Toughened ceramics effects

N.L. Hecht, "Environmental Effects in Toughened Ceramics," W.B.S. Element 3.3.1.4, University of Dayton Research Institute, Ceramic Technology for Advanced Heat Engines Project, Oak Ridge Notional Laboratory, Oak Ridge, Tennessee (1989),... 

Fatigue is also observed in transformation-toughened ceramics, like partially stabilised zirconium oxide (see sections 7.2.4 and 7.5.4), where phase transformations occur near the crack tip. This effect is attributed to the formation of microcracks in the vicinity of the crack tip [66]. 

The effect of SiC whisker content on toughness enhancement in different matrices. (From P. Becher, Microstructural design of toughened ceramics, /. Am. Ceram. Soc., 74,255-269,1991.)... 

Blattner, A., Lakshminarayanan, R., Shetty, D.K., Toughening of layered ceramic composites with residual surface compression effect of layer thickness, Eng. Fract. Mech. 68, 1-7, 2001. 

Pratapa, S. and Low, I.M. (1996). The Effects of Spodumene Addition on Properties of Functionally-graded Aluminium Titanate/Zirconia-toughened Alumina Composites . In Proceedings of the 2nd International Meeting of Pacific Rim Ceramic Societies. 

The effects of ceramic particles and filler content on the thermal shock behavior of toughened epoxy resins have been studied. Resins filled with stiff and strong particles, such as silicon nitride and silicon carbide, show high thermal shock resistance, and the effect of filler content is remarkable. At higher volume fractions (Vf > 40%), the thermal shock resistance of these composites reaches 140 K, whereas that of neat resin is about 90 K. The highest thermal shock resistance is obtained with silicon nitride. The thermal shock resistance of silica-filled composites also increases with increasing filler content, but above 30% of volume fraction it comes close to a certain value. On the contrary, in alumina-filled resin, the thermal shock resistance shows a decrease with increasing filler content. 

In any case, ductile reinforcing inclusions in composites offer the valuable possibility of improving the fracture toughness of the composite. The toughening effect of ductile reinforcements in brittle matrices has been studied both experimentally and theoretically for ceramics, e.g. Al Oj reinforced with Al, and metals (Sigl et al., 1988 Flinn etal., 1989 Ashby etal., 1989). Such a toughening effect has also been found for a TiAl/Nb model composite (Cao etal., 1989). 

In this section, the effects of chemical toughening using ion exchange by the paste method on the strength and lifetime of dental porcelains are shown. In this study, a feldspathic porcelain (Ultropaline Super Transparent, Jen Dental - UST) recommended for metal-ceramic or all ceramic restorations was used. The chemical composition of this porcelain is shown in Table 4. 

The effectiveness of the different toughening mechanisms for structural ceramics appears to decrease in the following order ... 

Explain how the addition of zirconia particles can lead to toughening of a ceramic. Suggest other additions that might produce similar toughening effects. 

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