Effect of TiB₂ on Microstructure Evolution and Mechanical Properties of SiC-B₄C-TiB₂ Composite Ceramics

SiC-B₄C-TiB₂ three-phase composite ceramics were prepared by using pressureless solid-phase sintering, with SiC, B₄C, TiO₂ and C as raw materials. It is found that TiO₂ can be completely converted to the TiB₂ during the sintering process.Simultaneously, densification of the SiC-B₄C composite ceramics during sintering was promoted by the increase in the content of TiB₂. The maximum relative density, bulk density and apparent porosity of the composite ceramics with 12 vol.% TiB₂ reached 97.82%, 3.12 g·cm^-3 and 2.6%, respectively. Mechanical properties of the composite ceramics are positively correlated with their relative density. Flexural strength, Vickers hardness and fracture toughness of the samples reached (491±24) MPa, (30.1±0.8) GPa and (5.17±0.23) MPa·m^1/2, respectively. Toughening mechanism of the SiC-B₄C-TiB₂ three-phase composite ceramics was dominated by the toughening of residual thermal stresses. Mechanisms such as crack deflection and immobilisation of diffuse particulate phases were present to achieve synergistic toughening.