Observation of Surface Relief due to
Martensitic Transformation in a Shape Memory Alloy

The sample here is a Ni-24Mn-24Ga at.% alloy. This is a shape memory alloy but in addition, the martensite if ferromagnetic. This means that the martensitic transformation can be induced by an applied magnetic field; alternatively, the twins in the martensite can undergo rearrangment or detwinning under the influence of a magnetic field. This magnetically-induced changes lead to a change in shape which can be exploited in devices.

In the experiment illustrated below, the surface of the sample is deformed by the formation of thermally-induced martensite, and the change in shape is then reversed by raising the temperature.

The observations are made using an optical microscope with polarized light and Nomarski prisms. The different colours correspond to different inclinations of the surface. The sample was put on a Peltier element and the temperature was changed between room temperature and about 273 K. The sample surface was covered with a droplet of Methanol/Glycerin mixture to prevent icing.

Ni-24Mn-24Ga shape memory martensite.	Ni-24Mn-24Ga shape memory martensite.	Ni-24Mn-24Ga shape memory martensite.
Ni-24Mn-24Ga shape memory martensite.	Ni-24Mn-24Ga shape memory martensite.	Ni-24Mn-24Ga shape memory martensite.
Ni-24Mn-24Ga shape memory martensite.	Ni-24Mn-24Ga shape memory martensite.	Ni-24Mn-24Ga shape memory martensite.

Movie

• Quicktime movie showing the changes in surface relief (75 Mb).

References

• K. Tsuchiya, A. Tsutsumi, H. Ohtsuka and M. Umemoto, Materials Science and Engineering A, 378 (2004) 370-376.

More information available on Materials Function Control Laboratory, Toyohashi University of Technology.

Acknowledgment

The movie has been provided for teaching purposes by Professor Koichi Tsuchiya of the Toyohashi University of Technology, Japan.

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