Introduction To Nitinol

Nitinol is the name of one member of a class of metals known as Shape Memory Alloys. The general phenomenon was discovered in the 1930s. Shape Memory Alloys have can take two different crystal structures. They have a "hot" phase in which the material is generally stiffer and has a higher yield point, and a "cool" phase which is less stiff and has a lower yield strength. In the lower crystal phase they are generally superelastic. This means they can be deformed far more than other metals of the same general family- like 10 times more. They can be formed into a shape at higher temperature, cooled, then formed to a different shape around room temperature. When heated, they return to the shape they had at the high temperature. There are several known metal combinations that have these properties.

Nitinol was developed by the Naval Ordnance Laboratory. The name comes from its composition and the discovery team who first recognized the potential of this powerful alloy (NIckel/ TItanium / Naval Ordinance Laboratory).

Nitinol alloys typically are made of 55%-56% Nickel and 44%-45% Titanium. Small changes in composition can significantly impact the properties of the material. There are two primary categories of Nitinol. The first, known as "SuperElastic", is characterized by extraordinary kink resistance and flexibility. The second category, "Shape Memory" alloys, is valued for the Nitinol's capacity to recover a pre-set shape when heated above its transformation temperature. The first category is often used for orthodontics- braces, wires, etc- and for eyeglasses. Dynalloy makes shape memory alloys, which are primarily useful for actuators, used in many different mechanical devices.