Sheng Xu

The elastocaloric effect, driven by stress-induced martensitic transformations, offers a promising route toward efficient and environmentally friendly solid-state cooling. However, its practical implementation has been hindered by an inherent trade-off: materials exhibiting large isothermal entropy changes typically operate over narrow temperature windows, thereby limiting their overall cooling performance. Here, we demonstrate an elastocaloric response in a Ti–Al–Cr superelastic alloy that overcomes this limitation. Direct measurements reveal a pronounced elastocaloric cooling effect over an ultra-wide temperature range of 305 K, from 97 K to 402 K. This temperature span exceeds that predicted by the Clausius–Clapeyron relationship (235 K), indicating a significant deviation from conventional thermodynamic expectations. At room temperature, a large adiabatic temperature change of ~10 K is directly measured, corresponding to a cooling output of 5.76 J·g⁻ ¹ and a material coefficient of performance of 4.6, demonstrating competitive cooling performance at practical operating conditions. In addition, the elastocaloric response is maintained over the entire temperature range despite the expected decrease in entropy change at lower temperatures, indicating that the conventional trade-off between temperature span and cooling strength is effectively mitigated. This exceptional behavior originates from a combination of anomalous temperature dependence of the critical stress for martensitic transformation and high mechanical strength, which together enable fully reversible stress-induced transformations across a broad thermal domain. Our findings reveal a new regime of elastocaloric behavior and establish a guiding principle for overcoming the apparent limitations imposed by Clausius–Clapeyron-based descriptions in caloric materials.

Fracture surface morphology reflects essential information on fracture processes in high-temperature structural materials, yet its quantitative relationship with fracture properties remains unclear. In this work, the fracture behavior of heat-treated Mo–Ti–C alloys is investigated using four-point bending tests combined with detailed fracture surface characterization by scanning electron microscopy and confocal laser scanning microscopy. Quantitative morphology descriptors, including gray-level co-occurrence matrix texture features, surface roughness parameters, and fractal descriptors, are systematically extracted and analyzed within an explainable, machine-learning-assisted framework. The results reveal distinct morphology dependencies for fracture energy and fracture toughness. Fracture energy was dominated by a few key descriptors, with higher texture contrast and fractal dimension associated with lower fracture energy levels, whereas fracture toughness depended on multiple texture- and fractal-related descriptors. This study establishes an interpretable quantitative framework linking fracture surface morphology to fracture properties, providing new insights for morphology-informed fracture assessment and microstructure-guided materials design.

We report direct evidence of tensile superelasticity in micron-sized specimens of a Fe–Ni–Co–Al–Ti–B shape memory alloy. Dog-bone-shaped micro-tensile specimens were fabricated by focused ion beam milling and tested in situ under a scanning electron microscope. The corrected stress–strain curves exhibit clear hysteresis loops and superelastic strains up to ~ 4.5%, demonstrating stable transformation-mediated superelasticity at the micron scale. Both the critical transformation stress (~ 1.2 GPa) and the stress hysteresis (~ 1 GPa) are greatly enhanced compared with the bulk, reflecting pronounced size effects. These findings extend size-dependent transformation studies to precipitation-strengthened Fe-based shape memory alloys and highlight their potential for microactuators and other small-scale functional applications.

Actuators are widely used in various mechanical products. However, there have been no actuators that can exhibit high actuation stresses and strains at cryogenic temperatures. Although shape memory alloys (SMAs) are attractive candidates for thermally driven actuators with high actuation stresses and strains, the operation of conventional SMAs is limited to a narrow temperature range near the room temperature. Here, we report the shape memory effect under tensile conditions with a high work output across a wide temperature range of 50–270 K in Cu-Al-Mn-based alloys. In addition, a mechanical heat switch using Cu-Al-Mn was designed for thermal insulation in space infrared telescope, and we demonstrated the operation at around 100 K. These results indicate that Cu-Al-Mn SMAs are potential cryogenic actuators with high actuation stress and strain that would contribute to the development of low temperature technologies in various fields including space astronomy, superconductivity, and liquefied gas industry.

In advanced applications such as aerospace and space exploration, materials must balance lightness, functionality and extreme thermal fluctuation resistance^1,2. 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^3–6. We hereby introduce a new shape-memory alloy that adheres to these stringent criteria. Predominantly composed of Ti and Al with a chemical composition of Ti_75.25Al₂₀Cr_4.75, this alloy is characterized by a low density (4.36 × 10³ kg m^{− 3}) and a high specific strength (185 × 10³ Pa m³ per kg) at room temperature, while showing excellent superelasticity. The superelasticity, owing to a reversible stress-induced phase transformation from an ordered body-centred cubic parent phase to an ordered orthorhombic martensite, allows for a recoverable strain exceeding 7%. 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 behaviour from the perspective of a temperature-dependent anomalous lattice instability of the parent phase. This alloy holds potential in everyday appliances requiring flexible strain accommodation, as well as components designed for extreme environmental conditions such as deep space and liquefied gases.