Thermal shock of particle- and whisker-reinforced CMCs

5 Thermal shock of particle- and whisker-reinforced CMCs 

The attraction of reinforcing ceramic matrices with particles or whiskers is that, with appropriate microstructural design and property tailoring, materials with property combinations not possible in monolithic ceramics can be obtained. In addition, the materials remain effectively isotropic and can be manufactured by well-established techniques already in use for the manufacture of monolithic ceramics (Hansson and Warren, 2000). 

5 The thermal shock behaviour of hot-pressed alumina, hot-pressed and sintered alumina reinforced with iron particles (reprinted from Journal of the European Ceramic Society, 19, Aldridge and Yeomans, The thermal shock behaviour of ductile particle toughened alumina composites, 1769-1775, copyright 1999, with permission from Elsevier). 

Studies have also shown that, since the amount of reinforcement added affects all mechanical and thermal properties, there is an optimum volume fraction of particle or whisker reinforcement that should be added to the matrix material to ensure superior resistance to thermal shock (Becher, 1981 Jia etal., 1996 Sbaizero and Pezzotti, 2003 Pettersson and Johnson, 2003). The shape of the reinforcement also plays an important role in determining behaviour under thermal shock. Sbaizero and Pezzotti (2003) showed that the use of coarse and elongated particles resulted in better CMC performance compared with the use of fine-grained particles. 

The behaviour of particle- and whisker-reinforced CMCs under conditions of thermal shock can be modelled successfully using the fracture mechanics methods outlined in the previous paragraph (e.g. Aldridge and Yeomans, 2001) while the thermal shock parameters (figures-of-merit) can also be useful for initial material comparison. 

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