GRAIN MORPHOLOGY AND INTERGRANULAR MICROSTRUCTURE OF WHISKER-REINFORCED SI3N4 CERAMICS

The effect of metal oxide and whisker additions on the grain morpholog y and intergranular microstructure of Si3N4-based ceramic materials ha s been characterized by analytical electron microscopy in combination with quantitative microscopy. The Si3N4 ceramics were formed either wi thout metal oxide sintering additives or with 2.5 wt% Y2O3 and 0.2 wt% Fe2O3. SiC or beta-Si3N4 whiskers were added to these two composition s. The microstructural analysis showed that both metal oxide and whisk er additions affect the Si3N4 microstructure. The addition of Y2O3 and Fe2O3 promoted the development of a fibrous beta-Si3N4 matrix with a larger fraction of intergranular amorphous phase. The presence of SiC whiskers suppressed beta-Si3N4 grain growth during densification while an addition of beta-Si3N4 whiskers resulted in a coarser microstructu re. The different microstructures were related to the mechanical prope rties of the ceramics and the results imply that the matrix microstruc ture has a significant influence upon the mechanical behaviour of Si3N 4-based ceramic composites. (C) 1996 Elsevier Science Limited.