Synergistic influence of SiC and C₃N₄ reinforcements on the characteristics of ZrB₂-based composites

In this work, ZrB₂–SiC and novel C₃N₄-doped ZrB₂–SiC composites were manufactured at 1850°C under an external load of 40 MPa for 6 min via spark plasma sintering. The effects of C₃N₄ on the mechanical characteristics (flexural strength, Vickers hardness, and fracture toughness) and microstructure of the ZrB₂–SiC-based composites were investigated. By adding 5 wt% g-C₃N₄, a fully dense ceramic composite was fabricated, compared to the C₃N₄-free ZrB₂–SiC composite with a relative density of 95%. Removal of ZrO₂ and B₂O₃ from the surface of ZrB₂ particles via chemical reactions with C₃N₄, and the in-situ synthesis of ZrC and BN as new phases were studied by XRD and SEM analyses. Indentation fracture toughness, flexural strength, and Vickers hardness improved from 4.5 MPa.m^1/2, 460.2 MPa and 17.4 GPa to 6.1 MPa.m^1/2, 580.2 MPa and 21.2 GPa, respectively, by adding g-C₃N₄ to the ZrB₂–SiC ceramic.