Effect of post treatments on the fatigue properties of EBM Ti-6Al-4VTuesday (26.05.2020) 15:10 - 15:30
Additive manufacturing (AM), can be used to produce complex 3D geometries which offer a large potential for weight reduction. The evaluation of the fatigue properties of such geometries is for the moment a bottleneck for their widespread use. In the literature researchers have extensively evaluated fatigue properties of AM materials on machined samples. During this machining step any defect initially present on the surface is removed (while internal ones might appear on the newly created surface). If this is a reasonable approach for designing components where a minimal machining can be applied to critical areas, in the case of complex geometries (e.g. lattices), the machining step is clearly more difficult if not completely impossible.
The objective of this work is to study the fatigue properties of Ti-6Al-4V thin samples produced by Electron Beam Melting (EBM). These samples are used to mimic the beams which are the "elementary bricks" of lattice structures. Fatigue mechanisms of those elementary struts have been first identified from cyclic tension-tension tests (constant stress amplitude R=0.1) performed on 2 mm diameter hour glass specimens. The geometrical features inherited from the EBM process: porosity, surface irregularities, roughness have been systematically characterized by laboratory X-ray tomography before the fatigue tests. SEM and tomographic observations of the fracture surfaces reveal that crack initiation always occurs at the surface from thin and relatively deep (up to 200 μm) notch-like defects. The fatigue resistance of as-built samples is therefore relatively low . Chemical etching, hot isostatic pressing as well as ultrasonic blasting  have been performed on the as built samples. The effect of those post treatments on fatigue properties are investigated and related to the “healing” of the aforementioned defects.
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