Influence of sol-gel derived ZrB₂ additions on microstructure and mechanical properties of SiBCN composites

A simple method for introducing ZrB₂ using sol-gel processing into a SiBCN matrix is presented in this paper. Zirconium n-propoxide (ZNP), boric acid and furfuryl alcohol (C₅H₆O₂) (FA) were added as the precursors of zirconia, boron oxide and carbon forming ZrB₂ dispersed in a SiBCN matrix. SiBCN/ZrB₂ composites with different contents of ZrB₂ (5, 10, 15, and 20 wt%) were formed at 2000 °C for 5 min by spark plasma sintering (SPS). The microstructures were carefully studied. TEM analysis showed that the as formed ZrB₂ grains were typically 100–500 nm in size and had uniform distribution. HRTEM revealed clean grain boundaries between ZrB₂ and SiC, however, a separation of C near the SiC boundary was observed. The flexural strength, fracture toughness, Young's modulus and Vicker's hardness of composites all improved with the ZrB₂ contents and SiBCN matrix containing 20 wt% of ZrB₂ could reach 351±18 MPa, 4.5±0.2 MPa m^1/2, 172±8 GPa and 7.2±0.2 GPa, respectively. The improvement in fracture toughness can be attributed to the tortuous crack paths due to the presence of reinforcing particles.