TY - CONF A1 - Griesche, Axel T1 - World Materials Research Institute Forum - An Introduction T2 - NIST Diffusion Workshop Series: Multicomponen Diffusion Data and Its Impact on the Materials Design Process: Data Needed; Data Acquisition; and Data Application CY - Gaithersburg, MD, USA DA - 2012-05-03 PY - 2012 AN - OPUS4-25896 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Griesche, Axel A1 - Altenkirch, J. A1 - Gibmeier, J. A1 - Beyer, Katrin A1 - Kromm, Arne A1 - Kannengießer, Thomas T1 - Welding problems - Investigations with neutrons of residual stress and of hydrogen diffusion in steels N2 - We report about investigations of typical material problems in steels. First, residual stresses in and around weld seams with low martensite transition temperature filler material were analyzed w/ and w/o additional transverse tensile load. The investigation was accompanied by x-ray diffraction measurements to track stress-induced phase transitions. Martensite formation during welding under external load yield strain gradients near the surface that improve the integrity of the weld. Further, the residual stress distribution close to laser-treated steel surfaces was analyzed. The method could be improved to reduce analysis artifacts. Finally, hydrogen diffusion in different steels was measured using neutron radiography and subsequent image analysis. Diffusion coefficients were derived by analyzing the time-dependent mass flux. In an outlook we describe the optimal ESS instrumentation from a metallurgist’s point of view. T2 - ESS Workshop "Science Vision for the European Spallation Source - German Perspectives" CY - Bad Reichenhall, Germany DA - 2011-10-10 PY - 2011 UR - http://www.fz-juelich.de/cae/servlet/contentblob/1058986/publicationFile/24649/Griesche_pdf.pdf UR - http://www.fz-juelich.de/sid_BD693DF17F42B3018726EE5C2558C56C/jcns/EN/Leistungen/ConferencesAndWorkshops/ESS/_node.html AN - OPUS4-24464 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Griesche, Axel A1 - Horbach, J. A1 - Meyer, A. T1 - Influence of thermodynamic forces on diffusion in melts N2 - We report about diffusion measurements and molecular dynamic simulations in Al-Ni and Al-Cu melts. Capillary methods were used to measure Ni and Cu self diffusion and to measure interdiffusion. The combination of the capillary set-up with X-ray radiography allowed in-situ detecting of convective contributions to the interdiffusion transport by tracking the time dependence of diffusion. Thus, the determination of the interdiffusion coefficient can be restricted to convection-free experiment times resulting in an increased accuracy of the measured interdiffusion coefficient. Additionally, quasielastic neutron scattering was used to measure convection-free Ni and Cu self diffusion. Molecular dynamics simulations were used to determine all diffusion coefficients and the thermodynamic factor. The comparison between experiment and simulation shows an excellent agreement of the interdiffusion coefficients as a function of temperature. It was found that interdiffusion is enhanced by thermodynamic forces with a maximum around the stoichiometric composition. T2 - TMS 2011 CY - San Diego, CA, USA DA - 2011-02-27 PY - 2011 AN - OPUS4-23340 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Griesche, Axel T1 - Diffusion of hydrogen in steels T2 - DLR-Seminar CY - Cologne, Germany DA - 2011-02-15 PY - 2011 AN - OPUS4-23341 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Griesche, Axel A1 - Beyer, Katrin A1 - Kannengießer, Thomas A1 - Solórzano, E. T1 - In-situ measurement of hydrogen diffusion in steels using neutron radiography T2 - DIMAT 2011, 8th International Conference On Diffusion In Materials CY - Dijon, France DA - 2011-07-03 PY - 2011 AN - OPUS4-24312 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Griesche, Axel A1 - Beyer, Katrin A1 - Kannengießer, Thomas A1 - Schillinger, B. T1 - In-situ observation of hydrogen diffusion in iron using neutron radiography N2 - Hydrogen assisted cracking of metals limits the durability of welds and constructions. Still the failure mechanisms are not fully understood, for instance the role of hydrogen mass transport during crack initiation. Measuring the hydrogen concentration as a function of time (and space) would allow to determine diffusion coefficients helping to enlighten this lack of understanding. Therefore, neutron radiography is a valuable tool for measuring in situ hydrogen transport in iron and steels [1]. The influence of grain boundaries on the hydrogen diffusion behaviour can be determined by comparing the diffusion behaviour of samples with e.g. different microstructure. In a first study we investigated in situ the simplest case, the hydrogen effusion out of pure iron (ARMCO) using neutron radiography at ANTARES [2]. Samples were charged electrochemically ex situ with a well defined amount of hydrogen, stored in liquid nitrogen and were then heat treated during a neutron radiography measurement whilst the change of neutron transmission was recorded. For analysis the gray values in the pictures were transformed into concentrations with help of an ex post calibration. Therefore, the experimental temperaturetime profile of the heat treatment has been repeated with identical samples in the home lab and the amount of effusing hydrogen was measured by carrier gas hot extraction. In a first approximation the concentration of hydrogen in the sample can be calculated by subtracting the hydrogen concentration in the atmosphere from the initial one in the sample. We were able to measure hydrogen concentrations as low as 65 wt.ppm. Simultaneously monitoring of hydrogenous sample and hydrogen-free reference allowed for in situ measurement of hydrogen effusion. Sample heating was done by infrared radiation. Diffusion coefficients for hydrogen effusion from iron have been calculated. They coincide fairly with literature data. T2 - 3rd FRM II User Meeting CY - Garching, Germany DA - 2010-10-15 PY - 2010 AN - OPUS4-22835 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -