Shape Memory Alloys in Mechanical Applications

Shape memory alloys (SMAs) are metallic materials capable of undergoing reversible, diffusionless phase changes that enable two hallmark behaviours: the shape memory effect and superelasticity. In the martensitic transformation, a low-temperature martensite phase reverts to a high-temperature austenite phase on heating, recovering pre-deformed shapes, while in superelasticity large strains are fully recovered upon unloading in the austenitic state. Predominantly based on Ni–Ti systems, but extending to Cu- and Fe-based alloys, SMAs combine high energy density, intrinsic damping and fatigue resistance. They serve as actuators, sensors, dampers and adaptive structures in aerospace morphing wings, automotive vibration control, civil-engineering seismic devices and biomedical implants, among others. Advances in alloy design, thermomechanical treatments and additive manufacturing have enhanced workability, scalability and functional performance, broadening global applications in energy-efficient actuation and smart structural components.

Research from Nature Portfolio

Recent studies have reported a Ti–Ni strain glass alloy exhibiting an exceptional combination of ultrahigh yield strength and ultralow elastic modulus alongside super-large rubber-like elastic strain across a broad temperature span. This microstructure arises from a dual-seed strain glass matrix that enables a nucleation-free reversible transition between strain glass and martensite phases, resulting in fatigue-resistant, polymer-like flexibility and strength. Another investigation has demonstrated that minute additions of titanium to Fe–Mn–Al–Ni alloys markedly promote abnormal grain growth, producing metre-scale single-crystal bars with enhanced recoverable strain and structural integrity, thereby positioning cost-efficient iron-based alloys for large-scale mechanical applications.

Shape Memory Alloys in Mechanical Applications publication trend

The graph below shows the total number of articles in shape memory alloys in mechanical applications across all publications each year (not limited to Nature Index journals).

Technical terms

Martensitic transformation: Diffusionless, reversible crystal-structure change between high- and low-temperature phases underpinning shape memory behaviour.

Shape memory effect: The ability of an alloy to recover its original form upon heating after deformation in the martensitic state.

Superelasticity: Pseudoelastic response that permits large, fully recoverable strains upon loading and unloading in the austenitic phase.

Strain glass: A disordered variant of martensite characterised by frozen local strain fields that confer high flexibility and strength.

Additive manufacturing: Layer-by-layer fabrication techniques, such as powder bed fusion and directed energy deposition, enabling complex SMA geometries.

References

1. A polymer-like ultrahigh-strength metal alloy. Nature (2024).
2. Laser powder bed fusion additive manufacturing of NiTi shape memory alloys: a review. International Journal of Extreme Manufacturing (2023).
3. Wire-based directed energy deposition of NiTiTa shape memory alloys: Microstructure, phase transformation, electrochemistry, X-ray visibility and mechanical properties. Additive Manufacturing (2022).
4. Promoting abnormal grain growth in Fe-based shape memory alloys through compositional adjustments. Nature Communications (2019).