Hierarchical Porous Monoliths of Steel with Self-Reinforcing Adaptive Properties.

Porous structures offer an attractive approach to reducing the amount of natural resources used while maintaining relatively high mechanical efficiency. However, for some applications the drop in mechanical properties resulting from the introduction of porosity is too high, which has limited the broader utilization of porous materials in industry. Here, we show that steel monoliths can be designed to display high mechanical efficiency and reversible self-reinforcing properties when made with porous architectures with up to three hierarchical levels. Ultralight steel structures that can float on water and autonomously adapt their stiffness were manufactured by the thermal reduction and sintering of three-dimensionally printed foam templates. Using distinct mechanical testing techniques, image analysis, and finite element simulations, we study the mechanisms leading to the high mechanical efficiency and self-stiffening ability of the hierarchical porous monoliths. The design and fabrication of mechanically stable porous monoliths using iron as a widely available natural resource is expected to contribute to the future development of functional materials with a more sustainable footprint. This article is protected by copyright. All rights reserved.