TY - CONF A1 - Ulbricht, Alexander T1 - Evolution of Creep Damage of 316L Produced by Laser Powder Bed Fusion N2 - The damage mechanisms of metallic components produced by process laser powder bed fusion differ significantly from those typically observed in conventionally manufactured variants of the same alloy. This is due to the unique microstructures of additively manufactured materials. Herein, the focus is on the study of the evolution of creep damage in stainless steel 316L specimens produced by laser powder bed fusion. X-ray computed tomography is used to unravel the influence of the process-specific microstructure from the influence of the initial void distribution on creep damage mechanisms. The void distribution of two specimens tested at 600 °C and 650 °C is analyzed before a creep test, after an interruption, and after fracture. The results indicate that the formation of damage is not connected to the initial void distribution. Instead, damage accumulation at grain boundaries resulting from intergranular cracking is observed. T2 - Annual International Solid Freeform Fabrication Symposium CY - Austin, TX, USA DA - 14.08.2023 KW - AISI 316L KW - Additive Manufacturing KW - Computed Tomography KW - Creep KW - Laser Powder Bed Fusion KW - Microstructure KW - PBF-LB/M/316L PY - 2023 AN - OPUS4-58285 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ulbricht, Alexander T1 - Formation of Creep Damage of 316L Produced by Laser Powder Bed Fusion N2 - The damage mechanisms of metallic components produced by process laser powder bed fusion differ significantly from those typically observed in conventionally manufactured variants of the same alloy. This is due to the unique microstructures of additively manufactured materials. Herein, the focus is on the study of the evolution of creep damage in stainless steel 316L specimens produced by laser powder bed fusion. X-ray computed tomography is used to unravel the influence of the process-specific microstructure from the influence of the initial void distribution on creep damage mechanisms. The void distribution of two specimens tested at 600 °C and 650 °C is analyzed before a creep test, after an interruption, and after fracture. The results indicate that the formation of damage is not connected to the initial void distribution. Instead, damage accumulation at grain boundaries resulting from intergranular cracking is observed. T2 - 4th Symposium on Materials and Additive Manufacturing - Additive 2024 CY - Berlin, Germany DA - 12.06.2024 KW - AISI 316L KW - Additive Manufacturing KW - Computed Tomography KW - Creep KW - Laser Powder Bed Fusion KW - Microstructure KW - PBF-LB/M/316L PY - 2024 AN - OPUS4-60295 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schröder, Jakob T1 - Laser Powder Bed Fusion: Fundamentals of Diffraction-Based Residual Stress Determination N2 - The general term additive manufacturing (AM) encompasses processes that enable the production of parts in a single manufacturing step. Among these, laser powder bed fusion (PBF-LB) is one of the most commonly used to produce metal components. In essence, a laser locally melts powder particles in a powder bed layer-by-layer to incrementally build a part. As a result, this process offers immense manufacturing flexibility and superior geometric design capabilities compared to conventional processes. However, these advantages come at a cost: the localized processing inevitably induces large thermal gradients, resulting in the formation of large thermal stress during manufacturing. In the best case, residual stress remains in the final parts produced as a footprint of this thermal stress. Since residual stress is well known to exacerbate the structural integrity of components, their assessment is important in two respects. First, to optimize process parameter to minimize residual stress magnitudes. Second, to study their effect on the structural integrity of components (e.g., validation of numerical models). Therefore, a reliable experimental assessment of residual stress is an important factor for the successful application of PBF-LB. In this context, diffraction-based techniques allow the non-destructive characterization of the residual stress. In essence, lattice strain is calculated from interplanar distances by application of Braggs law. From the known lattice strain, macroscopic stress can be determined using Hooke’s law. To allow the accurate assessment of the residual stress distribution by such methods, a couple of challenges in regard of the characteristic PBF-LB microstructures need to be overcome. This presentation highlights some of the challenges regarding the accurate assessment of residual stress in PBF-LB on the example of the Nickel-based alloy Inconel 718. The most significant influencing factors are the use of the correct diffraction elastic constants, the choice of the stress-free reference, and the consideration of the crystallographic texture. Further, it is shown that laboratory X-ray diffraction methods characterizing residual stress at the surface are biased by the inherent surface roughness. Overall, the impact of the characteristic microstructure is most significant for the selection of the correct diffraction elastic constants. In view of the localized melting and solidification, no significant gradients of the stress-free reference are observed, even though the cell-like solidification sub-structure is known to be heterogeneous on the micro-scale. T2 - 4th Symposium on Materials and Additive Manufacturing CY - Berlin, Germany DA - 12.06.2024 KW - Additive Manufacturing KW - Residual Stress KW - Electron Backscatter Diffraction KW - Laser Powder Bed Fusion PY - 2024 AN - OPUS4-60294 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schröder, Jakob T1 - Neutron Diffraction Based Residual Stress Analysis of Additively Manufactured Alloys N2 - Additive manufacturing methods such as laser powder bed fusion offer an enormous flexibility in the efficient design of parts. In this process, a laser locally melts feedstock powder to build up a part layer-by-layer. It is this localized processing manner imposing large temperature gradients, resulting in the formation of internal stress and characteristic microstructures. Produced parts inherently contain high levels of residual stress accompanied by columnar grain growth and crystallographic texture. On a smaller scale, the microstructure is characterized by competitive cell-like solidification with micro segregation and dislocation entanglement. In this context, it is crucial to understand the interplay between microstructure, texture, and residual stress to take full advantage of the freedom in design. In fact, X-ray and neutron diffraction are considered as the benchmark for the non-destructive characterization of surface and bulk residual stress. The latter, characterized by a high penetration power in most engineering alloys, allows the use of diffraction angle close to 90°, enabling the employment of a nearly cubic gauge volume. However, the complex hierarchical microstructures produced by additive manufacturing present significant challenges towards the reliable characterization of residual stress by neutron diffraction. Since residual stress is not the direct quantity being measured, the peak shift imposed by the residual stress present in a material must be converted into a macroscopic stress. First, an appropriate lattice plane must be selected that is easily accessible (i.e., high multiplicity) and insensitive to micro strain accumulation. Second, a stress-free reference must be known to calculate a lattice strain, which can be difficult to define for the heterogeneous microstructures produced by additive manufacturing. Third, an appropriate set of diffraction elastic constants that relate the lattice strain to the macroscopic stress must be known. In this presentation, advancements in the field of residual stress analysis using neutron diffraction are presented on the example of the Ni-based superalloy Inconel 718. The effect of the complex microstructure on the determination of residual stress by neutron diffraction is presented. It is shown, how to deal with the determination of the stress-free reference. It is also shown that the selection of an appropriate set of diffraction elastic constants depends on the microstructure. Finally, the role of the crystallographic texture in the determination of the residual stress is shown. T2 - Deutsche Neutronenstreutagung CY - Aachen, Germany DA - 16.09.2024 KW - Additive Manufacturing KW - Neutron Diffraction KW - Electron Backscatter Diffraction KW - Laser Powder Bed Fusion PY - 2024 AN - OPUS4-61476 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -