Abstract
Nowadays many materials such as steels, aluminium and titanium alloys can be realised by powder bed solutions melting subsequently powder layers by means of a laser or electron beam (Laser Beam Melting – LBM and Electron Beam Melting – EBM). The microstructure realised by layer-by-layer solidification having high cooling rate cannot be considered isotropic. Therefore, the mechanical properties could be influenced by the building direction. Regarding maraging steel, the study of the influence of the building direction and the heat treatment on the static and axial fatigue strength has been investigated in a previous contribution. A large scatter of the fatigue test results was found because of the presence of detrimental surface and subsurface defects. The aim of this contribution is to present additional axial fatigue test results of maraging steel characterized by different build orientation and providing an analysis of the defects observed at the crack initiation area of the fracture surface.
Highlights
1 Introduction In PBF technologies, such as Selective Laser Melting SLM and Electon Beam Melting (EBM) layers of metal powder are subsequently melted by a laser or an electron beam source in order to obtain the part designed by a CAD software without the typical constraints of traditional manufacturing processes [1,2,3,4]
For each batch the specimens were built with their axis oriented both at 0° and 90° with respect to the building direction that correspond to the translation of the platform which allows the deposition of the subsequent layer during the process
Since it is known that in additive components the residuals stress induced by rapid cooling of the melted zone might cause geometrical distortion, the gross section of each specimens were turned in order to reduce misalignments
Summary
In PBF technologies, such as Selective Laser Melting SLM (or Direct Metal Laser Sintering DMLS) and Electon Beam Melting (EBM) layers of metal powder are subsequently melted by a laser or an electron beam source in order to obtain the part designed by a CAD software without the typical constraints of traditional manufacturing processes [1,2,3,4]. As well-known from [17], the fatigue strength is controlled by the defects having the maximum size and given the complex geometries of the LOF is appropriate to adopt the √area parameter. In some contribution [18], statistics of extreme values has been applied in order to estimate the maximum size of the defect starting from inspection by CT scanning The aim of this contribution is to add axial fatigue results of maraging steel produced by SLM to those previously published [19] and quantify the √area of the defects present at the crack initiation zone of the fracture surface of the specimens by using a Scanning Electron Microscope (SEM)
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