In the world of commercial materials, lighter and cheaper is usually better, especially when those attributes are coupled with superior strength and special properties, such as a material's ability to remember its original shape after it's been deformed by a physical or magnetic force.
A new class of materials known as "magnetic shape-memory foams" has been developed by two research teams headed by Peter Mllner at Boise State University and David Dunand at Northwestern University, both funded by the National Science Foundation (NSF).
The foam consists of a nickel-manganese-gallium alloy whose structure resembles a piece of Swiss cheese with small voids of space between thin, curvy "struts" of material. The struts have a bamboo-like grain structure that can lengthen, or strain, up to 10 percent when a magnetic field is applied. Strain is the degree to which a material deforms under load. In this instance, the force came from a magnetic field rather a physical load. Force from magnetic fields can be exerted over long range, making them advantageous for many applications. The alloy material retains its new shape when the field is turned off, but the magnetically sensitive atomic structure returns to its original structure if the field is rotated 90 degrees--a phenomenon called "magnetic shape-memory."
Making large single crystals of the alloy material is too slow and expensive to be commercially viable -- one of the reasons why gems are so costly -- so the researchers make polycrystalline alloys, which contain many small crystals or grains. Traditional polycrystalline materials are not porous and exhibit near zero strains due to mechanical constraints at the boundaries between each grain. In contrast, a single crystal exhibits a large strain as there are no internal boundaries. By introducing voids into the polycrystalline alloy, the researchers have made a porous material that has less internal mechanical constraint and exhibits a reasonably large d
|Contact: Diane Banegas|
National Science Foundation