Alloy 718 manufactured by AM Selective Laser Melting : Evaluation of microstructure and weldability

Abstract: Inconel 718 is one of the main superalloys that are used in hot structures of jet engines today, because of its excellent mechanical properties at high temperatures and its good weldability. This material has been extensively used and studied in cast and wrought forms during the past decades. However, the amount of information on how alloy 718 is affected by Selective Laser Melting is still scarce. The goal of the project was to investigate the microstructure and mechanical properties of a Rear Turbine Component Bleed Panel, prior to and following a series of heat treatment procedures. The Bleed Panel was produced from a gas atomized Inconel 718 superalloy powder, by a Selective Laser Melting process. During the course of the project, other SLM 718 parts were also investigated, in order to obtain a more comprehensive knowledge on how the SLM process affects the material. The weldability of SLM 718 was investigated by performing bead-on-plate welds on different sections. SLM 718 components and welds passed the non-destructive tests. Cut-up and thermal processing procedures were then executed on the bleed panel, yielding samples with different microstructures. It was concluded that a homogenization (or a HIP) processing must be applied to SLM 718 components to remove the columnar grain structure. During examination of the samples, particle-filled small defects were noticed. Using EDS, it was determined that the defects were filled with aluminum-rich oxides. SLM 718 in aged condition exhibited higher average hardness than both cast and wrought 718.