W. Grünberger

Leibniz Institute for Solid State and Materials Research Dresden, Dresden, Saxony, Germany

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Publications (12)12.59 Total impact

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    ABSTRACT: We have proposed to build a 100 T/10 ms, 70 T/100 ms, 60 T/1 s pulsed field user facility with a 50 MJ capacitor bank at the Forschungszentrum Rossendorf near Dresden. This would provide the appealing possibility to have access to Zeeman energies in the energy range of the infrared free-electron-lasers (5 μm to 150 μm; 2 ps; cw; > 10 W) now under construction at the radiation source ELBE (superconducting electron linear accelerator; 40 MeV; 1 mA; 2 ps; cw) in Rossendorf. The work is accompanied by computer simulations of the planned coil systems, of the power supply, and by the development of high-strength conductors aiming at a tensile strength of about 1.5 GPa at σ ≈ σ Cu/2 (microcomposite CuAg alloys and Cu-steel macro compounds). With a view of gaining experience in the construction and operation of pulsed magnets, a pilot pulsed field laboratory was established at the Institute of Solid State and Materials Research Dresden (IFW Dresden). The laboratory includes short pulse magnets with peak field up to 60 T in a 24 mm bore and a rise time of about 10 ms (coil from NHMFL, Tallahassee), and a 40 T long pulse magnet with 24 mm bore and rise time of about 80 ms (coil from METIS, Leuven). The repetition rate of 20 min between pulses is limited by the cooling time of the coils. The coils are energized by a 1 MJ, 10 kV capacitor bank with some special features. With this set-up measurements of magnetization and magnetotransport on 4f-electron systems, for example RECu2, have been out in the temperature range of 1.5 to 300 K and at fields up to 52 T using high precision pick-up coils.
    International Journal of Modern Physics B 01/2012; 16(20n22). · 0.46 Impact Factor
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 01/2010; 29(22).
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    ABSTRACT: The nonequilibrium process of mechanical alloying was used to prepare nanocrystalline powder. The crystallization of the -type structure in mechanically alloyed Sm - Fe(Ga) - C material begins at about C. The single phase structure can be obtained after homogenization for one hour at temperatures between C and C. The coercivity increases to a maximum value of about 1.5 T after annealing at a temperature of C. The nearly square shape of the demagnetization curve suggests a very homogeneous microstructure of the highly coercive powder. By hot pressing, a fully dense magnet was successfully obtained with a density of 7.6 g and a coercivity of 1.5 T. No texture could be observed after a 75% hot deformation at C.
    Journal of Physics D Applied Physics 12/1998; 29(1):271. · 2.53 Impact Factor
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    ABSTRACT: The hydrogenation disproportionation desorption recombination (HDDR) process was applied to produce isotropic, submicron powder in 500 g batches in a specially designed HDDR reactor. The hot pressing characteristics of the material were determined and it was shown that the material has an excellent stability against grain growth. The coercivity of 1000-1080 is almost constant over a hot pressing temperature range of 700-, making the material highly suitable for subsequent hot deformation. Die-upset HDDR magnets were prepared in order to study the basic deformation behaviour. A remanence of 1.13 T in the axial direction and a coercivity of were achieved. Similar properties were obtained for the backward extruded magnets produced at and only a small decrease in alignment along the axial direction of the ring was found. Grain sizes were very uniform and on the submicron scale. Platelet-shaped grains were observed in the die-upset magnets. The formation of interaction domains, along the axial and radial directions for the die-upset and backward extruded magnets respectively, were established by high-resolution Kerr microscopy. The high degree of texture in the hot deformed HDDR magnets was also confirmed by Lorentz microscopy revealing continuous equispaced domains extending over the entire thinned sample with only small directional variations.
    Journal of Physics D Applied Physics 12/1998; 31(7):807. · 2.53 Impact Factor
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    ABSTRACT: Commercial melt-spun and HDDR Nd-Fe-B powders as well as mechanically alloyed Nd-Fe-B powders have been used for hot pressing and subsequent die upsetting. A comparison of all three types of magnets with respect to their magnetic properties and deformation behaviour is discussed in this paper. The highest values of remanence, , and energy density, , found for the die-upset melt-spun material can be explained in terms of its small Nd content of 14 at% and its high degree of texture connected with the strong shape anisotropy of the deformed nanocrystalline grains. Fracture surfaces of this material have coarse grains at the former flake boundaries which results in a coercivity, , of only 1 T. An energy density of has been measured for a die-upset mechanically alloyed material. In spite of a Nd content of 16 at% in this alloy, a remanence of 1.2 T and a coercivity of 1.6 T have been attained. The large coercivity is due to (i) a very homogeneous distribution of the Nd-rich intergranular phase, (ii) a grain size of only observed after die upsetting and (iii) the fact that there is no formation of faceted grains during hot deformation. The microstructure of HDDR magnets (14 at% Nd) has larger average grain sizes and some faceted grains. Consequently these magnets have the smallest values of the degree of texture, remanence, , and energy density, . By addition of further elements the coercivity of this material could be held at . After thermal demagnetization the three types of hot-deformed Nd-Fe-B magnets have a relatively large initial susceptibility, which is due to the presence of classical magnetic domains as well as interaction domains. For the investigated fine-grained Nd-Fe-B materials the deformation mechanism can be described by using a solution-precipitation creep model, governed by interface-reaction-controlled creep.
    Journal of Physics D Applied Physics 12/1998; 31(14):1660. · 2.53 Impact Factor
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    ABSTRACT: Isotropic fine-grained Nd1.65Febal.Ga0.6B6 was prepared by the HDDR process. Permanent magnets obtained by die upsetting of the HDDR material show a remanence of 1.1 T and a coercivity μ0JHc of 0.9 T. The hot deformation is dominated by a diffusion supported resolution process. The activation energy of this process is about 200 kJ/mol and the stress exponent is n ≈ 1.
    Materials Letters. 01/1998;
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    ABSTRACT: Isotropic, submicron grained Nd15Fe77B8 powder has been prepared by applying the HDDR process. Fully dense isotropic magnets have been produced by hot pressing, textured compacts have been obtained by subsequent die upsetting. Radially oriented ring magnets have been prepared by backward extrusion of the hot pressed compacts. Very encouraging magnetic properties have been achieved, the remanence measured in the radial direction is Br=1.07 T with a coercivity of iHc=575 kA/m. However, a decrease in alignment has been observed in the axial direction of the ring magnet. The effects of deformation temperature and speed have been investigated. Magnetic properties and the physical and magnetic microstructure have been characterised by VSM, SEM and high-resolution Kerr-effect microscopy, the latter showing the formation of interaction domains, which indicate a high degree of texture in a fine grained material, in both the die upset and the backward extruded ring magnet produced from Nd15Fe77B8 HDDR material.
    Journal of Magnetism and Magnetic Materials 01/1998; · 1.83 Impact Factor
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    ABSTRACT: In this work HDDR powders were used for the preparation of highly densified anisotropic NdFeB magnets by the die-upsetting process. HDDR powders with different Nd contents (14 at %, 16 at % and 18 at %) and different grain sizes were used in order to determine the most favourable composition and microstructure for a production of crack-free magnets with maximum texture and optimum magnetic properties. The powders were hot compacted in vacuum at 725°C and 150 MPa. Then the samples were hot deformed in an argon atmosphere at 750°C with a strain rate of 10−3 s−1. Using HDDR powders with grain sizes around 0.3 μm, corresponding to a coercivity μ0jHc of 1 T, a Nd content of 14 at % and a deformation degree of 0.9, a remanence of 1.2 T and a coercivity of 0.7 T were obtained. However a large amount of cracks were present in the die-upset sample with 14 at % Nd. By increasing the Nd content suppression of the cracks in the die-upset samples was achieved and an increase of the coercivity was observed, but the degree of texture and the remanence of the sample are reduced. For a Nd content of 16 at %, crack-free magnets with a coercivity of 0.95 T and a remanence of 1 T could be produced.
    Journal of Alloys and Compounds 01/1998; · 2.73 Impact Factor
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    ABSTRACT: Commercial melt-spun powders MQP-A and MQP-B were hot compacted in vacuum. Thereafter (i) die-upsetting experiments were performed under an argon atmosphere at 500 to 800 °C with strain rates of 10−4 to 10−1 s−1 or (ii) radially textured ring magnets were made by backward extrusion. The remanence achieved for die-upset MPQ-A samples is Br = 1.3 T (compared to 0.8 T obtained after hot-compaction). In the case of ring magnets typical values of Br, μ0Hcj and (BH)max are 1.25 T, 1.1 T and 280 kJ m−3, respectively. The deformation and formation-of-texture processes can be explained by the model of solution-precipitation creep. The main driving forces of the deformation processes are the chemical potentials of the atomic species in the liquid phase or at the surfaces of the crystallites. The activation energies of these processes are 280 and 400 kJ mol−1 for MQP-A and MQP-B samples, respectively. The strain rate was found to be proportional to σ3 and d−1 where σ is the flow stress and d is the mean grain size of the sample. These values indicate an interface-controlled solution-precipitation process. The liquid grain-boundary phase does not seem to be required for deformation and texturing. However its presence is necessary for a crack-free deformation at high strain rates.
    Journal of Alloys and Compounds. 01/1997;
  • 01/1996;
  • W. Grünberger, D. Hinz, D. Schläfer, L. Schultz
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    ABSTRACT: Radially-oriented NdFeB ring magnets have been prepared by backward extrusion of melt-spun material. The average remanence measured in the radial direction reaches values above 1.2 T. Due to the inhomogeneity of the deformation, the magnetic properties and X-ray diffraction patterns revealed a gradual improvement of the alignment from the outer shell to regions near the inner surface of the ring.
    Journal of Magnetism and Magnetic Materials - J MAGN MAGN MATER. 01/1996; 157:41-42.
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    ABSTRACT: We have proposed to build a 100 T/10 ms, 70 T/100 ms, 60 T/1 s pulsed field user facility with a 50 MJ capacitor bank at the Forschungszentrum Rossendorf near Dresden. This would provide the appealing possibility to have access to Zeeman energies in the energy range of the infrared free-electron-lasers (5 mm to 150 mm; 2 ps; cw; > 10 W) now under construction at the radiation source ELBE (superconducting electron linear accelerator; 40 MeV; 1 mA; 2 ps; cw) in Rossendorf. The work is accompanied by computer simulations of the planned coil systems, of the power supply, and by the development of high-strength conductors aiming at a tensile strength of about 1.5 GPa at s » sCu/2 (microcomposite CuAg alloys and Cu-steel macro compounds). With a view of gaining experience in the construction and operation of pulsed magnets, a pilot pulsed field laboratory was established at the Institute of Solid State and Materials Research Dresden (IFW Dresden). The laboratory includes short pulse magnets with peak field up to 60 T in a 24 mm bore and a rise time of about 10 ms (coil from NHMFL, Tallahassee), and a 40 T long pulse magnet with 24 mm bore and rise time of about 80 ms (coil from METIS, Leuven). The repetition rate of 20 min between pulses is limited by the cooling time of the coils. The coils are energized by a 1 MJ, 10 kV capacitor bank with some special features. With this set-up measurements of magnetization and magnetotransport on 4f-electron systems, for example RECu2, have been out in the temperature range of 1.5 to 300 K and at fields up to 52 T using high precision pick-up coils.
    International Journal of Modern Physics B, v.16, 3397-3397 (2002).