Microstructure and properties of solidified TiC TiB₂ composites prepared by combustion synthesis in high-gravity field

By changing the mole ratio of Ti, C and B in primary reaction system, TiC-TiB₂ composite ceramic with different TiB₂ mole content were prepared by combustion synthesis in high-gravity field. The microstructure of composites was characterized by FESEM. The influence of the TiB₂ composition on the mechanical properties of composite ceramic was studied. The results indicate that the matrix of TiC-TiB₂ composite ceramics transforms from TiC grains to TiB₂ platelets with increasing TiB₂ mole content, moreover, the fine-grained microstructures and even ultrafine-grained microstructures are achieved in TiC-50 %TiB₂, while volume fraction of α-Al₂O₃ inclusions in the ceramic also reaches the lowest value. The relative density, Vickers hardness and flexural strength of ceramics simultaneously reach the maximum values as the mole content of TiB₂ is 50% in the ceramic, whereas the maximum fracture toughness is achieved in TiC-66.7%TiB₂. FESEM fracture morphologies of the ceramics show that intercrystalline fracture is enhanced while transgranular fracture is weakened inversely with increasing mole content of TiB₂ to 66.7%. FESEM crack propagation paths of TiC-TiB₂ composite ceramics show that the highest flexural strength is achieved in TiC-50%TiB₂ composite ceramic due to both the achievement of solidified fine-grained and ultrafine-grained microstructures and the presence of intensive toughening mechanisms of crack deflection, frictionally crack-bridging and pull-out by a large number of fine TiB₂ platelets.