EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The use of additive manufacturing to fabricate metallic components following design optimization as well as the full Design for Additive Manufacturing (DfAM) paradigm, is now a consolidated reality. The ASTMF42 and ISOTC261 -defined powder bed fusion (PBF) and directed energy deposition (DED) processes are able to build metallic components using layer-upon-layer strategies, which are characterized by peculiar features. In the present study, two laser-based equipment from Prima Additive were used to fabricate samples starting from a micrometric pre-alloyed metal powder of 316L stainless steel. During the laser powder bed fusion (LPBF) process, powder particles in the range of 10-45 µm are spread on a building plate by a recoater blade and selectively fused by a laser source, while during the powder-DED process, particles with a diameter between 45 µm and 106 µm are injected through the path of a high-energy laser and deposited on the surface of interest as a molten metal. The main differences between the two process stand in the powder dimensions, energy input and overall speed of the process. These have a great influence on the final properties of the fabricated parts and on their microstructure, since LPBF has a resulting cooling rate which goes up to 106 K/s, while DED stand in the 103-105 K/s range. By using a wide range of characterization techniques, from optical and scanning electron microscopy (OM, SEM) to microhardness, energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), the present study shows that it is possible to tailor the process parameters (overlap/hatch spacing, layer thickness, build rate, laser power) and post-process parameters (i.e. time and temperature during heat treatments) in order to reach a unique microstructural and metallurgical configuration, without changing the crystallography and the chemical composition of the starting 316L stainless steel alloy.