Super-Duper Shape-Memory Alloy

A unique iron-based polycrystalline alloy can recover its shape after experiencing about twice the superelastic strain of being bent or twisted than any other polycrystalline shape-memory alloys, Japanese scientists report (Science 2010, 327, 1488). Traditional alloys that can be bent and return to their original shape include Ni-Ti and Cu-Zn-Al. In particular, Ni-Ti is a valuable material for medical applications such as stents and frames for eyeglasses. Ryosuke Kainuma and colleagues at Tohoku University developed the new alloy, with a composition of Fe-Ni-Co-Al-Ta-B. In addition to its superelastic strain of 13%—compared with 7% for Ni-Ti alloys—the material is exceptionally strong. It also has a high damping capacity and can reversibly change its magnetization when stressed and unstressed. Materials scientists Ji Ma and Ibrahim Karaman at Texas A&M University note in a perspective accompanying the report that developing shape-memory alloys for complex applications such as bridge dampers and artery stents that could signal their own actions will require clearing technical and economic hurdles. But the new alloy "is another example in which materials are no longer just a passive support," they say.