HIGH-HARDNESS Au ALLOY AND METHOD FOR PRODUCING HIGH-HARDNESS Au ALLOY

Abstract

To provide an Au alloy that includes an Au-based hypermaterial and that achieves higher hardness than the prior art while retaining a high Au content.SOLUTION: The present invention relates to a high-hardness Au alloy including an Au-rich phase and an HM phase composed of an Au-X-RE-based hypermaterial represented by the following formula. In the Au alloy according to the present invention, in a material structure at an arbitrary cross section, the Au-rich phase having an average equivalent circle diameter of 1.5 μm or less is distributed. In the above formula, X is at least one atom selected from the group consisting of Al, Ga, In, Si, Ge, and Sn. RE is a rare earth element. a represents a content of X in atom%, and satisfies 5≤a≤40, and b represents a content of RE in atom%, and satisfies 11≤b≤18.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an Au alloy containing Au as a main component, and more particularly to an Au alloy containing an Au-X-RE hypermaterial that can achieve high hardness while increasing Au purity, and a method for producing the Au alloy. [Background technology]

[0002] Due to its rarity, gold (Au) is one of the few metals that can be traded with monetary or asset value. Its appearance, combined with its appearance, has led to its long use as jewelry and decorative items. Furthermore, gold is highly valuable industrially. Au is an extremely chemically stable metal with good corrosion resistance and high electrical conductivity, making it also used as an electrode and wiring material for electrical and electronic devices.

[0003] While gold excels in many properties, one property that needs improvement is its mechanical properties, such as hardness. Gold has low hardness, with the Vickers hardness of pure gold (purity of 99.99% by weight or higher) being approximately 20Hv to 30Hv. A certain level of hardness is necessary for metal workability, and gold within this hardness range is too soft to be finely processed into wires or other objects. Furthermore, for items worn by people, such as jewelry and ornaments, gold's low hardness raises concerns about scratches on the surface. Therefore, gold used in jewelry and ornaments must be hard enough to be easily processed while also being scratch-resistant.

[0004] Improvements in the mechanical properties of gold are also desirable for industrial applications. In the past, gold was used industrially as an electrode and wiring material, where mechanical properties such as hardness were not particularly important. However, given gold's favorable electrical conductivity and chemical stability, gold is expected to be used as a contact material in motors, switches, and other devices. Currently, the mainstream precious metal contact material is silver or an Ag alloy. However, silver is not particularly corrosion-resistant, and its resistance to sulfurization is particularly poor. Ag also suffers from migration issues. Therefore, gold, which has the same electrical conductivity as silver but also superior chemical stability, is expected to be used as an alternative to silver-based contact materials. However, at present, gold's overwhelming hardness compared to silver-based materials makes this a difficult replacement.

[0005] While various methods are known for strengthening the mechanical properties of metallic materials, the most common method for strengthening gold is solid solution strengthening, which involves adding and alloying other elements. For example, in gold alloys containing Ni, the hardness increases with increasing Ni content, reaching approximately 200-300 Hv. However, increasing the amount of added elements reduces the purity of gold in the gold alloy, thereby reducing the added value of gold. Considering this reduction in added value, there is a limit to how much gold can be hardened by solid solution strengthening.

[0006] Given the above background, the inventors of the present application have proposed Au alloys, including Au-based hypermaterials, that contain high-purity Au and exhibit high hardness (Patent Document 1). Hypermaterials (HMs) are a term that refers to a group of substances that are uniformly described in a high-dimensional space, including complementary spaces. The structural units of conventionally understood metallic materials are crystalline and amorphous, which are classified according to the presence or absence of relatively short-term periodicity. Hypermaterials, unlike these, are substances (solids) that are composed of a large number of atomic groups with an ultra-long-term periodic structure. Due to the complex long-term periodicity of such a large number of atomic groups, hypermaterials can exhibit unique properties in terms of electrical and magnetic properties as well as mechanical properties.

[0007] Examples of materials specifically described as hypermaterials include quasicrystals and approximant crystals. Quasicrystals are compounds with a long-range ordered structure but lack the translational symmetry characteristic of ordinary crystals. Because of their unique structure, quasicrystals have various unique properties, including high hardness, a high melting point, and a low coefficient of friction, compared to crystalline intermetallic compounds with similar compositions. Approximant crystals are crystalline compounds with complex structures derived from quasicrystals, partially similar in structure to quasicrystals, and possess properties similar to those of the original quasicrystals.

[0008] The Au-based hypermaterial contained in the Au alloy of Patent Document 1 is an Au-X-RE-based hypermaterial, and is referred to as "Au 100-(a+b) X a RE b " where X is a metallic or semimetallic element such as Al, Ga, In, or Si, and RE is a rare earth element such as La or Gd. Au-X-RE hypermaterials have a complex and long-range periodicity of Au atoms, X atoms, and RE atoms, which forms an Au alloy phase that exhibits extremely high hardness.

[0009] The Au alloy of Patent Document 1 is a two-phase alloy in which Au-X-RE-based hypermaterials are dispersed in Au. As described above, AuAu-X-RE-based hypermaterials have high hardness, which can increase the hardness of Au alloys. Furthermore, AuAu-X-RE-based hypermaterials can contain a large amount of Au (Au atoms). As a result, the Au alloy of Patent Document 1 increases its hardness while increasing its overall Au content. In other words, it can exhibit the properties of a high-hardness material while maintaining its value as an Au alloy containing high-quality Au. As a result, Au alloys containing Au-based hypermaterials have potential not only for use in jewelry and decorative items, but also as industrial materials such as contact materials. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. WO2022 / 210430 Summary of the Invention [Problem to be solved by the invention]

[0011] As described above, Au alloys, including Au-based hypermaterials, contain high-purity Au and have increased hardness, but there is still room for improvement. According to Patent Document 1, the upper limit of the hardness of this Au alloy is approximately 200 Hv, depending on the type and content of the X and RE atoms that make up the hypermaterial. This hardness range is considered to be a good characteristic from the standpoint of processability, and is suitable for applications such as jewelry and ornaments, but is still insufficient as an industrial material such as a contact material.

[0012] The present invention was made under the above-mentioned background, and aims to provide an Au alloy including the above-mentioned conventional Au-based hypermaterial that has higher hardness than conventional ones while maintaining a high Au content. In this study, the inventors reviewed the manufacturing process of the Au-based hypermaterial and identified a suitable Au alloy while taking into consideration the workability into the target shape. [Means for solving the problem]

[0013] Au-X-RE hypermaterials (Au 100-(a+b) X a RE bIn addition to the advantages of the high Au content and high hardness mentioned above, this Au-based hypermaterial also has the advantage of being relatively easy to manufacture. That is, this Au-based hypermaterial can be formed by melt casting by appropriately adjusting the amounts (a, b) of the constituent elements X and RE. The melt casting process requires operation in an inert atmosphere, but no other special conditions or operations are required. After casting, a two-phase alloy consisting of an Au phase and an Au-X-RE-based hypermaterial phase (hereinafter sometimes referred to as the HM phase) is produced without any special thermomechanical treatment. To improve the hardness of this two-phase alloy, the inventors decided to improve the material structure and investigate a new manufacturing process for this purpose. As a result of extensive investigations, they discovered that an Au alloy containing an Au-X-RE-based hypermaterial phase manufactured by combining a melting and solidification process with powder metallurgy exhibits higher hardness than conventional techniques and exhibits a material structure different from that previously available, leading to the invention of the present invention.

[0014] That is, the present invention, which solves the above-mentioned problems, is a high-hardness Au alloy containing an Au-rich phase and an HM phase made of an Au-X-RE-based hypermaterial represented by the following formula, characterized in that the Au-rich phase having an average equivalent circle diameter of 1.5 μm or less is distributed in the material structure in an arbitrary cross section.

[0015] [ka] In the above formula, X is at least one atom selected from the group consisting of Al, Ga, In, Si, Ge, and Sn. RE is a rare earth element. a is the content of X in atomic percent, and is 5≦a≦40. b is the content of RE in atomic percent, and is 11≦b≦18.

[0016] The structure and manufacturing method of the Au alloy containing the Au-X-RE based hypermaterial phase according to the present invention will be described below.

[0017] I. Composition of the Au alloy according to the present invention As described above, the Au alloy according to the present invention is composed of an Au-rich phase containing Au as the main component and an Au-X-RE hypermaterial (Au 100-(a+b) X a RE b The alloy is a two-phase alloy consisting of an HM phase and an Au-rich phase. In any cross section, the alloy exhibits a material structure in which the Au-rich phase is distributed and refined to a predetermined circle equivalent diameter.

[0018] I-1 Au-X-RE hypermaterial phase (HM phase) The HM phase consisting of an Au-X-RE-based hypermaterial is included in the Au alloy of the present invention to improve mechanical properties such as hardness. The definition of a hypermaterial is as described above. Au-X-RE-based hypermaterials have forms such as quasicrystals and approximate crystals, and strengthen the Au alloy by using these structural factors. Quasicrystals are compounds with long-range ordered structures (a typical example is five-fold symmetry), and have a structure that differs from the translational symmetry of general crystalline compounds. Approximate crystals are crystalline compounds that have a complex structure derived from quasicrystals and partially share a structure similar to quasicrystals, and refer to compounds with properties similar to those of the quasicrystals.

[0019] A well-known form of Au-X-RE system hypermaterial is the Tsai-type approximant crystal. Au-X-RE system hypermaterials that are Tsai-type approximant crystals have a nested structure consisting of multiple concentric atomic polyhedra. Each atomic polyhedron is composed of multiple Au atoms and X atoms, and the number of atoms increases with each level, creating a complex, multidimensional periodic structure. This structure allows Au-X-RE system hypermaterials to have high hardness despite having Au as the main component.

[0020] The Au-X-RE-based hypermaterial that constitutes the HM phase is represented by the composition formula shown in Chemical Formula 1 above. In this composition formula, X represents at least one atom selected from the group consisting of Al, Ga, In, Si, Ge, and Sn. X may be composed of only one of the above atoms, or may be composed of two or more atoms. An example of X containing two types of atoms is when X is composed of Al and Ga. Meanwhile, RE in the composition formula represents a rare earth element. Examples of rare earth elements include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0021] Among these listed atoms, preferred X atoms are Al, Ga, Si, Ge, and Sn, more preferred are Al, Ga, Si, and Ge, and even more preferred are Si and Ge. HM phases with Si and Ge as X have particularly high hardness. Therefore, the hardness of the Au alloy can be maintained while increasing the Au purity with a small amount of added elements. When at least one of Si and Ge is selected as the X atom, the preferred RE atoms are La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Yb. From the viewpoint of obtaining a high-hardness Au alloy while increasing the Au purity, it is more preferable to use rare earth elements with small atomic numbers, and it is more preferable to use La, Ce, Pr, Nd, and Sm as the RE atoms.

[0022] The atomic % contents of X and RE in the Au-X-RE hypermaterial constituting the HM phase are represented by a and b, respectively, in the above composition formula. Furthermore, a and b are in the ranges of 5≦a≦40 and 11≦b≦18. By mixing an HM phase of this composition with an Au alloy, it is possible to obtain an Au alloy with high hardness while increasing the purity of gold. Furthermore, a is preferably in the range of 8≦a≦21, and more preferably in the range of 9≦a≦14. b is preferably in the range of 12≦b≦15, and more preferably in the range of 12≦b≦14.

[0023] Furthermore, the ratio of a to b (a:b) is more preferably 8 to 9.5: 7. Furthermore, when X is Si, which is preferred above, the ratio of a to b (a:b) is preferably 8 to 8.5: 7. When X is Ge, which is preferred above, the ratio of a to b (a:b) is preferably 9 to 9.5:7.

[0024] The structure of the Au-X-RE-based hypermaterial described above can be identified by X-ray diffraction (XRD) measurement. The X-ray source used in the XRD measurement is not particularly limited, but CuKα radiation is used. Furthermore, when analyzing the diffraction profile obtained by XRD measurement, by referring to known diffraction peaks resulting from the structures of quasicrystals and approximant crystals, it can be confirmed that the Au alloy according to the present invention contains an HM phase consisting of an Au-X-RE-based hypermaterial.

[0025] Furthermore, for composition analysis of the HM phase, i.e., identification of a and b in the above composition formula, the content of each constituent element can be measured by electron microprobe analysis (EPMA) in combination with a scanning electron microscope (SEM) or a transmission electron microscope (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray fluorescence analysis (XRF), or the like.

[0026] I-2 Au-rich phase The Au-rich phase is a metal phase containing Au as the main component. The Au-rich phase may contain 100 atomic % Au, or may contain other elements. The Au content in the Au-rich phase is preferably 98 atomic % or more. Constituent elements of the Au-rich phase other than Au include the above-mentioned X and RE. Furthermore, the Au-rich phase may contain unavoidable impurities derived from raw materials or manufacturing equipment in the manufacturing process of the Au alloy according to the present invention. Examples of such unavoidable impurities include C, O, etc.

[0027] As will be described later, in the Au alloy according to the present invention, the size of the Au-rich phase, that is, the average equivalent circle diameter, is specified. Because the Au-rich phase is not responsible for the strength and hardness of the Au alloy, the effect of improving hardness by the HM phase is supported by miniaturizing its size and distributing it.

[0028] For the identification and composition analysis of the Au-rich phase, similar to the HM phase, XRD, EDX in combination with SEM or TEM, EPMA, and XRF can be applied.

[0029] I-3 Material structure and overall composition of the Au alloy according to the present invention As described above, the Au alloy according to the present invention achieves higher hardness than Au alloys containing conventional Au-X-RE-based hypermaterials by adjusting the material structure. The Au alloy according to the present invention is characterized in that the material structure in an arbitrary cross section exhibits a structure in which an Au-rich phase having an average equivalent circle diameter of 1.5 μm or less is distributed. More specifically, the Au alloy according to the present invention has a material structure in which an HM phase serves as a matrix and the fine Au-rich phase described above is distributed within the matrix.

[0030] As will be explained in detail in the embodiments below, Au alloys produced by conventional melting and casting exhibit a material structure in which an amorphous HM phase and an Au-rich phase are mixed, with the Au-rich phase being relatively coarse. It is presumed that this non-uniform material structure results in an insufficient effect of the HM on improving the hardness of the entire Au alloy. In the Au alloy according to the present invention, the distribution of the refined Au-rich phase increases the uniformity of the material structure, allowing the hardening effect of the HM phase, which serves as the matrix, to be effectively exerted.

[0031] The shape of the Au-rich phase refined as described above is not particularly limited. The Au-rich phase may be circular in cross section, but may also be elliptical or irregular. The circle-equivalent diameter is the diameter of a circle having an area equal to the area of ​​the Au-rich phase in an arbitrary cross section. In the present invention, the average circle-equivalent diameter of the Au-rich phase distributed in the material structure is 1.5 μm or less. Au alloys containing Au-rich phases with an average circle-equivalent diameter exceeding 1.5 μm cannot obtain sufficient hardness. Furthermore, the average circle-equivalent diameter of the Au-rich phase is preferably 0.5 μm or more. This is because it is difficult to produce Au-rich phases finer than this. In the Au alloy of the present invention, the number of observed Au phases increases due to the refinement of the Au-rich phase. In the present invention, the number of observed Au phases is 40,000 / mm in an arbitrary observation area. 2 More than 600000 pieces / mm 2 The following Au-rich phases are distributed:

[0032] General methods can be applied to the observation of the material structure and measurement of the circle-equivalent diameter of the Au-rich phase in an arbitrary cross section of the Au alloy according to the present invention. The material structure can be observed by cutting the Au alloy at an arbitrary position, mirror-polishing it, and, if necessary, performing etching or ion milling, followed by observation using an SEM or TEM. In the image observed at this time, the Au-rich phase and the HM phase can be identified by their different color tones (the Au-rich phase is usually observed as a lighter color). The circle-equivalent diameter of the Au-rich phase can be calculated by measuring the area (cross-sectional area) of the Au-rich phase identified by the above observation. Furthermore, these measurements can be performed using image processing software as appropriate for image processing and calculation.

[0033] The Au alloy according to the present invention, which is composed of the Au-X-RE-based hypermaterial phase and Au-rich phase described above, preferably contains 80 mass% or more of Au in the overall alloy composition. This is to increase the Au quality of the Au alloy and ensure added value of the alloy. Furthermore, increasing the Au content of the Au alloy means reducing the contents of X and RE required to form the Au-X-RE-based hypermaterial phase. In other words, if the Au content of the Au alloy is excessively high, the content of the Au-X-RE-based hypermaterial phase, which has a hardness-improving effect, will decrease. From this perspective, the upper limit of the Au content of the overall Au alloy according to the present invention is preferably 95 mass%.

[0034] The Au content of the entire Au alloy according to the present invention can be measured by the composition analysis methods for the HM phase and the Au-rich phase described above. Furthermore, the Au content of the entire Au alloy can be easily measured by inductively coupled plasma (ICP) analysis.

[0035] II. Method for producing Au alloy according to the present invention Next, a method for producing an Au alloy according to the present invention will be described. As outlined above, in the present invention, an Au alloy is produced by combining a melting and solidification process with powder metallurgy to appropriately adjust the material structure of the Au alloy, including the Au-X-RE-based hypermaterial. The powder sintering method is a process for producing a bulk Au alloy by molding and heat-sintering an Au alloy powder having the same composition as the Au alloy to be produced. Rapidly solidified Au alloy powder can be produced by producing fine powder from the molten Au alloy. Rapidly solidified Au alloys from a molten state promote the formation of approximant crystals of the Au-X-RE-based hypermaterial and become Au alloy powders in which both the HM phase and the Au-rich phase are refined. Then, by sintering this Au alloy powder, an Au alloy having a material structure in which the fine Au-rich phase described above is distributed can be produced. That is, the method for producing an Au alloy according to the present invention includes the steps of melting Au, X, and RE in a non-oxidizing atmosphere to produce a molten Au alloy, rapidly solidifying the molten Au alloy to produce an Au alloy powder, and compressing and sintering the Au alloy powder.

[0036] In the step of producing a molten Au alloy in the method for producing an Au alloy according to the present invention, the raw materials Au, X, and RE are melted in a non-oxidizing atmosphere. The molten Au alloy can be produced by mixing and melting the simple substances Au, X, and RE. The raw materials Au, X, and RE are preferably each highly pure (preferably 99% by weight or more, more preferably 99.9% by weight or more, and particularly preferably 99.99% by weight or more). Alternatively, an Au alloy already alloyed with the same composition may be remelted. Furthermore, an Au alloy containing either X or RE (Au-X alloy) may be used. The raw materials for producing the molten Au alloy may have the same composition as the Au alloy to be produced (a corresponding to the X content, and b corresponding to the RE content).

[0037] The above raw materials are heated in a non-oxidizing atmosphere to suppress oxidation when melting them to produce a molten Au alloy. An inert atmosphere is preferable. The inert atmosphere is an inert gas atmosphere such as N2, Ar, or He. The melting method (heat source) for melting the raw materials can be arc melting, plasma melting, or high-frequency melting, but arc melting, which is used in a reduced pressure or vacuum atmosphere, is preferable. To produce a molten Au alloy, the object to be heated must be heated to 1500°C or higher. The current and voltage conditions for the above-mentioned arc melting can be adjusted so that heating at the above temperature is possible.

[0038] In the process of producing Au alloy powder by rapidly solidifying the Au alloy melt, known methods can be used to produce the powder. Methods for producing powder from the melt include atomization and melt spinning (single roll method). The atomization method is preferably used. The atomization method is classified into water atomization and gas atomization depending on the medium sprayed onto the molten metal, but in the present invention, gas atomization is preferred to suppress oxidation during spraying.

[0039] In the atomization method, water or gas is sprayed onto the falling molten gold alloy to generate and recover the gold alloy. The elements used in this process (molten gold alloy, spraying equipment, etc.) are preferably placed in a non-oxidizing atmosphere, particularly an inert atmosphere. In gas atomization, the gas used for spraying is preferably an inert gas.

[0040] The Au alloy powder produced in this process preferably has an average particle size of 10 μm to 100 μm. In the atomization method described above, the particle size of the produced powder can be adjusted by the atmospheric temperature, the flow rate of the molten Au alloy, the temperature and flow rate (pressure) of the spraying medium, etc., and it is preferable to adjust the particle size to fall within the above particle size range.

[0041] The Au alloy according to the present invention is produced by sintering the Au alloy powder produced as described above. In the sintering step of the present invention, the Au alloy powder can be sintered by a known sintering method such as hot pressing (HP), spark plasma sintering (SPS), or hot isostatic pressing (HIP), with SPS being preferred. Regarding the sintering conditions for the Au alloy powder, the sintering temperature varies depending on the composition of the Au alloy powder, but is preferably 500°C to 700°C. Furthermore, the pressure is preferably 15 MPa to 25 MPa, and sintering is preferably performed until the relative density of the Au alloy reaches 95% or more of the density estimated from the composition.

[0042] There are no limitations on the shape and dimensions of the sintering mold used in the sintering process. Therefore, by optimizing the sintering mold, the present invention makes it possible to produce an Au alloy with a near-net shape that is close to the shape of the final product. In other words, the Au alloy production method of the present invention can also contribute to optimizing the processability and formability of the Au alloy.

[0043] The Au alloy according to the present invention is produced by sintering the Au alloy powder as described above. After that, cleaning and appropriate secondary and tertiary processing can be carried out as necessary. [Effects of the Invention]

[0044] As described above, the Au alloy according to the present invention is an Au-X-RE type hypermaterial (composition formula: Au 100-(a+b) X a RE b The presence of the Au-rich phase and the distribution of fine Au-rich phases result in a hardness greater than that achieved by conventional techniques. The method for producing an Au alloy according to the present invention realizes the above-mentioned favorable material structure by applying a powder sintering method. Furthermore, the method for producing an Au alloy according to the present invention can produce an Au alloy with a near-net shape similar to the shape of the product, and also takes into consideration processability. [Brief explanation of the drawings]

[0045] [Figure 1] 3 is an SEM image showing the cross-sectional material structure of the Au alloys of Example 1 and Comparative Example 1 produced in the first embodiment. [Figure 2]10 is a graph showing the Au content and Vickers hardness of Au alloys of various compositions produced in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0046] First embodiment The following describes an embodiment of the present invention. In this embodiment, the Au-X-RE hypermaterial (Au 100-(a+b) X a RE b We fabricated several types of Au alloys using Ge and Si as X and La and Gd as RE. After observing the material structure, we measured and evaluated their hardness.

[0047] [Preparation of molten Au alloy] As the Au raw material, a commercially available Au plate with a purity of 99.99% was prepared; as the Ge and Si raw materials for X, commercially available flake Ge and Si with a purity of 99.99% were prepared; and as the RE, La and Gd, commercially available block La and Gd with a purity of 99.9% were prepared. Each raw material was cut to an appropriate size, washed, and then weighed and mixed. This mixed raw material was then placed on a water-cooled copper hearth and melted in a miniature vacuum arc melting apparatus (NEV-AD03, manufactured by Nisshin Giken Co., Ltd.). The mixed raw material was melted by filling the apparatus with 3 × 10 -3 After creating a vacuum of 0.1 Pa, Ar was introduced and an arc was applied under an Ar atmosphere with a current value adjusted to approximately 200 A to 350 A. During melting, the molten Au alloy was turned over twice using a turning rod to make it uniform.

[0048] [Production of Au alloy powder] Au alloy powder was produced from the Au alloy melt prepared above by gas atomization. The gas atomization conditions were Ar gas as the atomizing gas, atomization temperature set in the range of 1000-1200°C, and atomization gas pressure set in the range of 2-3 MPa. This resulted in Au alloy powder with a particle size of 100 μm or less.

[0049] [Sintering of Au alloy powder] The Au alloy powder produced by the gas atomization method was sintered by spark plasma sintering (SPS) to produce an Au alloy. In this sintering process, a graphite mold (φ30 mm) was used as the mold, and a spark plasma sintering apparatus (apparatus name: Plasman, manufactured by SS Alloy Co., Ltd.) was used. The sintering conditions were an Ar gas atmosphere, a sintering temperature of 500°C to 700°C, and a pressure of 20 MPa. The sintering process was carried out with a heating rate of 50°C / min up to the sintering temperature. After the sintering temperature was reached, pressure was applied at the pressure while monitoring the amount of displacement, and pressure was applied until no increase in the amount of displacement was observed. After sintering under the above conditions, the sintered body was removed and washed to obtain the Au alloy of each example.

[0050] Comparative Example To compare with the Au alloys of each example produced by powder sintering, Au alloys of the same composition as those of each example were produced by conventional melting and casting. These comparative examples were produced by casting the molten Au alloys obtained by arc melting in each example.

[0051] [Observation of material structure and composition analysis of each phase] The material structure of the various Au alloys produced in the examples and comparative examples was observed. Each sample was cut, embedded in resin, and mirror-polished. After that, an observation surface was created by ion milling (acceleration voltage 3 kV, discharge voltage 1.5 kV, discharge time 1 minute), and SEM observation was performed. The size of the Au-rich phase was confirmed based on the SEM images obtained for each example and comparative example. In this embodiment, the SEM images were binarized, and the circle-equivalent diameter of the Au-rich phase was measured using image processing software (product name: ImageJ), and the average value was taken as the average circle-equivalent diameter.

[0052] FIG. 1 shows an example of the results of observing the structure of the Au alloy produced in this embodiment. This SEM image is the same as that of Example 1 (Au 78.99 Si 9.80 Gd 11.21) The results of EDS analysis performed simultaneously with SEM observation show that the light gray areas represent the Au-rich phase, and the darker gray areas represent the HM phase. Figure 1 also shows binarized photographs of each SEM image. As can be seen from Figure 1, the Au alloys of Examples 1 to 3 produced through powder sintering exhibit a material structure in which fine granular or island-like Au-rich phases are distributed and surrounded by the HM phase. In contrast to the material structure of this example, the material structure of the Au alloy produced by melt casting in the comparative example has a coarse, blocky Au-rich phase. Table 1 shows the average equivalent circle diameter of the Au-rich phase obtained from the material structure observation for the Au alloys of the examples and comparative examples produced in this embodiment. Table 1 also shows the compositions of the Au-rich phase and the Au-X-RE-based hypermaterial phase obtained by EDS analysis.

[0053] [Table 1]

[0054] From Table 1, it was confirmed that the Au-rich phase in the Au alloy of each example had an average equivalent circle diameter of 1.5 μm or less, and was clearly finer than the Au-rich phase in the Au alloy of the comparative example. Furthermore, referring to the results of EDS analysis, it was confirmed that the composition (a, b) of the Au-X-RE hypermaterial phase in the Au alloy of each example closely approximates the concentrations of X and RE in the overall composition of the alloy. Furthermore, it was found that the Au-rich phase in this embodiment is an Au alloy phase containing less than 2 atomic % of X and RE in total.

[0055] [Hardness measurement] Next, the hardness of the Au alloys (Examples 1 to 7 and Comparative Examples 1 to 7) produced in this embodiment was measured. In this embodiment, a microhardness tester (HMV-G21, manufactured by Shimadzu Corporation) was used to measure the micro-Vickers hardness of each Au alloy at a measurement load of 0.3 kgf. The measurement results are shown in Table 2.

[0056] [Table 2]

[0057] From Table 2, it was confirmed that the Au alloys of Examples 1 to 7 had higher hardness than the Au alloys of the same composition of Comparative Examples 1 to 7. The Au alloys of each Example all had a Vickers hardness exceeding 300 Hv, and it was confirmed that adjusting the material structure by miniaturizing the Au-rich phase through optimization of the manufacturing process is effective in improving hardness.

[0058] Second embodiment In this embodiment, Au-X-RE type hyper material (Au 100-(a+b) X a RE b Au alloys having multiple compositions were produced by applying Si and Ge as X and La and Gd as RE in the above formula (1). Specifically, the mixed amount (mass) of Au was 88 g (Group I), 92 g (Group II), and 95 g (Group III), and the amount of X and RE added was adjusted for each group to produce 12 types of Au alloys (36 types in total). The compositions (mass %) of the Au alloys produced in this embodiment are shown in Table 3.

[0059] [Table 3]

[0060] The manufacturing process of the Au alloy was the same as that of the first embodiment, and the raw materials were mixed and arc-melted to produce the molten Au alloy, which was then water-atomized to produce Au alloy powder (particle size 100 μm or less), which was then sintered by SPS to produce the Au alloy.The Vickers hardness of each Au alloy was measured in the same manner as in the first embodiment.

[0061] The results of measuring the Vickers hardness of the Au alloys produced in this embodiment are shown in Figure 2. As can be seen from Figure 2, most of the 36 types of Au alloys produced in this embodiment were in the range of 250 Hv to 350 Hv, with some reaching 400 Hv. It was confirmed that the Au alloys produced in this embodiment achieved high hardness despite having an Au content of 80 mass% or more. When the material structure of the Au alloys produced in this embodiment was observed, the average equivalent circle diameter of the Au-rich phase was 1.5 µm or less in all cases.

[0062] As an example, the results of composition analysis of the HM phase in the Au alloys produced in this embodiment are shown in Table 4 for Au alloys Nos. 4 and 8 in Group I, Nos. 7 and 12 in Group II, and Nos. 2 and 10 in Group III.

[0063] [Table 4]

[0064] From the results of the investigations in the first and second embodiments, it was confirmed that the material structure of an Au alloy containing an Au-X-RE-based hypermaterial phase can be made high in hardness by refining the Au-rich phase. This material structure differs from Au alloys produced by conventional melting and casting. It was also confirmed that such a suitable material structure can be formed by a powder sintering process of Au alloy powder. [Industrial Applicability]

[0065] As described above, the Au alloy of the present invention contains an HM phase consisting of a high-hardness Au-X-RE-based hypermaterial, and achieves high hardness by improving the material structure to distribute a fine Au-rich phase. The Au alloy of the present invention has value as an alloy containing high-purity Au, while also exhibiting hardness greater than that of conventional technologies. The Au alloy of the present invention is useful not only for applications such as jewelry and ornaments, but also as an electrode and wiring material for electrical and electronic devices. In particular, it is expected to be applied to contact materials for various motors, switches, and other devices, where both electrical conductivity and hardness are important.

Claims

1. A high-hardness Au alloy including an Au-rich phase and an HM phase made of an Au-X-RE-based hypermaterial represented by the following formula: A high-hardness Au alloy characterized in that the Au-rich phase having an average equivalent circle diameter of 1.5 μm or less is distributed in the material structure in an arbitrary cross section. 【Chemistry 1】 In the above formula, X is at least one atom selected from the group consisting of Al, Ga, In, Si, Ge, and Sn, and RE is a rare earth element. Furthermore, a is the content of X in atomic %, and is 5≦a≦40, and b is the content of RE in atomic %, and is 11≦b≦18.

2. 2. The high-hardness Au alloy according to claim 1, wherein RE is at least one of La, Gd, Sc, Y, Ce, Pr, Nd, Sm, Eu, Tb, Dy, and Yb.

3. 3. The high-hardness Au alloy according to claim 1, wherein the Au content in the overall composition of the Au alloy is 80% by weight or more and 95% by weight or less.

4. 3. The high-hardness Au alloy according to claim 1, wherein the Au-rich phase contains 98 atomic % or more of Au.

5. 3. A method for producing a high-hardness Au alloy according to claim 1 or 2, a step of melting Au, X, and RE in a non-oxidizing atmosphere to produce a molten Au alloy; a step of rapidly solidifying the molten Au alloy to produce an Au alloy powder; and pressing and sintering the Au alloy powder.

6. 6. The method for producing a high-hardness Au alloy according to claim 5, wherein the step of producing the Au alloy powder is an atomization method.

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