High-hardness au-ni-pd-pt-based precious metal alloy

Abstract

The present invention relates to a high-hardness precious metal alloy that is useful for a probe pin or the like and is composed of an Au-Ni-Pd-Pt-based alloy having favorable machinability. The high-hardness precious metal alloy composed of an Au-Ni-Pd-Pt-based alloy according to the present invention contains 2 to 55 atom% of Au, 3 to 62.5 atom% of Ni, 0.15 to 40 atom% of Pd, and 7.5 to 72.5 atom% of Pt, and further contains 0.001 to 0.5 atom% of Bi. The precious metal alloy according to the present invention achieves high hardness through a modulated structure resulting from spinodal decomposition and / or an ordered phase resulting from ordering. Then, in the present invention, machinability is improved without impairing the high hardness by applying Bi as an essential additive element.

Description

High-hardness Au-Ni-Pd-Pt series precious metal alloy

[0001] The present invention relates to a high-hardness precious metal alloy containing Pt, Au, and Pd, which are precious metals, as essential constituent elements, and having improved machinability, namely, an Au-Ni-Pd-Pt series precious metal alloy. More specifically, the present invention relates to an Au-Ni-Pd-Pt series precious metal alloy strengthened by spinodal decomposition and / or regularization, which has high hardness and can efficiently perform cutting processing into a desired shape and dimension.

[0002] Precious metals such as Pt (platinum) and Au (gold) are metals that are excellent in chemical stability and corrosion resistance and also have good electrical properties such as electrical conductivity. Therefore, precious metals and their alloys are utilized in various fields such as the electric and electronic fields and the medical field. Examples of the use of precious metal alloys in the electric and electronic fields include probe pins used for inspections in the pre-process and post-process of semiconductors, electric contacts (sliding contacts and opening / closing contacts) such as motor brushes, relays, and switches. The use in the medical field has been attracting attention in recent years, and precious metal alloys are used as constituent materials for various medical devices. Examples of such medical devices include various forms of medical devices such as embolization coils, embolization clips, guide wires, stents, and catheters. Since these medical devices directly contact the human body and are implanted inside the human body, biocompatibility and chemical stability are required. In addition, medical devices are also required to have X-ray visibility in consideration of their use in surgery and diagnosis using X-rays. Precious metal alloys also have good biocompatibility and X-ray visibility.

[0003] For precious metal alloys used in the above various applications, improvement in mechanical properties such as hardness and strength is required. For example, probe pins are required to have wear resistance because they are repeatedly contacted with a mating material for a long period of time. In particular, in order to cope with the high integration of various devices and the high performance of motors in recent years, the development of probe pins with higher hardness is necessary. Regarding medical devices, for devices that move and are implanted inside pulsating and beating blood vessels, such as guide wires and embolization coils, mechanical properties such as strength and springiness are required so that their operation is not impaired.

[0004] Well-known methods for improving the strength and hardness of metallic materials include work hardening (dislocation strengthening), solid solution strengthening, and precipitation strengthening (dispersion strengthening), which are applied individually or in combination. Examples of hardening improvements for precious metal alloys applied to probe pins, contact materials, medical equipment, etc., include the Pt-Ni alloy described in Patent Document 1 and the Pt-W alloy described in Patent Document 2, which achieve increased hardness through work hardening with a high final processing rate, in addition to solid solution strengthening by alloying Pt with Ni, W, etc. Furthermore, Patent Document 3 (Ag-Pd-Cu alloy) and Patent Document 4 (Pt-Cr-Ni alloy) obtain high-hardness precious metal alloys through work hardening with an adjusted processing rate, in addition to solid solution strengthening and precipitation hardening using additive elements.

[0005] On the other hand, the applicant has developed a noble metal alloy with high hardness achieved by spinodal decomposition and / or ordering, as a material strengthening method different from the well-known techniques described above (Patent Document 5).

[0006] Spinodal decomposition is a form of phase separation in material microstructure, a phenomenon in which decomposition progresses due to a continuous increase in concentration fluctuations. The material microstructure generated by this spinodal decomposition caused by concentration fluctuations exhibits a very fine periodic structure of several nanometers to several tens of nanometers, called a modulated microstructure. In the modulated microstructure that appears in spinodal decomposition, the concentration of solute atoms in the crystal fluctuates periodically as a function of location, and the lattice constant also changes periodically. This generates a periodic internal stress field on the slip plane, which interacts with dislocations. The strengthening mechanism by spinodal decomposition is similar to precipitation strengthening by nucleation and growth, but differs in that it uses the internal stress field generated by concentration modulation, rather than precipitates, as an obstacle to dislocation movement.

[0007] Furthermore, ordering is a phenomenon in which the arrangement of the constituent elements of an alloy becomes orderly, thereby generating a ordered phase with a predetermined structure. The ordered phase generated by ordering contributes to the hardness of the alloy through the following factors: (i) the Burgers vector of dislocations becomes larger, (ii) inverse phase boundaries may be generated within the ordered phase, and (iii) the volume change associated with ordering distorts the lattice inside and outside the ordered phase, thereby suppressing dislocation motion. Ordering may occur in conjunction with the spinodal decomposition described above, or it may occur on its own.

[0008] Spinodal decomposition and ordering are phenomena that can result in a high increase in hardness due to unique material structures such as modulated and ordered phases. The well-known material strengthening methods described above, such as solid solution strengthening and precipitation strengthening, have limitations in the extent of hardness increase. Spinodal decomposition and ordering offer the potential for higher hardening compared to these conventional strengthening methods. Furthermore, while work hardening can increase hardness with increasing degree of processing, there are concerns about material embrittlement associated with hardening. Spinodal decomposition and ordering are considered useful as a means of improving hardness without causing material embrittlement.

[0009] Furthermore, the precious metal alloy by the applicant of this application (Patent Document 5) is composed of an Au-Ni-Pd-Pt precious metal alloy, which is a quaternary or higher alloy, in order to effectively exhibit strengthening effects through spinodal decomposition and ordering. Conventionally, binary alloys such as Pt-Au alloys and Pt-Ni alloys have been known as precious metal alloys that can exhibit spinodal decomposition and ordering, but their hardening amounts are not particularly high. The spinodal decomposition and ordering in these binary alloys do not surpass conventional strengthening methods such as work hardening and precipitation strengthening. The Au-Ni-Pd-Pt precious metal alloy by the applicant of this application is diversified compared to the aforementioned binary alloys, and by optimizing the composition range of each constituent element, it is possible to effectively exhibit strengthening effects through spinodal decomposition and / or ordering. Furthermore, spinodal decomposition and ordering in this Au-Ni-Pd-Pt precious metal alloy can be achieved by converting an alloy of the appropriate composition into a supersaturated solid solution containing a recrystallized structure through solution treatment, and then by subsequent aging treatment, thereby obtaining the desired hardness.

[0010] Japanese Patent Publication No. 2005-233967, Specification of Japanese Patent No. 6997354, Japanese Patent Publication No. 2012-242184, Specification of Japanese Patent No. 6372952, International Publication WO2023 / 063156

[0011] When using precious metal alloys for various applications such as probe pins and medical equipment, it is necessary to process the precious metal alloy ingots to the dimensions and shapes of each product. Here, the processability of the Au-Ni-Pd-Pt precious metal alloy described above by the applicant has been largely resolved regarding plastic deformation processes such as rolling and wire drawing. Specifically, the Au-Ni-Pd-Pt precious metal alloy described by the applicant changes its material structure depending on the heat treatment, resulting in different plastic workability. This precious metal alloy exhibits a two-phase separation structure that is most ductile and has good plastic workability when heat-treated at around 700 to 900°C. Furthermore, this precious metal alloy also has good processability in the cast structure (two-phase dendritic structure) after melting and casting. Therefore, when processing Au-Ni-Pd-Pt precious metal alloys into probe pins or the like, primary processing such as rolling and wire drawing is performed with a relatively high total processing rate while maintaining the aforementioned good machinability to produce raw materials such as wires.

[0012] Then, the rough material obtained from the primary processing can be subjected to secondary processing such as finish drawing, bending, coiling, skin passing, and straightening after solution treatment to shape it into the product shape or a shape and dimensions close to it. After that, aging treatment can be performed to impart the hardness required for the product. In this way, by applying a processing method suitable for the material structure of each heat treatment, high-hardness precious metal alloys of the desired shape and dimensions can be obtained.

[0013] However, the inventors have confirmed from their studies on the above processing processes for Au-Ni-Pd-Pt precious metal alloys that there is a need to improve the machinability (machinability) of these alloys. Machining is a processing step that can be performed on all of the microstructures of the above-mentioned precious metal alloys. For example, machining may be performed to adjust the shape or dimensions of the ingot surface before primary processing such as rolling. In this case, it is preferable to perform the machining when the precious metal alloy is in a cast microstructure or a two-phase separated microstructure, from the viewpoint of hardness and heat treatment costs. Machining is also often performed as a finishing process after secondary processing. In such cases, the precious metal alloy after solution treatment may be the target of machining. Furthermore, depending on the application, machining may be necessary even for precious metal alloys after aging treatment, from the viewpoint of dimensional changes due to heat treatment, etc. According to the inventors, there is room for improvement in machinability of Au-Ni-Pd-Pt precious metal alloys at each of these stages and material microstructures.

[0014] Improving machinability is crucial for obtaining shapes and dimensional accuracy that are difficult to achieve with plastic deformation when working with high-hardness precious metal alloys. For example, when using high-hardness precious metal alloys for probe pins, medical devices, etc., it is desirable that machinability be improved. Machinability refers to chip breaking ability, cutting resistance, surface roughness, tool wear, etc., but in this invention, machinability refers to chip breaking ability. It is preferable that the chips generated during cutting are broken into small pieces, as long pieces and lengths of chips are difficult to discharge from the machining area and tend to get entangled in the cutting tool. Such long chips reduce machining efficiency in order to remove them, and can also cause wear of the cutting tool, damage to the workpiece, a decrease in dimensional accuracy, and the generation of burrs, so improvement in chip breaking ability is required.

[0015] The present invention was made against the background described above, and provides a noble metal alloy made of Au-Ni-Pd-Pt type noble metal alloy, which undergoes aging treatment to undergo spinodal decomposition and / or ordering to achieve high hardness, and which has improved machinability.

[0016] The above-mentioned Au-Ni-Pd-Pt precious metal alloy (Patent Document 5) is an alloy that has not been studied much in terms of actively utilizing the strengthening effect by spinodal decomposition and / or ordering in precious metal alloys. Therefore, there are still many unknown areas regarding the properties and problems of Au-Ni-Pd-Pt precious metal alloys as high-hardness precious metal alloys. The lack of machinability in this alloy system is among these issues. Accordingly, the present inventors decided to investigate additive elements that have the effect of improving the machinability of Au-Ni-Pd-Pt precious metal alloys.

[0017] In this study, it is important to note that Au-Ni-Pd-Pt precious metal alloys require the occurrence of unique phase changes, namely spinodal decomposition and ordering, and the application of additive elements that ignore this point is inappropriate. The inventors conducted diligent research and found that Bi (bismuth) is an additive element that can improve machinability in Au-Ni-Pd-Pt precious metal alloys while ensuring hardness and strength that meet practical requirements, without hindering the occurrence of spinodal decomposition and ordering. The inventors then conceived the present invention, based on the finding that the addition of a minute amount of Bi to Au-Ni-Pd-Pt precious metal alloys can satisfy the above-mentioned prerequisites.

[0018] In other words, the present invention is an Au-Ni-Pd-Pt type precious metal alloy comprising 2 atomic% to 55 atomic% of Au, 3 atomic% to 62.5 atomic% of Ni, 0.15 atomic% to 40 atomic% of Pd, and 7.5 atomic% to 72.5 atomic% of Pt, and further comprising 0.001 atomic% to 0.5 atomic% of Bi.

[0019] Furthermore, the noble metal alloy according to the present invention contains Au, Ni, Pd, Pt, and Bi as essential constituent elements, while also being permitted to contain several additive elements. Specifically, the noble metal alloy according to the present invention may contain 0.003 atomic% to 8 atomic% of B. In addition, the noble metal alloy according to the present invention may also contain 0.1 atomic% to 27.5 atomic% of Cu.

[0020] Furthermore, the Au-Ni-Pd-Pt noble metal alloy according to the present invention may contain, as other optional additive elements, 0.15 atomic% to 5 atomic% of metal element α and / or 0.05 atomic% to 5 atomic% of metal element β. Here, metal element α is at least one of In, Sn, and Sb. Also, metal element β is at least one of Al, Ti, Zr, and Hf.

[0021] As described above, the Au-Ni-Pd-Pt noble metal alloy according to the present invention contains a modulated structure and / or an ordered phase due to spinodal decomposition when subjected to aging treatment after solution treatment.

[0022] As described above, the Au-Ni-Pd-Pt precious metal alloy according to the present invention achieves high hardness through spinodal decomposition and / or ordering. This highly hardened Au-Ni-Pd-Pt precious metal alloy has a Vickers hardness of 500 Hv or higher.

[0023] As described above, the Au-Ni-Pd-Pt precious metal alloy according to the present invention has improved machinability in the process of processing it to desired dimensions and shapes. According to the present invention, while maintaining the alloy properties of becoming highly hard after aging treatment, it is possible to ensure machinability to shapes according to various applications. Furthermore, the Au-Ni-Pd-Pt precious metal alloy according to the present invention is hardened by modulated structure due to spinodal decomposition and / or ordered phase due to ordering, achieved by aging treatment after solution treatment.

[0024] This figure shows the XRD diffraction pattern of the noble metal alloy (Au10-Ni37.48-Pd15-Pt37.47-Bi0.05) of Example 16 of the first embodiment.

[0025] Embodiments of the present invention will be described below. As described above, the noble metal alloy according to the present invention is an Au-Ni-Pd-Pt type noble metal alloy in which Bi is added as an essential additive element to the Au-Ni-Pd-Pt alloy. The composition of the noble metal alloy according to the present invention and its manufacturing method will be described below.

[0026] (A) Composition of the noble metal alloy according to the present invention (A-1) Constituent elements and composition range of the noble metal alloy according to the present invention The noble metal alloy according to the present invention contains Au, Ni, Pd, and Pt as essential constituent elements, and also contains Bi as an essential additive element. The following description clarifies the essential constituent elements and their composition ranges. In addition, various optional additive elements that are permitted to be added to the noble metal alloy according to the present invention and their addition concentrations will also be described.

[0027] (1) Essential constituent elements (Au, Ni, Pd, Pt) The precious metal alloy according to the present invention, by containing the above essential elements, exhibits at least one of spinodal decomposition and ordering, and has a hardness equal to or greater than that of conventional precious metal alloys strengthened by general strengthening mechanisms (solid solution strengthening, precipitation strengthening, work hardening).

[0028] As explained in Patent Document 5, which discloses an Au-Ni-Pd-Pt noble metal alloy by the present applicant, periodic concentration fluctuations occur in the modulated structure formed by spinodal decomposition, contributing to increased hardness by forming an internal stress field around it. The resistance force to dislocation motion in this periodic internal stress field (critical shear stress) is expressed by the following equation, and lattice strain (ε), elastic modulus (Y), and concentration modulation amplitude (A) are considered to be the dominant factors (for detailed references, see, for example, "Introduction to Dislocation Theory" by Masaharu Kato (published August 1999, Shokabo)).

[0029]

[0030] Furthermore, in light of the above formula, it is preferable that the constituent elements of a noble metal alloy in which material strengthening by spinodal decomposition is effectively exhibited meet three requirements: (1) the constituent elements include metals with high elastic moduli, (2) the mixing enthalpy between constituent elements is high and there is a strong tendency for phase separation in the low-temperature range, and (3) the difference in lattice constants between constituent elements is large and the lattice strain (ε) is also large.

[0031] Furthermore, regarding the manifestation of ordering, Pt and Ni, and Au and Pd are combinations of metals that can contribute to the formation of ordered phases through ordering.

[0032] The essential constituent elements of the noble metal alloy according to the present invention, Au, Ni, Pd, and Pt, are combinations of metals that can satisfy these requirements, and by setting them within the composition range described later, the strengthening ability by spinodal decomposition is effectively utilized. The specific functions and composition ranges of these essential constituent elements are explained below.

[0033] Au is an essential element for inducing spinodal decomposition in the alloy system of the present invention. Spinodal decomposition does not occur if the Au concentration is too low or too high; there is a necessary range of Au concentration for its occurrence. If the Au concentration is outside the optimal range, normal nucleation and growth are more likely to occur, making it impossible to obtain a desirable increase in hardness. Furthermore, Au is a metal that can form an ordered phase with Pd, and it also has the effect of contributing to the increase in hardness through ordering.

[0034] The Au concentration in the Au-Ni-Pd-Pt noble metal alloy according to the present invention is 2 atomic percent or more and 55 atomic percent or less. The Au concentration is preferably 4 atomic percent or more and 37.5 atomic percent or less, and more preferably 6 atomic percent or more and 20 atomic percent or less.

[0035] Ni acts as a strengthening factor when noble metal alloys undergo spinodal decomposition. Ni has a higher elastic modulus compared to Au, Pt, and Pd. Furthermore, because the lattice constant of Ni is smaller than that of Au, Pt, and Pd, it has a greater effect in increasing the lattice strain ε. Therefore, from the above equation 1, Ni has the effect of increasing the strengthening ability due to spinodal decomposition. In addition, Ni is a metal that can form an ordered phase with Pt, and also has the effect of contributing to an increase in hardness due to ordering.

[0036] Furthermore, since Ni is a congener of Pt and Pd and has a similar electronic structure, it can be used to form alloys with minimal loss of the corrosion resistance and oxidation resistance of precious metals. This also has the secondary effect of reducing the overall price of precious metal alloys.

[0037] The Ni concentration of the Au-Ni-Pd-Pt noble metal alloy according to the present invention is 3 atomic percent or more and 62.5 atomic percent or less. The Ni concentration is preferably 12.5 atomic percent or more and 55 atomic percent or less, and more preferably 15 atomic percent or more and 50 atomic percent or less.

[0038] Pd Pd expands the solid solubility limit of each element constituting the noble metal alloy, widens the concentration range when spinodal decomposition of the noble metal alloy occurs, and has the effect of promoting spinodal decomposition. By these means, Pd has the effect of improving the amount of hardening due to spinodal decomposition. Also, Au is a metal that can form a regular phase with Pd and also has the effect of contributing to an increase in hardness due to regularization. However, when Pd is added in excess, the spinodal decomposition temperature excessively decreases, and thus spinodal decomposition tends to be inhibited instead. Furthermore, excessive addition of Pd tends to suppress regularization and causes a decrease in the total amount of hardening of the alloy system. Therefore, in order to optimize the amount of hardening of the noble metal alloy, there is also an optimal concentration range for Pd as described above.

[0039] The Pd concentration of the Au-Ni-Pd-Pt series noble metal alloy according to the present invention is 0.15 atomic % or more and 40 atomic % or less. The Pd concentration is preferably 2 atomic % or more and 35 atomic % or less, and more preferably 4 atomic % or more and 30 atomic % or less.

[0040] Pt Pt is also an essential element for causing spinodal decomposition in the alloy system of the present invention. Spinodal decomposition does not occur when the Pt concentration is too low or too high, and there is a concentration range of Pt necessary for its occurrence. Also, Pt can form a regular phase with Ni and contribute to an increase in hardness. Further, since Pt has a relatively high elastic modulus, it can be expected as an element that increases the amount of hardening of the alloy when spinodal decomposition occurs.

[0041] The Pt concentration of the Au-Ni-Pd-Pt series noble metal alloy according to the present invention is 7.5 atomic % or more and 72.5 atomic % or less. The Pt concentration is preferably 12.5 atomic % or more and 60 atomic % or less, and more preferably 15 atomic % or more and 50 atomic % or less.

[0042] (2) Essential additive element (Bi) The Au-Ni-Pd-Pt-based noble metal alloy according to the present invention contains Bi as an essential additive element for improving machinability. Bi added to the Au-Ni-Pd-Pt-based noble metal alloy melts due to heat generation during cutting and embrittles the material structure. Due to such embrittling action of the material structure, it is considered that the chip breakability of the noble metal alloy is improved and the machinability is improved. In addition, Bi melted during cutting is also considered to have a lubricating effect between the noble metal alloy and the tool, contributing to a reduction in cutting resistance and an improvement in tool life. And Bi does not affect the occurrence of spinodal decomposition and normalization of the Au-Ni-Pd-Pt-based noble metal alloy. Furthermore, the mechanism of improving machinability by Bi described above acts in any of the material structures (including cast structure, two-phase separation structure, structure after annealing treatment including recrystallized structure, structure after aging treatment) of the noble metal alloy. Therefore, the noble metal alloy according to the present invention has good machinability at each stage after heat treatment.

[0043] The Bi concentration in the noble metal alloy according to the present invention is set to 0.001 atomic % or more and 0.5 atomic % or less. If it is less than 0.001 atomic %, it is difficult to exert the above-described action and no improvement in machinability is observed. On the other hand, in the noble metal alloy having a Bi concentration exceeding 0.5 atomic %, the plastic workability of the noble metal alloy is significantly reduced. When the Bi concentration becomes excessive and the plastic workability decreases, material damage such as cracking and breakage may occur during processing into a wire or the like. The Bi concentration is preferably 0.005 atomic % or more and 0.4 atomic % or less, and more preferably 0.01 atomic % or more and 0.25 atomic % or less.

[0044] (3) Optional additive elements (B, Cu, metal element α, metal element β) The Au-Ni-Pd-Pt-based noble metal alloy according to the present invention may contain optional additive elements in addition to Bi which is the above-described essential additive element. The optional additive elements are B, Cu, metal element α, and metal element β, and these elements have actions such as improving the ductility of the noble metal alloy, expanding the concentration range in which spinodal decomposition occurs, and increasing the hardness after aging. The details of the actions of each additive element and its concentration are as follows.

[0045] B. According to the inventors' studies, the Au-Ni-Pd-Pt precious metal alloy produced by the present applicant tends to have poor ductility in the microstructure including the recrystallized structure produced by solution treatment, etc. The ductility of precious metal alloys is related to many processing processes such as plastic working and straightening, and may reduce the manufacturing efficiency in the primary and secondary processing described above. Element B, an optional additive, imparts a significant ductility-improving effect to the Au-Ni-Pd-Pt precious metal alloy and is particularly effective in applications where ductility is required after solution treatment.

[0046] To explain this point in detail, according to the present inventors, in Au-Ni-Pd-Pt noble metal alloys in which spinodal decomposition and ordering can occur, grain boundary segregation of Au and / or Pd may occur in the recrystallized structure formed in part or all of the alloy by solution treatment. This grain boundary segregation can cause grain boundary embrittlement and lead to a decrease in ductility. The optional additive element B is recognized to exhibit grain boundary strengthening of the noble metal alloy by preferentially segregating at the grain boundaries of the recrystallized structure formed by solution treatment, etc. This suppresses the decrease in ductility or embrittlement due to the above grain boundary segregation and imparts suitable workability to the noble metal alloy containing the recrystallized structure.

[0047] When adding B, an optional additive element, to the noble metal alloy according to the present invention, its concentration is preferably 0.003 atomic% or more and 8 atomic% or less. Below 0.003 atomic%, the amount of segregation at the grain boundaries of the recrystallized structure is small, and the grain boundary strengthening effect described above cannot be sufficiently obtained. Furthermore, excessive addition exceeding 8 atomic% is undesirable because it reduces ductility not only in the recrystallized structure but also in the cast structure and two-phase structure. The concentration of B is preferably 0.0075 atomic% or more. The concentration of B can also be appropriately set to 0.01 atomic% to 4 atomic%, 0.1 atomic% to 3 atomic%, or 0.2 atomic% to 2.5 atomic%, while considering the overall alloy composition of the Au-Ni-Pd-Pt noble metal alloy.

[0048] The addition of B, an optional additive element, improves the workability of the noble metal alloy after solution treatment, resulting in better workability in primary processing (forging, rolling, wire drawing, etc.) and secondary processing (bending, coiling, straightening, etc.). Machining is often performed as a finishing process following secondary processing. Therefore, the effect of improving plastic workability by adding B, an optional additive element, in cooperation with the effect of improving machinability by Bi, an essential additive element, can favorably improve the overall workability of the noble metal alloy. However, in this invention, the addition of B is optional and not essential. B is preferably added when improved ductility is required for plastic workability or bending, especially when ductility is required after solution treatment. However, even with a noble metal alloy after solution treatment, if plastic processing requiring ductility is not performed, or if the product shape is obtained only by machining that does not require solution treatment, as described later, the addition of B is unnecessary and optional.

[0049] Cu expands the solid solubility limit between constituent elements of noble metal alloys, thereby broadening the concentration range for spinodal decomposition to occur. In this respect, Cu has a similar effect to Pd and can therefore be used as an additive element. However, even though some of the effects of Pd are similar, Cu is an optional additive element and not an essential constituent element like Pd. This is because while Cu broadens the concentration range for spinodal decomposition to occur, it does not have the effect of improving the amount of hardening caused by spinodal decomposition. Furthermore, as an optional additive element, Cu is an inexpensive metal compared to noble metals, so it has the secondary effect of reducing the overall price of the noble metal alloy.

[0050] When adding Cu, an optional additive element, to obtain the effects described above, it is preferable that its concentration be between 0.1 atomic% and 27.5 atomic%. Excessive Cu addition can lead to a decrease in the spinodal decomposition temperature, suppression of ordering, and a reduction in the total hardening of the alloy system. Furthermore, excessive Cu addition can also be a factor in reducing the corrosion resistance of the alloy. When adding Cu, it is more preferable that the Cu concentration be between 2.5 atomic% and 22.5 atomic% and particularly preferable that it be between 5 atomic% and 18.5 atomic%.

[0051] Metal element α (In, Sn, Sb) and metal element β (Ti, Zr, Hf, Al) The Au-Ni-Pd-Pt noble metal alloy according to the present invention may contain metal element α and metal element β as optional additive metal elements, in addition to the essential constituent elements and Cu mentioned above. Metal elements α and β have the effect of increasing the hardness of the noble metal alloy after aging treatment. The reason why the hardness of the noble metal alloy increases with the addition of metal elements α and β is not clear, but the inventors consider that it is related to an increase in the strength of the alloy matrix due to an increase in lattice strain, refinement of the crystal grains of the alloy after aging treatment, and the formation of precipitates containing the added elements. Furthermore, the addition of metal elements α and β does not inhibit the formation of a material structure including a modulated structure and / or an ordered phase. Metal elements α and β may be included individually or in combination.

[0052] Metal element α is at least one of In, Sn, and Sb. According to the inventors' studies, an increase in the hardness of the noble metal alloy of the present invention is observed with these metal elements. It is preferable to add one or more of In, Sn, and Sb as metal element α. The composition range of at least one of the elements In, Sn, and Sb that constitute metal element α is 0.15 atomic% to 5 atomic%. Addition amounts less than 0.15 atomic% do not contribute much to increasing the hardness of the noble metal alloy, and amounts exceeding 5 atomic% result in a decrease in plastic workability. The composition range of metal element α is preferably 0.3 atomic% to 3 atomic%, and more preferably 0.5 atomic% to 1.5 atomic%.

[0053] The metal element β is at least one of Ti, Zr, Hf, and Al. According to the inventors' studies, these metal elements result in grain refinement and increased hardness of the noble metal alloy of the present invention. It is preferable to add one or more of Ti, Zr, Hf, and Al as metal element β. The composition range of at least one of the elements Ti, Zr, Hf, and Al that constitute metal element β is 0.05 atomic% to 5 atomic%. Addition amounts less than 0.05 atomic% do not contribute much to grain refinement or increased hardness of the noble metal alloy, and exceeding 5 atomic% results in a noticeable decrease in plasticity. Furthermore, the composition range of metal element β is preferably 0.1 atomic% to 3 atomic%, and more preferably 0.15 atomic% to 1.5 atomic%.

[0054] Unavoidable Impurities The precious metal alloy according to the present invention contains Au, Ni, Pd, Pt, and Bi as essential elements within the composition range described above, and optionally contains B, Cu, metallic element α, and metallic element β. Preferably, the precious metal alloy can be composed of only these elements. However, the precious metal alloy according to the present invention may optionally contain unavoidable impurities. Unavoidable impurities are components that are inevitably included due to impurities in the raw materials or due to the manufacturing process, etc. Specific examples of unavoidable impurities include Rh, Ir, Ru, Y, Zn, Si, Th, H, and rare earth elements. Unlike Bi, which is essential and intentionally added in the present invention, these elements are unavoidable impurities that can be introduced from the raw materials and the crucible, mold, etc., during melting and casting. The content of these unavoidable impurities is preferably within a range that does not impair the properties of the precious metal alloy of the present invention, and is preferably less than 0.01 atomic percent per element. The total concentration of unavoidable impurities is preferably 0.5 atomic percent or less, and particularly preferably less than 0.1 atomic percent. It should be noted that when the above-mentioned unavoidable impurities are present in a precious metal alloy, it is difficult to clearly distinguish whether they are unavoidably present or intentionally added. In this invention, as long as the component does not significantly alter the properties of the precious metal alloy, it is treated as an unavoidable impurity without distinguishing the intent of its inclusion. The same applies to the elements contained in the precious metal alloy, regardless of whether they were intentionally added or not; this also applies to the additive elements of this invention: Bi, B, Cu, metal element α, and metal element β.

[0055] Furthermore, the concentrations of the constituent elements (Au, Ni, Pd, Pt, Bi, B, Cu, metal element α (In, Sn, Sb), metal element β (Ti, Zr, Hf, Al)) and unavoidable impurities of the noble metal alloy according to the present invention described above can be appropriately measured by known analytical methods, taking into account the type of each element and the expected concentration for each element. For example, glow discharge mass spectrometry (GDMS) and inductively coupled plasma emission spectrometry (ICP-OES) are known methods for accurately analyzing the concentration of each element in the noble metal alloy. In addition, inductively coupled plasma mass spectrometry (ICP-MS) may be applied to elements such as Bi and B that are expected to be added in trace amounts.

[0056] The spinodal decomposition and ordering of the precious metal alloy according to the present invention occur in a solution treatment in which a solid solution alloy within the above-mentioned composition range is held at a high temperature and then rapidly cooled, followed by an aging treatment process. The precious metal alloy of the present invention has a wide region of complete solid solution in the high-temperature range, while having a solubility gap in the low-temperature range. Therefore, it is thought that a supersaturated solid solution can be formed by rapidly cooling a precious metal alloy having the above-mentioned composition range after solution treatment in the high-temperature range, and that spinodal decomposition and ordering can occur through subsequent aging treatment. Furthermore, regarding the thermodynamic behavior of the precious metal alloy of the present invention (transformation point, phase equilibrium, solid solubility limit, melting point, etc.), the use of the CALPHAD method (Calculation of Phase Diagrams method) is also effective. For calculations using the CALPHAD method, it is preferable to use commercially available thermodynamic calculation software (for example, Thermo-Calc and a precious metal alloy database (for example, TCNOBL1)).

[0057] (A-2) Material structure of the noble metal alloy according to the present invention The noble metal alloy according to the present invention achieves increased hardness through spinodal decomposition and / or ordering. Therefore, the material structure of the noble metal alloy according to the present invention may include a finely modulated structure due to spinodal decomposition and / or an ordered phase due to ordering.

[0058] In the noble metal alloy according to the present invention, the modulated structure resulting from spinodal decomposition is a material structure in which the composition fluctuates with a modulation period of several nanometers to several tens of nanometers. Specifically, the modulated structure in the present invention is composed of two regions: a region where the Au and Pd concentrations are relatively high (a region where the Pt and Ni concentrations are relatively low) and a region where the Au and Pd concentrations are relatively low (a region where the Pt and Ni concentrations are relatively high).

[0059] Furthermore, the composition and structure of the ordered phase in the present invention are not entirely clear. However, it is believed that a phase having the same or similar crystal structure as the ordered phase that can be formed in Pt-Ni alloys or Au-Pd alloys, which are known as noble metal alloys in which ordering can occur, is also formed in the noble metal alloys of the present invention. Therefore, the ordered phase in the present invention is L1 ０ Type structure or L1 ２It is presumed to be a type structure, or a crystal structure similar thereto.

[0060] The microstructure of the precious metal alloy of the present invention can be confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron diffraction patterns of TEM, scanning transmission electron microscopy (STEM), TEM / STEM-EDS mapping images, TEM / STEM-EELS mapping images, three-dimensional atom probes, etc.

[0061] The modulated structure of the noble metal alloy of the present invention can be confirmed by diffraction, elemental analysis (elemental mapping), or both.

[0062] Diffraction methods include X-ray diffraction (XRD) to confirm the X-ray diffraction pattern or TEM to confirm the electron diffraction pattern. When confirming by diffraction, if a modulated structure is present, so-called sideband peaks (satellite peaks) or broad peaks called streaks are observed on at least one side (preferably both sides) of the main peak or regular reflection peak. The presence or absence of these sideband peaks or streaks can be used to determine whether a modulated structure due to spinodal decomposition is present. For example, in the diffraction pattern obtained by X-ray diffraction, since the crystal structure of the matrix of the noble metal alloy according to the present invention is face-centered cubic (fcc), Miller indices {111} plane, {200} plane, {220} plane, {311} plane, etc. appear as main peaks. In a spinodal decomposition structure, sideband peaks appear on either one or both sides of at least one of the above main peaks. If sideband peaks appear only on one side of the main peak, it is thought that this is because separation from the main peak is difficult.

[0063] On the other hand, methods for verification using elemental mapping include STEM-EDS / EELS and methods that visually confirm the intensity of atomic concentrations using three-dimensional atom probes.

[0064] Furthermore, to confirm the ordered phase, it is common to check for the presence or absence of ordered reflection peaks in the X-ray diffraction pattern or the electron diffraction pattern of a TEM. For example, when observing ordered reflection peaks in an X-ray diffraction pattern, in the case of θ-2θ measurement using CuKα rays as the X-ray source, ordered reflection peaks appear around 2θ = 22.5 to 27.5° and around 30 to 35°. In the case of an electron diffraction pattern, diffraction spots such as 100, 110, and 120, which do not appear in an fcc structure, appear.

[0065] (A-3) Hardness of the noble metal alloy according to the present invention The noble metal alloy according to the present invention has the composition range described above and is hardened by spinodal decomposition and / or ordering. The noble metal alloy according to the present invention can stably exhibit a Vickers hardness of 500 Hv or more. The Vickers hardness of the noble metal alloy according to the present invention is preferably 540 Hv or more, more preferably 590 Hv or more, and even more preferably 640 Hv or more. The noble metal alloy according to the present invention can be made into a high-hardness noble metal alloy having the Vickers hardness described above by heat treatment alone, without utilizing work hardening at all, that is, without causing material embrittlement due to dislocation strain.

[0066] Furthermore, while there is no particular upper limit to the hardness of the noble metal alloy according to the present invention, it is preferable that the upper limit be 850 Hv or less. If it exceeds 850 Hv, there is a risk of fracture or chipping during use. Also, the Vickers hardness described above is the value at room temperature. Vickers hardness can be measured using a known Vickers hardness tester. The measurement load is preferably 0.025 kgf or more and 0.5 kgf or less, and more preferably 0.1 kgf.

[0067] The shape and form of the precious metal alloy according to the present invention are not particularly limited. For the medical devices and probe pins mentioned above, the present invention can generally be used as a bulk (solid) alloy that has been appropriately processed. The present invention has improved machinability for processing into shapes and dimensions suitable for these applications. Furthermore, the present invention can also be formed in layers or films on an appropriate base material or substrate.

[0068] (B) Method for manufacturing the precious metal alloy according to the present invention Next, a method for manufacturing the precious metal alloy according to the present invention will be described. As described above, the precious metal alloy according to the present invention can be provided in various shapes and forms. In the following description, the method for manufacturing the bulk precious metal alloy, which is a frequently applied form, will be described in detail, and the method for manufacturing the layered and film-like precious metal alloys will also be mentioned.

[0069] In this invention, high hardness is achieved by optimizing the selection of constituent elements (essential constituent elements (Au, Ni, Pd, Pt, Bi) and optional added metal elements (B, Cu, metal elements α, β)) and their composition range, followed by spinodal decomposition and / or ordering of the precious metal alloy. The precious metal alloy of this invention is manufactured by producing and preparing an alloy ingot within the aforementioned composition range, in addition to carrying out an appropriate heat treatment process. The appropriate heat treatment process is a heat treatment process that combines solution treatment and aging treatment, and through these processes, spinodal decomposition and / or ordering proceed, resulting in high hardness and the precious metal alloy according to the present invention.

[0070] The method for producing a precious metal alloy according to the present invention will be described below, referring to each heat treatment step, solution treatment and aging treatment. In this invention, unless otherwise specified, the temperature, such as the heating temperature, in the various heat treatments described below refers to the temperature of the precious metal alloy being treated.

[0071] (B-1) Preparation Process (Preparation of Precious Metal Alloys) First, a precious metal alloy ingot within the composition range described above is prepared. Precursor precious metal alloy ingots can be manufactured by conventional melting and casting methods. The above-mentioned Au, Ni, Pd, Pt, along with the essential additive element Bi and the optional elements B, Cu, and metallic elements α and β, are weighed appropriately to achieve the above composition, and then melted and cast to produce alloy ingots. At this time, precious metal alloys that do not contain Bi, B, Cu, or metallic elements α and β (Au-Ni-Pd-Pt alloys), or binary alloys such as Au-Pd alloys and Pt-Ni alloys may be appropriately combined as master alloys and melted. The melting and casting of precious metal alloys can be carried out by known means such as arc melting, high-frequency melting, vacuum melting, continuous casting, liquid quenching, and micro-PD method.

[0072] The precious metal alloy may be prepared by methods other than melt casting, such as powder metallurgy. In powder metallurgy, an alloy ingot to be heat-treated can be obtained by sintering precious metal alloy powder prepared with the above composition (for example, precious metal alloy powder produced by atomization). Alternatively, a near-net shaped ingot may be manufactured using the precious metal alloy powder prepared with the above composition by known methods such as metal powder injection molding (MIM) or additive manufacturing (3D printing). Furthermore, a precious metal alloy layer of the above composition may be formed on any base material by known alloy forming means such as plating, sputtering, or thermal spraying.

[0073] (B-2) Solution Treatment A supersaturated solid solution is formed from the noble metal alloy prepared as described above by solution treatment. Solution treatment is a process in which the noble metal alloy is heated to a high temperature to increase the solid solution concentration, and then rapidly cooled to form a supersaturated solid solution. The heating temperature for solution treatment is preferably between (Tm - 500°C) and Tm (°C), where Tm is the melting point (solidus line) of the noble metal alloy. Below (Tm - 500°C), the solid solubility of each element is low and insufficient to form a supersaturated solid solution, and above Tm, melting of the material begins near the grain boundaries, which is undesirable. The holding time during heating is preferably in the range of 0.0001 hours to 168 hours. If it is less than 0.0001 hours, the formation of a supersaturated solid solution will be insufficient, and even if heated for 168 hours or more, it will not have a significant effect on the formation of a supersaturated solid solution, which is undesirable from the viewpoint of productivity. In this invention, the term "melting point" refers to the solidus temperature.

[0074] Furthermore, during cooling from the solution treatment temperature, rapid cooling is necessary, i.e., rapid cooling, to the extent that grain boundary reactions do not occur excessively in the high-temperature range. This is because if grain boundary reactions occur in the high-temperature range, although ductility is improved by strengthening the grain boundaries, the hardness after aging treatment may be insufficient. Specifically, it is preferable to have a cooling rate of 10°C / s or more, more preferably 50°C / s or more, and even more preferably 150°C / s or more. On the other hand, from the viewpoint of preventing quench cracking, dimensional changes, deformation, etc., it is preferable to have a slow cooling rate. Therefore, from the viewpoint of improving the hardness of the noble metal alloy, in the low-temperature range where grain boundary reactions and spinodal decomposition / ordering do not proceed excessively, it is not necessary to have the aforementioned cooling rate referred to as rapid cooling. For example, rapid cooling is not necessary in the temperature range below 250°C. Therefore, in order to suppress or reduce the occurrence of quench cracking, etc., for example, rapid cooling may be performed up to 200°C, and then air cooling may be performed in the temperature range below 200°C. Furthermore, it is preferable that the end point of cooling during the solution treatment in this process be room temperature.

[0075] (B-3) Aging Treatment In the noble metal alloy according to the present invention, spinodal decomposition and ordering proceed by aging the supersaturated solid solution formed by the solution treatment at a temperature lower than the spinodal decomposition temperature and the ordered-disordered transformation temperature.

[0076] For aging treatment of supersaturated solid solution noble metal alloys, the heating temperature is preferably between 250°C and 800°C. Below 250°C, spinodal decomposition or ordering does not proceed easily. Above 800°C, material softening due to grain boundary reactions is significant. A heating temperature of 350°C to 650°C is more preferable. Furthermore, the heating time for aging treatment is preferably between 0.001 hours and 168 hours. Below 0.001 hours, the transformation is insufficient, resulting in variations in hardness, and treatment for 168 hours or more is unproductive and increases manufacturing costs. There are no particular restrictions on the cooling method after the aging treatment is completed. The high-hardness noble metal alloy according to the present invention can be obtained by undergoing this aging treatment.

[0077] (B-4) Other Heat Treatment Processes In the production of the precious metal alloy according to the present invention, the solution treatment and aging treatment described above are essential processes, but other heat treatment processes may also be included. Examples of such other heat treatment processes include homogenization treatment, two-phase treatment, and intermediate annealing. However, these other heat treatments do not affect the progress of spinodal decomposition or ordering. Therefore, these heat treatments are optional processes.

[0078] Homogenization treatment is performed on precious metal alloys prepared by melt casting, with the aim of forming a metallic structure in which the distribution of elemental concentrations in the precious metal alloy is uniform. Homogenization treatment is a heat treatment in which the precious metal alloy is heated at a high temperature below its melting point for a long period of time (preferably between 0.1 hours and 72 hours).

[0079] The two-phase formation treatment is a process that forms a two-phase structure, which provides the best workability in the alloy system of the present invention, and is a heat treatment performed to facilitate hot working and cold working. The heating temperature for the two-phase formation treatment is 700°C to 950°C, more preferably 750°C to 900°C. The heating time is 0.1 hours to 10 hours, more preferably 0.2 hours to 2 hours.

[0080] Intermediate annealing is a heat treatment performed in conjunction with processing processes such as hot working and cold working, described later, that cause strain to accumulate in ingots of precious metal alloys. Intermediate annealing is a process to reduce material strength and restore workability. Since this alloy is most ductile in its two-phase structure state, the heating temperature for intermediate annealing is 700°C to 950°C, more preferably 750°C to 900°C. The heating time is 0.1 hours to 10 hours, more preferably 0.2 hours to 2 hours.

[0081] (B-5) Processing steps for the precious metal alloy according to the present invention The precious metal alloy according to the present invention can be processed into various shapes according to the application after the alloy ingot has been melted and cast. Processing steps that can be performed here include hot working, warm working, cold working, skin pass, straightening, coiling, bending, cutting, grinding, laser processing, etc. Hot working, warm working, and cold working are distinguished by the processing temperature and include forging, rolling, wire drawing, extrusion / drawing, etc. Hot working can destroy the solidification structure in the prepared precious metal alloy ingot and eliminate defects such as voids. Warm working and cold working have significance not only in changing the overall shape of the alloy but also in controlling the shape of the crystal grains. When warm working or cold working is performed multiple times, intermediate annealing as described above may be performed between processing passes.

[0082] Machining and grinding are processing methods performed to shape a material into a desired form. The improved machinability of the precious metal alloy according to the present invention is most effective in this machining process. The machining method and conditions for cutting can be carried out under normal conditions using tools and jigs capable of cutting and grinding precious metal alloys.

[0083] Furthermore, the precious metal alloy according to the present invention may contain B, an optional additive element for improving plastic workability. Since the B-added precious metal alloy has improved plastic workability, it is suitable for applications where it is plastically processed to a shape close to the final shape by hot working, warm working, cold working, skin pass, straightening, coiling, bending, etc. The B-added precious metal alloy according to the present invention can reduce the possibility of processing defects in the plastic processing process. When the efficiently processed precious metal alloy is then machined to its final shape, the improved machinability due to the addition of Bi is effective.

[0084] As described above, the precious metal alloy according to the present invention, after undergoing various processing steps, becomes highly hard through spinodal decomposition and / or ordering by aging treatment, and can be used to make products such as medical components and probe pins. Processing after aging treatment (after hardening) is not essential, but processing at this stage is not prohibited. Even the highly hardened precious metal alloy after aging treatment can be processed, and final adjustments such as grinding, polishing, cutting, electrical discharge machining, pressing, bending, and straightening are possible. The effect of Bi addition is also demonstrated in cutting processes during this time.

[0085] Furthermore, the spinodal decomposition and ordering observed in the noble metal alloy according to the present invention are reversible. Therefore, the solution treatment and aging treatment may be repeated. Processing may also be performed between multiple combinations of solution treatment and aging treatment.

[0086] (B-6) Other manufacturing methods for the precious metal alloy according to the present invention In the manufacturing method described above, the precious metal alloy according to the present invention is obtained by solution treatment and aging treatment of an alloy ingot that has undergone a melting and casting method. In the present invention, solution treatment is the main heat treatment, but in some cases, a precious metal alloy having a microstructure equivalent to that of a supersaturated solid solution with a recrystallized structure can be prepared without performing the solution treatment step. In such cases, the precious metal alloy of the present invention can be manufactured by aging treatment of the said precious metal alloy.

[0087] Processes for obtaining a supersaturated solid solution state of precious metal without solution treatment include, for example, liquid quenching methods applied to molten precious metal alloys, and rapid heating and cooling processes or rapid solidification processes using lasers applied to bulk metals. Furthermore, supersaturated solid solutions can sometimes be produced through various film formation processes such as welding, sputtering, plating, and thermal spraying. Precious metal alloys produced by these processes can be transformed into the precious metal alloy of the present invention by aging treatment without solution treatment. Even without solution treatment, the preferred conditions for aging treatment are the same as described above. These alloy manufacturing processes are useful for producing near-net precious metal alloys and layered / film-like precious metal alloys such as high-hardness coatings. The effect of Bi added in the present invention is realized when the precious metal alloy produced in this way is machined.

[0088] First Embodiment: The following describes specific embodiments of the present invention. In this embodiment, several Au-Ni-Pd-Pt noble metal alloys were manufactured by changing the composition of each element: Au, Ni, Pd, Pt, Bi, B, Cu, metal element α (In, Sn, Sb), and metal element β (Ti, Zr, Hf, Al). For each noble metal alloy, the machinability, hardness after aging treatment, and material structure (presence or absence of spinodal decomposition and ordering) were evaluated.

[0089] The compositions of the Au-Ni-Pd-Pt precious metal alloys produced in this embodiment are shown in Tables 1 to 3 below (Examples 1 to 58, Comparative Examples 1 to 5). In this embodiment, after producing ingots of each precious metal alloy composition, samples were prepared for each evaluation item.

[0090] [Manufacturing of Precious Metal Alloys (Ingots)] In the manufacturing of Au-Ni-Pd-Pt precious metal alloy ingots, high-purity raw materials of Au, Ni, Pd, Pt, Bi, B, Cu, metal element α, and metal element β were weighed and mixed to the predetermined composition, placed in an alumina crucible, and after vacuuming, melted by high-frequency induction under a reduced-pressure argon atmosphere. The mixture was then cast into copper molds (11 mm in diameter, 70 mm in length) to produce precious metal alloy ingots.

[0091] Then, using the precious metal alloy ingots manufactured as described above, evaluations were conducted on the following items: (i) machinability, (ii) hardness, and (iii) microstructure (confirmation of spinodal decomposition and / or order formation). The sample preparation method and evaluation test methods and conditions for each evaluation item (i) to (iii) are as follows.

[0092] (i) Machinability evaluation The alloy ingots obtained in the manufacturing process of the precious metal alloy ingots described above were heat-treated at 850°C for 1 hour (Examples 1 to 58 and Comparative Examples 1 to 5 in Tables 1 to 3 described later). At this time, the heat treatment atmosphere was vacuum (10 －２ The pressure was set to less than Pa, and the cooling method was water cooling. Subsequently, the outer diameter was machined to a diameter of 9 mm to smooth the casting surface, and this was used as the evaluation sample for cutting.

[0093] The machinability was evaluated by machining the machinability evaluation sample prepared above and examining the chip fragmentation during the process. The machinability evaluation sample was machined on a lathe (cutting tip material: CBN (corner radius 0.4)) under the following cutting conditions: depth of cut 0.2 mm, cutting speed 70 m / min, and feed rate 0.07 mm / rev. The chips generated during machining were collected and the number of turns in the chips was measured. If the proportion of chips with fewer than 10 turns accounted for 60% or more of the total chip weight, the chip fragmentation was judged as "excellent (◎)". If it was between 30% and 60%, the chip fragmentation was judged as "good (〇)". Furthermore, if the proportion of chips with fewer than 10 turns accounted for less than 30%, the chip fragmentation was judged as "poor (×)".

[0094] (ii) Hardness Evaluation The alloy ingots obtained in the manufacturing process of the precious metal alloy ingots described above were subjected to solution treatment and aging treatment to prepare samples for hardness measurement. The temperature conditions for the solution treatment and aging treatment are as shown in Tables 1 to 3 below, the holding time for both the solution treatment and aging treatment was 1 hour, and the heat treatment atmosphere was vacuum (10 －２ The pressure was set to less than Pa. For the cooling method after heat treatment, water cooling was used for solution treatment and air cooling was used for aging treatment.

[0095] Then, hardness measurements were performed using the prepared hardness evaluation samples. A hardness measuring device (HM-210, manufactured by Mitutoyo Corporation) was used, and measurements were taken at room temperature with a test load of 0.1 kgf. For hardness measurement, 10 measurements were taken randomly for each sample, and the average value was taken as the hardness value. For the measurement positions in each sample, multiple crystal grains were selected, and measurements were taken at the non-grain boundary reaction zone of each crystal grain, and as close to the center of the crystal grain as possible. However, the noble metal alloy in the example showed a minimum hardness of 500 Hv or higher.

[0096] (iii) Material structure evaluation Samples for material structure evaluation were prepared by solution treatment and aging treatment of alloy ingots obtained in the manufacturing process of the precious metal alloy ingots described above. The temperature conditions for the solution treatment and aging treatment are as shown in Tables 1 to 3 below, the holding time for both the solution treatment and aging treatment was 1 hour, and the heat treatment atmosphere was vacuum (10 －２ The pressure was set to less than Pa. For the cooling method after heat treatment, water cooling was used for solution treatment and air cooling was used for aging treatment.

[0097] Then, the microstructure was evaluated using the prepared samples for microstructure evaluation. The microstructure evaluation involved confirming the occurrence of spinodal decomposition and the formation of an ordered phase using XRD analysis. XRD analysis was performed on the noble metal alloy after solution treatment (solution-treated material) and the noble metal alloy after aging treatment following solution treatment (aged material). The results were compared to confirm the occurrence of spinodal decomposition and ordering due to aging treatment. The XRD analysis conditions were as follows:

[0098] [Common Conditions] ・XRD device: Rigaku SmartLab ・Target: Cu anode ・Optical system and detector: Focused optical system and semiconductor detector (HyPix-3000) ・Voltage and current: 40kV / 30mA ・Long-side limiting slit: 10mm

[0099] (a) Confirmation of spinodal resolution (sideband peaks) • 2θ scanning range: 20° to 130° • 2θ step size (°): 0.0012 • 2θ scanning speed (° / min): 6

[0100] (b) Confirmation of the ordered phase (ordered peak) 2θ scanning range: 20° to 38° 2θ step size (°): 0.0132 2θ scanning speed (° / min): 1.3

[0101] In the XRD analysis of spinodal resolution, the XRD diffraction profiles obtained under the above conditions were judged based on whether one or more sideband peaks appeared on one or both sides of the main peak (approximately ±0.5 to 5° in 2θ angle) for the Miller index {111}, {200}, {220}, and {311} planes. If one or more sideband peaks appeared, it was considered that spinodal resolution had occurred; if no sideband peaks appeared at all, it was evaluated that spinodal resolution had not occurred.

[0102] Furthermore, in the XRD analysis of the ordered phase, the presence or absence of an ordered reflection peak occurring around 2θ = 30° to 35° was used for determination. Specifically, if the intensity of the ordered reflection peak was higher than the background in that region, it was evaluated as the presence of an ordered phase; if the peak intensity was at or below the background level, it was evaluated as the absence of an ordered phase.

[0103] As an example of the results of XRD analysis performed on a precious metal alloy sample based on the above method, Figure 1 shows the XRD diffraction patterns of the solution-treated and aged materials of the precious metal alloy (Au10-Ni37.48-Pd15-Pt37.47-Bi0.05) from Example 16. Figure 1(a) shows the XRD diffraction profile for confirming spinodal decomposition (modulated structure), and Figure 1(b) shows the XRD diffraction profile for confirming ordering. Referring to Figure 1(a), in this precious metal alloy, clear peaks that can be identified as sideband peaks were confirmed on both sides of the peaks around 2θ = 40° to 42° corresponding to the {111} plane and the peaks around 2θ = 46.5° to 48.5° corresponding to the {200} plane. From this, it can be concluded that spinodal decomposition is occurring in this precious metal alloy.

[0104] Furthermore, referring to Figure 1(b), a peak (regular reflection peak) higher than the background is observed in the region around 2θ = 31.5° to 34°. From this, it can be concluded that regularization is also occurring in this precious metal alloy. XRD analysis was performed on samples from other examples and comparative examples in the same manner as in Example 16 to confirm the presence or absence of spinodal decomposition and regularization. The evaluation results for each sample are shown in Tables 1 to 3 below, with "○" indicating that spinodal decomposition and regularization were observed, and "×" indicating that they were not observed.

[0105] The composition and manufacturing conditions of the precious metal alloys produced in the first embodiment (Examples 1 to 58, Comparative Examples 1 to 5) and the results for each evaluation item of (i) machinability, (ii) hardness, and (iii) material structure are shown in Tables 1 to 3.

[0106]

[0107]

[0108]

[0109] Referring to Tables 1 to 3, we will examine the properties of each Au-Ni-Pd-Pt precious metal alloy in each example and comparative example. First, as a prerequisite for the present invention, it has been confirmed that each Au-Ni-Pd-Pt precious metal alloy in each example and comparative example exhibits spinodal decomposition and / or ordering, and shows a hardness of 500 Hv or higher. From this, it can be said that Au-Ni-Pd-Pt precious metal alloys, including those in the prior art, have suitable potential as high-hardness precious metal alloys.

[0110] Furthermore, when examining the improvement of machinability by adding Bi, which is the problem and feature of the present invention, Au-Ni-Pd-Pt-based precious metal alloys without Bi addition or with an insufficient Bi concentration (0.0005 atomic%) (Comparative Examples 1 to 5) were all judged to have poor machinability. Machinability improved when the Bi concentration was set to 0.001 atomic% (Example 1), and became excellent at 0.005 atomic% or higher (Example 2, etc.). From these results, it was confirmed that adding Bi of 0.001 atomic% or more is effective in improving the machinability of Au-Ni-Pd-Pt-based precious metal alloys, which is the problem of the present invention. In addition, from the comparison between Example 1 and Comparative Examples 1 and 2, Example 28 and Comparative Example 3, and Example 56 and Comparative Example 4, where the alloy composition and solution treatment temperature are similar, it was found that there is almost no decrease in hardness after aging treatment due to the addition of Bi. Moreover, at least one of spinodal decomposition and ordering occurred in all of the precious metal alloys. From this, it can be said that adding Bi to Au-Ni-Pd-Pt type precious metal alloys does not impair their properties as high-hardness precious metal alloys.

[0111] Furthermore, the machinability of Au-Ni-Pd-Pt noble metal alloys with the optional additive element B added was similarly investigated, and it was confirmed that the addition of Bi improved machinability (Examples 17-31, 47-58). It was also confirmed that spinodal decomposition and / or ordering occurred. These trends were similarly observed in Au-Ni-Pd-Pt noble metal alloys with the optional additive element Cu added. The effect of B addition on improving ductility will be specifically shown in the second embodiment described later.

[0112] Regarding the effects of adding optional metal elements α (In, Sn, Sb) and β (Ti, Zr, Hf, Al), an increase in hardness is observed when at least one of these elements is added. Depending on the composition of the noble metal alloy, this increase in hardness can exceed 50 Hv. Furthermore, it can be confirmed that neither metal elements α nor β inhibit the spinodal decomposition and ordering of Au-Ni-Pd-Pt noble metal alloys. In addition, it can be confirmed that the addition of Bi improves machinability in Au-Ni-Pd-Pt noble metal alloys with metal elements α and β added.

[0113] Second Embodiment: In this embodiment, the effect of adding B as an optional additive on improving ductility was confirmed for Au-Ni-Pd-Pt noble metal alloys. Here, the ductility after (iv) solution treatment was evaluated for the noble metal alloys of Examples 24-31 and Comparative Example 5 of the first embodiment (with B addition), and the noble metal alloys of Example 5, Comparative Example 1 and Comparative Example 2 (without B addition), which have similar concentrations of Au, Ni, Pd, and Pt, differing only in the presence or absence of B addition. In addition, the ductility after solution treatment was evaluated for the noble metal alloys of Examples 47, 52 and 56, which are noble metal alloys in which Cu, metal elements α and β are added along with B as optional additive elements.

[0114] (iv) Ductile evaluation A precious metal alloy ingot manufactured in the same manner as in the first embodiment was subjected to two-phase treatment (850°C for 60 minutes in a vacuum atmosphere), then cold swaging was performed until the diameter was 6 mm, and then cold groove rolling was performed until it was 2.5 mm square. In these processing steps, the processing rate per pass was set to 10-15%, and intermediate annealing (850°C for 60 minutes in a vacuum atmosphere) was performed within the range of a total processing rate of 30-50%. Furthermore, cold wire drawing was performed in a wire drawing machine with a processing rate of 10-20% per pass until the diameter was 0.6 mm. In this wire drawing process, intermediate annealing was performed within the range of a total processing rate of 30-60%.

[0115] After processing the material into a 0.6 mm diameter wire using the above steps, a solution treatment was performed at the heat treatment temperature shown in Table 4 below to produce a sample for ductility evaluation. The solution treatment time was 1 minute, and the heat treatment atmosphere was vacuum (10°C). －２ (Below Pa), the cooling method was water cooling.

[0116] Ductility evaluation was performed by measuring the bending angle in a bending test. For the ductility evaluation samples prepared as described above, a 180° bending test was conducted with a bending radius of 1 mm, and the bending angle until fracture was measured. The bending test was performed three times on the same sample, and the average bending angle was used for evaluation. For samples that did not fracture even when bent to 180°, the bending angle was set to 180°. The results of the above ductility evaluation tests are shown in Table 4.

[0117]

[0118] First, let's refer to the results of Comparative Example 1, which is an Au-Ni-Pd-Pt alloy without the addition of either Bi or B. The bending angle of this precious metal alloy in the bending test was 5°, confirming that the Au-Ni-Pd-Pt alloy, the basis of the precious metal alloy according to the present invention, has poor ductility after solution treatment. Furthermore, the results of Example 5 and Comparative Example 2 show that adding Bi to the Au-Ni-Pd-Pt alloy does not improve ductility after solution treatment. In Example 24, the precious metal alloy with 0.005 atomic% B added to the Au-Ni-Pd-Pt alloy achieved a bending angle of 95°, indicating a significant improvement in ductility with the addition of B. The bending angle increased to 180° by increasing the amount of B added, demonstrating further improvement in the ductility of the precious metal alloy (Examples 25-31).

[0119] These results show that the addition of B to Au-Ni-Pd-Pt alloys is useful for improving the ductility of noble metal alloys containing recrystallized structures after solution treatment, thereby improving the plastic workability of noble metal alloys containing recrystallized structures. The object of the present invention is to improve the machinability of Au-Ni-Pd-Pt alloys, so the addition of B is not essential, but the addition of B is useful when both machinability and ductility are to be improved after solution treatment, etc. Furthermore, the addition of B is similarly effective in Au-Ni-Pd-Pt noble metal alloys to which optional additive elements such as Cu and metal elements α and β are added (Examples 47, 52, 56).

[0120] Third Embodiment: In this embodiment, the effect of Bi on improving machinability was confirmed for an Au-Ni-Pd-Pt precious metal alloy that underwent a different heat treatment than in the first embodiment. In the first embodiment, the machinability of an Au-Ni-Pd-Pt precious metal alloy with a two-phase separation structure was evaluated by heating a precious metal alloy ingot to 850°C. In this embodiment, a solution treatment, which is a higher heat treatment than in the first embodiment, was performed, and the machinability of a precious metal alloy containing a recrystallized structure was evaluated.

[0121] In this embodiment, the machinability of noble metal alloys with the compositions of Examples 3, 5, 27, 43, 49, and 58 of the first embodiment and Comparative Examples 2 and 5 was evaluated. The ingots obtained in the same manner as in the first embodiment were heat-treated for 1 hour at the solution treatment temperatures listed in Table 5 below. Two different heat treatment temperatures were selected for each sample. The heat treatment atmosphere was vacuum (10°C). －２ The heat treatment was set to less than Pa, and the cooling method was water cooling. After heat treatment, the outer diameter was machined in the same manner as in the first embodiment to create a sample for cutting evaluation. In the evaluation method for machinability, the chip breakage during machining was examined, as in the first embodiment. The evaluation criteria at this time were also the same as in the first embodiment, and the chip breakage was determined as "excellent (◎)", "good (○)", or "poor (×)" by measuring and classifying the number of turns of the generated chips and measuring the weight ratio. The results of this machinability evaluation are shown in Table 5.

[0122]

[0123] Table 5 shows that the Au-Ni-Pd-Pt precious metal alloy with added Bi exhibits good machinability even after solution treatment (Examples 3, 5, 27, 43, 49, 58). In contrast, the Au-Ni-Pd-Pt precious metal alloy without Bi or with insufficient Bi concentration exhibits poor machinability even after solution treatment (Comparative Examples 2, 5). As described above, the inventors consider that the improvement in machinability occurs because Bi embrittles the material structure during machining. Given this mechanism, it is considered that the improvement in machinability occurs regardless of the type of material structure. Therefore, the precious metal alloy according to the present invention can be said to be useful during machining, which is performed as needed, regardless of the metallic state resulting from heat treatment.

[0124] As described above, the present invention is a high-hardness precious metal alloy obtained by spinodal decomposition and / or ordering, and has improved machinability (chip breaking ability) during machining. The precious metal alloy according to the present invention is expected to be applied to various uses such as electrical and electronic materials such as probe pins and electrical contacts, medical instruments, and high-hardness coated members, where high hardness and high wear resistance are required. In these applications, the machinability of the precious metal alloy is an important characteristic for processing it to the required shape and dimensions. The precious metal alloy according to the present invention can effectively meet the demand for improved machinability. The precious metal alloy according to the present invention can also be manufactured by alloy manufacturing methods other than melt casting, such as additive manufacturing technology, metal powder injection molding technology, rapid solidification technology, laser heating technology, overlay welding technology, and coating technologies such as sputtering, thermal spraying, and plating.

Claims

1. An Au-Ni-Pd-Pt noble metal alloy comprising 2 atomic% to 55 atomic% of Au, 3 atomic% to 62.5 atomic% of Ni, 0.15 atomic% to 40 atomic% of Pd, and 7.5 atomic% to 72.5 atomic% of Pt, further comprising 0.001 atomic% to 0.5 atomic% of Bi.

2. The Au-Ni-Pd-Pt noble metal alloy according to claim 1, comprising 0.003 atomic percent or more and 8 atomic percent or less of B.

3. The Au-Ni-Pd-Pt noble metal alloy according to claim 1 or claim 2, further comprising 0.1 atomic% to 27.5 atomic% of Cu.

4. The Au-Ni-Pd-Pt noble metal alloy according to claim 1 or claim 2, further comprising 0.15 atomic percent or more and 5 atomic percent or less of a metal element α, wherein the metal element α is at least one of In, Sn, and Sb.

5. The Au-Ni-Pd-Pt noble metal alloy according to claim 3, further comprising 0.15 atomic% to 5 atomic% of a metal element α, wherein the metal element α is at least one of In, Sn, and Sb.

6. The Au-Ni-Pd-Pt noble metal alloy according to claim 1 or claim 2, further comprising 0.05 atomic% to 5 atomic% of a metal element β, wherein the metal element β is at least one of Al, Ti, Zr, and Hf.

7. The Au-Ni-Pd-Pt noble metal alloy according to claim 3, further comprising 0.05 atomic% to 5 atomic% of a metal element β, wherein the metal element β is at least one of Al, Ti, Zr, and Hf.

8. The Au-Ni-Pd-Pt noble metal alloy according to claim 4, further comprising 0.05 atomic% to 5 atomic% of a metal element β, wherein the metal element β is at least one of Al, Ti, Zr, and Hf.

9. The Au-Ni-Pd-Pt noble metal alloy according to claim 5, further comprising 0.05 atomic% to 5 atomic% of a metal element β, wherein the metal element β is at least one of Al, Ti, Zr, and Hf.

10. The Au-Ni-Pd-Pt noble metal alloy according to claim 1 or claim 2, wherein the material structure includes a modulated structure due to spinodal decomposition.

11. The Au-Ni-Pd-Pt noble metal alloy according to claim 1 or claim 2, wherein the material structure includes an ordered phase.

12. The Au-Ni-Pd-Pt noble metal alloy according to claim 10, wherein the material structure includes an ordered phase.

13. The Au-Ni-Pd-Pt precious metal alloy according to claim 1 or claim 2, wherein the Vickers hardness is 500 Hv or higher.

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