Nitinol, the most common shape memory alloy (SMA), was first discovered by researchers at the U.S. Naval Ordnance Laboratory in 1963 while looking for noncorrosive marine alloys. SMAs undergo changes in shape and hardness which elicit great force when heated or cooled. Today, applications of nitinol have taken advantage of the shape changing characteristics of this alloy in imaginative new products.Made from nearly equal amounts of nickel and titanium, nitinol has a uniform crystal structure that radically changes at a distinct temperature. When the alloy is below its transition temperature, it can be stretched and deformed without permanent damage. If it is heated above its transition temperature, the alloy returns to its original shape, completely recovering from the deformation. This shape memory effect is illustrated by the deform/reform cycle shown in Figure 1.
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