Superelastic alloy

Abstract

The present invention provides a superelastic alloy formed by addition of Fe or Co to an AuCuAl alloy, including: Cu of 12.5% by mass or more and 16.5% by mass or less; Al of 3.0% by mass or more and 5.5% by mass or less; Fe or Co of 0.01% by mass or more and 2.0% by mass or less; and a balance Au, and a difference between Al content and Cu content (CuAl) is 12% by mass or less. The superelastic alloy according to the present invention has superelastic property while being Ni-free, excellent X-ray imaging property, processability, and strength property, and is suitable for a medical field.

Claims

1. A superelastic alloy formed by addition of Fe to an AuCuAl alloy, wherein the superelastic alloy comprises: Cu of 12.5% by mass or more and 16.5% by mass or less; Al of 3.1% by mass or more and 5.5% by mass or less; Fe of 0.9% by mass or more and 2.0% by mass or less; a balance of Au, and further wherein a difference between the Al content and the Cu content (CuAl) is 12% by mass or less: and wherein the superelastic alloy has a superelastic shape recovery rate of 40% or more calculated by a following equation based on a plastic strain at the time of 2% strain measured when the superelastic alloy is subjected to a tensile test and an unloaded residual strain:
Superelastic shape recovery rate (%)=(plastic strain (%) at the time of 2% strainresidual strain (%))/plastic strain at the time of 2% strain100[Equation 1] wherein plastic strain is a value obtained by exclusion of an elastic deformation strain from a total deformation strain.

2. The superelastic alloy according to claim 1, wherein the Au content is 78.7% by mass or more and 83.1% by mass or less.

3. A method of manufacturing the superelastic alloy according to claim 1, comprising the steps of: melting and casting an alloy including Cu of 12.5% by mass or more and 16.5% by mass or less, Al of 3.1% by mass or more and 5.5% by mass or less, Fe of 0.9% by mass or more and 2.0% by mass or less, and a balance of Au; and performing a final heat treatment of heating and maintaining the alloy at 300 to 500 C. and then quenching the alloy.

4. The method of manufacturing the superelastic alloy according to claim 3, comprising the step of cold working the alloy before the step of the final heat treatment.

5. A method of manufacturing the superelastic alloy according to claim 2, comprising the steps of: melting and casting an alloy including Cu of 12.5% by mass or more and 16.5% by mass or less, Al of 3.1% by mass or more and 5.5% by mass or less, Fe of 0.9% by mass or more and 2.0% by mass or less, and a balance of Au, wherein the Au content is 78.7% by mass or more and 83.1% by mass or less; and performing a final heat treatment of heating and maintaining the alloy at 300 to 500 C. and then quenching the alloy.

Description

DESCRIPTION OF EMBODIMENTS

First Embodiment

(1) Hereinafter, embodiments of the present invention will be described. In the present embodiment, AuCuAlFe alloys and AuCuAlCo alloys having varied concentrations of respective constituent elements were manufactured. After the alloys were processed in specimens, X-ray imaging property was evaluated, and presence or absence of superelastic property within a normal temperature range, processability and strength were measured.

(2) Various superelastic alloys used as samples were manufactured by use of 99.99% pure Cu, 99.99% pure Al, 99.99% pure Au, 99.9% pure Fe, and 99.9% pure Co as melting materials. These raw materials were dissolved in an Ar-1% H.sub.2 atmosphere by use of a non-consumable W electrode-type argon arc melting furnace to manufacture an alloy ingot. Thereafter, the alloy ingot was heated at 600 C. for six hours to be homogenized, and then annealed.

(3) Subsequently, a tensile test piece (thickness of 0.2 mm, width of 2 mmlength of 20 mm (length of measurement section of 10 mm)) was manufactured through electrical discharge machining with respect to the alloy ingot (thickness of 1 to 2 mm). After the specimens were processed, the alloys were subjected to a final heat treatment. In the final heat treatment, the alloys were heated at 500 C. for an hour, and then quenched.

(4) With respect to the respective manufactured specimens, X-ray imaging properties were first verified. In this test, the ingot was put between two acrylic plates from upper and lower sides and installed on an X-ray blood vessel photographing apparatus, and X-ray irradiation was conducted under a condition used in an actual X-ray diagnosis (X-ray tube voltage: 60 to 125 kV, X-ray tube current: 400 to 800 mA, irradiation time: 10 to 50 msec, Al filter (2.5 mm) was used). Then, an obtained transmission image was visually observed, and was determined to be when a sample shape was clearly viewed, and x when the sample shape was viewed as unclearly as or less clearly than TiNi.

(5) Subsequently, a tensile test (stress loading-unloading test) was conducted on each specimen, and superelastic property was evaluated. In the tensile test for evaluation of superelasticity, a load was applied in the atmosphere (at a room temperature) for 510.sup.4/sec until elongation of 2% was generated, and then removed. Then, a residual strain was measured to obtain a superelastic shape recovery rate. The superelastic shape recovery rate was obtained by the following Equation.
Superelastic shape recovery rate (%)=(Plastic strain (%) at the time of 2% strainResidual strain (%))/Plastic strain at the time of 2% strain100[Equation 1]
Herein, a value obtained by exclusion of an elastic deformation strain from a total deformation strain is set to a plastic strain.

(6) Presence or absence of superelasticity was determined to be present () when a calculated superelastic shape recovery rate was 40% or more, and absent (x) when the rate was less than 40% or a specimen was broken at the time of the tensile test.

(7) Further, a tensile test was conducted on each specimen to evaluate strength and processability. In the tensile test, a load was applied in the atmosphere (at a room temperature) for 510.sup.4/sec until the specimen was broken. A strain was measured when the specimen was broken to determine that processability was excellent () when a breaking strain of 2% or more was obtained, and poor (x) when the breaking strain was 2% or less. Additionally, strength was determined to be excellent () for a specimen which has strength exceeding 200 MPa when the specimen was broken, and poor (x) otherwise. When a specimen was not broken even when a strain of 10% or more from a test condition was applied, the test was ended and a value of 10% was adopted.

(8) Table 1 shows evaluation results with respect to X-ray imaging property, superelastic property, processability, and strength of each specimen.

(9) TABLE-US-00001 TABLE 1 Evaluation result X-ray Alloy composition (% by mass) imaging Au Cu Al Fe Co CuAl Superelasticity Strength Processibility property Example 1 83.1 13.2 3.7 0.04 9.5 Example 2 82.5 13.3 3.8 0.4 9.5 Example 3 81.8 13.5 3.8 0.9 9.7 Example 4 80.4 14.7 4.0 0.9 10.7 Example 5 81.2 14.1 3.8 0.9 10.3 Example 6 79.7 15.5 3.9 0.9 11.6 Example 7 79.2 15.7 4.2 0.9 11.5 Example 8 78.7 15.9 4.5 0.9 11.4 Example 9 79.2 14.9 5.0 0.9 9.9 Example 10 80.5 15.0 3.2 1.3 11.8 Example 11 81.9 13.4 3.8 0.9 9.6 Example 12 81.8 13.5 3.8 0.5 0.4 9.7 Comparative Example 1 77.4 16.7 5.9 10.8 x x x Comparative Example 2 77.9 17.6 4.5 13.1 x x Comparative Example 3 79.0 17.8 3.2 14.6 x x x Comparative Example 4 80.1 15.5 4.4 11.1 x x x Comparative Example 5 81.1 15.1 3.8 11.3 x x x Comparative Example 6 81.3 15.3 3.4 11.9 x x x Comparative Example 7 81.8 15.1 3.1 12.0 x Comparative Example 8 82.0 14.7 3.3 11.4 x Comparative Example 9 82.4 14.5 3.1 11.4 x x Comparative Example 10 82.9 14.3 2.8 11.5 x Comparative Example 11 82.9 12.9 4.2 8.7 x x Comparative Example 12 83.2 12.2 3.7 0.9 8.5 x Comparative Example 13 80.0 15.7 3.4 0.9 12.3 x Comparative Example 14 79.9 13.4 5.8 0.9 7.6 x Comparative Example 15 75.9 17.1 6.0 1.0 11.1 x Comparative Example 16 79.9 13.9 3.9 2.3 10.0 x

(10) Table 1 shows that Examples 1 to 11, in which content of each constituent element is within an appropriate range, exhibited superelasticity and had excellent processability and strength. On the other hand, an AuCuAl alloy to which Fe and Co were not added (Comparative Examples 1 to 11) did not exhibit superelasticity and had poor processability or strength in many cases. Additionally, even when Fe was added, if Cu and Al contents were inappropriate (Comparative Examples 12, and 14 to 16), superelasticity was not exhibited even though processability or strength was excellent. Further, it is shown that superelasticity was not exhibited when a difference between Cu and Al contents was inappropriate (Comparative Example 13). From above, in an AuCuAlFe (Co) alloy, an excellent characteristic such as exhibition of superelasticity, and importance of composition adjustment for the excellent characteristic are verified.

Second Embodiment

(11) Herein, influences of a final heat treatment temperature and cold working on alloy characteristics were examined with respect to an alloy of Example 3 of the first embodiment (81.8% Au13.5% Cu3.8% Al0.9% Fe).

(12) First, in order to examine an influence of the final heat treatment temperature, a heat treatment temperature was changed (100 C. (Reference Example 1), 200 C. (Reference Example 2), 300 C. (Example 13), 400 C. (Example 14), 600 C. (Reference Example 3)) after a tensile test piece was manufactured in a process of manufacturing a specimen of the first embodiment, and the final heat treatment for conducting quenching after the heat treatment was performed. Additionally, herein, characteristic of melted and cast alloy which is not subjected to the final heat treatment was evaluated (Example 15). This alloy was obtained by manufacture of a tensile test sample by wire discharge with respect to a melted and cast alloy ingot. Then, presence or absence of superelastic property, processability, and strength were measured on these specimens similarly to the first embodiment. Measurement results are shown in Table 2.

(13) TABLE-US-00002 TABLE 2 Final heat treatment Super- temperature elasticity Strength Processibility Reference 100 C. x (500 MPa) Elongation Example 1 3.8% Reference 200 C. x (700 MPa) Elongation Example 2 5.8% Example 13 300 C. (690 MPa) Elongation 6.3% Example 14 400 C. (750 MPa) Elongation 6.0% Example 3 500 C. (700 MPa) Elongation 6.2% Example 15 (350 MPa) Elongation 2.4% Reference 600 C. x x (100 MPa) x Elongation Example 3 0.8%

(14) Table 2 shows that a final heat treatment temperature mainly affects superelastic property, and superelastic property is excellent in a final heat treatment at 300 to 500 C. Additionally, when the final heat treatment temperature is excessively high (600 C.), superelastic property is not exhibited, and the temperature has a bad influence on strength and processability. As a result, a necessity for a final heat treatment within a suitable temperature range was confirmed.

(15) Additionally, a result of Example 15 shows that the final heat treatment is not an essential treatment in terms of exhibiting superelasticity and ensuring strength.

(16) Next, an influence of cold working before a final heat treatment was examined. With regard to the process of manufacturing the specimen of the first embodiment, an alloy ingot was heated at 500 C. for 1 hour, and then cold-rolled up to 0.2 mm (processing rate of 24%). Thereafter, a tensile test piece was processed and manufactured. Then, a final heat treatment for conducting quenching after the heat treatment was performed by setting of a treatment temperature to 300 C., 400 C., and 500 C., and presence or absence of superelastic property, processability, and strength were measured similarly to the first embodiment. Measurement results are shown in Table 3.

(17) TABLE-US-00003 TABLE 3 Final heat treatment Super- temperature Cold working elasticity Strength Processibility 300 C. Present (800 MPa) (Elongation 8.0%) Absent (690 MPa) (Elongation (Example 13) 6.3%) 400 C. Present (800 MPa) (Elongation 6.0%) Absent (750 MPa) (Elongation (Example 13) 6.0%) 500 C. Present (750 MPa) (Elongation 6.2%) Absent (700 MPa) (Elongation (Example 13) 6.2%)

(18) Table 3 shows that cold working performed before a final heat treatment can improve strength and processability of an alloy after the final heat treatment rather than exerting a bad influence on superelastic property. In this regard, even though an alloy according to the present invention has relatively high strength even when cold working is not performed, the strength is preferably ensured by cold working when the alloy is provided for use which requires higher strength.

INDUSTRIAL APPLICABILITY

(19) An elastic alloy according to the present invention does not contain Ni to have biocompatibility, and contains Au to have excellent X-ray imaging property. Furthermore, the elastic alloy can exhibit superelasticity at a normal temperature, and can be expected to be applied to various medical instruments.