Densification behaviour and mechanical properties of B4C-SiC intergranular/intragranular nanocomposites fabricated through spark plasma sintering assisted by mechanochemistry

High-performance B4C-SiC nanocomposites with intergranular/intragranular structure were fabricated through spark plasma sintering assisted by mechanochemistry with B4C, Si and graphite powders as raw materials. Given their unique densification behaviour, two sudden shrinkages in the densification curve were observed at two very narrow temperature ranges (1000-1040 °C and 1600-1700 °C). The first sudden shrinkage was attributed to the volume change in SiC resulting from disorder-order transformation of the SiC crystal structure. The other sudden shrinkage was attributed to the accelerated densification rate resulting from the disorder-order transformation of the crystal structure. The high sintering activity of the synthesised powders could be utilised sufficiently because of the high heating rate, so dense B4C-SiC nanocomposites were obtained at 1700 °C. In addition, the combination of high heating rate and the disordered feature of the synthesised powders prompted the formation of intergranular/intragranular structure (some SiC particles were homogeneously dispersed amongst B4C grains and some nanosized B4C and SiC particles were embedded into B4C grains), which could effectively improve the fracture toughness of the composites. The relative density, Vickers hardness and fracture toughness of the samples sintered at 1800 °C reached 99.2±0.4%, 35.8±0.9 GPa and 6.8±0.2 MPa m1/2, respectively. Spark plasma sintering assisted by mechanochemistry is a superior and reasonable route for preparing B4C-SiC composites.