Nitinol - Shaped Memory Alloy

Nitinol - Shaped Memory Alloy

Nitinol is an alloy of nickel and titanium that belongs to a class of materials call shaped memory alloys (SMA). SMA's have interesting mechanical properties. Nitinol for example contracts when heated, which is the opposite of what standard metals do when heated (expand). Not only does the alloy contract, but also it produces a 100 times greater thermal movement (expansion, contraction) than standard metals.

Another interesting property of SMA's is the shaped memory effect (SME). The alloy can be heat treated to remember a particular shape. Afterwards, if the shape is bent and distorted the alloy may be heated to regain its original shape. The SME property is used in a few toys like the Livewire (see figure 1.)

The Livewire is a fun little toy. According to the directions, you place it in cold water, bend the wire into any shape you want, then place it in hot water and the wire pops back into shape.

The Livewire toy is made of nitinol wire with a low transition temperature (the temperature of hot water). When placed in hot water the wire will unfold and unbend itself (if bent out of shape), reverting back to its original shape.