Additive Manufacturing (AM) promises high potentials and new possibilities for manufacturing of complex parts subjected to variable loadings. Due to high freeform capability, e.g. complex lightweight structures or internal cooling structures, optimized to individual applications, can be realized. Furthermore, AM enables the possibility to locally influence the materials properties with regard to application. To exploit the whole potential of AM, it is necessary to investigate the materials properties of additively manufactured (AM-) structures and to understand their correlation with manufacturing parameters.
In the present work, the influence of the building direction in AM processes and chemical composition of the used ingot powder on the mechanical properties and especially on the fatigue behavior of Selective Laser Melted (SLM) and Laser Deposition Welded (LDW) AISI 316L specimens is investigated. Especially, the microstructure and mechanical properties of horizontally (layer planes perpendicular to loading direction) and vertically built specimens (layer planes parallel to loading direction) are compared and discussed.
Cyclic microindentation tests (PhyBaLCHT) according to Kramer et al.  were performed to investigate the cyclic properties of the differently manufactured structures. To evaluate the fatigue behavior of the differently manufactured specimens under different loading levels, load increase tests (LITs) were conducted. The results were verified against S-N-curves from constant amplitude tests. To determine the cyclic deformation behavior, stress-strain measurements and high precision in-situ measurements of the change in specimens temperature and electrical resistance were performed during fatigue tests.
The cyclic indentation tests identify differences in cyclic hardening behavior of the AM-structures depending on the chemical composition, with a minor volume of material and effort. The LITs show the anisotropic behavior of AM-specimens depending on the building direction, which correlates well with the determined S-N-curves. Therefore, this short time procedure can be used to investigate the influence of different manufacturing parameters and post treatments on the anisotropic fatigue behavior of AM-specimens.
1. H. S. Kramer, P. Starke, M. Klein, D. Eifler, Cyclic hardness test PHYBALCHT – Short-time procedure to evaluate fatigue properties of metallic materials. International Journal of Fatigue, 2014. 63: p. 78-84.