TY - JOUR A1 - Laquai, Rene A1 - Müller, Bernd R. A1 - Schneider, Judith Ann A1 - Kupsch, Andreas A1 - Bruno, Giovanni T1 - Using SXRR to probe the nature of discontinuities in SLM additive manufactured inconel 718 specimens JF - Metallurgical and Materials Transactions A N2 - The utilization of additive manufacturing (AM) to fabricate robust structural components relies on understanding the nature of internal anomalies or discontinuities, which can compromise the structural integrity. While some discontinuities in AM microstructures stem from similar mechanisms as observed in more traditional processes such as casting, others are unique to the AM process. Discontinuities in AM are challenging to detect, due to their submicron size and orientation dependency. Toward the goal of improving structural integrity, minimizing discontinuities in an AM build requires an understanding of the mechanisms of formation to mitigate their occurrence. This study utilizes various techniques to evaluate the shape, size, nature and distribution of discontinuities in AM Inconel 718, in a non-hot isostatic pressed (HIPed) as-built, non-HIPed and direct age, and HIPed with two step age samples. Non-destructive synchrotron radiation refraction and transmission radiography (SXRR) provides additional information beyond that obtained with destructive optical microscopy. SXRR was able to distinguish between voids, cracks and lack of melt in, due to its sensitivity to the orientation of the discontinuity. Y1 - 2020 U6 - https://doi.org/10.1007/s11661-020-05847-5 SN - 1073-5623 SN - 1543-1940 VL - 51 IS - 8 SP - 4146 EP - 4157 PB - Springer CY - New York ER - TY - JOUR A1 - Schröder, Jakob A1 - Evans, Alexander A1 - Polatidis, Efthymios A1 - Mohr, Gunther A1 - Serrano-Munoz, Itziar A1 - Bruno, Giovanni A1 - Čapek, Jan T1 - Understanding the impact of texture on the micromechanical anisotropy of laser powder bed fused Inconel 718 JF - Journal of materials science N2 - The manufacturability of metallic alloys using laser-based additive manufacturing methods such as laser powder bed fusion has substantially improved within the last decade. However, local melting and solidification cause hierarchically structured and crystallographically textured microstructures possessing large residual stress. Such microstructures are not only the origin of mechanical anisotropy but also pose metrological challenges for the diffraction-based residual stress determination. Here we demonstrate the influence of the build orientation and the texture on the microstructure and consequently the mechanical anisotropy of as-built Inconel 718. For this purpose, we manufactured specimens with [001]/[011]-, [001]- and [011]/[11 (1) over bar]-type textures along their loading direction. In addition to changes in the Young's moduli, the differences in the crystallographic textures result in variations of the yield and ultimate tensile strengths. With this in mind, we studied the anisotropy on the micromechanical scale by subjecting the specimens to tensile loads along the different texture directions during in situ neutron diffraction experiments. In this context, the response of multiple lattice planes up to a tensile strain of 10% displayed differences in the load partitioning and the residual strain accumulation for the specimen with [011]/[(1) over bar 11]-type texture. However, the relative behavior of the specimens possessing an [001] /[011]- and [001]-type texture remained qualitatively similar. The consequences on the metrology of residual stress determination methods are discussed. Y1 - 2022 U6 - https://doi.org/10.1007/s10853-022-07499-9 SN - 0022-2461 SN - 1573-4803 VL - 57 IS - 31 SP - 15036 EP - 15058 PB - Springer CY - New York ER - TY - JOUR A1 - Sprengel, Maximilian A1 - Mohr, Gunther A1 - Altenburg, Simon J. A1 - Evans, Alexander A1 - Serrano-Munoz, Itziar A1 - Kromm, Arne A1 - Pirling, Thilo A1 - Bruno, Giovanni A1 - Kannengießer, Thomas T1 - Triaxial residual stress in Laser Powder Bed Fused 316L BT - effects of interlayer time and scanning velocity JF - Advanced engineering materials N2 - The control of residual stress (RS) remains a challenge in the manufacturing of metallic parts using the laser powder bed fusion process (LPBF). This layer-by-layer manufacturing approach gives rise to complex triaxial RS distributions, which require extensive characterization effort for a broader acceptance of LPBF in industry. This study focuses on the distribution of bulk triaxial RS and surface RS in LPBF austenitic steel 316L. The RS are determined by X-ray and neutron diffraction to characterize the RS distribution. Variations in the LPBF parameters interlayer time (ILT) and scanning velocity and their influence on the temperature distribution and resulting RS is investigated using thermographic data from in situ process monitoring. The RS in the LPBF 316L is tensile at the surface and compressive in the bulk. The RS is directly related to the thermal history of the part as shown by the in situ thermography data. Shorter ILT leads to higher temperatures of the part during the manufacturing, which decrease the RS and RS formation mechanisms. Interestingly, the surface RS does not agree with this observation. This study highlights the benefit of using multiple RS determination methods and in situ thermography monitoring to characterize the RS in LPBF processed parts. KW - in situ thermography KW - interlayer time KW - laser powder bed fusions KW - triaxial residual stresses KW - X-ray and neutron diffractions Y1 - 2021 U6 - https://doi.org/10.1002/adem.202101330 SN - 1438-1656 SN - 1527-2648 VL - 24 IS - 6 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Fernandez, Ricardo A1 - Gonzalez-Doncel, Gaspar A1 - Garces, Gerardo A1 - Bruno, Giovanni T1 - Towards a comprehensive understanding of creep BT - microstructural dependence of the pre-exponential term in Al JF - Materials science & engineering. A, Structural materials: properties, microstructure and processing N2 - We show that the equation proposed by Takeuchi and Argon to explain the creep behavior of Al-Mg solid solution can be used to describe also the creep behavior of pure aluminum. In this frame, it is possible to avoid the use of the classic pre-exponential fitting parameter in the power law equation to predict the minimum creep strain rate. The effect of the fractal arrangement of dislocations, developed at the mesoscale, must be considered to fully explain the experimental data. These ideas allow improving the recently introduced SSTC model, fully describing the primary and secondary creep regimes of aluminum alloys without the need for fitting. Creep data from commercially pure A199.8% and Al-Mg alloys tested at different temperatures and stresses are used to validate the proposed ideas. KW - creep KW - Aluminum alloys KW - dislocations KW - fractal KW - stress exponent Y1 - 2020 U6 - https://doi.org/10.1016/j.msea.2020.139036 SN - 0921-5093 SN - 1873-4936 VL - 776 PB - Elsevier CY - Lausanne ER - TY - JOUR A1 - Evsevleev, Sergei A1 - Mishurova, Tatiana A1 - Cabeza, Sandra A1 - Koos, R. A1 - Sevostianov, Igor A1 - Garcés, Gonzales A1 - Requena, Guillermo A1 - Fernandez, R. A1 - Bruno, Giovanni T1 - The role of intermetallics in stress partitioning and damage evolution of AlSil2CuMgNi alloy JF - Materials Science and Engineering: A-Structural materials: properties, microstructure and processing N2 - Load partitioning between phases in a cast AlSi12CuMgNi alloy was investigated by in-situ compression test during neutron diffraction experiments. Computed tomography (CT) was used to determine volume fractions of eutectic Si and intermetallic (IM) phases, and to assess internal damage after ex-situ compression tests. The CT reconstructed volumes showed the interconnectivity of IM phases, which build a 3D network together with eutectic Si. Large stresses were found in IMs, revealing their significant role as a reinforcement for the alloy. An existing micromechanical model based on Maxwell scheme was extended to the present case, assuming the alloy as a three-phase composite (Al matrix, eutectic Si, IM phases). The model agrees well with the experimental data. Moreover, it allows predicting the principal stresses in each phase, while experiments can only determine stress differences between the axial and radial sample directions. Finally, we showed that the addition of alloying elements not only allowed developing a 3D interconnected network, but also improved the strength of the Al matrix, and the ability of the alloy constituents to bear mechanical load. KW - Aluminum alloys KW - Neutron diffraction KW - Micromechanical modeling KW - Internal stress KW - Damage KW - Computed tomography Y1 - 2018 U6 - https://doi.org/10.1016/j.msea.2018.08.070 SN - 0921-5093 SN - 1873-4936 VL - 736 SP - 453 EP - 464 PB - Elsevier CY - Lausanne ER - TY - JOUR A1 - Serrano-Munoz, Itziar A1 - Mishurova, Tatiana A1 - Thiede, Tobias A1 - Sprengel, Maximilian A1 - Kromm, Arne A1 - Nadammal, Naresh A1 - Nolze, Gert A1 - Saliwan-Neumann, Romeo A1 - Evans, Alexander A1 - Bruno, Giovanni T1 - The residual stress in as-built laser powder bed fusion IN718 alloy as a consequence of the scanning strategy induced microstructure JF - Scientific reports N2 - 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 degrees) 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. KW - EBSD KW - components KW - deposition KW - diffraction KW - distortion KW - heat-treatment KW - mechanical properties KW - melting slm KW - superalloys KW - texture Y1 - 2020 U6 - https://doi.org/10.1038/s41598-020-71112-9 SN - 2045-2322 VL - 10 IS - 1 PB - Macmillan Publishers Limited, part of Springer Nature CY - London ER - TY - JOUR A1 - Mishurova, Tatiana A1 - Cabeza, Sandra A1 - Thiede, Tobias A1 - Nadammal, Naresh A1 - Kromm, Arne A1 - Klaus, Manuela A1 - Genzel, Christoph A1 - Haberland, Christoph A1 - Bruno, Giovanni T1 - The Influence of the Support Structure on Residual Stress and Distortion in SLM Inconel 718 Parts JF - Metallurgical and Materials Transactions A N2 - 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. Y1 - 2018 U6 - https://doi.org/10.1007/s11661-018-4653-9 SN - 1073-5623 SN - 1543-1940 VL - 49A IS - 7 SP - 3038 EP - 3046 PB - Springer CY - New York ER - TY - JOUR A1 - Chen, Cong A1 - Müller, Bernd R. A1 - Prinz, Carsten A1 - Stroh, Julia A1 - Feldmann, Ines A1 - Bruno, Giovanni T1 - The correlation between porosity characteristics and the crystallographic texture in extruded stabilized aluminium titanate for diesel particulate filter applications JF - Journal of the European Ceramic Society N2 - Porous ceramic diesel particulate filters (DPFs) are extruded products that possess macroscopic anisotropic mechanical and thermal properties. This anisotropy is caused by both morphological features (mostly the orientation of porosity) and crystallographic texture. We systematically studied those two aspects in two aluminum titanate ceramic materials of different porosity using mercury porosimetry, gas adsorption, electron microscopy, X-ray diffraction, and X-ray refraction radiography. We found that a lower porosity content implies a larger isotropy of both the crystal texture and the porosity orientation. We also found that, analogous to cordierite, crystallites do align with their axis of negative thermal expansion along the extrusion direction. However, unlike what found for cordierite, the aluminium titanate crystallite form is such that a more pronounced (0 0 2) texture along the extrusion direction implies porosity aligned perpendicular to it. KW - preferred orientation KW - X-ray refraction KW - pore orientation KW - crystal KW - structure KW - extrusion KW - microstructure-property relations Y1 - 2020 U6 - https://doi.org/10.1016/j.jeurceramsoc.2019.11.076 SN - 0955-2219 SN - 1873-619X VL - 40 IS - 4 SP - 1592 EP - 1601 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Magkos, Sotirios A1 - Kupsch, Andreas A1 - Bruno, Giovanni T1 - Suppression of cone-beam artefacts with Direct Iterative Reconstruction Computed Tomography Trajectories (DIRECTT) JF - Journal of imaging : open access journal N2 - The reconstruction of cone-beam computed tomography data using filtered back-projection algorithms unavoidably results in severe artefacts. We describe how the Direct Iterative Reconstruction of Computed Tomography Trajectories (DIRECTT) algorithm can be combined with a model of the artefacts for the reconstruction of such data. The implementation of DIRECTT results in reconstructed volumes of superior quality compared to the conventional algorithms. KW - iteration method KW - signal processing KW - X-ray imaging KW - computed tomography Y1 - 2021 U6 - https://doi.org/10.3390/jimaging7080147 SN - 2313-433X VL - 7 IS - 8 PB - MDPI CY - Basel ER - TY - JOUR A1 - Mishurova, Tatiana A1 - Stegemann, Robert A1 - Lyamkin, Viktor A1 - Cabeza, Sandra A1 - Evsevleev, Sergei A1 - Pelkner, Matthias A1 - Bruno, Giovanni T1 - Subsurface and bulk residual stress analysis of S235JRC+C Steel TIG weld by diffraction and magnetic stray field measurements JF - Experimental mechanics : an international journal of the Society for Experimental Mechanics N2 - Background Due to physical coupling between mechanical stress and magnetization in ferromagnetic materials, it is assumed in the literature that the distribution of the magnetic stray field corresponds to the internal (residual) stress of the specimen. The correlation is, however, not trivial, since the magnetic stray field is also influenced by the microstructure and the geometry of component. The understanding of the correlation between residual stress and magnetic stray field could help to evaluate the integrity of welded components. Objective This study aims at understanding the possible correlation of subsurface and bulk residual stress with magnetic stray field in a low carbon steel weld. Methods The residual stress was determined by synchrotron X-ray diffraction (SXRD, subsurface region) and by neutron diffraction (ND, bulk region). SXRD possesses a higher spatial resolution than ND. Magnetic stray fields were mapped by utilizing high-spatial-resolution giant magneto resistance (GMR) sensors. Results The subsurface residual stress overall correlates better with the magnetic stray field distribution than the bulk stress. This correlation is especially visible in the regions outside the heat affected zone, where the influence of the microstructural features is less pronounced but steep residual stress gradients are present. Conclusions It was demonstrated that the localized stray field sources without any obvious microstructural variations are associated with steep stress gradients. The good correlation between subsurface residual stress and magnetic signal indicates that the source of the magnetic stray fields is to be found in the range of the penetration depth of the SXRD measurements. KW - residual stress KW - magnetic stray field KW - synchrotron X-ray diffraction KW - neutron diffraction KW - TIG-welding Y1 - 2022 U6 - https://doi.org/10.1007/s11340-022-00841-x SN - 0014-4851 SN - 1741-2765 VL - 62 IS - 6 SP - 1017 EP - 1025 PB - Springer CY - New York ER -