Zirconia ceramic structural parts are made of zirconia (ZrO2) as the main material, high hardness, high temperature resistance, corrosion resistance, wear resistance, and are inorganic non-metallic materials with excellent electrical conductivity. Why is zirconia ceramic more wear-resistant and resistant than general ceramic structural parts?
Why zirconia ceramics are more wear-resistant and resistant than ordinary ceramic structural parts
Zirconia powder can be transformed into various ceramic structural parts, ceramic rods, ceramic plates, etc. after a series of processing.
At atmospheric pressure, pure ZrO2 is available in three crystalline forms: monoclinic (m-ZrO2), tetragonal (t-ZrO2) and cubic (c-ZrO2), which exist in different temperature ranges and can be interconverted.
The transformation between the tetragonal and monoclinic phases of ZrO2 is a martensitic phase transformation, due to a 3-5% volume expansion and 7-8% shear strain during the transformation of the tetragonal phase into the monoclinic phase. Therefore, pure ZrO2 products often undergo a phase transition from t-ZrO2 to m-ZrO2 during the production process (cooling process from high temperature to room temperature) and are accompanied by volume change and cracking, or even fragmentation, and therefore have little engineering value.
However, when appropriate stabilizers (such as Y2O3, MgO2, CaO, CeO2, etc.) are added, the phase transition temperature of c-ZrO2 → t-ZrO2 and t-ZrO2 → m-ZrO2 can be lowered, so that the high temperature stable c-ZrO2 and t-ZrO2 phases can also be stable or sub-stable at room temperature.
When enough stabilizer is added, the high-temperature stable c-ZrO2 can be maintained until room temperature without phase change. Further studies have found that zirconia undergoes martensitic phase transformation accompanied by volume and shape changes, which can absorb energy, slow down stress concentration at the crack tip, prevent crack expansion, and improve ceramic toughness. Therefore, the research and application of zirconia phase change toughened ceramics has been rapidly developed.
Why zirconia ceramics are more wear-resistant and resistant than ordinary ceramic structural parts Zirconia powder can be transformed into various ceramic structural parts, ceramic rods, ceramic plates, etc. after a series of processing. At atmospheric pressure, pure ZrO2 is available in three crystalline forms: monoclinic (m-ZrO2), tetragonal (t-ZrO2) and cubic (c-ZrO2), which exist in different temperature ranges and can be interconverted.
There are three types of zirconia phase change toughened ceramics, namely partially stabilized zirconia ceramics, tetragonal zirconia polycrystalline ceramics and zirconia toughened ceramics.
1. Partially stabilized zirconia ceramics
When the amount of stabilizer is added to ZrO2 in a certain range, the high-temperature stable c-ZrO2 precipitates many fine spindle-shaped t-ZrO2 grains (t-phase) in the large c-ZrO2 grains (c-phase) by aging treatment at a suitable temperature, forming a biphasic structure consisting of c-phase and t-phase. The c-phase is stable while the t-phase is sub-stable and preserved until room temperature. It is possible to induce a martensitic phase transition from the t-phase to the m-phase with volume expansion under external forces, which dissipates some of the energy and counteracts some of the external forces, thus providing a toughening effect, called stress-induced phase toughening. This kind of ceramics is called partially stabilized zirconia (PSZ), which is denoted as Ca-PSZ, Mg-PSZ, Y-PSZ, etc. when the stabilizers are CaO, MgO, and Y2O3, respectively.
2. Tetragonal zirconia polycrystalline ceramics
The tetragonal zirconia polycrystal (TZP) is a tetragonal zirconia polycrystal composed of t- ZrO2 fine crystals with a sub-stable structure when the amount of stabilizer added to ZrO2 is controlled in an appropriate amount to keep t-ZrO2 in a sub-stable state until room temperature. The phase transformation of phase changeable t-ZrO2 under the action of external forces toughens the non-phase changeable ZrO2 matrix and improves the overall fracture toughness of the ceramic. When the added stabilizer is Y2O3, CeO2, it is denoted as Y-TZP, Ce-TZP, etc. respectively.
3. Zirconia toughened ceramics
If a certain amount of ZrO2 is added to different ceramic matrix and the sub-stable tetragonal zirconia polycrystals are uniformly distributed in the ceramic matrix, the toughness of ceramics is significantly improved by using zirconia phase change toughening mechanism. Such zirconia phase change toughened ceramics are called ZirconiaToughened Ceramics (ZTC). If the ceramic matrix is Al2O3 , mullite (Mullite), etc., it is denoted as ZTA, ZTM, etc., respectively.
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