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 - Serrano-Munoz, Itziar A1 - Fritsch, Tobias A1 - Mishurova, Tatiana A1 - Trofimov, Anton A1 - Apel, Daniel A1 - Ulbricht, Alexander A1 - Kromm, Arne A1 - Hesse, Rene A1 - Evans, Alexander A1 - Bruno, Giovanni T1 - On the interplay of microstructure and residual stress in LPBF IN718 JF - Journal of materials science N2 - The relationship between residual stresses and microstructure associated with a laser powder bed fusion (LPBF) IN718 alloy has been investigated on specimens produced with three different scanning strategies (unidirectional Y-scan, 90 degrees XY-scan, and 67 degrees Rot-scan). Synchrotron X-ray energy-dispersive diffraction (EDXRD) combined with optical profilometry was used to study residual stress (RS) distribution and distortion upon removal of the specimens from the baseplate. The microstructural characterization of both the bulk and the near-surface regions was conducted using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). On the top surfaces of the specimens, the highest RS values are observed in the Y-scan specimen and the lowest in the Rot-scan specimen, while the tendency is inversed on the side lateral surfaces. A considerable amount of RS remains in the specimens after their removal from the baseplate, especially in the Y- and Z-direction (short specimen dimension and building direction (BD), respectively). The distortion measured on the top surface following baseplate thinning and subsequent removal is mainly attributed to the amount of RS released in the build direction. Importantly, it is observed that the additive manufacturing microstructures challenge the use of classic theoretical models for the calculation of diffraction elastic constants (DEC) required for diffraction-based RS analysis. It is found that when the Reuss model is used for the calculation of RS for different crystal planes, as opposed to the conventionally used Kroner model, the results exhibit lower scatter. This is discussed in context of experimental measurements of DEC available in the literature for conventional and additively manufactured Ni-base alloys. Y1 - 2020 U6 - https://doi.org/10.1007/s10853-020-05553-y SN - 0022-2461 SN - 1573-4803 VL - 56 IS - 9 SP - 5845 EP - 5867 PB - Springer CY - New York ER - TY - JOUR A1 - Oesch, Tyler A1 - Weise, Frank A1 - Bruno, Giovanni T1 - Detection and quantification of cracking in concrete aggregate through virtual data fusion of X-ray computed tomography images JF - Materials N2 - In this work, which is part of a larger research program, a framework called "virtual data fusion" was developed to provide an automated and consistent crack detection method that allows for the cross-comparison of results from large quantities of X-ray computed tomography (CT) data. A partial implementation of this method in a custom program was developed for use in research focused on crack quantification in alkali-silica reaction (ASR)-sensitive concrete aggregates. During the CT image processing, a series of image analyses tailored for detecting specific, individual crack-like characteristics were completed. The results of these analyses were then "fused" in order to identify crack-like objects within the images with much higher accuracy than that yielded by any individual image analysis procedure. The results of this strategy demonstrated the success of the program in effectively identifying crack-like structures and quantifying characteristics, such as surface area and volume. The results demonstrated that the source of aggregate has a very significant impact on the amount of internal cracking, even when the mineralogical characteristics remain very similar. River gravels, for instance, were found to contain significantly higher levels of internal cracking than quarried stone aggregates of the same mineralogical type. KW - X-ray computed tomography (CT) KW - concrete KW - alkali-silica reaction (ASR) KW - ASR-sensitive aggregate KW - solubility test KW - specific surface area KW - crack KW - detection KW - automated image processing KW - damage quantification Y1 - 2020 U6 - https://doi.org/10.3390/ma13183921 SN - 1996-1944 VL - 13 IS - 18 PB - MDPI CY - Basel ER - TY - JOUR A1 - Mishurova, Tatiana A1 - Sydow, Benjamin A1 - Thiede, Tobias A1 - Sizova, Irina A1 - Ulbricht, Alexander A1 - Bambach, Markus A1 - Bruno, Giovanni T1 - Residual stress and microstructure of a Ti-6Al-4V Wire Arc Additive Manufacturing hybrid demonstrator JF - Metals N2 - Wire Arc Additive Manufacturing (WAAM) features high deposition rates and, thus, allows production of large components that are relevant for aerospace applications. However, a lot of aerospace parts are currently produced by forging or machining alone to ensure fast production and to obtain good mechanical properties; the use of these conventional process routes causes high tooling and material costs. A hybrid approach (a combination of forging and WAAM) allows making production more efficient. In this fashion, further structural or functional features can be built in any direction without using additional tools for every part. By using a combination of forging basic geometries with one tool set and adding the functional features by means of WAAM, the tool costs and material waste can be reduced compared to either completely forged or machined parts. One of the factors influencing the structural integrity of additively manufactured parts are (high) residual stresses, generated during the build process. In this study, the triaxial residual stress profiles in a hybrid WAAM part are reported, as determined by neutron diffraction. The analysis is complemented by microstructural investigations, showing a gradient of microstructure (shape and size of grains) along the part height. The highest residual stresses were found in the transition zone (between WAAM and forged part). The total stress range showed to be lower than expected for WAAM components. This could be explained by the thermal history of the component. KW - residual stress KW - WAAM KW - Ti-6Al-4V KW - additive manufacturing KW - neutron KW - diffraction KW - hybrid manufacturing Y1 - 2020 U6 - https://doi.org/10.3390/met10060701 SN - 2075-4701 VL - 10 IS - 6 PB - MDPI CY - Basel ER - TY - JOUR A1 - Mishurova, Tatiana A1 - Bruno, Giovanni A1 - Evsevleev, Sergei A1 - Sevostianov, Igor T1 - Determination of macroscopic stress from diffraction experiments BT - a critical discussion JF - Journal of applied physics N2 - The paper is motivated by some inconsistencies and contradictions present in the literature on the calculation of the so-called diffraction elastic constants. In an attempt at unifying the views that the two communities of Materials Science and Mechanics of Materials have on the subject, we revisit and define the terminology used in the field. We also clarify the limitations of the commonly used approaches and show that a unified methodology is also applicable to textured materials with a nearly arbitrary grain shape. We finally compare the predictions based on this methodology with experimental data obtained by in situ synchrotron radiation diffraction on additively manufactured Ti-6Al-4V alloy. We show that (a) the transverse isotropy of the material yields good agreement between the best-fit isotropy approximation (equivalent to the classic Kroner's model) and the experimental data and (b) the use of a general framework allows the calculation of all components of the tensor of diffraction elastic constants, which are not easily measurable by diffraction methods. This allows us to extend the current state-of-the-art with a predictive tool. Y1 - 2020 U6 - https://doi.org/10.1063/5.0009101 SN - 0021-8979 SN - 1089-7550 VL - 128 IS - 2 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Magkos, Sotirios A1 - Kupsch, Andreas A1 - Bruno, Giovanni T1 - Direct iterative reconstruction of computed tomography trajectories reconstruction from limited number of projections with DIRECTT JF - Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques N2 - X-ray computed tomography has many applications in materials science and non-destructive testing. While the standard filtered back-projection reconstruction of the radiographic datasets is fast and simple, it typically fails in returning accurate results from missing or inconsistent projections. Among the alternative techniques that have been proposed to handle such data is the Direct Iterative REconstruction of Computed Tomography Trajectories (DIRECTT) algorithm. We describe a new approach to the algorithm, which significantly decreases the computational time while achieving a better reconstruction quality than that of other established algorithms. Y1 - 2020 U6 - https://doi.org/10.1063/5.0013111 SN - 0034-6748 SN - 1089-7623 SN - 1527-2400 VL - 91 IS - 10 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Léonard, Fabien A1 - Zhang, Zhen A1 - Krebs, Holger A1 - Bruno, Giovanni T1 - Structural and morphological quantitative 3D characterisation of ammonium nitrate prills by X-ray computed tomography JF - Materials N2 - The mixture of ammonium nitrate (AN) prills and fuel oil (FO), usually referred to as ANFO, is extensively used in the mining industry as a bulk explosive. One of the major performance predictors of ANFO mixtures is the fuel oil retention, which is itself governed by the complex pore structure of the AN prills. In this study, we present how X-ray computed tomography (XCT), and the associated advanced data processing workflow, can be used to fully characterise the structure and morphology of AN prills. We show that structural parameters such as volume fraction of the different phases and morphological parameters such as specific surface area and shape factor can be reliably extracted from the XCT data, and that there is a good agreement with the measured oil retention values. Importantly, oil retention measurements (qualifying the efficiency of ANFO as explosives) correlate well with the specific surface area determined by XCT. XCT can therefore be employed non-destructively; it can accurately evaluate and characterise porosity in ammonium nitrate prills, and even predict their efficiency. KW - ANFO KW - explosives KW - specific surface area KW - porosity KW - XCT KW - data processing Y1 - 2020 U6 - https://doi.org/10.3390/ma13051230 SN - 1996-1944 VL - 13 IS - 5 PB - MDPI CY - Basel ER - 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 - 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 - Fernandez, Ricardo A1 - Bruno, Giovanni A1 - Garces, Gerardo A1 - Nieto-Luis, H. A1 - Gonzalez-Doncel, Gaspar T1 - Fractional brownian motion of dislocations during creep deformation of metals JF - Materials science & engineering. A, Structural materials N2 - The present work offers an explanation on how the long-range interaction of dislocations influences their movement, and therefore the strain, during creep of metals. It is proposed that collective motion of dislocations can be described as a fractional Brownian motion. This explains the noisy appearance of the creep strain signal as a function of time. Such signal is split into a deterministic and a stochastic part. These terms can be related to two kinds of dislocation motions: individual and collective, respectively. The description is consistent with the fractal nature of strain-induced dislocation structures predicated in previous works. Moreover, it encompasses the evolution of the strain rate during all stages of creep, including the tertiary one. Creep data from Al99.8% and Al3.85%Mg tested at different temperatures and stresses are used to validate the proposed ideas: it is found that different creep stages present different diffusion characters, and therefore different dislocation motion character. KW - Creep KW - Aluminum alloys KW - Dislocation motion KW - Diffusion KW - Fractal KW - structures Y1 - 2020 U6 - https://doi.org/10.1016/j.msea.2020.140013 SN - 0921-5093 SN - 1873-4936 VL - 796 PB - Elsevier CY - Lausanne ER - TY - JOUR A1 - Evsevleev, Sergei A1 - Paciornik, Sidnei A1 - Bruno, Giovanni T1 - Advanced deep learning-based 3D microstructural characterization of multiphase metal matrix composites JF - Advanced engineering materials N2 - The quantitative analysis of microstructural features is a key to understanding the micromechanical behavior of metal matrix composites (MMCs), which is a premise for their use in practice. Herein, a 3D microstructural characterization of a five-phase MMC is performed by synchrotron X-ray computed tomography (SXCT). A workflow for advanced deep learning-based segmentation of all individual phases in SXCT data is shown using a fully convolutional neural network with U-net architecture. High segmentation accuracy is achieved with a small amount of training data. This enables extracting unprecedently precise microstructural parameters (e.g., volume fractions and particle shapes) to be input, e.g., in micromechanical models. KW - computed tomography KW - convolutional neural networks KW - deep learning KW - metal KW - matrix composites KW - segmentations Y1 - 2020 U6 - https://doi.org/10.1002/adem.201901197 SN - 1438-1656 SN - 1527-2648 VL - 22 IS - 4 PB - Wiley-VCH CY - Weinheim 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 -