Memory Metal
In 1965, the first of a series of metal alloys of nickel and titanium was produced by the Naval Ordnance Laboratory. These alloys are called Nitinol, for Nickel Titanium Naval Ordnance Laboratory. Many of the alloys have a rather remarkable property: they remember their shape. This "smart" property is the result of the substance's ability to undergo a phase change - a kind of atomic ballet in which atoms in the solid subtly shift their positions in response to a stimulus like a change in temperature or application of mechanical stress. A simple demonstation involves bending a sample, then exposing it to a source of heat like hot air or hot water. The sample recovers its original shape as its temperature is raised above the temperature corresponding to the phase change. This temperature may be tuned by varying the ratio of nickel to titanium atoms in the solid by a few percent relative to a 1:1 ratio.
Memory Metal | Exploring the Nanoworld