Shape memory alloys (SMAs) with high transformation temperatures can enable simplifications and improvements in operating efficiency of many mechanical components designed to operate at tem...

High temperature shape memory alloys

In superelastic alloys, large deformation can revert to a memorized shape after removing the stress. However, the stress increases with increasing temperature, which limits the practical use over a wide temperature range. Polycrystalline Fe-Mn-Al-Ni shape memory alloys show a small temperature dependence of the superelastic stress because of a small transformation entropy change brought about by a magnetic contribution to the Gibbs energies. For one alloy composition, the superelastic stress varies by 0.53 megapascal/°C over a temperature range from -196 to 240°C.

https://science.sciencemag.org/content/sci/333/6038/68.full.pdf

Superelastic effect in polycrystalline ferrous alloys.

Iron-based shape memory alloys for civil engineering structures: An overview

Functionally graded materials for orthopedic applications – an update on design and manufacturing

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.

https://science.sciencemag.org/content/sci/341/6153/1500.full.pdf

Abnormal Grain Growth Induced by Cyclic Heat Treatment

Effect of grain size and texture on pseudoelasticity in Cu–Al–Mn-based shape memory wire

A new type of medical guide wire with functionally graded hardness from the tip to the end was developed with the use of Cu-Al-Mn–based alloys. The superelasticity (SE) of the Cu-Al-Mn–based alloys in the tip is drastically improved by controlling the grain size, whereas the end of the wire is hardened using bainitic transformation by aging at around 200–400 °C. Therefore, the tip of the guide wire shows a superelasticity and its end has high stiffness. This guide wire with functionally graded characteristics shows excellent pushability and torquability, superior to that of the Ni-Ti guide wire. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 69B: 64–69, 2004

Development of medical guide wire of Cu-Al-Mn-base superelastic alloy with functionally graded characteristics.

Ti–Mo–Sn alloys have been developed as a substitute for Ti–Ni alloys in the biomedical field. The effect of heat treatment on shape memory and superelastic properties in Ti–Mo–Sn alloys has been investigated. The shape memory effect is improved by aging at 873 K for 180–420 s in the Ti–5 mol% Mo–4 mol% Sn alloy and superelasticity is improved by aging at 873 K for 180–300 s in the Ti–5 mol% Mo–5 mol% Sn alloy. A large superelasticity with the recovery strain of 3.5% is obtained in the Ti–5 mol% Mo–5 mol% Sn alloy aged at 873 K for 300 s at room temperature. It has been understood that the improvement of superelasticity is due to an increment in the recovery strain with the reverse transformation of stress induced martensite. The superelasticity in Ti–5 mol% Mo–5 mol% Sn alloy aged at 873 K for 300 s is superior to that in the solution-treated alloy over wide temperature range.

Effect of heat treatment on shape memory effect and superelasticity in Ti–Mo–Sn alloys

The effects of Sn content and aging conditions on superelasticity in Ti-Mo-Sn alloys were investigated. Martensitic transformation temperature decreased with an increasing of Sn content. A large superelastic strain of 3.0% was obtained in a solution-treated Ti-5 mol%Mo-5 mol%Sn alloy in the tensile test. The superelasticity in the Ti-5 mol%Mo-5 mol%Sn at room temperature was improved by aging at 873 K for short periods between 180 and 420 s. A specimen aged at 873 K for 300s exhibited superelasticity with a recovery strain of 3.5% in the tensile test. A recovery strain of 3.0% was consistently achieved in cyclic tensile deformations.

https://www.jstage.jst.go.jp/article/matertrans/47/3/47_3_513/_pdf

Effects of Sn Content and Aging Conditions on Superelasticity in Biomedical Ti-Mo-Sn Alloys

An ingrowing toenail has no definitive treatment. Previously, effective methods were complicated but easy ones had less effect. We show both an easy and an effective way with Cu-Al-Mn-based shape-memory alloys (SMAs). They have a characteristic shape which patients themselves can detach easily without any pain. But they also have enough corrective force. Cu-based SMAs cost much less than Ni-Ti-based alloys. Despite not being appropriate for all cases of ingrowing toenails, it is an easy, effective and less costly alternative.

Kiyoshi Yamauchi

Papers

Effect of grain size and texture on pseudoelasticity in Cu–Al–Mn-based shape memory wire

Development of medical guide wire of Cu-Al-Mn-base superelastic alloy with functionally graded characteristics.

Effect of heat treatment on shape memory effect and superelasticity in Ti–Mo–Sn alloys

Effects of Sn Content and Aging Conditions on Superelasticity in Biomedical Ti-Mo-Sn Alloys

A simple method to treat an ingrowing toenail with a shape‐memory alloy device