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Anisotropy and Local Property Evolution of WAAM 316L and 17-4PH During Low-Cycle Fatigue

Additive manufacturing (AM) offers significant advantages in terms of design freedom and topological optimization as well as the possibility to vary the material properties locally. Thus, AM is a promising solution for producing complex and multifunctional high-performance components. However, the inherent layer-by-layer manufacturing process results in a unique microstructure and a strong dependency of the material properties on the orientation to the building direction. Especially for the design of cyclically loaded components, this mechanical anisotropy is highly relevant. Moreover, the impact of the cyclic loading on the local material properties, e.g. electrical and magnetic properties, needs to be understood in the context of multifunctionality. To gain a sound knowledge on that,…

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Additive manufacturing (AM) offers significant advantages in terms of design freedom and topological optimization as well as the possibility to vary the material properties locally. Thus, AM is a promising solution for producing complex and multifunctional high-performance components. However, the inherent layer-by-layer manufacturing process results in a unique microstructure and a strong dependency of the material properties on the orientation to the building direction. Especially for the design of cyclically loaded components, this mechanical anisotropy is highly relevant. Moreover, the impact of the cyclic loading on the local material properties, e.g. electrical and magnetic properties, needs to be understood in the context of multifunctionality. To gain a sound knowledge on that, advanced characterization techniques for capturing these local phenomena are required.
The presented work, which is part of the Collaborative Research Centre / Transregio (TRR) 375, investigates the process-structure-property relationship of specimens manufactured by Wire and Arc Additive Manufacturing (WAAM) using the two CrNi-steels 316L and 17-4PH. Moreover, the influence of the process-induced anisotropy on the low-cycle fatigue (LCF) behaviour as well as on the load-induce changes in electrical and magnetic properties was investigated. Therefore, for each material, three different directions of the build orientation to the loading direction were tested, i.e., parallel, in 45° and perpendicular.
As expected, the results show higher LCF strength for the 17-4PH specimens than for the 316L specimens, which can be attributed to their smaller grain sizes as well as the higher fractions of δ-ferrite and martensite. Moreover, both materials demonstrate a pronounced anisotropy in fatigue life, which is directly linked to the loading orientation, and is a result of the anisotropic microstructure caused by the manufacturing process. In-situ Digital Image Correlation (DIC) revealed that this mechanical response corresponds to anisotropic strain localization, which develops along the preferential grain orientations. In addition to mechanical testing, the evolution of local magnetic and electric changes was characterized in different stages of the fatigue life. These measurements show a continuous increase in magnetic phase content and electrical resistivity at cyclic loading, which can be partly contributed to the deformation induced transformation of austenite into α´-martensite. The observed changes in magnetic and electrical properties furthermore exhibit local variations that spatially correlate with the strain localizations identified by DIC, establishing a direct link between microstructural evolution and localized plastic deformation.

Reference
LCF10-2026-019

Title
Anisotropy and Local Property Evolution of WAAM 316L and 17-4PH During Low-Cycle Fatigue
Author(s)
M. A. Hoffmann, M. Faßhauer, T. Hassel, T. Beck, B. Blinn
DOI
10.48447/LCF10-2026-019
Event
Tenth International Conference on Low Cycle Fatigue (LCF-10)
Year of publication
2026
Publication type
conference paper (PDF)
Language
English
Keywords
Wire and Arc Additive Manufacturing (WAAM),Low-Cycle Fatigue (LCF),Digital Image Correlation (DIC),Electrical and Magnetic Properties,Mechanical Anisotropy