Expression of Additive Manufacturing Surface Irregularities through a Flaw-Based Assessment

摘要

Metal additive manufacturing (AM) has progressed from a pure research topic to an indispensable manufacturing process for many industries within the past 15 years. For the space industry, the performance of a variety of products, including structures, antennas, propulsion parts, and optical equipment is being improved through this manufacturing technique. Process-inherent defects are still encountered and may lead to significant safety factors, particularly for highly loaded, mission-critical applications. An analysis of the fatigue properties of AISi10Mg produced by selective laser melting (SLM) has shown that the fatigue strength and fatigue life of machined specimens could be accurately predicted by adopting a defect-tolerant design concept. In details, the fatigue strength appeared to be controlled by the defect with the maximum stress intensity factor (SIF) present in each specimen. The fatigue properties could be predicted by treating the lack-of-fusion defects as short cracks. For near-net-shaped (i.e., not machined) surfaces, a previous investigation studied the influence of building direction, platform temperature, powder layer thickness, surface finish, and heat treatment on fatigue properties of AM AISi10Mg and X-ray computed tomography (XCT) was performed to research the defect population. The work showed that processing parameters and surface treatment influenced fatigue properties, as expected for conventionally produced material. This study conducted an accurate analysis of the subsurface features at the fracture origin of AISi10Mg specimens, manufactured by SLM and treated with different surface finish. On the basis of these results, a simple fracture mechanics assessment inside the Kitagawa diagram is proposed, which relies on the size of critical defects and the residual stress obtained on the surface. The applicability of this approach to define the quality of AM material in the near-net-shaped condition is discussed.