Alloy for medical use, and method for producing same

Abstract

The present invention provides an alloy for medical use including an Au—Pt alloy, in which the Au—Pt alloy has a Pt concentration of 24 mass % or more and less than 34 mass % with the balance being Au, and has at least a material structure in which a Pt-rich phase having a Pt concentration higher than that of an α-phase is distributed in an α-phase matrix, the Pt-rich phase has a Pt concentration that is 1.2 to 3.8 times the Pt concentration of the α-phase, and the Pt-rich phase has an area ratio of 1 to 22% in any cross-section. This alloy is an artifact-free alloy material that exhibits excellent compatibility with a magnetic field environment such as an MRI and has magnetic susceptibility of ±4 ppm with respect to magnetic susceptibility of water.

Claims

1. A method for producing an alloy for medical use, wherein the alloy consists of an Au—Pt alloy, wherein the Au has a purity of 99.99 mass % or more and the Pt has a purity of 99.99 mass % or more, wherein the Au—Pt alloy has a Pt concentration of 28 mass % or more and less than 34 mass % with a balance being Au, and has at least a material structure in which a Pt-rich phase having a Pt concentration higher than that of an α-phase is distributed in an α-phase matrix, the Pt-rich phase exhibits a lamella structure directed into a grain from a grain boundary of the Au-Pt alloy, the Pt-rich phase has a Pt concentration that is 1.2 to 3.8 times the Pt concentration of the a-phase, and the Pt-rich phase has an area ratio of 1 to 22% in any cross-section, and the Au-Pt alloy has magnetic susceptibility from —13 ppm to −5 ppm, the method comprising: performing a heat treatment on a supersaturated solid solution of the Au—Pt alloy having a Pt concentration of 28 mass % or more and less than 34 mass % with the balance being Au at a temperature of 600 to 1000° C. to precipitate the Pt-rich phase.

2. The method for producing an alloy for medical use according to claim 1, further comprising a step of producing the supersaturated solid solution of the Au—Pt alloy comprising the steps of: melting and casting an alloy ingot comprising the Au—Pt alloy having a Pt concentration of 28 mass % or more and less than 34 mass % with the balance being Au; and subsequently performing, at least twice, a single-phase forming treatment that comprises cold rolling and a heat treatment at 1150 to 1250° C., on the alloy ingot.

3. A method for producing an alloy for medical use according to claim 1, the alloy consisting of an Au—Pt alloy, wherein the Au has a purity of 99.99 mass % or more and the Pt has a purity of 99.99 mass % or more, wherein the Au—Pt alloy has a Pt concentration of 28 mass % or more and less than 34 mass % with a balance being Au, and has at least a material structure in which a Pt-rich phase having a Pt concentration higher than that of an α-phase is distributed in an α-phase matrix, the Pt-rich phase exhibits a lamella structure directed into a grain from a grain boundary of the Au—Pt alloy, the Pt—rich phase has a Pt concentration that is 1.2 to 3.8 times the Pt concentration of the α-phase, and the Pt-rich phase has an area ratio of 1 to 22% in any cross-section, the Au—Pt alloy has magnetic susceptibility from −13 ppm to −5 ppm, the Pt-rich phase is distributed as an α.sub.2-phase, and the Pt-rich phase has an area ratio of 5 to 15% in any cross-section wherein the supersaturated solid solution of the Au—Pt alloy has a Pt concentration of 28 mass % or more.

4. A method for producing an alloy for medical use according to claim 1, the alloy consisting of an Au—Pt alloy, wherein the Au has a purity of 99.99 mass % or more and the Pt has a purity of 99.99 mass % or more, wherein the Au—Pt alloy has a Pt concentration of 28 mass % or more and less than 34 mass % with a balance being Au, and has at least a material structure in which a Pt-rich phase having a Pt concentration higher than that of an α-phase is distributed in an α-phase matrix, the Pt-rich phase exhibits a lamella structure directed into a grain from a grain boundary of the Au—Pt alloy, the Pt-rich phase has a Pt concentration that is 1.2 to 3.8 times the Pt concentration of the α-phase, and the Pt-rich phase has an area ratio of 10 to 22% in any cross-section, the Au—Pt alloy has magnetic susceptibility from −13 ppm to —5 ppm, and the Pt concentration of the Pt-rich phase is 86 to 90 wt % wherein the supersaturated solid solution of the Au—Pt alloy has a Pt concentration of 28 mass % or more.

5. A method for producing an alloy for medical use according to claim 1, the alloy consisting of an Au—Pt alloy, wherein the Au has a purity of 99.99 mass % or more and the Pt has a purity of 99.99 mass % or more, wherein the Au—Pt alloy has a Pt concentration of 28 mass % or more and less than 34 mass % with a balance being Au, and has at least a material structure in which a Pt-rich phase having a Pt concentration higher than that of an α-phase is distributed in an α-phase matrix, the Pt-rich phase exhibits a lamella structure directed into a grain from a grain boundary of the Au—Pt alloy, the Pt-rich phase has a Pt concentration that is 1.2 to 3.8 times the Pt concentration of the α-phase, and the Pt-rich phase has an area ratio of 1 to 13% in any cross-section, and the Au—Pt alloy has magnetic susceptibility from −13 ppm to −5 ppm, and the Pt concentration of the Pt-rich phase is 86 to 90 wt %, and wherein the supersaturated solid solution of the Au—Pt alloy has a Pt concentration of 28 mass % or more.

6. The method for producing an alloy for medical use according to claim 2, wherein the cold rolling during the single-phase forming treatment employs a working ratio of 10 to 30%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a phase diagram of an Au—Pt-based alloy.

(2) FIG. 2 is an SEM photograph of an Au-28Pt alloy (heat treatment temperature: 900° C.).

(3) FIG. 3 is an SEM photograph of an Au-26Pt alloy (working ratio: 30%, heat treatment temperature: 850° C.).

(4) FIG. 4 shows imaging results of the Au-30Pt alloy and the Au-26Pt alloy by an MRI apparatus.

DESCRIPTION OF EMBODIMENTS

(5) Embodiments of the invention will be described below. In the embodiments, examinations were made with respect to magnetic susceptibility measurement and probability of artifact occurrence after producing an Au—Pt alloy ingot with varying Pt concentration and performing a single-phase forming treatment, performing a heat treatment for phase separation on the Au—Pt alloy ingot, and confirming a phase structure of the Au—Pt alloy ingot.

First Embodiment

(6) In this embodiment, an Au—Pt alloy having a Pt concentration of 28 mass % or more and less than 34 mass % was produced. Pure Au and pure Pt (both of them having purity of 99.99%: produced by Tanaka Kikinzoku Kogyo K.K) were weighed to be a target composition and were subjected to high-frequency melting, whereby an alloy ingot was cast. The alloy ingot of 60 g was produced as criteria. The molten and cast alloy ingot was subjected to hot forging. The hot forging was performed at a forging temperature of 1000° C.

(7) Subsequently, the alloy ingot was subjected to a single-phase forming treatment to produce a supersaturated solid solution alloy of an α-single phase. As the single-phase forming treatment, first, the alloy ingot was subjected to cold groove rolling and then was subjected to cold working (working ratio: 40%). Then, the alloy ingot was heated for one hour at 1200° C., and thereafter introduced into ice water to be rapidly cooled. The single-phase forming treatment, which was a combination of the cold working and the heat treatment, was performed three times.

(8) A heat treatment was performed on the alloy subjected to the single-phase forming treatment to precipitate a Pt-rich phase. A temperature of the heat treatment was set between 600° C. and 950° C. In the heat treatment, after being heated, with a time interval, the alloy was introduced into ice water to be rapidly cooled. The heat-treated alloy was subjected to cold groove working to obtain an Au—Pt alloy wire.

(9) With respect to the produced Au—Pt alloy wire, a cross-section was observed by use of an SEM, a structure of the cross-section was observed (observation visual field: 140 μm×100 μm), and an area ratio of an α.sub.2-phase of a Pt-rich phase and a total area ratio of an α.sub.1-phase and the α.sub.2-phase were calculated.

(10) Subsequently, volume magnetic susceptibility was measured. The magnetic susceptibility was measured on each of the alloy samples by use of a superconducting quantum interference device (SQUID) apparatus (7T-SQUID fluxmeter manufactured by Quantum Design, Inc.). A measurement temperature was set to be 37° C. When the measured magnetic susceptibility was in the range of −5 to −13 ppm, which is a target range, it was determined to be acceptable “◯”, and it was out of the above range, it was determined to be not acceptable “X”. Results of the above analysis and measurement were indicated in Table 1, respectively.

(11) TABLE-US-00001 TABLE 1 Heat Phase Magnetic Alloy treatment structure susceptibility composi- Temper- α.sub.1 + Measurement Determi- tion ature Time α.sub.2 α.sub.2 result nation Au-28% Untreated single  0% 0% −22.7 ppm X Pt phase 600° C. 24 h 30% 10%  −10.1 ppm ◯ 700° C. 24 h 25% 8% −12.1 ppm ◯ 700° C. 36 h 28% 9% −10.9 ppm ◯ 800° C. 24 h 22% 7% −15.5 ppm X 850° C. 24 h 20% 7% −19.5 ppm X 900° C. 24 h 18% 6% −20.7 ppm X Au-30% Untreated single  0% 0% −20.5 ppm X Pt phase 600° C. 24 h 28% 9% −6.8 ppm ◯ 700° C. 24 h 25% 8% −8.3 ppm ◯ 800° C. 24 h 22% 7% −10.1 ppm ◯ 850° C. 24 h 18% 6% −11.7 ppm ◯ 850° C. 12 h 18% 6% −12.3 ppm ◯ 900° C. 24 h 16% 5% −13.8 ppm X Au-33% Untreated single  0% 0% −13.9 ppm X Pt phase 600° C. 24 h 26% 9% −0.6 ppm X 700° C. 24 h 24% 8% −2.8 ppm X 800° C. 24 h 21% 7% −4.2 ppm X 850° C. 24 h 18% 6% −5.7 ppm ◯ 900° C. 24 h 16% 5% −6.4 ppm ◯ 950° C. 12 h 14% 5% −8.9 ppm ◯

(12) Table 1 shows that all of the Au—Pt alloys (Pt concentration: 28 mass %, 30 mass %, and 33 mass %) produced in this embodiment had suitable magnetic susceptibility (−9 ppm±4 ppm) by appropriate setting of a heat treatment temperature and by precipitation of the proper amount of Pt-rich phase (α.sub.2-phase) depending on the Pt concentration. Preferred ranges of the distribution amount (area ratio) of the Pt-rich phase (α.sub.2-phase) are different from each other by the Pt concentration, but the preferred range in each alloy of this embodiment is 8 to 10% (Pt concentration: 28 mass %), 6 to 9% (Pt concentration: 30 mass %), or 5 to 6% (Pt concentration: 33 mass %), and the Pt-rich phase is reduced with an increase of the Pt concentration. Additionally, the heat treatment temperature for the suitable magnetic susceptibility is 600 to 700° C. (Pt concentration: 28 mass %), 600 to 850° C. (Pt concentration: 30 mass %), or 850 to 950° C. (Pt concentration: 33 mass %), and it is found that the heat treatment temperature preferably rises with the increase of the Pt concentration. In each of the alloys of this embodiment, the α.sub.2-phase had the Pt concentration in the range of 45±5 mass %.

(13) FIG. 2 is an SEM photograph of an Au-28Pt alloy (heat treatment temperature of 900° C.). From the image, a precipitated phase was confirmed to have a lamella shape directed into grains from grain boundaries in the alloy structure. From an EDX analysis of multiple points including precipitates in an image, the precipitated phase was confirmed to be formed in such a manner that the Pt-rich α.sub.2-phase and the Au-rich α.sub.1-phase were alternately laminated.

Second Embodiment

(14) In this embodiment, an Au—Pt alloy having a Pt concentration of 24 mass % or more and less than 28 mass % was produced. A step of producing an alloy ingot by use of melting and casting and a step of producing a supersaturated solid solution alloy of an α-single phase by a single-phase forming treatment were similar to the steps in the first embodiment.

(15) In this embodiment, the Au—Pt alloy was subjected to cold working prior to a heat treatment for precipitation of a Pt-rich phase, and thus working strain was introduced. The Au—Pt alloy was subjected to cold groove rolling with a working degree of 10 to 30% at room temperature and was worked to an alloy wire. Then, each of the worked alloy wires was a heat treatment, and thus a Pt-rich phase was precipitated. A heat treatment temperature was set to 700 to 850° C.

(16) For each of the samples subjected to the heat treatment, a structure was observed in the same manner as in the first embodiment, and an area ratio of the Pt-rich phase was measured. Additionally, a Pt concentration of the Pt-rich phase was measured by an EDX analysis. Then, magnetic susceptibility of each of the samples was measured. Measurement results were indicated in Table 2.

(17) TABLE-US-00002 TABLE 2 Pt-rich Magnetic Heat phase susceptibility Alloy Working treatment Pt Area Measurement composition ratio Temperature Time concentration ratio result Determination Au-24% Pt Untreated single —  0% −26.3 ppm X phase  0% 800° C. 5 h 44  5% −23.8 ppm X 10% 800° C. 5 h 87  6% −20.3 ppm X 850° C. 5 h 86  8% −15.2 ppm X 900° C. 5 h 89 10% −12.8 ppm ◯ 20% 800° C. 5 h 90 10% −12.5 ppm ◯ 850° C. 5 h 87 13% −10.8 ppm ◯ 900° C. 5 h 88 16% −8.6 ppm ◯ 30% 800° C. 5 h 86 14% −9.5 ppm ◯ 850° C. 5 h 87 17% −6.9 ppm ◯ 900° C. 5 h 89 20% −5.3 ppm ◯ Au-26% Pt Untreated single —  0% −24.8 ppm X phase  0% 850° C. 5 h 46  4% −22.8 ppm X 10% 750° C. 5 h 86  5% −19.3 ppm X 800° C. 5 h 87  7% −16.3 ppm X 850° C. 5 h 88 10% −12.3 ppm ◯ 20% 750° C. 5 h 87  7% −15.9 ppm X 800° C. 5 h 88 10% −11.7 ppm ◯ 850° C. 5 h 89 14% −9.4 ppm ◯ 30% 750° C. 5 h 87 10% −12.2 ppm ◯ 800° C. 5 h 88 14% −8.5 ppm ◯ 850° C. 5 h 89 18% −5.3 ppm ◯

(18) From Table 2, it can be confirmed that the alloys having these composition ranges also had suitable magnetic susceptibility after the heat treatment. However, the α-single phase alloy is essentially worked before the heat treatment in the Au—Pt alloys having these composition ranges, the amount of the Pt-rich phase to be precipitated is small and the Pt concentration of the Pt-rich phase is low even when the heat treatment is performed in the absence of the working of the α-single phase alloy, and thus the magnetic susceptibility is on a greater negative side. Additionally, a difference in suitability for the magnetic susceptibility may occur due to the working ratio before the heat treatment.

(19) FIG. 3 is an SEM photograph of an Au-26Pt alloy (working ratio: 30%, heat treatment temperature: 850° C.). It was confirmed from the image that, in the alloys having these composition ranges, a granular precipitated phase concentrically remained in grain boundaries and also remained in grains. As indicated in Table 2, the precipitated phase has the Pt concentration in the range of 86 to 90 mass %, which is a higher Pt concentration than the Pt-rich phase (α.sub.2-phase) of the alloy of the first embodiment.

Third Embodiment

(20) In this embodiment, an Au—Pt alloy having a Pt concentration of 28 mass % or more and less than 34 mass % was produced by a combination of cold working and a heat treatment as a method of separating phases from a supersaturated solid solution of a single phase. An alloy ingot was produced by melting and casting as in the first embodiment and was subjected to a single-phase forming treatment, the supersaturated solid solution alloy of the single phase was subjected to cold groove rolling with a working degree of 10 to 30% cold working, and the rolled alloy was subjected to a heat treatment at a heat treatment temperature of 750 to 850° C. Thereafter, structure observation, measurement of the Pt concentration of the Pt-rich phase, and measurement of the magnetic susceptibility were performed. The measurement results are indicated in Table 3.

(21) TABLE-US-00003 TABLE 3 Pt-rich Magnetic Heat phase susceptibility Alloy Working treatment Pt Area Measurement composition ratio Temperature Time concentration ratio result Determination Au-28% Pt Untreated single — 0% −22.7 ppm X phase 10% 700° C. 5 h 87 3% −19.8 ppm X 750° C. 5 h 88 5% −12.5 ppm ◯ 800° C. 5 h 89 8% −7.9 ppm ◯ 20% 700° C. 5 h 86 4% −13.7 ppm ◯ 750° C. 5 h 88 8% −8.2 ppm ◯ 800° C. 5 h 89 11%  −5.0 ppm ◯ 30% 700° C. 5 h 86 8% −8.5 ppm ◯ 750° C. 5 h 87 11%  −5.2 ppm ◯ 800° C. 5 h 88 14%  −3.8 ppm X Au-30% Pt Untreated single — 0% 20.5 ppm X phase 10% 650° C. 5 h 87 2% −16.1 ppm X 700° C. 5 h 87 3% −12.7 ppm ◯ 750° C. 5 h 88 5% −6.1 ppm ◯ 20% 650° C. 5 h 86 3% −13.0 ppm ◯ 700° C. 5 h 88 5% −5.6 ppm ◯ 750° C. 5 h 88 8% −3.8 ppm X 30% 650° C. 5 h 88 5% −5.9 ppm ◯ 700° C. 5 h 89 8% −3.4 ppm X 750° C. 5 h 90 11%  1.2 ppm X Au-33% Pt Untreated single — 0% −13.9 ppm X phase 10% 600° C. 5 h 86 1% −10.6 ppm ◯ 650° C. 5 h 87 3% −5.6 ppm ◯ 700° C. 5 h 88 4% −3.1 ppm X 20% 600° C. 5 h 87 2% −7.9 ppm ◯ 650° C. 5 h 87 4% −3.6 ppm X 700° C. 5 h 88 6% −0.3 ppm X 30% 600° C. 5 h 86 3% −5.8 ppm ◯ 650° C. 5 h 88 6% 0.8 ppm X 700° C. 5 h 90 9% 3.2 ppm X

(22) From Table 3, it was confirmed that suitable magnetic susceptibility can also be exhibited in the Au—Pt alloy having the Pt concentration of 28 mass % or more and less than 34 mass % by the combination of the cold working and the heat treatment. Further, for example, an Au-33 mass % Pt alloy cannot exhibit the suitable magnetic susceptibility unless the heat treatment is performed at a temperature of 850° C. or higher (Table 1), but it can be found that the Au-33 mass % Pt alloy can exhibit the suitable magnetic susceptibility even by the heat treatment at 600° C. in combination with the cold working. It is considered that the heat treatment temperature can be lowered by the combination of the cold working during the phase separation.

(23) Among the Au—Pt alloys produced in the above embodiments, for four alloys of the Au-30Pt alloys (subjected to the heat treatment at heat treatment temperature of 850° C. (no working) and not subjected to the heat treatment (no working)) in the first embodiment and the Au-26Pt alloys (subjected to the heat treatment at heat treatment temperature of 800° C. (working ratio: 30%) and not subjected to the heat treatment (no working)) in the second embodiment, whether the artifact is present or not was evaluated by use of an MRI apparatus (Magnetom Sonata 1.5T manufactured by Siemens Inc.). In the test, the alloy sample fixed with an agarose gel in a Pyrex (registered trademark) test tube (ϕ 3.5 mm) was imaged by use of the MRI apparatus and whether the artifact is present or not was visually confirmed. The alloy sample was imaged by use of a gradient echo method (TR: 270 ms, TE: 15 ms) and a spin echo method (TR: 500 ms, TE: 20 ms).

(24) FIG. 4 shows measurement results of each Au—Pt alloy by use of the MRI apparatus. From FIG. 4, the artifact is clearly seen in the Au—Pt alloy in which the phase structure is not adjusted by the heat treatment and the working. In contrast, it can be confirmed that the Au—Pt alloy of this embodiment is free of the artifact.

INDUSTRIAL APPLICABILITY

(25) An alloy for medical use composed of an Au—Pt alloy of the present invention has suitable magnetic susceptibility to suppress an artifact. This alloy has also excellent characteristics such as biocompatibility, corrosion resistance, or workability required for the alloy for medical use. The present invention is useful for a medical appliance such as an embolus coil, a clip, a catheter, a stent, or a guide wire and for a medical appliance to be used in a magnetic field environment such as an MRI.