Bulk and nano-scale characterization of polymer derived silicon carbide and comparison with sintered silicon carbide

Abstract

Among all the ceramics, silicon carbide (SiC) is most commonly used for structural as well as nuclear applications due to its superior properties. Different processing routes are followed for the fabrication of silicon carbide. Powder processing techniques, such as sintering, are most common but require high temperature and pressure. An alternative processing route is polymer infiltration and pyrolysis. This offers various advantages over conventional processing, such as near net shape fabrication, relatively low temperature processing and the ability to tailor the microstructure. In this study, fabrication of polymer derived SiC using polymer infiltration and pyrolysis technique along with characterization of silicon carbide is performed. Allylhydridoploycarbosilane (AHPCS) was used as a preceramic polymer. Final processing temperatures were varied to observe the change in microstructure as well as physical and mechanical properties. Density, porosity and thermal conductivity of SiC as a function of processing temperature were determined. Non-contact mode atomic force microscopy was done to determine the degree of crystallinity as a function of processing temperature. The degree of crystallinity followed an increasing trend with increasing processing temperature. Ring-on-ring tests were done on bulk samples to determine biaxial flexure strength. Hardness and modulus were determined using nanoindentation. Hardness and modulus of SiC is primarily influenced by the degree of crystallinity. Finally, a comparative study of AHPCS derived SiC was carried out with commercially available sintered silicon carbide.