TABLE OF CONTENTS Engineering ceramics based on silicon nitride are well known as low-density materials with high strength and toughness. With the combination of these properties, silicon nitride ceramics are an ideal candidate for several structural and functional applications. However, because of the relatively high brittleness of ceramics there is a continual need to improve their mechanical characteristics. At the same time, intensive research is being performed to improve the thermal and electrical properties of ceramics. In general, there are two ways to improve the mechanical properties of ceramics: controlling the microstructure, and preparation of the composite.
In connection to the microstructure-property relationship, new observations have been performed on structural and morphological development of silicon nitride ceramics [ [1], [2]]. It was found that the development of an interlocking microstructure of elongated grains is vital to ensure that this family of ceramics has good damage tolerance. A fast (within minutes) in situ formation of a tough microstructure has been observed by a so-called dynamic Ostwald ripening process that results from the rapid heating rate. In this way, through formation of a tough interlocking microstructure (e.g. elongated ?-Si 3N 4 grains), mechanical properties may be improved.
On the other hand, physical and mechanical properties of ceramics can be improved through nanocomposite processing [ [3], [4], [5]]. To increase the fracture toughness, various energy-dissipating components have been incorporated into ceramic matrices [ [4]
