Effect of Si/C ratio and their content on the microstructure and properties of Si–B–C–N Ceramics prepared by spark plasma sintering techniques

Nano-sized Si–B–C–N powders nearly amorphous with different mole ratio of Si/C were prepared by mechanical alloying (MA) technique using cubic silicon (c-Si), hexagonal boron nitride (h-BN) and graphite powder (Cp) as starting materials, then consolidated at 1800 °C under a pressure of 40 MPa for 3 min by spark plasma sintering (SPS). Sub-micrometer sized β-SiC and nano-sized BCN phase were formed as the final components in the ceramics. The grain size of the β-SiC tend to be a little coarser with the increase of the Si/C ratio as well as their total content, but no changes are observed for the fine sub-micrometer structure characteristics of β-SiC and BCN grains. Mechanical properties of the Si–B–C–N ceramics were found remarkably increased with the increase of the mole ratio of Si/C and their total relative content. Thermal physical properties, including thermal diffusivity, heat capacity, thermal conductivity, as well as thermal expansion coefficient were also studied.

Research highlights▶ Si–B–C–N powders were prepared by two-step high energy ball milling. ▶ Si–B–C–N powders, with different contents of elements, were consolidated by SPS. ▶ SiC, BCN phase and small content of amorphous structure were formed in ceramics. ▶ Mechanical properties increase greatly with the increasing of content of Si and C.