Dissemination of IT for the Promotion of Materials Science (DoITPoMS)

DoITPoMS Teaching & Learning Packages Superelasticity and Shape Memory Alloys Applications
Superelasticity and Shape Memory Alloys AimsBefore you startIntroductionMartensitic Phase Transformations - A Simple ExampleMartensitic Phase Transformations - Basic ThermodynamicsMartensitic Phase Transformations - Hysteresis CharacteristicsSuperelasticity - Strain Accommodation by Martensite FormationSuperelasticity - Hysteresis in the Stress-Strain BehaviourShape Memory Effect - "Training" of the TransformationShape Memory Effect - The "Ferris Wheel" ExperimentMicrostructural Changes during Thermo-Mechanical TreatmentLimits of SuperelasticityApplicationsSummaryQuestionsGoing further
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Applications

The most widely used shape memory alloy is the equi-atomic Nickel Titanium alloy known commercially as Nitinol.

Superelasticity

Superelastic stents are used to hold open arteries or other vessels. They can be tightly compressed while being guided into the body then, when released, they spring back to their larger shape.

They are also used to hold together broken bones.  Conventional pins need to be tightened as bone heals, which either involves further operations or an external framework.  Superelastic devices, on the other hand, contract as the bone heals and provide guiding pressure, forcing the bones back to the correct shape.

Other uses include spectacle frames and brassiere wires. If superelastic material is bent out of shape, it quickly returns to its original shape.

Shape memory effect

Shape memory effects are used in actuators , to produce motion in response to temperature changes. A simple example is a greenhouse window, which automatically opens and closes in response to temperature changes.

Other examples include the new Boeing 787 where small chevrons on the trailing edge of the engine move with varying temperature.

On take off the engine is hotter and they move into a position which makes the engine run more quietly. However once away from the airport the engine cools in higher air and the flaps move to give better fuel economy.

Another example is in clips used to hold solar panels in place on both the Hubble Space Telescope and the International Space Station. When cold they hold the panels closed up, but when out in space when the panels heat due to the sun the clips undo and allow the panels to unravel to their full size.
These mechanical solutions are preferred to electrical systems because they are more reliable as there are fewer things to go wrong.

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