Introduction to  Shape Memory Alloys Seminar Topic:

They are the metals alloys that do not lose their shape. Means their shape cannot be changed. They have martensitic phase transformation. They have two unique properties: shape memory effect and pseudo-elasticity.

Martensitic transformation means deformation of lattice of crystals. Means their shape is not changed only their lattice transformation have taken place.

  • Shape memory effect: that transformation that begins in the absence of stress at a certain temperature M0s. These transformations will be continued until the temperature of the stress reaches to M0f. the reverse transformation will take place at A0s and finally at this temperature A0f material will be fully austenite.
  • Pseudo-elasticity: this transformation takes place without the change of temperature. This process takes place upon loading and un-loading. It is just like the rubber effect.

Stress in an important factor in transformation. Because on applying stress temperature rises that may expand the metal.

Alloy composition controls the transformation from martensitic to Austenite form, as it controls the temperature.

SMA: first of all wire taken either hot or cold when they are martensitic form. Then this wire is loaded to heat till it reaches the temperature Af. Then this wire is allowed to cool to reach the state of martensitic. This results in the formation of two stable shapes of solid.

shape memory alloys applications

They are used in daily life applications. They are widely used in bone treatment as plates. They are also used in dental and orthodontic application for band support during wiring process in teeth’s.  They are used as stent. They are bio compatible and have very large field of applications. It has very nice and reliable mechanical property. But it is costly too and one major problem is that it has poor fatigue property.

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