JP3943142B2 - Manufacture of bi-directional shape memory device - Google Patents

Abstract

A process is provided for the manufacture of a two-way shape memory alloy an d device. The process of the invention allows a reversible adjustment of the characteristic transformation temperatures, as well as the direction of the two-way shape memory effect, at the final stage of manufacture.

Description

Field of Invention
The present invention relates generally to shape memory alloys (SMAs), that is, alloys that can change from one shape to another in a “memory” state upon temperature change. More particularly, the present invention relates to a nickel-titanium based SMA, also known as nitinol.
Background of the Invention
Various metal alloys have the ability to change their shape as a result of temperature changes. Such SMAs have a relatively soft and deformable material.Martensite formThe material has superelastic properties and is relatively hardAustenitic formIn addition, it can be reversibly transformed.Martensite formFromAustenitic formThe transformation to can be expressed here as the “austenite transformation”, the other,Austenitic formFromMartensite formThe transformation to can be described as a “martensite transformation”. The austenite transformation occurs in a temperature range higher than the temperature range where the reverse transformation occurs. This is because once the SMA is transformed to the austenite state, the SMA is at a temperature higher than the temperature at which the martensite transformation begins, even when cooled to a temperature lower than the temperature at which the austenite transformation has begun. This means that it can be maintained as long as it is.
A specific class of SMAs are nickel and titanium alloys-NiTi alloys. NiTi alloys have found various uses in medicine, as in other fields. Medical applications of SMA, particularly NiTi based alloys, are described in US Pat. Nos. 4,665,906, 5,067957, European Patent Application No. 143,580, US Pat. No. 4,820,298 and many others.
For medical applications, it is usually desirable that the alloy can undergo austenite transformation in a well-defined range with a narrow width. For example, a bi-directional SMA type conduit stent as described in European Patent Application Publication No. 625153, when it is martensitic at body temperature and then heated,Austenitic formAfter being transformed into a body temperature,Austenitic formAs such, it is typically deployed within the body. It can be appreciated that if excessive heating is required to transform the SMA from martensite to austenite, this is undesirable because it damages the surrounding tissue. Thus, it would be ideally desirable that the austenite transformation can begin at a temperature several degrees above body temperature and can be in a temperature range that cannot cause tissue damage due to excessive heating.
WO 8910421-A discloses a method for controlling the physical and mechanical properties of a nickel-titanium alloy exhibiting a shape memory effect, said method comprising the following steps:
-Annealing at a temperature of 300-950 ° C for 5 minutes to 2 hours
-Cold work in the range of 6 to 60%
-Mold to the desired outer shape
-Heat-treating at a memory-imparting temperature selected from 400 to 600 ° C;
-And cool.
Summary of the invention
It is an object of the present invention to provide a NiTi alloy processing method for obtaining an alloy having a bidirectional shape memory effect (SME), reversibly adjustable and having a specific transformation temperature.
More particularly, it is an object of the present invention to provide such a method that yields a bidirectional SME that does not require multi-cyle “training” to generate the bidirectional SME.
Furthermore, an object of the present invention is to provide a method for obtaining a bidirectional SME having a narrow temperature range in which austenite transformation occurs.
The present invention has two surface areas. According to one surface, here it is often referred to as “the first measurement,Martensite formAn alloy is produced that has directions of austenitic and martensitic transformations dictated by the direction of the coordinating transformation to. According to another aspect of the present invention, often referred to herein as a “second aspect”, the method isMartensite formTo produce alloys having the direction of martensitic or austenitic transformation independent of the deformation introduced into the steel.
In the following description and claims, the term “NiTi alloy” is used primarily to refer to alloys containing nickel and titanium atoms, but may also contain other trace metals). NiTi alloys typically have the following empirical formula:
Ni_lTi_mA_n
In this formula, A represents Ni, Cu, Fe, Cr or V, l, m, and n represent the proportion of metal atoms in the alloy, and the values of l, m, and n are approximately as follows: It is.
l: 0.5
m = 0.5-n
n = 0.003 to 0.02
According to the present invention, a bi-directional shape memory effect (SME) is exhibited, thereby corresponding to an austenite shape and a martensite shape, respectively.Austenitic memory formandMartensite memory formA raw NiTi alloy having an initial shape to obtain an alloy having a final shape, comprising:
(A) To obtain an evaluation of the internal structure of the alloy, A_sPoint and A_fTest the raw NiTi alloy by measuring the difference from the point,
(B) subjecting the raw NiTi alloy to a first heat treatment based on the results obtained in (a) to produce an alloy having an initial internal structure condition with essentially uniformly random dislocation density;The first heat treatment is defined as follows:
If the temperature difference is less than 7 ° C, heat-treat the alloy to a temperature of 450-500 ° C for 0.5-1.0 hours,
If the temperature difference is greater than 7 ° C., heat-treat the alloy to a temperature of 510-550 ° C. for 1.0-2.5 hours;
(C) To produce a polygonal subgrain dislocation structure decorated by precipitation during dynamic aging (aging during indentation) (eg by warm rolling or warm drawing)When the melting temperature of the alloy is Tm with Kelvin, the temperature is 0.3 Tm.Subjecting the alloy to a thermomechanical treatment (TMT) involving plastic deformation of the alloy with simultaneous heating;
(D) If the deformation in step (c) did not form the final shape, subject the alloy to an intermediate heat treatment to complete one cycle of subgrain dislocation structure formation;
(E) Repeat steps (c) and (d) until the final shape is achieved,
(F) subjecting the alloy to a final heat treatment and a memory treatment;
A method comprising each step is provided.
TMT, several steps if it can be done in a single step in some cases while the total strain value can exceed the critical value that can result in the formation of pre-cracks in the alloy (crack nucleation) It is often necessary to do that. TMT is typically0.3-0.6TmThis is done while warming the alloy to (melting temperature at Tm = ° K).
According to one aspect of the invention, the method comprises:
(A) A raw NiTi alloy sample0.5-2.5 hours, 450-550 ° C temperatureAfter heating to A_sPoint and A_fTest sample for temperature difference from point, (b) A obtained in step (a)_fPoint-A_sA first heat treatment based on the point difference is applied to the raw NiTi alloy as follows:
If the temperature difference is less than 7 ° C, heat-treat the alloy to a temperature of 450-500 ° C for 0.5-1.0 hours,
If the temperature difference is greater than 7 ° C., heat-treat the alloy to a temperature of 510-550 ° C. for 1.0-2.5 hours;
(C) 5 sec involving internal heating of part of the alloy where deformation occurs to a temperature of 250-550 ° C. simultaneously^-1The alloy is subjected to a thermomechanical treatment that includes plastically deforming the alloy at a strain rate of less thanLess than 55%, preferably less than 40%Is,
(D) If the deformation in step (c) did not form the final shape,0.5-2 hours, temperature of 500-550 ° CRepeating the step (c) after subjecting the alloy to an intermediate heat treatment at
(E) subjecting the alloy to a final heat treatment and memory treatment;
Each step is provided.
The details of the final heat treatment and the storage process are different between the first side and the second side. According to the first aspect, this process comprises:
(I) the alloyAustenitic formForming into the shape to be taken in,
(Ii) To produce random dislocation arrays in the alloyPolygon processing in the range from 450 ℃ to 550 ℃And then subjecting it to a solution treatment to release the dislocation dislocations from the precipitation and to cause their rearrangement, followed by an aging treatment,
(Iii) The alloy is deformed to take an adjusted shape, and the alloy is in the state formed under the above (i)Austenitic formAnd the alloy has a martensite shape with intermediate deformation between the austenite shape and the adjusted shapeMartensite formAnd remember the alloyHeat treatment in the range of 600 ° C. to 800 ° C., then polygon treatment and solution treatment, then aging treatment, forming the alloy into the austenite shape, memory heat treatment and aging treatment to the alloy Applying,including.
Preferably, steps (ii) and (iii) of the first aspect include
(Ii) To alloy,Polygonized at 450-550 ° C. for 0.5-1.5 hours, then solution treated at 600-800 ° C. for 2-50 minutes, then 0.15-2.5 hours, 350 Apply aging treatment at ~ 500 ° CThat, and
(Iii) The alloy is deformed to take an adjusted shape,Less than 15%, preferably less than 7%And at a temperature T satisfying the following equation:
T <M_s+ 30 ° C
Where M_sIs the temperature at which martensitic transformation begins, and then includes heating the alloy above the temperature at which the austenite transformation of the alloy ends.
According to the second aspect, the final heat treatment and storage treatment are:
(I) forming the alloy into a shape different from the shape it should take in the austenitic state;
(Ii) The alloy is first heat treated and thenPolygon processingAnd solution treatment, then optionally aging treatment,
(Iii) alloy, itAustenitic formForming into the shape to be taken in,
(Iv) The alloy is subjected to memory heat treatment and aging treatment,
Thereby, the alloy has the austenite shape it takes in (iii) aboveAustenitic formAnd the alloy has a martensite shape, which is a shape having intermediate deformation between the shape formed in (i) and the austenite shape.Martensite formBeing adjusted to remember
including.
According to a preferred embodiment of said aspect, steps (ii) and (iv)
(Ii)The alloy is subjected to a heat treatment at 450-500 ° C. for 0.5-2 hours, then subjected to a polygonization and solution treatment at 600-800 ° C. for 2-50 minutes, then 0-2 hours, 350 ~ 500 ° CAging the alloy with
(Iv)The alloy was subjected to memory heat treatment at 500-600 ° C. for more than 10 minutes, then 0.15-2.5 hours, 350-500 ° C.Aging the alloy with
including.
Following processing according to both the first and second aspects, A_fThe point is10 to 60 ° CCan be between. A_fDot and A_sTo raise the point, the alloy then350-500 ° CAging heat treatment at a temperature of A_fDot and A_sTo lower the point, the alloy then510 to 800 ° CA solution treatment at a temperature of
Due to different aging or solution treatments in different parts, the alloy can have different austenite transformation temperatures. This is sometimes desirable, for example, in the case of medical stents, having portions with different transition temperatures of austenite and / or martensitic transformations.
By the above process, SMA for various applications can be prepared. Examples are non-medical devices such as tube joints as well as medical devices such as various orthopedic devices, root implants, medical stents, intrauterine implants. Such a method for preparing a medical device forms an aspect of the present invention as well as a device prepared by such a method.
[Brief description of the drawings]
FIG. 1 shows A at different aging temperatures._fThe relationship between points and aging time is shown.
Detailed Description of the Invention
The temperature range at which austenite transformation occurs is important in various medical applications. A particular case of interest is a medical stent such as that made from a bidirectional shape memory alloy (SMA) as described in European Patent Application No. 626153. Such shape memory (SM) devices are deployed in tubular organs at body temperature and then heated to allow the austenite transformation to occur. Once heated, it is at body temperatureAustenitic formIt remains and supports the tubular organ wall. Such SM devices are designed so that the onset of austenite transformation can occur at temperatures above 40 ° C. However, it will be appreciated that the temperature range at which austenite transformation occurs should desirably be narrow since excessive heating over a wide temperature range can cause tissue damage. In addition, the narrow temperature range is also generallyMartensite formFromAustenitic formCan guarantee a more rapid transition to.
In the following description, the invention can often be described with specific reference to the application to the preparation of medical SM devices having a narrow austenite transformation range. However, it will be appreciated that the invention is not so limited and the application of the invention to the preparation of medical stents is merely exemplary. According to the present invention, the raw NiTi alloy, supplied by the manufacturer, typically in the form of a wire or rod, is initially A_sDot and A_fEvaluated for point differences. A small material sample is used for this purpose. A_sPoint-A_fPointTemperature differenceThe alloy, eg wire or rod, is then subjected to a first heat treatment.
Subsequent to the first heat treatment, the alloy is subjected to a thermomechanical treatment (TMT) in which the alloy is simultaneously heated and subjected to mechanical deformation. In the case of methods intended for the manufacture of medical SM devices, the mechanical deformation may change the shape of the alloy from the initial shape of the wire or rod to the shape of a ribbon, band, etc., or else the wire or rod may have a smaller diameter. Typically including changing to a wire or rod. In order to preserve the shape memory effect (SME) of the alloy, the total degree of deformation during TMT should be less than 55%, preferably less than 40%. If the overall required final deformation exceeds 55%, TMT is performed in two steps with an intermediate heat treatment.
The heat treatment can be, for example, warm rolling where the alloy is processed to be used as a medical stent, warm drawing where the alloy is processed to be used as an orthopedic root implant, and the like. In warm rolling or warm drawing, the alloy typically0.3-0.6Tm(Tm is the melting temperature in ° K). The heating of the deformed part is for example500-2000A / cm ² Must be by electrical stimulation at a current density of. The major benefit of such a process is that, in addition to causing mechanical deformation, a relatively high current at such a pre-crack that results in selective overheating at such location and selective heating of the pre-crack. It also leads to pre-crack heating with high dislocation density due to resistance. Moreover, the warm TMT of electrical stimulation at the current density accelerates the dislocation reaction, which results in the formation of a complete dislocation subgrain structure. In addition, the heating current results in a dynamic aging treatment with second phase precipitation on the subgrain dislocation cell walls. This structure shows that the shape memory alloy has a very narrow temperature interval A of austenite transformation._fPoint-A_sIt gives a point and various other beneficial properties as described below. In an electrically stimulated warm rolling, the current density is 500 A / cm.²When lowering or lowering the deformation strain rate5 sec ^-1 If higher, there is a random increase in dislocation density that can reduce the degree to which the subgrain structure is complete. Narrow A_fPoint-A_sDue to the spacing of the points, as complete a subgrain structure as possible is required. Therefore, with increasing random dislocation density, A_fPoint-A_sThere is an increase in point spacing. For example, the current density is400A / cm ² Or the strain rate is8 sec ^-1 A after the final heat treatment_fPoint-A_sThe point spacing is10-12 ° CIt can be. further,2000A / cm ² Increasing the current density higher leads to a recrystallization process that prevents the formation of the required subgrain cell with precipitation on the cell walls. The amnestic treatment is the two forms that the alloy takes during its use:Martensite formShape ("Martensite shape") andAustenitic formAn adjustment step in which microscopic changes in the alloy are adjusted to memorize the shape (“austenite shape”).
According to the first aspect, the alloy comprisesAustenitic formFor example, in the case of a stent, this isAustenitic formAnd wrapping around a mandrel having a stent diameter. The alloy is then typically placed in a vacuum or inert atmosphere furnace in which0.5-1.5 hours, 450-550 ° COf amnestics and internal tissues at the temperature ofPolygon processingIs given first, then2 to 50 minutes, 600 to 800 ° CTo be heated. During this latter heating, the alloy undergoes a solution treatment with rearrangement of dislocations released after the solution treatment. Subsequently, the alloy0.15-2.5 hours, 350-500 ° CThe final aging treatment at the temperature of is performed.
The result of the above treatment is a subgrain structure that provides an alloy with several characteristics. For one, the austenite transformation temperature, Af point,1-5 ° CA with very narrow spacing_fPoint-A_sIt can be adjusted within the range of 10-60 ° C. with points.
A_fIf it is desirable to reduce the point, the alloy510-800 ° CThe solution treatment can be performed at a temperature of Desirable A_fThe temperature can be controlled as well as the aging time to achieve the point. For example, Nitinol alloy after final heat treatment45 ° CA_sDot and48 ℃A_fIf you have a point,5 minutesAfter solution treatment at 640 ° C., A_sDot and A_fEach point is23 ° CAnd drop to 27 ° C. After 10 minutes of solution treatment at 640 ° C., A_sDot and A_fEach point is11 ° CAnd drop to 15 ° C.
A_fTo raise the point, the alloy350-500 ° CAging heat treatment is performed at a temperature of. Here again, desirable A_fThe temperature can be controlled as well as the aging time to achieve the point. This can be achieved, for example, by an aging time at two different temperatures (380 ° C. and 480 ° C.) followed by a solution treatment at 640 ° C. for 20 minutes._fThe relationship between the points is shown in FIG. As can be appreciated, for example,100 minutesThe aging treatment at 380 ° C.40 ° CThe same A_fThe point is40 minutesAchieved by aging at 480 ° C.80 minutes, 450 ° CAging at a temperature of46 ° CA_sDot and49 ° CA_fIt can be a point (not shown in FIG. 1).
A unique feature of the process of the present invention is the fact that a bidirectional SME is induced with only one cycle of deformation. In the case of the first aspect of the invention, this is the alloy A_fFollowing the heating to a temperature above the point, the temperature T <M_sIt can be achieved by deforming the alloy into an adjusted shape at point + 30 ° C. This deformation should be less than 15%, preferably less than 7%. Deformation higher than 15% can affect the internal structure of the material,Austenitic formLoss of all or part of the memory shape. A deformation between 7% and 15% may only have such a partial inhibitory effect. The martensite memory shape taken by the alloy after the adjustment step is an intermediate shape between the austenite memory shape and the adjustment shape. The direction of a bi-directional SME following such a storage process isMartensite formConsistent with the direction to deformation. For example,Martensite formIf the deformation in includes a reduction in diameter,Martensite formThe diameter of the alloy atAustenitic formThe diameter may be less than or vice versa.
In general, the treatment according to the first aspect allows a reversible adjustment of the specific transformation temperature as well as the direction of the bidirectional SME in the final manufacturing process.
The final storage process according to the second aspect of the present invention produces a bidirectional SME without requiring a final deformation to induce the bidirectional SME. This effect isDirect SMEIf occurs, it is not measured. The second aspect is useful, for example, in the manufacture of a stent having a bidirectional SME, and the following description will refer to this particular embodiment. NiTi ribbons or wires can be used to normalize and texture the internal structure.0.5-2.0 hours, 450-550 ° C2R trapped and placed in a vacuum furnace at a temperature of₁Around a mandrel having a diameter equal to. Similar to the above, the alloy is then subjected to a solution treatment and structure improvement at a temperature of 600 to 800 ° C. for 2 to 50 minutes, and thereafter an aging treatment at 350 to 500 ° C. for 0 to 2.5 hours. Applied. Then the ribbon or wire has a diameter 2R which is the diameter that the stent should take in the austenitic state.₂The mandrel is wound again and then subjected to a storage treatment at 500 to 600 ° C. and an aging treatment at a temperature of 350 to 500 ° C. for 0.15 to 2.5 hours for more than 10 minutes. The distortion of this process is ε_treat= 1 / 2w (1 / R₂-1 / R₁) <0 (w is the thickness for ribbons and the diameter for wires), the corresponding strain in the two-way SME during cooling is ε_tw= 1 / 2w (1 / R_tw-1 / R₂)> 0 (2R_twIsMartensite formIs the diameter of the stent), and vice versa. As a result of this treatment, as described above, between 10 ° C. and 60 ° C._fA very narrow temperature range in which the austenite transformation occurs with the possibility of changing points, A_fPoint-A_sThere are points = 1-5 ° C.
The bidirectional SME during cooling isMartensite formIt can be either the same as the deformation direction or the opposite. R₂Is R₁If greater than R_twIs R₂Smaller diameter and the device will shrink when it is cooled. R₂Is less than 0, that is, reverse bending, and R₂Is R_twOtherwise, the device can expand as it cools.
Finally, another result of the process of the present invention is the high resistance of the forming alloy to pitting corrosion and hydrogen embrittlement that can occur in biological media having relatively high chloride ion content.
The present invention is further illustrated herein by several specific examples.
Example 1-Preparation of bile stent
The starting material was a 1.5 mm diameter superelastic NiTi wire. The Ti and Ni contents of the alloy are 50-50.8 atomic% (atomic% =% of the total number of atoms in the alloy) and 49.1 atomic%, respectively.And the remainder is an inevitable impurity elementMet. The sample wire was processed at 500 ° C. for 1.5 hours, and temperature interval A_fPoint-A_sA point was measured and found to be 15 ° C.
The wire is then subjected to a first heat treatment at 550 ° C. for 2 hours, after which the current density is 900 A / cm.²And the strain rate is 0.3 sec.^-1An electrical stimulation heat treatment was applied. TMT was repeated three times, each with two intermediate heat treatments at 500 ° C. for 1 hour. The ribbon thickness was finally reduced to 0.25 mm.
Next, the ribbon is wound and restrained by a mandrel having a diameter of 8 mm, placed in a vacuum furnace, heated to 500 ° C. for 0.6 hours, and then subjected to a solution treatment at 650 ° C. for 30 minutes. It was given. Subsequently, an aging treatment at 400 ° C. was performed for 1 hour.
The resulting helical coil stent has an A of 40 ° C._sPoint and 43 ° C A_fHad a point.
The stent was then wrapped around a 3 mm diameter mandrel at a temperature of 25 ° C. and heated above 43 ° C. for shape recovery. This yields a stent with a bi-directional SME having an austenite memory shape with a diameter of 8 mm and a martensite memory shape with a diameter of 7.3 mm and contracted when cooled below 25 ° C. It was.
To place the stent in-situ within the body, it was wrapped around a catheter and then inserted into the desired location within the bile duct. The stent was then activated by raising its temperature above 43 ° C. In order to remove the stent, it needs to be cooled below 25 ° C. and can be pulled apart after contraction.
Example 2-Esophageal stent
Stents were prepared from TiNi wires similar to those used in Example 1. This wire was subjected to a first heat treatment, as described in Example 1, followed by TMT, with the difference that the resulting wire had a final thickness of 0.28 mm. Met.
Next, the ribbon was wound and restrained on a mandrel having a diameter of 70 mm, heated to 500 ° C. for 1 hour, and then subjected to a solution treatment at 650 ° C. for 20 minutes. Thereafter, the ribbon was wound and restrained on a mandrel having a diameter of 16 mm, subjected to a storage treatment at 520 ° C. for 30 minutes, and then an aging treatment at 400 ° C. for 2 hours. The stent obtained after this treatment had the following parameters: A_sPoint = 42 ° C; A_fPoint == 45 ° C .; the temperature of the martensitic transformation is 27 ° C.Austenitic formExpanded from 16 mm in diameter to 18 mm in the martensite state.
For deployment, the stent is wrapped around a 5 mm diameter catheter, inserted into the desired location within the esophageal canal, and activated by heating above 45 ° C. When the stent is cooled, it expands to prevent the stent from descending into the stomach.
Example 3-Esophageal stent
A stent was prepared in a manner similar to that of Example 2, with the difference that the ribbon was wrapped around a mandrel having a diameter of 5 mm and, after heat treatment, wrapped around the mandrel in the opposite direction. After heat treatment, similar to Example 2, the stent expands from 16 mm diameter to 25 mm diameter upon cooling.
Example 4-Shape memory element for orthopedic compression screw
The starting material was a 1.5 mm diameter NiTi wire (alloy composition was 50.5 atomic% Ni and 49.5 atomic% Ti).And the remainder is an inevitable impurity elementMet). The wire was subjected to TMT after the first heat treatment, as described in Example 1 (but using warm drawing instead of warm rolling).
Next, the wire was heat treated under conditions constrained by a straight line at a temperature of 500 ° C. for 0.5 hour, and then subjected to a solution treatment at 650 ° C. for 20 minutes. The wire was then released and subjected to a storage treatment at 520 ° C. for 30 minutes, followed by an aging treatment at 450 ° C. for 1 hour. After stretching the wire to 20-21mm, A_sPoint = 39 ° C. and A_fA shape memory effect with point = 41 ° C. is obtained, and after cooling to 25 ° C., the bi-directional shape memory effect occurs immediately after heat treatment (without training) and increases after training treatment (stretching heating).
Example 5-Shape Memory Medical Staple
The starting material and treatment were similar to that of Example 4. The final diameter achieved (by warm drawing) was 0.25 mm. The wire was constrained to the required shape and after 0.5 hour TMT at 520 ° C., it was solution treated at 680 ° C. for 10 minutes and aged at 450 ° C. for 1.5 hours.
After bending the staple, A_sPoint = 42 ° C. and A_fA shape memory effect with point = 45 ° C. was obtained.
Example 6-root implant
The starting material was a 10 mm diameter superelastic Nitinol (50.8 atomic% Ni) rod. After the first heat treatment at 550 ° C. for 2 hours, the rod was TMT-500 ° C., strain rate 0.5 sec.^-1Was pulled out. TMT was repeated twice with an intermediate heat treatment at 500 ° C. for 1 hour. The rod had a final diameter of 6.0 mm.
There are 6 rods to anchor the jawbonesegmentMachined into the shape of a root implant with (leg). Leg lengths were 3, 4 and 5 mm for different implants. The implant is then placed at 500 ° C for 1 hourPolygon processingAfter being applied, the leg of the implant was twisted into a mandrel and the implant was subsequently heat treated at 650 ° C. for 30 minutes and aged at 480 ° C. for 1.5 hours. The implant legs were then forced with a conical cup (closed from 5.0 mm diameter to 3.0 mm diameter). While heating the implant, it_sPoint = 38 and A_fThe point is opened at a temperature of 42 ° C., resulting in a very gentle pressure on the jawbone and a very safe implant activity. Single-cycle implant leg stretching and subsequent heating induces a bi-directional SME in the direction of leg coupling with cooling, a property that is useful for implant removal.
Example 7-Narrow A_fPoint-A_sBidirectional tube coupling with point spacing
The same 10 mm NiTi rod as provided as starting material in Example 6 was processed in a similar manner as described in Example 6 to obtain a 6 mm diameter rod. This rod was then machined into a hollow cylindrical shape with an inner diameter (ID) of 4.4 mm. The cylinder is then held at 500 ° C. for 1 hour.Polygon processingThereafter, a solution treatment at 680 ° C. was performed for 20 minutes. It was then cooled and expanded with a 4.5 mm diameter mandrel and subjected to a storage treatment at 530 ° C. for 30 minutes and an aging heat treatment at 430 ° C. for 40 minutes. The tube coupling was then cooled and expanded with a mandrel to an inner diameter of 4.75 mm.
Coupling is heated (A_sPoint = 15 ° C, A_fAfter point = 18 ° C), the tubes are connected and have a bi-directional SME in the direction of decreasing ID. Thus, even when cooled, it maintains the pressure on the connected tubes. In comparison, conventional couplings in which a bi-directional SME is induced during attachment (expansion and heating) in the direction of expansion causes coupling slacking upon cooling.

Claims (13)

Raw shape having an initial shape to obtain a bi-directional shape memory effect (SME), thereby obtaining an alloy having a final shape with austenite and martensite memory states corresponding respectively to austenite and martensite shapes A method of treating a NiTi alloy comprising:
(A) in order to obtain an evaluation of the internal structure of the alloy, by measuring the temperature difference between A _s point and A _f point, tested raw NiTi-based alloy, wherein A _s point austenite transformation, i.e., the temperature at which transformation begins between martensite form to austenite form, a _s point is the temperature at which austenite transformation is completed,
(B) A first heat treatment based on the results obtained in (a) is applied to the raw NiTi-based alloy to produce an alloy with an initial internal structure condition having an essentially uniformly random dislocation density. The first heat treatment is defined as follows:
If the temperature difference is less than 7 ° C, heat-treat the alloy to a temperature of 450-500 ° C for 0.5-1.0 hours,
If the temperature difference is greater than 7 ° C., heat-treat the alloy to a temperature of 510-550 ° C. for 1.0-2.5 hours;
(C) Simultaneous electrical stimulation during dynamic aging treatment to a temperature of 0.3 Tm when the melting temperature of the alloy is Tm with Kelvin to produce a polygonal subgrain dislocation structure decorated by precipitation Subjecting the alloy to a thermomechanical treatment (TMT) involving plastic deformation of the alloy with heating by
(D) if the deformation in step (c) did not form the final shape, subject the alloy to an intermediate heat treatment to complete one cycle of subgrain dislocation structure deformation;
(E) Repeat steps (c) and (d) until the final shape is achieved,
(F) subjecting the alloy to a final heat treatment and memory treatment to produce two memory forms consisting of an austenite form in which the alloy has an austenite form and a martensite form, the treatment comprising:
(I) forming the alloy into an austenite shape, subjecting the alloy to a polygonization treatment in the range of 450 ° C. to 550 ° C. to produce a random dislocation array, and then releasing the unaligned dislocations from precipitation and Applying solution treatment to produce their rearrangement, followed by aging treatment, and deforming the alloy to take an adjusted shape having a higher degree of deformation than the martensite shape and two memory forms Heating to produce,
(Ii) deforming the alloy into an adjusted shape having a degree of deformation higher than the martensite shape, subjecting the alloy to heat treatment in the range of 600 ° C. to 800 ° C., and then subjecting it to a polygonizing treatment and a solution treatment. Then, applying an aging treatment, forming the alloy into the austenite shape, and applying a memory heat treatment and an aging treatment to the alloy,
including,
A method comprising each step. (A) a raw NiTi alloy samples, 0.5 to 2.5 hours, to test the test the temperature difference between A _s point and A _f point is heated to a temperature of 450 to 550 ° C.,
(B) A first heat treatment based on the temperature difference between the A _f point and the A _s point obtained in the step (a) is performed on the raw NiTi alloy as follows.
Heat treating the alloy to a temperature of 450-500 ° C. for 0.5-1.0 hours if the temperature difference is less than 7 ° C .;
Heat treating the alloy to a temperature of 510-550 ° C. for 1.0-2.5 hours if the temperature difference is greater than 7 ° C .;
(C) When deformation occurs at a temperature of 250-550 ° C., the alloy is subjected to TMT including plastic deformation of the alloy at a strain rate of less than 4 sec ⁻¹ with simultaneous electrical stimulation heating of a portion of the alloy. , The deformation of this process is less than 55%,
(D) If the deformation in step (c) did not form the final shape, subject the alloy to an intermediate heat treatment at a temperature of 500-550 ° C. for 0.5-2 hours and then repeat step (c).
(E) Final heat treatment and memory treatment are performed on the alloy, and the alloy consists of an austenite form having an austenite shape and a martensite form having a martensite form in which the alloy has a higher degree of deformation than the austenite form. Giving rise to two storage forms,
(I) forming the alloy into an austenite shape, subjecting the alloy to a polygonization treatment to produce an array of random dislocations, and then releasing the dislocation dislocations from precipitation and solutionizing to cause their rearrangement. Applying a treatment followed by an aging treatment and heating the alloy to deform to take an adjusted shape having a degree of deformation higher than the martensite shape and to produce two memory forms;
(Ii) deforming the alloy into an adjusted shape having a degree of deformation higher than that of the martensite shape, subjecting the alloy to heat treatment, then subjecting it to a polygonization treatment and a solution treatment, and then subjecting the alloy to an aging treatment; Forming the austenite shape, as well as subjecting the alloy to memory heat treatment and aging treatment,
including,
The method according to claim 1, comprising each step. The method of claim 2, wherein the deformation in step (c) is less than 40%. Final heat treatment and memory treatment
(I) forming the alloy into the austenite shape;
(Ii) The alloy is subjected to a polygonization treatment at 450 to 550 ° C. for 0.5 to 1.5 hours, then subjected to a solution treatment at 600 to 800 ° C. for 2 to 50 minutes, and then 0.15 to Applying an aging treatment at 350 to 500 ° C. for 2.5 hours,
(Iii) The alloy is deformed to take an adjusted shape, the deformation being performed at a temperature T that is less than 15% and satisfies the following equation:
T <M _s + 30 ° C
Where M _s is the temperature at which martensitic transformation begins, and then heating the alloy above the temperature at which the austenite transformation of the alloy ends,
The method according to claim 1, comprising: The method of claim 4 wherein the deformation of the alloy to take the adjusted shape in step (iii) is less than 7%. Final heat treatment and memory treatment
(I) forming the alloy into the adjusted shape;
(Ii) The alloy is subjected to a heat treatment at 450 to 500 ° C. for 0.5 to 2 hours, and then subjected to a polygonization treatment and a solution treatment at 600 to 800 ° C. for 2 to 50 minutes, and then 0 to 0 Subjecting the alloy to an aging treatment at 350-500 ° C. for 2 hours,
(Iii) forming the alloy into an austenite shape;
(Iv) subjecting the alloy to a memory heat treatment at 500-600 ° C. for more than 10 minutes, followed by an aging treatment at 350-500 ° C. for 0.15-2.5 hours,
The method according to claim 1, comprising: TMT is any one method of claims 4-6 including an electric stimulation current density of 500~2000A / cm ^2. A method for preparing a medical device comprising a shape memory alloy (SMA) that embodies a bi-directional shape memory effect, wherein the SMA is processed by a method as defined in any one of claims 1-7. Including methods. The method of claim 8, wherein the medical device is a stent. A wire having a first diameter, having either a wire shape having a second diameter or a band shape, and having an austenite memory form and a martensite memory form corresponding to the austenite form and the martensite form, respectively. A method of manufacturing a medical stent exhibiting a bidirectional shape memory effect (SME) from a NiTi alloy comprising:
(A) the NiTi wire sample, 0.5 to 2.5 hours, then heated to a temperature of 450 to 550 ° C., then testing a sample for temperature difference between A _s point and A _f point, wherein A _s The point is the austenite transformation, that is, the temperature at which transformation begins between the martensite form and the austenite form, and the _Af point is the temperature at which the austenite transformation ends.
(B) The wire is subjected to a first heat treatment based on the temperature difference between the A _f point and the A _s point obtained in step (a) as follows:
Heat treating the wire to a temperature of 450-500 ° C. for 0.5-1.0 hours if the temperature difference is less than 7 ° C .;
Heat treating the wire to a temperature of 510-550 ° C. for 1.0-2.5 hours if the temperature difference is greater than 7 ° C .;
(C) A part of the wire undergoing deformation is subjected to thermomechanical treatment including warm rolling of the wire at a strain rate of less than 5 sec ⁻¹ with simultaneous heating by electrical stimulation at a current density of 500 to 2000 A / cm ^2. The deformation of this process is less than 55%,
(D) If the deformation in step (c) did not form the final cross-sectional shape, the wire was subjected to an intermediate heat treatment at a temperature of 500 to 550 ° C. for 0.5 to 2 hours, and then step (c) was performed. repeat,
(E) (i) winding the wire or band obtained in step (c) around a mandrel having a diameter that the stent should take in austenite form;
(Ii) The wire is subjected to a polygonization treatment at 450 to 550 ° C for 0.5 to 1.5 hours, followed by a solution treatment at 600 to 800 ° C for 2 to 50 minutes, and then 0.15 to Applying an aging treatment at 350 to 500 ° C. for 2.5 hours,
(Iii) The wire is deformed by wrapping it around a mandrel having an adjustable straight line, the deformation being performed at a temperature T that is less than 7% and satisfies the following equation:
T <M _s + 30 ° C
Where M _s is the temperature at which martensitic transformation begins, and then heating the wire or band above the temperature at which austenite transformation ends,
Subjecting the wire to a final heat treatment and memory treatment, including
Thereby, a stent having an austenite form with the diameter that the stent takes in (i) above and a martensite form with a diameter that is an intermediate diameter between the adjusted diameter and the austenite diameter is obtained.
A method comprising each step. From a NiTi wire having a first diameter, either a wire shape having a second diameter or a band shape, and having an austenite memory form and a martensite memory form respectively corresponding to an austenite form and a martensite form A method of manufacturing a medical stent exhibiting a bidirectional shape memory effect (SME) comprising:
(A) a sample of the NiTi wire, 0.5 to 2.5 hours, then heated to a temperature of 450 to 550 ° C., then testing the sample for temperature difference between A _s point and A _f point, wherein Where the A _s point is the temperature at which the austenite transformation, that is, the transformation starts between the martensite form and the austenite form, and the A _f point is the temperature at which the austenite transformation ends,
(B) The wire is subjected to a first heat treatment based on the temperature difference between the A _f point and the A _s point obtained in step (a) as follows:
Heat treating the wire to a temperature of 450-500 ° C. for 0.5-1.0 hours if the temperature difference is less than 7 ° C .;
Heat treating the wire to a temperature of 510-550 ° C. for 1.0-2.5 hours if the temperature difference is greater than 7 ° C .;
(C) Warm rolling of the wire at a strain rate of less than 5 sec ⁻¹ with simultaneous internal heating of the part of the wire undergoing deformation by electrical stimulation at a current density of 500 to 2000 A / cm ² on the wire. The deformation of this process is less than 55%.
(D) If the deformation in step (c) did not form the final cross-sectional shape, the wire was subjected to an intermediate heat treatment at a temperature of 500 to 550 ° C. for 0.5 to 2 hours, and then step (c) was performed. repeat,
(E) (i) winding the wire or band obtained in step (c) around a mandrel having an adjusted diameter different from the diameter that the stent should take in the austenitic state;
(Ii) The wire is subjected to heat treatment at 450 to 500 ° C. for 0.5 to 2 hours, then subjected to polygonization heat treatment and solution treatment at 600 to 800 ° C. for 2 to 50 minutes, and then 0 to 2 Applying an aging treatment at 350 to 500 ° C. for a time,
(Iii) wrapping a wire or band around a mandrel having a diameter that the stent should take in austenite form;
(Iv) The alloy is subjected to a memory heat treatment at 500-600 ° C. for more than 10 minutes, followed by an aging treatment at 350-500 ° C. for 0.15 to 2.15 hours, whereby the wire is processed A stent is obtained having an austenitic form having a diameter formed in (iii) and a martensite form having a diameter that is an intermediate diameter between the adjusted diameter and the diameter of the stent in the austenitic form.
A method comprising each step. A method for producing a root implant having a bidirectional shape memory effect having a two-way shape memory effect having an austenite memory form and a martensite memory form respectively corresponding to an austenite shape and a martensite shape, from a NiTi alloy,
(A) a NiTi rod sample, 0.5 to 2.5 hours, then heated to a temperature of 450 to 550 ° C., then testing a sample for temperature difference between A _s point and A _f point, wherein A _s The point is the temperature at which the austenite transformation, that is, the transformation between the martensite form and the austenite form begins, and the _Af point is the temperature at which the austenite transformation ends.
(B) The rod is subjected to a first heat treatment based on the temperature difference between the A _f point and the A _s point obtained in step (a) as follows:
If the temperature difference is less than 7 ° C., heat the rod to a temperature of 450-500 ° C. for 0.5-1.0 hours;
If the temperature difference is greater than 7 ° C., heat the rod to a temperature of 510-550 ° C. for 1.0-2.5 hours;
(C) subjecting the rod to a heat treatment including warm drawing with a strain rate of less than 5 sec ⁻¹ with heating by electrical stimulation , the total strain in this step being less than 55%;
(D) If the deformation in step (c) did not form the final cross-sectional shape, the rod was subjected to an intermediate heat treatment at a temperature of 500-550 ° C. for 0.5-2 hours, and then step (c) repeat,
(E) machining the rod to form the shape of the implant into segments of the implant;
(F) (i) expanding the segments of the implant to the diameter that the implant should take in the austenitic form;
(Ii) The implant segment is subjected to a polygonization treatment at 450 to 550 ° C. for 0.5 to 1.5 hours, followed by a solution treatment at 600 to 800 ° C. for 2 to 50 minutes, and then 0 Applying an aging treatment at 350 to 500 ° C. for 15 to 2.5 hours,
(Iii) transforming said implant segment to an adjusted diameter having a strain of less than 7% and at a temperature T <M _s + 30 ° C., where M _s is the temperature at which the martensitic transformation begins; Heating the segment of the implant above the temperature at which the austenite transformation ends,
Subjecting the implant segment to a final heat and memory treatment comprising:
Thereby, an implant is obtained having an austenite form with the diameter that the segments of the implant take in (i) above and a martensite form with a diameter that is an intermediate diameter between the adjusted diameter and the austenite diameter, A method comprising each step. A method of manufacturing a tube coupling exhibiting a bidirectional shape memory effect having an austenite memory form and a martensite memory form respectively corresponding to an austenite shape and a martensite shape, from a NiTi alloy,
(A) a NiTi rod sample, 0.5 to 2.5 hours, then heated to a temperature of 450 to 550 ° C., then testing a sample for temperature difference between A _s point and A _f point, wherein A _s The point is the austenite transformation, that is, the temperature at which transformation begins between the martensite form and the austenite form, and the _Af point is the temperature at which the austenite transformation ends.
(B) The rod is subjected to a first heat treatment based on the temperature difference between the A _f point and the A _s point obtained in step (a) as follows:
Heat treating the wire to a temperature of 450-500 ° C. for 0.5-1.0 hours if the temperature difference is less than 7 ° C .;
Heat treating the wire to a temperature of 510-550 ° C. for 1.0-2.5 hours if the temperature difference is greater than 7 ° C .;
(C) The rod is subjected to a thermomechanical treatment including warm drawing with a strain rate of less than 5 sec ⁻¹ with simultaneous electrical stimulation , the total strain in this step being less than 55%.
(D) If the deformation in step (c) did not form the final cross-sectional shape, the rod was subjected to an intermediate heat treatment at a temperature of 500-550 ° C. for 0.5-2 hours, and then step (c) repeat,
(E) the rod is machined into a cylinder to form a hollow cylinder coupling with an adjustable spacing diameter;
(F) (i) The cylindrical body is subjected to a polygonization treatment at 450 to 550 ° C. for 0.5 to 1.5 hours, and then subjected to a solution treatment at 600 to 800 ° C. for 2 to 50 minutes. Next, an aging treatment at 350 to 500 ° C. is performed for 0 to 2.5 hours,
(Ii) expanding the cylinder to a diameter that the coupling should take in austenite form;
(Iii) applying a storage heat treatment at 500 to 600 ° C. for more than 10 minutes, and then subjecting the cylindrical body to an aging treatment at 350 to 500 ° C. for 0.15 to 2.5 hours. The cylindrical body is subjected to the heat treatment and memory treatment of
Thereby, an austenite form with the coupling formed diameter in step (ii) and a martensite form with a diameter that is intermediate between the diameter to which the coupling is adjusted and the diameter of the coupling in the austenite form; A method comprising each step, wherein a coupling having:

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