Enhancing the bond strength in the meta-crystal lattice of architected materials by harnessing the non-equilibrium solidification in metal additive manufacturing

Architected materials produced by metal additive manufacturing techniques offer realization of complex structural hierarchies that mimic the principles of crystal plasticity while still being ultralight-weight. However, they suffer from deep-rooted multiscale defects including microstructural heterogeneity caused by the complex thermo-mechanical transients in the melt pool. Here we manufacture meta-crystal 316L stainless steel microlattice structures for utilizing the strain localization mechanism in bulk structures akin to dislocation slip mediated plasticity. These lattices are characterized here using scanning and transmission electron microscopy, along with energy dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD) to reveal the microstructural, chemical and crystallographic orientation information at various locations in the struts and joints. The presence of inherent voids was the major drawback that would undermine their structural performance as mechanical metamaterials. Nevertheless, other defects in the form of spatially correlated dislocation networks and micro-segregated cellular substructures overcome the strength-ductility trade-off and render the bulk structures comparable to other engineering materials including conventional steels. By exploiting this intrinsic strengthening mechanism due to the rapid (i.e. non-equilibrium) solidification phenomenon, the bond (i.e. strut) strength of meta-crystals can be enhanced (or controlled) on top of employing hardening principles of metallurgy to design architected materials with tailored properties.