MICROSTRUCTURAL BEHAVIOR OF SI3N4 CERAMIC S DURING CREEP

TEM and HREM investigations were performed on two types of silicon nit ride ceramics: A - GPS Si3N4 + 9 wt.% Y2O3 + 1 wt.% Al2O3 in which the intergranular phase was present in thick layers; and B - HP Si3N4 + 5 wt.%, Yb2O3, with very thin layers of the glassy phase (< 10 nm). The results were related to those obtained from the creep tests and the h igh temperature deformation mechanisms were identified. In the case of the first material an intensive cavitation causing a low creep resist ance took place, while for the high creep resistance of the second mat erial the mechanisms of diffusion were probably decisive.