Why can oxidation limit the use of whiskers and fibres in ceramic-matrix composites at high temperatures?

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advanced structural ceramics Figure 1: Resistance to cracking in transformation-toughened zirconia. In a ceramic composed of tetragonal zirconia dispersed in a zirconia matrix, the stress field advancing ahead of a propagating crack transforms the small tetragonal particles to larger monoclinic particles. The larger particles exert a crack-closing force in the process zone behind the crack tip, effectively resisting propagation of the crack.

In ceramic-matrix composites, whiskers and fibres are used to improve fracture toughness through mechanisms like crack deflection and crack bridging. However, these reinforcements are often susceptible to high-temperature oxidation.1

When oxidation occurs at elevated temperatures, it effectively eliminates the whiskers and fibres as functional toughening agents. As a result, the composite loses its enhanced toughness and reverts to the inherent brittle behavior characteristic of conventional ceramics. Developing tough ceramic microstructures that remain stable under these high-temperature conditions remains a significant challenge for ceramic engineers.1