Abstract
High Pressure hot-pressing of Si3N4 without additives was performed using various kinds of Si3N4 powder as starting materials, and the relation between densification and α→β phase transformation was studied. The temperature dependences of Vickers microhardness and fracture toughness were also examined. Densification of Si3N4 was divided into three stages, and it was found that densification and phase transformation of Si3N4 under pressure were closely associated. The results of the temperature dependence of Vickers microhardness indicated that the high temperature hardness was strongly influenced not only by the density and microstructure of sintered body but also by the purity of starting powder.
The fracture toughness values of Si3N4 bodies without additives were 3.29-4.39MN/m3/2 and independent of temperature up to 1400°C.
