On torsional behavior of 3D printed 17-4 PH-SS-Ni-625-Ti-6Al-4V compositionally graded structures with lattice interlayers for biomedical applications

Powder bed fusion–laser beam (PBF-LB) has emerged as a highly adaptable 3D printing technique for fabricating compositionally graded, multi-material structures with tunable mechanical properties. However, limited studies have been reported on the torsional behavior of such graded structures (fabricated by 3D printing), especially those incorporating lattice interlayers for biomedical load-bearing applications. In this study, compositionally graded specimens were fabricated using PBF-LB, consisting of a 17-4 PH stainless steel (SS) base layer, a Ni-625 intermediate layer, and a Ti-6Al-4V top layer. To improve mechanical performance (under torsion), different interlayer architectures, solid, octet-truss, and Weaire Phelan lattices were introduced within the graded structure. The fabricated samples were characterized using SEM/EDS, porosity, and grain-size analysis. In addition, Thermo-Calc simulations were performed to examine phase stability at multi-material interfaces. Among the topologies, the Weaire-Phelan lattice-based graded structure demonstrated a torsional resistance of 9.7 Nm, comparable to the torque typically required for pedicle screw insertion in lumbar spine applications. The study suggests that incorporating architected lattice interlayers can effectively balance strength and compliance, making these 3D-printed graded structures a viable solution for advanced biomedical applications.