Rod Flame Spraying
October 18, 2014

Here we make a comparison of three kinds of partially stabilized zirconias (PSZ).

1, Y-TZP, Yttria Stabilized Zirconia

The atomic fraction of the stabilizer Y2O3 in Y-TZP is usually from 2% to 3%. Compared with other ceramics, Y-TZP has a low sintering temperature about 1400-1550 ° C, and Y-TZP has good performance and high density. Y-ZTP has excellent mechanical properties at room temperature, the bending strength is usually above 1000 MPa, the highest is up to 2 Gpa, and the fracture toughness is generally 10-15 mpa m^1/2, up to 30 mpa m^1/2. Y-TZP also exhibits good wear resistance, corrosion resistance and biocompatibility. It is considered to be one of the most promising ceramic materials. It has developed a variety of reinforced zirconia composite ceramics. Studies have shown that when Y2O3 is 3%, the comprehensive mechanical properties of 3Y-TZP are optimal.

However, Y-TZP has a significant disadvantage, that is, when used in a low temperature range of 100-400 ° C for a long time, the surface of the material undergoes an isothermal phase transition of t→m to the inside, resulting in a sharp drop in mechanical properties, that is, low temperature performance aging occurs. The aging phenomenon is most prominent in the temperature range of 200-300 ° C, and the aging speed is obviously accelerated in the humid air or water environment.

2, Mg-PSZ, Magnesia Partially Stabilized Zirconia

Compared with Y-TZP, Mg-PSZ has the outstanding advantages of excellent mechanical properties and creep resistance at relatively high temperatures, and is a structural ceramic used a temperature lower than 800 °C. However, the research and development of Mg-PSZ is constrained by two unfavorable factors: First, the solid solution temperature of MgO in the cubic region of ZrO2 is as high as 1700 °C, resulting in a high sintering temperature of Mg-PSZ (generally at 1700-1800 ° C). The preparation and industrialization of materials is very difficult. Secondly, Mg-PSZ is prone to crystal phase separation and a large number of tetragonal phase destabilization at temperatures above 1000 °C, which leads to the deterioration of material properties and severely restricts its application in high temperatures.

3, Ce-TZP, Ceria Stabilised Zirconia

CeO2 is an ideal zirconia stabilizer. As a stabilizer, it has the following advantages as Y2O3: it is inexpensive and can form a tetragonal phase solid solution zone with zirconia in a wide range. In the solid solution range, the initial phase transition temperature of t→m can be greatly reduced. For example, the phase transition temperature of 3.5Y-TZP is about 560 °C, and the phase transition temperature of 20Ce-TZP can be lowered to below 25 °C. On the other hand, the critical phase change grain size of Ce-TZP is larger than that of Y-TZP, so that a zirconia ceramic material with better performance can be obtained without using ultrafine powder.

Compared with Y-TZP, Ce-TZP has higher fracture toughness and good resistance to low temperature hydrothermal aging. The disadvantage is that hardness and strength are low. The Ce-TZP material cannot be sintered under a reducing atmosphere, and it is easy to cause coarse grains. The results show that Ce-TZP has the highest flexural strength of 800Mpa when CeO2 atomic fraction is 10-20%, while hardness and fracture toughness have a strong dependence on grain size. This macroscopic mechanical property is microscopically characterized by a phase change region at the crack tip that increases as the Ce-TZP grain size increases. Therefore, the key to the preparation of Ce-TZP ceramics is to properly control the growth of the crystal grains and obtain excellent mechanical properties.

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