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 (C-p) as starting materials, then consolidated at 1800 degrees C under a pressure of 40 MPa for 3 min by spark plasma sintering (SPS). Sub-micrometer sized beta-SiC and nano-sized BCN phase were formed as the final components in the ceramics. The grain size of the beta-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 beta-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. (C) 2010 Elsevier B.V. All rights reserved.