Math 2.0

Mechanics of deformable solids Definition

Shape-memory alloy

Builds on Martensitic transformation

Definition

A shape-memory alloy is a metal alloy with these properties.

  1. It has a high-temperature crystal phase, called austenite, and a low-temperature crystal phase of lower symmetry, called martensite.
  2. The two phases are related by a reversible martensitic transformation, a diffusionless change of the crystal lattice.
  3. A specimen deformed in the martensite phase recovers its original shape when it is heated into the austenite phase.

Property 3 is called the shape-memory effect.

Remarks

Example: nickel–titanium (nitinol) satisfies the definition. Its martensite can be deformed by rearranging its variants, and heating above the austenite finish temperature restores the original shape.

Non-example: ordinary steel can form martensite by quenching, but a deformed piece of steel does not recover its shape on heating, so clause 3 fails.

The temperatures MsM_s, MfM_f, AsA_s, AfA_f denote the start and finish of the martensite and austenite transformations. The transformation shows hysteresis: in general AsA_s and MsM_s differ.

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Further reading

  1. Web https://en.wikipedia.org/wiki/Shape-memory_alloy
About this page
TagNPV5VAXC0V
URIm2://NPV5VAXC0V
Kinddefinition
WritingW0 stub
MSC74N10, 74N30, 74N05
DefinesShape-memory alloy
UsesMartensitic transformation
Changed3 November 2026

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