Comparison of TiB2–h-BN composites prepared by reactive and conventional spark plasma sintering

Sintering method greatly affects the sintering behavior, microstructure and properties of the ceramic composites. In the present work, TiB2–h-BN composites prepared by reactive spark plasma sintering (RSPS) and conventional spark plasma sintering (CSPS) are compared. Due to the in-situ synthesized TiB2 and h-BN particles during sintering process, the reactive sintering not only inhibits the orientation of TiB2 grains but also prevented the formation of the Card-house structure. TiB2–h-BN composites obtained by RSPS (R series) exhibit higher sintering activity and finer microstructure, which results in better mechanical performance than those prepared by CSPS (C series). As the SPS temperature is 1600 °C, the relative density of the composite in R series is as high as 97.3%, much higher than that (89.3%) in C series. The composite obtained by RSPS at 1600 °C also exhibits excellent mechanical properties with a bending strength of 205.3 MPa and a Vickers hardness of 2.50 GPa, respectively, which exceeds all composites prepared by CSPS at 1600–2000 °C. When the SPS temperature is 1800 °C or above, for both series, the increase of SPS temperature greatly enhances the Vickers hardness but has litter effect on the strength and electrical resistivity, which is attributed to the comprehensive effect of the density increase and microstructure coarsening. The present work indicates that in-situ reactive sintering has obvious advantages in preparing TiB2–h-BN composites with excellent mechanical properties at low temperature.