Hierarchical materials are known to show outstanding mechanical behaviours in nature (e.g. nacre, enamel, bone). In the case of nanoscale network materials, recently, it has been demonstrated with dealloyed nanoporous metals that stiffness and strength scale with the solid fraction and they can be enhanced through structural hierarchy [1]. However, the investigation of structural or topological parameters on their mechanical properties are highly limited to nanoporous metals with the number of hierarchical levels up to two. The mechanical behaviours of nanoscale network materials with multiple length scale are still not well understood. In this work, we propose a unique fabrication method for three-level hierarchical nanoporous gold. In addition to creating two levels (middle and lower level) by a common two-step electrochemical dealloying process, a third level (upper level) is created via additive manufacturing assisted casting method. A polymer with the desired upper-level structure was produced by additive manufacturing and used as a template. After metal plating and casting, the polymer network was replaced with Ag93Au7 alloy. Finally, a two-step dealloying was performed on the Ag93Au7 network material as in Ref [1] to obtain a three-level hierarchical nanoporous gold.

[1] Shi, S.; Li, Y.; Ngo-Dinh, B.-N. et al.: Scaling behavior of stiffness and strength of hierarchical network nanomaterials. In: Science (New York, N.Y.), Vol. 371 (2021), Iss. 6533, pp. 1026-1033. https://doi.org/10.1126/science.abd9391.