Effect of Unit Cell Size on the Compressive Deformation Behavior of Inconel 718 Lattice Structures Fabricated by Laser Powder Bed Fusion Process

This study investigates the mechanical behavior and deformation characteristics of Inconel 718 lattice structures with different unit cell sizes fabricated by laser powder bed fusion (LPBF). Two body-centered cubic (BCC) lattice structures with unit cell sizes of 2 mm (BCC 2) and 4 mm (BCC 4) were designed while maintaining a constant strut diameter. The measured relative densities were 31.48% for BCC 2 and 8.67% for BCC 4, indicating a significant reduction in density as the lattice size increased. Although the relative densities differed considerably, both lattices exhibited similar microstructural features such as columnar grains, melt pool boundaries, and surface-attached partially melted powders. No distinct thermal influence was observed with varying unit cell size, demonstrating that uniform build quality was maintained regardless of geometric scale under the given LPBF conditions. Compressive testing revealed that BCC 2 exhibited substantially higher compressive strength (58.47±3.23 MPa) than BCC 4 (1.78±0.11 MPa), which was attributed to enhanced structural stability and a higher number of struts and nodes. Digital Image Correlation (DIC) analysis and cross-sectional microstructure observations confirmed that BCC 2 displayed progressive densification and buckling-dominated deformation, while BCC 4 predominantly exhibited bending-dominated failure with localized deformation. Notably, despite the narrower strut spacing in BCC 2, no discernible thermal influence—such as melt pool distortion or grain coarsening—was identified, indicating that the effect of unit cell size on thermal behavior during LPBF processing remained negligible under the given conditions. These findings were discussed in terms of the effects of lattice unit cell size on microstructure, compressive properties, and deformation behavior.