Spark-plasma-sintering kinetics of ZrC–SiC powder mixtures subjected to high-energy co-ball-milling

The effect of SiC addition (5, 17.5, or 30 vol%) on the spark-plasma sinterability of ZrC ultra-high-temperature ceramics (UHTC) was investigated as a function of the intensity of high-energy co-ball-milling. It was found that the spark-plasma-sintering (SPS) kinetics of the ZrC–SiC powder mixtures is enhanced progressively with increasing co-milling time, which is due to the progressive refinement of the crystallite sizes. It was also found that in practice the SiC addition is beneficial for the SPS kinetics of ZrC if the co-milling time is short enough so as to refine the SiC crystallite size only to the submicrometre range, although the improvement in sinterability does not correlate with the SiC content. On the contrary, the SiC addition is increasingly detrimental for those co-milling times that promote SiC refinement to the nanoscale. This unexpected trend is due to slower ZrC crystallite size refinement in the presence of SiC and, especially, to the complex role played during SPS by the passivating SiO2 films formed on the SiC particles, and is different from what has been observed in ZrB2–SiC. Finally, implications of interest for the UHTC community are discussed.