Shape memory alloys (SMA)

The alloys that experience a thermoelastic martensitic transformation are called Shape Memory Alloys. This martensitic transformation takes place between two different crystallographic structures and it can be produced by different stimuli (temperature, mechanical stresses, or magnetic field). Our group has focalized its study in different kinds of alloys, namely, Fe-Pd, Co-Al-Ni, or Ni-Mn-based. Recently, special attention has been paid to Ni-Mn-based alloys, concretely Ni-Mn-Sn-Co and Ni-Mn-In-Co alloys because they present higher magnetization change during the martensitic transformation and as consequence higher magnetic entropy change.

The most challenging goal of our group is to introduce these materials in practical applications. In this sense, two different types of composites formed by the combination of these materials in a powder state (micro-nanoparticles) with polymers and or with metals with a low-temperature melting point for 3D-printing. Besides the effect of the induced defects by milling or the evolution of those defects by annealing is analyzed.

Some examples of the studied SMA are shown below.

• Martensitic variants (1): during martensitic transformation, the martensitic structure grows in different orientations as it can be seen in the example shown in Fe-Pd alloy obtained by optic microscopy.
  
  
  Image: Optical microscope picture of the martensitic growth structure in Fe-Pd alloys.
   
• Ni-Mn-In-Co composite (2): composite produced by mixing Ni-Mn-In-Co particles with epoxy in a cylinder shape. On the right appears an optic microscopy analysis to obtain the particle size distribution in different places of the composite.
  
  
  Image: Left: cylindrical  Ni-Mn-In-Co based plastic composite. Right: optical microscope picture of the composite constituent particles.

Contact: José Ignacio Pérez de Landazábal Berganzo