High and very high cycle fatigue failure mechanisms in selective laser melted aluminum alloys
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Selective laser melting, a laser-based additive manufacturing process, can manufacture components with good geometrical integrity. Application of the selective laser melting process for serial production is subject to its reliability on mechanical properties, especially on fatigue behavior, when it is required to be applied for dynamic applications. This study focuses on microstructural, quasistatic, high cycle fatigue (HCF), and very high cycle fatigue (VHCF) mechanisms of aluminum alloys manufactured by selective laser melting. Manufacturing of hybrid structures by selective laser melting process is also investigated. Microstructural features were investigated for process-induced effects and the corresponding influence on quasistatic and fatigue properties. The microstructural features can be controlled in the selective laser melting process for required properties. Joining strengths in hybrid structures can be improved by post process heat-treatments. Material constants in different fatigue regions were determined, and higher fatigue strength of hybrid alloys was achieved in HCF as well as VHCF regimes.
I. INTRODUCTION
In selective laser melting (SLM), micro layers of powder material are consolidated by a laser fusion source, which scans the coated powder layers of the three-dimensional computer-aided design (3D-CAD) model in a chessboard like fashion. Controls of the laser source follow standard tessellation language file format to slice the 3D-CAD model and establish the contours of the current layer above which, a new layer is deposited.1,2 The process schematic is portrayed in Fig. 1(a), which shows that after part slicing, a sequential process starts with the exposure of one powder layer to the laser energy, which fuses the selective layer locations. After selective melting of one layer, the build platform is lowered, equivalent to the thickness of one layer, and a new powder layer is spread by the coater and then exposed to the laser energy. So in this layer-wise fashion, a complete metallic component can be built and then removed from the build platform resulting in a part with near-net shape characteristics without extensive tooling requirements. With vast freeform fabrication capability, tailored medical implants were first of the various fields to tap the capabilities of the new technology.3 This technology along with other emerging processes like electron beam melting (EBM) made low batch and job shop production economic again after the mass production revolution of subtractive and formative manufacturing
Contributing Editor: Mathias Göken a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.314
processes.4,5 With short lead times, less tooling requirements, and extensive functional tailoring capability, additive manufacturing processes seem to be on the way to transform mass production concepts into mass customization ones. Considering functional components, attempts have been made at producing tool inserts for machining processes by the deposition of
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