Additively manufactured Ti-6Al-4V thin struts via laser powder bed fusion: Effect of building orientation on geometrical accuracy and mechanical properties

Porous metal lattice structures have a very high potential in biomedical applications, setting as innovative new generation prosthetic devices. Laser powder bed fusion (L-PBF) is one of the most widely used additive manufacturing (AM) techniques involved in the production of Ti6Al4V lattice structures. The mechanical and failure behavior of lattice structures is strongly affected by geometrical imperfections and defects occurring during L-PBF process. Due to the influence of multiple process parameters and to their combined effect, the mechanical properties of these structures are not yet properly understood. Despite the major commitment to characterize and better comprehend lattice structures, little attention has been paid to the impact that single struts have on the overall lattice properties. In this work, the authors have investigated the tensile strength and fatigue behavior of thin L-PBF Ti6Al4V lattice struts at different building orientations (0°, 15°, 45°, and 90°). This investigation has been focused on the effect that microstructural defects (particularly porosity) and actual surface geometry (including surface texture and geometrical errors such as varying cross-section shape and size) have on the mechanical performances of the struts in relation to their building direction. The results have shown that there is a tendency, particularly for low printing angles, of fatigue life to decrease with decreasing of the building angle. This is mainly due to the surge in surface texture and loss in cross-sectional regularity. On the other hand, the monotonic tensile test results have shown a low sensitivity to these factors. The strut failure behavior has been examined employing dynamic digital image correlation (DIC) of tensile tests and scanning electron imaging (SEM) of the fracture surfaces.