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Why is transformation-toughened zirconia sometimes called ceramic steel?
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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.
Transformation-toughened zirconia (TTZ) is often referred to as "ceramic steel" for two primary reasons related to its mechanical behavior and internal structure:
- Stress-Strain Response: The material's strain, or change in dimension in response to stress, resembles that of steel rather than the typical brittle behavior associated with conventional ceramics.1
- Martensitic Transformation: The underlying mechanism that provides its toughness is a phase transformation called "martensitic," which is named after a similar transformation that occurs in rapidly quenched steel to form a phase known as martensite.1
In this process, the material utilizes a volume expansion that occurs when tetragonal zirconia particles transform into a monoclinic form under stress. This expansion exerts a closing force on advancing cracks, significantly increasing the material's fracture toughness and allowing it to resist crack propagation in a manner far superior to traditional ceramics.1