Rate-dependent strength and ductility of binder jetting 3D-printed stainless steel 316L: Experiments and modeling

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.