Gold alloys and methods for manufacturing gold alloys

Abstract

The present invention provides a gold alloy and a method for producing the same, the gold alloy including: gold; and an Au-X-RE-based hypermaterial represented by the compositional formula Au100-(a+b)XaREb, X in the compositional formula being at least one atom selected from the group consisting of Al, Ga, In, Si, Ge, and Sn, RE representing a rare earth element, and a and b being respectively the content of X and RE in at%, and the Au-X-RE-based hypermaterial satisfying conditions (1) and (2), the Au-X-RE-based hypermaterial being dispersed in a gold parent phase.

Description

[Technical Field]

[0001] This disclosure relates to gold alloys and methods for manufacturing gold alloys. [Background technology]

[0002] Gold, with its beautiful luster and high rarity, has been highly valued as a precious metal since ancient times and is also the oldest metal used by humankind for ornaments. Gold is highly malleable and ductile, making it easy to process, but on the other hand, it is soft and easily scratched, so its hardness needs to be increased when used in jewelry.

[0003] For example, as a method for increasing the hardness of an aluminum alloy, which is a metal other than gold, Japanese Patent Publication No. 2009-191327 discloses a method for strengthening an aluminum alloy substrate by forming a reinforcing film on the surface of the aluminum alloy substrate, characterized in that the reinforcing film is formed by a non-melting process using a reinforcing material having higher strength than the aluminum alloy substrate.

[0004] Furthermore, as a high-strength aluminum alloy, Japanese Patent Publication No. 2008-069438 lists a composition formula Mg 100-(a+b) Zn a X b The relationship is expressed as follows: X is one or more elements selected from Zr, Ti, and Hf, a and b are the Zn and X content expressed in at% respectively, and the relationship is given by the following equations (1), (2), and (3): a / 28 ≤ b ≤ a / 9 ... (1) 2 <a<10·······(2) 0.05 <b<1.0···(3) A high-strength magnesium alloy is disclosed that satisfies the following conditions and is characterized in that Mg-Zn-X quasicrystals and their approximate crystals are dispersed in the Mg matrix in the form of fine particles.

[0005] Furthermore, Japanese Patent Publication No. 2005-113235 contains the composition formula Mg 100-(a+b) Zn a Y bIt is represented by, where a and b are the contents of Zn and Y respectively expressed in at%, and satisfy the following relationships of formulas (1) and (2): a / 12 ≦ b ≦ a / 3 ··· (1) 1.5 ≦ a ≦ 10 ····· (2) There is disclosed a high-strength magnesium alloy characterized in that Mg3Zn6Y1 quasicrystal and its approximate crystal as age-precipitated phases are dispersed in the form of fine particles.

SUMMARY OF THE INVENTION

Advantages of the Invention

[0010] [ [According to one embodiment of the present disclosure, a gold alloy with high gold purity and high hardness is provided. Furthermore, according to another embodiment of the present disclosure, a method for manufacturing a gold alloy with high gold purity and high hardness is provided. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 shows the XRD diffraction results of an example of a gold alloy obtained by the gold alloy manufacturing method described herein. [Figure 2] Figure 2 shows the XRD diffraction results of an example of a gold alloy obtained by the gold alloy manufacturing method described herein. [Figure 3] Figure 3 is an example of an SEM image of an example of a gold alloy obtained by the gold alloy manufacturing method described herein. [Figure 4] Figure 4 is a graph showing the relationship between rare earth elements contained in an example of a gold alloy obtained by the gold alloy manufacturing method described herein, and the Vickers hardness of the gold alloy. [Figure 5] Figure 5 is a graph showing the relationship between the Au purity of an example of a gold alloy obtained by the gold alloy manufacturing method described herein and the Vickers hardness of the gold alloy. [Modes for carrying out the invention]

[0012] The contents of this disclosure will be described in detail below. The descriptions of the constituent elements described below may be based on representative embodiments of this disclosure, but this disclosure is not limited to such embodiments. In this disclosure, a numerical range indicated using "~" means a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Also, in numerical ranges described in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples. In this disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

[0013] In this disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, as long as their intended purpose is achieved.

[0014] In this specification, "gold (Au) purity" and "gold (Au) content" are synonymous. For example, "gold purity of 95% by mass" means that the gold content relative to the total mass of the gold-containing compound (gold alloy) is 95% by mass. Furthermore, in this specification, "high hardness" means that the Vickers hardness of the resulting alloy is 100 or higher.

[0015] (Gold alloy) The gold alloy relating to this disclosure is made of gold and the chemical formula Au 100-(a+b) X a RE b It is represented as, In the above compositional formula, X represents at least one atom selected from the group consisting of Al, Ga, In, Si, Ge, and Sn. RE stands for rare earth elements. a and b are the X and RE content expressed in at% respectively, and the Au-X-RE hypermaterial satisfies the following conditions (1) and (2), 10 ≤ a ≤ 40 (1) 13 ≤ b ≤ 17 (2) The gold alloy contains Au-X-RE-based hypermaterial dispersed in the gold matrix. The gold alloy according to this disclosure has the above configuration, resulting in high gold purity and high hardness.

[0016] As mentioned above, gold is used in jewelry because of its beautiful hue, low yield, and high price. Pure gold (so-called 24K, with a gold content of 99.99% by mass) has a hardness (Vickers hardness) of about 20HV to 30HV, making it too soft and easily scratched. Furthermore, when trying to process pure gold for jewelry, it is difficult to create thin shapes such as gold wire. On the other hand, for example, carbon steel SS400, a structural steel material, has a hardness (Vickers hardness) of about 130HV to 140HV and is easy to process, so it is widely used in building structures, machinery, etc. Generally, a known method for strengthening gold is solid solution strengthening, which involves solid-solution strengthening in which solute atoms (e.g., Ag, Cu, etc.) are dissolved in the gold matrix. However, while solid solution strengthening can increase the hardness of gold, there is a concern that the purity of the gold may decrease due to the inclusion of other elements. Thus, in order to produce a gold alloy with high added value, a high purity of gold and a hardness sufficient for good workability (preferably the hardness of low-carbon steel, more preferably the hardness of iron ore) are required. Through diligent research, the inventors discovered that by dispersing a hypermaterial with a specific composition in a gold matrix, a gold alloy with increased hardness can be obtained without reducing the purity of the gold.

[0017] The detailed mechanism by which the above effects are achieved is unknown, but it is speculated to be as follows. Hypermaterials are a type of intermetallic compound, and intermetallic compounds are generally known to have high hardness due to their resilient dislocations. In particular, hypermaterials are crystals with hundreds of atoms in their unit cell, and we believe that this complex, long-period structure, in addition to being an intermetallic compound, is a factor in their high hardness. Furthermore, since Au-based hypermaterials contain a large amount of Au in their crystal structure, it is possible to suppress the decrease in Au concentration when Au-based hypermaterials are dispersed in a gold matrix. Furthermore, the gold alloy relating to this disclosure has high hardness and excellent machinability because it contains a hypermaterial with higher hardness than the gold matrix. The following describes the various components of the gold alloy related to this disclosure.

[0018] <Au-X-RE-based hypermaterial> The Au-X-RE-based hypermaterial is a hypermaterial represented by the composition formula Au 100-(a+b) X a RE b Here, the hypermaterial means a group of substances uniformly described in a high-dimensional space including a complementary space, that is, a substance (material) in a high-dimensional space (hyperspace). The hypermaterial has a cluster structure in which atomic polyhedra are nested. As an example of the cluster of the hypermaterial, the regular icosahedron symmetric cluster in the Tsai-type Au-X-RE-based hypermaterial is shown below. However, the present disclosure is not limited thereto. In the Tsai-type Au-X-RE-based hypermaterial, the innermost shell (shown at the left end below) is a tetrahedron made of Au atoms or X atoms, and the outside thereof is surrounded by a second shell of a regular dodecahedron made of Au or X atoms (shown second from the left below). Further, the outside thereof is surrounded by a third shell of a regular icosahedron made of rare earth elements (corresponding to RE in the composition formula) (shown second from the right below), and the outermost shell is surrounded by an icosidodecahedron (12·20 polyhedron) made of 30 Au and X atoms (shown at the right end below). Note that a cluster configured by such a concentric arrangement of four shells is called a Tsai-type cluster.

[0019] [[ID=二十一]]

Chemical formula

[0020] Specific examples of the hypermaterial include quasicrystals, approximate crystals, etc. Here, a quasicrystal refers to a compound with a long-range ordered structure (typically possessing five-fold symmetry) but lacking the translational symmetry characteristic of ordinary crystals. Compositions known to produce quasicrystals include Al-Pd-Mn, Al-Cu-Fe, Cd-Yb, and Mg-Zn-Y. Due to their unique structure, quasicrystals possess various distinctive properties compared to crystalline intermetallic compounds of similar composition, including high hardness, high melting point, and low coefficient of friction. An approximate crystal is a crystalline compound that has a complex structure derived from a quasicrystal, possesses a structure partially similar to that of a quasicrystal, and has properties similar to the original quasicrystal.

[0021] Furthermore, the Au-X-RE hypermaterial dispersed in the gold alloy can be confirmed by XRD (X-ray diffraction) measurements. Specifically, the sample can be measured using a powder X-ray diffractometer (MiniFlex600, manufactured by Rigaku Corporation, source: CuKα), and the resulting XRD peak waveform can be compared with the hypermaterial-specific peaks (peaks of known quasicrystals and approximate crystals) for confirmation.

[0022] <Composition formula Au 100-(a+b) X a RE b > [X] In the empirical formula, X represents at least one atom selected from the group consisting of Al, Ga, In, Si, Ge, and Sn. The above compositional formula may contain only one type of X, or it may contain two or more types of X. An example of a compositional formula in which X contains two types of atoms is the compositional formula represented by Au-Al-Ga-Gd, etc. From the viewpoint of increasing the purity of gold in the gold alloy, X preferably contains at least one atom selected from the group consisting of Al, Ga, Si, Ge, and Sn, more preferably Al, Ga, Si, Ge, or Sn, even more preferably Al, Ga, Si, or Ge, and particularly preferably Si or Ge.

[0023] [RE] In the chemical formula, RE represents a rare earth element. There are no particular restrictions on the rare earth elements, and examples include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu. Among these, from the viewpoint of increasing the purity of gold in the gold alloy, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, or Yb are preferred as RE, and La, Ce, Pr, Nd, or Sm are more preferred.

[0024] From the viewpoint of obtaining a gold alloy with high gold purity and high hardness, X preferably contains at least one atom selected from the group consisting of Al, Ga, Si, Ge, and Sn (more preferably Al, Ga, Si, Ge, or Sn, even more preferably Ga, Si, or Ge, particularly preferably Si or Ge), and RE is preferably La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, or Yb (more preferably La, Ce, Pr, Nd, or Sm).

[0025] From the viewpoint of obtaining a gold alloy with high gold purity and high hardness, when X is Si, RE is preferably La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, or Yb, and among these, RE is more preferably a rare earth element with a small atomic number, and is preferably La, Ce, Pr, Nd, or Sm.

[0026] From the viewpoint of obtaining a gold alloy with high gold purity and high hardness, when X is Ge, RE is preferably La, Pr, Nd, Sm, Eu, or Gd, and among these, RE is more preferably a rare earth element with a small atomic number, and is preferably La, Ce, Pr, Nd, or Sm.

[0027] In the composition formula, a and b are the content of X and RE, expressed in at%, respectively, and satisfy either (1) or (2) below. By dispersing a hypermaterial that satisfies (1) and (2) below into a gold matrix, a gold alloy with high gold purity and high hardness can be obtained. From the above viewpoint, it is preferable that a and b in the composition formula further satisfy (3) (i.e., satisfy (1) to (3) below), and more preferably satisfy (1), (2) and (3') below. 10 ≤ a ≤ 40 (1) 13 ≤ b ≤ 17 (2) The at% ratio of a to b (a:b) is 8-9.5:7 (3) The at% ratio of a to b (a:b) is 8:7 or 9.5:7 (3') at% stands for atomic percentage.

[0028] The compositional formula Au found in gold alloys 100-(a+b) X a RE b The types of X and RE of the hypermaterial represented by [formula], and whether or not they satisfy the above conditions (1) and (2), can be confirmed using a scanning electron microscope (SEM-EDS). Specifically, after mirror-polishing the obtained gold alloy sample, it can be observed with SEM-EDS, and the elements contained and their content can be confirmed using EDS (energy-dispersive X-ray spectrometer) in the gray area of ​​the SEM image (the part corresponding to the Au-X-RE hypermaterial).

[0029] From the viewpoint of obtaining a gold alloy with high gold purity and high hardness, it is preferable that equation (1) is 10 ≤ a ≤ 21, and more preferably 10 ≤ a ≤ 14.

[0030] From the viewpoint of obtaining a gold alloy with high gold purity and high hardness, it is preferable that equation (2) is 13 ≤ b ≤ 15, and more preferably 13 ≤ b ≤ 14.

[0031] From the viewpoint of obtaining a gold alloy with high gold purity and high hardness, when X is Si in the compositional formula, it is preferable that the at% ratio of a to b (a:b) in the compositional formula is 8:7, and the gold alloy is composed of Au 85 It is more preferable that it be represented as Si8RE7.

[0032] From the viewpoint of obtaining a gold alloy with high gold purity and high hardness, when X is Ge in the compositional formula, it is preferable that the at% ratio of a to b (a:b) in the compositional formula is 9.5:7, and the gold alloy is composed of Au 83.5 Ge 9.5 It is more preferable to represent it as RE7.

[0033] <Gold content> From the viewpoint of high added value, the gold content is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass, based on the total mass of the gold alloy.

[0034] (Method of manufacturing gold alloy) The method for producing a gold alloy according to this disclosure includes the step of dissolving Au, at least one atom selected from the group consisting of Al, Ga, In, Si, Ge, and Sn, and one rare earth element in an inert atmosphere. The method for manufacturing a gold alloy according to this disclosure, by including the above-mentioned steps, yields a gold alloy with high gold purity and high hardness.

[0035] In the method for producing a gold alloy according to this disclosure, at least one atom selected from the group consisting of Al, Ga, In, Si, Ge, and Sn is the above-mentioned composition formula Au 100-(a+b) X a RE b This is synonymous with X represented by [the symbol], and the preferred form is similar. The rare earth element used in the gold alloy manufacturing method relating to this disclosure is the above-mentioned composition formula Au. 100-(a+b) X a RE b This is synonymous with RE, and the preferred form is the same.

[0036] In the method for producing a gold alloy according to this disclosure, the purity of Au, at least one atom selected from the group consisting of Al, Ga, In, Si, Ge, and Sn, and one rare earth element (hereinafter sometimes simply referred to as "raw materials") is preferably 99% by mass or higher, more preferably 99.9% by mass or higher, and even more preferably 99.99% by mass, from the viewpoint of easily obtaining a high-purity hypermaterial.

[0037] There are no particular restrictions on the shape of Au; it may be foil-shaped, plate-shaped, or the like. At least one atom selected from the group consisting of Al, Ga, In, Si, Ge, and Sn, as well as rare earth elements, are not particularly limited in shape and can be selected as appropriate. Examples of shapes include granular, foil-like, plate-like, and lump-like forms. If the raw material is in granular form (grain), it is preferably 1 mm to 8 mm in size, and more preferably 2 mm to 5 mm.

[0038] As for the method of dissolving the above raw materials, there are no particular restrictions as long as each raw material is dissolved in an inert atmosphere, but from the viewpoint of easier dissolution, arc melting is preferred. Arc melting is preferably carried out in an inert atmosphere such as helium, argon, or nitrogen, and more preferably in an inert atmosphere substituted with argon. In the method for producing a gold alloy according to this disclosure, it is preferable to perform arc melting in an argon inert atmosphere after creating a vacuum atmosphere, from the viewpoint of further preventing oxidation. Arc melting can be performed using a vacuum arc melting apparatus. Specifically, arc melting is carried out by placing samples prepared as raw materials for each element on the same water-cooled copper hearth, creating a vacuum to a predetermined pressure, and applying a desired current value under an inert gas atmosphere. The pressure during arc melting is, for example, 1 × 10⁻¹⁰ when vacuumed. -2 Pa or less, preferably 1 × 10⁻⁶ -3The pressure can be adjusted to a range of Pa or less. For example, after vacuuming, arc melting can be performed under an inert gas pressure of, for example, 0.01 MPa to 0.1 MPa.

[0039] The current applied during arc melting is preferably adjusted to a range of, for example, 20A (amperes) to 100A. The voltage application time can be appropriately selected depending on the situation, for example, by applying the voltage for 5 to 30 seconds, for example, four times.

[0040] The method for manufacturing a gold alloy relating to this disclosure may include steps other than those described above (other steps) as necessary. Other processes include the preparation of raw materials and the refining of the resulting gold alloy. [Examples]

[0041] The present disclosure will be described in detail below with reference to examples. However, the present disclosure is not limited in any way by these examples.

[0042] (Example 1) (1) As the raw material for gold (Au), an Au plate (shape: irregular, purity: 99.99%) manufactured by Katagiri Precious Metals Co., Ltd. was prepared. As one of the raw materials (X in the composition formula) for the Au-X-RE hypermaterial, we prepared germanium (Ge) raw material Ge grains (shape: grain 2mm~5mm, purity: 99.99%) manufactured by Kojun Chemical Laboratory Co., Ltd., and silicon (Si) raw material Si grains (shape: grain, purity 99:999%) also manufactured by Kojun Chemical Laboratory Co., Ltd. As rare earth elements (RE in the chemical formula), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), and ytterbium (Yb) were prepared as raw materials in the form of grains (shape: irregular lumps of 5mm to 10mm, purity: 99.9%, packaging: oil immersion) manufactured by Nippon Yttrium Co., Ltd.

[0043] (2) The above-mentioned La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Yb raw materials were placed in a beaker (B-100SCI, manufactured by HARIO Corporation) with acetone manufactured by Gordo Co., Ltd. and washed for 10 minutes using an ultrasonic cleaner (Au-16C, manufactured by Aiwa Medical Industry Co., Ltd.) in order to remove oil.

[0044] (3) The above raw materials Au, Ge, Si, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Yb were cut into pieces measuring 1 mm to 3 mm x 1 mm to 3 mm using nippers (TESKYU-260TYPE, manufactured by ENUSHIKI Co., Ltd., N-31, manufactured by HOZAN Co., Ltd.) to obtain samples.

[0045] (4) The resulting gold alloy has the composition formula Au 83.5 Ge 9.5 RE7 (where RE represents La, Ce, Pr, Nd, Sm, Eu, or Gd, and the numbers represent at%; the same applies hereafter), or the chemical formula Au 85 Seventeen types of mixed samples were obtained by weighing each of the samples obtained in (3) above so as to satisfy the formula Si8RE7 (where RE represents La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, or Yb, and the numbers each represent at%; the same applies hereinafter) and so that the total mass is 1 g.

[0046] (5) Next, using a miniature vacuum arc melting apparatus (NEV-AD03 model, manufactured by Nisshin Giken Co., Ltd.), the mixed samples weighed as described above were placed on a water-cooled copper hearth and vacuumed for approximately 2 hours to a pressure of 3 × 10⁻¹⁰ -3 After reaching Pa, the current was adjusted to approximately 40A to 80A under an argon atmosphere, and each mixed sample was arc-melted. To ensure uniform dissolution of the mixed sample, the sample was first irradiated with an arc, then inverted using a reversing rod, and irradiated with the arc again. This procedure was repeated twice. As a result, 17 spherical alloy samples ranging from 4mm to 7mm in diameter were obtained: Au 83.5 Ge 9.5 RE7 (RE = La, Ce, Pr, Nd, Sm, Eu or Gd) and Au 85Si8RE7 (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy or Yb) was obtained.

[0047] (6) The obtained alloy sample was cut with an Isomet (manufactured by Buehler). (7) Using a polishing table (Doctor Lap, manufactured by MARUTO) and polishing papers (Carbomac Paper, manufactured by Refine Tech Co., Ltd.), the cut sample was polished step by step in the order of particle sizes P800, 1000, and 2000 to adjust it to a mixed sample with parallel upper and lower surfaces. Further, a few drops of diamond suspension (MetaDiTM Supreme Polycrystalline Diamond Suspension, manufactured by Buehler) were dropped onto a polishing cloth (TriDent Polishing Cloth, manufactured by Buehler), and the alloy sample was mirror-polished in the order of diamond sizes 3 μm and 1 μm.

[0048] <Evaluation by X-ray diffraction> (8) The mirror-polished alloy sample was evaluated using a powder X-ray diffractometer (MiniFlex600, manufactured by Rigaku Corporation, radiation source: CuKα). The XRD (X-ray diffraction) patterns are shown in FIGS. 1 and 2. As shown in FIGS. 1 and 2, it can be seen that the characteristic peaks of the Au-X-RE-based hypermaterial and Au can be confirmed in the composition of any alloy sample. Note that the 1 / 1 hypermaterial is described as a crystal structure having a body-centered cubic structure in which Tsai-type clusters are arranged at each vertex and the center of a cube and having a symmetry of Im-3. As shown in FIGS. 1 and 2, Au 83.5 Ge 9.5 RE7 (RE = Gd, Eu, Sm, Nd, Pr, Ce, or La), and Au 85 It can be seen that the Au-X-RE-based hypermaterial and the two-phase alloy of gold were successfully produced with Si8RE7 (RE = Yb, Dy, Tb, Gd, Eu, Sm, Nd, Pr, Ce, or La).

[0049] <Evaluation by SEM> (9) Again, the alloy samples were polished in stages using the polishing stand and abrasive paper shown in (7), in the order of grit sizes P1000, 2000, and 4000. A few drops of diamond suspension were placed on TriDent abrasive paper, and the alloy samples were mirror-polished in the order of diamond sizes 3 μm and 1 μm. A few drops of alumina suspension (MasterPrep™ Polishing Suspension 0.05 μm) were placed on abrasive paper (MasterTex Polishing Cloth, manufactured by Buehler), and the alloy samples were mirror-polished. The alloy samples obtained in (10) and (9) were evaluated using a scanning electron microscope (SEM-EDS) (JSM-IT100, JEOL). The results are shown in Figure 3. In Figure 3, the white areas represent Au, and the gray areas represent Au-X-RE hypermaterials. From Figure 3, it can be seen that the Au-X-RE hypermaterials are dispersed in the gold matrix. Furthermore, EDS analysis of the hypermaterial (Au-Ge-La) contained in the obtained gold alloy revealed that Au was 74 at%, Ge was 13 at%, (a in the composition formula) and La was 13 at%, (b in the composition formula), and the hypermaterial (Au-Ge-La) satisfied equations (1) and (2).

[0050] <Hardness> (11) The micro-Vickers hardness of alloy samples was measured and evaluated using a Shimadzu microhardness tester (HMV-G21, manufactured by Shimadzu Corporation). The results are shown in Figure 4 and Table 1. All of the alloy samples had a Vickers hardness exceeding 156 HV.

[0051] [Table 1]

[0052] (Example 2) (12) The resulting gold alloy has the composition formula Au x Ge y La z (x=81.2, 86.0, 91.3, or 97 at%, y:z=9.5:7 (at% ratio)), Aux Si y Ce z The raw materials prepared in Example 1 were weighed out so that (x = 87 or 89 at%, y:z = 8:7 (at% ratio)) and the total mass was 1 g, and six types of mixed samples were prepared. (13) Except for using the six mixed samples prepared above, an alloy sample was obtained by arc melting under the same conditions as in (5) of Example 1. The alloy samples obtained in (14) and (13) were cut, polished, and mirror-polished under the same conditions as in (6), (7), and (8) of Example 1, and then subjected to X-ray diffraction measurements. (15) The mirror polishing was performed again under the same conditions as in (7) of Example 1, and the material structure was evaluated using SEM-EDS. (16) The micro-Vickers hardness was measured under the same conditions as in (11) of Example 1. The results are shown in Figure 5.

[0053] A Vickers hardness of 130 HV to 140 HV represents a hardness suitable for processes such as rolling and wire drawing (i.e., a hardness with excellent workability), and is ideal for jewelry materials. For reference, pure gold (gold with a purity of 99.99%) has a Vickers hardness of 20 HV to 30 HV. In the gold alloys containing dispersed Au-Ge-La and Au-Si-Ce hypermaterials prepared in Example 2, a linear relationship was observed between gold purity and hardness, indicating that hardness changes linearly with increasing hypermaterial dispersion. Furthermore, in the gold alloy containing dispersed Au-Si-Ce hypermaterials, the Vickers hardness ranged from 145 HV to 200 HV when the gold purity was in the range of 93% to 96% mass.

[0054] As shown in Examples 1 and 2, the method for manufacturing a gold alloy according to this disclosure and the gold alloy obtained by this method exhibit high gold purity and high hardness. Furthermore, it was revealed that the desired hardness can be achieved with extremely high gold purities (gold content) of 93.1% by mass and 95.9% by mass, respectively, in Au-Ge-La and Au-Si-Ce gold alloys. This is a higher purity than the 18K gold (Au content: 75% by mass) commonly used in jewelry.

[0055] The gold alloy and its manufacturing method disclosed herein are the results of the Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research: Innovative Areas (Research Area Proposal Type) "Hypermaterials: New Material Science Created by Complementary Space" (Project Numbers: 19H05817, 19H05818, FY2019-FY2023).

[0056] The disclosure of Japanese Patent Application No. 2021-056093, filed on 29 March 2021, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

Claims

1. Gold and, Composition formula Au １００－（ａ＋ｂ） X ａ RE ｂ It is represented as, In the above compositional formula, X represents Ge and RE represents Gd, Eu, Sm, Nd, Pr, Ce, or La, or X represents Si and RE represents Yb, Dy, Tb, Gd, Eu, Sm, Nd, Pr, Ce, or La, a and b are the X and RE content expressed in at% respectively, and the Au-X-RE hypermaterial satisfies the following (1) and (2), 10 ≤ a ≤ 40 (1) 13 ≤ b ≤ 17 (2) It consists only of, The Au-X-RE hypermaterial is dispersed in the gold matrix phase. A gold alloy in which the Au content is 80% by mass or more and 95% by mass or less, relative to the total mass of the gold alloy.

2. A step of dissolving Au, Ge, Gd, Eu, Sm, Nd, Pr, Ce, or La in an inert atmosphere. including, A method for producing a gold alloy according to claim 1.

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