Synchrotron and Neutron Studies of Additive-Manufactured Metallic Nuclear Fusion Components

The current paradigm shift in industry, with the advent of the fourth industrial revolution, is driving increasingly fast evolutions in manufacturing technologies. Amidst the rise and abundance of cyber-physical systems have emerged a wide variety of computer-controlled, layer-wise material processing techniques, technically known as Additive Manufacturing (AM) or, more commonly, 3D-printing. Among AM technologies, Powder Bed Fusion - Laser Beam Melting (PBF-LB/M) and powder-based Laser Directed Energy Deposition (L-DED) have consistently and reliably fulfilled certain novel needs of the industry. In both of these processes, a high-energy laser beam is used to locally melt a micrometric metallic powder in a layer-by-layer fashion, leading upon solidification to the production of components with precise and complex geometries. Metallic AM is a complex thermo-physical process that involves many individual, codependent parameters. Fast dynamics, combined with highly localized temperature gradients and extreme cooling rates, give rise to distinctly out-of-equilibrium transformations and the development of important residual stresses. The complex phenomena involved require equally advanced characterization techniques capable of producing comprehensible results through cross-analysis of various sources. In this context, operando (meaning in-process) characterization at synchrotrons and neutron sources is especially relevant, as it allows to directly correlate the structure and properties of a material with its function or its manufacturing process as it operates, revealing complex mechanisms impossible to see otherwise. MADISON-X (Multimodal Advanced DED Investigation System for Operando Neutron and X-ray science) was therefore developed as a platform for operando studies at large-scale facilities during L-DED of most metallic materials. Designed for a scientific community of users, it is capable of multi-material processing, functional grading, and in-situ alloying of any two metallic powders, and was specially engineered to allow operando X-ray tomography during the L-DED process. Its nozzle can also be swapped with a welding torch for Wire Arc Additive Manufacturing (WAAM) operation. Its construction and current capabilities are presented in this thesis. Multimodal advanced characterization is all-the-more relevant in commissioning AM for nuclear applications, e.g. for the production of fusion reactor plasma facing components (PFCs). Complying with nuclear safety regulations requires an outstanding level of understanding and control of a material's microstructure, only complete with the knowledge provided by experiments at large-scale facilities. This work demonstrates how conventional microstructure characterization techniques (such as EBSD mapping) can miss, or misrepresent deeply embedded structures as in the present case, retained austenite formed in the bulk of a PBF-LB/M ferritic-martensitic steel. The application of PBF-LB/M for PFCs manufact