Effect of gradient direction on the compressive and energy absorption characteristics of Ti-6Al-4V metamaterials

• Directionally graded Ti-6Al-4V TPMS metamaterials (1D, 2D, 3D) were fabricated using PBF-LB with Ti-6Al-4V. • 3D graded gyroid showed the highest elastic modulus (3.36 GPa) and energy absorption. • Grading direction significantly influenced failure modes and mechanical behavior. • Ti-6Al-4V Graded metamaterials closely matched bone-like properties for orthopaedic implants. Triply periodic minimal surface (TPMS) graded lattices have attracted significant interest for biomedical applications owing to their structural efficiency and bone-mimicking mechanical properties. This study introduces a novel design methodology for spatially grading Ti-6Al-4V TPMS lattices, with grading orientations classified as one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D), and fabricated by laser powder-bed fusion (PBF-LB). The primary aim was to evaluate the influence of gradient direction on mechanical response and energy absorption through quasi-static compression testing. The experimental results highlight that the grading orientation plays a crucial role in tailoring lattice performance. At 30 % RD, the 3-D graded gyroid exhibited superior properties with an elastic modulus of 3.36 ± 0.14 GPa and yield strength of 107.93 ± 2.8 MPa, outperforming the 1-D graded gyroid (2.48 ± 0.11 GPa modulus; 78.94 ± 2.2 MPa yield strength). Enhanced energy absorption was also observed for the 3-D grading technique, confirming the advantage of multi-directional density variations. An exception was noted for the 3-D graded diamond at 20 % RD. Overall, graded TPMS lattices enable structural flexibility and mechanical performance comparable to natural bone. The findings provide important insights for designing orthopaedic implants. The developed grading technique has great potential in bone replacement biomaterials.