Nitinol is the trade name for a nearly equiatomic binary mixture of nickel and titanium. It is a relatively new formulated metal that has two unique properties, shape memory and superelasticity.
Unlike most alloys, Nitinol can be programmed with a temperature range to create a desired shape without losing the material’s structural integrity. This makes it ideal for hermetically sealing pipe couplers, thermally actuated valves, linear actuators and other applications that require a combination of form and function.
The nitinol formula is based on its atomic crystal lattice of nickel and titanium in a body-centered cubic (austenite) structure at high temperatures and a face-centered cubic structure at low temperatures. When cooled below the austenite transformation temperature (Ms), the material spontaneously transforms to a face-centered cubic (martensite) structure, which allows it to be deformed without breaking its atomic bond. This phenomenon is called twinning and is responsible for the shape memory and superelastic effect observed in this material.
These properties are important for making a material highly resistant to fatigue and kink, as well as extremely flexible at very low temperatures. These characteristics are critical for medical devices, such as catheter tubes, guidewires, stone retrieval baskets, filters and other surgical instruments.
It is also the material of choice for self-expanding stents used to hold open circulatory vessels in arteries. These devices rely on the springy, corrosion-resistance and excellent mechanical damping properties of Nitinol to ensure that they maintain their integrity while being subjected to extraordinary strains.