Influence of as-built surface on fatigue strength and notch sensitivity of Ti6Al4V alloy produced by DMLS

Direct Metal Laser Sintering (DMLS) is one of the additive manufacturing technologies involving a metal powder bed and a laser source to obtain components of complex geometry. The fatigue life of an as-built DMLS part is negatively influenced by the rough surface compared to a machined surface. Since most DMLS components are expected to have also stress concentrations, here the combined effect on fatigue of a as-built surface and a geometrical notch in as-built DMLS Ti6Al4V was investigated using a new test methodology. Miniature specimens having three different directions with respect to build direction were fabricated and tested determining the directional fatigue notch sensitivity of as-built DMLS Ti6Al4V Optical inspection of notch surface quality and roughness measurements demonstrated a ranking of the directional notches that inversely correlated to the measured fatigue performance. The link among the curved surface orientation, the peculiar layer-wise additive manufacturing fabrication and the fatigue notch sensitivity is clarified.