TY - THES

T1 - Combinatorial study of process parameters, microstructure and mechanical properties in Inconel 718 parts produced by additive manufacturing

AU - Bodner, Sabine

N1 - embargoed until 17-11-2022

PY - 2018

Y1 - 2018

N2 - Functional properties of Ni-basis Inconel 718 alloy components synthetized using selective laser melting depend on a variety of process parameters. In this thesis, the effects of the laser power, the scanning velocity and the layer thickness on the surface quality, the mechanical properties, the microstructure and the residual stress gradients in a variety of as-built structures are analyzed. Based on an experimental design schema, first, 41 process parameter combinations were systematically selected and applied to manufacture the structures. The combinatorial study has indicated complex correlations between the process and the sample parameters. Surfaces roughnesses were optimized to mean values of ~14 and 19 µm for vertical, 45°-upskin and 45°-downskin oriented surfaces, respectively. A maximal ultimate tensile strength of ~670 MPa and a strain at fracture of up to ~33.5 % were obtained in the as-built structures without further surface post-processing. Secondly, the results were used to select representative conditions for the production of six near-product sample geometries, which were further analyzed at the synchrotron beamline P07 of DESY in Hamburg. Three specimens were produced using constant deposition conditions and, for another three geometries, the volumetric energy density was varied during the building process. Horizontal and vertical synchrotron scanning experiments were performed to characterize stress and texture evolutions across the samples. The correlation of the experimental data allowed the understanding of the influence of the specific process parameters on the mechanical properties, the microstructure, the residual stress distributions and the surface quality. Finally, this multi-parameter study based on a variety of experimental techniques and applied process conditions demonstrate that it is actually possible to perform knowledge-based design of the functional properties and the corresponding microstructure of as-built components by applying purposefully selected input parameters during the additive manufacturing process.

AB - Functional properties of Ni-basis Inconel 718 alloy components synthetized using selective laser melting depend on a variety of process parameters. In this thesis, the effects of the laser power, the scanning velocity and the layer thickness on the surface quality, the mechanical properties, the microstructure and the residual stress gradients in a variety of as-built structures are analyzed. Based on an experimental design schema, first, 41 process parameter combinations were systematically selected and applied to manufacture the structures. The combinatorial study has indicated complex correlations between the process and the sample parameters. Surfaces roughnesses were optimized to mean values of ~14 and 19 µm for vertical, 45°-upskin and 45°-downskin oriented surfaces, respectively. A maximal ultimate tensile strength of ~670 MPa and a strain at fracture of up to ~33.5 % were obtained in the as-built structures without further surface post-processing. Secondly, the results were used to select representative conditions for the production of six near-product sample geometries, which were further analyzed at the synchrotron beamline P07 of DESY in Hamburg. Three specimens were produced using constant deposition conditions and, for another three geometries, the volumetric energy density was varied during the building process. Horizontal and vertical synchrotron scanning experiments were performed to characterize stress and texture evolutions across the samples. The correlation of the experimental data allowed the understanding of the influence of the specific process parameters on the mechanical properties, the microstructure, the residual stress distributions and the surface quality. Finally, this multi-parameter study based on a variety of experimental techniques and applied process conditions demonstrate that it is actually possible to perform knowledge-based design of the functional properties and the corresponding microstructure of as-built components by applying purposefully selected input parameters during the additive manufacturing process.

KW - additive manufacturing

KW - selective laser melting

KW - powder bed

KW - Inconel 718

KW - nickel-basis alloy

KW - residual stress distribution

KW - design of experiments

KW - multi-parameter study

KW - generative Fertigung

KW - additive Fertigung

KW - selektives Laserschmelzen

KW - Pulverbett

KW - Inconel 718

KW - Nickel-Basis Legierung

KW - Eigenspannungsverlauf

KW - statistische Versuchsplanung

KW - Multiparameterstudie

M3 - Master's Thesis

ER -