Effects of Surface Preparation, Support Structures and Build Orientation on the Cyclic Stress-Strain Behavior of Inconel®718 Produced by SLM

The flexibility in design offered by advanced additive manufacturing technologies makes these processes more and more attractive for automotive and aircraft applications and, also, for the production of safety relevant metal components. The high strength, thermally resistant nickel-based alloy Inconel®718 is widely used by the aircraft industry and its low level of machinability makes it an optimal candidate for AM technologies. The challenge, together with improving the process, is now to build the path that will bring AM technologies from rapid prototyping to series production. Therefore, it is essential to investigate additively manufactured materials and the effect that subsequent processing, such as, for example surface preparation, has on their properties. Furthermore, while the static properties of additively manufactured Inconel®718 have already been investigated, this work aims to describe its cyclic stress-strain behavior, which can be used for fatigue assessment. Small scale flat specimens, produced by Selective Laser Melting (SLM) of Inconel®718 powder, are subjected to Incremental Step Tests in order to evaluate the cyclic stress-strain behavior of the material. To state the initial situation, specimens oriented along different directions with respect to the build platform are produced using standard process parameters. Individually adapted support structures, when needed, are subsequently removed and portions of the specimens are left in the as-built state, while others are subjected to mechanical polishing or to electrochemical polishing. The effects of surface preparation, support structures removal and build orientation on the cyclic stress-strain behavior of the material are evaluated and discussed.