Superplasticity in Ceramics

As previously indicated, zirconia is a typical superplastic ceramic and was among the first oxide ceramics to be smdied. As early as 1986, Wakai et al. studied 

In the above, 1 and lo are the elongated and original gage lengths, respectively. The true stress is related to the tme strain by  

Superplasticity is not limited to zirconia-type ceramics. Other ceramics have also been found to exhibit superplasticity, such as nitrides or carbides. Representative examples are Si3N4 and SiC. In these cases, superplasticity occurs in single-phase ceramics. Section 2.1.3.1 (i) A superplasticity of 470 % in Si3N4 (Fig. 2.44) has been mentioned above. 

1 is a constant. The immediate strain rate is expressed as  

For the corrected flow stress the stress exponent, n, must be known and is given as  

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In the next section, we will analyse the mechanisms that are considered to control superplasticity in ceramics with secondary phases. 

In order to outline the future trends in superplasticity in ceramics, first of all it is necessary to give an answer to the following question why is superplasticity in ceramics so important The potential use of these materials in more and more severe applications makes superplasticity in ceramics an important tool for their processing, as happened with metals at the beginning of the 1960s. 

The mechanism for superplasticity in ceramics must clearly be different from that in metal alloys because there... 

Superplasticity in Ceramics Accommodation-Controlling Mechanisms Revisited... 

Many investigations have been conducted on the influence of grain boundary segregation on superplasticity in ceramics. Indeed, it has been shown successively that the yttrium in YTZP polycrystals segregates at the grain boundaries, and that this segregation was the possible cause of the threshold stress (Oq). It also helped to explain (quantitatively) the dependence of Oq with temperature and grain size [23]. A detailed analysis is provided later in the chapter. 

Another important consideration that attributes to the rapid increase in the use of the CAPAD technique is the improved properties of materials processed by this method. A wide range of enhanced properties has been reported for materials consolidated by the CAPAD method including, for example, improved optical properties,electrical and mechanical properties. There are also some investigations on enhanced superplasticity in ceramics through processing by CAPAD. 

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