Liquid phase sintering of Si3N4/SiC nanopowders derived from silica fume

In this study, liquid phase sintering (LPS) of the nanostructured Si3N4/SiC powder synthesized from silica fume is investigated. Two major processing parameters, one being the composition of the powder bed that surrounds the part to be liquid phase sintered and the other the volume fraction of the sintering aid, are studied. It is shown that both of these processing parameters are crucial in achieving high density Si3N4/SiC nanocomposites and controlling their microstructure and thus their mechanical properties. With the proper powder bed composition and sufficient volume fraction of the sintering aid, dense Si3N4/SiC composites composed of a bi-modal distribution of equiaxed and elongated Si3N4 grains along with nanoscale SiC particles can be formed via LPS, and such composites offer a good combination of hardness and toughness. The mechanisms via which the two processing parameters play their critical roles in controlling the densification and microstructure have been identified.