Orientation-dependent fatigue assessment of Ti6Al4V manufactured by L-PBF: Size of surface features and effect

The fatigue behaviour of as-built parts produced by means of Laser-Powder Bed Fusion process (L-PBF) is primarily influenced by the presence of stress raisers on the surface, whose morphology strongly depends on the relative orientation between the surface and the build direction. This study aims to shed light into the factors representing the surface morphology that correlate with the fatigue performance of L-PBF Ti6Al4V specimens manufactured in four different orientations. A Fracture Mechanics-based model based on measurable roughness parameters was employed for the prediction of the fatigue properties in both the finite life and endurance limit regions. The fatigue model considers an initial equivalent defect corresponding to the roughness parameter R-v,R-max. In addition, it includes a geometric factor (F) over bar accounting for the shielding present at the roots of the micro-notches which was calculated starting from profile roughness parameters determined by X-ray Computer Tomography (XCT) scans. The predicted stress-life curves show that the adoption of the maximum profile depth R-v,R-max and the shielding factor (F) over bar yields precise life predictions considering the effect of the surface orientation.