Hirobumi Tobe

Assistant Professor,Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency*Profile is at the time of the award.

2020Inamori Research GrantsScience & Engineering

Research topics
Development of new Pd-Ti-Zr alloys with high temperature shape memory properties
Shape-memory alloys are used in a wide range of fields as compact, lightweight, high-power drives that do not require motors, because they themselves change their shape in response to heat and force. On the other hand, the driving temperature of currently available alloys is below 100°C, and new shape-memory alloys that can drive at temperatures above 100°C are required for home appliances, automobiles, aircraft, space probes, nuclear reactors, etc. The aim of this study is to improve the properties of a new shape-memory alloy, Pd (palladium)-Ti (titanium)-Zr (zirconium), for practical use.


I would like to express my sincere gratitude for the Inamori Foundation Research Grant. With your support, I would like to continue my research and contribute to making the world a better place.

Outline of Research Achievments

Alloys composed of Ti (titanium), Zr (zirconium), Ni (nickel), and Pd (palladium) were prepared by arc melting with varying compositions, and their driving temperatures and crystal structures as shape memory alloys were systematically investigated. As a result, 49.7Pd–(50.3-x)Ti–xZr (at.%) ternary alloys (x = 15–20) and those alloys with a small addition of Ni were selected as candidate shape memory alloys with high driving temperatures above 100°C, high alloy strength and large shape recovery strain. Among these candidates, we focused on the 49.7Pd–30.3Ti–20Zr (at.%) alloy and investigated the optimization of heat treatment conditions. By clarifying the effects of heat treatment temperature and duration on the driving temperature and the type and size of precipitates, an excellent shape memory effect with strain generation at very low stress (200 MPa) and shape recovery as large as 4.5% with subsequent heating was obtained under the optimum heat treatment temperature (650°C) condition. Although the number of driving cycles is limited to one to several, the new shape memory alloy is suitable for applications such as solar array panel deployment in space probes.

  1. Tobe H, et al. (2022) Facilitation of detwinning through controlling crystal structure in Ti–Zr–Ni–Pd high temperature shape memory alloys. Acta Materialia 229: 117811. https://doi.org/10.1016/j.actamat.2022.117811

  2. Tobe H, et al. (2022) Novel Ti­–20Zr–­49.7Pd high temperature shape memory alloy with facilitated detwinning and precipitation strengthening. Materials Transactions 63: 975–980. https://doi.org/10.2320/matertrans.MT-M2022034

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