Fabrication and microstructural study of TiB2-based ceramics with SiC and Si3N4 additives

In this research, four titanium diboride based ultra-high temperature ceramics: monolithic TiB2 (additive free), TiB2-5 wt% Si3N4, TiB2-20 vol% SiC and TiB2-20 vol% SiC-5 wt% Si3N4 samples were fabricated by spark plasma sintering process at 1900 °C for 7 min under 40 MPa. The microstructures of TiB2-based composites were affected by the introduction of SiC and Si3N4 additives as the relative densities and sinterability of the samples significantly improved. The XRD, SEM and EDS analyses as well as density measurements were employed as the characterization methods. Based on these analyses, the in-situ formation of TiN, SiO2 and BN nano-platelets in the TiB2-Si3N4 and TiB2-SiC-Si3N4 samples, due to the chemical reaction of SiC and Si3N4 with the surface oxide impurities of TiB2 particles (TiO2 and B2O3) was verified. The elimination of such harmful oxide films and the in-situ formation of several secondary phases led to the prevention of fanatic grain growth of TiB2 matrix and microstructural development and phase evolution of TiB2-based ceramics. In addition, the sinterability of samples increased via liquid phase sintering mechanism as a result of formation of molten SiO2 during the sintering process.