Toughening method of zirconia ceramic matrix composites---phase transformation toughening

The brittleness of zirconia ceramics has always been a problem that scientific research institutions have been working hard to solve in recent years, so that the processing performance of ceramics will increase, making zirconia ceramics suitable for more industries. The following is the first introduction of Kezhong Ceramics Factory. Toughening method of ceramic matrix composites --- phase change toughening

ZrO2 phase change primary ceramics is a promising new type of structural ceramics. It mainly uses phase change characteristics to improve the fracture toughness and flexural strength of ceramic materials, so that it has excellent mechanical properties, low thermal conductivity and Good heat resistance.

This is one of the important ways of toughening in composite materials and composite ceramics. The typical phase change toughened ceramic A2O3/ZrO2 was developed in 1977. It uses the volume change after ZrO2 phase change to make Al2O3 tougher. Stress-induced transformation toughening is to use stress-induced tetragonal ZrO martensitic transformation to change the toughness of ceramic materials.

Since ZrO2 is a monoclinic crystal system at room temperature, when the temperature reaches 1170 ° C, the monoclinic crystal system transforms into a metastable tetragonal crystal form. Under the action of stress, the metastable tetragonal crystal form ZrO2 can induce phase Change into monoclinic crystal form again, accompanied by volume expansion at this time, resulting in the closure of micro-cracks, thereby toughening the ceramics.

When sintering at high temperature, ZrO2 particles exist in the tetragonal phase, and when the sintering is dense and cooled, the tetragonal ZrO2 particles will transform into monoclinic phase particles. If at this time, part of the tetragonal ZrO2 is retained at room temperature by adding a stabilizer, Under the action of the stress field at the crack tip, ZrO2 particles will undergo a phase transition from tetragonal phase to monoclinic phase and absorb energy, and the external force will do work, thereby improving the fracture toughness, but due to the change of temperature, its volume will expand violently and shrink, resulting in cracking.

In order to solve this problem, a stabilizer must be added to zirconia to form a solid solution with it, so that all or part of praseodymium dioxide maintains a high-temperature tetragonal or cubic phase, forming fully and partially stable zirconia. This type of material has excellent friction properties as a tough material, and has been applied in machine quilts, and is also used as cutting tool materials. The wear resistance of Al2O3/ZrO2 ceramic tools is very good, which has been confirmed in the practice of cutting carbon steel, and the impact resistance is improved due to the stress on the surface of the tool

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