Densification of Ca-αSiAlON nano particles by spark plasma

Nano-composites have excellent properties, such as high strength. This work presents a study to develop of a Ca-alpha sialon nano ceramics and improve their properties. Spark plasma sintering (SPS) of Ca-alpha sialon powder synthesized by carbothermal reduction-nitridation of SiO2-Al2O3-CaO system at 1450degreesC for 120 min was investigated. After grinding in an alumina mortar, the powder was fired at 1650-1800degreesC for 1-20 min by SPS. Densification was easily achieved by low temperature firing for a short time. TEM and FESEM photographs show that the primary grain size is 10-30 rim and 100 rim, indicating that the powder has a bimodal particle size distribution. From TEM, it was confirmed that the sintered body has a very fine-grained microstructure of 20 run and 100 rim in diameter, which is almost the same size as starting powder. Furthermore, glassy phase was found on the grain boundary. Consequently, SPS was found to be advantageous for the fabrication of Ca-a sialon ceramics with high density and nano-sized grains. Although the fracture toughness of Ca-a sialon nano ceramics is lowe than that of Si3N4 ceramics, it had higher hardness than Si3N4.