Multi-material direct ink writing (DIW) for complex 3D metallic structures with removable supports

Direct ink writing (DIW) combined with post-deposition thermal treatments is a safe, cheap, and accessible additive manufacturing (AM) method for the creation of metallic structures. Single-material DIW enables the creation of complex metallic 3D structures featuring overhangs, lengthy bridges, or enclosed hollows, but requires the printing supporting structures. However, the support printed from the same material becomes inseparable from the building structure after the thermal treatment. Here, a multi-material DIW method is developed to fabricate complex three-dimensional (3D) steel structures by creating a removable support printed from a lower melting temperature metal (i.e., copper) or a ceramic (i.e., alumina). The lower melting temperature metal completely infiltrates the porous steel structures for a hybrid configuration, while the ceramic offers a brittle support that can be easily removed. The influence of the support materials on the steel structure properties is investigated by characterizing the dimensional shrinkage, surface roughness, filament porosity, electrical conductivity, and tensile properties. The hybrid configuration (i.e., copper infiltrated steel structures) improves the electrical conductivity of the fabricated steel structure by 400% and the mechanical stiffness by 34%. The alumina support is physically and chemically stable during the thermal treatment, bringing no significant contamination to the steel structure.