High-pressure synthesis of fully dense polymer-derived SiCN ceramics: Structural evolution and mechanical properties

This study explored the microstructural evolution and mechanical behavior of dense amorphous SiCN ceramics by consolidating the PDCs-SiCN powder through high-pressure sintering at different temperatures. The results indicate that the SiCN ceramics remain in an amorphous state under pressures of 5 GPa and temperatures below 1200 degree celsius. As the temperature increases, the density increases steadily while the porosity decreases, exhibiting excellent properties with a porosity of 0.208 %, hardness and elastic modulus of 26.04+1.29 GPa and 223.8 +6 GPa, respectively. As the temperature increases further, the amorphous three-dimensional network deteriorates, leading to a phase transition from amorphous to crystalline. This simultaneous presence of amorphous and crystalline phases can result in an increased formation of pores in ceramics. Precipitation of the soft phase "graphite" and the appearance of high porosity significantly diminish the mechanical properties of bulk ceramics. The high-pressure method represents an attractive avenue for the development of high-performance amorphous Si-based composite ceramics.