The development and application of metallic materials have shaped human society since the dawn of civilization. Archaeologists have divided prehistoric ages into periods based on the adoption of bronze and iron. Conventional metallic materials, such as steel, are strong, durable, and hard compared to polymers. However, higher strength typically comes at the cost of flexibility, making metallic materials prone to permanent deformation under large strains. Overcoming this intrinsic trade-off, shape-memory alloys exhibit polymer-like large recoverable strain while maintaining characteristic metallic properties. This large recoverable strain, called superelasticity, resembles elastic deformation macroscopically but occurs through reversible phase transformations at the atomic scale. Shape-memory alloys, such as the well-known nitinol, are extremely useful in medical, robotics, architectural, and aerospace applications. However, these alloys typically show superelasticity only within a narrow temperature range. We have reported a superelastic titanium-aluminum-based (Ti-Al-Cr, Figure 1) shape-memory alloy that functions over a wide temperature range, from liquid helium temperature to above the boiling point of water, while combining high strength and lightweight properties.

Beyond terrestrial applications, the newly developed superelastic alloy is extremely promising for deep space exploration. For example, the recent development of the “Superelastic Tire” highlights its potential. NASA and its partners have announced the ambitious Artemis missions for long-term lunar exploration and future Mars missions. These missions require surface vehicles capable of long-range planetary exploration. Unlike Earth vehicles that use conventional rubber pneumatic tires, manned lunar vehicles require a different approach. The Apollo Lunar Rover used tires made of woven piano wire mesh, designed to withstand the Moon's extreme temperature fluctuations (ranging from −173 °C to 127 °C), intense solar radiation, and the risk of catastrophic deflation. However, the original Apollo tire design had limited longevity due to the small elastic deformation range of conventional metals. Scientists at NASA's Glenn Research Center addressed this limitation by incorporating nitinol shape-memory alloy into the design, creating what they call the game-changing Superelastic Tire. However, the commercially successful nitinol alloy, as well as the majority of existing shape-memory alloy families, has a limited superelastic temperature window of less than 80 °C, with the midpoint set at around room temperature.

Using rational alloy design, we identified a promising titanium-aluminum shape-memory alloy system. This new alloy not only exhibits large recoverable strain and strength comparable to commercial nitinol but also boasts significantly lower density and enhanced functionality across an unprecedented temperature range (from −269 °C to 127 °C), making it an ideal lightweight alloy system (Figure 2, Figure 3). This achievement partly stems from the formation of a body-centered cubic parent phase with long-range atomic ordering. The discovery is particularly noteworthy because aluminum typically destabilizes body-centered cubic phases in titanium alloys, making the observed parent phase counterintuitive and explaining why this alloy remained undiscovered until now. This new alloy holds great promise for making next-generation Superelastic Tires capable of performing under extreme conditions. Does a superelastic alloy work for deep space exploration? Absolutely—this superelastic alloy even "walks" for deep space exploration (Figure 4)!

We have also found a previously unknown phenomenon that extends beyond the traditional thermodynamic concept of phase transformation in superelasticity. We suggest that the temperature dependence of superelasticity is also influenced by changes in the crystal lattice's instability, as indicated by variations in elastic constants. These findings not only extend the superelastic temperature range but also clarify the physical mechanisms underlying superelastic behavior.

Furthermore, our shape-memory alloy achieves its excellent properties using more readily available or less environmentally impactful alloying elements, aligning with the growing need for sustainable metallurgy. When designing new alloys, performance must be balanced against environmental impact, which extends beyond the material's service life. This principle explains why most practical metallic materials, such as steel, are designed for versatility, durability, and recyclability. The titanium-aluminum-based alloy's reduced reliance on critical raw materials, combined with its favorable mechanical properties, suggests potential economic and environmental advantages for large-scale applications.

While the findings are promising, there remains room for improvement. For instance, while the stress serrations observed at ultra-low temperatures are academically fascinating, they pose potential safety concerns for practical applications. Future research could explore new alloy design strategies to control or eliminate such mechanical instabilities.

This work has also been highlighted in the News & Views section of Nature in the same issue (https://www.nature.com/articles/d41586-025-00301-1).