Effects of porosity gradient pattern on mechanical performance of additive manufactured Ti-6Al-4V functionally graded porous structure

• A method to regulate the porosity gradient pattern of FGPS was developed. • An equation to calculate the mechanical properties of FGPS was developed. • Lattice with solid core structure has the best mechanical properties in all FGPSs. • Failure mechanisms of the lattice with solid core structure were revealed. • Stress protection effect inside the lattice with solid core structure was proposed. Mechanical performance is crucial for lattice structures used in orthopedic applications because they should simultaneously possess high strength and high porosity. Although the additively manufactured Ti-6Al-4 V functionally graded porous structure (FGPS) has proven to be the most promising material owing to its good mechanical performance, the impact of porosity gradient pattern on their mechanical performance has scarcely been investigated. In this study, FGPSs with varied porosity gradient pattern and same overall porosity were designed by triply periodic minimal surface and fabricated by laser powder bed fusion (L-PBF), and their structural and mechanical properties were analyzed. A semi-empirical equation was derived to predict the mechanical properties of FGPSs. Hence, we discovered that the lattice with solid core exhibited the best mechanical performance among all FGPS designs. X-ray microscopy (XRM) analysis revealed a strong relationship between the internal micro-porosity of the L-PBF-fabricated samples and the dimensions of the manufactured components, further proving the rationale of the lattice with solid core design. In situ compression tests under XRM visualized the different failure mechanisms in the porous and dense portion of the lattice with solid core. The strengthening mechanism of the lattice with solid core was further revealed by finite element analysis.