The complex geometries feasible with Laser Powder Bed Fusion (PBF-LB/M) lead to varying sizes of scanned cross sections within the layers and hence differing cooling rates. Since PBF-LB/M results in intragranular cell structures, which cause relatively high strengths in the austenitic steel AISI 316L, the influence of changes in the specimen size on the cell structure was investigated. The results obtained from the geometries realized in this work showed no significant influence of the specimen size on the cell sizes. To analyze the relation between the cell structure and the mechanical properties, cyclic indentation tests (CIT) were performed accordingly, revealing no clear influence of the specimen size on the mechanical properties and no correlation between the cell size and the mechanical properties. Additionally, the impact of the cell size on the well-known anisotropy in mechanical properties of AISI 316L produced via PBF-LB/M was investigated. While the cell size was observed to be independent of the specimen orientation on the build plate, the orientation between the direction of loading and the building direction reveals a slight influence on the mechanical properties obtained from CIT. In comparison to the properties determined using CIT, a stronger influence of the orientation between the load and the building direction was observed in tensile tests, which was not caused by the intragranular cells. It was concluded that the anisotropy in the tensile properties is mainly affected by the texture, the elongated grains, and the layer orientation.

Additive manufacturing of metallic components, in particular laser powder bed fusion (PBF-LB/M), is gaining industrial importance due to its geometric design freedom. However, reliable design and fatigue life predictions of additively manufactured (AM) components remain challenging. The FKM-Guideline Nonlinear (FKM-NL) is an established method to assess the fatigue strength of conventionally manufactured components. However, because of the process-related characteristics of AM materials, such as anisotropy in the mechanical properties, defects and the as-built surface, a direct transfer of this approach is only possible to a limited extent. Therefore, this study systematically investigates the applicability of the FKM-NL approach in the high-cycle fatigue (HCF) regime for AISI 316L manufactured by PBF-LB/M. First, orientation-dependent material calculation parameters were determined based on experimental tension/compression fatigue tests conducted on polished specimens. Subsequently, fatigue lives were calculated for experiments with varying orientations between load and build direction, surface condition and specimen geometry. The comparison between calculated and experimentally determined fatigue lives demonstrates an overall good predictive accuracy. However, some systematic deviations were observed, indicating optimization potentials for a modification of the FKM-NL regarding AM materials. It was shown that process-induced defects have a strong influence, but a change in failure mechanism occurs, depending on the orientation, the load type and the surface condition. These aspects must be considered in fatigue strength assessment. Moreover, a need for another surface parameter was identified to consider the as-built surface, that leads to crack initiation at process-induced defects, which cannot be characterized by conventional surface roughness parameters.

Laser-Powder Bed Fusion (PBF-LB/M) allows for the implementation of topology-optimized structures resulting in complex loading conditions beyond uniaxial tension/compression (T/C). Therefore, this work investigated the influence of the load type, i.e., T/C, rotating bending (RB), and torsional (T) loading, on the cyclic deformation behavior, the damage mechanisms, and the fatigue life. Moreover, the interrelating influence of the orientation-dependent fatigue properties was analyzed. Hence, specimens made of AISI 316L with different orientations between the load and build direction were manufactured via PBF-LB/M and were tested under these load types. The results obtained show no significant differences in the cyclic deformation behavior between the load types. However, T/C led to lower cycles to failure (Nf) than RB, while T resulted in the highest Nf. Considering anisotropy, the orientation-dependency of Nf was mostly visible in T/C and only partially in RB, whereas under T no difference was observed. The cause for these observations is the interaction between the anisotropy and the load type and can be partly attributed to changes in the damage mechanisms: while RB led to defect-based and T to defect-free failure for all orientations, T/C resulted in defect-based failure for two orientations and defect-free failure for the other orientation. Furthermore, the results obtained in this work using the physically based lifetime calculation method PhyBaLLIT, which enables an estimation of the S-Nf curves based on the cyclic deformation behavior, show that PhyBaLLIT can be applied to T loading and enables the estimation of the fatigue strength, excluding the influence of defects.