July 01, 2011

Superelastic Effect in Polycrystalline Ferrous Alloys

Journal Science - Superelastic Effect in Polycrystalline Ferrous Alloys

In superelastic alloys, large deformation can revert to a memorized shape after removing the stress. However, the stress increases with increasing temperature, which limits the practical use over a wide temperature range. Polycrystalline Fe-Mn-Al-Ni shape memory alloys show a small temperature dependence of the superelastic stress because of a small transformation entropy change brought about by a magnetic contribution to the Gibbs energies. For one alloy composition, the superelastic stress varies by 0.53 megapascal/°C over a temperature range from –196 to 240°C.

Prior to this discovery, alloys were only able to revert to their original form in the much narrower range of -20 to 80 degrees Celsius.

Superelastic alloys are used in many applications such as eyeglasses, antennas, and medical tools and equipment. 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.

The research team added a small amount of nickel to an iron based alloy.

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