Dokument-ID Dokumenttyp Autoren/innen Persönliche Herausgeber/innen Haupttitel Abstract Auflage Verlagsort Verlag Herausgeber (Institution) Erscheinungsjahr Titel des übergeordneten Werkes Jahrgang/Band ISBN Veranstaltung Veranstaltungsort Beginndatum der Veranstaltung Enddatum der Veranstaltung Ausgabe/Heft Erste Seite Letzte Seite URN DOI Lizenz Datum der Freischaltung OPUS4-44175 Zeitschriftenartikel Nadammal, Naresh; Kromm, Arne; Saliwan Neumann, Romeo; Farahbod, Lena; Haberland, Christoph; Portella, Pedro Dolabella Influence of support configurations on the characteristics of selective laser-melted Inconel 718 Samples fabricated using two different support configurations by following identical scan strategies during selective laser melting of superalloy Inconel 718 were characterized in this study. Characterization methods included optical microscopy, electron back-scattered diffraction and x-ray diffraction residual stress measurement. For the scan strategy considered, microstructure and residual stress development in the samples were influenced by the support structures. However, crystallographic texture intensity and the texture components formed within the core part of the samples were almost independent of the support. The formation of finer grains closer to the support as well as within the columnar grain boundaries resulted in randomization and texture intensity reduction by nearly half for the sample built on a lattice support. Heat transfer rates dictated by the support configurations in addition to the scan strategy influenced the microstructure and residual stress development in selective laser-melted Inconel 718 samples. USA Springer 2018 JOM-The Journal of The Minerals, Metals & Materials Society (TMS) 70 3 343 348 10.1007/s11837-017-2703-1 2018-02-16 OPUS4-45100 Zeitschriftenartikel Mishurova, Tatiana; Cabeza, Sandra; Thiede, Tobias; Nadammal, Naresh; Kromm, Arne; Klaus, Manuela; Genzel, Christoph; Haberland, Christoph; Bruno, Giovanni The influence of the support structure on residual stress and distortion in SLM Inconel 718 parts The effect of support structure and of removal from the base plate on the residual stress state in selective laser melted IN718 parts was studied by means of synchrotron X-ray diffraction. The residual stresses in subsurface region of two elongated prisms in as-built condition and after removal from the base plate were determined. One sample was directly built on a base plate and another one on a support structure. Also, the distortion on the top surface due to stress release was measured by contact profilometry. High tensile residual stress values were found, with pronounced stress gradient along the hatching direction. In the sample on support, stress redistribution took place after removal from the base plate, as opposed to simple stress relaxation for the sample without support. The sample on support structure showed larger distortion compared to sample without support. We conclude that the use of a support decreases stress values but stress-relieving heat treatments are still needed. New York, NY Springer Sciences & Business Media 2018 Metallurgical and materials transactions A 49A 7 3038 3046 10.1007/s11661-018-4653-9 2018-06-05 OPUS4-45855 Zeitschriftenartikel Stegemann, Robert; Cabeza, Sandra; Pelkner, Matthias; Lyamkin, Viktor; Pittner, Andreas; Werner, Daniel; Wimpory, R.; Boin, M.; Kreutzbruck, Marc; Bruno, Giovanni Influence of the microstructure on magnetic stray fields of low-carbon steel welds This study examines the relationship between the magnetic mesostructure with the microstructure of low carbon steel tungsten inert gas welds. Optical microscopy revealed variation in the microstructure of the parent material, in the heat affected and fusion zones, correlating with distinctive changes in the local magnetic stray fields measured with high spatial resolution giant magneto resistance sensors. In the vicinity of the heat affected zone high residual stresses were found using neutron diffraction. Notably, the gradients of von Mises stress and triaxial magnetic stray field modulus follow the same tendency transverse to the weld. In contrast, micro-X-ray fluorescence characterization indicated that local changes in element composition had no independent effect on magnetic stray fields. New York Springer US 2018 Journal of Nondestructive Evaluation 37 3 66,1 18 10.1007/s10921-018-0522-0 2018-09-06 OPUS4-46569 Zeitschriftenartikel Sonntag, Nadja; Cabeza, S.; Kuntner, M.; Mishurova, Tatiana; Klaus, M.; Kling e Silva, L.; Skrotzki, Birgit; Genzel, Ch.; Bruno, Giovanni Visualisation of deformation gradients in structural steel by macroscopic magnetic domain distribution imaging (Bitter technique) Abstract While classically used to visualise the magnetic microstructure of functional materials (e.g., for magnetic applications), in this study, the Bitter technique was applied for the first time to visualise macroscopic deformation gradients in a polycrystalline low-carbon steel. Spherical indentation was chosen to produce a multiaxial elastic-plastic deformation state. After removing the residual imprint, the Bitter technique was applied, and macroscopic contrast differences were captured in optical microscopy. To verify this novel characterisation technique, characteristic "hemispherical" deformation zones evolving during indentation were identified using an analytical model from the field of contact mechanics. In addition, near-surface residual stresses were determined experimentally using synchrotron radiation diffraction. It is established that the magnetic domain distribution contrast provides deformation-related information: regions of different domain wall densities correspond to different "hemispherical" deformation zones (i.e., to hydrostatic core, plastic zone and elastic zone, respectively). Moreover, the transitions between these three zones correlate with characteristic features of the residual stress profiles (sign changes in the radial and local extrema in the hoop stress). These results indicate the potential of magnetic domain distribution imaging: visualising macroscopic deformation gradients in fine-grained ferromagnetic material with a significantly improved spatial resolution as compared to integral, mean value-based measurement methods. Wiley 2018 Strain 54 6 e12296, 1 15 10.1111/str.12296 2018-11-15 OPUS4-46512 Zeitschriftenartikel Häberle, Nicolas; Pittner, Andreas; Rethmeier, Michael; Falkenberg, Rainer; Kahlcke, Ole Application of multi-phase viscoplastic material modelling to computational welding mechanics of grade-s960ql steel The sound numerical prediction of welding-induced thermal stresses, residual stresses, and distortions strongly depends on the accurate description of a welded material's thermomechanical deformation behaviour. In this work, we provide experimental data on the viscoplastic deformation behaviour of a grade-s960ql steel up to a temperature of 1000 ◦C. In addition, a multi-phase viscoplastic material model is proposed, which accounts for the experimentally observed isothermal deformation behaviour of grade-s960ql steel base and austenitised material, as well as for athermal contributions that originate from solid-state phase transformations. The multi-phase viscoplastic and a classic rateindependent isotropic hardening material model were applied in the numerical simulations of both-ends-fixed bar Satoh tests and a single-pass gas metal arc weld. The influence of material modelling choices on the agreement between numerical simulation and experimental results is discussed, and recommendations for further work are given. Elsevier Masson SAS 2018 Comptes Rendus Mecanique - Computational methods in welding and additive manufacturing/Simulation numérique des procédés de soudage et de fabrication additive 346 11 1018 1032 10.1016/j.crme.2018.08.001 2018-11-08 OPUS4-46673 Zeitschriftenartikel Thiede, Tobias; Cabeza, S.; Mishurova, Tatiana; Nadammal, N.; Kromm, Arne; Bode, Johannes; Haberland, C.; Bruno, Giovanni Residual stress in selective laser melted Inconel 718: Influence of the removal from base plate and deposition hatch length The residual stress distribution in IN718 elongated prisms produced by Selective Laser Melting was studied by means of neutron (bulk) and laboratory X-ray (surface) diffraction. Two deposition hatch lengths were considered. A horizontal plane near the top surface (perpendicular to the building direction) and a vertical plane near the lateral surface (parallel to the building direction) were investigated. Samples both in as-built (AB) condition and removed (RE) from the base plate were characterized. While surface stress fields seem constant for AB condition, X-ray diffraction shows stress gradients along the hatch direction in the RE condition. The stress profiles correlate with the distortion maps obtained by tactile probe measurements. Neutron diffraction shows bulk stress gradients for all principal components along the main sample directions. We correlate the observed stress patterns with the hatch length, i.e. with its effect on temperature gradients and heat flow. The bulk stress gradients partially disappear after removal from the baseplate. USA, West Conshohocken ASTM International 2018 Materials, Performance & Characterization 7 4 717 735 10.1520/MPC20170119 2018-11-21 OPUS4-51176 Zeitschriftenartikel Serrano Munoz, Itziar; Mishurova, Tatiana; Thiede, Tobias; Sprengel, Maximilian; Kromm, Arne; Nadammal, Naresh; Nolze, Gert; Saliwan Neumann, Romeo; Evans, Alexander; Bruno, Giovanni The residual stress in as‑built Laser Powder Bed Fusion IN718 alloy as a consequence of the scanning strategy induced microstructure The effect of two types of scanning strategies on the grain structure and build-up of Residual Stress (RS) has been investigated in an as-built IN718 alloy produced by Laser Powder Bed Fusion (LPBF). The RS state has been investigated by X-ray diffraction techniques. The microstructural characterization was performed principally by Electron Backscatter Diffraction (EBSD), where the application of a post-measurement refinement technique enables small misorientations (< 2°) to be resolved. Kernel average misorientation (KAM) distributions indicate that preferably oriented columnar grains contain higher levels of misorientation, when compared to elongated grains with lower texture. The KAM distributions combined with X-ray diffraction stress maps infer that the increased misorientation is induced via plastic deformation driven by the thermal stresses, acting to self-relieve stress. The possibility of obtaining lower RS states in the build direction as a consequence of the influence of the microstructure should be considered when envisaging scanning strategies aimed at the mitigation of RS. 2020 Scientific reports 10 1 14645 urn:nbn:de:kobv:b43-511769 10.1038/s41598-020-71112-9 https://creativecommons.org/licenses/by/4.0/deed.de 2020-09-09 OPUS4-53604 Zeitschriftenartikel Sprengel, Maximilian; Ulbricht, Alexander; Evans, Alexander; Kromm, Arne; Sommer, Konstantin; Werner, Tiago; Kelleher, J.; Bruno, Giovanni; Kannengießer, Thomas Towards the optimization of post-laser powder bed fusion stress-relieve treatments of stainless steel 316L This study reports on the stress relaxation potential of stress-relieving heat treatments for laser powder bed fused 316L. The residual stress is monitored non-destructively using neutron diffraction before and after the heat treatment. Moreover, the evolution of the microstructure is analysed using scanning electron microscopy. The results show, that a strong relaxation of the residual stress is obtained when applying a heat treatment temperature at 900°C. However, the loss of the cellular substructure needs to be considered when applying this heat treatment strategy. Boston Springer 2021 Metallurgical and materials transactions A 52 12 5342 5356 urn:nbn:de:kobv:b43-536045 10.1007/s11661-021-06472-6 https://creativecommons.org/licenses/by/4.0/deed.de 2021-10-25 OPUS4-51171 Zeitschriftenartikel Charmi, Amir; Falkenberg, Rainer; Ávila, Luis; Mohr, Gunther; Sommer, Konstantin; Ulbricht, Alexander; Sprengel, Maximilian; Saliwan Neumann, Romeo; Evans, Alexander; Skrotzki, Birgit Mechanical anisotropy of additively manufactured stainless steel 316L: An experimental and numerical study The underlying cause of mechanical anisotropy in additively manufactured (AM) parts is not yet fully understood and has been attributed to several different factors like microstructural defects, residual stresses, melt pool boundaries, crystallographic and morphological textures. To better understand the main contributing factor to the mechanical anisotropy of AM stainless steel 316L, bulk specimens were fabricated via laser powder bed fusion (LPBF). Tensile specimens were machined from these AM bulk materials for three different inclinations: 0◦, 45◦, and 90◦ relative to the build plate. Dynamic Young's modulus measurements and tensile tests were used to determine the mechanical anisotropy. Some tensile specimens were also subjected to residual stress measurement via neutron diffraction, porosity determination with X-ray micro-computed tomography (μCT), and texture analysis with electron backscatter diffraction (EBSD). These investigations revealed that the specimens exhibited near full density and the detected defects were spherical. Furthermore, the residual stresses in the loading direction were between −74 ± 24 MPa and 137 ± 20 MPa, and the EBSD measurements showed a preferential ⟨110⟩ orientation parallel to the build direction. A crystal plasticity model was used to analyze the elastic anisotropy and the anisotropic yield behavior of the AM specimens, and it was able to capture and predict the experimental behavior accurately. Overall, it was shown that the mechanical anisotropy of the tested specimens was mainly influenced by the crystallographic texture. Elsevier B.V. 2021 Materials Science and Engineering: A 799 140154 urn:nbn:de:kobv:b43-511719 10.1016/j.msea.2020.140154 https://creativecommons.org/licenses/by/4.0/deed.de 2020-09-09 OPUS4-52066 Zeitschriftenartikel Fritsch, Tobias; Sprengel, Maximilian; Evans, Alexander; Farahbod-Sternahl, L.; Saliwan Neumann, Romeo; Hofmann, M.; Bruno, Giovanni On the determination of residual stresses in additively manufactured lattice structures The determination of residual stresses becomes more complicated with increasing complexity of the structures investigated. Additive manufacturing techniques generally allow the production of 'lattice structures' without any additional manufacturing step. These lattice structures consist of thin struts and are thus susceptible to internal stress-induced distortion and even cracks. In most cases, internal stresses remain locked in the structures as residual stress. The determination of the residual stress in lattice structures through nondestructive neutron diffraction is described in this work. It is shown how two difficulties can be overcome: (a) the correct alignment of the lattice structures within the neutron beam and (b) the correct determination of the residual stress field in a representative part of the structure. The magnitude and the direction of residual stress are discussed. The residual stress in the strut was found to be uniaxial and to follow the orientation of the strut, while the residual stress in the knots was more hydrostatic. Additionally, it is shown that strain measurements in at least seven independent directions are necessary for the estimation of the principal stress directions. The measurement directions should be chosen according to the sample geometry and an informed choice on the possible strain field. If the most prominent direction is not measured, the error in the calculated stress magnitude increases considerably. 2021 Journal of Applied Crystallography 54 228 236 urn:nbn:de:kobv:b43-520663 10.1107/S1600576720015344 https://creativecommons.org/licenses/by/4.0/deed.de 2021-02-03