Additive Manufacturing of IN718 superalloys and Characterization

Additive Manufacturing is a modern technique that has been being widely utilized and advancing the massive production to higher efficiency since 1980s which takes advantages from traditional industrial production methods by saving time and lowering cost, simultaneously resolve perplex?ity of the product structure as insurmountable obstacle in fabrication among several fields such as aerospace and automotive. So far, researches have racked that Additive Manufacturing con?sidering rapid solidification contributes distinctions to microstructural characteristics of the final product varying the associated mechanical properties. Among numerous methods, Power Bed Fusion-Laser (PBF-L) is commonly used for metallic alloys as feedstock material. The main ob?jective of this thesis is to demonstrate how Additive Manufacturing with heat treatments will involve the microstructure and improve corresponding mechanical properties of the target mate?rial by contrast to as-build study previously done. The analysis was performed on IN718 Ni-based super alloy in bulk and lattice structure assigned as the counterpart regarding to extraordinary traits such as light-weighting to reduce the amount of redundant materials under fabrication in non-critical region retaining integrity and ability to absorb impact energy due to porosity. The samples were fabricated by CIM 4.0 from powders with solution annealing and ageing rendered in as heat treatments. In this thesis, analysis applied on the bulk and lattice samples is identical and to facilitate the next characterization, all the samples had been cut along xy, xz and diagonal direction to create surfaces for observation. The entire characterizations included identification of phase distribution by using XRD and SEM, with help of chemical composition revealing by EDS on the surfaces before which and more microstructural peculiarity were acquired and compared after etching with performance of same processes. Moreover, Differential Scanning Calorimetry manifests thermal features and solidification information including sequence of phase formation and potential transformation of Inconel 718 super alloys in this project. Ultimately, as for mechan?ical aspects, Vickers hardness test and compression test were performed to discriminate different behaviour under loading and correlate it to the type of structure with help from Politechnico Milano. Consequently, by evaluation of the obtained results from considered aspects and with consideration of the previous as-build study, heat treatments will change the preferential orienta?tion of crystal growth and maintain physical properties as well as chemical composition of IN718 super alloys. Moreover, heat treatments curbed the formation of other phases such as δ and Laves with no detrimental effects and leaves γ matrix and γ′/γ′′ precipitates. They also modified the micorstructure of IN718 where the size of γ′/γ′′ became finer dispersed in γ matrix within grains and coarser γ′′ pinned at the grain boundaries instead of dendrite and inter-dendrite pattern in as-build case, maintaining anisotropy along different directions. It has been proved that the predominant γ′′ phase contributes the most to strength enhancement already formed during heat treatments according to DSC plot. Additionally, the subsequent hardness and compression tests demonstrated that heat treatments will ameliorate mechanical properties of IN718 super alloys due to microstructure evolution. Potential conver