Zirconia is the 20th century, 70 years developed a new type of structural ceramics, with excellent mechanical properties, widely used. (C) to the tetragonal phase (t) to the monoclinic phase (m), where t to m phase transition occurs at about 1150 ° C, and the following phase transition occurs during the transition from high temperature to room temperature: Accompanied by a volume expansion of about 5%. If the t-m transition point of ZrO2 is stabilized to room temperature, it is induced by stress to produce t to m phase transition, which absorbs a large amount of fracture energy due to the volume effect of phase change, so that the material exhibits abnormally high Of the fracture toughness, resulting in phase change toughening, high toughness and high wear resistance.
2, stabilizer stabilization of zirconia ceramics
Common ZrO2 stabilizers are rare earth or alkaline earth oxides, and only the ionic radius and Zr4 + radius of not more than 40% of the oxide can be used as a stabilizer of zirconium oxide stabilization mechanism is not very clear. The addition of different amounts of stabilizer can obtain zirconia ceramics with different phase composition. If the partial t-ZrO2 is stabilized to room temperature, some stable zirconia (PSZ) is obtained. If t-ZrO2 is all partially stabilized to room temperature, (Abbreviated as TZP); if c-ZrO2 is stabilized to room temperature, c-ZrO2 single-phase material is obtained, that is, stable zirconia (FSZ). PSZ and TZP all contain phase change of the tetragonal phase, is the commonly used phase change toughened ceramics, the author of these two types of stable zirconia ceramics research are reviewed.
3, commonly used stable zirconia ceramic performance
Single stabilizer stabilized zirconia ceramic
Initially, Y2O3, MgO, CeO 2, CaO and other stabilizers are mainly added zirconia alone, thus forming a different stabilizer stabilized zirconia ceramic, the stability of the stability of ZrO2 substantially the same, but by their stable after the ZrO2 performance But not the same, and the same amount of stabilizer added ZrO2 performance is also a big difference. Applications are often based on the actual use of the request to choose to add a reasonable, appropriate amount of stabilizer. The characteristics of the three zirconia ceramics which are widely studied and applied are briefly described.
Y-TZP in the stabilizer Y2O3 atomic fraction (the same below) is usually 2% to 3%. Compared with other ceramics, Y-TZP sintering temperature is low, about 1400 ~ 1550 ℃, the material sintering performance is good, high density. The ceramic has excellent mechanical properties at room temperature, bending strength is usually above 1000 MPa, up to 2 GPa, fracture toughness is generally 10 ~ 15 MPa · m1 / 2, up to 30 MPa · m 1/2.
Mg-PSZ compared with Y-TZP, its outstanding advantages are relatively high temperature with excellent mechanical properties and creep resistance, belonging to the use of temperature below 800 ℃ in the temperature of structural ceramic materials. However, the development and development of Mg-PSZ are constrained by two unfavorable factors: firstly, the solution temperature of MgO in the cubic zone of ZrO2 is as high as 1700 ℃, which leads to the high sintering temperature of Mg-PSZ (usually 1700 ~ 1800 ℃) The preparation and industrialization of the materials are very difficult. Second, the Mg-PSZ is prone to crystal decomposition and a large amount of tetragonal phase instability at temperatures above 1000 ℃, resulting in the deterioration of the material properties and severely restricting its application in the high temperature region.
CeO2 is an ideal zirconia stabilizer. Compared with Y2O3, stabilizer has the following advantages: low cost and can form tetragonal solid solution with zirconia in a wide range. In the range of solid solution, the starting phase transition temperature of t to m can be greatly reduced. On the other hand, the critical phase transition grain size of Ce-TZP is larger than that of Y-TZP, so that it is possible to obtain zirconia ceramic material with better performance without superfine powder.
A variety of stabilizers for compound stabilized zirconia ceramics
The use of a variety of stabilizers to stabilize the role of a certain extent to make up for each other between the individual stability of the shortcomings, not only to improve the sintering properties of materials, and can greatly improve its mechanical properties. The addition of CeO2 in Y-TZP can effectively suppress the low temperature aging by using Ce-TZP good anti-low temperature hydrothermal corrosion, which has become one of the important ways to improve the stability of Y-TZP.
4, other stable zirconia ceramic materials
In addition to several commonly used stabilized zirconia ceramic materials, in recent years, some researchers have studied and studied other rare earth oxide stabilized zirconia ceramics. One of the more representative of the stabilizer is Nb2O5, Ta2O5, La2O3 and so on.
The study of stabilized zirconia ceramics has achieved fruitful results, which not only created the necessary conditions for the practical application of zirconia ceramic materials in engineering, but also laid a solid foundation for the research and development of multi-composite reinforced zirconia-based structural ceramics. However, it must be seen that these results are mostly produced on the basis of the experiment, but also the lack of necessary theoretical support, and zirconium oxide on the stability mechanism of the study there are still large gaps, so the theoretical study of zirconia stability, will become the future domestic The important direction of the researchers' efforts.
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