Abstract
Binder-jetting is an additive manufacturing process for metals which involves the rapid making of a binder bonded metal powder part followed by the removal of the binder and creation of a fully dense part in a subsequent sintering step. This emerging process has the potential of high cost efficiency as compared to selective laser melting (SLM) or shaped metal deposition. Here, we determine the rate-dependent plasticity and fracture properties of binder-jetted stainless steel 316L. Electron Back-Scattered Diffraction (EBSD) analysis and tomography revealed an equi-axed grain structure with an initial porosity of 3%. The latter is due to pores with an average size of 20μm that are clustered in layers perpendicular to the build direction. The observed stress-strain curve of the binder-jetted material always lies below that of wrought stainless steel 316L with a 50% lower initial yield stress and a 30% lower ultimate strength. Both the material anisotropy and strain rate sensitivity may be considered as second order effects in that comparison. The equivalent plastic strain obtained from fracture experiments for different stress states is also always lower for the binder-jetted material. The observations for the binder-jetted material therefore stand in stark contrast to those for SLM-made stainless steel which can provide an even higher yield strength than the wrought material. From a mechanism point of view, the low mechanical properties of the binder-jetted material may be explained by the high initial porosity which is reminiscent of cast metals.
Highlights
Over the last decade, Additive Manufacturing (AM) techniques have become a field of major interest both in research as well as in industrial applications
Representative micro-CT images are shown in Fig. 3 for a sample whose cylinder axis was aligned with the build direction
The overall porosity content is about 3% of the total sample volume with most of the pores exhibiting a radius between 10μm and 20μm
Summary
Additive Manufacturing (AM) techniques have become a field of major interest both in research as well as in industrial applications. Kumar et al ([16]) investigated the tensile response and high-cycle fatigue of binder jetted 316L and compared it to SLM and conventionally manufactured (hot-rolled and air-cooled) counterparts. They found a high degree of similarity between the binder jetted and the hot rolled material, especially with respect to the hardening and fatigue response, which is explained by the similarities in the planar slip deformation mechanism and the absence of severe local thermal gradients during the manufacturing process Another noteworthy aspect is the transformation of austenite to martensite induced by plastic deformation [17]. The strain rate and stress-state dependent plasticity and fracture properties of binder jetting manufactured stainless steel 316L are investigated. A modified Johnson-Cook type plasticity model with a Hill’ non-associated flow rule and a Hosford-Coulomb fracture initiation model are identified based on the experimental results
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