Nickel-titanium-rare earth alloy and method of processing the alloy

1. A method of processing a nickel-titanium-rare earth alloy, the method comprising:

providing a nickel-titanium-rare earth alloy comprising nickel at a concentration of from about 40 at.% to about 60 at.%, titanium at a concentration of 34 at.% to about 60 at.%, at least one rare earth element at a concentration of from about 1.5 at.% to about 12 at.%, and boron at a concentration of up to about 0.1 at.%;

heating the nickel-titanium-rare earth alloy in a homogenization temperature range below a critical temperature; and

forming spheroids of a rare earth-rich second phase in the nickel-titanium-rare earth alloy while in the homogenization temperature range,

wherein the critical temperature is an incipient melting temperature of the rare earth-rich second phase.

2. The method of claim 1 , wherein the rare earth element comprises Er and the critical temperature is about 925° C.

3. The method of claim 2 , wherein the homogenization temperature range is from about 750° C. to about 875° C.

4. The method of claim 1 , wherein forming the spheroids includes keeping the nickel-titanium-rare earth alloy in the homogenization temperature range over a time duration of from about 24 h to about 72 h.

5. The method of claim 1 , further comprising thermal cycling the nickel-titanium-rare earth alloy.

6. The method of claim 1 , further comprising hot working the alloy.

7. The method of claim 6 , wherein the hot working comprises applying pressure to the alloy at an elevated temperature below the critical temperature after the heating.

8. The method of claim 7 , wherein the elevated temperature is within the homogenization temperature range.

9. The method of claim 6 , further comprising, after hot working, cold working the alloy.

10. The method of claim 9 , wherein the alloy is cold worked to achieve at least a 30% reduction in dimension without cracking.

11. The method of claim 1 , wherein the 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.

12. The method of claim 11 , wherein the alloy comprises 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.%.; the balance being titanium, wherein the alloy has a radiopacity greater than that of a binary nickel-titanium alloy.

13. A method of processing a nickel-titanium-rare earth alloy, the method comprising:

providing a nickel-titanium-rare earth alloy comprising nickel at a concentration of from about 34 at.% to about 60 at.%, titanium at a concentration of 34 at.% to about 60 at.%, and at least one rare earth element at a concentration of from about 0.1 at.% to about 15 at.%;

heating the nickel-titanium-rare earth alloy in a homogenization temperature range below a critical temperature;

forming spheroids of a rare earth-rich second phase in the nickel-titanium-rare earth alloy while in the homogenization temperature range; and

thermal cycling the nickel-titanium-rare earth alloy,

wherein the critical temperature is an incipient melting temperature of the rare earth-rich second phase.

14. A method of processing a nickel-titanium-rare earth alloy, the method comprising:

providing a nickel-titanium-rare earth alloy comprising nickel at a concentration of from about 34 at.% to about 60 at.%, titanium at a concentration of 34 at.% to about 60 at.%, and erbium at a concentration of from about 0.1 at.% to about 15 at.%;

heating the nickel-titanium-rare earth alloy in a homogenization temperature range below a critical temperature of about 925° C.; and

forming spheroids of an erbium-rich second phase in the nickel-titanium-rare earth alloy while in the homogenization temperature range.