Why can fibres and whiskers stop toughening ceramic composites at elevated temperatures?

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advanced ceramics Steps in doctor blading, a tape-casting process employed in the production of ceramic films. Ceramic powder and solvent are mixed to form a slurry, which is treated with various additives and binders, homogenized, and then pumped directly to a tape-casting machine. There the slurry is continuously cast onto the surface of a moving carrier film. The edge of a smooth knife, generally called a doctor blade, spreads the slurry onto the carrier film at a specified thickness, thereby generating a flexible tape. Heat lamps gently evaporate the solvent, and the dry tape is peeled away from the carrier film and rolled onto a take-up reel for additional processing.

In fibre- and whisker-reinforced ceramic composites, the toughening mechanisms—such as crack deflection and crack bridging—rely on the integrity of the reinforcing agents within the matrix.

At elevated temperatures, these fibres and whiskers are often susceptible to high-temperature oxidation. This chemical degradation virtually eliminates their effectiveness as toughening agents, causing the ceramic matrix to revert to its inherent brittle behaviour. Consequently, the loss of these reinforcements prevents the material from maintaining the enhanced fracture toughness required for demanding structural applications.1