Iron-based alloy could allow better quake proofing
Polycrystalline Fe-Mn-Al-Ni is a superelastic alloy: a material with shape memory that can revert to its original form after a large deformation. Unlike other materials of its type, however, it can be used across a wide range of temperatures. Superelastic alloys are used in many applications such as eyeglasses, antennas, and medical tools and equipment. Lead scientist, Toshihiro Omori, says he hopes that this new alloy—because of its ability to revert in virtually any real world temperature conditions—can be used in buildings to protect against earthquake damage, or in other applications where things get hot under stress, such as in cars, airplanes and spacecraft.
Until now, Ti-Ni was used for this purpose but, because its raw materials are expensive—as is forming and machining it—its implementation has been limited to a few historic buildings. The Fe-Mn-Al-Ni alloy is composed of common metals, has high workability, low temperature dependence, and so could be used more widely in seismic dampers and isolators. For medical uses, nickel-titanium was used extensively, including to build the tiny tubes through which stents are positioned in clogged blood vessels to the heart, neck, legs etc. However its use had been restricted to larger veins because the material is not strong enough to be suitable for the tiny vessels such as those in the brain. The new alloy’s strength, coupled with it’s elasticity, should therefore make these new applications possible.
Who, Where, and When?
The new development has come from a team of researchers in the Department of Materials Science at Tohoku University, which is located in the earthquake/tsunami ravaged city of Sendai in the north of Japan. The lab where the work was done specializes, among other things, in smart materials. Their recent innovation has been described in two recent papers (see Literature?) in Science magazine, the lead and corresponding author of the most recent being Toshihiro Omori. The work was supported by the Grants-in-Aid for Scientific Research from Japan Society for the Promotion of Science and by the Global Center of Excellence Program “Materials Integration (International Center of Education and Research), Tohoku University,” Ministry of Education, Culture, Sports, Science, and Technology. A patent application has been filed on the materials, including the alloy described here.
The reason that superelastic allows are able to revert to their prior shape is due to their unique crystal structure that allows all of the atoms it’s made of to shift as one when a force is applied, as opposed to normal metals where the force is diffused through the crystal structure changing it’s composition.1 The Fe-Mn-Al-Ni has reduced temperature dependence in its superelastic stress because of a small transformation entropy change brought about by a magnetic contribution to the Gibbs energies.
No obvious road blocks for the technology so far.
- Japanese material scientists develop new superelastic alloy, 23 March 2010.
- Y. Tanaka, Y. Himuro, R. Kainuma, Y. Sutou, T. Omori, K. Ishida, Ferrous polycrystalline shape-memory alloy showing huge superelasticity, Science, pp. 1488–1490, 2010.
- Experts design elastic iron for surgeries, 18 March 2010.
- Y. Tanaka, Y. Himuro, R. Kainuma, Y. Sutou, T. Omori, and K. Ishida, Superelastic effect in polycrystalline ferrous alloys, Science, pp. 68–71, 2011.