Surface texture optimization of Ti-6Al-4V AM-built components for biomedical applications

Additive Manufacturing (AM) is gaining traction in the production of medical devices due to its ability to generate patient-matched parts with irregular geometries and/or dimensions designed for a specific patient's anatomy. Nevertheless, AM-built parts have the inherent characteristic of as-printed rough surfaces, packed with surface and near-surface defects. Common surface defects found on AM surfaces are partially melted/sintered powder, v-notches, remnants of melt pools (fish scaling), and remaining support structures, all of which can cause undesirable effects. For example, deep valleys on the surface can be a host of corrosion sites associated with fretting, crevice corrosion, and pitting corrosion. Partially attached/sintered powder at the surface causes cleanliness problems on the component if not eliminated during post-processing, and loose powder can leach out of the component once it is fully implanted. Likewise, the presence of high surface roughness and deep notches compromises the mechanical properties of the as-built components and can lead to detrimental effects especially on fatigue properties. Moreover, the sub-surface porosity often found near the surface caused by non-optimized process parameters on the hatching and contour scans can reduced the components' performance. One way to improve the mechanical performace of AM-built medical components to meet industry standards is to improve their as-printed surfaces. However, due to the complexity of some AM-built parts, traditional surface finishing methods cannot be considered. This paper will review and discuss the surface features associated with early fatigue failures on AM-built components, and surface finishing techniques that can be employed to overcome these challenges. The surface texture improvement via a combination of surface finishing methods was studied on Ti-6Al-4V built by powder bed fusion. Tensile strength and high cycle fatigue experiments were performed at different surface finishing levels to understand the implications of the surface texture on the mechanical performance of the AM-built Ti-6Al-4V components.