5;

[0206] b * , ranging from 6.2 to 10.5, preferably 6.6 to 10.

[0207] Applicants note that the color measurement standard used to obtain the above values is ISO 8654.

[0208] In particular, the subfamily of alloys to which compositions 848, 849 and 850 belong exhibits a substantially grey color within the CIELAB 1976 color range and is defined by the following color coordinates according to the color measurement conditions of CIE D65:

[0209] L * , between 80 and 84.5, preferably between 81 and 84;

[0210] a * , ranging from 1.2 to 2.4, preferably from 1.5 to 2.1;

[0211] b * , ranging from 6.7 to 8.5, preferably 7 to 8.3.

[0212] In particular, the subfamily of alloys to which composition 844 belongs exhibits a substantially grey color within the CIELAB 1976 color range and is defined by the following color coordinates according to the color measurement conditions of CIE D65:

[0213] L * , between 83 and 84.5, preferably between 83.2 and 84.3;

[0214] a * , between 2.7 and 3.7, preferably between 2.9 and 3.5;

[0215] b * , ranging from 8.9 to 9.9, preferably 8.7 to 9.7.

[0216] The color of gold alloys is uniquely measured within the CIELAB 1976 color range, which is based on the first parameter L * 、The second parameter a * and the third parameter b * Defines the color, where the first parameter L * Identifies the brightness and takes values between 0 (black) and 100 (white), while the second parameter a * and the third parameter b * Represents the chromaticity parameter. In particular, in the CIELAB 1976 color range, the non-color gray is composed of * =b * = 0 to mark the point; the second parameter a * The positive value of the second parameter indicates that the higher the value of the second parameter, the more the color tends to red; the second parameter a * A negative value indicates that the second parameter a *The higher the absolute value, the more the color tends to be green, even if it is a negative value; the third parameter b * The positive value of the third parameter indicates that the higher the value of the third parameter, the more yellow the color tends to be; the third parameter b * A negative value indicates that the third parameter b * The higher the absolute value of , the more the color tends to be blue, even if it is a negative value. In addition, the second parameter a can be * and the third parameter b * Converted into polar coordinate parameters defined as follows:

[0217]

[0218]

[0219] Define the Cab* parameter as "chroma"; Cab * The higher the parameter value, the higher the color saturation; Cab * The lower the value of the parameter, the lower the color saturation, which will tend to be gray. To the best of the applicant's knowledge, alloys with a gold content higher than 750‰ can be used as, for example, white gold alloys or gray gold alloys and do not require rhodium plating surface treatment, any Cab shown * <8 value. h ab* The parameter identifies the hue.

[0220] In particular, ISO 8654:2017 rules define seven color names for gold alloys for jewelry. Specifically, these alloys are defined according to the following table, where the colors are defined according to standard reference materials designated from 0N to 6N.

[0221] color name 0N yellow-green 1N light yellow 2N light yellow 3N yellow 4N pink 5N red 6N deep red

[0222] Table 5

[0223] Specifically for the measurement of the colour of gold alloys, rule ISO 8654 states that the measuring equipment must comply with publication CIEN 15.

[0224] In addition, the ISO 8654:2017 rule sets the L in the trichromatic coordinates of the standard color 0N-6N alloy to * 、a * 、b * The nominal values are tabulated, including tolerances. Below is an extract from the rule, where the alloy color limits defined by ISO 8654:2017 are defined as pink / red.

[0225]

[0226]

[0227]

[0228] Table 6

[0229] With respect to the above table, a plurality of regions can be obtained within the CIELAB 1976 color range, each representing a color range in which an alloy can be identified showing a color of 0N ... 6N. The gray alloys disclosed herein show significantly different color coordinates relative to alloys according to composition 0N-6N.

[0230] ISO 8654 rules make further recommendations on the chemical composition of each of the 0N-6N alloys. In particular, for the pink / red alloy, the composition is shown in the table:

[0231]

[0232]

[0233] Table 7

[0234] Gold alloys have been previously described as showing improved mechanical properties.

[0235] Figure 2 The figure shows a Cartesian diagram in which the abscissa is the distance corresponding to the displacement of the gold alloy test sample when subjected to a bending force, and the ordinate is the bending force. The displacement of the test sample is measured in μm and the bending force is measured in Newton.

[0236] Figure 2 The graphs are obtained according to a 3-point bending test method, in which each test specimen is subjected to a gradually increasing bending force corresponding to the center line until a linear displacement equal to 4000 μm is reached along the direction of force application. When a linear deformation equal to 4000 μm along the direction of force application is reached, the bending force of the test specimen is gradually reduced, and the residual deformation value when the test specimen is subjected to a bending force of 10 N is determined.

[0237] Typically, in order to evaluate the excellence of a gold alloy in terms of deformation recovery, some test specimens of the gold alloy are subjected to an initially increasing (especially gradually increasing and then gradually decreasing) deformation force F. In a 3-point bending test, the deformation force F at a predetermined deformation force (F) is measured during the application of increasing forces. test ) is evaluated at the midpoint height or position L1. Subsequently, the deformation force continues to increase until it reaches the midpoint (L t ) of the predetermined maximum displacement value. Once the predetermined maximum displacement value is reached, the deformation force F gradually decreases until it reaches the predetermined deformation force value (F test ), in this case, the new height or position L2 of the midpoint is detected.

[0238] For the applicant, the smaller the difference ΔL, the better the alloy's performance in terms of deformation recovery. ΔL is defined as:

[0239] ΔL=L 2,Ftest,递增 -L 1,Ftest,递减

[0240] According to the purpose of obtaining Figure 2 The smaller the above differences are, the more the gold alloy under consideration exhibits optimal characteristics from the point of view of recovery after deformation, since the lower residual displacement of the test specimen will also determine the lower deformation of the objects prepared by the alloy itself.

[0241] exist Figure 2 In the example of the graph of test =10N, Dt=4000μm.

[0242] Figure 2 The graph compares the gold alloys according to the 848, 849 and 850 embodiments with some other alloys: 3N, 5N and Pd125 according to the compositions given in Table 5.

[0243] The following values were obtained:

[0244] ΔL 848 =470μm

[0245] ΔL 849 =600μm

[0246] ΔL 850 =950μm

[0247] ΔL 844 =1250μm

[0248] ΔL 5N =400μm

[0249] ΔL 3N =600μm

[0250] ΔL Pd125 =1700μm

[0251] Furthermore, it was observed that for the same palladium content (compositions 848, 849, 850), the gold alloys showed better performance if the cobalt content was increased.

[0252] The following table shows hardness values for specific embodiments of gold alloys contemplated by applicants.

[0253]

[0254] Table 8

[0255] The method for hardening the gold alloys described herein is performed by exposing the alloys to a specific and predetermined hardening temperature for each specific formulation for a period of time substantially equal to 1 hour, followed by cooling the alloys to room temperature. The purpose of hardening is to promote the formation of precipitates and / or crystallographic transformations activated by the high temperature, which allows the alloys to achieve a greater hardness than after annealing.

[0256] The hardening temperatures described in this recipe are shown in the table below:

[0257]

[0258]

[0259] Table 9

[0260] Cooling of the test specimens of the alloys in Table 9 was carried out by immersion in water at room temperature.

[0261] It is particularly observed that compositions 848 and 849 show significantly higher hardness relative to the other compositions (particularly after hardening) due to their high cobalt content.The hardness according to Table 8 was measured using a Vickers hardness scale with an applied load of 1 kgf.

[0262] The invention also relates to a method for producing the gold alloy.

[0263] In one of its more general embodiments, the method for producing a gold alloy according to the invention consists, starting from the pure elements according to the above, in mixing at least:

[0264] - Gold, 700 wt‰ to 800 wt‰,

[0265] - copper, 25 wt.‰ to 170 wt.‰,

[0266] - Palladium, 50 wt.‰ to 165 wt.‰,

[0267] - Cobalt, 7% to 40% by weight.

[0268] Other weight ranges for mixing have been described previously and will not be repeated hereafter.

[0269] The method described herein comprises the steps of introducing the mixture into a melting crucible, and subsequently melting the mixture by heating until the mixture introduced into the melting crucible is completely melted.

[0270] The starting elements for preparing the alloys described herein are pure elements; preferably, gold is 99.99% pure, copper is 99.99% pure, palladium is 99.95% pure, silver is 99.99% pure, cobalt and iridium are 99.95% pure, and gallium is 99.99% pure.

[0271] The method may include the step of pre-alloying CuIr in the combination of the aforementioned elements.

[0272] Therefore, a particular embodiment comprises the steps of preparing a CuIr pre-alloy, and mixing:

[0273] - Gold, 700 wt‰ to 800 wt‰,

[0274] - copper, 9‰ to 79‰ by weight,

[0275] - Palladium, 85 wt.‰ to 165 wt.‰,

[0276] - cobalt, 7 wt‰ to 40 wt‰,

[0277] - Silver, 7‰ to 60‰ by weight,

[0278] The content of CuIr pre-alloy is 16 wt‰.

[0279] The melting method is preferably a continuous casting melting method, i.e. a process in which solidification and extraction of solidified gold are continuously performed starting from the free end of a gold bar or gold melt. In particular, in a continuous melting process, a graphite mold is used.

[0280] The use of a graphite die is useful because graphite is a solid lubricant and generally exhibits low friction between its surface and the surface of the molten metal, generally allowing easy extraction of elements contained therein without cracking and with a minimum of defects on its surface.

[0281] The melting process of the pure elements for producing the gold alloy according to the invention can in particular be a discontinuous gold melting process or a continuous gold melting process.

[0282] The discontinuous gold melting method is a method in which the mixture is melted and cast into a mold or ingot made of graphite. In this case, the above elements are melted and cast in a controlled atmosphere. More specifically, the melting operation is only carried out after preferably at least three cycles of conditioning the atmosphere in the melting chamber. This conditioning first involves reducing the vacuum level to below 1×10 -2 The mixture is heated to a pressure of about 1250° C. and in any case to a temperature above 1200° C. in order to homogenize the chemical composition of the metal bath. During the superheating step, the pressure in the melting chamber again reaches a value below 1×10 -2 A vacuum level of millibars is useful for removing part of the slag produced by pure element melting.

[0283] At this point, in a casting step, the molten material is poured into a mold or ingot made of graphite and the melting chamber is pressurized again with an inert gas, preferably argon, injected at a pressure above 700 mbar, in particular above 800 mbar.

[0284] Once solidified, the rod or casting is removed from the holder. As the alloy solidifies, the gold alloy rod or casting is removed from the graphite conduit and rapidly cooled by a water immersion step to reduce and possibly avoid phase changes. In other words, the rod or casting is subjected to a rapid cooling step, preferably, but not limited to, in water, to avoid phase changes in the solid state.

[0285] In light of the foregoing, the advantages of the gold alloys according to the present invention are readily apparent. In particular, due to their improved mechanical properties, they enable the manufacture of items, even for fine jewelry, that rarely change their dimensions even when subjected to relevant and / or repeated deforming forces, thereby providing a longer service life for both themselves and any items to which they are attached or incorporated. Deformation recovery properties are comparable to those of 3N and 5N alloys and significantly better than those of commercial gray alloys that do not contain Ni.

[0286] Furthermore, the gold alloy according to the present invention can also be processed in a particularly efficient manner to produce a uniform surface free of visible second phases or carbides. Thus, the gold alloy according to the present invention can be advantageously used in fine jewelry applications, in particular for the manufacture of fine jewelry items.

[0287] Non-limiting examples of jewelry items made at least in part from the gold alloys described herein are: bracelets, watch bracelets, clasps, watch cases, watch hands, watch internal mechanisms, bracelet bezels, earrings, ornaments, rings, gemstone mountings, ingots, especially collectible gold bars, collectible coins, necklaces, necklace clasps, earring or bracelet accessories.

[0288] The gold alloy according to the present invention can be applied to articles that come into direct contact with human skin and has a low allergy risk.

[0289] Finally, it is clear that additions, modifications or variations obvious to a person skilled in the art may be made to the subject matter of the invention without thereby departing from the scope provided by the accompanying claims.

Claims

1. A gold alloy for jewelry applications, in particular for the manufacture of jewelry items having at least partial shape and / or dimensional recovery properties after application of a deforming force, said gold alloy comprising: - Gold, 700 wt‰ to 800 wt‰, - copper, 25‰ to 170‰ by weight, - Palladium, 50 wt.‰ to 165 wt.‰, - Cobalt, 7% to 40% by weight.

2. The gold alloy of claim 1 , wherein the gold alloy comprises: - Gold, 700 wt‰ to 800 wt‰, - copper, 25‰ to 95‰ by weight, - Palladium, 85 wt.‰ to 165 wt.‰, - cobalt, 7 wt‰ to 40 wt‰, - Silver, 7‰ to 60‰ by weight.

3. The gold alloy according to claim 1 or 2, wherein the gold alloy further comprises gallium and / or at least one grain refining element, preferably at least one of iridium, rhenium or ruthenium, and wherein the weight content of gallium and / or at least one grain refining element, preferably at least one of iridium, rhenium or ruthenium is determined to be up to 1000 wt.‰; The gold alloy is characterized in that it contains no nickel, no arsenic, and no platinum; The alloy is grey alloy. The gray is within the CIELAB 1976 color range and, according to the color measurement conditions of CIE D65, is defined by the following color coordinates: L * , between 80 and 84.5, preferably between 81 and 84; a * , ranging from 1.2 to 3.7, preferably from 1.5 to 3.5; b * , ranging from 6.2 to 10.5, preferably 6.6 to 10.

4. The gold alloy according to claim 2 or 3, wherein the gold alloy comprises 1 wt% to 10 wt% gallium, preferably 2 wt% to 9 wt% gallium, more preferably 3 wt% to 8 wt% gallium.

5. The gold alloy according to claim 3, wherein the content of the at least one grain refining element is up to 1 wt%; Optionally, wherein the iridium is pre-alloyed with copper, and / or wherein the rhenium and / or ruthenium is pre-alloyed with palladium.

6. The gold alloy according to one or more of claims 2 to 5, wherein the gold alloy comprises: - Gold, 730 wt‰ to 770 wt‰, - copper, 40 wt.‰ to 90 wt.‰, - Palladium, 100 wt.‰ to 150 wt.‰, - cobalt, 8 wt‰ to 30 wt‰, - Silver, 8 ‰ to 55 ‰ by weight.

7. The gold alloy of claim 6, wherein the gold alloy comprises: - Gold, 740 wt‰ to 760 wt‰, - copper, 50 wt.‰ to 90 wt.‰, - Palladium, 100 ‰ to 150 ‰ by weight, - cobalt, 8 wt‰ to 30 wt‰, - Silver, 8 ‰ to 55 ‰ by weight.

8. The gold alloy of claim 7, wherein the gold alloy comprises: - Gold, 740 wt‰ to 760 wt‰, - copper, 50 wt.‰ to 90 wt.‰, - palladium, 110 to 140 wt. ‰, preferably 115 to 135 wt. ‰, - cobalt, 10 wt.‰ to 25 wt.‰, - Silver, 8 ‰ to 50 ‰ by weight.

9. Gold alloy according to one or more of the preceding claims 1 to 5, wherein: - a copper content of 45 wt ‰ to 65 wt ‰, preferably 50 wt ‰ to 60 wt ‰, and a silver content of 35 wt ‰ to 52 wt ‰; or The copper content is from 75 wt ‰ to 95 wt ‰, preferably from 80 wt ‰ to 90 wt ‰, and the silver content is from 7 wt ‰ to 13 wt ‰, preferably from 8 wt ‰ to 12 wt ‰.

10. The gold alloy according to one or more of the preceding claims, wherein the gold alloy is nickel-free.

11. The gold alloy of claim 1 , wherein the gold alloy comprises: - gold, 730 to 770 wt.‰, preferably 740 to 760 wt.‰, - copper, 150 to 170 wt.%, preferably 155 to 165 wt.%, - palladium, 50% to 70% by weight, preferably 55% to 65% by weight, - cobalt, 7 wt‰ to 13 wt‰, - iron, 10‰ to 30‰ by weight, Optionally, at least one grain refining element, preferably at least one of iridium, rhenium or ruthenium, The sum of gold, copper, palladium, cobalt, iron and optionally at least one grain refining element, preferably at least one of iridium, rhenium or ruthenium, amounts to 1000 wt. ‰.

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