Densification and mechanical properties of cBN–TiN–TiB2 composites prepared by spark plasma sintering of SiO2-coated cBN powder

cBN–TiN–TiB2 composites were fabricated by spark plasma sintering at 1773–1973 K using cubic boron nitride (cBN) and SiO2-coated cBN (cBN(SiO2)) powders. The effect of SiO2 coating, cBN content and sintering temperature on the phase composition, densification and mechanical properties of the composites was investigated. SiO2 coating on cBN powder retarded the phase transformation of cBN in the composites up to 1873 K and facilitated viscous sintering that promoted the densification of the composites. Sintering at 1873 K, without the SiO2 coating, caused the relative density and Vickers hardness of the composite to linearly decrease from 96.2% to 79.8% and from 25.3 to 4.4 GPa, respectively, whereas the cBN(SiO2)–TiN–TiB2 composites maintained high relative density (91.0–96.2%) and Vickers hardness (17.9–21.0 GPa) up to 50 vol% cBN. The cBN(SiO2)–TiN–TiB2 composites had high thermal conductivity (60 W m−1 K−1 at room temperature) comparable to the TiN–TiB2 binary composite.