Ni-free beta Ti alloys with shape memory and super-elastic properties
A group of substantially nickel-free beta-titanium alloys have shape memory and super-elastic properties suitable for, e.g., medical device applications. In particular, the present disclosure provides a titanium-based group of alloys including 16-20 at. % of hafnium, zirconium or a mixture thereof, 8-17 at. % niobium, and 0.25-6 at. % tin. This alloy group exhibits recoverable strains of at least 3.5% after axial, bending or torsional deformation. In some instances, the alloys have a capability to recover of more than 5% deformation strain. Niobium and tin are provided in the alloy to control beta phase stability, which enhances the ability of the materials to exhibit shape memory or super-elastic properties at a desired application temperature (e.g., body temperature). Hafnium and/or zirconium may be interchangeably added to increase the radiopacity of the material, and also contribute to the superelasticity of the material.
1. A substantially nickel-free beta-titanium alloy, comprising:
between 16 at. % and 20 at. % hafnium, zirconium, or a combination thereof, wherein the alloy includes a minimum of 1 at. % hafnium;
between 8 at. % and 17 at. % niobium;
between 0.25 at. % and 6 at. % tin; and
balance titanium and impurities,
wherein the alloy exhibits superelastic behavior with an isothermally recoverable strain of at least 3.5%, and
wherein the alloy is formed into a shape set component.
2. The alloy of claim 1 , wherein the alloy exhibits superelastic behavior with an isothermally recoverable strain of at least 5%.
3. The alloy of claim 1 , wherein the alloy includes zirconium, with a ratio of hafnium to zirconium between 3:1 and 1:17.
4. The alloy of claim 1 , wherein the alloy includes between 16 at. % and 20 at. % hafnium and substantially no zirconium.
5. The alloy of claim 1 , wherein the alloy exhibits the superelastic behavior at body temperature.
6. The alloy of claim 1 , wherein the alloy is biocompatible.
7. The alloy of claim 1 , wherein the shape set component is a drawn component.
8. The alloy of claim 7 , wherein the drawn component is one of a wire, a tube and a rod.
9. The alloy of claim 7 , wherein the drawn component is a wire having a cross-sectional area between 0.13×10 −6 and 63.6×10 −6 square inches and a ratio of hafnium to zirconium between 3:1 and 10:1.
10. The alloy of claim 7 , wherein the drawn component is a wire having a cross-sectional area between 63.6×10 −6 and 176.7×10 −6 square inches and a ratio of hafnium to zirconium between 3:1 and 1:5.
11. The alloy of claim 7 , wherein the drawn component is a wire having a cross-sectional area between 176.7×10 −6 and 706.9×10 −6 square inches and a ratio of hafnium to zirconium between 1:5 and 1:8.
12. The alloy of claim 7 , wherein the drawn component is a rod having a cross-sectional area between 5.0×10 −3 and 31.4×10 −3 square inches and a ratio of hafnium to zirconium between 1:8 and 1:17.
13. The alloy of claim 7 , wherein the drawn component is a composite wire comprising a shell having a central cavity and a core received within the shell.
14. The alloy of claim 1 , wherein the alloy has retained cold work between 75% and 99%.
15. The alloy of claim 1 , wherein the alloy comprises between 2.0 and 5.0 at. % tin.
16. The alloy of claim 1 , wherein the alloy comprises less than 500 parts per million of nickel.
17. The alloy of claim 1 , wherein the alloy comprises less than 0.01 wt. % nickel.
18. The alloy of claim 1 , wherein the alloy exhibits fatigue strength such that the alloy survives 0.5% alternating strain for 10 6 cycles.
19. The alloy of claim 1 , wherein the alloy exhibits an ultimate tensile strength which reaches 120 ksi.
20. A substantially nickel-free beta-titanium material, comprising:
between 16 at. % and 20 at. % hafnium, zirconium, or a combination thereof, wherein the alloy includes a minimum of 1% hafnium;
between 8 at. % and 17 at. % niobium;
between 0.25 at. % and 6 at. % tin; and
balance titanium and impurities,
wherein the material exhibits superelastic behavior with a isothermally recoverable strain of at least 3.5%, and
wherein the material is a drawn construct.
21. The material of claim 20 , wherein the material exhibits superelastic behavior with an isothermally recoverable strain of at least 5%.
22. The material of claim 20 , wherein the material includes zirconium, with a ratio of hafnium to zirconium between 3:1 and 1:17.
23. The material of claim 20 , wherein the material includes between 16 at. % and 20 at. % hafnium and substantially no zirconium.
24. The material of claim 20 , wherein the drawn construct is one of a wire, a tube and a rod.
25. The material of claim 20 , wherein the drawn construct has retained cold work between 75% and 99%.
26. The material of claim 20 , wherein the material comprises between 2.0 and 5.0 at. % tin.
27. The material of claim 20 , wherein the material comprises less than 500 parts per million of nickel.
28. The material of claim 20 , wherein the drawn construct comprises less than 0.01 wt. % nickel.
29. The material of claim 20 , wherein the drawn construct exhibits fatigue strength such that the material survives 0.5% alternating strain for 10 6 cycles.
30. The material of claim 20 , wherein the drawn construct exhibits an ultimate tensile strength which reaches 120 ksi.
31. The material of claim 20 , wherein the alloy exhibits the superelastic behavior at body temperature.
32. The material of claim 20 , wherein the alloy is biocompatible.