Effect of Intergranular Microstructure on Properties of Si3N4 Based Composite Ceramic Materials
The microstructures of Si3N4 based ceramic materials containing ZrO2 have been characterized by analytical electron microscopy and x-ray diffractometry. The ceramics were fabricated by hot isostatic pressing (HIP) and contained different additions of Al2O3, AlN and Y2O3 as sintering additives. Ceramics fonned without the separate addition of Y2O3 were densinfied in the presence of a transient liquid phase; these microstructures contained an extremely small volume fraction of residual glass. Increased volumes of intergranular glass fonned in materials containing larger additions of separately added Y2O3. These larger glass volumes had a negative influence on hardness. Formation of prismatic β-Si3N4 grains was promoted by additions of Y2O3 either separately or in the form of Y2O3 stabilized ZrO2 starting powder. This morphology of the Si3N4, as well as larger additions of ZrO2, increased toughness.
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