Types and Characteristics of Zirconia Toughened Ceramics
Based on the phase transformation toughening effect of metastable tetragonal zirconia under stress induction, zirconia phase transformation toughening ceramics mainly include Tetragonal Zirconia Polycrystalline (TZP), Partially Stabilized Zirconia (PSZ), and Zirconia Toughened Ceramics (ZTC).
Tetragonal Zirconia Polycrystalline (TZP) Ceramics
When an appropriate amount of stabilizer is added to zirconia, it preserves the t-ZrO₂ phase in a metastable state at room temperature. The microstructure is characterized by fine tetragonal zirconia grains forming the majority of the material, known as Tetragonal Zirconia Polycrystalline (TZP). These ceramics are typically sintered in the single-phase tetragonal zone, avoiding phase transformation during cooling, and retaining most or all tetragonal phase at room temperature. The content of tetragonal zirconia in the sintered body depends on grain size and density, which are controlled by sintering temperature and dwell time. Common TZP materials include Y-TZP (Yttria-stabilized) and Ce-TZP (Cerium-stabilized).
Partially Stabilized Zirconia (PSZ) Ceramics
When the amount of stabilizer in zirconia falls within a specific range, the highly stable cubic phase (c-ZrO₂) can undergo aging treatment at an appropriate temperature, causing large cubic grains to precipitate numerous small, spindle-shaped tetragonal grains. This results in a dual-phase structure comprising cubic and tetragonal phases. The cubic phase remains stable, while the tetragonal phase is metastable and persists at room temperature. Under external stress, the induced t→m phase transformation, accompanied by volumetric expansion, dissipates part of the energy and counteracts external forces, thus providing toughening effects. These ceramics are referred to as Partially Stabilized Zirconia (PSZ).
PSZ ceramics are usually sintered in the cubic solid solution zone, forming a uniform cubic phase matrix. Subsequent cooling induces the uniform precipitation of fine tetragonal grains between the cubic phase grains. When the tetragonal grains are at their critical size, the toughening effect is maximized. The morphology and size of these tetragonal grains can be controlled during production through adjustments to the heat treatment temperature and duration. Common PSZ ceramics include MgO-PSZ (Magnesia Partially Stabilized Zirconia) and CaO-PSZ (Calcia Partially Stabilized Zirconia).
Zirconia Toughened Ceramics (ZTC)
Zirconia Toughened Alumina ZTA ceramic components
If a certain amount of tetragonal zirconia is added to another type of ceramic matrix and uniformly dispersed within, the phase transformation toughening mechanism of zirconia significantly improves the toughness of the ceramic. Such materials are referred to as Zirconia Toughened Ceramics (ZTC). Common ZTC materials include Zirconia Toughened Alumina (ZTA) and Zirconia Toughened Mullite (ZTM).
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