Researchers from Tohoku University’s Graduate School of Engineering have discovered a novel iron-based superelastic alloy (SEA) capable of withstanding extreme temperatures—both high and low. A paper on the work is published in Science.
SEAs are found in a wide variety of commercial applications because of their superelasticity, allowing 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 at Tohoku University, Toshihiro Omori and his team developed an iron-based SEA system, known as Fe-Mn-Al-Cr-Ni. This cost-effective SEA can operate at a much wider temperature range.
A comparison of the stress-strain curves of the new iron-based SEA in comparison to Nickel-Titanium alloy. Credit: Tohoku University
A significant advantage of the new SEA is its controllable temperature-dependence. Increasing the amount of Chromium allowed the researchers to change the temperature dependence from a positive to a negative. Balancing the Chromium content resulted in zero temperature dependence with the critical stress remaining almost constant at various temperatures.
The discovery possesses wide-spread application for outer-space exploration given the large temperature fluctuations that occur, said Professor Omori.
Omori points to NASA’s work on a superelastic tire that can withstand excessive deformation for Moon and Mars missions. The temperature differences between night and day on the Moon and Mars are -170 ˚C to 120 ˚C and -150 ˚C to 20 ˚C respectively.
Ji Xia, Yuki Noguchi, Xiao Xu, Takumi Odaira, Yuta Kimura, Makoto Nagasako, Toshihiro Omori, Ryosuke Kainuma (2020) “Iron-based superelastic alloys with near-constant critical stress temperature dependence” Science doi: 10.1126/science.abc1590