Browsing by Author "Funk, Alexander"

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    Getting magnetocaloric materials into good shape: Cold-working of La(Fe, Co, Si)13 by powder-in-tube-processing
    (Amsterdam [u.a.] : Elsevier Ltd., 2018) Funk, Alexander; Freudenberger, Jens; Waske, Anja; Krautz, Maria
    The powder-in-tube (PIT) technology was applied to La(Fe, Co, Si)13 powder cladded by a thin seamless austenitic steel jacket. Wires appear to be promising in the search for alternative regenerator geometries, since they offer various possibilities of arrangements allowing to optimise heat transfer and pressure loss within the boundaries set by parallel plate and sphere beds. Here, pre-alloyed La(Fe, Co, Si)13 powder was filled in a AISI 316L austenitic steel tube and swaged to wires with an outer diameter of 1 mm. By mechanical deformation, the steel jacket thickness was reduced to about 100 μm surrounding the magnetocaloric core. A post-annealing of only 10 min at 1050 °C is sufficient to form the magnetocaloric NaZn13-type phase resulting in an entropy change close to the value of a pure reference sample. The presented technology is not limited to La(Fe, Co, Si)13/steel combination but can be extended to material pairs involving wire core materials with a first order transition, such as Fe2P-type or Heusler alloys.
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    Microstructure and Deformation Response of TRIP-Steel Syntactic Foams to Quasi-Static and Dynamic Compressive Loads
    (Basel : MDPI, 2018-4-24) Ehinger, David; Weise, Jörg; Baumeister, Joachim; Funk, Alexander; Waske, Anja; Krüger, Lutz; Martin, Ulrich
    The implementation of hollow S60HS glass microspheres and Fillite 106 cenospheres in a martensitically transformable AISI 304L stainless steel matrix was realized by means of metal injection molding of feedstock with varying fractions of the filler material. The so-called TRIP-steel syntactic foams were studied with respect to their behavior under quasi-static compression and dynamic impact loading. The interplay between matrix material behavior and foam structure was discussed in relation to the findings of micro-structural investigations, electron back scatter diffraction EBSD phase analyses and magnetic measurements. During processing, the cenospheres remained relatively stable retaining their shape while the glass microspheres underwent disintegration associated with the formation of pre-cracked irregular inclusions. Consequently, the AISI 304L/Fillite 106 syntactic foams exhibited a higher compression stress level and energy absorption capability as compared to the S60HS-containing variants. The α′ -martensite kinetic of the steel matrix was significantly influenced by material composition, strain rate and arising deformation temperature. The highest ferromagnetic α′-martensite phase fraction was detected for the AISI 304L/S60HS batches and the lowest for the TRIP-steel bulk material. Quasi-adiabatic sample heating, a gradual decrease in strain rate and an enhanced degree of damage controlled the mechanical deformation response of the studied syntactic foams under dynamic impact loading.