Nano-diamond reinforced ZrB₂–SiC composites

The effect of adding various amounts of nano-diamond additive (0, 1, 2, and 3 wt%) on the densification behavior and mechanical properties of ZrB₂-25 vol% SiC samples were investigated in this research. All samples were spark plasma sintered at 1900 °C under 40 MPa external pressure for 7 min. Relative density (RD) values higher than 99.9% were obtained for the samples with 0, 1, and 2 wt% nano-diamond, while adding 3 wt% diamond dropped the RD by ~1.2%. The XRD and microstructural evaluations revealed the formation of some in-situ phases, namely ZrC and B₄C. The highest Vickers hardness (24.7 GPa) and fracture toughness (5.8 MPa m^1/2) were achieved for the samples doped with 2 and 3 wt% nano-diamond, respectively. Ultimately, the SEM micrographs indicated the role of different toughening mechanisms on obtaining such a high value of fracture toughness.