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 Müllner 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."
"The base alloy material was previously known, but it wasn't very effective for shape-memory applications," Dunand said. "The porous nature of the material amplifies the shape-change effect, making it a good candidate for tiny motion control devices or biomedical pumps without moving parts."
NSF Program Director Harsh Deep Chopra agrees. "It's the first foam to exhibit magnetic shape memory - it has great potential for uses that require a large strain and light weight such as space applications and automobiles. These materials are able to do more with less material given their foamy structure and provide a sustainable approach to materials development."
The work was funded by NSF through grant DMR-0502551 to expand basic knowledge about the microstructural properties of shape memory alloys influenced by magnetic fields and through grant DMR-0505772 to develop new shape-memory foams.