University of Twente Student Theses


Additive Manufacturing of Inconel 718 for Aerospace Applications : Towards Process-Microstructure-Property relationships

Hooghiemster, A. (2021) Additive Manufacturing of Inconel 718 for Aerospace Applications : Towards Process-Microstructure-Property relationships.

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Embargo date:18 February 2025
Abstract:Additive manufacturing (AM) opens up new worlds of design freedom, enabling the rapid and mouldfree production of complex parts for various industries, including the aerospace industry. Laser powder bed fusion (L-PBF) is an AM process capable of manufacturing complex-shaped parts by melting metallic powder using a laser, in a layer by layer fashion, directly from a Computer-aided design (CAD) model. In recent years the field of AM employing L-PBF has advanced rapidly. The quality of the produced parts is approaching the level required by the aerospace industry, mainly through advances in process control and process monitoring. Hence, the emphasis on the development of the L-PBF process may change from process control to microstructure control in order to prevent inconsistencies in the mechanical properties of complex-shaped aerospace parts. This research project explores the relations between the process conditions, the development microstructure and the (mechanical) properties of a complex-shaped aerospace part employing Inconel 718, which is a well-known creep resistant, weldable and corrosion-resistant nickel-based superalloy. The influence of different geometrical features (i.e. overhangs, thin or thick sections and complex shapes), located within the complex aerospace part, on the microstructure and (mechanical) properties was studied. Also, the influence of a post-manufacturing heat treatment on the resulting microstructure and (mechanical) properties was included. The examined aerospace part showed gas-induced porosity, lack of fusion and micro-scaled cracks close to the surface. Gas-induced porosity type was predominant, but the local density of the aerospace part was according to the requirement of 8.1 g/cm3. Large variations in surface roughness between different surfaces appeared. These were larger than the requirement of 3.175 mm, except for the horizontal surface. Down-skin surface showed the highest average surface roughness of 21.3 mm, compared to the lowest on the horizontal surface of 2.5 mm. The as-built parts showed an inhomogeneous dendritic microstructure comprising in general columnar grains, oriented mostly parallel to the build direction. The grains extend through multiple as-deposited layers, due to epitaxial growth. The differences in local process conditions led to variations in the mechanical properties of the different geometrical features as observed through hardness measurements. After the post-manufacturing heat treatment, the samples showed a considerable increase in the hardness, with an average increase of 33 %. Moreover, the variations in hardness of the different geometrical features were also removed, yielding a part with almost uniform mechanical properties. Apparently, the post-manufacturing heat treatment is not only a powerful treatment to enhance the mechanical properties, but it also removes inhomogeneities in the mechanical properties, which are almost inevitable during manufacturing of products with complex features.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
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