@article{LaquaiMuellerSchneideretal.2020, author = {Laquai, Rene and M{\"u}ller, Bernd R. and Schneider, Judith Ann and Kupsch, Andreas and Bruno, Giovanni}, title = {Using SXRR to probe the nature of discontinuities in SLM additive manufactured inconel 718 specimens}, series = {Metallurgical and Materials Transactions A}, volume = {51}, journal = {Metallurgical and Materials Transactions A}, number = {8}, publisher = {Springer}, address = {New York}, issn = {1073-5623}, doi = {10.1007/s11661-020-05847-5}, pages = {4146 -- 4157}, year = {2020}, abstract = {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.}, language = {en} } @article{SchroederEvansPolatidisetal.2022, author = {Schr{\"o}der, Jakob and Evans, Alexander and Polatidis, Efthymios and Mohr, Gunther and Serrano-Munoz, Itziar and Bruno, Giovanni and Čapek, Jan}, title = {Understanding the impact of texture on the micromechanical anisotropy of laser powder bed fused Inconel 718}, series = {Journal of materials science}, volume = {57}, journal = {Journal of materials science}, number = {31}, publisher = {Springer}, address = {New York}, issn = {0022-2461}, doi = {10.1007/s10853-022-07499-9}, pages = {15036 -- 15058}, year = {2022}, abstract = {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.}, language = {en} } @article{FernandezGonzalezDoncelGarcesetal.2020, author = {Fernandez, Ricardo and Gonzalez-Doncel, Gaspar and Garces, Gerardo and Bruno, Giovanni}, title = {Towards a comprehensive understanding of creep}, series = {Materials science \& engineering. A, Structural materials: properties, microstructure and processing}, volume = {776}, journal = {Materials science \& engineering. A, Structural materials: properties, microstructure and processing}, publisher = {Elsevier}, address = {Lausanne}, issn = {0921-5093}, doi = {10.1016/j.msea.2020.139036}, pages = {7}, year = {2020}, abstract = {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.}, language = {en} } @article{EvsevleevMishurovaCabezaetal.2018, author = {Evsevleev, Sergei and Mishurova, Tatiana and Cabeza, Sandra and Koos, R. and Sevostianov, Igor and Garc{\´e}s, Gonzales and Requena, Guillermo and Fernandez, R. and Bruno, Giovanni}, title = {The role of intermetallics in stress partitioning and damage evolution of AlSil2CuMgNi alloy}, series = {Materials Science and Engineering: A-Structural materials: properties, microstructure and processing}, volume = {736}, journal = {Materials Science and Engineering: A-Structural materials: properties, microstructure and processing}, publisher = {Elsevier}, address = {Lausanne}, issn = {0921-5093}, doi = {10.1016/j.msea.2018.08.070}, pages = {453 -- 464}, year = {2018}, abstract = {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.}, language = {en} } @article{MishurovaCabezaThiedeetal.2018, author = {Mishurova, Tatiana and Cabeza, Sandra and Thiede, Tobias and Nadammal, Naresh and Kromm, Arne and Klaus, Manuela and Genzel, Christoph and Haberland, Christoph and Bruno, Giovanni}, title = {The Influence of the Support Structure on Residual Stress and Distortion in SLM Inconel 718 Parts}, series = {Metallurgical and Materials Transactions A}, volume = {49A}, journal = {Metallurgical and Materials Transactions A}, number = {7}, publisher = {Springer}, address = {New York}, issn = {1073-5623}, doi = {10.1007/s11661-018-4653-9}, pages = {3038 -- 3046}, year = {2018}, abstract = {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.}, language = {en} } @article{ChenMuellerPrinzetal.2020, author = {Chen, Cong and M{\"u}ller, Bernd R. and Prinz, Carsten and Stroh, Julia and Feldmann, Ines and Bruno, Giovanni}, title = {The correlation between porosity characteristics and the crystallographic texture in extruded stabilized aluminium titanate for diesel particulate filter applications}, series = {Journal of the European Ceramic Society}, volume = {40}, journal = {Journal of the European Ceramic Society}, number = {4}, publisher = {Elsevier}, address = {Oxford}, issn = {0955-2219}, doi = {10.1016/j.jeurceramsoc.2019.11.076}, pages = {1592 -- 1601}, year = {2020}, abstract = {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.}, language = {en} } @article{MishurovaStegemannLyamkinetal.2022, author = {Mishurova, Tatiana and Stegemann, Robert and Lyamkin, Viktor and Cabeza, Sandra and Evsevleev, Sergei and Pelkner, Matthias and Bruno, Giovanni}, title = {Subsurface and bulk residual stress analysis of S235JRC+C Steel TIG weld by diffraction and magnetic stray field measurements}, series = {Experimental mechanics : an international journal of the Society for Experimental Mechanics}, volume = {62}, journal = {Experimental mechanics : an international journal of the Society for Experimental Mechanics}, number = {6}, publisher = {Springer}, address = {New York}, issn = {0014-4851}, doi = {10.1007/s11340-022-00841-x}, pages = {1017 -- 1025}, year = {2022}, abstract = {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.}, language = {en} } @article{MuellerCooperLangeetal.2017, author = {M{\"u}ller, B. R. and Cooper, R. C. and Lange, A. and Kupsch, Andreas and Wheeler, M. and Hentschel, M. P. and Staude, A. and Pandey, A. and Shyam, A. and Bruno, Giovanni}, title = {Stress-induced microcrack density evolution in beta-eucryptite ceramics}, series = {Acta materialia}, volume = {144}, journal = {Acta materialia}, publisher = {Elsevier}, address = {Oxford}, issn = {1359-6454}, doi = {10.1016/j.actamat.2017.10.030}, pages = {627 -- 641}, year = {2017}, abstract = {In order to investigate their microcracking behaviour, the microstructures of several beta-eucryptite ceramics, obtained from glass precursor and cerammed to yield different grain sizes and microcrack densities, were characterized by laboratory and synchrotron x-ray refraction and tomography. Results were compared with those obtained from scanning electron microscopy (SEM). In SEM images, the characterized materials appeared fully dense but computed tomography showed the presence of pore clusters. Uniaxial tensile testing was performed on specimens while strain maps were recorded and analyzed by Digital Image Correlation (DIC). X-ray refraction techniques were applied on specimens before and after tensile testing to measure the amount of the internal specific surface (i.e., area per unit volume). X-ray refraction revealed that (a) the small grain size (SGS) material contained a large specific surface, originating from the grain boundaries and the interfaces of TiO2 precipitates; (b) the medium (MGS) and large grain size (LGS) materials possessed higher amounts of specific surface compared to SGS material due to microcracks, which decreased after tensile loading; (c) the precursor glass had negligible internal surface. The unexpected decrease in the internal surface of MGS and LGS after tensile testing is explained by the presence of compressive regions in the DIC strain maps and further by theoretical arguments. It is suggested that while some microcracks merge via propagation, more close mechanically, thereby explaining the observed X-ray refraction results. The mechanisms proposed would allow the development of a strain hardening route in ceramics.}, language = {en} } @article{ThiedeCabezaMishurovaetal.2018, author = {Thiede, Tobias and Cabeza, Sandra and Mishurova, Tatiana and Nadammal, Naresh and Kromm, Arne and Bode, Johannes and Haberland, Christoph and Bruno, Giovanni}, title = {Residual Stress in Selective Laser Melted Inconel 718}, series = {Materials performance and characterization}, volume = {7}, journal = {Materials performance and characterization}, number = {4}, publisher = {American Society for Testing and Materials}, address = {West Conshohocken}, issn = {2379-1365}, doi = {10.1520/MPC20170119}, pages = {717 -- 735}, year = {2018}, abstract = {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 from the base plate (RE) were characterized. While surface stress fields seem constant for the 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 base plate.}, language = {en} } @article{FernandezCabezaMishurovaetal.2018, author = {Fernandez, R. and Cabeza, Sandra and Mishurova, Tatiana and Fernandez-Castrillo, P. and Gonzalez-Doncel, Gaspar and Bruno, Giovanni}, title = {Residual stress and yield strength evolution with annealing treatments in an age-hardenable aluminum alloy matrix composite}, series = {Materials Science and Engineering: A}, volume = {731}, journal = {Materials Science and Engineering: A}, publisher = {Elsevier}, address = {Lausanne}, issn = {0921-5093}, doi = {10.1016/j.msea.2018.06.031}, pages = {344 -- 350}, year = {2018}, abstract = {We investigated the possibility of minimizing tensile matrix residual stresses in age hardenable aluminum alloy metal matrix composites without detrimentally affect their mechanical properties (such as yield strength). Specifically, we performed thermal treatments at different temperatures and times in an age-hardenable aluminum matrix composite 2014Al-15vol\%Al2O3. Using X-ray synchrotron radiation diffraction and mechanical tests, we show that below a certain treatment temperature (250 degrees C) it is possible to identify an appropriate thermal treatment capable of relaxing residual stress in this composite while even increasing its yield strength, with respect to the as processed conditions.}, language = {en} }