Characterization of the Evolution and Properties of Silicon Carbide Derived From a Preceramic Polymer Precursor

This study reports on the fabrication and characterization of polymer-derived amorphous and nano-grained SiC, by controlled pyrolysis of allylhydridopolycarbosilane (AHPCS) under inert atmosphere. Processing temperatures and hold times at final temperatures are varied to study the influence of processing parameters on the structure and resulting properties. Chemical changes, phase transformations, and microstructural changes occurring during the pyrolysis process are studied. Polymer cross-linking and polymer to ceramic conversion is studied using infrared spectroscopy (FTIR). Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) are performed to monitor the mass loss and phase change as a function of temperature. X-ray diffraction studies are performed to study the intermediate phases and microstructural changes. Hardness and modulus measurements are carried out using instrumented nanoindentation to establish processing-property-structure relationship for SiC derived from the polymer precursor. It is seen that the presence of nanocrystalline domains in amorphous SiC significantly influences the modulus and hardness. A nonlinear relationship is observed in these properties with optimal mechanical properties observed for SiC processed to 1150 degrees C for 1h hold duration, having average grain size of 3nm. In addition, bulk mechanical characterization, in terms of biaxial flexure strength, is done for SiC-SiC particulate composites purely derived from the polymer precursor.