Abstract
The bending fatigue resistance of superelastic shape memory alloys (SMAs) is a key determinant for their reliable function in cyclic applications such as biomedical implants, adaptive actuators, and elastocaloric devices. However, conventional NiTi alloys exhibit limited fatigue life due to premature crack initiation and propagation under cyclic tensile loading. Here, we report a surface engineering strategy that overcomes this limitation by inducing a hierarchical surface architecture via pre-strain warm laser shock peening (pw-LSP). This architecture integrates a high-strength titanium nitride-enriched top layer, an ultrafine-grained layer with an inverse grain size gradient and a B19′–R–B2 phase gradient, and a substantial compressive residual stress exceeding 1 GPa. These features act synergistically to suppress crack nucleation and arrest propagation through a crack-tip shielding mechanism. As a result, the treated NiTi demonstrates a bending fatigue life exceeding 5 million cycles at a maximum surface tensile strain of 1.94%—representing a more than 3000-fold enhancement over untreated nanocrystalline NiTi. This work presents a robust and scalable approach for designing fatigue-resistant SMAs with broad implications for high-cycle, high-reliability applications.
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Acknowledgements
The authors thank Dr. Hongyang Lin of the Hong Kong University of Science and Technology (HKUST) for conducting part of the fatigue testing, as well as the Core Research Facilities at Southern University of Science and Technology and the Materials Characterization and Preparation Facility (MCPF) at HKUST for their technical support. This work was supported by National Natural Science Foundation of China (grants nos. 52371251 (F.R.), 52122102 (F.R.) and 12302095 (K.Y.)), the Basic and Applied Basic Research Foundation of Guangdong Province (grants no 2025A1515011336 (K.C.)), the Hong Kong Research Grant Council (grant no. 16212322 (Q.S.)), and the Project of Hetao Shenzhen-Hong Kong Science and Technology Innovation Cooperation Zone (grant nos. HZQB-KCZYB-2020083 (Q.S.) and STG2/E-605/23-N (Q.S.)).
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Yan, K., Chu, K., Wang, M. et al. Bending-fatigue-resistant hierarchical NiTi shape memory alloy. Nat Commun (2026). https://doi.org/10.1038/s41467-026-72857-z
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DOI: https://doi.org/10.1038/s41467-026-72857-z
