Most common metals and many ceramics are known as “polycrystals,” materials consisting of a collection of randomly oriented crystals. When such materials are exposed to a magnetic field, each individual grain moves in a different direction, cancelling out the overall deformation, so that the alloy ends up not moving at all. A single crystal of the new Ni-Mn-Ga alloy deforms at a rate of approximately 10% when exposed to the force of a magnetic field. The alloy retains its new shape but returns to its original formation if the magnetic field is rotated by 90 degrees. This is what scientists refer to as “magnetic shape memory”.
While the single crystals morph 10%, the foam as a whole moved by only 0.12%. ”It was very exciting because we went from zero to an actual value, albeit small, but comparable to the best competitor,” said Professor David Dunand from Northwestern University. Prof. Dunand hopes to be able to optimize the Ni-Mn-Ga foam through casting it differently or perhaps by heat-treating it differently.
The scientists hope this foam will be used in devices that require small, rapid movement, like very small motors that do not have room for normal components such as rotors, stators, gears and shafts. Another possible application for the foam is in biomedicine. The material may even be used to control slight changes in the shape of airplane wings in order to make them more aerodynamic, based on the speed of the aircraft.
Earlier this year, TFOT covered Penetron’s waterproof concrete, a surface-applied crystalline material composed of Portland cement, specially treated quartz sand, and a compound of active chemicals. TFOT also covered an easy to produce material that has the rare ability to bend light in the opposite direction from all naturally occurring materials.
More on the Ni-Mn-Ga foam can be found here.