the toughening mechanism of ZTA ceramic

Toughening mechanism of ZTA ceramics is whisker and fiber reinforced and dispersed second phase strengthening and toughening, ZrO2 phase transformation toughening, and with metal complex formation of metal matrix composite ceramics, residual stress toughening and so on. Following is a brief description of several research hot way to toughen mechanism.

1, the stress induced transformation toughening for the ZrO2/Al2O3 system, the main toughening methods is transformation toughening produced by ZrO2 Li Shipu et al. Interpreted as: ZrO2 particles dispersed in Al2O3 matrix, due to the different thermal expansion coefficient between the two, after the completion of sintering, during the cooling process, a force of around ZrO2 particles the situation is different, when suppressing it by the matrix, the phase transition will also be inhibited by ZrO2. In addition, ZrO2 has another characteristic, is the phase transition temperature decreases with decreasing particle size, has been reduced to room temperature or below. The party matrix has enough compressive stress on the ZrO2 and ZrO2 particles is small enough, the phase transition temperature can be reduced to below room temperature at room temperature, so ZrO2 can still maintain a tetragonal phase. When a material is subjected to external stress, inhibition of matrix of ZrO2 relaxation, ZrO2 particle is the four phase to the The transition of the single phase and the crack in the matrix, which absorbs the energy of the main crack growth, can achieve the effect of increasing the fracture toughness, which is the stress induced phase transformation toughening of ZrO2.

2, micro crack toughening without doubt, in most cases, there is a ceramic body including crack, surface crack, process defects, induced defects under the environmental conditions, when the external force or the existence of stress concentration, the crack will lead to the rapid expansion of ceramic body damage. Therefore, we should prevent crack propagation, eliminate stress concentration that is the key to solve the problem. The toughening stabilized ZrO2 in t-ZrO2 to m-ZrO2 martensitic transformation, transformation the volume expansion caused by micro cracks. So whether the ZrO2 Ceramics produced transformation induced during the cooling process of micro cracks, micro cracks or cracks formed in the tip region in the expansion process should be stress induced transformation result, will play the role of the main crack tip energy dispersion, thus improving the fracture energy, achieve the toughening effect. However, in order to realize Al2O3 ceramic toughening effect, ZrO2 particle size Inch is also very important, the fineness of the particles should be small, otherwise than room temperature critical phase transition diameter of about 0.7 m and narrow particle size range to in order to make the ZTA ceramics at the same time, the stress induced phase transformation toughening and microcrack toughening mechanism.