Densification behavior and properties of hot-pressed ZrC ceramics with Zr and graphite additives

Densifications of hot-pressed ZrC ceramics with Zr and graphite additives were studied at 1800–2000 °C. ZrC with 8.94 wt% Zr additive (named ZC10) sintered at 1900–2000 °C achieved higher relative densities (>98.4%) than that of additive-free ZrC (<83%). The densification improvement was attributed to the formation of non-stoichiometric ZrC0.9, whereas there had rapid grain growth with grain size about 50–100 μm in ZC10. By adding co-doped additive of Zr plus C and adjusting the molar ratio of Zr/C, ZrC with co-doped additives with Zr/C molar ratio at 1:2 (named ZC12), ZrC ceramics with both high relative density (98.4%) and fine microstructures (grain size about 5–10 μm) were obtained at 1900–2000 °C. Effect of formation of non-stoichiometric ZrC1−x on densification of ZrC was discussed. The Vickers hardness and indentation toughness of ZC10 and ZC12 samples sintered at 1900 °C were 17.8 GPa and 3.0 MPa m1/2, 16.2 GPa and 4.7 MPa m1/2, respectively.