Laser powder bed fusion (LPBF) is one of the leading AM technologies to process metallic materials. It enables the fabrication of patient specific implants and new implant designs that are not feasible with conventional manufacturing technologies. A majority of current research regarding LPBF of titanium alloys focusses on Ti-6Al-4V as it is widely used as implant material. However, beta-type Ti-(40-45 wt.%)Nb alloys are promising materials to replace Ti-6Al-4V owing to their low Young’s modulus and their excellent biocompatibility and corrosion resistance. This work illustrates different approaches to tailor the mechanical properties of the beta-type Ti-42Nb alloy by LPBF.

The first approach involves the specific adjustment of LPBF process parameters to control the microstructure and thus the mechanical anisotropy of bulk samples. Samples with a high relative density (>99%) and a pure beta-type microstructure were obtained for a broad processing window. However, the resulting grain size, grain morphology and texture vary widely depending on process parameters. Tensile tests of specimens with different orientations, with respect to the building direction (BD), were conducted to study the mechanical behavior. Samples with a nearly isotropic microstructure show only a small influence of the testing direction on the Young’s modulus. In contrast, for samples with a strong (001)-texture in BD and coarse columnar grains, the Young’s modulus measured parallel to BD is significantly lower than for other tensile test directions. This enables the fabrication of patient-specific implants with an adapted low Young’s modulus along the main loading direction.

In a second approach, triply periodic minimal surface (TPMS) designs are used to produce open porous scaffolds by LPBF. Gyroid and Schoen I-WP lattices designed with cell sizes ranging from 4 mm to 1.3 mm and a solid volume fraction of 25% were fabricated. Computed tomography (CT) scans reveal a clear dependence of the dimensional accuracy of the as-built lattices from the cell type and size. Higher deviations are observed for I-WP lattices and for smaller cell sizes. In addition, the applied LPBF processing parameters also have a major influence on the dimensional accuracy and geometrical imperfections. Under uniaxial compression loading, all lattice structures show a high ductility, an exceptionally low stiffness, and a high yield strength, which makes them suitable candidates for implant applications.

The authors gratefully acknowledge funding from the German Research Foundation (DFG) within the framework of the research projects GE1106/12-1 and ZI/1006/16-1 (no 419952351).