Nitinol shape metal memory

A very special class of materials can “remember” their shape. After deformation you can just heat them and they return to their original form. A number of different shape memory materials have been developed, but one in particular has become a standby in many applications.Nitinol’s unique properties of shape memory and superelasticity result from a phase transformation within its crystal structure that happens with temperature change. At lower temperatures the structure is martensite, a weaker form, and at higher temperatures, austenite, which is stronger. In addition, martensite can also occur at higher temperatures where the material is stressed. The mechanical properties of Nitinol actually change with stress, and with relatively small changes in temperature.

Shape memory
To demonstrate shape memory behavior you can deform a Nitinol item at a low temperature, really bending it out of shape. Then heat it and watch it return to its original shape, as if by magic. Nitinol in its martensitic (low temperature) state is easily bent or twisted into a new shape. Then, as it is heated it passes through a narrow range of temperatures where it changes to an austenitic structure and reverts to its previous shape.