A Lightweight shape-memory alloy with superior temperature-fluctuation resistance

Song, Y.*; Xu, S.*; Sato, Shunsuke*; Lee, I.*; Xu, X.*; Omori, Toshihiro*; Nagasako, Makoto*; Kawasaki, Takuro   ; Kiyanagi, Ryoji  ; Harjo, S.   ; Gong, W.   ; Grabec, T.*; Stoklasov, P.*; Kainuma, Ryosuke*

In advanced applications like aerospace and space exploration, materials must balance lightness, functionality, and extreme thermal fluctuation resistance. Shape-memory alloys show promise with strength, toughness, and substantial strain recovery due to superelasticity, but maintaining low mass and effective operation at cryogenic temperatures is challenging. We hereby introduce a novel shape-memory alloy that adheres to these stringent criteria. Predominantly composed of Ti and Al with a chemical composition of TiAlCr, this alloy 25 is characterized by a low density (4.3610 kg/m) and a high specific strength (18510 Pam/kg) at room temperature, while exhibiting excellent superelasticity. The superelasticity, owing to a reversible stress-induced phase transformation from an ordered body-centered cubic parent phase to an ordered orthorhombic martensite, allows for a recoverable strain exceeding 7%. Remarkably, this functionality persists across a broad range of temperatures, from deep cryogenic 4.2 K to above room temperature, arising from an unconventional temperature dependence of transformation stresses. Below a certain threshold during cooling, the critical transformation stress inversely correlates with temperature. We interpret this behavior from the perspective of a temperature-dependent anomalous lattice instability of the parent phase. This alloy holds potential in everyday appliances requiring flexible strain accommodations, as well as components designed for extreme environmental conditions such as deep space and liquefied gases.