A metal with a memory
Unlike other shape-retaining alloys, this nickel-titanium alloy (NiTi) can’remember’ its original dimensional configuration. That’s a remarkable property that has changed the way engineers build products, from a rover on Mars that flexes around rocks to surgeons who install tiny mesh tubes that dilate blood vessels without any mechanical input.
Nitinol is one of a growing group of “smart” materials, and its many applications are diverse. They include eyeglass frames, coffee pot thermostats, electrical connectors, deicing systems, heat pipes, clamps, and sculptures.
In medicine, nitinol is used to make self-expanding stents that are placed in peripheral arteries and have good stress resistance and kink resistance. They also have biocompatibility.
Shape-retaining alloys
Nitinol was discovered in 1959 by William J. Buehler at the U.S. Naval Ordance Laboratory, and has since been used in orthopedic and cardiovascular surgery, solid-state heat engines, shrink-to-fit pipe couplers for aircraft, safety products, eyeglass frames, and toys.
A metal with a memory
Nitinol, an alloy of nickel and titanium, has a remarkable ability to retain its dimensional configuration when it is heated or cooled. That capability is what’s known as the shape-memory effect.
The temperature that triggers the transformation is controlled by a fine-tuned ratio of nickel to titanium. This makes NiTi very flexible and durable in harsh environments.
Smart,’smart’ material
The most important property to specify about nitinol is its transformation temperature (Active Af), which represents the finish of its transformation from martensite to austenite upon heating and is the temperature at which a trained shape can be recovered.