Gold alloy with deformation recovery properties

Abstract

Gold alloy for jewelry or watchmaking applications, specifically destined to realize jewelry objects having at least partial shape and / or size recovery properties after the application of a deformation force, comprising: —Gold, between 700‰ in weight and 800‰ in weight, —Copper, between 25‰ in weight and 170‰ in weight, —Palladium, between 50‰ in weight and 165‰ in weight, —Cobalt, between 7‰ in weight and 40‰ in weight. The Gold alloy is a gray color alloy.

Description

TECHNICAL FIELD

[0001] The present disclosure refers to the field of metallurgy, in particular to the field of Gold alloys. In particular, the present disclosure concerns a Gold alloy for jewelry and watchmaking applications.

[0002] The present disclosure also concerns an object of jewelry and watchmaking at least partially realized by means of the Gold alloy described herein.BACKGROUND ART

[0003] Objects realized in metallic material exhibit deformability characteristics. The deformation of a body can be of an elastic or plastic type. The deformation occurs as a result of the application on the material of a traction, compression or bending force.

[0004] An elastic type deformation is characterized in that the body, upon cessation of a deformation force, is capable of returning to an original size and / or shape.

[0005] A plastic type deformation is characterized in that the body, upon cessation of a deformation force, is no longer capable of returning to its original size and / or shape; in other words, its size and / or shape results irreversibly changed with respect to its original one.

[0006] The plastic type deformation typically occurs with the application of forces greater with respect to the forces necessary to deform in an elastic way a body. The yield strength is that force which, when applied to the above-mentioned body, determines the passage from the elastic behaviour to the plastic behaviour.

[0007] The maximum deformation force limit that a body can endure is named breaking load.

[0008] In particular, the objects realized in Gold alloy can also be subject to elastic or plastic type deformations.

[0009] Determined objects realized in Gold alloy are subject to, during their operational life, to various applications of static or cyclic deformation forces: where the object realized in Gold alloy is connected with other similar or different objects, or is integrated in a more complex object, any plastic deformations can form, plays, frictions, misalignments.

[0010] Consequently, the objects realized in Gold alloy can result, over time, in a modified size and / or shape with respect to the original one.

[0011] The alteration of the shape of the object realized in Gold alloy is inconvenient, because the functionality of the object can be compromised by the difference in size or shape by effect of the application of a force greater with respect to the yield strength.

[0012] Normally, it is observed that yellow (according to 3N ISO 8654) and red (according to 5N ISO 8654) Gold alloys are typically known to exhibit good mechanical properties, among which are high yield strength, hardness and resilience, and are therefore commonly used successfully where the use is directed towards jewelry or watchmaking objects that, in the course of their operational life, are subject to particularly significant stresses.

[0013] Gray Gold alloys with recovery properties of undergone deformation are also known to exhibit significant mechanical properties among which are high yield strength, hardness and resilience. Normally, such alloys exploit the properties of Nickel to obtain higher mechanical deformation recovery performances with respect to Gold alloys free from Nickel.

[0014] Document U.S. Pat. No. 5,173,132 shows a Gold alloy 14 k wherein is present Cobalt in the range 1‰ and 7‰ and Nickel between 10‰ and 50‰; Cobalt and Nickel are used for grain refining in order to further improve the workability of the alloy.

[0015] However, the use of Nickel is strongly discouraged where the alloys are to be used for objects destined to come into direct contact with the human skin, and in particular for Gold alloys destined to jewelry applications destined to realize objects that come into direct contact with the human skin. In fact, Nickel is known to cause allergic reactions.

[0016] The purpose of the present disclosure is to describe a Gold alloy that allows to overcome the above-described drawbacks. The purpose of the present disclosure is also to describe a jewelry or watch-making object comprising the Gold alloy which allows to overcome the above-described drawbacks.

[0017] The purpose of the present disclosure is finally to describe a production method for a Gold alloy that allows to overcome the above-described drawbacks.SUMMARY

[0018] The Applicant has conceived a plurality of Gold alloys with improved mechanical characteristics, that is herein described in some of its main aspects. These aspects can be combined with each other or with portions of the detailed description or claims.

[0019] According to an aspect of the disclosure, a Gold alloy for jewelry applications is described herein, comprising:

[0020] Gold, between 700‰ in weight and 800‰ in weight,

[0021] Copper, between 25‰ in weight and 170‰ in weight,

[0022] Palladium, between 50‰ in weight and 165‰ in weight,

[0023] Cobalt, between 7‰ in weight and 40‰ in weight,

[0024] The Applicant notes that the Gold alloy is specifically destined to realize jewelry objects with improved mechanical properties, in particular characterized by the increase in yield strength in order to make it comparable to that of 3N and 5N alloys.

[0025] The Applicant notes that the yield strength is significantly higher with respect to the one of commercial Nickel-free gray Gold alloys.

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

[0027] Gold, between 700‰ in weight and 800‰ in weight,

[0028] Copper, between 25‰ in weight and 95‰ in weight,

[0029] Palladium, between 85‰ in weight and 165‰ in weight,

[0030] Cobalt, between 7‰ in weight and 40‰ in weight,

[0031] Silver, between 7‰ in weight and 60‰ in weight.

[0032] According to a further non-limiting aspect, the alloy comprises: Gallium and / or at least a grain refining element, preferably at least one between Iridium, Rhenium and Ruthenium.

[0033] According to a further non-limiting aspect, said at least a grain refining element is present in pre-alloy, said pre-alloy having the following basis:

[0034] Copper, where the grain refining element is Iridium, or

[0035] Palladium, where the grain refining element is Rhenium or Ruthenium.

[0036] According to a further non-limiting aspect, the amount in weight of Gallium and / or of said at least a grain refining element, preferably at least one among Iridium, Rhenium or Ruthenium, determines the reaching of 1000‰ in weight.

[0037] According to a further non-limiting aspect, said Gold alloy is characterized in that it is free from Nickel.

[0038] According to a further non-limiting aspect, said Gold alloy is characterized in that it is free from Arsenic.

[0039] According to a further non-limiting aspect, said Gold alloy is characterized in that it is free from Platinum.

[0040] According to a further non-limiting aspect, said Gold alloy comprises Gallium between 1‰ in weight and 10‰ in weight, preferably between 2‰ in weight and 9‰ in weight, more preferably between 3‰ in weight and 8‰ in weight.

[0041] According to a further non-limiting aspect, Gallium is present in the amount substantially comprised between 4‰ in weight and 7‰ in weight.

[0042] According to a further non-limiting aspect, Gallium is present in the amount comprised between 3.5‰ in weight and 4.5‰ in weight.

[0043] According to a further non-limiting aspect, said alloy comprises at least a grain refining element, preferably at least one among Iridium, Rhenium or Ruthenium.

[0044] According to a further non-limiting aspect, said Iridium is pre-alloyed with Copper.

[0045] According to a further non-limiting aspect, said Rhenium and / or Ruthenium is pre-alloyed with Palladium.

[0046] According to a further non-limiting aspect, the at least a grain refining element, in particular the at least one among Iridium, Rhenium or Ruthenium, is present in the amount until 1‰ in weight.

[0047] According to a further non-limiting aspect, the Gold alloy comprises:

[0048] Gold, between 730‰ in weight and 770‰ in weight,

[0049] Copper, between 40‰ in weight and 90‰ in weight,

[0050] Palladium, between 100‰ in weight and 150‰ in weight,

[0051] Cobalt, between 8‰ in weight and 30‰ in weight,

[0052] Silver, between 8‰ in weight and 55‰ in weight.

[0053] According to a further non-limiting aspect, the Gold alloy comprises:

[0054] Gold, between 740‰ in weight and 760‰ in weight,

[0055] Copper, between 50‰ in weight and 90‰ in weight,

[0056] Palladium, between 100‰ in weight and 150‰ in weight,

[0057] Cobalt, between 8‰ in weight and 30‰ in weight,

[0058] Silver, between 8‰ in weight and 55‰ in weight.

[0059] According to a further non-limiting aspect, the Gold alloy comprises:

[0060] Gold, between 740‰ in weight and 760‰ in weight,

[0061] Copper, between 50‰ in weight and 90‰ in weight,

[0062] Palladium, between 110‰ in weight and 140‰ in weight, preferably between 115‰ in weight and 135‰ in weight,

[0063] Cobalt, between 10‰ in weight and 25‰ in weight,

[0064] Silver, between 8‰ in weight and 50‰ in weight.

[0065] According to a further non-limiting aspect, the Gold alloy comprises:

[0066] Palladium, between 120‰ in weight and 130‰ in weight.

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

[0068] Copper, between 45‰ in weight and 65‰ in weight, preferably between 50‰ in weight and 60‰ in weight, and Silver, between 35‰ in weight and 52‰ in weight; or

[0069] Copper, between 75‰ in weight and 95‰ in weight, preferably between 80‰ in weight and 90‰ in weight, and Silver, between 7‰ in weight and 13‰ in weight, preferably between 8‰ in weight and 12‰ in weight.

[0070] According to a further non-limiting aspect, the Gold alloy has a color defined, on the CIELAB 1976 color range, and according to the color measurement conditions according to CIE D65, by the following color coordinates:

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

[0072] a*, comprised between 1.2 and 3.7, preferably between 1.5 and 3.5;

[0073] b*, comprised between 6.2 and 10.5, preferably between 6.6 and 10.

[0074] According to a further non-limiting aspect, said color is gray and / or said Gold alloy is a gray Gold alloy.

[0075] According to a further non-limiting aspect, the Gold alloy has a color defined, on the CIELAB 1976 color range, and according to the color measurement conditions according to CIE D65, by the following color coordinates:

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

[0077] a*, comprised between 1.2 and 2.4, preferably between 1.5 and 2.1;

[0078] b*, comprised between 6.7 and 8.5, preferably between 7 and 8.3.

[0079] For the purposes of the present disclosure, Gold alloys whose color falls within the aforementioned coordinates, and in particular within a square defined on the coordinates a* and b* when placed on orthogonal axes in a color chart, is considered gray.

[0080] According to a further non-limiting aspect, said Gold alloy is a gray Gold alloy.

[0081] According to a further non-limiting aspect, the Gold alloy has a color defined, on the CIELAB 1976 color range, and according to the color measurement conditions according CIE D65, by the following color coordinates:

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

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

[0084] b*, comprised between 8.9 and 9.9, preferably between 8.7 and 9.7.

[0085] According to a further non-limiting aspect, the Gold alloy comprises:

[0086] Gold, between 730‰ in weight and 770‰ in weight, preferably between 740‰ in weight and 760‰ in weight,

[0087] Copper, between 150‰ in weight and 170‰ in weight, preferably between 155‰ in weight and 165‰ in weight,

[0088] Palladium, between 50‰ in weight and 70‰ in weight, preferably between 55‰ in weight and 65‰ in weight,

[0089] Cobalt, between 7‰ in weight and 13‰ in weight,

[0090] Iron, between 10‰ in weight and 30‰ in weight,

[0091] optionally at least a grain refining element, preferably at least one among Iridium, Rhenium or Ruthenium, in the amount until 1‰ in weight.

[0092] According to a further non-limiting aspect, the sum of Gold, Copper, Palladium, Cobalt, Iron, and optionally the at least a grain refining element, reaches the 1000‰ in weight.

[0093] According to a further non-limiting aspect, the Gold alloy consists of:

[0094] Gold, between 700‰ in weight and 800‰ in weight,

[0095] Copper, between 25‰ in weight and 75‰ in weight,

[0096] Palladium, between 85‰ in weight and 165‰ in weight,

[0097] Cobalt, between 7‰ in weight and 40‰ in weight,

[0098] Silver, between 7‰ in weight and 60‰ in weight,

[0099] Gallium, between 1‰ in weight and 10‰ in weight, preferably between 2‰ in weight and 9‰ in weight, more preferably between 3‰ in weight and 8‰ in weight,

[0100] at least a grain refining element, preferably at least one among Iridium, Rhenium or Ruthenium, in the amount until 1‰ in weight.

[0101] According to a further aspect, a jewelry object comprising a Gold alloy according to one or more of the aspects described herein is also described.

[0102] According to a further non-limiting aspect, jewelry object has a yield strength comparable to the one of a corresponding jewelry object realized in 3N or 5N alloy.

[0103] In particular, said yield strength is greater with respect to the one of the yield strength of a corresponding jewelry object realized in gray Gold alloy not containing Nickel and commercially known.

[0104] According to a further non-limiting aspect, said Gold alloy is a gray Gold alloy.

[0105] According to a further non-limiting aspect, the jewelry object comprises a jewel or a watch or a watch bracelet or a movement or part of a mechanical watch movement.

[0106] According to a further non-limiting aspect, the watch or mechanical watch movement are configured for being respectively worn or installed in wristwatches.

[0107] According to the present disclosure is furthermore described a method of producing a Gold alloy, comprising a mixing step at least of Gold, Copper, Palladium and Cobalt in the amounts described in one or more of the above-mentioned aspects.

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

[0109] Gold, between 700‰ in weight and 800‰ in weight,

[0110] Copper, between 9‰ in weight and 79‰ in weight,

[0111] Palladium, between 85‰ in weight and 165‰ in weight,

[0112] Cobalt, between 7‰ in weight and 40‰ in weight,

[0113] Silver, between 7‰ in weight and 60‰ in weight,

[0114] with a pre-alloy of CuIr at 16‰ in weight.FIGURES

[0115] The alloy object of the present disclosure will now be described with reference to some preferred embodiments, and with reference to the attached figures. A short description of the figures is given below.

[0116] FIG. 1 shows a Cartesian diagram showing a monotonic traction test wherein on the abscissa is indicated the relative deformation (percentage) undergone by the test piece and on the ordinate is indicated the stress to which it is subjected.

[0117] FIG. 2 shows a Cartesian diagram wherein on the abscissa is present a distance corresponding to a displacement in correspondence of a midpoint of a Gold alloy test specimen when subjected to a bending force in three points and wherein on the ordinate is present a bending force.

[0118] FIG. 3 shows a Cartesian diagram representing a color chart according to the coordinates a* and b* of the CIELAB 1976 color range, wherein are present certain compositions specifically studied by the Applicant. The colors detected on the graph of FIG. 2 are obtained according to the measurements according to CIE D65.DETAILED DESCRIPTION

[0119] The present disclosure shows a Gold alloy with improved deformation recovery properties. The Gold alloy described herein is advantageously applicable preferably to objects which during their operational life are subjected to various applications of deformation force, which must remain below the yield strength. These objects can be objects of high jewelry or watchmaking, and be connected to other identical or similar objects or be integrated into a more complex object. In a non-limiting embodiment, these objects can be parts of bracelets, bracelets, or parts of a watch movement.

[0120] As it will be better clarified by the following description, the Applicant has focused on embodiments of the Gold alloy which present an observably different color with respect to the one encoded by the ON-6N standards according to ISO 8654. In particular, the family of alloys conceived by the Applicant is a family of gray Gold alloys.

[0121] The Applicant has conceived a family of gray Gold alloys with amount of Gold substantially equal to 18 k, with the following characteristics:

[0122] Gold, between 700‰ in weight and 800‰ in weight,

[0123] Copper, between 25‰ in weight and 170‰ in weight,

[0124] Palladium, between 50‰ in weight and 165‰ in weight,

[0125] Cobalt, between 7‰ in weight and 40‰ in weight.

[0126] This family of alloys, optionally, comprises Silver, between 7‰ in weight and 60‰ in weight.

[0127] Depending on whether Silver is present or not, in a non-limiting embodiment, the sum of the amount in weight of Gold, Copper, Palladium, Cobalt, or of Gold, Copper, Palladium, Cobalt and Silver, is equal to 1000‰ in weight. For this reason, it is clear that the present disclosure shows a specific family of Gold alloys constituted by Gold, between 700‰ in weight and 800‰ in weight, Copper, between 25‰ in weight and 170‰ in weight, Palladium, between 50‰ in weight and 165‰ in weight, Cobalt, between 7‰ in weight and 40‰ in weight or constituted by Gold, between 700‰ in weight and 800‰ in weight, Copper, between 25‰ in weight and 170‰ in weight, Palladium, between 50‰ in weight and 165‰ in weight, Cobalt, between 7‰ in weight and 40‰ in weight and Silver, between 7‰ in weight and 60‰ in weight.

[0128] The Applicant has highlighted, from this general family of Gold alloys, a more restricted family comprising the following elements in the following compositions:

[0129] Gold, between 700‰ in weight and 800‰ in weight,

[0130] Copper, between 25‰ in weight and 95‰ in weight,

[0131] Palladium, between 85‰ in weight and 165‰ in weight,

[0132] Cobalt, between 7‰ in weight and 40‰ in weight,

[0133] Silver, between 7‰ in weight and 60‰ in weight.

[0134] Preferably, but non-limiting thereto, the Gold alloys according to the above-described composition can be exclusively realized with the above-mentioned materials, i.e. the amount of Gold, Copper, Palladium, Cobalt, Silver reaches the 1000‰ in weight.

[0135] The alloys of the family herein described are free from Nickel, so as to guarantee a compatibility with all those applications wherein the object realized with the Gold alloy must come into direct contact with human skin.

[0136] The Gold alloys of the family herein described are furthermore free from Arsenic.

[0137] Some embodiments of the alloys of the present disclosure have improved performances in terms of mechanical performances, comprise furthermore Gallium, between 1‰ and 10‰ in weight, preferably between 2‰ in weight and 9‰ in weight, more preferably between 3‰ in weight and 8‰ in weight.

[0138] Some embodiments, in particular, have Gallium comprised in the amount substantially comprised between 4‰ in weight and 7‰ in weight. The Applicant has in particular studied two main families of Gold alloys, which have Gallium in the amount equal to 4‰ in weight, or which have Gallium in the amount equal to 7‰ in weight.

[0139] Cobalt, in particular, and Gallium, perform their function as thermosetting agents through a process of solubilization and precipitation.

[0140] Among the alloys studied by the Applicant, some preferred embodiments include Iridium as a grain refiner. Other embodiments of Gold alloy disclosed herein comprise grain refiners selected between Rhenium and / or Ruthenium. More grain refiners can be simultaneously present.

[0141] In an embodiment, the amount in weight of Gallium and / or of the at least a grain refiner, preferably at least one among Iridium, Rhenium or Ruthenium, determines the reaching of 1000‰ in weight. The grain refiner can be present in the amount until 1‰ in weight.

[0142] In fact, the Applicant has conceived particular embodiments of Gold alloy wherein the amount of Gold, Copper, Silver, Cobalt, Palladium and Gallium reaches the 1000‰ in weight. These alloys are alloys exclusively composed of six elements.

[0143] Furthermore, the Applicant has conceived particular embodiments of Gold alloy wherein the amount of Gold, Copper, Silver, Cobalt, Palladium, Gallium and at least a grain refining element (Iridium and / or Rhenium and / or Ruthenium) reaches the 1000‰ in weight.

[0144] However, it is pointed out that the use of the at least a grain refining element, in particular the at least one among Iridium, Rhenium or Ruthenium, can be subject to the inclusion in the pre-alloy.

[0145] In particular, the alloys that are subject of the present disclosure are alloys free from Platinum.

[0146] From the previous general family, the Applicant has studied the behaviour of a family of Gold alloys comprising:

[0147] Gold, between 730‰ in weight and 770‰ in weight,

[0148] Copper, between 40‰ in weight and 90‰ in weight,

[0149] Palladium, between 100‰ in weight and 150‰ in weight,

[0150] Cobalt, between 8‰ in weight and 30‰ in weight,

[0151] Silver, between 8‰ in weight and 55‰ in weight,later closing its focus to a family of Gold alloys comprising Gold, between 740‰ in weight and 760‰ in weight, Copper, between 50‰ in weight and 90‰ in weight, and Palladium, Cobalt and Silver in the above-described ranges, optionally with the presence of Gallium and a grain refining element as above described.

[0152] Further studies were realized on a family of Gold alloys comprising:

[0153] Gold, between 730‰ in weight and 770‰ in weight,

[0154] Copper, between 40‰ in weight and 90‰ in weight,

[0155] Palladium, between 110‰ in weight and 140‰ in weight, preferably between 115‰ in weight and 135‰ in weight,

[0156] Cobalt, between 10‰ in weight and 25‰ in weight,

[0157] Silver, between 8‰ in weight and 50‰ in weight.

[0158] The Applicant has carried out studies on two subfamilies of Gold alloys that are centered on a content of Copper equal to 55‰ in weight and of Silver comprised between 40‰ and 50‰ in weight, or on a higher content of Copper, substantially equal to 85‰ in weight and having a more reduced content of Silver, around 10‰ in weight.

[0159] In particular, two sub-families of alloys have been identified, which have: Copper, between 45‰ in weight and 65‰ in weight, preferably between 50‰ in weight and 60‰ in weight, and Silver, between 35‰ in weight and 52‰ in weight; or Copper, between 75‰ in weight and 95‰ in weight, preferably between 80‰ in weight and 90‰ in weight, and Silver, between 7‰ in weight and 13‰ in weight, preferably between 8‰ in weight and 12‰ in weight. These subfamilies were studied with combinations of Gold, between 700‰ in weight and 800‰ in weight, Palladium, between 85‰ in weight and 165‰ in weight, Cobalt, between 7‰ in weight and 40‰ in weight, and with further combinations of Gallium and / or Iridium as above described. Some specific embodiments of Gold alloy have been obtained from these two subfamilies, which have been encoded with the references 848, 849, 850.

[0160] The following table shows some specific compositions studied in detail by the Applicant. The amounts of the Gold alloy elements are shown in the table in ‰ in weight.TABLE 1AuCuAgPdCoGa848751544012525484975184101252548507515447125157

[0161] In the compositions according to Table 1, the addition of 1‰ of a grain refining element comprising at least one among Iridium, Rhenium or Ruthenium, preferably in pre-alloy with Copper or Palladium, and / or of at least one among Copper, Silver, Palladium, Cobalt or Gallium, determines the reaching of 1000‰ in weight of the alloy.

[0162] Further variants of the Gold alloys according to compositions 848, 849 and 850 are for example those according to the following sub-family:

[0163] Gold, between 740‰ in weight and 760‰ in weight, Copper, between 50‰ in weight and 60‰ in weight, Palladium, between 100‰ in weight and 150‰ in weight and preferably between 115‰ in weight and 135‰ in weight, Cobalt, between 20‰ and 30‰ in weight, Silver, between 35‰ and 55‰ in weight, Gallium between 3‰ in weight and 8‰ in weight and preferably between 3‰ in weight and 5‰ in weight or between 6‰ in weight and 8‰ in weight, and optionally at least a grain refining element comprising at least one among Iridium, Rhenium or Ruthenium, preferably in pre-alloy with Copper or Palladium, and / or at least one among Copper, Silver, Palladium, Cobalt or Gallium in the amount until 1‰ in weight is such as to determine the reaching of 1000‰ in weight for the Gold alloy.

[0164] Furthermore, further variants of the Gold alloys according to compositions 848, 849 and 850 are for example those according to the following sub-family:

[0165] Gold, between 740‰ in weight and 760‰ in weight, Copper, between 50‰ in weight and 60‰ in weight, Palladium, between 100‰ in weight and 150‰ in weight and preferably between 115‰ in weight and 135‰ in weight, Cobalt, between 20‰ and 30‰ in weight, Silver, between 35‰ and 55‰ in weight, Gallium between 3‰ in weight and 8‰ in weight and preferably between 3‰ in weight and 5‰ in weight or between 6‰ in weight and 8‰ in weight, and optionally at least a grain refining element comprising at least one among Iridium, Rhenium or Ruthenium, preferably in pre-alloy with Copper or Palladium, wherein the amount of Gold, Copper, Silver, Palladium, Cobalt, Gallium and optionally the at least a grain refining element, is such as to determine the reaching of 1000‰ in weight.

[0166] Furthermore, further variants of the Gold alloys according to compositions 848, 849 and 850 are for example those according to the following sub-family:

[0167] Gold, between 740‰ in weight and 760‰ in weight, Copper, between 70‰ in weight and 95‰ in weight, Palladium, between 100‰ in weight and 150‰ in weight and preferably between 115‰ in weight and 135‰ in weight, Cobalt, between 20‰ and 30‰ in weight, Silver, between 7‰ and 13‰ in weight, Gallium between 3‰ in weight and 8‰ in weight, and optionally at least a grain refining element comprising at least one among Iridium, Rhenium or Ruthenium, preferably in pre-alloy with Copper or Palladium, and / or at least one among Copper, Silver, Palladium, Cobalt or Gallium in the amount until a 1‰ in weight is such as to determine the reaching of 1000‰ in weight for the Gold alloy.

[0168] Furthermore, further variants of the Gold alloys according to compositions 848, 849 and 850 are for example those according to the following sub-family:

[0169] Gold, between 740‰ in weight and 760‰ in weight, Copper, between 70‰ in weight and 95‰ in weight, Palladium, between 100‰ in weight and 150‰ in weight and preferably between 115‰ in weight and 135‰ in weight, Cobalt, between 20‰ and 30‰ in weight, Silver, between 7‰ and 13‰ in weight, Gallium between 3‰ in weight and 8‰ in weight, and optionally at least a grain refining element comprising Iridium, Rhenium or Ruthenium, wherein the amount of Gold, Copper, Silver, Palladium, Cobalt, Gallium and optionally the at least a grain refining element, is such as to determine the reaching of 1000‰ in weight.

[0170] A further family of Gold alloys studied by the Applicant is the one comprising:

[0171] Gold, between 730‰ in weight and 770‰ in weight, preferably between 740‰ in weight and 760‰ in weight,

[0172] Copper, between 150‰ in weight and 170‰ in weight, preferably between 155‰ in weight and 165‰ in weight,

[0173] Palladium, between 50‰ in weight and 70‰ in weight, preferably between 55‰ in weight and 65‰ in weight,

[0174] Cobalt, between 7‰ in weight and 13‰ in weight.

[0175] In particular, it has been studied a Gold alloy which comprises, in addition to the amounts of the elements described in the previous paragraph, Iron, between 10‰ in weight and 30‰ in weight.

[0176] The studies of the Applicant are in particular focused on a family of alloys wherein, in addition to Iron, can furthermore be present Iridium as a grain refiner. From this particular family, it has been extracted the composition 844, which is indicated in the following table.TABLE 2AuCuAgPdCoGaFe844751159601020

[0177] In the composition 844, the 1‰ in weight missing to complete the 1000‰ in weight can be at least a grain refining element, preferably at least one among Iridium, Rhenium or Ruthenium, and / or can be one among Copper, Silver, Palladium, Cobalt, Gallium or Iron.

[0178] Further variants of Gold alloys according to composition 844 are for example the following:

[0179] Gold, between 740‰ in weight and 760‰ in weight, Copper, between 150‰ in weight and 170‰ in weight, Palladium, between 40‰ in weight and 80‰ in weight and preferably between 50‰ in weight and 70‰ in weight, Cobalt, between 5‰ in weight and 15‰ in weight, Iron, between 10‰ in weight and 30‰ in weight, and optionally at least a grain refining element, preferably comprising at least one among Iridium, Rhenium or Ruthenium; the amount of Gold, Copper, Palladium, Cobalt, Iron, and optionally the at least a grain refining element, preferably comprising at least one among Iridium, Rhenium or Ruthenium, is such as to determine the reaching of 1000‰ in weight.

[0180] The above-described performances of the Gold alloys were compared with those of two reference Gold alloys, which are indicated herein below:TABLE 3AuCuAgPdInGaFePd125751110125104Pd6075116960205N750205453N750125125

[0181] As shown in FIG. 1, the alloys of the above-described family, when tested in the thermally aged (hardened) state, show a traction yield strength comparable to the one shown by a 5N alloy tested in turn in the hardened state. Furthermore, the yield strength achieved by the alloy subject of the invention results to be higher with respect to the one shown by a 3N alloy and commercial Nickel free gray alloys, which in turn are subjected to traction stress in the thermally aged (hardened) state.

[0182] In particular, in the graph of FIG. 1 are shown the stress-deformation curves of monotonic traction tests conducted on different alloys, among which those subjects of the present disclosure.

[0183] As an index of improved mechanical properties, it has been considered the yield strength value (Rp 0.2) measured in MPa and identified according to ISO 6892 regulation for traction tests on metallic materials, as the point determined by the intersection of the deformation stress curve and a line having a slope equal to the elastic module of the material and intercepting the abscissa axis in correspondence of the value 0.002.

[0184] From the results obtained, it was observed that the yield strength value obtained for the compositions subject of the disclosure is substantially at least comparable with the yield strength value of a 5N alloy tested in the hardened state.

[0185] In particular, for the composition LRS 848 shown in FIG. 3, the value of yield strength is higher with respect to the yield strength of a corresponding test sample realized in 3N alloy.

[0186] Test samples realized with the alloys according to the present disclosure, and in particular the test sample realized with the composition LRS 848, show a value of yield strength higher than the one of corresponding test samples realized in the alloys Pd125 and Pd60, commercially known, when subject to traction and after thermal ageing.

[0187] From the application point of view, the mechanical properties obtained for the alloy subject of the invention, improved with respect to those shown by commercial gray Gold alloys, allowed to guarantee to the material an increase in the elastic recovery after the undergone deformation.

[0188] The 3N and 5N alloys show a good behaviour in terms of elastic return, while the compositions Pd125 and Pd60 show a poor behaviour. The Applicant notes that the Pd125 and Pd60 alloys are used for their thermosetting properties.

[0189] The Applicant has observed that the composition 844 shows limited effectiveness in terms of elastic return, when compared with the other compositions previously mentioned in Table 1. It is observed that the 5N alloy is a red Gold alloy, and by composition, the alloys close to the 5N standard typically show an optimal behaviour in terms of return after deformation. The 3N alloy is a yellow Gold alloy.

[0190] The above-described embodiments show the colors indicated in table 5.TABLE 4L*ab84882.01.77.684982.21.77.285081.61.98.0844843.29.4Pd60 83.63.810Pd12581.52.27.1

[0191] FIG. 3 shows the colors of the alloys of table 4 in a Cartesian graph on the color coordinates a* and b*.

[0192] The color of the alloy has been measured by means of a light source according to CIE D65, according to which it is used a source with a color temperature of about 6500K. In particular, the Applicant has carried out color measurements by means of a spectrophotometer mod. Konica-Minolta CM3610d, using a light source according to D65 standard with color temperature equal to 6504K, and with observation angle of 2° and on a measurement area of 6 mm.

[0193] The table 5 includes color coordinates which are expressed according to a particular color scale and according to a particular color measurement hereinafter described.

[0194] Within the above-described general family of alloys, we have focused on the alloys that show a substantially gray color, defined, on the CIELAB 1976 color range, and according to the color measurement conditions according to CIE D65, by the following color coordinates:

[0195] L*, comprised between 80 and 84.5, preferably between 81 and 84;

[0196] a*, comprised between 1.2 and 3.7, preferably between 1.5 and 3.5;

[0197] b*, comprised between 6.2 and 10.5, preferably between 6.6 and 10.

[0198] The Applicant notes that the color measurement standard used to obtain the above-described values is ISO 8654.

[0199] In particular, the alloys of the subfamily to which the compositions 848, 849 and 850 belong show a substantially gray color, defined, on the CIELAB 1976 color range, and according to the color measurement conditions according to CIE D65, by the following color coordinates:

[0200] L*, comprised between 80 and 84.5, preferably between 81 and 84;

[0201] a*, comprised between 1.2 and 2.4, preferably between 1.5 and 2.1;

[0202] b*, comprised between 6.7 and 8.5, preferably between 7 and 8.3.

[0203] In particular, the alloys of the subfamily to which the composition 844 belongs shows a substantially gray color, defined, on the CIELAB 1976 color range, and according to the color measurement conditions according to CIE D65 by the following color coordinates:

[0204] L*, comprised between 83 and 84.5, preferably between 83.2 and 84.3;

[0205] a*, comprised between 2.7 and 3.7, preferably between 2.9 and 3.5;

[0206] b*, comprised between 8.9 and 9.9, preferably between 8.7 and 9.7.

[0207] The colors of the Gold alloys are univocally measured in the CIELAB 1976 color range, which defines a color on the basis of a first parameter L*, a second parameter a* and a third parameter b*, wherein the first parameter L* identifies the brightness and assumes values between 0 (black) and 100 (white) while the second parameter a* and the third parameter b* represent chromaticity parameters. In particular, in the CIELAB 1976 color range, the achromatic gray scale is identified by the points wherein a*=b*=0; positive values for the second parameter a* indicate a color tending more towards red the more the value of the second parameter is high; negative values for the second parameter a* indicate a color tending more towards green the more the value of the second parameter a* is high in absolute value, even if negative; positive values for the third parameter b* indicate a color tending more towards yellow the more the value of the third parameter is high; negative values for the third parameter b* indicate a color tending more towards blue the more the value of the third parameter b* is high in absolute value, even if negative. Furthermore, it is possible to transform the second parameter a* and the third parameter b* into polar parameters defined as follows:Cab*=(a*2+b*2)hab*=tan-1(b*a*)

[0208] The Cab* parameter is defined as “chroma”; the higher is the value of the Cab* parameter, the higher will be the saturation of the color; the lower is the value of the Cab* parameter, the lower will be the color saturation, which will tend towards the gray scale. To the knowledge of the Applicant, the alloys with a content of Gold higher than 750‰, that can be used as such as white or gray Gold alloys and do not require rhodium-plating surface treatments, arbitrarily show values of Cab*<8. The hab+ parameter identifies the color tone.

[0209] In particular, ISO 8654:2017 regulation defines seven color designations for Gold alloys for jewelry. In particular, these alloys are defined according to the following table, in which the color is defined on a standard reference named between 0N and 6N.TABLE 5ColorDesignation0NYellow-green1NPale yellow2NLight yellow3NYellow4NPink5NRed6NDark red

[0210] For the measurement of the color of a Gold alloy, in particular, regulation ISO 8654 clarifies that the measuring device must comply with the publication CIE N° 15.

[0211] The regulation ISO 8654:2017 furthermore, tabulates the L*, a*, b* nominal values in trichromatic coordinates for the ON-6N alloys of standard color, including tolerances. The following is an excerpt from the regulation wherein the chromatic limits of the alloys defined by ISO 8654:2017 standard are defined as pink / red.TABLE 6Trichromatic coordinates (observer 2°)TolerancesNominal valuesL* [Max / ColorL*a*b*Min]a*b*0N93.9−3.0221.3995.4−1.6523.14−1.4019.2192.2−4.1419.58−4.8823.551N92.40.3222.2594.01.4723.671.2920.4190.7−0.7020.79−0.7924.112N91.11.1925.6292.82.3626.892.1323.9189.40.1324.330.1427.343N89.93.6723.6291.64.9625.064.3821.6788.22.4922.142.8225.594N88.96.1321.2390.67.4822.456.6319.4487.14.8919.985.4823.065N87.78.3218.5889.49.7419.558.6216.9785.96.9617.557.8920.196N86.310.1315.5788.111.6516.4410.1414.0684.48.7014.659.9917.12

[0212] In relation to the preceding table it is thus possible to obtain, within the CIELAB 1976 color range, a plurality of areas each representing the color ranges within which it is possible to assert that an alloy shows a 0N . . . 6N color. The gray alloys herein disclosed show significantly different color coordinates with respect to those of the alloys according to the compositions 0N-6N.

[0213] ISO 8654 regulation proposes furthermore recommended chemical compositions for each of the ON-6N alloys. Specifically for the pink / red alloys, the compositions are as indicated in table:TABLE 7Chemical composition-% in weightColorAuAgCu4N75.08.5-9.5Remaining part5N75.04.5-5.56N75.0  0-1.0

[0214] It has been previously described that the Gold alloys show improved mechanical characteristics.

[0215] The graph of FIG. 2 shows a Cartesian diagram wherein in the abscissa there is a distance corresponding to a displacement of a test sample of a Gold alloy when subject to a bending force and wherein in the ordinate there is a bending force. The displacement of the test sample is measured in μm. The bending force is measured in N.

[0216] The graph of FIG. 2 is obtained according to a 3-point bending test method, wherein each test sample is subject to an increasing bending force in correspondence of the midline, until reaching a linear displacement, along the direction of force application, equal to 4000 μm. Upon reaching a linear deformation, along the direction of force application, equal to 4000 μm, the bending force of the test sample is progressively reduced, and the value of residual deformation when the test sample is subject to a bending force of 10N is identified.

[0217] Generally, in order to assess the goodness of the Gold alloy in terms of deformation recovery, some test samples of Gold alloy are subject to an initially increasing deformation force F, in particular progressively increasing and then progressively decreasing. In a 3-point bending test, during the application of an increasing force, the height or position L1 of the midpoint assessed at a predetermined deformation force (Ftest) is measured. Subsequently, the deformation force continues to be increased until reaching a predetermined maximum displacement value of the midpoint (Lt). Once the predetermined maximum displacement value is reached, the deformation force F is progressively reduced until reaching the predetermined deformation force value (Ftest) and in that condition the new height or position L2 of the midpoint is detected.

[0218] For the Applicant, the performances of the alloy in terms of deformation recovery are all the better the smaller the difference ΔL is, defined as:Δ⁢L=L2,Ftest,crescente-L1,Ftest,decrescente

[0219] According to the measurement process carried out in order to obtain the graph of FIG. 2, the smaller the above-mentioned difference is, the more the Gold alloy taken into consideration shows optimal characteristics from the point of view of return after deformation, since a lower residual displacement of the test sample will also determine a lower deformation of the object realized by means of the alloy itself.

[0220] In the example of the graph of FIG. 2, Ftest=10N, Dt=4000 μm

[0221] The graph of FIG. 2 compares the Gold alloy according to the 848, 849 and 850 embodiment with some other alloys: 3N, 5N and Pd125 according to the compositions given in table 5.

[0222] The following values have been obtained:Δ⁢L848=470⁢ μmΔ⁢L849=600⁢ μmΔ⁢L850=950⁢ μmΔ⁢L844=1250⁢ μmΔ⁢L5⁢N=400⁢ μmΔ⁢L3⁢N=600⁢ μmΔLPd⁢125=1700⁢ μm

[0223] It is furthermore observed that with the same Palladium content (compositions 848, 849, 850), the Gold alloys show better performances if the content of Cobalt is increased.

[0224] The following table shows the hardness values of the specific embodiments of Gold alloy conceived by the Applicant.TABLE 8AnnealedHardenedHV1HV1844164246848170293849174285850163253Pd125155210Pd60 169263

[0225] The hardening process for the Gold alloys herein described takes place by exposing the above-mentioned alloys to a specific and predefined hardening temperature for each specific formulation, for a time substantially equal to 1 h, then allowing the alloy to cool until room temperature. The purpose of hardening is to promote the formation of precipitates and / or crystalline phase changes, activated by the high temperature, which allow the alloy to acquire a greater hardness with respect to the hardness after annealing.

[0226] The hardening temperatures described in the present formulation are indicated in the following table:TABLE 9HardeningResidencetemperaturetime(° C.)(h)5N28013N2801Pd1254752Pd60 30018443001848450184940018504501

[0227] The cooling of the test samples of the alloys in table 9 has been carried out by immersion in water at room temperature.

[0228] It is observed in particular that compositions 848 and 849, due to the high content of Cobalt, show a significantly higher hardness with respect to the other compositions in particular after hardening. The hardnesses according to Table 8 are measured on the Vickers scale with an applied load of 1 kgf.

[0229] The present disclosure furthermore refers to a process of production of a Gold alloy.

[0230] In one of its more general embodiments, the process of production of the Gold alloy according to the invention comprises, starting from the pure elements according to the above, the mixing of at least:

[0231] Gold, between 700‰ in weight and 800‰ in weight,

[0232] Copper, between 25‰ in weight and 170‰ in weight,

[0233] Palladium, between 50‰ in weight and 165‰ in weight,

[0234] Cobalt, between 7‰ in weight and 40‰ in weight.

[0235] Further ranges in weight of mixing are previously described and not repeated hereafter.

[0236] The method herein described comprises a step of introduction of the mixture into a melting crucible, and of a subsequent melting by heating until complete melting by introduction into the melting crucible.

[0237] The starting elements from which the alloys herein described are realized are pure elements; preferably, Gold has a purity of 99.99%, Copper has a purity of 99.99%, Palladium has a purity of 99.95%, Silver has a purity of 99.99%, Cobalt and Iridium have a purity of 99.95% and Gallium has a purity of 99.99%.

[0238] The method can comprise a step of mixing a pre-alloy of CuIr within the previously described assembly of elements.

[0239] Therefore, a particular embodiment comprises a step of realizing a pre-alloy of CuIr, and of mixing:

[0240] Gold, between 700‰ and 800‰ in weight,

[0241] Copper, between 9‰ and 79‰ in weight,

[0242] Palladium, between 85‰ and 165‰ in weight,

[0243] Cobalt, between 7‰ and 40‰ in weight,

[0244] Silver, between 7‰ and 60‰ in weight,

[0245] with a pre-alloy of CuIr at 16‰ in weight.

[0246] The melting process is preferably a continuous casting melting process, i.e. a process wherein the solidification and extraction of the solidified Gold are carried out continuously starting from a free end of a bar or melt of Gold. In particular, in the continuous melting process, a graphite die is used.

[0247] The use of a graphite die is useful because graphite is a solid lubricant, and typically shows low friction among its surfaces and those of the melted metal typically allowing to obtain an easy extraction of the element contained therein without fractures and with the minimum amount of defects present on its surface.

[0248] The melting process of the pure elements for the creation of Gold alloys according to the invention can be in detail a discontinuous Gold melting process or a continuous Gold melting process.

[0249] The discontinuous Gold melting process is a process wherein the mixture is melted and cast into a mould or ingot, realized in graphite. In this case, the above indicated elements are melted and cast in a controlled atmosphere. More in particular, the melting operations are carried out only after having preferably conducted at least 3 cycles of conditioning of the atmosphere in the melting chamber. This conditioning involves first of all the reaching of a vacuum level down to pressures lower than 1×10−2 mbar and a subsequent partial saturation with Argon at 500 mbar. During the melting, the Argon pressure is maintained at pressure levels between 500 mbar and 800 mbar. When it is reached the complete melting of the pure elements, a step of superheating of the mixture takes place, in which the mixture is heated up to a temperature 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 step of superheating, the value of pressure in the melting chamber again reaches a vacuum level lower than 1×10−2 mbar, useful for eliminating part of the slag produced by the melting of pure elements.

[0250] At this point, in a step of casting, the melted material is poured into a mould or ingot realized in graphite, and the melting chamber is again pressurized with an inert gas, preferably argon, injected at a pressure higher than 700 mbar and in particular higher than 800 mbar.

[0251] Once solidified, the bars or castings are extracted from the bracket. When the alloy is solidified, Gold alloy bars or castings are obtained from the graphite conduit and are subject to a rapid cooling by a step of water immersion, in order to reduce and possibly avoid phase variations. In other words, the bars or castings are subject to a step of rapid cooling, preferably but not limited in water, in order to avoid phase changes at the solid state.

[0252] The advantages of Gold alloys according to the present disclosure are clear in light of the above description. In particular, due to their improved mechanical properties, they allow to realize objects-even for high jewelry-which even if subject to relevant and / or repeated deformation forces change their size very little, and consequently provide a longer operational life both to themselves and to any objects to which they are connected or within which they are included. The deformation return properties are comparable to those of the 3N and 5N alloys and significantly better with respect to those of commercial gray alloys not containing Ni.

[0253] Furthermore, the Gold alloys according to the present disclosure can also be processed in a particularly effective manner to result with uniform surfaces, free from visible second phases or carbides. Therefore, the Gold alloys according to the present disclosure can be favorably used for high jewelry applications, and in particular for realizing high jewelry objects.

[0254] Non-limiting examples of jewelry objects realized at least partially by means of the Gold alloy herein described are: bracelets, watch bracelets, buckles, watch cases, watch hands, watch inner mechanisms, bracelet bezels, earrings, ornaments, rings, gemstone holders, ingots, in particular collector's ingots, collector's coins, necklaces, necklace closing elements, for earrings or for bracelets.

[0255] The Gold alloys according to the present disclosure can be applicable for objects which enter in direct contact with the human skin, and are at low allergy risk.

[0256] It is finally clear that to what forms the subject of the present invention can be applied additions, modifications or variants that are obvious to the expert in the art, without thereby departing from the scope provided by the attached claims.

Claims

1. A gold alloy for jewelry applications, suitable for forming jewelry objects exhibiting at least partial recovery of shape and / or size following application of a deformation force, the gold alloy comprising:gold, between 700‰ in weight and 800‰ in weight;copper, between 25‰ in weight and 170‰ in weight;palladium, between 50‰ in weight and 165‰ in weight; andcobalt, between 7‰ in weight and 40‰ in weight;the gold alloy being free from nickel, arsenic and platinum.

2. The gold alloy according to claim 1, wherein:said copper is present in an amount between 25‰ in weight and 95‰ in weight;said palladium is present in an amount between 85‰ in weight and 165‰ in weight; andthe gold alloy further comprises silver in an amount between 7‰ in weight and 60‰ in weight.

3. Gold alloy according to claim 1, further comprising gallium and / or at least a grain refining element, preferably at least one among iridium, rhenium or ruthenium, and wherein the amount in weight of gallium and / or of said at least a grain refining element, preferably at least one among iridium, rhenium or ruthenium, determines the reaching of 1000‰ in weight;said alloy being a gray color alloy;said gray color being defined, on the CIELAB 1976 color range, and according to the color measurement conditions according to CIE D65 and in accordance to ISO 8654, by the following color coordinates:L*, comprised between 80 and 84.5, preferably between 81 and 84;a*, comprised between 1.2 and 3.7, preferably between 1.5 and 3.5; andb*, comprised between 6.2 and 10.5, preferably between 6.6 and 10.

4. The gold alloy according to claim 2, comprising gallium between 1‰ in weight and 10‰ in weight, preferably between 2‰ in weight and 9‰ in weight, more preferably between 3‰ in weight and 8‰ in weight.

5. The gold alloy according to claim 3, wherein said at least a grain refining element is present in the amount up to 1‰ in weight;optionally wherein said iridium is pre-alloyed with copper and / or wherein said rhenium and / or ruthenium is pre-alloyed with palladium.

6. The gold alloy according to claim 2, wherein:said gold is present in an amount between 730‰ in weight and 770‰ in weight;said copper is present in an amount between 40‰ in weight and 90‰ in weight;said palladium is present in an amount between 100‰ in weight and 150‰ in weight;said cobalt is present in an amount between 8‰ in weight and 30‰ in weight; andsaid silver is present in an amount between 8‰ in weight and 55‰ in weight.

7. The gold alloy according to claim 6, wherein:said gold is present in an amount between 740‰ in weight and 760‰ in weight;said copper is present in an amount between 50‰ in weight and 90‰ in weight;said palladium is present in an amount between 100‰ in weight and 150‰ in weight;said cobalt is present in an amount between 8‰ in weight and 30‰ in weight; andsaid silver is present in an amount between 8‰ in weight and 55‰ in weight.

8. The gold alloy according to claim 7, wherein:said gold is present in an amount between 740‰ in weight and 760‰ in weight;said copper is present in an amount between 50‰ in weight and 90‰ in weight;said palladium is present in an amount between 110‰ in weight and 140‰ in weight, preferably between 115‰ in weight and 135‰ in weight;said cobalt is present in an amount between 10‰ in weight and 25‰ in weight; andsaid silver is present in an amount between 8‰ in weight and 50‰ in weight.

9. The gold alloy according to claim 1, wherein:said copper is present in an amount between 45‰ in weight and 65‰ in weight, preferably between 50‰ in weight and 60‰ in weight, and said silver is present in an amount between 35‰ in weight and 52‰ in weight; orsaid copper is present in an amount between 75‰ in weight and 95‰ in weight, preferably between 80‰ in weight and 90‰ in weight, and said silver is present in an amount between 7‰ in weight and 13‰ in weight, preferably between 8‰ in weight and 12‰ in weight.

10. The gold alloy according to claim 1, wherein:said gold is present in an amount between 730‰ in weight and 770‰ in weight, preferably between 740‰ in weight and 760‰ in weight;said copper is present in an amount between 150‰ in weight and 170‰ in weight, preferably between 155‰ in weight and 165‰ in weight;said palladium is present in an amount between 50‰ in weight and 70‰ in weight, preferably between 55‰ in weight and 65‰ in weight;said cobalt is present in an amount between 7‰ in weight and 13‰ in weight;said gold alloy further comprising Iron, iron between 10‰ in weight and 30‰ in weight; andoptionally further comprising at least a grain refining element, preferably at least one among iridium, rhenium or ruthenium;wherein said amounts of said gold, said copper, aid palladium, said cobalt, said iron, and optionally the at least a grain refining element, preferably at least one among iridium, rhenium or ruthenium, together sum to 1000‰ in weight of said gold alloy.

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