What is the name of the metal that remembers a shape after being removed from that shape?

Question

There is this metal that you put under warm/cold water, and then remove it, bend it into a different shape, then put it in the opposite temp water, then put it back and it will go to its original shape?

Answer 1

Austenite is the phase of NiTi stable at high temperature, while martensite is more stable at room temperature. Although austenite is the less dense phase, it is more rigid than martensite. At room temperature, the metal is in the martensite phase. When pressure is applied, the metal atoms easily slide by one another, and the shape changes. Heating the metal to about 50oC changes it to the rigid austenite phase. The dislocations between the crystalline grains of the metal (see topic "Simulation of Dislocations in Metals") will return to their original positions, and the metal will "remember" its original shape. Upon cooling, the metal returns to the martensite phase, but will retain its shape until pressure is applied.

Answer 2

It is called nitinol (from its composition as being an alloy of Nickel and Titanium, and from where it was first developped, the Naval Ordnance Laboratory), although alternate composition were later found (copper-zinc-aluminium, copper-aluminium-nickel). The proportion of the various metals determines the temperature that allows the shape to be set and that at which it will revert to the previously set shape.

Answer 3

Memory metal!

http://jchemed.chem.wisc.edu/JCESoft/CCA/CCA2/MAIN/MEMORYM/CD2R1.HTM

It is a nickel-titanium alloy.