Nonoxide ceramics microstructure

The resulting microstructure for each of these cases is shown in Figure 14.33. The process of LPS is also important in forming dense powder compacts of nonoxide ceramics such as the nitrides. In these ceramics, where the bonding is predominantly covalent, atomic mobility is limited and sintering to high density is difficult in the absence of a liquid phase or without the application of high pressure. 

G. Wotting, B. Kanka and G. Ziegler, Microstructural Development, Micccrostructural Characterization and Relation to Mechanical Properties of Dense Silicon Nitride , Nonoxide Ceramic, 1986, 83-95. 

Possible errors and limitations. It is often impossible to lap oxide ceramics or nonoxide ceramics (e.g., silicon carbide or silicon nitride) to a sufficiently low thickness. As a result, certain microstructural components and grains that are smaller than the section thickness can overlap, rendering them impossible to detect with certainty. 

A review of Slow Crack Growth (SCG) results obtained for different oxide and nonoxide ceramics at ambient temperature, under different enviromnents, is presented. They are analyzed on the basis of their crack velocity (V) versus stress intensity factor (Ki) diagrams. The aim of this paper is to consider mechanisms acting at the crack tip (i.e. at the nano-scale) and microstructural mechanisms occurring in the crack wake or at the crack front (i.e. at the micro-scale) to rationalize the approach of SCG. 

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