Transmission Electron Microscopy Study on Nucleation Process of Precursor-derived Si-B-C-N Ceramics

Advanced TEM techniques were applied for studying precursor derived Si-B-C-N (T2-1) ceramics, which provided a direct view of nano-scaled microstructure evolution and nucleation. The results showed that after directly pyrolysis at 1400 SiC and Si3N4 nano-crystals, graphitic and BCN clusters nucleated from T2-1 amorphous matrix. In order to avoid the high temperature decomposition caused by the reaction between carbon and Si3N4, as well as to keep the strength of material and also improve its high temperature stability, T2-1 was also produced at relatively lower pyrolysis temperature (1000 for study and comparison. Different from T2-1 pyrolyzed at 1400 the results of microstructure show that lower pyrolysis temperature efficiently retards the crystallization of Si3N4, which is approved by the samples further annealed at 1400 Such phenomenon is believed being caused by early stage phase separation, which only provides SiC an advantage of nucleation. Thus, pyrolysis process is approved becoming one of the effective methods not only to control microstructure development, but also to improve the high-temperature stability of this material.