Abstract
The Si3N4-(4-12)mo1%Y2O3-6 mo1%Al2O3 compacts were sintered under 0.1 MPa of nitrogen at 2023 K for 0.9-36 ks. The microstructure and some properties of the sintered compact were investigated.
The results obtained were as follows; (1) The weight loss of the compact due to the sintering, the relative density and the thickness of the microstructural heterogeneous layer near the surface of the compact increased with increasing sintering time (ts). (2) The crystalline grain boundary phases were found to be Y10(SiO4)6N2 or Y4Si2O7N2 at short ts and YSiO2N or Y2Si3O3N4 at long ts. The crystalline grain boundary phases except for YSiO2N were observed as large white domains in the optical micrographs. (3) The room temperature transverse-rupture strength and hardness increased in general with increasing ts. The maximum strength was generally obtained in 8-10 mol% Y2O3 compact at any ts. The strength, even for the compact with Y2O3 content as small as 4 mo1%, attained to 0.85 GPa at long ts. These results were discussed in relation to the relative density, the microstructural defects which acted as fracture source, the grain boundary phase and the grain size of Si3N4 particles.
