Study of the as-built and post-processed Inconel 939 alloy produced by laser powder bed fusion

This thesis deals with the study of the Ni-based superalloys Inconel 939 (IN939) processed by Laser Powder Bed Fusion (LPBF). This is an Additive Manufacturing (AM) process that allows obtaining the final components by a layer-by-layer process, using a 3D model. This process is useful to obtain components with complex geometry in a single process, reducing costs, time and obtain parts with a lower weight than traditional technologies. IN939 is a Ni-based superalloy particularly suitable for applications at high temperatures and it can be a good candidate for aeronautical turbine blades. IN939 has excellent mechanical characteristics and resistance to corrosion and oxidation at high temperatures, keeping its microstructure stability up to around 850 °C. At the beginning, various combinations of process parameters like laser power, scanning speed, hatching distance were employed. The percent of defects were evaluated for the different conditions to determine the best set of process parameters. For all the conditions, the material showed cracks formation mainly along the grain boundaries. It was performed a Hot isostatic pressing (HIP) on a condition with a low presence of defects in order to close the cracks and porosity. It seems that HIP is effective in close the cracks and reduce the porosity under 0.1 %. Afterward, it was studied the microstructure and hardness of the samples subjected to solutioning and different aging steps. The solutioning was carried out at a temperature of 1160 °C for 4 hours. This heat treatment helps to dissolve a fraction of the carbides within the austenitic gamma matrix, reducing the hardness with respect to the HIP condition. The last treatments were two aging steps, the first at 1000 °C for 6 hours and the second at 800 °C for 4 hours. These aging steps mainly involved the formation of gamma prime phases, increasing the mechanical properties of the alloy. The formation of phases allows reaching a Brinell hardness of around 376 after the second aging step.