Electrically conductive ZrO2–TiN composites

1.75 mol% Y2O3-stabilized ZrO2–TiN composites could be fully densified by hot pressing for 1 h at 1550 °C in vacuum under a mechanical pressure of 28 MPa. Composites with 35–95 vol% TiN were investigated and the best mechanical properties, i.e., a Vickers hardness of 14.7 GPa, an indentation toughness of 5.9 MPa m1/2 and an excellent bending strength of 1674 MPa were obtained with 40 vol% TiN. The active toughening mechanisms were identified and their contribution to the overall composite toughness as function of the TiN content was modelled, experimentally verified and discussed. Transformation toughening was found to be the primary toughening mechanism. The TiN grain size was found to increase with increasing TiN content, resulting in a decreasing hardness and strength. A maximum strength was obtained at 40 vol% TiN. The electrical resistivity of the composites decreases exponentially with increasing TiN content and correlates well with the Polder-Van Santen mixture rule. Thus at around 40 vol% TiN, the conductivity is high enough to allow EDM machining of the composite, therefore avoiding the expensive grinding operation for final shaping and surface finishing of components.