Nickel-titanium-rare earth alloy and method of processing the alloy
A nickel-titanium-rare earth (Ni—Ti-RE) alloy comprises nickel at a concentration of from about 35 at. % to about 65 at. %, a rare earth element at a concentration of from about 1.5 at. % to about 15 at. %, boron at a concentration of up to about 0.1 at. %, with the balance of the alloy being titanium. In addition to enhanced radiopacity compared to binary Ni—Ti alloys and improved workability, the Ni—Ti-RE alloy preferably exhibits superelastic behavior. A method of processing a Ni—Ti-RE alloy includes providing a nickel-titanium-rare earth alloy comprising nickel at a concentration of from about 35 at. % to about 65 at. %, a rare earth element at a concentration of from about 1.5 at. % to about 15 at. %, the balance being titanium; heating the alloy in a homogenization temperature range below a critical temperature; and forming spheroids of a rare earth-rich second phase in the alloy while in the homogenization temperature range.
1. A nickel-titanium-rare earth alloy comprising:
nickel at a concentration of from about 34 at. % to about 65 at. %;
at least one rare earth element at a concentration of from about 0.1 at. % to about 15 at. %;
boron at a concentration from about 0.001 at. % to about 0.1 at. %; and
titanium at a concentration of from about 34 at. % to about 60 at. %.
2. The alloy of claim 1 , wherein the at least one rare earth element is selected from the group consisting of: La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
3. The alloy of claim 2 , wherein the rare earth element is Er.
4. The alloy of claim 1 , wherein the concentration of the at least one rare earth element is from about 1.5 at. % to about 12 at. %.
5. The alloy of claim 1 , wherein the concentration of boron is from about 0.005 at. % to about 0.1 at. %.
6. The alloy of claim 1 , wherein the concentration of nickel is from about 45 at. % to about 55 at. %.
7. The alloy of claim 1 being superelastic at body temperature.
8. The alloy of claim 1 having an A f temperature of about 35° C. or less.
9. The alloy of claim 1 , further comprising iron at a concentration of up to about 3 at.%.
10. The alloy of claim 9 , wherein the iron is present at concentration of up to about 1 at.%.
11. The alloy of claim 10 , wherein the iron is present at a concentration of from about 0.1 at.% to about 1 at.%.
12. The alloy of claim 1 , comprising:
nickel at a concentration of from about 45 at. % to about 55 at. %;
erbium at a concentration of from about 4.5 at. % to about 6 at. %;
boron at a concentration of from about 0.005 at. % to about 0.1 at. %.;
titanium at a concentration of from about 34 at. % to about 60 at. %
wherein the alloy has a radiopacity greater than that of a binary nickel-titanium alloy.
13. The alloy of claim 12 , further comprising iron at a concentration of up to about 3 at.%.
14. The alloy of claim 13 , wherein the iron is present at concentration of up to about 1 at.%.
15. The alloy of claim 14 , wherein the iron is present at a concentration of from about 0.1 at.% to about 1 at.%.