Single crystal shape memory alloy devices and methods

• US 7,544,257 B2
• Filed: 05/04/2005
• Issued: 06/09/2009
• Est. Priority Date: 05/06/2004
• Status: Active Grant

• Current Assignee: Ensign-Bickford Aerospace & Defense Company (Dyno Nobel Holding ASA)
• Original Assignee: TiNi Alloy Company
• Inventors: Bokaie, Michael, Martynov, Valery, Johnson, A. David
• Primary Examiner(s): Wyszomierski; George
• Assistant Examiner(s): Shevin; Mark L
• Application Number:
  US10/588,413
• Publication Number:
  US 20070137740A1
• Time in Patent Office: 1,497 Days
• Field of Search: 117/16, 117/25, 148/402, 148/562, 148/563, 420/485, 420/486, 420/489, 420/496, 420/902
• US Class Current: 148/562
• CPC Class Codes: A61L 2400/16 Materials with shape-memory or superelastic properties
• CPC Class Codes: A61L 31/022 Metals or alloys
• CPC Class Codes: A61L 31/088 Other specific inorganic materials not covered by A61L31/084 or A61L31/086
• CPC Class Codes: A61L 31/10 Macromolecular materials
• CPC Class Codes: A61L 31/14 Materials characterised by their function or physical properties , e.g. injectable or lubricating compositions, shape-memory materials, surface modified materials
• CPC Class Codes: A61M 2025/09141 made of shape memory alloys which take a particular shape at a certain temperature
• CPC Class Codes: A61M 25/00 Catheters; Hollow probes dilators A61M29/00; peritoneal catheters A61M1/285; tracheal tubes A61M16/04; for drainage A61M27/00; for uterus, vagina or rectum A61M31/00 ; for measuring or testing A61B; materials for catheters A61L29/00
• CPC Class Codes: C22C 9/01 with aluminium as the next major constituent
• CPC Class Codes: C22F 1/006 Resulting in heat recoverable alloys with a memory effect
• CPC Class Codes: C30B 15/00 Single-crystal growth by pulling from a melt, e.g. Czochralski method under a protective fluid C30B27/00
• CPC Class Codes: C30B 29/52 Alloys
• CPC Class Codes: F16F 1/021 characterised by their composition, e.g. comprising materials providing for particular spring properties composition and manufacture of clock or watch springs G04B1/145
• CPC Class Codes: F24S 2030/11 Driving means
• CPC Class Codes: F24S 30/20 for linear movement
• CPC Class Codes: F28D 15/0241 the tubes being flexible
• CPC Class Codes: H01H 37/323 making use of shape memory materials in thermal relays H01H61/0107; release mechanism H01H71/145; treatment of SMF alloys C22F1/006; for control of temperature G05D23/024
• CPC Class Codes: Y02E 10/40 Solar thermal energy, e.g. solar towers
• CPC Class Codes: Y02E 10/47 Mountings or tracking

Abstract

Devices and methods of making devices having one or more components made of single crystal shape memory alloy capable of large recoverable distortions, defined herein as “hyperelastic” SMA. Recoverable Strains are as large as 9 percent, and in special circumstances as large as 22 percent. Hyperelastic SMAs exhibit no creep or gradual change during repeated cycling because there are no crystal boundaries. Hyperelastic properties are inherent in the single crystal as formed: no cold work or special heat treatment is necessary. Alloy components are Cu—Al—X where X may be Ni, Fe, Co, Mn. Single crystals are pulled from melt as in the Stepanov method and quenched by rapid cooling to prevent selective precipitation of individual elemental components. Conventional methods of finishing are used: milling, turning, electro-discharge machining, abrasion. Fields of application include aerospace, military, automotive, medical devices, microelectronics, and consumer products.

Claims

1. A method of fabricating an anisotropic, single crystal shape memory alloy having hyperelastic properties for use as a guidewire, the anisotropic single crystal shape memory alloy material formed being deformable at a constant force at recoverable strain of at least 9% with a very narrow loading-unloading hysteresis, a recovery which is completely repeatable and complete and a very low yield strength when martensitic, the method comprising the steps of:

lowering a seed of a copper aluminum based alloy into a molten melt of a copper aluminum based alloy, wherein the seed is aligned on the <

100>

crystallographic direction in a direction of pulling,

pulling a column of the alloy of a length greater than 42 inches from the melt by pulling at a predetermined pulling rate so that the rising column is cooled relative to the melt, to form a crystallization front above the surface of the melt, wherein the melt has a composition so that the pulled single crystal column has a transition temperature from martensite to austenite that is below 37 degrees Celsius,

applying a predetermined hydrostatic pressure on the column and heating the column to a predetermined temperature, the predetermined pulling rate, hydrostatic pressure and temperature being sufficient to crystallize the alloy in the column into a single crystal, and

rapidly quenching the single crystal.

2. A method as in claim 1 in which the predetermined temperature is at least about 1000 degrees Celsius and the quenching step is carried out by quenching from about 850 degrees Celsius.

3. A method as in claim 1 in which the compositions of the alloy are substantially 80 percent Cu, 15 percent Al and 5 percent of a metal selected from the group consisting of Ni, Co, Mn, Fe.

4. A method as in claim 1 in which the quenching step is carried out by quenching the alloy in salt water.

5. A method as in claim 1, further comprising grinding the surface of the wire to a diameter in the range of from 0.012 inches to 0.039 inches.

6. A method as in claim 1 in which the grinding step is carried out by centerless grinding of the surface.

7. A method as in claim 5 and further comprising the step of electropolishing the wire to a smoothness of less than 0.0001 inches.

8. A method as in claim 5 and further comprising the step of coating the surface of the wire with a material selected from the group consisting of gold, a biocompatible plastic, and a biocompatible polymer.

9. A method as in claim 5 and further comprising the step of coating the surface of the wire with a lubricant.

10. A method as in claim 5 and further comprising the step of etching a portion of the surface of the wire in a mixture of hydrofluoric acid and nitric acid in amounts which reduce the diameter of the wire sufficient to increase the flexibility of the portion.

11. A method as in claim 1 in which the step of pulling the column is carried out by pulling a hollow cross-sectional elongated shaped column.

12. A method as in claim 5 in which the column has an outer layer comprised of CuAlNi polycrystal, and further comprising the step of removing the polycrystal in the outer layer.

13. A method as in claim 1, further comprising re-heating the column, and rapidly quenching to retain the nickel and aluminum dissolved in the copper matrix.

14. A method as in claim 1, further comprising maintaining a constant temperature of the melt as the column is pulled.

15. The method of claim 1, further comprising pulling the column through a die at the surface of the melt so that the crystallization front is above the surface of the melt and the die.

16. The method of claim 1, further comprising altering the composition of the melt to form a region of the pulled column that has a transition temperature above 37 degrees Celsius, and thereby forming a non-elastic segment.

17. The method of claim 16, wherein the step of altering the composition is performed to form a non-elastic tip region on the formed guidewire.