Memory Metal - Demonstration

When memory metal is bent, it deforms. When placed into hot water, the metal "remembers" its original shape.

When a piece of metal wire spelling the letters ICE is pulled apart, it deforms. When the wire is placed in hot water, it "remembers" its original shape, once again forming the letters ICE. (The memory metal used in this demonstration was provided by the Institute for Chemical Education.) A simulation of the processes at the atomic level is shown.


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 50°C 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.

To provide it with a new memory, the metal must be held in a new shape and heated to about 500°C (where there is enough energy to allow the defects to relax into new positions) and then slowly cooled. This is an annealing process, similar to the one demonstrated in the topic "Heat Treatment of a Metal Bobby Pin".

  • Design
    • Institute for Chemical Education University of Wisconsin - Madison, Madison, WI 53706
  • Demonstration
    • Kelly Houston Jetzer University of Wisconsin - Madison, Madison, WI 53706
  • Text
    • Kelly Houston Jetzer University of Wisconsin - Madison, Madison, WI 53706
    • Nancy S. Gettys University of Wisconsin - Madison, Madison, WI 53706
    • David Phillips Wabash College, Crawfordsville, IN 47933
  • Video
    • Jerrold J. Jacobsen University of Wisconsin - Madison, Madison, WI 53706