Browsing by Author "Rapp, Maximilian"

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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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    Spark plasma sintering of electric discharge machinable 1.5Yb-1.5Sm-TZP-WC composites
    (2022) Walter, Ella; Rapp, Maximilian; Kern, Frank
    Electrically conductive zirconia tungsten carbide composites are attractive materials for manufacturing precision components by electrical discharge machining due to their high strength, toughness and electrical conductivity. In this study, nanocomposite ceramics with a ytterbia samaria co-stabilized zirconia 1.5Yb-1.5Sm-TZP matrix and 24–32 vol.% tungsten carbide dispersion were manufactured by spark plasma sintering (SPS) at 1400 °C for 15 min at 60 MPa pressure. The materials exhibited high strengths of 1300–1600 MPa, a moderate fracture resistance of 6 MPa√m and an ultrafine microstructure with grain sizes in the 150 nm range. Scanning electron microscopy and RAMAN spectroscopy revealed the in situ formation of carbon during the SPS process and carbon formation scales with tungsten carbide content, and this apparently impedes bending strength.