Browsing by Author "Gommeringer, Andrea"

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    Electrical discharge machinable ytterbia samaria co-stabilized zirconia tungsten carbide composites
    (2021) Rapp, Maximilian; Gommeringer, Andrea; Kern, Frank
    Composite ceramics of stabilizer oxide coated ytterbia-samaria costabilized zirconia (1.5Yb1.5Sm-TZP) and 24-32 vol% of tungsten carbide as an electrically conductive dispersion were manufactured by hot pressing at 1300-1400 °C for 2 h at 60 MPa pressure. The materials were characterized with respect to microstructure, phase composition, mechanical properties and electrical discharge machinability by die sinking. Materials with a nanocomposite microstructure and a strength of up to 1700 MPa were obtained. An attractive toughness of 6-6.5 MPa√m is achieved as 40-50% of the zirconia transformed upon fracture. The materials show fair material removal rates of 1 mm³/min in die sinking. Smooth surfaces indicate a material removal mechanism dominated by melting.
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    Mechanical properties and electrical discharge machinability of alumina-10 vol% zirconia-28 vol% titanium nitride composites
    (2020) Gommeringer, Andrea; Kern, Frank
    Electrical discharge machinable ceramics provide an alternative machining route independent on the material hardness which enables manufacturing of customized ceramic components. In this study a composite material based on an alumina/zirconia matrix and an electrically conductive titanium nitride dispersion was manufactured by hot pressing and characterized with respect to microstructure, mechanical properties and ED-machinability by die sinking. The composites show a combination of high strength of 700 MPa, hardness of 17-18 GPa and moderate fracture resistance of 4.5-5 MPa√m. With 40 kS/m the electrical conductivity is sufficiently high to ensure ED-machinability.
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    Mechanical properties of 2Y-TZP fabricated from detonation synthesized powder
    (2020) Kern, Frank; Gommeringer, Andrea
    Yttria stabilized zirconia (Y-TZP) is frequently used in dental and engineering applications due to its high strength and fracture resistance. In this study, 2Y-TZP samples were manufactured from commercially available powder produced by detonation synthesis. Tests of the mechanical properties exhibited an unusual combination of both very high strength and toughness. The materials show a very weak correlation between toughness and grain size. The transformability, measurable by XRD, cannot explain the high toughness. Fractographic analysis revealed a broad transformation affected zone with secondary cracks and shear bands on the tensile side of bending bars which can be made responsible for the high toughness and non-linear stress-strain curves.