Why do tetragonal zirconia particles transform near an advancing crack?

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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 advanced structural ceramics, tetragonal zirconia particles transform into a monoclinic form near an advancing crack because they are triggered by the material's stress field.

While these particles are typically kept in a stable tetragonal state at room temperature by the surrounding matrix, the high stress present at the tip of an advancing crack overcomes this stability. As the particles transform, they undergo a 3 percent volume expansion. This cumulative increase in volume creates a process zone behind the crack tip where the expanded particles exert a closing force on the crack. This mechanism, known as transformation toughening, effectively resists further crack propagation and significantly increases the material's fracture toughness.1