JP2014084485A - Au-BASED SUPERELASTIC ALLOY - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide alloy which can be applied to a medical field from the point of view of constituent elements and can exhibit superelastic phenomenon at an ordinary temperature range to conventional Au-Ti-based alloy.SOLUTION: The invention relates to quaternary or quinary Au-based superelastic alloy obtained by adding Mo and/or Nb to Au-Ti-Co alloy. The quaternary or quinary Au-based superelastic alloy comprises, by molar concentration, Au of 27% to 45%, Ti of 46% to 54%, Co of over 10% and less than 17%, Mo of 0.5% or more and less than 3%, and/or Nb of 1% or more and less than 3%, where the total concentration of Au and Co is 44% to 52% and total of Co concentration, Mo concentration and Nb concentration is 18% or less. Mo and Nb can be both added, total of Mo concentration and Nb concentration is 1% or more and less than 3% in that case.

Description

  The present invention relates to an Au (gold) -based superelastic alloy, and more particularly, to a superelastic alloy that can exhibit superelasticity at room temperature and has excellent workability.

  The superelastic alloy has a property of immediately recovering its original shape even when it is deformed at a temperature equal to or higher than the reverse transformation temperature (synonymous with the reverse transformation start temperature (As point)). The deformation range at this time is extremely wider than the elastic range of other metal materials (superelasticity), and those having a relatively low reverse transformation point are called superelastic alloys. Superelastic alloys are alloy materials that are expected to be applied to medical devices such as orthodontic appliances, catheters, stents, and bone plates.

  Studies on superelastic alloys have been made in various alloy systems based on knowledge about shape memory alloys. Here, as a superelastic alloy that is most known at present from the viewpoint of practicality, a Ni—Ti-based shape memory alloy can be cited. Since the Ni-Ti shape memory alloy has a reverse transformation temperature of 100 ° C. or less and can exhibit superelasticity even at the body temperature of the human body, it can be said that it can be applied to a medical device in terms of characteristics.

  However, since the Ni—Ti-based shape memory alloy contains Ni, there is a concern about biocompatibility due to metal allergy when considering application to a medical device. Further, since the Ni—Ti alloy is composed of relatively light elements, there is a problem that the contrast property at the time of X-ray imaging is poor.

  Therefore, there is an Au—Ti alloy described in Patent Document 1 as an alloy material that can exhibit shape memory characteristics while being Ni-free. Since this Au-based alloy does not contain Ni, the biocompatibility problem due to metal allergy can be solved. In addition, since it contains a heavy metal such as Au, the X-ray contrast is good, so that it can be expected to be applied to a medical instrument.

JP 09-165633 A

  However, Au-Ti alloys have a high reverse transformation temperature of 300 ° C. or higher, and cannot be expected to exhibit superelasticity in the normal temperature range, and have the characteristics most required for application to medical devices. There is a problem of not having. For this reason, the Au-based alloy has many advantages as described above, but the problem of lowering the reverse transformation temperature remains for its practical use.

  Therefore, an object of the present invention is to provide an alloy that can be applied to the medical field from the viewpoint of a constituent element and can develop a superelastic phenomenon in a normal temperature range.

  In order to solve the above-mentioned problems, the present inventors have made studies based on the above-described Au—Ti-based shape memory alloy. As described above, this alloy does not contain Ni but contains Au, and can be expected to be applied to the medical field from the viewpoint of biocompatibility and X-ray contrast enhancement. The inventors of the present invention applied Au-Ti-Co alloys in which a part of Au was replaced with Co as a means of developing superelasticity at room temperature by lowering the reverse transformation temperature of Au-Ti alloys. I came up with it. According to the present inventors, it has been confirmed that the Au-Ti-Co alloy has a reverse transformation temperature that decreases with an increase in the amount of Co added, and exhibits superelasticity at room temperature when a predetermined amount or more of Co is added. ing.

  However, according to detailed studies by the present inventors, it has been confirmed that Co lowers the toughness of the alloy and deteriorates the workability together with the action of lowering the reverse transformation temperature. It can be said that the workability affects the usefulness of the superelastic alloy. This is because medical devices such as orthodontic appliances, catheters, and stents are manufactured through high-precision processing, and the quality of workability is important for these applications.

  Therefore, the present inventors examined a means for suppressing an incidental problem of deterioration in workability caused by the occurrence of superelasticity at room temperature due to Co. As a result, the inventors have conceived the addition of trace amounts of Mo and Nb as additional additive elements to the Au—Ti—Co alloy. And the suitable range of Co addition amount with respect to an Au-Ti type alloy and the addition amount of Mo and Nb is examined, and it is made into this invention as a superelastic alloy with a good balance of superelasticity expression and workability ensuring in normal temperature range. I came up with it.

  That is, the present invention is a quaternary or quinary Au-based superelastic alloy obtained by adding Mo and / or Nb to an Au-Ti-Co alloy and has a molar concentration of 27% or more and 45% or less. Au, 46% to 54% Ti in molar concentration, Co in excess of 10% to less than 17% in molar concentration, Mo in molar concentration to 0.5% to less than 3% and / or 1 in molar concentration. %, And the total of Au concentration and Co concentration is 44% or more and 52% or less, and the total of Co concentration, Mo concentration and Nb concentration is 18% or less. Au-based superelastic alloy.

  Hereinafter, the present invention will be described in more detail. The Au-based superelastic alloy according to the present invention is either an Au-Ti-Co-Mo quaternary alloy, an Au-Ti-Co-Nb quaternary alloy, or an Au-Ti-Co-Mo-Nb quaternary alloy. Therefore, the content of each constituent element is made appropriate, and the superelastic property in the normal temperature range is developed under these balances. Hereinafter, each constituent element will be described.

  First, the Au superelastic alloy according to the present invention is an improvement over a conventional Au—Ti superelastic alloy, and Au and Ti are main constituent metals. In the present invention, Au is made 27% to 45% in terms of molar concentration. The reason why the Au concentration falls within the above range is that if it is less than 27%, the superelastic property is not exhibited, and if it exceeds 45%, the reverse transformation temperature is high and it tends to be difficult to achieve superelasticity at room temperature. The Au concentration is preferably 30% or more and 40% or less, and more preferably 30% or more and 38% or less.

On the other hand, about Ti, it is set as 46% or more and 54% or less by molar concentration. When Ti is less than 46%, a second phase of Au ₂ Ti is generated, which adversely affects workability. And if it exceeds 54%, transformation hysteresis will become large and it will be inferior to a superelastic property. Therefore, by making Ti 46% or more and 54% or less, a single-phase region and a superelastic property are exhibited. In addition, about Ti, it is more preferable to set it as 48% or more and 52% or less.

  Co is an additive element for substituting a part of Au, and is an essential additive element for lowering the reverse transformation temperature and developing superelasticity at room temperature. Co is more than 10% and less than 17% in molar concentration. If it is 10% or less, the transformation temperature cannot be sufficiently lowered, but if it is 17% or more, the workability deteriorates. On the other hand, if it is 17% or more, the transformation temperature becomes too low, and transformation itself is difficult to occur. Co is preferably more than 10% and 16% or less, and more preferably 12% or more and 15% or less.

  As described above, Co lowers the reverse transformation temperature, but deteriorates the workability of the alloy, so its addition amount is limited. If the amount of Co is limited, the amounts of Au and Ti must be increased, and there is a concern about an increase in reverse transformation temperature or a decrease in superelastic characteristics. Therefore, the present invention adds a suitable amount of Mo and / or Nb as a further additive element. Mo and Nb have the action of substituting Au and / or Ti sites for addition to the Au—Ti—Co alloy and suppressing the increase of the reverse transformation temperature due to the reduction of the amount of Co.

  The addition amount of Mo and Nb is such that Mo is 0.5% or more and less than 3% and Nb is 1% or more and less than 3% in molar concentration. The effect is not seen below these lower limits, and conversely when the upper limit is exceeded, the alloy becomes brittle and cannot be processed. As for the more preferable addition amount of Mo and Nb, Mo is 0.5% or more and 2% or less, and Nb is 1% or more and 2% or less. Note that only one of Mo and Nb may be added, or both may be added. However, in the case of both additions, it is preferable that the sum of the Mo addition amount and the Nb addition amount be 1% or more and less than 3%.

And the sum of Au concentration and Co concentration needs to be 44% or more and 52% or less. As described above, the Au-based superelastic alloy according to the present invention is obtained by replacing a part of Au in the Au—Ti-based superelastic alloy with Co, and the total concentration thereof is the concentration of Ti as the other main element. Influences. And by making the sum of Au concentration and Co concentration 44% or more and 52% or less, an alloy can be maintained in a single phase area | region and workability can be ensured. Outside these ranges, a large amount of the second phase (Au ₂ Ti, Ti ₃ Au, etc.) is generated, and the workability deteriorates.

  Furthermore, in the relationship between the Co concentration, the Mo concentration, and the Nb concentration, it is necessary that the total concentration is less than 18%). This is because when the total of these elements exceeds 18%, workability is poor and neither shape memory characteristics nor superelasticity is exhibited.

  Although the production of the Au-based superelastic alloy according to the present invention can be more produced by a normal melting casting method, it is preferable to perform an aging heat treatment after casting. This is because the superelastic effect is more effectively exhibited by performing the aging heat treatment. This aging heat treatment is preferably held at 200 to 500 ° C. for 5 minutes to 24 hours.

  As described above, the Au-based superelastic alloy according to the present invention is an alloy that can exhibit superelasticity at room temperature while being Ni-free. And workability is also favorable.

  The Au-based superelastic alloy according to the present invention has good biocompatibility because it is Ni-free, and also has good X-ray contrast properties because it uses a heavy metal such as Au as a constituent element. Since the present invention has the above characteristics, it can be expected to be applied to medical instruments. Specifically, the present invention is applied to orthodontic appliances, artificial roots, clips, staples, catheters, stents, bone plates, and other medical instruments. Application is possible.

  Hereinafter, embodiments of the present invention will be described. In the present embodiment, an Au—Ti—Co—Mo (Nb) alloy in which the concentration of each constituent element is changed is manufactured, and the workability is evaluated while processing this into a test piece. The presence / absence and X-ray contrast properties were evaluated.

Preparation of various Au—Ti—Co—Mo (Nb) superelastic alloys as samples is as a melting raw material with a purity of 99.99% Ti, a purity of 99.9% Co, a purity of 99.95% Au, and a purity of 99.99%. Mo, purity 99.99% Nb was used. These raw materials using a non-consumable W electrode type argon arc melting furnace to produce an alloy ingot by dissolving in Ar-1% H ₂ atmosphere. In order to increase the homogeneity of the alloy, the work of turning it over before melting each alloy was performed six times. And the homogenization process for eliminating segregation about the alloy ingot after casting was performed. The homogenization was performed by hot pressing at 1100 ° C. for 3 hours and then cooling in a furnace. Furthermore, for solution treatment, the ingot was sealed in an opaque quartz tube having an internal pressure of 4 × 10 ⁻³ Pa or less, placed in an electric furnace, held at 900 ° C. for 30 minutes to 1 hour, and immediately washed with quartz in water. The tube was broken and water cooled. And the aging heat processing was performed about the ingot after solution treatment. The aging heat treatment was performed at a temperature of 300 ° C. for 1 hour in a vacuum.

First, the X-ray imaging property of the manufactured ingot was confirmed. In this test, an ingot is sandwiched from above and below by two acrylic plates and installed in an X-ray angiography apparatus. Conditions used in actual X-ray diagnosis (tube voltage: 60 to 125 kV, tube current: 400 to 800)
X-ray irradiation was performed with mA, irradiation time: 10 to 50 msec, using an Al filter (2.5 mm). Then, the obtained transmission image was visually observed, and when the sample shape was clearly seen, it was judged as “◯”, and when the opacity was equal to or less than TiNi, it was judged as “x”.

  Next, each ingot (thickness 0.4 mm) was rolled and processed into a test piece (thickness 0.25 mm). In this processing step, workability was also evaluated. In the processability evaluation, it was judged that the processability was good when the ingot was rolled and processed at a reduction rate exceeding 20%. Those with inferior processability in this processability evaluation were excluded from the superelastic property evaluation test. And about the alloy which can be processed, the cutting shape was prepared with the wire electric discharge machine, it grind | polished, and the oxide film on the sample surface was removed. After heating this as it was or between 200 degreeC and 500 degreeC for 5 minutes-24 hours, the presence or absence of superelasticity was examined.

  Confirmation of superelasticity is achieved by wrapping a test piece in a U-shape around a round bar (diameter 7 mm), introducing processing strain, and determining that the shape recovery rate is 50% or more after unloading is superelastic. did.

  From Table 1, the Au—Ti—Co—Mo (Nb) alloy having a preferred composition in the present invention has good workability and can exhibit superelastic properties at room temperature. Moreover, when it sees about the addition amount of each structural element, it turns out that workability deteriorates by adding 3% or more of Mo and Nb (Comparative Examples 2 to 7). In addition, Co deteriorates workability due to excessive addition (Comparative Examples 9 to 14), but processing is possible when the addition amount is small (Comparative Example 8). However, in that case, superelasticity did not appear.

  Moreover, it is necessary to control Au and Ti as main constituent elements within a predetermined range (Comparative Examples 15 to 17). The addition amount of Au also affects the numerical value of the sum (Au + Co) with the addition amount of Co, and therefore needs to be in an appropriate range.

  The Au-based superelastic alloy according to the present invention has biocompatibility because it does not contain Ni, and also has good X-ray contrast properties because it contains Au. In addition, superelasticity at room temperature can be expressed, and application to various medical devices can be expected.

Claims (2)

A quaternary or quinary Au-based superelastic alloy obtained by adding Mo and / or Nb to an Au-Ti-Co alloy,
Au in a molar concentration of 27% or more and 45% or less;
Ti at a molar concentration of 46% or more and 54% or less,
More than 10% and less than 17% Co in molarity;
Mo in a molar concentration of 0.5% or more and less than 3% and / or Nb in a molar concentration of 1% or more and less than 3% (However, when both Mo and Nb are included, the sum of Mo concentration and Nb concentration is 1%. And less than 3%)
Furthermore, the Au-based superelastic alloy, wherein the sum of the Au concentration and the Co concentration is 44% or more and 52% or less, and the sum of the Co concentration, the Mo concentration, and the Nb concentration is 18% or less. A molar concentration of 30% to 40% Au and a molar concentration of 46% to 54% Ti;
More than 10% and less than 16% Co in molarity;
The Au-based superelastic alloy according to claim 1, comprising Mo in a molar concentration of 0.5% to 2% and / or Nb in a molar concentration of 1% to 2%.