Additive manufacturing of metastable beta Ti-Nb-Fe-Sn alloys with tuned mechanical properties for biomedical implants: Processing-structure-property relationships and alloy selection for implant design

Abstract

The development of femoral stems for hip implants with a gradient in chemical composition offers a promising strategy to mitigate the stress shielding effect by tailoring mechanical properties along the stem. To identify optimal alloy compositions, comprehensive experimental characterization is essential. In this study, ten distinct alloys of the metastable beta Ti-Nb-Fe-Sn alloy family were fabricated using powder bed fusion via laser beam (PBF-LB) under nine different processing conditions. The printed specimens were systematically investigated to determine the most favorable conditions for further development of a compositionally graded implant. Microstructural analysis revealed that processing at 100 mm/s scan speed and 100 W laser power yielded equiaxed grains and homogeneous composition. Elastic properties determined by resonant ultrasound spectroscopy showed a composition-dependent Young's moduli ranging from similar to 60 to 100 GPa. Microhardness results indicated strengthening of single phase beta material by Fe additions with values between similar to 250 and 320 HV. These findings demonstrate that PBF-LB can produce Ti-Nb-Fe-Sn alloys with tunable properties suitable for graded implant design, providing low modulus compositions for the distal side (inserted into the bone) and high strength on the proximal side (neck).