Introduction of New Technology of Dispersion Toughening Mechanism of Zirconia Ceramics

There are various toughening methods for zirconia ceramics. After toughening, the processing performance of the ceramics will increase. In fact, the dispersion toughening of alumina ceramics can be combined with the phase change toughening of zirconia ceramics. The following is given by Kezhong Ceramics Factory Let's analyze it.

From the analysis of the initial mechanism, the phase transformation toughening effect of ZrO2 and the dispersion toughening of Al2O can be superimposed. The pinning of cracks by Al2O makes up for the effect of microcracks on strength, so that the values of flexural strength and fracture toughness of composite ceramics gradually appear at the same firing temperature. The Al2O/ZrO2 powder with a particle size of 15nm was prepared by ammonia co-precipitation method, which is mainly composed of tetragonal phase ZrO2 and Al2O3.

Corresponding conclusions have also been drawn after testing, and it is concluded that the addition of Al2O3 is beneficial to the retention of tetragonal phase in ZrO2 ceramics, improving the hardness and elastic modulus of ZrO2 ceramics, and meeting the requirements for making roll-rolled welded pipes. It can be seen from the above several groups of experiments that when an appropriate amount of A2O is added, on the one hand, Al2O) can inhibit the growth of ZrO2 particles, and at the same time, ZrO2 can also inhibit the growth of A2O) particles, so the grains are fine and uniform. Al2O particles with high elastic modulus (its elastic modulus is about twice that of ZO2) can significantly increase the phase transition stress of ZrO phase transition toughened ceramics, which also makes the actual contribution strengthen at the crack site.

Furthermore, since the thermal expansion coefficient of Al2O is about 8× 10-· °C-1, which is smaller than the thermal expansion coefficient of ZrO, when Al2O) is distributed in the ZrO2 matrix, the Al2O) grains are in a state of compressive stress, and AlO and ZrO2 are in a state of compressive stress. The boundary is well combined and has good grain boundary strength, so that cracks are not easy to form at the grain boundary of AlO and ZrO2. Therefore, the addition of Al2O can soften the grain boundary of ZO2 ceramics, and the phase transition of ZrO2 can be improved, so that the ZrO2 ceramics Flexural strength and fracture toughness are improved.

But when the content of Al1O) is high (more than 50%), Al2O3 is no longer a dispersed phase. At this time, the relative content of ZrO2 that can undergo phase transition has been greatly reduced. Therefore, the effect of phase transition toughening is weakened, making ZrO2 / AL2O3 ceramic bending strength decreased instead. In recent years, ZrO2 toughened and cut Al2O2 ceramics as a promising medium and low temperature (<800C) structural material has been called the most active topic in the field of materials. Now the research on ZrO2 initialized Al2O2 ceramic materials is concentrated on adding unstabilized, partially Stabilized or tetragonal ZrO2 polycrystalline, using t&rarr;m phase transition to achieve the purpose of toughening.

As shown in Figure 4-3, when the pressure is low, the fracture strength increases with the increase of ZrO2 content, which is consistent with the change trend of its density, which shows that the main factor affecting the fracture strength at this time is the density of the material. The pressure is 25MPa and the fracture strength of the material produced by cooling and holding pressure has a large value, and then decreases with the increase of ZrO2 content. According to this, it is inferred that the damage to the fracture strength at this time is caused by the thermal expansion difference between Al2O3/cZrO2 tensile stress and microcracks.

Since the residual compressive stress produced by the preparation process is basically constant, and the more ZrO2 content, the larger the grain size, the greater the tensile stress generated, and the more microcracks. Therefore, when the ZrO2 content is high enough, residual tensile stress exists in the sample. Stress, when the tensile stress exceeds its interfacial bonding force, microcracks are generated, thereby reducing the strength, so the peak of fracture toughness is higher, and it appears in the sample with a higher volume fraction of cZrO2. This shows that the addition of cZrO2 to the Al2O3 matrix is not a lack of phase transition and particle shrinkage but a monotonous decrease in fracture toughness.

This is quite different from Lange's result that Kc decreases monotonously with the addition of c-ZrO2 particles.

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