Atmospheric and Surface Processes, and Feedback Mechanisms Determining Arctic Amplification: A Review of First Results and Prospects of the (AC)3 Project

Mechanisms behind the phenomenon of Arctic amplification are widely discussed. To contribute to this debate, the (AC)3 project has been established in 2016. It comprises modeling and data analysis efforts as well as observational elements. The project has assembled a wealth of ground-based, airborne, ship-borne, and satellite data of physical, chemical, and meteorological properties of the Arctic atmosphere, cryosphere, and upper ocean that are available for the Arctic climate research community. Short-term changes and indications of long-term trends in Arctic climate parameters have been detected using existing and new data

Time Resolved Neutron Bragg Edge Imaging A Case Study by Observing Martensitic Phase Formation in Low Temperature Transformation LTT Steel during GTAW

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 amp; 945; 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 m. The transmitted monochromatic neutron beam intensity at a wavelength of amp; 955; 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 imagin

Imaging with Cold Neutrons at the CONRAD 2 Facility

CONRAD 2 is an imaging instrument using low energy cold neutrons. The instrument is installed at the end of a curved neutron guide which avoids the direct line of sight towards the reactor core. This ensures a very low background of high energy neutrons and amp; 947; photons at the sample position. The cold neutron beam provides a wavelength range which is suitable for phase and diffraction contrast imaging such as grating interferometry and Bragg edge mapping. The instrument is well suited for high resolution imaging due to the high efficiency of the very thin scintillators that can be used for the detection of cold neutrons. An instrument upgrade was performed recently as a part of an upgrade program for the cold neutron instrumentation at HZB. The parameters of the instrument as well as some research highlights will be presented

Imaging of hydrogen in steels using neutrons

Abstract 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.</jats:p

Three dimensional imaging of hydrogen blister in iron with neutron tomography

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 threedimensional model of 25 lm. We made the unique observation that cracks were filled with molecular hydrogen and that cracks were surrounded by a 50 lm 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 micropore

Measuring hydrogen distributions in iron and steel using neutrons

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 surfac

Time resolved Bragg edge neutron radiography for observing martensitic phase transformation from austenitized super martensitic steel

Neutron Bragg edge imaging was applied for the visualization of a amp; 947; austenite to amp; 945; amp; 8242; 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 amp; 955; 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

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