Sintering of Nanocrystalline Silicon Carbide in Plasma Pressure Compaction System

Nanostructured ceramics offer significant improvements in properties over the corresponding materials with grain sizes on the order of tens to hundreds of microns. Silicon carbide (SiC) is an important structural ceramic whose properties can potentially be enhanced due to nanoscale microstructures. It has been suggested that SiC samples with grain sizes on the order of a few hundred nanometers can result in significant improvements in flexural strength, chemical resistance, thermal stability and electrical resistivity. To realize these properties, it is important to be able to sinter SiC powder to full density while avoiding exaggerated grain growth. Hence, sintering behavior and microstructural evolution in nanocrystalline SiC has been investigated in this study. Nanocrystalline SiC samples (average size ~ 70 nm) were fabricated in a plasma pressure compaction (P2C) system, a novel sintering technique. Master Sintering Curve (MSC) analysis was used to correlate the densification in SiC to the amount of work put into the system. MSC as a function of pressure for were generated. The activation energy, Q, for sintering was determined for three different pressures of 10, 30 and 50 MPa and found to be 1666, 1034 and 1162 kJ/mol, respectively. The variation of Q with pressure was reasoned to be an effect of various competing mechanisms. Taguchi analysis was used to study the effect of sintering parameters such as time, temperature, pressure and heating rate on the properties of the sintered part such as density, hardness and fracture toughness. Optimal operating conditions were determined and it was also found that each parameter affected the final properties almost equally. Complete densification of SiC samples was achieved at 1600 °C which is ~150 °C lower than reported in the literature for other sintering techniques