High-hardness precious metal alloy and method for manufacturing the same

Abstract

The present invention is a noble metal alloy mainly made from a Pt-Au-Ni-Pd quaternary alloy. The noble metal alloy contains 7.5 at% to 72.5 at% inclusive of Pt, 5.5 at% to 62.5 at% inclusive of Au, 3 at% to 62.5 at% inclusive of Ni and 0.15 at% to 38 at% inclusive of Pd. When the concentrations (at%) of Pt, Au, Ni and Pd are respectively defined as CPt, CAu, CNi and CPd, the value of a first composition parameter z1 mentioned below is 0.5 to 2.88 inclusive and the concentration of Pd CPd is CPd ≤ z2 relative to the value of a second composition parameter z2 mentioned below. The noble metal alloy according to the present invention is a high-hardness noble metal alloy to which a strengthening mechanism by spinodal decomposition and / or ordering is applied. z1 = (CPt×CAu×CNi) / 10000 z2 = a×(CAu)3+b×(CAu)2+c×CAu+d In the formulae, variables a, b, c and d are respectively the following values. a = 0.00077, b = -0.102, c = 3.607, d = 1.722

Description

[Technical Field]

[0001] This invention relates to a high-hardness precious metal alloy in which the precious metals Pt, Au, and Pd are essential constituent metals. More specifically, it relates to a Pt-Au-Ni-Pd quaternary alloy that achieves a higher hardness than conventional alloys through spinodal decomposition and / or ordering. [Background technology]

[0002] Precious metals such as platinum (Pt) and gold (Au) are metals that have excellent chemical stability and corrosion resistance, as well as good electrical properties such as conductivity. For this reason, precious metals and their alloys are used in various fields such as the electrical and electronic fields and the medical field. Examples of the use of precious metal alloys in the electrical and electronic field include probe pins incorporated into probe cards for testing semiconductor devices, motor brushes, relays, switches, and other electrical contacts (sliding contacts and switching contacts). In the medical field, their use has attracted attention in recent years, and precious metal alloys are used as constituent materials for various medical devices. Examples of these medical devices include various forms of medical devices such as embolization coils, embolization clips, guide wires, stents, and catheters. Since these medical devices are instruments that come into direct contact with the human body and are implanted inside the body, biocompatibility and chemical stability are required. Medical devices also require X-ray visibility for use in surgery and diagnosis using X-rays. Precious metal alloys have good biocompatibility and X-ray visibility.

[0003] Furthermore, in order to be used in the various applications mentioned above, precious metal alloys are required to have improved mechanical properties such as hardness and strength. For example, probe pins are subjected to repeated contact with mating materials over long periods of time, so wear resistance is required. 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. Also, in the case of medical devices, instruments that move and are implanted in pulsating blood vessels, such as guide wires and embolization coils, are required to have mechanical properties such as hardness and springiness so that their operation does not become distorted.

[0004] Since precious metal alloys are also metals, the general strengthening mechanisms for metallic materials can be applied to improve their hardness. Specifically, the hardness of precious metal alloys has been improved by applying a combination of strengthening mechanisms such as work hardening (dislocation strengthening), solid solution strengthening, and precipitation hardening (dispersion strengthening). As an example of improving the hardness of precious metal alloys used as probe pins and contact materials, the Pt-Ni alloy described in Patent Document 1 achieves increased hardness through solid solution strengthening by alloying Ni etc. with Pt, as well as work hardening with a high final processing rate. Furthermore, Patent Document 2 (Ag-Pd-Cu alloy) and Patent Document 3 (Pt-Cr-Ni alloy) obtain high-hardness precious metal alloys through solid solution strengthening and precipitation hardening by added elements, as well as work hardening with an adjusted processing rate. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2005-233967 [Patent Document 2] Japanese Patent Publication No. 2012-242184 [Patent Document 3] Patent No. 6372952 specification [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] As mentioned above, there is a demand for improved mechanical properties such as hardness in precious metal alloys for various applications. To meet this demand, it can be said that further strengthening through the various strengthening mechanisms described above is necessary. However, while attempts have been made to optimize the selection and amount of additive elements and manufacturing processes such as heat treatment for solid solution strengthening and precipitation strengthening, there are limits to the amount of hardening that can be achieved by these methods. For example, the amount of hardening by precipitation hardening in the precious metal alloys described in Patent Documents 2 and 3 is about 150 Hv, and sufficient hardness cannot be achieved by precipitation hardening alone. In reality, for these precious metal alloys, work hardening is used to supplement the hardness in addition to precipitation hardening.

[0007] Furthermore, there are concerns about the excessive application of work hardening. While work hardening is a useful strengthening method that allows for a large degree of hardening, it can also lead to material embrittlement. Material embrittlement can cause wire breakage during wire drawing, cracking or fracture during secondary processing (pressing, coiling, bending, etc.), and during actual use. Electrical materials such as probe pins and medical devices such as guide wires and embolization coils are manufactured by processing fine wires, so ensuring processability in fine wire processing is necessary. Therefore, considering the issues of material embrittlement and processability, it must be said that there are limits to the amount of hardening that can be achieved through work hardening.

[0008] The present invention was developed against the background described above, and provides a noble metal alloy with increased hardness by applying a strengthening mechanism different from conventionally used methods. In addressing this issue, the present invention presents a material strengthening method based on a process mainly involving heat treatment, without relying on work hardening. [Means for solving the problem]

[0009] To solve the above problems, the present inventors focused on spinodal decomposition as a strengthening method different from the strengthening mechanisms described above. Spinodal decomposition is a form of phase separation in material microstructure, in which decomposition proceeds not by nucleation and growth processes as applied to precipitation hardening, but by a continuous increase in concentration fluctuations. The material microstructure generated by this spinodal decomposition caused by concentration fluctuations exhibits an extremely 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. As a result, a periodic internal stress field is generated on the slip plane, which interacts with dislocations.

[0010] This strengthening mechanism by spinodal decomposition is similar to precipitation strengthening by nucleation and growth, but it differs in that it uses changes in the lattice constant caused by concentration modulation, rather than precipitates, to hinder dislocation movement. Furthermore, as mentioned above, spinodal decomposition strengthening exhibits a high degree of hardening due to its finely modulated structure, making it a useful means of improving hardness without causing material embrittlement like work hardening.

[0011] However, the phenomenon of spinodal decomposition and the microstructure formed by this phenomenon are well known, and the strengthening mechanism due to this phenomenon has also been elucidated to some extent. Furthermore, among precious metal alloys, Pt-Au alloys are known to undergo spinodal decomposition. Figure 1 shows the phase diagram of the Pt-Au system. In Pt-Au alloys, thermodynamic calculations have revealed the region (chemical spinodal curve) that indicates the composition and temperature range in which spinodal decomposition can occur.

[0012] However, even if Pt-Au alloys harden through spinodal decomposition, the amount of hardening is at most about 160 Hv, and the resulting hardness is limited to about 500 Hv. Furthermore, although the phenomenon and mechanism of spinodal decomposition are well known, there are few examples of its application, especially to precious metal alloys. The inventors believed that there was room for improvement in spinodal decomposition strengthening as a hardening and strengthening method for precious metal alloys, and decided to conduct further investigations. As a result, the inventors concluded that there are limits to optimizing the composition within the range of binary alloys in order to maximize the hardening ability of precious metal alloys through spinodal decomposition, and that alloys with three or more elements should be applied. After diligent investigations, the inventors found that by optimizing the composition of a quaternary alloy of Pt, Au, Ni, and Pd, and by performing appropriate heat treatment, it is possible to increase the hardness through spinodal decomposition.

[0013] Furthermore, during the above investigation process, the inventors also discovered that the Pt-Au-Ni-Pd quaternary alloy of the above-mentioned predetermined composition can undergo ordering of its constituent elements, either together with or independently of spinodal decomposition. This ordering creates a ordered phase with a predetermined structure, resulting in an increase in hardness. The inventors realized that hardening due to such an ordered phase can act on the Pt-Au-Ni-Pd alloy either independently or in combination with hardening due to spinodal decomposition.

[0014] Furthermore, if the Pt-Au-Ni-Pd alloy is a noble metal alloy that can be hardened by spinodal decomposition and ordering, then there must naturally be a composition range in which these properties manifest. As a result of further investigation, the inventors explored the composition range of alloys that become highly hardened by spinodal decomposition, etc., and found that defining such a range requires not only specifying the composition range for each metal element (Pt, Au, Ni, Pd), but also introducing parameters related to their interrelationships (hereinafter referred to as composition parameters). The inventors then optimized the alloy composition range in which high hardness can occur by spinodal decomposition and ordering, as well as two composition parameters, and arrived at the present invention.

[0015] In other words, the present invention is a noble metal alloy comprising 7.5 atomic% to 72.5 atomic% of Pt, 5.5 atomic% to 62.5 atomic% of Au, 3 atomic% to 62.5 atomic% of Ni, and 0.15 atomic% to 38 atomic% of Pd, wherein the concentrations (atomic%) of Pt, Au, Ni, and Pd are each C Pt , C Au , C Ni , C Pd In this case, the value of the first composition parameter z1, shown by the following formula, is between 0.5 and 2.88, and furthermore, the Pd concentration C Pd However, for the second composition parameter z2 shown in the following formula, C Pd It is a precious metal alloy where z ≤ z².

[0016]

number

[0017] [Numerical]

[0018] Further, the present invention provides a noble metal alloy comprising Pt in an amount of 10 atomic% to 67.5 atomic%, Au in an amount of 5.85 atomic% to 40 atomic%, Ni in an amount of 10 atomic% to 60 atomic%, and Pd in an amount of 0.2 atomic% to 34 atomic%, and satisfying the requirements for the first and second composition parameters described above.

[0019] Furthermore, the present invention provides a noble metal alloy comprising Pt in an amount of 17.5 atomic% to 60.5 atomic%, Au in an amount of 6.25 atomic% to 30 atomic%, Ni in an amount of 15 atomic% to 57.5 atomic%, and Pd in an amount of 0.75 atomic% to 24.5 atomic%, and satisfying the requirements for the first and second composition parameters described above.

[0020] And, as described above, the Pt-Au-Ni-Pd alloys falling within the above three composition ranges include a modulated structure formed by spinodal decomposition and / or an ordered phase.

[0021] The present application also provides a method for producing the noble metal alloy described above. Specifically, the method for producing a noble metal alloy according to the present invention comprises: a step of preparing a noble metal alloy comprising Pt in an amount of 7.5 atomic% to 72.5 atomic%, Au in an amount of 5.5 atomic% to 62.5 atomic%, Ni in an amount of 3 atomic% to 62.5 atomic%, and Pd in an amount of 0.15 atomic% to 38 atomic%; a solution treatment step of heating the noble metal alloy at a temperature of 850°C to 1350°C and then quenching the same; and an aging treatment step of heating the noble metal alloy after the solution treatment at a temperature of 300°C to 700°C.

[0022] Furthermore, another method for producing a precious metal alloy according to the present invention is a method for producing a precious metal alloy comprising the steps of: preparing a precious metal alloy containing 7.5 atomic% to 72.5 atomic% of Pt, 5.5 atomic% to 62.5 atomic% of Au, 3 atomic% to 62.5 atomic% of Ni, and 0.15 atomic% to 38 atomic% of Pd; and a heat treatment step of heating the precious metal alloy at a temperature of 850°C to 1350°C and then cooling it, wherein the cooling in the heat treatment step is a process of rapid cooling in a temperature range of 600°C or higher below the melting point, and then cooling in a temperature range of less than 600°C at a cooling rate of 2.5°C / s or less. [Effects of the Invention]

[0023] As described above, the present invention provides a noble metal alloy in which material strengthening is achieved by modulated structure and ordered phases due to spinodal decomposition, instead of the solid solution strengthening, precipitation strengthening, and work hardening methods that have been widely used to date as material strengthening methods. According to the present invention, a noble metal alloy with unprecedented hardness can be obtained without relying on work hardening (dislocation strengthening), which may lead to material embrittlement. [Brief explanation of the drawing]

[0024] [Figure 1] A diagram showing the phase diagram of the Pt-Au system and the spinodal curve in Pt-Au alloys. [Figure 2] This figure shows the XRD results of the solution-treated and aged materials for Example 20 (Pt67.5-Au10-Ni17.5-Pd5). [Figure 3] This figure shows the XRD results of the solution treatment material and aged material for Example 36 (Pt35-Au10-Ni35-Pd20). [Figure 4] This figure shows the XRD results for the solution-treated and aged materials of Example 71 (Pt42.5-Au10-Ni42.5-Pd5). [Figure 5] This figure shows the XRD results of the solution-treated and aged materials of Example 75 (Pt37.5-Au10-Ni37.5-Pd15). [Figure 6] This figure shows the XRD results for the solution-treated and aged materials of Comparative Example 13 (Pt22.5-Au10-Ni22.5-Pd45). [Figure 7] This figure shows the XRD results for the solution-treated and aged materials of Comparative Example 11 (Pt30-Au10-Ni30-Pd30). [Figure 8] STEM-EDS mapping image showing the modulated structure of Example 75 (Pt37.5-Au10-Ni37.5-Pd15). [Figure 9] Electron diffraction pattern showing the ordered phase (L12 structure) of Example 75 (Pt37.5-Au10-Ni37.5-Pd15) [Modes for carrying out the invention]

[0025] Embodiments of the present invention are described below. As described above, the noble metal alloy according to the present invention is a Pt-Au-Ni-Pd quaternary alloy, and its hardening factor includes at least one of a modulated structure due to spinodal decomposition and a ordered phase due to ordering. In the following description, each strengthening mechanism in the present invention will be explained, the constituent metals of the noble metal alloy of the present invention and their composition range and two composition parameters will be explained, and the material structure characteristics and hardness of the noble metal alloy of the present invention will be explained. In addition, the manufacturing method (heat treatment process) of the noble metal alloy according to the present invention will also be explained.

[0026] (A) Composition of the precious metal alloy according to the present invention (A-1) Strengthening mechanism of precious metal alloys in the present invention (1) Spinodal decomposition As already mentioned, the structure formed by spinodal decomposition is called a modulated structure. In a modulated structure, periodic concentration fluctuations occur, 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)).

[0027]

number

[0028] In the analysis based on Equation 3 above, the general trend is that the elastic modulus is proportional to the Young's modulus of each constituent metal, and the lattice strain ε is proportional to the difference in lattice constants between the constituent metals. Furthermore, the concentration modulation amplitude A in Equation 3 is considered to be larger the larger the mixing enthalpy between each metal element. The lattice constants of Pt, Au, Ni, and Pd constituting the Pt-Au-Ni-Pd alloy of the present invention are known as shown in Table 1 below. The mixing enthalpy values ​​are known as shown in Table 2 below (Reference: Akira Takeuchi, Akihisa Inoue, "Classification of Bulk Metallic Glasses by Atomic Size Difference, Heat of Mixing and Period of Constituent Elements and Its Application to Characterization of the Main Alloying Element", Materials Transactions, vol46(2005), p2817-2829.)

[0029] [Table 1]

[0030] [Table 2]

[0031] Referring to Table 2, the enthalpy of mixing is positive for the combinations of Au-Pt, Au-Ni, and Pt-Pd. While single phases are obtained at high temperatures in Au-Pt and Au-Ni alloys, their binary phase diagrams reveal that they exhibit very high values ​​for enthalpy of mixing. The occurrence of spinodal decomposition and significant hardening due to modulated structures in the noble metal alloys according to the present invention can be estimated by considering Equation 3, based on the binary phase diagrams of each constituent metal, and referring to the lattice constants in Table 1 and the enthalpy of mixing in Table 2. A more detailed explanation of this point will be provided later.

[0032] (2) Regularization (regular phase) The ordered phase generated by ordering contributes to the increased hardness of the alloy through the following factors: (i) the Burgers vector of dislocations becomes larger, (ii) inverse phase boundaries can 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.

[0033] The noble metal alloy according to the present invention contains both metals that constitute a Pt-Ni alloy, which is known as a combination of metals that undergoes ordering. Ordering in Pt-Ni alloys is known to occur through solution treatment and aging treatment, and hardening occurs through aging treatment within the ordered-disordered transformation region or air cooling from the single-phase region. Furthermore, in the ordering of Pt-Ni alloys, hardening can occur due to an ordered phase with an L10-type structure or an L12-type structure.

[0034] The noble metal alloy according to the present invention can achieve high hardness through a ordered phase formed by ordering, similar to the Pt-Ni alloy described above. Although the composition of the ordered phase in the present invention is not entirely clear, it is considered to be a phase having the same or similar crystal structure as the ordered phase formed in the Pt-Ni alloy described above. That is, it is a phase containing at least Pt and Ni and having an fcc structure and / or fct structure. Furthermore, the ordered phase in the present invention is presumed to preferably be a phase with an L10 type structure, an L12 type structure, or a crystal structure similar thereto.

[0035] (A-2) The function of the constituent metals of the noble metal alloy according to the present invention The noble metal alloy according to the present invention is a Pt-Au-Ni-Pd quaternary alloy. Referring to the binary phase diagrams composed of each of the metal elements Au, Ni, Pd, and Pt, it can be seen that Au-Ni, Au-Pt, and Pt-Pd alloys are of the two-phase separation type. Furthermore, according to Table 2 above, it can be seen that there are many combinations of elements where the mixing enthalpy between the metal elements Au, Ni, Pd, and Pt is positive. From this, it can be seen that the Pt-Au-Ni-Pd alloy has a high mixing enthalpy and a strong tendency towards phase separation in the low-temperature range. Therefore, the Pt-Au-Ni-Pd quaternary alloy is likely to undergo spinodal decomposition, and the resulting concentration amplitude (A) is also considered to be large. In addition, since Pt and Ni have relatively high Young's moduli, their elastic modulus (Y) is also considered to be high. Furthermore, since Ni has a large difference in lattice constants with Au, Pt, and Pd, it is considered to have a large lattice strain (ε). Considering these factors and equation 3, the constituent metals of the noble metal alloy according to the present invention are considered to be a suitable combination for inducing spinodal decomposition and achieving high hardness through spinodal decomposition. The functions of each metal constituting the present invention will be explained below.

[0036] Pt Pt is an essential element for spinodal decomposition in the alloy system of the present invention. Spinodal decomposition does not occur if the Pt concentration is too low or too high; there is a necessary concentration range for Pt to occur. Furthermore, Pt can form an ordered phase with Ni and contribute to an increase in hardness. In addition, Pt has a relatively high Young's modulus of 169.9 GPa. As can be seen from equation 3 above, Pt can be expected to be a metal that increases the amount of hardening of the alloy when spinodal decomposition is induced.

[0037] Au Au is also 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.

[0038] Ni Ni acts as a strengthening factor when spinodal decomposition occurs in the noble metal alloy of the present invention. Ni has a higher Young's modulus compared to Au, Pt, and Pd. Also, as can be seen from Table 1 above, Ni has a large difference in lattice constants with each of the metals Au, Pt, and Pd, which increases the lattice strain ε. Therefore, from Equation 3 above, Ni has the effect of increasing the strengthening ability due to spinodal decomposition. Furthermore, 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.

[0039] 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 the precious metals. This also has the secondary effect of reducing the overall price of the precious metal alloy.

[0040] Pd Pd expands the solid solubility limits of each element constituting the noble metal alloy of the present invention, broadening the concentration range in which spinodal decomposition occurs in the noble metal alloy according to the present invention, and also promotes spinodal decomposition, thereby improving the amount of hardening due to spinodal decomposition. However, if Pd is added in excess, the spinodal decomposition temperature drops excessively, which tends to inhibit spinodal decomposition. Furthermore, excessive addition of Pd also tends to suppress ordering, leading to 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 an optimal concentration range for Pd as described above. Also, as will be described later, the Pd concentration will be regulated by compositional parameters related to the Au concentration.

[0041] (A-3) Composition range of the noble metal alloy according to the present invention (1) Composition range of each metallic element The noble metal alloy according to the present invention defines the composition range of each metal element, Pt, Au, Ni, and Pd, in order to exhibit the effects described above. This composition range is as follows: Pt: 7.5 atomic% to 72.5 atomic%, Au: 5.5 atomic% to 62.5 atomic%, Ni: 3 atomic% to 62.5 atomic%, and Pd: 0.15 atomic% to 38 atomic%. This concentration range is defined to induce spinodal decomposition and ordering, which are effective in increasing the hardness of the noble metal alloy. In the following, this composition range may be referred to as composition range A1.

[0042] The details of the manufacturing method for the noble metal alloy of the present invention will be described later, but spinodal decomposition occurs in the solution treatment and aging treatment steps in which the solid solution alloy of the above composition is rapidly cooled, and high hardness can be obtained. The noble metal alloy of the present invention has a wide range of regions where complete solid solution occurs in the high temperature range, while having a solubility gap in the low temperature range. Therefore, it is thought that the noble metal alloy of the present invention having the above composition range can form a supersaturated solid solution by rapidly cooling after solution treatment in the high temperature range, and spinodal decomposition can occur by subsequent aging treatment. Furthermore, regarding the thermodynamic behavior of the noble 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 (e.g., Thermo-Calc (Itochu Techno-Solutions Corporation)) and a noble metal alloy database (e.g., TCNOB1 (Itochu Techno-Solutions Corporation)).

[0043] (2) Composition parameters z1, z2 In addition to having the above-mentioned composition range for each constituent metal element, the noble metal alloy according to the present invention must satisfy the first and second composition parameters z1 and z2, which relate to the interrelationship of the concentrations of each metal element. These two composition parameters specify the concentrations (atomic %) of Pt, Au, and Ni in the noble metal alloy, respectively, C Pt, C Au , C Ni , C Pd , it is defined as follows.

[0044] The first composition parameter z1 is defined by the following formula based on the concentrations of Pt, Au, and Ni (C Pt , C Au , C Ni ).

[0045] [Num.]]

[0046] In the present invention, the value of the first parameter z1 is required to be 0.5 or more and 2.88 or less. When the value of z1 is less than 0.5, the spinodal strengthening ability is weak, and sufficient hardness cannot be obtained even after aging treatment. On the other hand, when the value of z1 exceeds 2.88, the solid solubility limit of each element is low, and the two-phase separation tendency becomes excessively strong. Therefore, a sufficient supersaturated solid solution cannot be obtained even by solution treatment, resulting in insufficient hardness after aging treatment. The value of the first composition parameter z1 is more preferably 1.0 or more and 2.7 or less, and even more preferably 1.1 or more and 2.6 or less.

[0047] The second composition parameter z2 is defined by the following formula based on the Au concentration (C Au ) in the noble metal alloy.

[0048] [Num.]]

[0049] The second composition parameter z2 defines the upper limit of the Pd concentration in the noble metal alloy (the Pd concentration defined by this composition parameter z2 is sometimes referred to as the Pd critical concentration). In the noble metal alloy according to the present invention, the Pd concentration is required to be z2 or less. When the Pd concentration exceeds z2, spinodal decomposition and / or ordering of the noble metal alloy is suppressed, resulting in insufficient overall hardening. The second composition parameter z2 is a composition parameter set based on this finding.

[0050] The second composition parameter z2 is defined by the coefficients a, b, c, and d in the above formula. These coefficients a, b, c, and d are a=0.00077, b=-0.102, c=3.607, and d=1.722. The parameter z2 obtained using these coefficients is preferably a=0.00143, b=-0.155, c=4.739, and d=-10.201. More preferably, the composition parameter z2 is calculated using a=0.00310, b=-0.255, c=6.047, and d=-18.974.

[0051] The composition of the precious metal alloy according to the present invention must satisfy both the compositional range of each metal element described above and the requirements defined based on the two compositional parameters z1 and z2 described above.

[0052] Furthermore, the present invention relates to a noble metal alloy containing Pt, Au, Ni, and Pd within the above range, and more preferably a noble metal alloy consisting of Pt, Au, Ni, and Pd within the above range and unavoidable components. Unavoidable components are components that are inevitably included due to impurities in the raw materials or due to the manufacturing process, etc. Specifically, unavoidable components include Ag, Rh, Ir, Ru, Al, Mg, Ca, Fe, Mn, Sc, Y, Zr, Zn, Re, Mo, Cr, Nb, Ta, V, Hf, Ti, W, Co, Si, Sn, Cu, Th, B, C, N, S, P, O, H, rare earth elements, etc. These unavoidable impurities are introduced from the raw materials and the equipment used during melting and casting. The content of these unavoidable impurities is preferably within a range that does not impair the properties of the noble metal alloy of the present invention, preferably 0.1 atomic% or less per element, preferably 0.5 atomic% or less in total, and particularly preferably 0.1 atomic% or less in total. Furthermore, when the above-mentioned unavoidable components are present in a precious metal alloy, it is difficult to clearly distinguish whether they are components that were unavoidably included or components that were intentionally added. In this invention, as long as the component does not alter the properties of the precious metal alloy, it is considered an unavoidable component without distinguishing the intention behind its inclusion.

[0053] (A-3) Material structure of the precious 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. Its material structure includes a finely modulated structure and / or ordered phase due to spinodal decomposition. The modulated structure is a material structure in which the composition fluctuates with a modulation period at the nanoscale. These material structures can be confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron diffraction patterns of TEM, and scanning transmission electron microscopy (STEM).

[0054] In X-ray diffraction (XRD) patterns or electron diffraction patterns obtained by TEM, broad peaks known as sideband peaks (satellite peaks) are observed on at least one side (preferably both sides) of the main peak. The presence or absence of these sideband peaks can be used to determine whether a spinodal decomposition structure is present. Since the crystal structure of the matrix of the noble metal alloy according to the present invention is face-centered cubic (fcc), Miller indices such as the {111}, {200}, {220}, and {311} planes 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.

[0055] Furthermore, the ordered phase can be confirmed by observing ordered reflection peaks in X-ray diffraction patterns or electron diffraction patterns. For example, in the observation of ordered reflection peaks in X-ray diffraction patterns, when using CuKα rays as the X-ray source for θ-2θ measurements, ordered reflection peaks appear around 2θ = 30° to 35°.

[0056] Furthermore, the modulated structure in the noble metal alloy composed of Pt, Au, Ni, and Pd according to the present invention tends to consist 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). In addition, the ordered phase formed in the noble metal alloy according to the present invention includes at least one of an L10-type structure or an L12-type structure, and in particular tends to include an L12-type structure.

[0057] (A-4) Hardness of the precious metal alloy according to the present invention The noble metal alloy according to the present invention has the above-mentioned composition range and satisfies two composition parameters z1 and z2, thereby achieving hardening by spinodal decomposition and / or ordering. The noble metal alloy according to the present invention exhibits a Vickers hardness of 500 Hv or higher. Furthermore, the noble metal alloy according to the present invention can be made into the aforementioned high-hardness noble metal alloy by heat treatment alone, without utilizing work hardening at all, that is, without causing material embrittlement due to dislocation strain.

[0058] Furthermore, the hardness value of the precious metal alloy according to the present invention can be adjusted depending on its composition range. Within the above composition range A1, the precious metal alloy exhibits a Vickers hardness of 500 Hv or higher. Within this composition range, the composition range of Pt: 10 atomic% to 67.5 atomic%, Au: 5.85 atomic% to 40 atomic%, Ni: 10 atomic% to 60 atomic%, and Pd: 0.2 atomic% to 34 atomic%, exhibits a Vickers hardness of 550 Hv or higher (hereinafter sometimes referred to as composition range A2). Furthermore, by setting the composition range to Pt: 17.5 atomic% to 60.5 atomic%, Au: 6.25 atomic% to 30 atomic%, Ni: 15 atomic% to 57.5 atomic%, and Pd: 0.75 atomic% to 24.5 atomic%, it exhibits a Vickers hardness of 620 Hv or higher (hereinafter sometimes referred to as composition range A3). Furthermore, the requirements based on the two compositional parameters z1 and z2 described above also apply to the compositional ranges A2 and A3. In addition, the preferred or more preferred values ​​of a, b, c, and d for z2 can be similarly applied to the compositional ranges A2 and A3.

[0059] Furthermore, while there is no particular upper limit to the hardness of the precious metal alloy according to the present invention, it is preferable that the upper limit be 800 Hv or less. If it exceeds 800 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 with a known Vickers hardness tester. The measurement load is preferably 0.05 kgf or more and 0.5 kgf or less, and more preferably 0.2 kgf.

[0060] (B) Method for producing a precious metal alloy according to the present invention Next, a method for producing a precious metal alloy according to the present invention will be described. In this invention, a high-hardness precious metal alloy is produced by selecting constituent metals (Pt, Au, Ni, Pd) and optimizing their composition ranges to induce spinodal decomposition and / or ordering. This precious metal alloy is produced by limiting the composition range of the constituent metals and by an optimal heat treatment process for the precious metal alloy. The optimal heat treatment process is a heat treatment process that combines solution treatment and aging treatment, through which spinodal decomposition and / or ordering proceeds, resulting in high hardness. The method for producing a precious metal alloy according to the present invention is a method that hardens the material by heat treatment without relying on work hardening. The method for producing a precious metal alloy according to the present invention will be described below, referring to each heat treatment process. 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.

[0061] However, the precious metal alloy according to the present invention is not produced solely by the optimal heat treatment process described above. Depending on the cooling conditions during the cooling process of the solution treatment, spinodal decomposition and / or ordering may occur during the solution treatment, and the precious metal alloy according to the present invention can be obtained when the solution treatment is completed. In other words, the precious metal alloy according to the present invention can be produced even if the aging treatment under the above conditions is omitted. This manufacturing method can also be called a preferred manufacturing method, and this manufacturing method will be explained after the optimal heat treatment process described above.

[0062] (B-1) Preparation process (Preparation of precious metal alloys) First, a pre-fermented precious metal alloy, which will serve as a precursor to the precious metal alloy of the present invention, is prepared. The precursor alloy can be manufactured by a conventional melting and casting method. The above-mentioned metal raw materials of Pt, Au, Ni, and Pd are appropriately weighed and adjusted to the above composition, and then melted and cast to produce an alloy ingot. At this time, alloys (master alloys) such as Au-Pd alloy and Pt-Ni alloy may be appropriately combined and melted. The melting and casting of the precious metal alloy can be carried out by known means such as arc melting, high-frequency melting, vacuum melting, and continuous casting.

[0063] 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 a known additive manufacturing method with precious metal alloy powder prepared with the above composition. Furthermore, a precious metal alloy layer of the above composition may be formed on any base material using known alloy forming means such as sputtering or thermal spraying.

[0064] (B-2) Heat treatment process (1) Solution treatment A supersaturated solid solution is formed from the precious metal alloy prepared as described above by solution treatment. Solution treatment is a process in which the precious metal alloy is heated to a high temperature to form a single phase or a solid solution structure similar to a single phase, 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 precious metal alloy. Temperatures below (Tm-500°C) are undesirable because the solid solubility of each element is low and insufficient to form a supersaturated solid solution, and temperatures above Tm are undesirable because melting of the material begins near the grain boundaries. The holding time during heating is preferably in the range of 0.01 hours to 168 hours. If it is less than 0.01 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 melting point refers to the solidus line temperature.

[0065] Furthermore, when cooling from the solution treatment temperature, it is necessary to cool quickly enough to prevent grain boundary reactions from occurring in the high-temperature range. In other words, rapid cooling is necessary. The cooling rate at this time is preferably 10°C / s or higher, and more preferably 50°C / s or higher. On the other hand, from the viewpoint of preventing quench cracking, dimensional changes, and deformation, a slower cooling rate is preferable. Therefore, from the viewpoint of improving the hardness of the precious metal alloy, in the low-temperature range where grain boundary reactions do not occur and spinodal decomposition and / or ordering do not proceed excessively, the aforementioned cooling rate referred to as rapid cooling is not necessary. For example, rapid cooling is not necessary in the temperature range below 400°C. Therefore, in order to suppress or reduce the occurrence of quench cracking, etc., rapid cooling may be performed up to 300°C, for example, and then air cooling may be performed in the temperature range below 300°C. It should be noted that the end point of cooling in the solution treatment here is preferably room temperature.

[0066] (2) Prescription The spinodal decomposition and ordering of the noble metal alloy according to the present invention proceed by aging the supersaturated solid solution formed above in a temperature range lower than the spinodal decomposition temperature and the ordered-disordered transformation temperature.

[0067] For aging treatment of supersaturated solid solutions, the heating temperature should be between 300°C and 700°C. Below 300°C, transformation is difficult to proceed. Above 700°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 should preferably be between 0.01 hours and 168 hours. Below 0.01 hours, transformation is insufficient, resulting in variations in hardness, and treatment for more than 168 hours is unproductive and increases manufacturing costs. There are no particular restrictions on the cooling method after the aging treatment is completed.

[0068] By undergoing the optimal heat treatment processes described above, namely solution treatment and aging treatment, a high-hardness precious metal alloy according to the present invention can be obtained. Furthermore, processing and heat treatment may be performed before and after the preparation and heat treatment processes of the precious metal alloy as needed. Examples of these optional processing and heat treatment processes include hot working such as hot forging and hot rolling, and homogenization treatment. Hot working can destroy the solidification structure in the prepared precious metal alloy ingot and eliminate defects such as voids. 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. Homogenization treatment can create a metallic structure with a uniform elemental concentration distribution in the prepared precious metal alloy. However, these processing and heat treatment processes do not affect the progress of spinodal decomposition or ordering. Therefore, these processing and heat treatment processes are optional.

[0069] (3) Other manufacturing methods (other heat treatment processes) Furthermore, as mentioned above, the precious metal alloy according to the present invention is not manufactured solely by a combination of solution treatment and aging treatment. The precious metal alloy according to the present invention can be manufactured without the aging treatment described above by adjusting the cooling conditions during the solution treatment. Here, a preferred manufacturing method for producing the precious metal alloy according to the present invention using only this solution treatment will be described.

[0070] A preferred method for manufacturing this precious metal alloy is the same as described above up to the preparation step of the precious metal alloy and heating for solution treatment, but in the subsequent cooling treatment, rapid cooling is performed in the temperature range of 600°C or higher below the melting point, and cooling at a cooling rate of 2.5°C / s or less in the temperature range below 600°C. That is, rapid cooling is performed in the high temperature range of 600°C or higher below the melting point where grain boundary reactions are likely to occur, but cooling is performed at a slow cooling rate of 2.5°C / s or less in the intermediate temperature range below 600°C where spinodal decomposition and / or ordering proceeds. Regarding this cooling treatment, rapid cooling in the high temperature range is synonymous with the rapid cooling in the solution treatment described above, and a cooling rate of 10°C / s or higher is preferred, and 50°C / s or higher is more preferred. In addition, in the temperature range below 600°C, the cooling rate is 2.5°C / s or less, but preferably 1°C / s or less. In the temperature range below 600°C, isothermal holding or cooling to room temperature by adjusting the cooling rate is preferred. Thus, by increasing the residence time in the temperature range below 600°C, spinodal decomposition and / or ordering can be promoted, making it possible to produce the noble metal alloy according to the present invention.

[0071] Although controlling the cooling rate is difficult, the manufacturing method for precious metal alloys, which includes the above-described cooling treatment, has the same effect as the manufacturing method that combines solution treatment and aging treatment. Furthermore, this manufacturing method allows for the omission of the aging treatment step. This manufacturing method also has the advantage of suppressing or reducing quench cracking, dimensional changes, and deformation that may occur when excessive rapid cooling is performed during the solution treatment.

[0072] Furthermore, even in the preferred manufacturing method described above, which does not involve aging treatment, hot working, homogenization, etc., may be optionally performed before or after the preparation of the precious metal alloy and the solution treatment process. [Examples]

[0073] The following describes specific embodiments of the present invention. In these embodiments, several Pt-Au-Ni-Pd alloys were manufactured by changing the composition of Pt, Au, Ni, and Pd, and their hardness was measured.

[0074] [Manufacturing of precious metal alloys] As raw materials, high-purity ingots of Pt, Au, Ni, and Pd were weighed and mixed to the specified composition, and an alloy ingot was melted and cast by arc melting in an inert gas. Then, a test piece (5mm x 5mm x 3mm) was cut from the alloy ingot.

[0075] [Heat treatment process (solution treatment)] The prepared test specimens were subjected to solution treatment and aging treatment. In the solution treatment, the test specimens were heated to a temperature of 1100°C to 1250°C, and then cooled with water until they reached room temperature.

[0076] [Heat treatment process (aging treatment)] For the aging treatment, the test specimens after solution treatment were heated and held at 300-650°C for 1 hour. Subsequently, the aged specimens were embedded in resin to remove residual stress due to the oxide layer and thermal strain, and then subjected to rough polishing (#500, #800, #1200) and mirror polishing with 1 μm and 1 / 4 μm diamond suspensions. Through these steps, samples of various compositions were prepared.

[0077] Furthermore, in this embodiment, as reference examples, an Au-Pt alloy, which is a noble metal alloy capable of exhibiting spinodal decomposition, and a Pt-Ni alloy, which is a noble metal alloy capable of exhibiting ordered hardening, were manufactured, and samples were prepared in the same manner as in the above embodiment by performing solution treatment and aging treatment (Reference Examples 1-6).

[0078] [Hardness measurement] Hardness measurements were performed on samples of each precious metal alloy manufactured as described above. Hardness measurements were conducted using a measuring device (Mitutoyo HM-210) with a test load of 0.2 kgf at room temperature. The measurement results are shown in Table 1. For each sample, 15 random measurements were taken, and the average value was used as the hardness value. For each sample, multiple crystal grains were selected, and measurements were taken at the non-grain boundary of each crystal grain, as close to the center of the crystal grain as possible. The measurement results for samples classified according to the compositional regions A1, A2, and A3 are shown in Tables 3 to 5. Furthermore, the measurement results for comparative examples and reference examples of precious metal alloys are shown in Table 6.

[0079] [Table 3]

[0080] [Table 4]

[0081] [Table 5]

[0082] [Table 6]

[0083] Tables 3 to 5 show that the Pt-Au-Ni-Pd alloys in Examples 1 to 89, which are noble metal alloys within the composition range of the present invention, all exhibited a Vickers hardness of 500 Hv or higher. Examples 23 to 52 in Table 4 are alloys that satisfy the above composition range A2, and achieve a hardness of 550 Hv or higher after heat treatment. Furthermore, the noble metal alloys in Examples 53 to 74, which are within the composition range A3, exhibit particularly high hardness of 620 Hv or higher after heat treatment.

[0084] On the other hand, referring to the results of Comparative Examples 1-8 and 13 in Table 6, even quaternary alloys consisting of Pt, Au, Ni, and Pd, if they do not meet the requirements for an appropriate composition range, have a hardness of less than 500 Hv even after heat treatment. Furthermore, Comparative Examples 9 and 10 are noble metal alloys that, although they meet the requirements for a composition range, have a first composition parameter z1 of less than 5.0 (Comparative Example 9) or greater than 2.88 (Comparative Example 10). In addition, Comparative Examples 11 and 12 meet the requirements for a composition range, but their Pd concentrations exceed the critical Pd concentration calculated as the second composition parameter z2. These noble metal alloys suffered from insufficient hardening through spinodal decomposition and ordering, and were unable to harden sufficiently even after heat treatment, resulting in a hardness of less than 500 Hv. From the comparison of these examples with comparative examples, it was confirmed that in order to obtain suitable high hardness in a quaternary alloy consisting of Pt, Au, Ni, and Pd, it is necessary to optimize the concentration range of each constituent metal, as well as to satisfy the requirements of the first and second compositional parameters.

[0085] Furthermore, when examining Au-Pt alloys (Reference Examples 1-3) that can undergo spinodal decomposition similar to the present invention, and Pt-Ni alloys (Reference Examples 4-6) that can exhibit ordered hardening, some alloys with relatively high hardness approaching 500 Hv were observed (Reference Examples 2 and 3), but it was not possible to achieve a hardness of 500 Hv or higher. Reference Examples 2 and 3 are thought to have achieved high hardness through spinodal decomposition, confirming the usefulness of spinodal decomposition as a material strengthening mechanism. In addition, it is thought that hardening due to an ordered phase occurred in the Pt-Ni alloy of Reference Example 5. This Pt-Ni alloy has an equimolar composition of Pt and Ni concentrations, which is presumed to have made it easier for ordered formation to occur. This precious metal alloy of Reference Example 5 also shows good hardness, indicating that the ordered phase is also a useful strengthening mechanism. Thus, it was confirmed that the precious metal alloy according to the present invention can exhibit hardness that surpasses these reference examples by utilizing at least one of spinodal decomposition and ordered formation.

[0086] [Examination of material structure using XRD analysis] XRD analysis was performed on the precious metal alloy of this embodiment manufactured as described above to confirm (a) spinodal decomposition and (b) ordered phase formation. The analytical conditions, such as sample size, for each XRD study were as follows. The heat treatment process (solution treatment and aging treatment) and resin embedding and polishing after heat treatment were carried out in the same manner as described above. Furthermore, this XRD analysis was performed on the precious metal alloy after solution treatment (solution treated material) and the precious metal alloy after aging treatment (aged material), and the results were compared to confirm the occurrence of spinodal decomposition and ordering due to aging treatment.

[0087] [Common conditions] • Sample size: φ22mm x 2mmt • XRD device: PANalytical X'Pert PRO MPD • Target: Cu anode ·Optical system ·Detector: Concentrated optical system ·One-dimensional semiconductor detector (PIXcel 1D) Current / Voltage: 45kV / 40mA

[0088] (a) Confirmation of spinodal resolution (sideband peaks) • 2θ scanning range: 20°~130° • 2θ step size (I): 0.0013 • 2θ scanning speed (I / s): 0.1094

[0089] (b) Confirmation of the rule phase (rule peak) 2θ scanning range: 20°~38° 2θ step size (I): 0.0131 2θ scanning speed (I / s): 0.0223

[0090] In the XRD analysis of spinodal resolution, the XRD diffraction profiles obtained under the above conditions were evaluated based on whether one or more sideband peaks appeared on one or both sides of the main peak (approximately ±0.5 to 3° in 2θ angle) for the Miller index {111}, {200}, {220}, and {311} planes. If one or more sideband peaks appeared, spinodal resolution was considered to have occurred; if none appeared, spinodal resolution was not considered to have occurred; and if the sideband peaks overlapped with the main peak and could not be determined, it was evaluated as unidentifiable.

[0091] Furthermore, in the XRD analysis of the ordered phase, the appearance and intensity of the ordered reflection peak were first confirmed in the XRD diffraction profile of Reference Example 5 (Pt50-Ni50) around 2θ = 30° to 35°. Referring to this, the presence or absence of an ordered peak in the aforementioned angular range was confirmed for the XRD diffraction profile of each sample. Then, it was confirmed whether the ordered peak intensity was higher than the background in that region. In this case, if the ordered peak intensity was higher than the background, it was evaluated as the presence of an ordered phase. On the other hand, if the peak intensity was at or below the background level, it was evaluated as the absence of an ordered phase.

[0092] In this embodiment, the above XRD analysis was performed on the noble metal alloys of Examples 10, 16, 20, 34, 36, 38, 39, 44, 52, 67, 68, 71, 72, 73, and 75, and Comparative Examples 4, 11, and 13. The presence or absence of sideband peaks and ordered peaks in each noble metal alloy was then confirmed. The evaluation results are shown in Table 7. Figures 2, 3, 4, and 5 show the XRD results for the noble metal alloys of Example 20 (Pt67.5-Au10-Ni17.5-Pd5), Example 36 (Pt35-Au10-Ni35-Pd20), Example 71 (Pt42.5-Au10-Ni42.5-Pd5), and Example 75 (Pt37.5-Au10-Ni37.5-Pd15). Figures 6 and 7 show the XRD results for comparative example 13 (Pt22.5-Au10-Ni22.5-Pd45) and comparative example 11 (Pt30-Au10-Ni30-Pd30) of the noble metal alloy. In each figure, (a) shows the XRD diffraction profile for confirming spinodal decomposition, and (b) shows the XRD diffraction profile for confirming the ordered phase.

[0093] [Table 7]

[0094] The analysis of the XRD analysis performed in this embodiment will be explained with reference to Figures 2 to 7. Referring to the results for the noble metal alloy Example 20 (Pt67.5-Au10-Ni17.5-Pd5) in Figure 2, in this noble metal alloy, peaks that can be identified as sideband peaks are observed on both sides of the peak around 2θ = 40° to 41° corresponding to the {111} plane (Figure 2(a)). In addition, for the peaks corresponding to other crystal planes, peaks that can be seen as sideband peaks are observed on one side. On the other hand, looking at Figure 2(b), no peaks that can be said to be higher than the background (ordered peaks) were observed in the region around 2θ = 30° to 35°. From these, it is presumed that spinodal decomposition occurred in Example 20, but ordering did not occur.

[0095] Next, we refer to the results for the noble metal alloys of Example 36 (Pt35-Au10-Ni35-Pd20) in Figure 3, Example 71 (Pt42.5-Au10-Ni42.5-Pd5) in Figure 4, and Example 75 (Pt37.5-Au10-Ni37.5-Pd15) in Figure 5. Referring to Figures 3(a), 4(a), and 5(a), in these noble metal alloys, clear peaks that can be identified as sideband peaks were observed on both sides of the peaks around 2θ=40°~41° corresponding to the {111} plane and the peaks around 2θ=47°~48° corresponding to the {200} plane. Furthermore, for the peaks corresponding to other crystal planes, peaks that can be visually identified as sideband peaks were observed on both sides or on one side. Furthermore, Figures 3(b), 4(b), and 5(b) show that in the region around 2θ = 30° to 35°, a clearly higher peak (ordered peak) than the background was observed in all of the noble metal alloys. From these findings, it can be inferred that both spinodal decomposition and ordering occurred in the noble metal alloys of Examples 36, 71, and 75.

[0096] In contrast to these examples, neither sideband peaks nor ordered peaks were observed in the noble metal alloys of Comparative Example 4 and Comparative Example 13. Figure 5 shows the XRD results for the noble metal alloy of Comparative Example 13 (Pt22.5-Au10-Ni22.5-Pd45). In the XRD profile of the aged noble metal alloy of Comparative Example 13, no sideband peaks were observed on either side of the diffraction peak, nor were any sideband peaks observed on one side. Furthermore, no peaks with higher intensity than the background were observed in the region around 2θ = 30° to 35°.

[0097] On the other hand, referring to the XRD results of the noble metal alloy (Pt30-Au10-Ni30-Pd30) of Comparative Example 11 shown in Figure 6, the peak around 2θ = 47°~48° corresponding to the {200} plane shows the presence of weak peaks on both sides of it that can barely be identified as sideband peaks. Furthermore, looking at Figure 5(b), no peaks with an intensity higher than the background were observed in the region around 2θ = 30°~35°. From these findings, it can be inferred that while spinodal decomposition occurred to a small extent in the noble metal alloy of Comparative Example 11, ordering did not occur.

[0098] Referring to Table 7, and considering the hardness of each precious metal alloy in conjunction with the results of XRD analysis, it can be confirmed that by appropriately adjusting the composition range and composition parameters (z1, z2) of the precious metal alloy and effectively inducing spinodal decomposition and / or ordering, desirable high hardness can be achieved. In the precious metal alloys of Examples 34, 36, 39, 44, 67, 68, 71, 72, 73, and 75, where both spinodal decomposition and ordering occurred, high hardness exceeding 580 Hv was observed, and some even exceeded 700 Hv. Furthermore, the precious metal alloys of Examples 16, 20, 38, and 52, where only spinodal decomposition occurred, also exhibited good hardness. In addition, although a clear sideband peak was not observed, as in the precious metal alloy of Example 10, an ordering peak was confirmed, and the precious metal alloy also showed a hardness exceeding 500 Hv. From these results, it was confirmed that the hardness of precious metal alloys is increased by the occurrence of at least one of spinodal decomposition and ordering. Furthermore, in Comparative Examples 4 and 13, which are outside the composition range specified in the present invention and do not exhibit both spinodal decomposition and ordering, the hardness is clearly lower compared to each example. Considering the results for the noble metal alloy in Comparative Example 11, it was also confirmed that the noble metal alloy of the present invention should also be considered in terms of the range (composition parameter z2) that appropriately exhibits the effects of spinodal decomposition and ordering.

[0099] [Confirmation of material structure using TEM / STEM] The microstructure (emergence of modulated structures due to spinodal decomposition and ordered phases due to ordering) of the noble metal alloy in Example 75 (Pt37.5-Au10-Ni37.5-Pd15) was confirmed. This examination was performed by TEM / STEM analysis. An atomic resolution electron microscope (JEOL Ltd. JEM-ARM300F GRAND ARM) was used for the TEM / STEM analysis (acceleration voltage 300kV). Prior to TEM / STEM analysis, heat treatment processes (solution treatment and aging treatment) and resin embedding and polishing after heat treatment were performed in the same manner as described above, and then samples for TEM / STEM analysis were prepared using a focused ion beam (FIB).

[0100] Figure 8 shows the STEM-EDS mapping results for each constituent element (Pt, Au, Ni, Pd) of the noble metal alloy of Example 75 (Pt, Au, Pd: L line, Ni: K line). From Figure 8, it can be seen that the material structure of the noble metal alloy of this embodiment has a modulated structure with two regions: one with relatively high Au and Pd concentrations and another with relatively low Au and Pd concentrations, and these regions are alternately connected. Since this modulated structure does not have a clear interface, it is presumed to be due to spinodal decomposition.

[0101] Figure 9 shows the TEM analysis of the noble metal alloy of Example 75. <001> This is the electron diffraction pattern obtained under the zone axis incidence condition. As shown in Figure 9, in the noble metal alloy of this embodiment, diffraction spots due to the ordered phase were observed in addition to the fundamental reflection due to the fcc structure. The diffraction spots of the ordered phase are thought to be due to the L12 structure, based on their appearance location, intensity, and interplanar spacing. Therefore, it is thought that the noble metal alloy according to the present invention can be ordered by aging treatment to generate an ordered phase with an L12 structure. [Industrial applicability]

[0102] As described above, the present invention relates to a noble metal alloy having a novel structure and composition range that can exhibit high hardness through spinodal decomposition and / or ordering. According to the present invention, a high-hardness alloy material can be obtained without relying on work hardening (dislocation strengthening). Therefore, high hardness can be achieved without concern for embrittlement associated with work hardening. The noble metal alloy according to the present invention is expected to be applied to various uses where high hardness and high wear resistance are required, such as electrical and electronic materials like probe pins and electrical contacts, medical instruments, and coated members by sputtering, thermal spraying, plating, etc.

Claims

1. A noble metal alloy consisting of 7.5 atomic% to 72.5 atomic% of Pt, 5.5 atomic% to 62.5 atomic% of Au, 3 atomic% to 62.5 atomic% of Ni, 0.15 atomic% to 38 atomic% of Pd, and unavoidable impurities. The concentrations (atomic %) of Pt, Au, Ni, and Pd are given in C Ｐｔ , C Ａｕ , C Ｎｉ , C Ｐｄ In this case, the value of the first composition parameter z1, shown by the following formula, is between 0.5 and 2.

88. Furthermore, the concentration of Pd C Ｐｄ However, C Ｐｄ A precious metal alloy where z ≤ z². [Math 1] [Math 2]

2. The noble metal alloy according to claim 1, comprising 10 atomic% to 67.5 atomic% of Pt, 5.85 atomic% to 40 atomic% of Au, 10 atomic% to 60 atomic% of Ni, 0.2 atomic% to 34 atomic% of Pd, and unavoidable impurities.

3. The noble metal alloy according to claim 1, comprising 17.5 atomic% to 60.5 atomic% of Pt, 6.25 atomic% to 30 atomic% of Au, 15 atomic% to 57.5 atomic% of Ni, 0.75 atomic% to 24.5 atomic% of Pd, and unavoidable impurities.

4. A noble metal alloy according to any one of claims 1 to 3, wherein the material structure includes a modulated structure due to spinodal decomposition.

5. A noble metal alloy according to any one of claims 1 to 4, wherein the material structure includes an ordered phase.

6. A method for manufacturing a precious metal alloy according to any one of claims 1 to 5, A process for preparing a noble metal alloy consisting of 7.5 atomic% to 72.5 atomic% Pt, 5.5 atomic% to 62.5 atomic% Au, 3 atomic% to 62.5 atomic% Ni, 0.15 atomic% to 38 atomic% Pd, and unavoidable impurities. The aforementioned precious metal alloy is heated to a temperature of 850°C or higher and then rapidly cooled in a solution treatment process, A method for manufacturing a precious metal alloy, comprising an aging treatment step of heating the precious metal alloy after the solution treatment at a temperature of 300°C to 700°C.

7. A method for manufacturing a precious metal alloy according to any one of claims 1 to 5, A process for preparing a noble metal alloy consisting of 7.5 atomic% to 72.5 atomic% Pt, 5.5 atomic% to 62.5 atomic% Au, 3 atomic% to 62.5 atomic% Ni, 0.15 atomic% to 38 atomic% Pd, and unavoidable impurities. The process includes a heat treatment step of heating the aforementioned precious metal alloy at a temperature of 850°C to 1350°C and then cooling it. A method for manufacturing a precious metal alloy, wherein the cooling in the heat treatment step is a process of rapid cooling in a temperature range of 600°C or higher below the melting point, and then cooling in a temperature range of less than 600°C at a cooling rate of 2.5°C / s or less.

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