Electrohydrodynamic redox printing vs magnetron sputtering: Enhancing hardness of nanoporous silver with twinning and structural order

Nanoporous (np) metals are used for a variety of applications including actuators, catalysts, and sensors. 3D printing enabled multi-functional design offers a pathway for enhancing performance in these applications. Electrohydrodynamic redox printing (EHD-RP), is a high resolution additive manufacturing technique which can produce complex 3D metal alloys that allows for the fabrication of np metal structures. To determine the influence of this additive manufacturing process on the mechanical properties, we compare EHD-RP derived np-Ag to films made via magnetron sputtering. Samples fabricated by EHD-RP exhibit higher hardness than sputtered films for similar relative densities as demonstrated with nanoindentation. To explain these differences we used FIB-tomography to quantify structural features in the np networks including ligament width, relative density, connectivity, and topology. Materials factors like twin density and grain size were investigated using STEM analysis. Together, the higher twin density and more ordered network structure found in EHD-RP explain the enhanced mechanical behaviour of np-Ag and highlight a key opportunity for additive manufacturing to enhance both materials and structural design in np networks. • Nanoporous Ag networks fabricated by EHD-RP show nanoindentation hardness values twice as high as networks fabricated by PVD. • The non-equilibrium nature of deposition via EHD-RP leads to a higher twin boundary density in the final nanoporous network. • Layer-by-layer deposition in EHD-RP leads to more order in the nanoporous Ag networks when compared to networks made by PVD.