Role of h-BN content on microstructure and mechanical properties of hot-pressed ZrB₂–SiC composites

The addition of h-BN flacks (0–35 vol%) into the ZrB₂–SiC composites was investigated in the present research. The composites were consolidated at a temperature of 1800 °C for 1 h under 40 MPa uniaxial pressure by a hot-pressing facility. The properties of the composites, such as density, hardness, bending strength, the microstructure, and phase evolution, were evaluated with various contents of h-BN. Densification of the hot-pressed composites improved by the addition of BN, as a nearly full densification was achieved by adding 2.5 vol% BN. X-ray diffraction analysis disclosed the formation of the Zr₃N₄, B₄C, and SiCN phases in the as-sintered triplet composites. The highest bending strength of 350 MPa was obtained for the composite containing 2.5 vol% BN. Due to the poor sinterability of boron nitride flakes, the addition of higher amounts of h-BN (>5 vol%) dramatically decreased the bending strength and Vickers hardness.