Method of modifying the transition temperature range of TiNi base shape memory alloys

• US 4,283,233 A
• Filed: 03/07/1980
• Issued: 08/11/1981
• Est. Priority Date: 03/07/1980
• Status: Expired due to Term

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Sery, Robert S., Goldstein, David, Jones, Richard E.
• Primary Examiner(s): Dean, R.
• Application Number:
  US06/128,326
• Time in Patent Office: 522 Days
• Field of Search: 148/11.5 N, 148/11.5 F, 148/11.5 R
• US Class Current: 148/563
• CPC Class Codes: C22F 1/006 Resulting in heat recoverable alloys with a memory effect

Abstract

A method of changing the shape change transition temperature range (TTR) of an object made from a nickel-titanium based shape change memory alloy by selection of the final annealing temperature.

Claims

1. In the process of forming an article with a shape change memory from a nickel-titanium based shape change memory alloy by annealing the object at a temperature above the transition temperature range (TTR) while the object is restrained in its permanent shape and then reshaping the object into another shape at a temperature below the transition temperature range, the improvement comprising:

determining the annealing temperature which produces the desired transition temperature range for the article by performing the following steps in order;

(1) forming the alloy into the desired permanent shape of the article;

(2) restraining the article in this permanent shape;

(3) annealing the article at a temperature above the TTR;

(4) cooling the alloy down to a temperature below the TTR;

(5) removing the restraint from the article;

(6) forming the article into an intermediate shape taking care not to cause more than 7 percent deformation in the material;

7) determining the TTR by slowly heating up the article and observing the temperature range over which it recovers its permanent shape; and

(8) deciding the next steps as follows;

(a) if the TTR is lower than that desired, steps (2) through (8) are repeated using a higher annealing temperature in step (3);

(b) if the TTR is higher than that desired, steps (1) through (8) are repeated using fresh alloy and a lower annealing temperature in step (3);

but

(c) if the TTR is that desired, the annealing temperature last used in step (3) is used in the process.

2. The process of claim 1 wherein the nickel-titanium base shape change memory alloy comprises from 43 to 47 weight percent of titanium, from more than zero to 6 weight percent of cobalt, the remainder of the alloy being nickel.

3. The process of claim 1 wherein the nickel-titanium shape change memory alloy comprises from 47 to 53 weight percent of titanium, the remainder of the alloy being nickel.

4. The process of claim 1 wherein the titanium-nickel based shape change memory alloy comprises a mixture of 23 to 55 wt. % nickel, from 40 to 46.5 wt. % titanium and 0.5 to 30 wt. % copper with the balance being from 0.01 to 5 wt % of at least one element selected from the group consisting of aluminum, zirconium, cobalt, chromium and iron.