Effect of Zr and C co-addition on the characteristics of ZrB₂-based ceramics: Role of spark plasma sintering temperature

This study investigates the effect of Zr and C co-addition on the spark plasma sintered ZrB₂-5 vol% Zr/graphite composites. Spark plasma sintering method was applied to consolidate and reinforce the composites by in-situ synthesis of ZrC through a chemical reaction between metallic Zr and graphite precursors. The effect of sintering temperature on the phase arrangement of the obtained composites was investigated by employing microstructural characterization techniques, mechanical properties measurements, and thermodynamic calculations. Results showed that the formation of ZrC cannot occur directly, while the in-situ reinforcement can be achieved indirectly if favorable thermodynamic and kinetic conditions provided. The sample sintered at 1700 °C showed a considerable amount of in-situ formed ZrC. However, in samples sintered at 1750 °C and 1800 °C, a diversity of phases was observed, mainly including ZrO₂ polymorphs. It was also indicated that although higher sintering temperatures may improve hardness and densification of the composites, but may also cause poor fracture toughness. Consequently, the effect of sintering temperature on the phase arrangement and consequent characteristics of the prepared composites were fully addressed.