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- Zeitschriftenartikel (38) (entfernen)
Schlagworte
- Neutron imaging (10)
- Neutron tomography (7)
- Neutron radiography (5)
- Tomography (5)
- Fuel cell (4)
- Bragg-edge imaging (3)
- Computed tomography (3)
- Debye–Waller factor (3)
- Phase distribution (3)
- Austenite-to-martensite transformation (2)
- Brennstoffzellen (2)
- Catalyst (2)
- Computertomographie (2)
- Darkfield imaging (2)
- Electron tomography (2)
- Gas tungsten arc welding (GTAW) (2)
- Geometrical effect (2)
- Hydrogen diffusion (2)
- Hydrogen embrittlement (2)
- Low transformation temperature (LTT) steel (2)
- Magnetic domains (2)
- Reconstruction algorithm (2)
- Rectangular cross-section (2)
- Torsion (2)
- Water management (2)
- X-ray imaging (2)
- 4D tomographic data (1)
- Anosteocytic bone (1)
- Backlighting (1)
- Biodegradable implant (1)
- Blister (1)
- Bone porosity (1)
- Bragg-edge (1)
- Bragg-edge neutron 2D imaging (BENI) (1)
- Brennstoffzelle (1)
- Catalyst Layer (1)
- Cells (1)
- Compression effect (1)
- Crystallographic texture control (1)
- Debye-Waller-Faktor (1)
- Diffraction contrast neutron imaging (1)
- Digital detector array (1)
- Electron backscatter diffraction (EBSD) (1)
- Elektronentomographie (1)
- Energy-dispersive x-ray spectroscopy (1)
- Fiber composites (1)
- Full-field phase tomography (1)
- Gas diffusion electrodes (1)
- Gas diffusion layer (1)
- Gas evolution (1)
- Grating interferometry (1)
- IN718 PBF-LB/M (1)
- Imaging (1)
- In situ (1)
- In-Situ-Radiologie (1)
- Instrumentation for neutron sources (1)
- Iron (1)
- Laser powder-bed fusion (1)
- Lithium-ion battery (1)
- Magnesium-gadolinium alloy (1)
- Manifold stack (1)
- Materialcharakterisierung (1)
- Metal additive manufacturing (MAM) (1)
- Metal foam microstructure (1)
- Micro-computed tomography (1)
- Microporous Layer (1)
- Multi-energy CT (1)
- Multimodal analysis (1)
- Neutron Bragg edge imaging (1)
- Neutron computed tomography (1)
- Neutron detectors (cold, thermal, fast neutrons) (1)
- Neutron instrument (1)
- Neutron scattering (1)
- Neutronen-Radiographie (1)
- Neutronen-Tomographie (1)
- Neutronenlaminographie (1)
- Neutronentomographie (1)
- Nneutron imaging (1)
- Non-destructive testing (1)
- Operando cell (1)
- PEM fuel cell (1)
- Phase transformation (1)
- Polymer Electrolyte Membrane Fuel Cell (1)
- Polymer electrolyte membrane fuel cell (1)
- Polymer electrolyte membrane fuel cell (PEMFC) (1)
- Preferential orientation (1)
- Primary Battery (1)
- Proteoglycans (1)
- Radiography (1)
- Radiology (1)
- Reconstruction algrorithm (1)
- Resolution (1)
- Room-temperature (1)
- Scintillator (1)
- Shearing gratings (1)
- Spectral CT (1)
- Stromdichtemessung (1)
- Super martensitic stainless steel (1)
- Synchrotron (1)
- Synchrotronstrahlung (1)
- Talbot-Lau (1)
- Talbot-Lau interferometer (1)
- Talbot-Lau neutron tomography (1)
- Temperature-dependent neutron transmission (1)
- Texture (1)
- Thermal runaway (1)
- Three-dimensional data quantification (1)
- Tomographic reconstruction (1)
- Tomographische Rekonstruktionsalgorithmen (1)
- Two-phase flow (1)
- Wassermanagement (1)
- Water Distribution (1)
- Water permeability (1)
- Water transport (1)
- X-Ray imaging (1)
- X-ray CT (1)
- X-ray compton scattering (1)
- X-ray radiography (1)
- X-ray tomography (1)
- Zerstörungsfrei (1)
Organisationseinheit der BAM
A systematic study has been carried out to investigate the neutron transmission signal as a function of sample temperature. In particular, the experimentally determined wavelength-dependent neutron attenuation spectra for a martensitic steel at temperatures ranging from 21 to 700°C are compared with simulated data. A theoretical description that includes the Debye–Waller factor in order to describe the temperature influence on the neutron cross sections was implemented in the nxsPlotter software and used for the simulations. The analysis of the attenuation coefficients at varying temperatures shows that the missing contributions due to elastic and inelastic scattering can be clearly distinguished: while the elastically scattered intensities decrease with higher temperatures, the inelastically scattered intensities increase, and the two can be separated from each other by analysing unique sharp features in the form of Bragg edges. This study presents the first systematic approach to quantify this effect and can serve as a basis , for example, to correct measurements taken during in situ heat treatments, in many cases being a prerequisite for obtaining quantifiable results.
In various kinds of radiography, deficient transmission imaging may occur due to backlighting inside the detector itself arising from light or radiation scattering. The related intensity mismatches barely disturb the high resolution contrast, but its long range nature results in reduced attenuation levels which are often disregarded. Based on X-ray observations and an empirical formalism, a procedure is developed for a first order correction of detector backlighting. A backlighting factor is modeled as a function of the relative detector coverage by the sample projection. Different cases of sample transmission are regarded at different backlight factors and detector coverage. The additional intensity of backlighting may strongly affect the values of materials’ attenuation up to a few 10%. The presented scenario provides a comfortable procedure for corrections of X-ray or neutron transmission imaging data.
Die Computer-gestützte Laminografie (CL) wurde als komplementäre Methode zur Computertomografie für die dreidimensionale Bildgebung von lateral ausgedehnten Objekten entwickelt. Ursprünglich für medizinische Zwecke verwendet, wurde diese Methode kürzlich als zerstörungsfreie nicht-invasive Methode nicht nur in der Materialforschung, sondern auch mit steigendem Interesse für kunsthandwerkliche und historische Objekte eingesetzt. Hier wird die Computer-gestützten Laminografie mit polychromatischer Neutronenstrahlung an einer historischen Tsuba eingesetzt, einem Stichblatt eines japanischen Schwerts. Eine Analyse der Lötstellen gibt Rückschlüsse auf das Herstellungsverfahren. Zudem wurden unterschiedliche Materialsysteme gefunden, vermutlich um dem Tsuba lokal eine höhere Stabilität zu verleihen. Die Messungen wurden an der Imaging-Beamline CONRAD-2 an der Neutronenquelle BER 2 des Helmholtz-Zentrums Berlins (HZB) durchgeführt.
Aufgrund des hohen Wirkungsgrades und der vielfältigen Einsatzmöglichkeiten können Brennstoffzellen einen wichtigen Beitrag zur zukünftigen Energieversorgung leisten. Für die Optimierung der Brennstoffzellentechnik ist es erforderlich, die während des Zellbetriebs ablaufenden Prozesse zu verstehen und exakt zu charakterisieren. Ein ausbalanciertes Wassermanagement ist die Grundlage für die optimale Leistungsfähigkeit einer wasserstoffbetriebenen Zelle. Das während des Betriebs entstehende Wasser muss die Membran ausreichend befeuchten, um deren Protonenleitfähigkeit aufrechtzuerhalten. Andererseits behindern zu große Wasseransammlungen in der Zelle die Gaszufuhr durch die porösen Materialien sowie in den Kanälen der Gasverteilerstrukturen. Alterungsphänomene einzelner Zellkomponenten können die Verteilung der Wasseransammlungen und somit das Wassermanagement empfindlich stören und so die Leistungsfähigkeit der Brennstoffzelle herabsetzen. Zur Analyse der Wasserverteilung werden zerstörungsfreie, bildgebende Methoden, wie die Ex-situ-Neutronentomografie und die In-situ-Synchrotronradiografie, eingesetzt. Diese Methoden können während des Brennstoffzellenbetriebs mit weiteren Messverfahren, beispielsweise der ortsaufgelösten Stromdichtemessung, kombiniert werden. Auf diese Weise werden einzelne Komponenten, wie zum Beispiel die Gasdiffusionsschichten, charakterisiert.
Neutron Bragg-edge imaging was applied for the visualization of a γ-Austenite to α'-martensite phase transformation. In the present study, a super martensitic
stainless steel sample was heated until complete austenitization and was subsequently cooled down to room temperature. The martensitic phase Transformation started at Ms = 190 °C. Using a monochromatic neutron beam with λ = 0.390 nm, the transmitted intensity was significantly reduced during cooling below Ms, since the emerging martensitic phase has a higher attenuation coefficient than the austenitic phase at this wavelength. The phase Transformation process was visualized by filming the transmission images from a scintillator screen with a CCD camera with a temporal resolution of 30 s and a spatial
resolution of 100 µm.
Neutron tomography has been applied to investigate the mechanism of hydrogen assisted cracking in technical iron and supermartensitic steel. Rectangular technical iron block samples showed blistering due to intense hydrogen charging and the tomographic method revealed in situ the spatial distribution of hydrogen and cracks. Hydrogen accumulated in a small region around cracks and the cracks are filled with hydrogen gas. Cracks close to the surface contained no hydrogen. Hydrogenous tensile test samples of supermartensitic steel were pulled until rupture and showed hydrogen accumulations at the notch base and in the plastically deformed region around the fracture surface.
We investigated hydrogen embrittlement and blistering in electrochemically hydrogen-charged technical iron samples at room temperature. Hydrogen-stimulated cracks and blisters and the corresponding hydrogen distributions were observed by neutron tomography. Cold neutrons were provided by the research reactor BER II to picture the sample with a spatial resolution in the reconstructed three-dimensional model of ~25 µm. We made the unique observation that cracks were filled with molecular hydrogen and that cracks were surrounded by a 50 µm wide zone with a high hydrogen concentration. The zone contains up to ten times more hydrogen than the bulk material. The hydrogen enriched zone can be ascribed to a region of increased local defect density. Hydrogen also accumulated at the sample surface having the highest concentration at blistered areas. The surfaces of the brittle fractured cracks showed micropores visualized by scanning electron microscopy. The micropores were located at grain boundaries and were surrounded by stress fields detected by electron backscattered diffraction. The cracks clearly originated from the micropores.
We investigated the hydrogen distribution spatially and temporally in technical iron at room temperature. Samples were charged electrochemically and subsequently analysed by means of neutron radiography and tomography. The radiographic images allowed for a time-resolved analysis of hydrogen fluxes. The three-dimensional distribution of hydrogen measured by neutron tomography delivered valuable information for the damage analysis of hydrogen-induced cracks. For the first time hydrogen concentration gradients inside the material could be detect directly together with the cracks. The neutron radiography and tomography results were gained at the Research Reactor BER II of the HZB in Berlin.
Polychromatic and wavelength-selective neutron transmission radiography were applied during bead-on-plate welding on 5 mm thick sheets on the face side of martensitic low transformation temperature (LTT) steel plates using gas tungsten arc welding (GTAW). The in situ visualization of austenitization upon welding and subsequent α’-martensite formation during cooling could be achieved with a temporal resolution of 2 s for monochromatic imaging using a single neutron wavelength and of 0.5 s for polychromatic imaging using the full spectrum of the beam (white beam). The spatial resolution achieved in the experiments was approximately 200 µm. The transmitted monochromatic neutron beam intensity at a wavelength of λ = 0.395 nm was significantly reduced during cooling below the martensitic start temperature Ms since the emerging martensitic phase has a ~10% higher attenuation coefficient than the austenitic phase. Neutron imaging was significantly influenced by coherent neutron scattering caused by the thermal motion of the crystal lattice (Debye–Waller factor), resulting in a reduction in the neutron transmission by approx. 15% for monochromatic and by approx. 4% for polychromatic imaging.
Polychromatic and wavelength-selective neutron transmission radiography were applied during bead-on-plate welding on 5 mm thick sheets on the face side of martensitic low transformation temperature (LTT) steel plates using gas tungsten arc welding (GTAW). The in situ visualization of austenitization upon welding and subsequent α’-martensite formation during cooling could be achieved with a temporal resolution of 2 s for monochromatic imaging using a single neutron wavelength and of 0.5 s for polychromatic imaging using the full spectrum of the beam (white beam).
The spatial resolution achieved in the experiments was approximately 200 µm. The transmitted monochromatic neutron beam intensity at a wavelength of λ = 0.395 nm was significantly reduced during cooling below the martensitic start temperature M s since the emerging martensitic phase has a ~10% higher attenuation coefficient than the austenitic phase. Neutron imaging was significantly influenced by coherent neutron scattering caused by the thermal motion of the crystal lattice (Debye–Waller factor), resulting in a reduction in the neutron transmission by approx. 15% for monochromatic and by approx. 4% for polychromatic imaging.