LPBF-fabricated superelastic Ti–Zr–Nb open cell lattice structures for orthopedic implants: Process optimization, geometric conformity, microstructure, static and fatigue mechanical behavior

Additively manufactured orthopedic implants are required to simultaneously offer a high geometric accuracy, a low elastic modulus, and an excellent fatigue resistance. In this study, we optimized laser powder bed fusion (LPBF) process parameters to fabricate three open cell lattice structures from a superelastic Ti-Zr-Nb alloy: a rhombic dodecahedron, a sheet gyroid, and a Voronoi polyhedral. In these structures, the strut thickness ranged between 200 and 400 μm and the functional porosity, between 65 and 80%. Geometric conformity and defect porosity were quantified using microcomputed tomography, revealing that the optimized processing limited the maximum deviations in functional porosity to 9%, with the gyroid architecture demonstrating the highest dimensional accuracy. At the same time, the defect porosity in all the structures did not exceed 0.2%. After the heat treatment, microstructural analysis and mechanical testing confirmed the presence in these structures of metastable β-phase. Under quasi-static compression, the lattice specimens manifested a yield plateau associated with stress-induced martensitic transformation. Fatigue testing of Ti-Zr-Nb structures demonstrated a stable cyclic performance and competitive fatigue resistance up to 5×10 6 cycles as compared to their benchmark Ti-6Al-4V counterparts. The results obtained highlight the potential of LPBF-fabricated superelastic Ti-Zr-Nb lattice specimens for load-bearing implant applications, owing to their reduced stiffness and enhanced long-term mechanical durability.