Implications of additive manufacturing processes and design complexity on long-term material behavior

Additive manufacturing (AM) technologies have developed rapidly from the 1980s prototyping applications and are becoming an established manufacturing method of today. In contrast to traditional manufacturing, AM enables producing parts with unprecedented levels of geometrical complexity. The increased freedom of design translates into functional, operational, and economic benefits. However, the AM principle of material addition and solidification in layers creates material anisotropies. Fast cooling rates and complex thermal histories result in unique microstructures, in-process defects, and residual stresses. Furthermore, the advantage of geometrical complexity is not without consequences. The size and shape of part features inversely influence the manufacturing process. Fine features in geometrically complex parts can induce local microstructure variation and lead to unexpected failure modes. Extending the application space and part optimization potential of AM to safety-critical components requires a better understanding of how complex geometries and process-induced effects may influence the long-term environmental durability of end-use parts. The dissertation contributes to the cause with exploratory studies where the environmental durability of AM materials is assessed in the context of plastic material weathering and metal corrosion. In addition, a large part of the contribution is linked to method development for microcomputed X-ray tomography. The work focuses on powder bed fusion, a technique most prevalently used across industries. The AM process and part orientation influence on plastic degradation is studied with accelerated weathering, tensile testing, and fractography on simple geometries. In the study of corrosion, the evaluation is extended to geometrical complexity. Lattice structures, with identical units repeating in three dimensions, are employed to reveal any relations between part size or shape with corrosion susceptibility. The weathering durability of AM plastics was not found to alter significantly due to a varying build orientation. In contrast, the corrosion experiments suggested a higher susceptibility to localized corrosion for the finest wall-thickness lattice structures, although, noise sources in the novel experimental setup hindered numerical validation. In this regard, the method requires further development. Nevertheless, the time-lapse microcomputed X-ray tomography workflow enables localization, indexing, and characterization of minute corrosion-induced changes. Furthermore, the same method is applicable to other research fields.