[en] The target for the Munich Fission Fragment Accelerator (MAFF) consists of typically 1 g of the fission material ²³⁵U in the form of UC₂, dispersed homogeneously in a cylindrical graphite matrix, which is encapsulated in a protective Re container. This special type of target is currently under development. The problems related to its manufacture are discussed. To enable diffusion and extraction of the fission products, the target has to be maintained at a temperature of up to 2700 K during operation. Extensive tests are required to study the long-term behaviour of the involved materials at these conditions. For this purpose a resistively heated high vacuum furnace has been set up, which allows high-temperature heat treatment of target samples for a period of up to 1000 h

[en] Lightweight construction materials, in particular aluminum alloys, have recently become more important as construction materials due to their low weight with high strength and sufficient wear and corrosion properties. In order to be able to use the advantages resulting from the use of aluminum alloys, powerful and reliable thermal joining methods are required which reduce the heat input into the component and thus the distortion and change the set structure as less as possible. New approach here is the NV-EB brazing at low acceleration voltage. In particular, two aspects must be solved for process-reliable brazing of aluminum alloys. On the one hand, the oxide layer on the surface of the aluminum workpiece must be removed. On the other hand, sufficient heat must be put into the solder and base material in order to both melt the solder and to heat the base material sufficiently, but below the solidus temperature. Often the “Nocolok” potassium tetrafluoroaluminate flux is used. In addition, the harmful to health cesium fluoroaluminate and mixtures of both fluxes are used. Apart from health aspects, the use of fluxes has led to increased pollution of an equipment and corrosion, which contributes to process instability. By reason of described above, the investigation of a fluxless brazing of aluminum alloys using non vacuum electron beam by 60kV acceleration voltage is of great interest. (paper)

[en] Nimonic 101 is one of the early nickel-based superalloys developed for the use in gas turbines. In such environments, the material is exposed to a combination of both high temperatures and mechanical loads for a long duration. Hence, thermal creep is of the utmost concern as it often limits service life. This study focuses on creep tests, carried out on Nimonic 101 at different temperatures under a constant tensile load of 735 MPa. To characterize the microstructural evolution, electron backscatter diffraction (EBSD) measurements were employed before and after loading. At higher temperatures, a significant change of the microstructure was observed. The grains elongated and aligned their orientation along the load axis. In parallel, a crystal plasticity material model has been set up in the classical large deformation framework. Modeling results are compared to the acquired EBSD data.

[en] In Garching near Munich the new research reactor FRM II is under construction. It is supposed to be commissioned in 2001. The reactor will have a power of 20 MW, a rather small core diameter of 25 cm and a maximum neutron flux of 8·10¹⁴ n/cm²·s. Many new powerful instruments and novel experiments are planned in material science, solid state physics, nuclear physics, fundamental physics, chemistry, biology, medicine and technology. Consequently, the applications will range from material science diffractometers and inelastic neutron scattering over neutron tomography and cancer therapy to fusion producing the heaviest elements using accelerated fission fragments. The acceleration for radioactive isotope beams (RIB) is an important new field in nuclear physics and many new facilities are planned or under construction all over the world. Nuclear fission is the most suitable method to produce neutron-rich isotopes due to the large fission cross sections of thermal neutrons and the high thermal neutron flux in modern research reactors. Consequently, the new facility MAFF (Munich Accelerator for Fission Fragments) is foreseen for the new FRM II reactor. Beams of about 10¹¹ atoms/s are expected for ⁹¹ Kr, ¹³² Sn, ¹⁴⁴ Cs from a ²³⁵ U source in a graphite cylinder close to the reactor core placed in a through-going beam-tube. Laser ionisation and a linear accelerator with IH and RFQ structures will provide the possibility to accelerate many different isotopes up to about 6 MeV/nucleon. Neutron-rich isotope beams are most interesting, because they will allow the investigation of several exciting new areas: i) Production of heavy and superheavy and superheavy elements. ii) Atomic physics and chemistry of the heaviest elements. iii) Nuclear structure of astrophysically relevant nuclides and data for the r-process nucleosynthesis. iv) Isospin dependence of nuclear reactions. v) Application of radioactive isotope beams for solid state physics, medicine and radioactive waste management (Authors)

[en] A new model is proposed to successfully predict the initiation and evolution of the austenite-to-bainite phase transformation, capturing specifically the time-dependent transformation kinetics. In particular, the isothermal bainitic transformation in 51CrV4 steel is experimentally observed for various constant stress conditions, and significant improvement is obtained in comparison with the existing models. Specifically, both the transformation kinetics and the resultant transformation strains can be simultaneously predicted using the same variant growth approach. Simulation results are in good agreement with the experiments, evidencing the success of the proposed model in describing the transformation phenomena in terms of kinetics and transformation plasticity. Furthermore, the proposed formulation provides a basis for incorporating variant–variant interactions and cementite formation in the residual austenite matrix

No abstract available

[en] Localized oxidation and corrosion behavior of a nickel–titanium (NiTi) shape memory alloy (SMA) was investigated via static immersion experiments in a simulated body fluid solution. Detailed electron microscopy examinations on the sample surfaces revealed preferential formation of local oxide particles around dislocation networks, which constitute high-energy zones. Moreover, various intermediate phases were detected in addition to the parent NiTi phase around dislocation networks. These are also areas with enhanced diffusion, which promotes Ni release. These findings emphasize the significant role of fine microstructural features, such as dislocation networks, on the oxidation and Ni release, and thus, the biocompatibility of the NiTi SMAs.

[en] Beside lithium batteries, PEM fuel cells are the most promising strategy as a power source to achieve the targets for introducing and increasing the usage of electric vehicles. Due to limited space and weight problems, water cooled, metallic bipolar plates in a fuel cell metal stack are preferred in motor vehicles. These plates are stamped metal sheets with a complex structure, interconnected media-tight. To meet the multiple tasks and requirements in use, complex and expensive combinations of materials are currently in use (carbon fiber composites, graphite, gold-plated nickel, stainless and acid resistant steel). The production of such plates is expensive as it is connected with considerable effort or the usage of precious metals. As an alternative, metalloid nitrides (CrN, VN, W_2N, etc.) show a high chemical resistance, hardness and a good conductivity. So this material category meets the basic requirements of a top layer. However, the standard methods for their production (PVD, CVD) are expensive and have a slow deposition rate and a lower layer thicknesses. Because of these limitations, a full functionality over the life cycle of a bipolar plate is not guaranteed. The contribution shows the development and quantification of an alternative production process for bipolar plates. The expectation is to get significant advantages from the combination of chromium electrodeposition and thermochemical treatment to form chromium nitrides. Both processes are well researched and suitable for series production. The thermochemical treatment of the chromium layer also enables a process-integrated brazing. (paper)

[en] A reverse computation procedure is proposed for calculating parent austenite orientations, which are experimentally challenging to obtain, based on the final texture after austenite-to-bainite and austenite-to-martensite phase transformations. Specifically, post-transformation electron backscatter diffraction scans of bainite and martensite were carried out in order to identify the product crystal orientations within a single former austenite grain. Subsequently, the Kurdjumov–Sachs relationship was utilized to compute the parent austenite crystal orientation based on these data. The proposed method provided a unique solution for the initial austenite grain orientation in most of the cases. Overall, the proposed computational procedure constitutes a means of understanding the factors influencing microstructural evolution in displacive phase transformations. (paper)

[en] We have developed optical filters for the German X-ray astronomy satellite ABRIXAS (A BRoadband Imaging X-ray All Sky Survey)(1). Specific CCD's (2) will be used as detectors in the focal plane on board the observatory. Since these detectors are sensitive from the X-ray to the near infrared spectral range, X-ray observations require optical filters, which combine high transmittance for photon energies in the soft X-ray region and a high absorptance for ultraviolet and visible radiation. With respect to the mission goal in orbit a spectral transmission function is required attenuating radiation below photon energies of 10 eV by more than 7 orders of magnitude and transmitting soft X-ray photon energies above 1000 eV by more than 90 percent. This was realized by a 0.80 μm thick polypropylene foil, which is coated with approximately 60 nm aluminum on both sides. The filters have an effective diameter of 73 mm without any support structure. Environmental tests have been performed and proved the filters to be resistant against sound pressure and vibrational load stresses during the launch of the spacecraft. Synchroton radiation was used to characterize the properties of the filters in the soft X-ray photon energy range 60 eV< E<2000 eV. We describe the measurements determining the spectral transmittance function in the center of the filters, and the transmission topography at discrete photon energies across the effective area, and present the resulting performance data