Metallic Architectures from 3D-Printed Powder-Based Liquid Inks

From the early Copper Age several millennia ago, to the beginning of the Steel Age in the 19th century, our capacity to access and manipulate metals has created the foundation for the modern world. Today, metal structures are ubiquitous— from the tallest skyscrapers to the most elegant of jewelry—that we often forget much of it originated from metal containing ores, comprised of metal compounds, including oxides, reduced at high temperature into liquid metal and cast into ingots. Powder metallurgy provides an alternate approach to metal forming. Traditional powder metallurgy utilizes metal powders that are shaped and compacted into dense metallic objects through hot isostatic pressing [ 1 ] or dynamic compaction. [ 2 ] An alternative, indirect approach is to fi rst fabricate objects of the desired architectures from metal precursors, such as metal oxides, and then thermochemically reduce and sinter them to form metallic counterparts, [ 3–6 ] including porous, cellular architectures that cannot be formed via direct metal casting. Among the many established approaches for using metallic powders to create metallic architectures directly, there have been several previous examples that utilize the general approach of creating metal oxide powder objects and transforming them into disordered metallic foams [ 5–8 ] and linear cellular architectures. [ 3,4,9 ] In these instances, powder-based, metal-oxide green bodies are created and subsequently thermochemically reduced and sintered at elevated temperatures in reducing atmosphere (e.g., H 2 gas) to produce metallic structures with water vapor as a byproduct. Although effective in producing metallic objects, metal and metal oxide green body fabrication through traditional methods such as freeze-casting [ 7,8 ] and die extrusion [ 3,4 ]