Localized strengthening of triply periodic minimal surface lattice structures via tuning the internal material distribution at the grain level

Grain coarsening delivers the potential to enhance the multifunctional performances of triply periodic minimal surface (TPMS) structures, such as thermal and electrical conductivity, but it usually results in a weakening effect on the strength of the components. In this research, an abnormal phenomenon of coarse grains and slender walls-induced mechanical strengthening behavior was observed in the stainless steel 316 L TPMS structures fabricated via micro-laser powder bed fusion (μLPBF). The results indicate that a homogenized internal material distribution at the grain level leads to obvious localized strengthening behaviors in the TPMS structures during the localized and densification stage in the compression process. As the grains become coarser or the walls become thinner, the deformation mode of the TPMS structures transforms from the localized collapse deformation to the localized coordinated deformation, in which a homogeneous internal grain distribution is triggered by grain coarsening and wall thinning, promoting a homogeneous stress distribution. Particularly, Diamond (D)-type structures with the middle grains of 25.7 μm in the deformation direction show a 2.32 % enhancement in the energy absorption capacity compared to that of fine-grained (20.2 μm) components. This research outlines a guideline for acquiring an excellent synergy of the mechanical properties and multifunctional performances of the TPMS structures.