Effect of TiB2 content on microstructure and mechanical properties of in-situ fabricated TiB2/B4C composites

The fully dense boron carbide matrix composites containing 10%-40% (volume fraction) TiB2(TiB2/B4C) were in-situ fabricated via chemical reaction of B4C, TiO2 and graphite powders at 2 050 degrees C under a pressure of 35 MPa. Scanning electron microscopy (SEM) and transmission election microscopy (TEM) observations show that the sub-micron/ nano-sized TiB2 particles are uniformly located within the matrix grains and at the B4C grain boundaries. With the increase of TiB2 content, the elastic modulus and fracture toughness of composites increase remarkably. However, the situation is reversed for Vickers hardness and flexural strength. The fracture toughness exhibits a maximum value of 8.2 MPa.m(1/2) for the 40% (volume fraction) TiB2/B4C composite. The main toughening mechanisms of TiB2/B4C composites are microcrack toughening and crack deflection toughening.