Research Highlights

The quest for the next shape memory alloys (SMAs) for transformative applications in aerospace and medicine requires a departure from conventional alloys based on heavy metals such as Ni, Fe, Co, and Cu. To this end, Mg–Sc alloys, with extremely low densities and inherent biocompatibility, promise to be the ideal candidates—provided that a mechanism conducive to shape memory can be demonstrated in Mg-based alloys.

In a recent article, an AIMR team led by Yuji Sutou and Daisuke Ando addressed this problem by focusing on the effects of abnormal grain growth on the superelasticity of polycrystalline Mg–Sc alloys¹.

“Grain enlargement is a known approach to improving superelasticity in conventional Cu- and Fe-based SMAs,” says Sutou. “Here, we use cyclic heat treatment (CHT) to investigate the mechanism of the abnormal grain growth in Mg–Sc alloys—aiming to improve the alloys’ superelasticity.”

The analysis of each stage of the CHT revealed that a lower holding temperature, longer solution heat treatment time, and slower heating rates resulted in more effective grain growth, lager and more uniform grains, and sharper subgrains, respectively, improving Mg–Sc superelasticity.

“The understanding of how CHT controls Mg–Sc grain enlargement is an important step towards isolating the ultra-light biocompatible SMA,” explains Sutou. “It gave us the ability to use the composition and microstructure to control Mg–Sc properties such as high strength and larger elongation²—all relevant to the design of future SMAs and related materials.”

(Author: Patrick Han)