Abstract
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.
Highlights
Conductive and, thereby, electric discharge machinable ceramics for mechanical engineering application can be manufactured by consolidating mixtures of a structural ceramic matrix such as alumina, zirconia or silicon carbide or nitride and a percolating electrically conductive dispersion such as a transition metal carbide, nitride or boride, carbon nanotubes or graphene [1,2,3,4,5,6,7]
As most ceramic compositions designed for electric discharge machining (EDM) are, due to the pinning effect of the dispersion, not sufficiently sinterable, pressure assisted sintering processes such as hot isostatic pressing (HIP), hot axial pressing (HP), gas pressure sintering (GPS) or spark plasma sintering (SPS) are frequently applied to obtain dense and defect-free semifabricates [12]
1.5Yb1.5Sm-TZP composites with 24–32 vol.% electrically conductive WC dispersion were successfully densified by SPS to full density
Summary
Discharge Machinable 1.5Yb-1.5Sm-Electrically conductive and, thereby, electric discharge machinable ceramics for mechanical engineering application can be manufactured by consolidating mixtures of a structural ceramic matrix such as alumina, zirconia or silicon carbide or nitride and a percolating electrically conductive dispersion such as a transition metal carbide, nitride or boride, carbon nanotubes or graphene [1,2,3,4,5,6,7]. Fine tungsten carbide dispersions of 24–40 vol.% are known to provide sufficient electrical conductivity in the range of >20 kS/m to enable electric discharge machining (EDM) [9,10]. EDM is today widely applied to machine metals or cemented carbides for mechanical engineering applications, especially for applications in tools, dies or other customized mechanical engineering components of high geometrical complexity [11]. As most ceramic compositions designed for EDM are, due to the pinning effect of the dispersion, not sufficiently sinterable, pressure assisted sintering processes such as hot isostatic pressing (HIP), hot axial pressing (HP), gas pressure sintering (GPS) or spark plasma sintering (SPS) are frequently applied to obtain dense and defect-free semifabricates [12]
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