Effects of TiB₂ on Microstructure and Mechanical Properties of Pressure-less-sintered B₄C-TiB₂ Composites

Boron carbide matrix composites containing boron carbide (B₄C), titanium diboride (TiB₂) at 20%(mass fraction) and 30%, and titanium carbide (TiC) were fabricated at 2130℃using a pressure-less sintering method. Different amounts of TiB₂ and TiC particles were added to B₄C. TiB₂ content was chosen as the main variable to study the effect on the composites. The density, hardness, bending strengths and fracture toughness measurements were performed to obtain the physical and mechanical properties of the samples. The results indicate that by adding 30%TiB₂ sub-micron particles at 2130℃, the bending strength and fracture toughness of 277.6MPa and 5.38MPa•m^1/2 were obtained for the composite. Particle pullout and crack micro-bridging play an effective role in toughening the composite ceramics. The main toughening mechanisms of the B₄C-TiB₂ composites are noted to possess microcrack and crack deflection toughening owing to the residual stresses resulting from the mismatch of the thermal expansion coefficient between TiB₂ and B₄C.