Abstract
Many established, but also potential future applications of NiTi-based shape memory alloys (SMA) in biomedical devices and solid-state refrigeration require long fatigue life with 107–109 duty cycles1,2. However, improving the fatigue resistance of NiTi often compromises other mechanical and functional properties3,4. Existing efforts to improve the fatigue resistance of SMA include composition control for coherent phase boundaries5,6,7 and microstructure control such as precipitation8,9 and grain-size reduction3,4. Here, we extend the strategy to the nanoscale and improve fatigue resistance of NiTi via a hybrid heterogenous nanostructure. We produced a superelastic NiTi nanocomposite with crystalline and amorphous phases via severe plastic deformation and low-temperature annealing. The as-produced nanocomposite possesses a recoverable strain of 4.3% and a yield strength of 2.3 GPa. In cyclic compression experiments, the nanostructured NiTi micropillars endure over 108 reversible-phase-transition cycles under a stress of 1.8 GPa. We attribute the enhanced properties to the mutual strengthening of nanosized amorphous and crystalline phases where the amorphous phase suppresses dislocation slip in the crystalline phase while the crystalline phase hinders shear band propagation in the amorphous phase. The synergy of the properties of crystalline and amorphous phases at the nanoscale could be an effective method to improve fatigue resistance and strength of SMA.
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Data availability
The datasets that support the findings of this study are available in the figshare repository, https://doi.org/10.6084/m9.figshare.13116578. Source data are provided with this paper.
Code availability
The codes for the finite element modelling are available in the figshare repository, https://doi.org/10.6084/m9.figshare.13116578.
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Acknowledgements
This work was financially supported by the Hong Kong Research Grants Council (GRF project no. 16208420) and the Science, Technology and Innovation Commission of Shenzhen Municipality (project no. SGDX2019081623360564) and the National Natural Science Foundation of China (project no. 11532010). The neutron diffraction was conducted at BL20 iMATERIA of J-PARC MLF (proposal nos. 2018B0109, 2019A0102 and 2019PM3002). We are grateful for Q. Li’s (Wuhan University) help in processing the neutron diffraction data and H. Lin’s (HKUST) assistance in measuring the elastocaloric property. All data supporting the findings of this study are available within the paper.
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P.H. and Q.S. designed the experiments and wrote the manuscript. Data came from all authors. M.X. did the cold rolling. P.H. did the heat treatment, fabrication and nanocompression of micropillars, SEM, TEM characterization and finite element analysis. Y.O. performed the neutron diffraction at BL20 iMATERIA of J-PARC MLF. All authors discussed the results and commented on the manuscript.
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Peer review information Nature Nanotechnology thanks Jun Cui and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Extended data
Extended Data Fig. 1 Effects of sample size on the stress-strain responses of the NiTi crystalline-amorphous nanocomposite.
The sizes of the macro-pillar are 1 mm × 1 mm × 2 mm. The quasi-static compression of the two samples was conducted at the strain rate of 5 × 10−3 s−1 at room temperature (298 K).
Extended Data Fig. 2 Temperature oscillation of the NiTi crystalline-amorphous nanocomposite macro-pillars under 20 Hz cyclic compression.
a, Cyclic stress-strain responses. b, Temperature oscillation. The sizes of the macro-pillars are 1 mm × 1 mm × 2 mm. ΔT: Amplitude of temperature oscillation. COP = λΔT/H: coefficient of cooling performance. λ = 3.225 MJ/(m3 · K): heat capacity per unit volume. H: hysteresis loop area, equals to the density of the dissipated work.
Supplementary information
Supplementary Information
Supplementary Figs. 1–13.
Source data
Source Data Fig. 2
Source data for Fig. 2.
Source Data Fig. 3
Source data for Fig. 3. The unprocessed source images are available in figshare (DOI: 10.6084/m9.figshare.13116578).
Source Data Fig. 4
Source data for Fig. 4. The unprocessed source images are available in figshare (DOI: 10.6084/m9.figshare.13116578).
Source Data Extended Data Fig. 1
Source data for Extended Data Fig. 1.
Source Data Extended Data Fig. 2
Source data for Extended Data Fig. 2.
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Hua, P., Xia, M., Onuki, Y. et al. Nanocomposite NiTi shape memory alloy with high strength and fatigue resistance. Nat. Nanotechnol. 16, 409–413 (2021). https://doi.org/10.1038/s41565-020-00837-5
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DOI: https://doi.org/10.1038/s41565-020-00837-5
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