Methods of processing Si3N4/SiC nano-nano composites from polymer precursor

Three approaches have been attempted in this investigation to bring the grain size of silicon nitride and silicon carbide composites into the truly nanometric range, i.e., where the grain size of both silicon nitride and silicon carbide phases are within the 100 nm limit. The first approach was crystallization of amorphous Si-C-N bulk materials which were first synthesized by a processing route based on pyrolysis of polymer precursor in order to obtain the polycrystalline silicon nitride/silicon carbide composites with grain size of 30-50 nm with varied phase proportions. The second processing method was high pressure sintering. Oxide additives were incorporated into precursor pyrolysis-derived powders, and sintering was conducted at 1400-1600 °C under a pressure of 1-2 GPa. The crystallinity and grain size of the sintered product can be controlled by the sintering temperature. The third method was electric field assisted sintering. With decreased additive amounts, the grain size of the sintered materials can be controlled to grain diameter as small as 38 nm.