Abstract
The optical and SEM microstructures and the room temperature mechanical properties of Si3N4-Er2O3-CaO-6 mol%, Al2O3 compact sintered under 0.1 MPa of nitrogen gas at 1973-2073 K for 3.6 ks were mainly investigated as a function of Er2O3 (2, 4, 8 mol%) and GaO (0-10 mol%) contents.
The results obtained were as follows; (1) The additions of Er2O3 and CaO to Si3N4-Al2O3 compact increased the relative density. (2) The a-β phase transformation and the grain growth of Si3N4 phase were restricted with increasing CaO content. (3) The crystalline grain boundary phases in Si3N4-8 mol%Er203-CaO-A12O3 compact were found to be mainly Er4Si2O7N2 and Er2Si3O3N4 at small and large CaO contents, respectively. (4) The transverse-rupture strength showed a maximum generally at about 8 mol%Er2O3 and 2 mol%CaO. The hardness increased with increasing CaO content. The result on the strength was discussed in relation to the relative density, grain size, kinds of grain boundary phases, fracture toughness, fracture source, etc.
