3D Printing of Hierarchical Porous Steel and Iron-Based Materials

Abstract

Iron is a cheap and environmentally friendly metal that is produced at the gigaton scale every year. While porous metals have long been used as filters in chemical processes and electrodes in functional devices, steel and iron-based structures with highly tunable porosity have only recently been explored as sustainable, lightweight materials for a variety of structural, biomedical, and energy-related applications. Here, an extrusion-based 3D printing process is reported to manufacture steel- and iron-based structures with ultrahigh porosity distributed over three hierarchical levels. Using particle-stabilized foams as printing inks, pores are generated at multiple length scales by controlling the print path, the concentration of air bubbles in the ink, and the thermal reduction and sintering process of the metal oxide precursor particles. This enables the manufacturing of iron and iron-based alloys with an elastic modulus above 300 MPa and a density below 1 g cm−3 while keeping the mechanical efficiency expected for porous structures. The potential applications of such hierarchical porous iron and iron alloys are illustrated by printing structures with tunable chemical compositions that are ultra-lightweight, magnetoresponsive, and capable of spontaneously absorbing oil spills and of vaporizing liquids using low electric power.