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Shape-memory alloys (SMAs),which display shape recovery upon heating, aswell as superelasticity, offermany technological advantages in various applications.Those distinctive behaviors have been observed in many polycrystalline alloy systems such as nickel titantium (TiNi)–, copper-, iron-, nickel-, cobalt-, and Ti-based alloys but not in lightweight alloys such as magnesium (Mg) and aluminum alloys. Here we present aMg SMA showing superelasticity of 4.4% at –150°C and shape recovery upon heating.The shape-memory properties are caused by reversible martensitic transformation.This Mg alloy includes lightweight scandium, and its density is about 2 grams per cubic centimeter, which is one-third less than that of practical TiNi SMAs.This finding raises the potential for development and application of lightweight SMAs across a number of industries. [ABSTRACT FROM AUTHOR]

In polycrystalline materials, grain growth occurs at elevated temperatures to reduce the total area of grain boundaries with high energy. The grain growth rate usually slows down with annealing time, making it hard to obtain grains larger than a millimeter in size. We report a crystal growth method that employs only a cyclic heat treatment to obtain a single crystal of more than several centimeters in a copper-based shape-memory alloy. This abnormal grain growth phenomenon results from the formation of a subgrain structure introduced through phase transformation. These findings provide a method of fabricating a single-crystal or large-grain structure important for shape-memory properties, magnetic properties, and creep properties, among others. [ABSTRACT FROM AUTHOR]