Spark plasma sintering of TiN–TiB2–hBN composites and their properties

TiN–TiB2–hBN composites (where hBN denotes hexagonal boron nitride) were prepared by spark plasma sintering at 1973 K for 300 s under 100 MPa. The hBN content was varied from 0 to 30% of the total volume of the composite, while maintaining a TiN:TiB2 ratio of 30:70 vol%. The effects of hBN content on the densification, microstructure, mechanical properties and thermal conductivities of the composites were investigated. Regardless of hBN content, TiN–TiB2–hBN composites showed high relative densities (96–97%). At the optimal hBN content (15 vol%), the composites also showed high hardness and fracture toughness (20.1 GPa and 4.3 MPa m1/2, respectively), and their thermal conductivity increased from 58.1 to 63.4 W m−1 K−1 as the temperature was increased from 293 to 973 K. In contrast, the thermal conductivity of most ceramics decreases with increasing temperature.