In advanced fields like aerospace and space exploration, materials must combine low weight, high functionality, and resilience to extreme temperature fluctuations. Shape-memory alloys are promising candidates, offering impressive strength, toughness, and the ability to recover from deformation due to their superelastic properties.
However, achieving low mass and reliable performance at cryogenic temperatures remains challenging. A team of researchers, namely Yuxin Song, Shunsuke Sato, Sheng Xu and Inho Lee, have developed a newly developed shape-memory alloy specifically engineered to meet these demanding requirements.
Composed of aluminium and titanium with a chemical composition of Ti₇₅.₂₅Al₂₀Cr₄.₇₅, this alloy features a low density of 4.36 × 10³ kg/m³ and a high specific strength of 185 × 10³ Pa·m³/kg at room temperature. It also exhibits outstanding superelasticity. This property results from a reversible stress-induced phase transformation between an ordered body-centred cubic parent phase and an ordered orthorhombic martensite phase, enabling a recoverable strain greater than 7 per cent.
This remarkable functionality remains stable across a wide temperature range from deep cryogenic levels at 4.2 K to above room temperature thanks to the unconventional temperature dependence of the transformation stresses. Notably, below a specific threshold during cooling, the critical stress required for phase transformation decreases as the temperature drops. This inverse relationship is attributed to temperature-sensitive anomalous lattice instability in the parent phase.