Mechanical Properties of Bicrystal-Inspired Lattice Structures Fabricated by Additive Manufacturing

While crystal-inspired design has become a promising strategy for developing advanced mechanical metamaterials, the specific role of individual grain boundary interfaces on the macroscopic mechanical properties has remained unclear. This study aims to elucidate the importance of this interface by designing, fabricating, and testing bicrystal-inspired lattice structures. Using the Coincident Site Lattice (CSL) theory, we modeled various Σ5 tilt grain boundaries in a bicrystal configuration. These structures were fabricated from SUS316L powder using a powder bed fusion (PBF) additive manufacturing process. Compression tests revealed that the presence and type of the macroscopic “grain boundary” interface are critical determinants of the mechanical response, with symmetric bicrystal structures exhibiting a distinct two-stage collapse. More importantly, by engineering the fine structure of the interface itself, such as the density of connecting struts, the mechanical properties can be precisely tuned, achieving a systematic variation in yield strength from 9.1 MPa to 11.5 MPa. This work clarifies the crucial role of interfacial structure in crystal-inspired metamaterials and provides a clear design principle for creating lightweight, damage-tolerant structures with programmable mechanical responses.