These unique metals made from combinations of two or more elements, exhibit hardness and elasticity properties that change radically at distinct temperatures. First observed in 1932 in a Gold-Cadmium alloy (expensive and toxic), interest and research greatly expanded upon the discovery of a Nickel-Titanium (lower cost and non-toxic) alloy in the 1960's.
After alloying and basic processing, Muscle Wires® can be formed into a shape (for example, a coil spring), and then set to that shape by a high heat treatment. When cooled, they may be bent, stretched or deformed (within limits) and then with subsequent moderate heating (well below the heat setting temperature), they can recover some or all of the deformation - the move when heated!
Muscle Wires® have found use in everything from space missions (Clementine, Pathfinder and many more) to floral arrangement (animated butterflies, dragonflies and fairies), from arterial stents for restoring blood flow to clogged arteries, to actuators for miniature robots. And cell phone antennas, orthodontic braces and even eyeglasses use Muscle Wires® wires for their extreme flexibility.
Q: So what is the difference between these shape memory alloy terms: Nitinol, Muscle Wires®, and Flexinol®?
A: Excellent question! All these terms refer to a class of metal alloys having physical properties that change greatly at distinct temperatures (shape memory alloys), but the details of their performance, ease of use and what you can do with them varies widely.
Nitinol in the shape memory alloy world is a generic term, similar to saying “plastic”, because there are so many different types. This is often used to broadly reference the alloys.
Flexinol® is a specific type of NiTi alloy, commonly referred to as actuator wire. Flexinol® is made using different methods than other shape memory alloys. The result is a product with more repeatable actuator wire properties. In short if Flexinol® is used within the acceptable parameters, you will see a very stable product having nearly the same parameters in both austenite (hot) and martensite (cold) phases over many cycles.
Muscle Wire® is a more generic term and while it may include Flexinol® actuator wire, it also includes items like springs and other shape set forms. After alloying and processing these alloys can be formed into a shape (for example, a coil spring), and then set to that shape by a high heat treatment. When cooled, they may be bent, stretched or deformed (within limits) and then with subsequent moderate heating (well below the heat setting temperature), they can recover some or all of the deformation - then move when heated!