Role of carbon morphology on the synthesizability of ZrC during spark plasma sintering of ZrB₂–Zr–C composites

ZrB₂-based composites were consolidated through reactive spark plasma sintering of the powder mixtures containing relatively 5 vol.% of metallic Zr particles, and graphite flakes (GF) or carbon nanotubes (CNT) as the carbon source, with the aim of ZrC in-situ synthesis in ZrB₂ matrix. Microstructural and phase analyses indicated that GFs cannot result in detectable ZrC in the final microstructure. Contrarily, it was found that CNTs promote the in-situ synthesizability of zirconium carbide in the composite system. However, the sample containing graphite flakes presented better densification outcomes. The mechanism of ZrC formation in the composites, based on the carbon source, was finally discussed and illustrated.