Ductile Ceramics at Low or Ambient Temperatures

This section deals with the features of ductile ceramics and, in some cases, the modifications in composition that induce ductility at low temperatures, as well as additives to base ceramics, such as metals, which also promote ductility. 

Polycrystalline ceramics are of great interest for specific industrial applications, but the primary drawback of using ceramic materials in structural applications is their inherent brittleness, which results from the strong bonding between the metallic and non-metallic components. In general, most ceramics are brittle and 

A slip-band structure may be seen in Fig. 2.37, showing specimens deformed at RT and at 1240 °C. This band stmcture is similar to the dislocation band structure revealed by hot etching 100 faces of a (111) specimen just yielded at about 650 °C and then air-quenched (Fig. 2.38). In Fig. 2.34, the RT true strain at failure 

As indicated above, the effects of impurities and surface reactions with components of the air exert control over ductility. It was predicted by researchers that a class of materials, normally considered brittle (i.e., ionic solids having cubic crystal stmctures) would possess a degree of ductility. Experiments performed on ionic materials indicate that face-centered cubic and body-centered cubic ionic materials can exhibit a considerable amoimt of ductility under controlled conditions, such as induced by impurities and surface effects. For instance, the ductility of MgO is shown in Fig. 2.39. 

The stress-deflection curve for a MgO single crystal is indicated in Fig. 2.40. To eliminate the environmental effect, these specimens were cleaved and tested under oil. The base material was of commercial grade, thus the crystals were impure, 

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