  Architected materials produced by powder bed fusion metal additive
manufacturing technique offer realization of complex structural hierarchies
that mimic the principles of crystal plasticity while still being
ultralight-weight, though suffering 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 by selective laser melting process for utilizing
the strain localization mechanism in bulk structures akin to dislocation slip
mediated plasticity. The build angle was observed to be the primary influencer
of defects generated and the presence of inherent voids was the major drawback
that would undermine their structural performance as mechanical metamaterials.
However, 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, the bond strength of meta-crystals (i.e. strut
strength) can be enhanced (or controlled) on top of employing hardening
principles of metallurgy to design materials with desired properties.
