Nitinol material is commonly specified and sold for applications that demand the unique properties of superelasticity—that is, the ability of the material to experience large deformations and recover to the original shape without any permanent set. Most commercially successful medical applications of nitinol rely on superelastic properties of the material at body temperature. NDC’s designation for this material is SE508, which stands for superelastic 50.8 atomic percent nickel, and this is the most commonly sold and used nitinol composition. In some other applications, nitinol is used for its shape-memory characteristics. By adjusting the metal’s composition or how it is processed, it can be made very soft and ductile under normal operating temperatures, but it can remember its original shape when it is exposed to elevated temperatures. NDC’s designation for this material is SM495, which stands for shape-memory 49.5 atomic percent nickel.

Superelastic nitinol wire and tube are typically cold worked by a drawing process to achieve desired straightness and mechanical properties, including the ultimate strength of the material, upper plateau stress, lower plateau stress, and so on. Generally, cold working increases strength, while subsequent thermal treatments required to shape-set the material or achieve a desired transition temperature decrease strength. Generally, the increase in strength comes at a cost of fatigue durability. Consequently, when designing any nitinol component, the designer must make judgments about the relative importance of strength versus fatigue performance and select an appropriate material composition and thermal processing strategy. For applications in which strength or superelasticity are not important, a designer may choose to specify partially or fully annealed material, thus reducing strength while increasing fatigue performance. NDC can apply any custom heat treatment to our standard materials to meet customer requirements, including full or partial annealing of superelastic material.