Study on pressureless sintering of Al2O3/SiC nanocomposite ceramics

β-SiC nanometer powder with the mean particle size of 30-35 nm, as the strengthening phases, was added into α-Al2O3 powder with the mean particle size of 0.37 μm. The pressureless sintering technology was used to prepare the Al2O3/SiC nanocomposite ceramics. The experimental results show that the relative density of the sintered body can reach 98.82%, and the flexural strength and the fracture toughness reach 489 MPa and 6.67 Mpa&middotm1/2 respectively. The microstructure was observed by means of SEM. It has been found that the grain boundary structure of alumina ceramics consists of both the bridge of Al2O3-SiC-Al2O3 and the phase boundary of SiC- Al2O3, forming a firmly combined composite boundary. This composite boundary raises the strength of the grain boundary, and limits the crack producing and growing only within the grain. The fracture mode is transformed from brittle intergranular fracture to intergranular fracture. Both the sub-structure and nano SiC particles within the grain can slow down the growing speed of cracks and increase strength and toughness greatly. The amount of O2 existing in nanopowder can bring a serious influence to the properties and microstructure of the sintered body. The contrast test of utilizing Si/C/N amorphous compound powder as the strengthening phases was done, too.