Densification and phase transformation of Si3N4 by high pressure hot-pressing.

Densification and phase transformation of Si3N4 were studied by high pressure hot-pressing without additives. The α to β phase transformation rate was accelerated by the application of pressure. The fracture surface showed the existence of self-bonding and formation of polyhedrons. When the α-Si3N4 powder was hot-pressed at 1600°C under 3.0GPa, a fully dense body was obtained at about 10wt% of β phase, and the maximum Vickers microhardness of 2200kg/mm2 was observed at about 40wt% of β phase transformed. There was no difference in densification behaviors in either case when α or β phase Si3N4 was used as starting materials.