Spark Plasma Sintering of Silicon Carbide with Al2O3 and CaO: Densification Behavior, Phase Evolution and Mechanical Properties

Liquid phase sintering (LPS) often yield an amorphous grain boundary region which deteriorates the high temperature properties of the sintered ceramics and thus ceramists prefer to obtain a crystalline grain boundary after LPS. This paper deals with LPS of silicon carbide ceramics to near theoretical density, understanding the densification behavior, evolution of gehlenite phase and subsequent evaluation of their mechanical properties. High density SiC ceramics were fabricated from sub-micrometre alpha-SiC powders with the aid of refractory phase forming metal oxide additives by spark plasma sintering. Sintering temperature and holding time at peak temperature were varied to study their effect on densification and mechanical properties. Density of the sintered ceramics reached similar to 97% at 1800 degrees C. Microstructural features and crack propagation mode were studied using scanning electron microscopy. XRD analysis confirmed the presence of crystalline gehlenite phase in the sintered samples. Hardness, fracture toughness and flexural strength of the sintered ceramics were determined by standard test procedures.