Superelastic alloy
Researchers from Tohoku University’s Graduate School of Engineering (Sendai, Japan; www.eng.tohoka.ac.jp) have discovered a novel iron-based superelastic alloy (SEA) capable of withstanding extreme temperatures — both high and low. SEAs are found in a wide variety of commercial applications because of their superelasticity, which allows them to regain their original shape. Superelasticity occurs when the metal undergoes deformation at the point known as critical stress.
Generally, SEAs have a positive temperature dependence; the critical stress increases as the temperature rises. Conventional metal-based SEAs, such as Ti-Ni, cannot be used at temperatures lower than –20°C or higher than 80°C and are costly to make. This limits their application to the form of thin wires or tubes.
Associate professor Toshihiro Omori and his team developed an iron-based SEA system, known as Fe-Mn-Al-Cr-Ni. This cost-effective SEA can also operate at a much wider temperature range of –273 to over 120°C. Another significant advantage of the new SEA is its controllable temperature dependence. Increasing the amount of chromium enables the researchers to change the temperature dependence from a positive to a negative. Balancing the Cr content resulted in zero temperature dependence with the critical stress remaining almost constant at various temperatures.
“The discovery possesses widespread application for outer-space exploration given the large temperature fluctuations that occur,” says Omori. Also, “it can potentially be used in tension braces in buildings or column elements in bridges — providing greater resistance to earthquakes,” adds Omori.