National Aerospace Laboratory NLR
Round specimens of AlSi10Mg, Ti-6Al-4V and Inconel 718 are printed with laser-powder bed fusion (L-PBF) and machined & polished to obtain the bulk material fatigue lives and exclude influences from surface roughness or porosity between the hatch and the contour lines. The fatigue lives give information on material properties and the maximum of the defect distribution inside specimens. Tensile and fatigue specimens are printed with different settings, because the mechanical properties and defect distribution can vary with build parameters, location & orientation and post processing. The long axis of the specimens are printed in three orientations with respect to the build direction. The results for Inconel 718 are compared with results from fatigue tests on Inconel 718 plate material that received a similar heat treatment. The results show significant higher fatigue lives for the printed material in all three orientations compared to the fatigue tests on Inconel 718 plate material and results from literature, despite the presence of typical defects such as porosity. Fractography and microstructural analysis indicate that the higher fatigue lives likely originate from the subcellular microstructure. The specimens of Ti-6Al-4V show lower fatigue lives compared to those of plate material in literature due to the presence of typical L-PBF defects such as porosity. Fractography on Ti-6Al-4V and AlSi10Mg specimens allowed to establish a fracture mechanics informed relationship between the size of surface defects, the applied stress and fatigue life. Hence, this general relationship can be used to determine the effect of defects on the fatigue life
Abstract
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