Mechanical metamaterials made of freestanding quasi-BCC nanolattices of gold and copper with ultra-high energy absorption capacity

Fabrication of nanolattices with sub-100 nm beam diameter is challenging and their mechanical properties are ambiguous. Herein, we fabricate gold and copper quasi-BCC nanolattices with beam diameter as small as 34 nm that show the highest energy absorption capacity among nanolattice materials.
Mechanical metamaterials made of freestanding quasi-BCC nanolattices of gold and copper with ultra-high energy absorption capacity
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Energy absorption mechanical metamaterials have been the subject of intense interest because they offer exciting opportunities for highly efficient absorption of mechanical energy, which is crucial for several applications. The energy absorbed by a material is given by the integral of the plateau stress and the failure or densification strain. In most cases, unfortunately, these properties are substantially in contradictory, i.e., high yield or fracture strength is generally gained at the price of low failure strain, and vice versa.  For a mechanical metamaterial, its energy absorption capacity is essentially dominated by the material’s properties, including size- and microstructure-induced enhancement, and architectural design. Metals possess natural high strength and high ductility and thus are unparallel candidates for the pursuit of high energy absorption capacity. It is reasonable to speculate that higher energy absorption capacity could be pursued with nanobeams structured metals under properly designed architecture. Up till now, however, such metamaterials have seldom been reported. Herein, we report gold and copper quasi-body centered cubic (quasi-BCC) nanolattices with the diameter of the nanobeams as small as 34 nm.

The gold and copper quasi-BCC nanolattices are prepared by ion track technology1 and their mechanical properties are studied by compression tests (Fig. 1). Unexpectedly, the yield strengths of Au-34 and Cu-34 quasi-BCC nanolattices have high values, i.e., 107±11 MPa for gold and 153±15 MPa for copper, which outweigh gold (100 MPa) and copper (130 MPa) bulk counterparts.

Fig. 1 Compression tests on the gold and copper quasi-BCC nanolattices. a SEM snapshots of the deformation process of the sample Au-69. b Stress–strain curves of the gold and copper quasi-BCC nanolattices of the samples Au-117, Au-86, Au-69, Au-34, Cu-34, respectively. c Compressive stiffness versus relative density and d Compressive strength versus relative density of gold and copper quasi-BCC nanolattices.
Fig. 1 Compression tests on the gold and copper quasi-BCC nanolattices. a SEM snapshots of the deformation process of the sample Au-69. b Stress–strain curves of the gold and copper quasi-BCC nanolattices of the samples Au-117, Au-86, Au-69, Au-34, Cu-34, respectively. c Compressive stiffness versus relative density and d Compressive strength versus relative density of gold and copper quasi-BCC nanolattices.

Compared to previous micro/nanolattices, our gold and copper quasi-BCC nanolattices exhibit higher energy absorption capacity (up to 100±6 MJ m-3 and 110±10 MJ m-3 for gold and copper quasi-BCC nanolattices, respectively), surpassing most micro/nanolattices, while being 1-3 orders of magnitude larger than those of natural porous materials with comparable densities (Fig. 2)2-14

Fig. 2 Ashby map of energy absorption per unit volume versus density of gold and copper quasi-BCC nanolattices and previously reported micro/nanolattice metamaterials.
Fig. 2 Ashby map of energy absorption per unit volume versus density of gold and copper quasi-BCC nanolattices and previously reported micro/nanolattice metamaterials

In this study, we provide an in-depth exploration of mechanical gold and copper quasi-BCC nanolattices using experiments, theoretical calculation, and finite element analysis. Our work establishes that gold and copper quasi-BCC nanolattices have excellent compressive strength and energy absorption capacity, which substantially result from the synergy of the naturally high mechanical strength and plasticity of metals, the relevant size reduction-induced mechanical enhancement, and the quasi-BCC nanolattice architecture. We hope that this work provides some hints for the further design and fabrication of lightweight porous metals with high strength, energy absorption, electrical, and thermal conductivity, and thereby offering promising prospects for realizing high-performance multifunctional applications.

More details can be found in our paper "Mechanical metamaterials made of freestanding quasi-BCC nanolattices of gold and copper with ultra-high energy absorption capacity" published in Nature Communications.

References

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2. Bauer J., Schroer A., Schwaiger R. & Kraft O. Approaching theoretical strength in glassy carbon nanolattices. Nat. Mater. 15, 438-443 (2016).

3. Bauer J., Hengsbach S., Tesari I., Schwaiger R. & Kraft O. High-strength cellular ceramic composites with 3D microarchitecture. Proc. Natl. Acad. Sci. 111, 2453-2458 (2014).

4. Meza L. R., Das S. & Greer J. R. Strong, lightweight, and recoverable three-dimensional ceramic nanolattices. Science 345, 1322-1326 (2014).

5. Gu X. W. & Greer J. R. Ultra-strong architected Cu meso-lattices. Extreme Mech. Lett. 2, 7-14 (2015).

6. Mieszala M., et al. Micromechanics of amorphous metal/polymer hybrid structures with 3D cellular architectures: size effects, buckling behavior, and energy absorption capability. Small 13, 1602514 (2017).

7. Schaedler T. A., et al. Ultralight metallic microlattices. Science 334, 962-965 (2011).

8. Zheng X., et al. Ultralight, ultrastiff mechanical metamaterials. Science 344, 1373-1377 (2014).

9. Zheng X., et al. Multiscale metallic metamaterials. Nat. Mater. 15, 1100-1106 (2016).

10. Bonatti C. & Mohr D. Smooth-shell metamaterials of cubic symmetry: Anisotropic elasticity, yield strength and specific energy absorption. Acta Mater. 164, 301-321 (2019).

11. Bonatti C. & Mohr D. Large deformation response of additively-manufactured FCC metamaterials: From octet truss lattices towards continuous shell mesostructures. Int. J. Plast. 92, 122-147 (2017).

12. Feng X., et al. Microalloyed medium-entropy alloy (MEA) composite nanolattices with ultrahigh toughness and cyclability. Mater. Today 42, 10-16 (2021).

13. Zhang X., et al. Three-dimensional high-entropy alloy–polymer composite nanolattices that overcome the strength–recoverability trade-off. Nano Lett. 18, 4247-4256 (2018).

14. Tancogne‐Dejean T., Diamantopoulou M., Gorji M. B., Bonatti C. & Mohr D. 3D plate‐lattices: an emerging class of low‐density metamaterial exhibiting optimal isotropic stiffness. Adv. Mater. 30, 1803334 (2018).

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