High-productivity PBF-LB/M processing of Ti–Nb–Ta alloys: tailoring microstructure and phase evolution for low-modulus orthopedic implants

Abstract

Abstract Metallic bone implants with a high Young’s modulus can cause stress shielding, leading to bone resorption and long-term failure. β-stabilized titanium alloys have been widely explored to overcome this limitation due to their lower elastic stiffness. In this study, Ti-20Nb-6Ta and Ti–35Nb–6Ta alloys were produced by Powder Bed Fusion Laser Beam of Metals (PBF-LB/M) using increased layer thicknesses to improve productivity while preserving suitable microstructural and mechanical performance. A systematic parametric investigation defined optimized conditions for 30 µm and 150 µm layers, including geometries representative of orthopedic devices. Microstructural, textural, and thermal analyses indicated that thicker layers intensified interlayer heat accumulation, promoting in-situ thermal effects and modified phase transformation routes. For Ti–20Nb–6Ta, the larger layer thickness stimulated decomposition of metastable α″ and formation of α + β microstructures, increasing tensile strength. Conversely, Ti–35Nb–6Ta remained predominantly β, resulting in greater ductility and lower modulus. At 150 µm, both alloys developed strong ⟨001⟩ cube textures parallel to the build direction, contributing to reduced elastic stiffness. Dilatometry and X-ray diffraction confirmed layer-dependent phase evolution, while electron microscopy showed columnar grains aligned with the build direction. Tensile tests demonstrated that Young’s modulus reached values as low as 50 GPa for Ti–35Nb–6Ta. The combination of reduced stiffness in Ti–35Nb–6Ta and higher strength in Ti–20Nb–6Ta highlights the potential of these alloys for the future development of functionally graded orthopedic implants. Overall, adopting a 150 µm layer thickness represents a promising route to enhance PBF-LB/M productivity without compromising structural integrity or biomechanical compatibility.