Reactions between SiC and sintering aids in Si3N4/SiC nanocomposites and their consequences

Si3N4/SiC nanocomposites were fabricated by hot-pressing mixtures of submicron α- Si3N4, SiC nanopowders with sintering aids. XRD, TEM and SEM were used to study the effects of SiC additions on sintering behavior and microstructure of Si3N4; EDAX was employed to investigate the composition of interfaces. The results showed that nano-SiC addition led to loss and compositional modification of intergranular phases and limited the densification and phase transformation of Si3N4. Reactions between sintering aids and nano-SiC are thermodynamically calculated and the temperature and N2 pressure dependence of the reactions are also theoretically analyzed. Influences of these reactions on the effects of SiC additions are discussed.