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

Abstract

The present invention is drawn to a Au-Ni-Pd-Pt-based precious metal alloy, resulting from addition of a metal element α to a base alloy including Au, Ni, Pd, and Pt. In the present invention, the metal element α is at least any one metal element selected from In, Sn, Mg, Al, and Ti. The precious metal alloy of the present invention contains 4% by atom or more and 24% by atom or less of Au, 5% by atom or more and 60% by atom or less of Ni, 2.5% by atom or more and 40% by atom or less of Pd, 10% by atom or more and 60% by atom or less of Pt, 0.15% by atom or more and 7.5% by atom or less of the metal element α, and inevitable impurities. The precious metal alloy of the present invention is enhanced in hardness by a modulated texture by spinodal decomposition and / or an ordered phase by ordering, and thus achieves a Vickers hardness of 500 Hv or more. The precious metal alloy of the present invention is a high-hardness precious metal alloy obtained by application of a strengthening mechanism different from a method which has been routinely used such as work hardening and precipitation hardening.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a high-hardness precious metal alloy where Au, Pt, and Pd as precious metals are essential constituent metals, particularly to a precious metal alloy which uses a Au-Ni-Pd-Pt alloy as a base alloy with a predetermined metal element α added to the base alloy, and achieves increased hardness by spinodal decomposition and / or ordering.DESCRIPTION OF THE RELATED ART

[0002] Precious metals such as Pt (platinum) and Au (gold) are metals not only excellent in chemical stability / corrosion resistance, but also favorable in electric characteristics such as conductivity. Therefore, precious metals and alloys thereof are utilized in various fields, for example, in the electric / electronic field and in the medical field. Examples of use of precious metal alloys in the electric / electronic field include probe pins incorporated in probe cards for inspection of semiconductor devices or the like, and electric contacts (sliding contacts / switching contacts) such as brushes for motors, relays, and switches. Use in the medical field has recently attracted attentions, and precious metal alloys are used as constituent materials of various medical instruments. Examples of such medical instruments include various types of medical instruments, such as embolization coils and embolization clips, guide wires, stents, and catheters. Such medical instruments are tools to be directly contacted with the human body and embedded in the human body and thus are required to have biocompatibility and chemical stability. Such medical instruments are also required to have X-ray visibility in consideration of use in surgery / diagnosis with X-ray. Precious metal alloys are also favorable in such biocompatibility and X-ray visibility.

[0003] Precious metal alloys to be subjected to various uses described above are required to be enhanced in mechanical properties such as hardness and strength. For example, probe pins are to be repeatedly contacted with mating materials for a long period, and thus are required to have wear resistance. In particular, higher-hardness probe pins are needed to be developed in order to address recent high integration of various devices and recent high performance of motors. Medical tools such as guide wires and embolization coils, which are travelled in pulsing / beating vessels and then embedded, are required to have mechanical properties such as hardness and spring properties so that operations of such tools are made without any failures.

[0004] Precious metal alloys are also metal materials, and thus common strengthening mechanisms for metal materials can be applied for an enhancement in hardness of such alloys. In other words, conventional precious metal alloys have been tried to be enhanced in hardness by application of any combination of strengthening mechanisms including work hardening (dislocation strengthening), solid solution strengthening, and precipitation hardening (dispersion strengthening). Examples of an enhancement in hardness of the above precious metal alloys as probe pins or contact materials include an increase in hardness by not only solid solution strengthening for alloying of Pt with Ni, W, or the like, but also work hardening for an increase in final rate of working, as in a Pt-Ni alloy described in Patent Document 1, and a Pt-W alloy described in Patent Document 2. In Patent Document 3 (Ag-Pd-Cu-based alloy) and Patent Document 4 (Pt-Cr-Ni-based alloy), a high-hardness precious metal alloy is obtained with not only solid solution strengthening and precipitation hardening with additive elements, but also work hardening where the rate of working is adjusted.Prior Art DocumentPatent Document

[0005] Patent Document 1 Japanese Patent Application Laid-Open No. 2005-233967 Patent Document 2 Japanese Patent No. 6997354 Patent Document 3 Japanese Patent Application Laid-Open No. 2012-242184 Patent Document 4 Japanese Patent No. 6372952 SUMMARY OF THE INVENTIONTECHNICAL PROBLEM

[0006] As described above, precious metal alloys are required to be enhanced in mechanical properties such as hardness in various uses. In order to respond to such requirements, it is also deemed that there is a need for further strengthening with various strengthening mechanisms described above. However, solid solution strengthening and precipitation strengthening, while are tried to achieve selection of an additive element and optimization of the amount of such an additive element, as well as optimization of a production process such as a heat treatment, have limitations to the amount of hardening with these trials. For example, the extent of increase in hardness by precipitation hardening of the precious metal alloys of Patent Documents 3 and 4 is about 150 Hv, and no sufficient hardness is achieved with only precipitation hardening. These precious metal alloys actually make up hardness with not only precipitation hardening, but also work hardening.

[0007] If work hardening is excessively applied, there is a problem to be concerned. Work hardening, while provides a large amount of hardening and is deemed to be a useful strengthening method, sometimes causes embrittlement of a material. Such material embrittlement can be a factor of disconnection during wire drawing, or of breakage or fracture in secondary working (pressing, coiling, bending, or the like) or in actual use. Electric materials such as probe pins and medical tools such as guide wires and embolization coils are produced by working of thin wires, and thus it is necessary to ensure workability in thin-wire working. Therefore, there are also naturally limitations to the amount of hardening by work hardening, in consideration of the problems of material embrittlement and workability.

[0008] The present invention has been made against the background of the above circumstances, and provides a precious metal alloy containing precious metals of Au, Pd, and Pt as essential constituent elements, and increased in hardness by application of a strengthening mechanism different from a method which has been routinely used. In particular, the present invention provides a material-strengthening mechanism based on a process involving mainly a heat treatment without depending on work hardening which may cause embrittlement.SOLUTION TO PROBLEM

[0009] In order to solve the above problems, the present inventors have focused on two phenomena of spinodal decomposition and ordering as a strengthening method different from a method which has been routinely used as noted above.

[0010] Spinodal decomposition corresponds to one mode of phase separation in a material texture, and is a phenomenon where decomposition progresses due to a continuous increase in variation in concentration without a nucleation / growth process to be applied to precipitation hardening. A material texture generated by spinodal decomposition due to the variation in concentration exhibits a very fine periodic structure of several nanometers to several tens of nanometers, called modulated texture. A modulated texture expressed by spinodal decomposition is periodically varied in concentration of a solute atom in a crystal, as a function of location, and is also periodically changed in lattice constant. Thus, a periodic internal stress field is generated on a sliding surface, and the field interacts with dislocation. While such a strengthening mechanism by spinodal decomposition is deemed to be similar to precipitation strengthening due to nucleation / growth, both are different in that the change in lattice constant, imparted with not a precipitate but the modulation in concentration, contributes a hindrance to dislocation movement. Such strengthening by spinodal decomposition provides a high amount of hardening due to a fine modulated texture as described above, and thus is deemed to be useful as a procedure for enhancing hardness without causing any material embrittlement as in work hardening.

[0011] On the other hand, ordering is a phenomenon in which an ordered phase with a predetermined structure is generated by ordering the arrangement of constituent elements in an alloy. The ordered phases generated by ordering contribute to increase in hardness of an alloy due to each of factors of: (i) an increase in the Burgers vector of dislocation, (ii) potential occurrence of antiphase boundary within the ordered phase, and (iii) volume change associated with ordering, which distorts the lattice both inside and outside the ordered phase, resulting in hindering dislocation motion. Ordering may occur in conjunction with spinodal decomposition mentioned above, or ordering may occur independently.

[0012] The phenomena of spinodal decomposition and ordering, and material textures to be expressed by these phenomena themselves are known. In addition, it is also known that there are precious metal alloys with compositions where spinodal decomposition and ordering can occur. As for spinodal decomposition, Pt-Au alloys are known as precious metal alloys where spinodal decomposition can occur. Fig. 1 illustrates a Pt-Au system phase diagram. A Pt-Au alloy is also revealed from thermodynamic calculation, with respect to a region (chemical spinodal curve) indicating composition and temperature regions which allow for the occurrence of spinodal decomposition.

[0013] On the other hand, as for ordering of precious metal alloys, a Pt-Ni-based alloy is known as an alloy capable of expressing ordering. The ordering in a Pt-Ni-based alloy is expressed by a solution treatment and an aging heat treatment, and is known to be achieved by an aging heat treatment in an order-disorder transformation region or air cooling or the like started from a single phase region to result in hardening. In the ordering of this Pt-Ni-based alloy, an ordered phase of an L1 0 -type structure or an L1 2 -type structure can be generated. Besides, although not as well-known as the Pt-Ni-based alloy, a Au-Pd-based alloy is also pointed out as an alloy in which ordering may be expressed. When ordering occurs in a Au-Pd-based alloy, it is predicted that similar ordered phases to those in a Pt-Ni-based alloy will be generated, resulting in hardening.

[0014] However, it is known that spinodal decomposition and ordering can contribute to an increase in hardness of an alloy material, by which extent of increase in hardness is not particularly large in known alloy systems. For example, even if the above Pt-Au alloy is hardened by spinodal decomposition, the extent of increase in hardness is at most about 160 Hv, and it is difficult to increase hardness of a precious metal alloy stably to 500 Hv or more. Also a Pt-Ni alloy capable of expressing ordering is difficult to achieve a hardness of 500 Hv or more.

[0015] In addition, while spinodal decomposition and ordering are known about the phenomena and mechanisms, there are a few specific application examples, in particular, application examples to precious metal alloys. The present inventors have considered that there is a significant room of improvement in spinodal decomposition and ordering, as a method for hardening / strengthening a precious metal alloy, and have decided to make further considerations. As a result, the present inventors have perceived improvement from the following two approaches.

[0016] The first approach for increasing hardness of a precious metal alloy by the present inventors involves employing a multi-component configuration for the precious metal alloy. The present inventors have considered that composition optimization within the range of binary alloys (such as a Pt-Au alloy, a Pt-Ni alloy, and a Au-Pd-based alloy, and the like) has limitations to maximum exhibition of the hardening ability of a precious metal alloy by spinodal decomposition and ordering, and that a ternary or more-component alloy is to be applied. The present inventors have then made intensive studies, and as a result, have found that an increase in hardness by spinodal decomposition and / or ordering can be effectively achieved not only by optimization of the composition of a quaternary alloy of Au, Ni, Pd, and Pt as a configuration of a precious metal alloy, but also by an appropriate heat treatment.

[0017] Besides, the second approach for increasing the hardness of a precious metal alloy involves using the aforementioned Au-Ni-Pd-Pt alloy as a base alloy and further adding another metal element to this base alloy. This additive element is referred to as a metal element α in the present invention. The metal element α does not change the material texture resulting from spinodal decomposition and / or ordering expressed in a Au-Ni-Pd-Pt alloy, but imparts an additional increase in hardness to the base alloy already strengthened by spinodal decomposition and / or ordering. Although the mechanism of this additional hardness increase is not clear, the present inventors presume several factors, such as the effect of the metal element α on the matrix.

[0018] Based on the two approaches described above, the present inventors have made detailed studies on the range of the metal element α to be added to the base alloy of a Au-Ni-Pd-Pt alloy, and the composition range of the Au-Ni-Pd-Pt-based alloy that would effectively achieve an increase in hardness through spinodal decomposition and / or ordering in considering the metal element α being added, and thus have conceived the present invention.

[0019] In other words, the present invention is drawn to a Au-Ni-Pd-Pt-based precious metal alloy resulting from addition of a metal element α to a base alloy including Au, Ni, Pd, and Pt, wherein the metal element α is at least any one metal element selected from In, Sn, Mg, Al, and Ti, and the Au-Ni-Pd-Pt-based precious metal alloy contains 4% by atom or more and 24% by atom or less of Au, 5% by atom or more and 60% by atom or less of Ni, 2.5% by atom or more and 40% by atom or less of Pd, 10% by atom or more and 60% by atom or less of Pt, 0.15% by atom or more and 7.5% by atom or less of the metal element α, and inevitable impurities.

[0020] As described above, the precious metal alloy including the Au-Ni-Pd-Pt-based alloy of the present invention contains a modulated texture by spinodal decomposition, and / or an ordered phase.

[0021] The Au-Ni-Pd-Pt-based precious metal alloy of the present invention is enhanced in hardness by spinodal decomposition and / or ordering. This Au-Ni-Pd-Pt-based precious metal alloy thus increased in hardness has a Vickers hardness of 500 Hv or more.ADVANTAGEOUS EFFECTS OF THE INVENTION

[0022] As described above, a precious metal alloy of the present invention is strengthened in material with a modulated texture by spinodal decomposition and / or an ordered phase by ordering, instead of solid solution strengthening, precipitation strengthening, or work hardening which has been widely used as a material-strengthening method. The present invention allows for achieving a high-hardness precious metal alloy with unprecedented strengthening ability without any work hardening (dislocation strengthening) which may cause material embrittlement.BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Fig. 1 is a diagram illustrating a Pt-Au system phase diagram and a spinodal curve of a Pt-Au alloy; Fig. 2 is a diagram illustrating the results of XRD of a solid solution material and an aging material in a precious metal alloy B-5 of Example (Au 12.5-Ni30.625-Pd25-Pt30.625-Sn 1.25); Fig. 3 is a STEM-EDS mapping image illustrating a modulated texture in the precious metal alloy B-5 of Example (Au12.5-Ni30.625-Pd25-Pt30.625-Sn1.25); and Fig. 4 is an electron diffraction pattern illustrating an ordered phase (L1 2 structure) in the precious metal alloy B-5 of Example (Au12.5-Ni30.625-Pd25-Pt30.625-Sn1.25). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, embodiments of the present invention are described. As described above, the precious metal alloy of the present invention includes a Au-Ni-Pd-Pt-based alloy resulting from addition of a predetermined metal element α to a base alloy of a Au-Ni-Pd-Pt alloy. The precious metal alloy of the present invention includes, as a hardening factor, at least either of a modulated texture by spinodal decomposition and an ordered phase by ordering. The following descriptions are provided, in order to disclose (A) the configuration of the present inventive precious metal alloy, each for (A-1) respective strengthening mechanisms (spinodal decomposition and ordering) applied in the present invention, (A-2) constituent metals of the present inventive precious metal alloy and those composition ranges, (A-3) a material texture of the present inventive precious metal alloy, and (A-4) hardness of the present inventive precious metal alloy. Besides, (B) a method for producing the present inventive precious metal alloy (heat treatment step) is also described.(A) Configuration of present inventive precious metal alloy(A-1) Strengthening mechanisms of present inventive precious metal alloy(1) Spinodal decomposition

[0025] As described above, a texture formed by spinodal decomposition is referred to as so-called modulated texture. The modulated texture is periodically varied in concentration, and circumferentially forms an internal stress field and thus contributes to an increase in hardness. The resistance force (critical shear stress) of dislocation motion in such a periodic internal stress field is expressed by the following expression, and the lattice strain (ε), the elastic coefficient (Y), and the modulation amplitude in concentration (A) are considered to be control factors (examples of specific reference documents include Masaharu KATO, Introduction to the Theory of Dislocations (issued on August, 1999, publication: Shokado).). τ = YA ε 6 τ: Critical shear stress Y: Elastic coefficient A: Modulation amplitude in concentration ε: Lattice strain

[0026] It is considered in studies based on Expression 1 described above that, roughly, the elastic coefficient is proportional to the Young's modulus of each constituent metal and the lattice strain ε is proportional to the difference in lattice constant between the constituent metals. It is also considered that the modulation amplitude in concentration A in Expression 3 indicates a larger value as the mixing enthalpy between metal elements is larger. Values in Table 1 below are known with respect to the lattice constants of Au, Ni, Pd, and Pt constituting the Au-Ni-Pd-Pt alloy as the base alloy of the present invention. Values in Table 2 below are known with respect to values of mixing enthalpy (Reference Document: 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, vol 46 (2005), p 2817-2829.). [Table 1]AuPtNiPdLattice constant (Å)4.083.923.523.89 [Table 2] AuPtNiPdAu-470Pt4--52Ni7-5-0Pd020- (unit: kJ / mol)

[0027] With reference to Table 2, the mixing enthalpy is positive in combinations of Au-Pt, Au-Ni, and Pt-Pd. It is understood from binary phase diagrams of Au-Pt-based and Au-Ni-based alloys that these alloys are characterized by providing a single phase at a high temperature, but being very high in value itself of mixing enthalpy. Expression of spinodal decomposition and remarkable hardening with the modulated texture in the precious metal alloy of the present invention can be presumed in consideration of Expression 3 with reference to the lattice constant in Table 1 and the mixing enthalpy in Table 2 described above, based on each binary phase diagram between the constituent metals. This point is described below in more detail.(2) Ordering (ordered phase)

[0028] An ordered phase generated by ordering contributes to an increase in hardness of the alloy due to each of factors of: the Burgers vector of dislocation, occurrence of an antiphase boundary in the ordered phase, and the lattice strain caused by the volume change associated with ordering. The precious metal alloy of the present invention includes both combinations of metals constituting a Pt-Ni-based alloy and a Au-Pd-based alloy known as a combination of metals which generate ordering.

[0029] The precious metal alloy of the present invention can achieve also increased hardness with an ordered phase generated by the expression of ordering as in the above Pt-Ni-based alloy or Au-Pd-based alloy. Although the configuration of the ordered phase in the present invention is not necessarily completely clear, the configuration is considered to correspond to a phase having a crystal structure same as or similar to the ordered phase which can be generated in the Pt-Ni-based alloy or the Au-Pd-based alloy. In other words, it is a phase including Pt and Ni, or Au and Pd, and having a fcc structure and / or a fct structure. The ordered phase in the present invention is presumed to be preferably a phase of an L1 0 -type structure (PtNi, AuPd) or an L1 2 -type structure (Pt 3 Ni, Ni 3 Pt, Au 3 Pd, Pd 3 Au), or a crystal structure similar to these.(A-2) Respective constituent metals and composition ranges of present inventive precious metal alloy

[0030] The precious metal alloy of the present invention is formed from the base alloy of the Au-Ni-Pd-Pt alloy having a predetermined composition with the metal element α added to this base alloy. Hereinafter, constituent metals and composition ranges of the base alloy, as well as a range and an additive concentration of elements usable as the metal element α will be described.(1) Constituent metals of base alloy (Au-Ni-Pd-Pt alloy)

[0031] The base alloy underlying the present invention is a quaternary Au-Ni-Pd-Pt alloy. The base alloy expresses at least either of spinodal decomposition and ordering, which are strengthening mechanisms applied in the present invention to ensure fundamental material texture and material strength. In other words, the base alloy itself exhibits high hardness, and possesses hardness equal to or greater than that of precious metal alloys achieved through conventional common strengthening mechanisms (solid solution strengthening, precipitation strengthening, and work hardening).

[0032] The base alloy is constituted from metal elements (Au, Ni, Pd, Pt) for effectively expressing spinodal decomposition and / or ordering. With respect to whether or not spinodal decomposition is expressed, referring to a binary phase diagram constituted with the respective constituent metals of the base alloy, Au-Ni-based, Au-Pt-based, and Pt-Pd-based alloys are two-phase separation type alloys. It can be seen from Table 2 above that there are many combinations of elements, in which the mixing enthalpy between metal elements among Au, Ni, Pd, and Pt is positive. It is thus considered that the Au-Ni-Pd-Pt-based alloy is highly liable to have a high mixing enthalpy and exhibit phase separation in a low temperature region. Therefore, it is considered that the Au-Ni-Pd-Pt quaternary alloy highly possibly expresses spinodal decomposition and the concentration amplitude (A) due to such expression is also large. Pt and Ni are relatively high in Young's modulus and thus are considered to be also high in elastic coefficient (Y). Furthermore, Ni is large in difference in lattice constant from those of Au, Pt, and Pd and thus is considered to be also high in lattice strain (ε). In consideration of these and Expression 3, the constituent metals of the base alloy of the present invention are considered to correspond to a suitable combination for achieving expression of spinodal decomposition and an increase in hardness due to spinodal decomposition.

[0033] With respect to the possibility of expression of ordering, as mentioned above, Pt and Ni, as well as Au and Pd, are combinations of metals which can contribute to the generation of ordered phases through ordering. The specific actions of the respective metals constituting the base alloy are described as follows.Au

[0034] Au is an essential element for expression of spinodal decomposition in the alloy system of the present invention. Spinodal decomposition is not expressed at a too high or too low Au concentration, and the concentration range of Au, necessary for expression, is present. If the Au concentration is out of an optimal range, usual nucleation / growth easily occurs and no suitable increase in hardness can be obtained. Besides, Au and Pd are metals capable of forming an ordered phase, and also act to contribute to an increase in hardness by ordering.Ni

[0035] Ni acts as a strengthening factor in expression of spinodal decomposition in the base alloy. Ni is higher in Young's modulus than Au, Pt, and Pd. As can be seen with respect to Table 1 above, Ni is large in difference in lattice constant from those among each metal of Au, Pt, and Pd, and increases the lattice strain ε. Accordingly, Ni acts to increase strengthening ability due to spinodal decomposition, as can be seen from Expression 3. Furthermore, Ni and Pt are metals capable of forming an ordered phase, and also act to contribute to an increase in hardness by ordering.

[0036] Ni is a congener with and is similar in electron structure to Pt and Pd, and thus can constitute an alloy without any losses in corrosion resistance and oxidation resistance of a precious metal as much as possible. Thus, Ni also has a secondary effect of reducing the price of the entire precious metal alloy.Pd

[0037] Pd acts to not only extend the solid solubility limit of each element constituting the base alloy and expand the concentration region which allows for expression of spinodal decomposition in the base alloy, but also promote spinodal decomposition. Owing to these actions, Pd has an effect of enhancing the amount of hardening due to spinodal decomposition. Besides, Au and Pd are metals capable of forming an ordered phase, and also act to contribute to an increase in hardness by ordering. However, if Pd is excessively added, the spinodal decomposition temperature is excessively reduced and thus spinodal decomposition is liable to be inhibited on the contrary. Furthermore, excess addition of Pd is also liable to suppress ordering, leading to a reduction in amount of hardening of the alloy system as a whole. Accordingly, Pd also has an optimal concentration range as described above in order to optimize the amount of hardening of the precious metal alloy.Pt

[0038] Pt is also an essential element for spinodal decomposition in the alloy system of the present invention. Spinodal decomposition is not expressed at a too high or too low Pt concentration, and the concentration range of Pt, necessary for expression, is present. Pt can be taken with Ni to form an ordered phase, contributing to an increase in hardness. The Young's modulus of Pt is as relatively high as 169.9 GPa. As can be seen from Expression 3 described above, Pt can be expected as a metal which allows for an increase in amount of hardening of the alloy in expression of spinodal decomposition.(2) Metal element usable as metal element α

[0039] The present invention is drawn to the precious metal alloy resulting from addition of the metal element α to the base alloy of the Au-Ni-Pd-Pt alloy having the above configuration. The metal element α acts to increase the hardness of the precious metal alloy after aging heat treatment without changing the material texture of the base alloy. In other words, the base alloy has a material texture including a modulated texture due to spinodal decomposition and / or an ordered phase due to ordering, and the metal element α is an additive element that does not affect these. The reason why the addition of the metal element α increases the hardness of the precious metal alloy is not clear, but the present inventors consider one possible factor to be increased strength of the alloy matrix due to increased lattice strain.

[0040] The metal element α is In, Sn, Mg, Al, or Ti. The studies made by the present inventors provide an observation of an increase in the hardness of the Au-Ni-Pd-Pt alloy with these metal elements used. At least one element selected from the group of the above metal elements is added as the metal element α.(3) Composition of present inventive precious metal alloy

[0041] The composition ranges of respective constituent metals of the precious metal alloy of the present invention, for Au, Ni, Pd, and Pt, are set as follows: The composition range of Au is 4% by atom or more and 24% by atom or less, that of Ni is 5% by atom or more and 60% by atom or less, that of Pd is 2.5% by atom or more and 40% by atom or less, and that of Pt is 10% by atom or more and 60% by atom or less. These composition ranges are concentration ranges defined for expressing spinodal decomposition and ordering effective for increase in hardness.

[0042] Besides, the aforementioned composition ranges of Au, Ni, Pd, and Pt are concentration ranges in which an increase in hardness due to the addition of the metal element α is expected. In other words, only from the viewpoint of allowing for expression of spinodal decomposition and / or ordering, it is possible to set composition ranges expanded beyond the aforementioned ranges. However, in such expanded composition ranges, increase in hardness due to the addition of the metal element α may not be observed. The composition ranges of Au, Ni, Pd, and Pt in the present invention are ranges in which a definite increase in hardness is expected due to both spinodal decomposition and / or ordering, and the effect of adding the metal element α.

[0043] The composition range of at least one element selected from In, Sn, Mg, Al, and Ti as the metal elements α is 0.15% by atom or more and 7.5% by atom or less. An addition amount of less than 0.15% by atom makes contribution to increase in hardness of the base alloy difficult. Alternatively, even if the addition amount of the metal element α exceeds 7.5% by atom, no difference is caused in the effect of increasing hardness, while ductility is liable to decrease.

[0044] Spinodal decomposition and ordering are expressed in a solution treatment for quenching a solid solution alloy having the above composition range and an aging heat treatment step. The precious metal alloy of the present invention, while exhibits a region allowing for a whole solid solution widely extending in a high temperature region, has a miscibility gap in a low temperature region. Therefore, it is considered that the precious metal alloy, in which the metal element α is added to the base alloy having the above composition range, can be subjected to a solution treatment in a high temperature region and then quenched to form a supersaturated solid solution and be subjected to a subsequent aging heat treatment to generate spinodal decomposition and ordering. It is here also effective to utilize a CALPHAD method (Calculation of Phase Diagrams method) with respect to thermodynamic behaviors (transformation point, phase equilibrium, solid solubility limit, melting point, and the like) of the precious metal alloy of the present invention. Calculation by a CALPHAD method is preferably made by use of commercially available thermodynamic calculation software (for example, Thermo-Calc (ITOCHU Techno-Solutions Corporation)) and precious metal alloy database (for example, TCNOB1 (ITOCHU Techno-Solutions Corporation)).

[0045] The present invention is here drawn to a precious metal alloy including Au, Ni, Pd, and Pt in the above composition ranges, the metal element α, and an inevitable impurity, preferably a precious metal alloy including Au, Ni, Pd, and Pt in the above ranges, the metal element α, and an inevitable impurity. The inevitable impurity is an unavoidable component included in impurities in a raw material or included due to a production step or the like. Specific examples of the inevitable impurity include Ag, Rh, Ir, Ru, Fe, Sc, Y, Zn, Re, Mo, Cr, Nb, Ta, V, W, Co, Si, Cu, Th, H, and rare-earth elements. Such inevitable impurities are incorporated from a raw material, and an apparatus and the like in melting and casting. The content of such inevitable impurities is preferably within a range not inhibiting characteristics of the precious metal alloy of the present invention, the content per element is preferably 0.1% by atom or less, and the total is preferably 0.5% by atom or less, particularly preferably 0.1% by atom or less. Herein, when the inevitable impurity is included in the precious metal alloy, it is difficult to clearly distinguish whether the inevitable impurity is a component inevitably included or a component willingly added. In the present invention, as long as the component does not modify characteristics of the precious metal alloy, it is considered to be an inevitable impurity without any distinction of the object of such incorporation.(A-3) Material texture of present inventive precious metal alloy

[0046] The precious metal alloy of the present invention achieves an increase in hardness by spinodal decomposition and / or ordering. Therefore, the material texture of the precious metal alloy of the present invention may include a fine modulated texture by spinodal decomposition, and / or an ordered phase by ordering. The modulated texture is a material texture varied in composition with a modulation cycle at a nanometer level. Such material textures can be confirmed with X-ray diffraction (XRD), a transmission electron microscope (TEM), an electron diffraction pattern with TEM, a scanning transmission electron microscope (STEM), or a STEM-EDS mapping image.

[0047] A broad peak referred to as so-called side band peak (satellite peak) is observed in at least one side portion (preferably both side portions) of a main peak in an X-ray diffraction pattern with X-ray diffraction (XRD) or an electron beam diffraction pattern with TEM. Whether or not a texture by spinodal decomposition is presented can be determined with the presence or absence of the side band peak. A crystal structure of a matrix of the precious metal alloy of the present invention is a face-centered cubic lattice (fcc), and Miller indices {111} plane, {200} plane, {220} plane, {311} plane, and the like appear as main peaks. A side band peak assigned to a texture by spinodal decomposition appears at both sides or one side of at least any of the main peaks above described. Herein, the reason why such a side band peak appears at only one side of such any main peak is considered because separation from the main peaks is difficult.

[0048] An ordered phase with respect to an X-ray diffraction pattern or an electron diffraction pattern is confirmed by observation of an ordered reflection peak. For example, an ordered reflection peak appears at 20 = around 30° to 35° in the case of θ-2θ measurement with CuKα ray as an X-ray source, in observation of an ordered reflection peak in an X-ray diffraction pattern.

[0049] Herein, the modulated texture of the precious metal alloy of the present invention is liable to be configured from two regions of one where the Au and Pd concentrations are relatively high (the Pt and Ni concentrations are relatively low) and the other one where the Au and Pd concentrations are relatively low (the Pt and Ni concentrations are relatively high). The ordered phase generated in the precious metal alloy of the present invention includes at least any of an ordered phase of an L1 0 -type structure and an L1 2 -type structure, and is particularly liable to include an ordered phase of an L1 2 -type structure.(A-4) Hardness of present inventive precious metal alloy

[0050] The precious metal alloy of the present invention has the above composition range, and thus achieves hardening by spinodal decomposition and / or ordering. The precious metal alloy of the present invention can stably exhibit a hardness of 500 Hv or more in terms of Vickers hardness. Moreover, an effect of adding the metal element α can be expected to further increase the hardness, and a high hardness of 550 Hv or more, or 600 Hv or more in terms of Vickers hardness can be exhibited. The precious metal alloy of the present invention can be the high-hardness one having the above Vickers hardness only by the heat treatment without use of any work hardening at all, namely, without the occurrence of material embrittlement due to dislocation strain.

[0051] The upper limit of the hardness of the precious metal alloy of the present invention is not to be particularly limited, and the upper limit value is preferably 850 Hv or less. If the value is more than 850 Hv, fracture and chipping in the course of use may occur. The Vickers hardness described above is a value at room temperature. The Vickers hardness can be measured with a known Vickers hardness meter. The measurement load is preferably 0.05 kgf or more and 0.5 kgf or less, more preferably 0.2 kgf.

[0052] The shape and form of the precious metal alloy of the present invention are not especially limited. For the aforementioned medical tools, probe pins, and the like, the present invention can generally be used as an alloy in the form of a bulk (lump) that has been subjected to appropriate working. Alternatively, the present invention can also be formed in a layer / film shape on an appropriate base material / substrate.(B) Method for producing present inventive precious metal alloy

[0053] Next, a method for producing a present inventive precious metal alloy is described. As described above, the precious metal alloy of the present invention can be provided in various shapes and forms. The following description provides details of a method for producing a precious metal alloy in a bulk form, which is frequently applied, and will also mention a method for producing a precious metal alloy in a layer / film shape.

[0054] In the present invention, hardness is enhanced by spinodal decomposition and / or ordering in addition to selection of constituent metals (Au, Ni, Pd, Pt, the metal element α) of the precious metal alloy and optimization of the composition ranges of such metals. The precious metal alloy of the present invention is produced by implementing an appropriate heat treatment step in addition to producing an alloy bulk (ingot) with the composition ranges. The appropriate heat treatment step is a heat treatment step with combination of a solution treatment and an aging heat treatment, and these are performed to result in progression of spinodal decomposition and / or ordering and then an increase in hardness. The method for producing the precious metal alloy of the present invention is one for achieving material hardening by a heat treatment without any work hardening.

[0055] Hereinafter, the method for producing a precious metal alloy of the present invention is described, with each heat treatment step being mentioned. Besides, working methods that can be performed during or after the production of the precious metal alloy of the present invention will also be described. In the present invention, the temperature, for example, heating temperature of various heat treatments described below, is that of the precious metal alloy to be treated, unless particularly specified.(B-1) Provision step (production of precious metal alloy)

[0056] First, a precious metal alloy ingot before the effect, serving as a precursor of the precious metal alloy of the present invention, is provided. The precious metal alloy ingot serving as the precursor can be produced by a usual melting and casting method. Respective raw materials of metals of Au, Ni, Pd, Pt, and the metal element α described above are appropriately weighed or the like to allow for adjustment to the above composition, and molten / cast, and thus an alloy ingot is produced. Here, alloys such as a Au-Ni-Pd-Pt alloy of the base alloy, or a binary alloy of a Au-Pd alloy, a Pt-Ni alloy or the like may be appropriately combined as a mother alloy and molten. The melting and casting of such a precious metal alloy can be performed with a known procedure such as arc melting, high-frequency melting, vacuum melting, or continuous casting.

[0057] Such a precious metal alloy may also be provided by any method other than melting and casting, such as a powder metallurgy method. In the powder metallurgy method, a precious metal alloy powder (for example, a precious metal alloy powder produced by atomizing) which is adjusted so as to have the above composition is sintered, and then an alloy ingot to be subjected to a heat treatment is provided. Alternatively, such a precious metal alloy powder which is adjusted so as to have the above composition may also be used to produce an ingot having a near-net shape by a known additive fabrication method. Furthermore, a precious metal alloy layer having the above composition may also be formed on any mother material by a known alloy formation procedure such as sputtering or thermal spray.(B-2) Solution treatment

[0058] A supersaturated solid solution of such a precious metal alloy provided as above is formed by a solution treatment. The solution treatment is a step of heating such a precious metal alloy at a high temperature to provide a solid solution texture of a single phase or a single phase analog, and then quenching the texture to form a supersaturated solid solution. The heating temperature of the solution treatment is preferably a temperature of (Tm - 500°C) or more and Tm or less under the assumption that the melting point (solidus line) of such a precious metal alloy is Tm (°C). A temperature of less than (Tm - 500°C) leads to low solid solubility of each element and is insufficient for formation of the supersaturated solid solution, and a temperature of more than Tm is not preferable because material melting begins from the vicinity of a grain boundary. The holding time during heating is preferably in the range of 0.0001 hours or more and 168 hours. A holding time of less than 0.0001 hours is not preferable from the viewpoint of productivity because formation of the supersaturated solid solution is insufficient, and even heating for 168 hours or more has no large effect on formation of the supersaturated solid solution. In the present invention, the melting point means a solidus temperature.

[0059] In addition, cooling from the solution treatment temperature is needed to be rapidly made to such an extent that no grain-boundary reaction excessively occurs in a high temperature region. In other words, quenching is needed. This is because if a grain-boundary reaction occurs in a high-temperature region, although the ductility improves due to the strengthening of the grain boundaries, hardness after aging heat treatment may sometimes be insufficient. Specifically, the cooling rate is here preferably 10°C / s or more, more preferably 50°C / s or more. On the other hand, the cooling rate is preferably low from the viewpoints of preventing quench crack, change in dimension, deformation, and the like. Therefore, the above cooling rate, called quenching, is not needed in a low temperature region where no grain-boundary reaction occurs and no spinodal decomposition and / or no ordering excessively proceed(s), from the viewpoint of an enhancement in hardness of the precious metal alloy. For example, no quenching is needed in the case of the cooling rate in a temperature region of 300°C or less. Therefore, the occurrence of quench crack and the like is suppressed or decreased, and thus, for example, air cooling may also be adopted in a temperature region of 200°C or less after quenching to 200°C. The end point of cooling in the solution treatment is here preferably room temperature.(B-3) Aging heat treatment

[0060] Spinodal decomposition and ordering in the precious metal alloy of the present invention progress by an aging heat treatment of the supersaturated solid solution formed above, in a lower temperature region than the spinodal decomposition temperature and the order-disorder transformation temperature.

[0061] The heating temperature as a condition of the aging heat treatment for the supersaturated solid solution is 300°C or more and 700°C or less. A temperature of less than 300°C makes progression of transformation difficult. A temperature of more than 700°C remarkably causes material softening due to grain-boundary reaction. The heating temperature is more preferably 350°C or more and 650°C or less. The heating time in the aging heat treatment is preferably 0.001 hours or more and 168 hours or less. The heating time of less than 0.001 hours causes insufficient transformation and leads to the variation in hardness, and a treatment for 168 hours or more results in poor productivity and an increase in production cost. The cooling method after termination of the aging heat treatment is not particularly limited.(B-4) Other heat treatment step

[0062] The precious metal alloy of the present invention is produced through the aforementioned solution treatment and aging heat treatment, but the production process may include other heat treatment steps. Examples of such other heat treatment steps include a homogenization treatment, a two-phase treatment, and an intermediate annealing. However, these other heat treatment steps do not have an effect of affecting the progress of spinodal decomposition or ordering. Therefore, these heat treatments are optional.

[0063] A homogenization treatment is performed on a precious metal alloy provided by melt casting in order to form a metal texture with a uniform distribution of elemental concentrations in the precious metal alloy. The homogenization treatment is a heat treatment in which a precious metal alloy is heated at a high temperature below its melting point for a long time (preferably 0.1 hours or more and 72 hours or less).

[0064] A two-phase treatment is a treatment for forming a two-phase texture state, which provides the best workability in the alloy system of the present invention, and is a heat treatment performed to facilitate warm working and cold working. The heating temperature in the two-phase treatment is 700°C or more and 900°C or less, and more preferably 750°C or more and 850°C or less. The heating time is 0.1 hours or more and 10 hours or less, and more preferably 0.2 hours or more and 2 hours or less.

[0065] Intermediate annealing is a heat treatment performed during the working process such as warm working or cold working to be described later, in which strains of an ingot or the like of a precious metal alloy are accumulated. The intermediate annealing is a treatment for reducing material strength to restore workability. The heating temperature in the intermediate annealing is 700°C or more and 900°C or less, and more preferably 750°C or more and 850°C or less. The heating time is 0.1 hours or more and 10 hours or less, and more preferably 0.2 hours or more and 2 hours or less.(B-5) Working step of present inventive precious metal alloy

[0066] The precious metal alloy of the present invention can be worked into various shapes depending on the use, through at least one working step, before the aging treatment is performed. Examples of such working steps include hot working, warm working, cold working, skin pass, straightening, coiling, and bending. In hot working, it is possible to break down a solidified texture and eliminate defects such as voids in a provided precious metal alloy ingot. Warm working and cold working, in addition to changing the overall shape of the alloy, are significant for controlling the shape of crystal grains. When warm working or cold working is performed a plurality of times, the aforementioned intermediate annealing may be carried out between working paths.

[0067] In particular, warm working, cold working, skin pass, straightening, coiling, and bending after the solution treatment are useful working steps for the precious metal alloy of the present invention. This is because the precious metal alloy after the solution treatment has the improved ductility. After the solution treatment (and before aging), the precious metal alloy can be worked, by the various working methods mentioned above, into its final shape or a shape close to it depending on the use.

[0068] However, for the precious metal alloy of the present invention, working after the aging treatment (after hardening) is not precluded. Even a precious metal alloy having the hardness increased after the aging treatment can be subjected to working. Besides, a precious metal alloy after the aging treatment can be also subjected to working for final adjustment such as grinding / polishing, cutting, electrical discharge, pressing, bending, and straightening. Further, since spinodal decomposition and ordering expressed in the precious metal alloy of the present invention are reversible, the solution treatment and the aging treatment may be repeatedly performed. Working may also be carried out between combinations of a plurality of times of solution treatments and aging treatments.(B-6) Other method for producing present inventive precious metal alloy

[0069] In the production method described above, the precious metal alloy of the present invention is obtained by subjecting an alloy ingot produced by a melting and casting method to the solution treatment and the aging treatment. In the present invention, while the solution treatment is a crucial heat treatment step, even without performing the solution treatment step, a precious metal alloy in a texture state equivalent to that of a solid solution obtained by the solution treatment can be provided in some cases. In such cases, the precious metal alloy of the present invention can be produced by subjecting that precious metal alloy to the aging treatment.

[0070] Examples of a step of obtaining a precious metal alloy in a solid solution state without performing the solution treatment include a liquid quenching method applied to a precious metal alloy in a molten state, and a step of applying a rapid heating and quenching process or a rapid solidification process using a laser or the like applied to a bulk metal. Alternatively, even various film formation processes, such as welding, sputtering, plating, and thermal spraying, can also produce a precious metal alloy in a state approximate to a supersaturated solid solution state in some cases. Precious metal alloys produced by these processes can be the precious metal alloy of the present invention after the aging treatment was performed. These processes are useful for productions of near-net shaped precious metal alloys, and of layer / film shaped precious metal alloys with high-hardness coatings or the like. As in these processes, even when the aging heat treatment is performed without the solution treatment, the preferred conditions remain the same as described above.EXAMPLES

[0071] Hereinafter, Examples as specific embodiments of the present invention are described. In the present embodiments, a plurality of Au-Ni-Pd-Pt-based precious metal alloys were produced with the variation in composition of Au, Ni, Pd, Pt, and the metal element α, and the hardness was measured. In the present embodiments, In, Sn, Mg, Al, and Ti were added as the metal element α.[Production of precious metal alloy]

[0072] High-purity bare metals of respective metals of Au, Ni, Pd, Pt, and the metal element α (In, Sn, Mg, Al, Ti) as raw materials, were weighed and mixed so that a predetermined composition was achieved, and an alloy ingot was molten and cast in an inert gas by arc melting. A test piece (5 mm × 5 mm × 3 mm) was cut out from the alloy ingot.[Heat treatment step (solution treatment)]

[0073] The test piece produced was subjected to a solution treatment and an aging heat treatment. In the solution treatment, the test piece was heated and held at a temperature of 1050°C to 1250°C for 16 hours, and then cooled to room temperature with water.[Heat treatment step (aging heat treatment)]

[0074] The heating temperature in the aging heat treatment was set at intervals of 25°C, ranging from 450°C to 600°C, and the test piece after the solution treatment was heated and held at the corresponding aging heat treatment temperature for 1 hour, and then cooled to room temperature with water. Thereafter, such a specimen piece after the aging heat treatment was embedded in a resin for removal of an oxidized layer and residual stress on a surface layer due to thermal strain, and for obtaining a hardness measurement sample, and then subjected to rough polishing (#500, #800, #1200) and mirror polishing in diamond suspensions of 1 µm and 1 / 4 µm. As described above, samples of various compositions were produced.

[0075] In the present embodiment, Au-Ni-Pd-Pt-based precious metal alloys including Au, Ni, Pd, Pt, and the metal element α (In, Sn, Mg, Al, Ti) were produced as Examples.

[0076] Besides, Au-Ni-Pd-Pt alloys with compositions approximate to those of the precious metal alloys of each Example, with no metal element α added, were produced as Reference Examples. Furthermore, Au-Ni-Pd-Pt alloys out of the composition range of the present invention were produced as Comparative Examples, and a Au-Pt alloy and a Pt-Ni alloy that are precious metal alloys capable of expressing spinodal decomposition or ordering were produced as Conventional Examples. Also in these Reference Examples, Comparative Examples, and Conventional Examples, samples were produced with the solution treatment and the aging heat treatment performed in the same manner as in the above embodiments.[Hardness measurement]

[0077] Hardness measurement was performed about the samples of the respective precious metal alloys produced as described above. Hardness measurement was performed at a test load of 0.2 kgf and at room temperature with a measurement apparatus (HM-210 manufactured by Mitutoyo Corporation). The measurement results are shown in Table 1. Hardness measurement was performed randomly at 15 points on each of the samples, and the average value was defined as the hardness value. The measurement positions in each of the samples were determined by selection of a plurality of crystal grains, and measurement was performed in a non-grain boundary portion of and around the most center of each crystal grain. In the results of the hardness measurement presented below (Tables 3 and 4), the aging heat treatment temperature at which the highest hardness was obtained, among a plurality of aging heat treatment temperatures set within the range of 450°C to 600°C, were shown along with the hardness value. However, the precious metal alloys of Examples exhibited 520 Hv or higher at lowest hardness.[Study of material texture with XRD analysis]

[0078] Each of the precious metal alloys were subjected to XRD analysis in order to perform (a) confirmation of spinodal decomposition and (b) confirmation of generation of an ordered phase. Analysis conditions such as a sample size in each study item in XRD were set respectively, as follows. This XRD analysis was to be performed on the precious metal alloy (solid solution material) after the solution treatment and the precious metal alloy (aging material) after the aging heat treatment so that expression of spinodal decomposition and ordering with the aging heat treatment could be confirmed with the analysis results being compared.[Common conditions]

[0079] Sample size: φ22 mm × 2 mmt XRD apparatus: SmartLab manufactured by Rigaku Target: Cu anode Optical system-detector: focusing optical system-semiconductor detector (HyPix-3000) Current-voltage: 40 kV-30 mA Length limiting slit: 10 mm (a) Confirmation of spinodal decomposition (side band peak)

[0080] 20 scanning range: 20° to 130° 20 step size (°): 0.0012 20 scanning rate (° / min): 6 (b) Confirmation of ordered phase (ordered peak)

[0081] 20 scanning range: 20° to 38° 20 step size (°): 0.0132 20 scanning rate (° / min): 1.3

[0082] In the study of spinodal decomposition with XRD, determination was made about whether or not one or more side band peaks appeared on one side or both sides about both ends (about ± 0.5 to 3° in terms of 20) of a main peak observed with respect to each of Miller indices {111} plane, {200} plane, {220} plane, and {311} plane in an XRD diffraction profile obtained in the above conditions. Evaluation was performed as follows: a case where one or more side band peaks appeared was regarded as the occurrence of spinodal decomposition, and a case where no side band peaks appeared at all was regarded as no occurrence of spinodal decomposition.

[0083] In the study of an ordered phase with XRD, determination was made about the presence or absence of an ordered reflection peak generated around 2θ = 30° to 35°. Specifically, a case where the intensity of an ordered peak was higher than the background of the corresponding region was evaluated as the presence of an ordered phase, and a case where the peak intensity was equal to or lower than the background was evaluated as the absence of an ordered phase.

[0084] As an example of the results of the XRD analysis performed in the present embodiment, the XRD diffraction pattern for the alloy B-5 (Au12.5-Ni30.625-Pd25-Pt30.625-Sn1.25) of Example is illustrated in Fig. 2. Fig. 2(a) illustrates an XRD diffraction profile for confirming spinodal decomposition, and Fig. 2(b) illustrates an XRD diffraction profile for confirming an ordered phase. Referring to Fig. 2(a), in this precious metal alloy, clear peaks identifiable as sideband peaks were observed on both sides of a peak in the vicinity of 20 = 40° to 41° corresponding to the {111} plane, and a peak in the vicinity of 20 = 46.5° to 47.5° corresponding to the {200} plane. Furthermore, broad peaks viewable as sideband peaks were also confirmed on both sides or one side also of peaks corresponding to other crystal planes. From this, it is presumed that spinodal decomposition was expressed in this precious metal alloy. Besides, referring to Fig. 2(b), in a region in the vicinity of 20 = 30° to 35°, a peak (an ordered peak) that is definitely higher than the background was observed. From this, it is presumed that ordering was also expressed in this precious metal alloy.

[0085] This precious metal alloy B-5 was subjected to TEM / STEM analysis. The TEM / STEM analyzer used was an atom resolution electron microscope (JEM-ARM300F GRAND ARM manufactured by JEOL Ltd.) (acceleration voltage 300 kV). Herein, a specimen for TEM / STEM analysis was produced before TEM / STEM analysis, with focused ion beam (FIB) after the heat treatment step (solution treatment and aging heat treatment) and resin embedding-polishing after the heat treatment were performed in the same manner as described above.

[0086] Fig. 3 illustrates the results (Pt, Au, Pd, Sn: L-line, Ni: K-line) of mapping measurement of each constituent element (Au, Ni, Pd, Pt, Sn), with STEM-EDS. It was found from Fig. 3 that the material texture of such precious metal alloys of the present embodiments had a modulated texture having two regions of one where the Au and Pd concentrations were relatively high and the other one where the Au and Pd concentrations were relatively low, and these regions were alternately connected. The modulated texture has no clear interface, and thus was presumed to be due to spinodal decomposition. Besides, based on the distribution of Sn, no precipitates and the like were confirmed, and it seems that solid solution was preferentially allowed in the region where the Au and Pd concentrations were relatively high. From the above results, it is deemed that Sn does not significantly affect the material texture (modulated structure, ordering) of the precious metal alloy.

[0087] Fig. 4 illustrates an electron beam diffraction pattern of the alloy B-5 of Example, obtained with TEM analysis (<001>crystal zone axis incident conditions). It was confirmed from Fig. 4 that not only basic reflection with a fcc structure, but also a diffraction spot due to an ordered phase was observed in the precious metal alloy B-5 of the present embodiment. The diffraction spot due to an ordered phase is presumed to be an L1 2 structure in consideration of the position of appearance, the intensity, and the place spacing.

[0088] Tables 3 and 4 show the measurement results of the hardness of the precious metal alloys of Examples, Reference Examples, Comparison Examples, and Conventional Examples produced in the present embodiments. These tables also show whether or not modulated textures (sideband peaks) and ordered phases (ordered peaks) were observed with XRD analysis. In these tables, in order to confirm the effect of adding the metal element α in the present embodiments, the alloys were divided into groups by precious metals having similar base alloy compositions (element concentrations each of Au, Ni, Pd, and Pt), and alloys of each group were then numbered with an alphabet (A to I) and a number. [Table 3]Alloy group No.Alloy composition (at%)Treatment temperature (°C)Hardness (Hv)Material texture (XRD)NoteAuNiPdPtInSnMgAlTiSolution treatmentAging treatmentModulated textureOrdered phaseA-17.538.7512.538.752.5----1200550710expressedexpressedExampleA-27.537.512.537.5-5---1150550700expressedexpressedExampleA-37.538.7512.538.75--2.5--1150550680expressedexpressedExampleA-47.537.512.537.5---51200550660expressedexpressedExampleA-57.537.512.537.5----51200600604expressedexpressedExampleA-67.54012.540-----1200550580expressedexpressedReference ExampleB-112.531.1252531.1250.25---1200550592expressedexpressedExampleB-212.531.1252531.1250.25---1200550602expressedexpressedExampleB-312.53125310.5---1200550605expressedexpressedExampleB-412.5312531-0.5---1200550606expressedexpressedExampleB-512.530.6252530.625-1.25---1200550655expressedexpressedExampleB-612.531.1252531.125--0.25--1200550590expressedexpressedExampleB-712.531.1252531.125---0.25-1200550601expressedexpressedExampleB-812.5302530---2.5-1200600614expressedexpressedExampleB-912.5302530----2.51200600590expressedexpressedExampleB-1012.5302530-2.5---1200550680expressedexpressedExampleB-1112.530.6252530.6250.6250.625---1200550655expressedexpressedExampleB-1212.531.252531.25-----1200550568expressedexpressedReference Example [Table 4] Alloy group No.Alloy composition (at%)Treatment temperature (°C)Hardness (Hv)Material texture (XRD)NoteAuNiPdPtInSnMgAlTiSolution treatmentAging treatmentModulated textureOrdered phaseC-16.2543.125543.125-2.5---1200550711expressedexpressedExampleC-26.2544.375544.373-----1200550580expressedexpressedReference ExampleD-1151510555----1200550662expressedexpressedExample0-215151060-----1250550590expressednot expressedReference ExampleE-115561018-1---1050450585expressedexpressedExampleE-215571018-----1050550520expressedexpressedReference ExampleF-120511513.50.5----1200550624expressedexpressedExampleF-22051.51513.5-----1100500578expressedexpressedReference ExampleG-1207.51556.25--1.25--1200600540expressednot expressedExampleG-2207.51557.5-----1250550520expressednot expressedReference ExampleH-120152040--5--1200550612expressedexpressedExampleH-220152045-----1200525597expressedexpressedReference ExampleI-12020.6253520.625--3.75--1200500558expressedexpressedExampleI-22022.53522.5-----1200550507expressedexpressedReference ExampleS-11010575-----1250600441not expressednot expressedComparative ExampleS-21022.54522.5-----1200500295not expressednot expressedComparative ExampleS-327232723-----1200550596expressedexpressedComparative ExampleS-425.752325.75232.5----1200550601expressedexpressedComparative ExampleX-140--60-----1275400492expressednot expressedConventional ExampleY-1-50-50-----1300400461not expressedexpressedConventional Example

[0089] Tables 3 and 4 reveal that spinodal decomposition was expressed in all the precious metal alloys of Examples and Reference Examples in which the Au-Ni-Pd-Pt-based alloys had compositions set within the range of the present invention (alloys belonging to the groups A to I). Besides, as for ordering, the generation of an ordered phase was confirmed, with some exceptions. As for the ordered phase, the L1 2 structure was identified as in the result for the alloy B-5 mentioned above. All of these precious metal alloys of Examples and Reference Examples exhibited a hardness more than 500 Hv. The hardness of these precious metal alloys was higher than those of the Au-Pt alloy (alloy X-1) and the Pt-Ni alloy (alloy Y-1) in which spinodal decomposition and / or ordering can occur. It is considered that the effect of increasing hardness by spinodal decomposition and / or ordering was favorably exhibited by employing multi-component configurations for the alloys.

[0090] In studies of the precious metal alloys belonging to each of the groups A to I, comparing the hardness by groups between Examples and Reference Examples, it was confirmed that Examples where the metal element α was added to the Au-Ni-Pd-Pt alloys showed a distinct increase in hardness compared to Reference Examples where the metal element α was not added. The extent of increase in hardness due to the metal element α varied depending on the alloy composition, but was at lowest 15 Hv or more, and in some compositions, increase in hardness of 100 Hv or more was observed. From this comparison result, it was confirmed that while the Au-Ni-Pd-Pt alloy of the base alloy is a high-hardness precious metal alloy by itself, the addition of the metal element α allows for a further increase in hardness.

[0091] Furthermore, even in Au-Ni-Pd-Pt alloys, like the alloys S-1 and S-2 of Comparative Examples, neither spinodal decomposition nor ordering may occur depending on the composition ranges of Au, Ni, Pd, and Pt. These precious metal alloys exhibited a hardness of less than 500 Hv, and thus, it was understood that setting of the composition range for the base alloy is fundamentally important.

[0092] The alloys S-3 and S-4 of Comparative Examples are precious metal alloys having the alloy composition (Au concentration) that deviates from the range of the present invention, and were for confirming the effect of increasing hardness by the presence or absence of addition of the metal element α. Both of these precious metal alloys expressed spinodal decomposition and ordering, and exhibited a hardness of 500 Hv or more. However, when these were compared, the extent of increase in hardness due to the addition of the metal element α was less than 10 Hv (6 Hv), and it is deemed that almost no effect of adding metal element α was obtained. Based on these, it was confirmed that although spinodal decomposition and / or ordering can occur even in a composition out of the composition range of the present invention, the specified composition range of the present invention is preferably applied for maximizing increase in hardness by the effect of adding the metal element α.INDUSTRIAL APPLICABILITY

[0093] As described above, the present invention is drawn to a precious metal alloy which can exhibit an increase in hardness due to spinodal decomposition and / or ordering and which has novel configuration / composition ranges. The present invention allows for achieving a high-hardness alloy material without any work hardening (dislocation strengthening). Therefore, an increase in hardness can be achieved without any concern about embrittlement along with work hardening.

[0094] The precious metal alloy of the present invention is expected to be applied to various uses where high hardness / high wear resistance is required, for example, electric / electronic materials such as probe pins and electric contacts, medical tools, high-hardness coating members and the like. The precious metal alloy of the present invention can be produced by subjecting, to an aging heat treatment, a precious metal alloy obtained by, for example, melt casting and a solution treatment, additive fabrication techniques, rapid solidification techniques, coating techniques such as sputtering, thermal spraying, and plating, and is applicable to the above various uses.

Claims

1. A Au-Ni-Pd-Pt-based precious metal alloy resulting from addition of a metal element α to a base alloy comprising Au, Ni, Pd, and Pt, wherein the metal element α is at least any one metal element selected from In, Sn, Mg, Al, and Ti, and the Au-Ni-Pd-Pt-based precious metal alloy contains 4% by atom or more and 24% by atom or less of Au, 5% by atom or more and 60% by atom or less of Ni, 2.5% by atom or more and 40% by atom or less of Pd, 10% by atom or more and 60% by atom or less of Pt, 0.15% by atom or more and 7.5% by atom or less of the metal element α, and inevitable impurities.

2. The Au-Ni-Pd-Pt-based precious metal alloy according to claim 1, wherein a material texture includes a modulated texture expressed by spinodal decomposition.

3. The Au-Ni-Pd-Pt-based precious metal alloy according to claim 1 or 2, wherein a material texture includes an ordered phase.

4. The Au-Ni-Pd-Pt-based precious metal alloy according to claim 1, having a Vickers hardness of 500 Hv or more.

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