The toughening research of phase-change ceramics around the relevant properties of zirconia has attracted much attention since Garvie et al. published the article "Ceramic Steel" in the journal Nature in 1975. Since then, zirconia has been dispersed in the matrix of various ceramic materials for testing, and high-performance ceramic materials have been prepared successively. The most classic is to inject zirconia into alumina ceramics to obtain Zirconia Toughened Aluminum (ZTA) ceramics.
 

 

1. Performance characteristics and the correlation between performance and alumina powder

 

ZTA ceramics are a kind of complex phase ceramics with excellent chemical stability, thermal stability and high strength, but the reliability is low, the production cost is high, and the application is limited.

 

The flexural performance and fracture toughness of ZTA ceramics are related to the particle size of the alumina powder, and its sinterability increases as the alumina particles used decrease. Experiments have shown that ZTA made of sub-micron alumina produced by mechanical grinding has good mechanical properties when sintered at 1500℃. Its flexural strength reaches 720Mpa and fracture toughness reaches 6.86MPa·m1/2, and its performance is better. Alumina composite ZTA ceramic prepared by chemical method. However, it is not that the finer the particles, the better the mechanical properties of ZTA, it is also related to the sintering temperature. Under the same temperature sintering condition, too large alumina crystal grains will also inhibit the phase transformation of zirconia and affect the performance of the final ZTA ceramics.

 

2. Preparation method of ZTA composite powder

 

The preparation technology of ZTA composite powder includes mixing method, precipitation method and precipitation coating method. However, the problems of agglomeration of ultrafine powders and uneven dispersion of ZrO2 in the matrix have always been difficulties in process control. In recent years, researchers have made many new process improvements based on the original method.

 

①Mechanical mixing method: the powders that make up the composite powder are mixed, ball milled, and then sintered. This method is straightforward and simple, but it cannot guarantee the uniform dispersion of multiphase components. Experiments have found that if the ceramic material prepared by the composite powder prepared by this method is not uniformly mixed, it is easy to have a higher porosity, which will reduce the mechanical properties of the material.

 

②Multiphase suspension mixing method: by adding a dispersant and adjusting the pH value, firstly prepare a single-phase stable suspension with fully dispersed components, and then find out the mixing and suspension conditions under which the particles of each phase can be uniformly dispersed. Single-phase suspension is mixed, and then a uniformly mixed powder can be prepared by finding common flocculation conditions.

 

③Sol-suspension mixing method: Because the suspension of nano-sol is not affected by the pH value of the liquid, it greatly facilitates the uniform mixing with other suspensions. When the solid content of the two liquids is high, it can be stirred, heated or Airflow drying to obtain high-mixed nano-composite ceramics.

 

④ Sol-gel method: It is a method of converting metal oxide or hydroxide sol into gel, and then drying and calcining the gel to prepare oxide. This method is suitable for preparing uniformly mixed nano powders.

 

3. Application direction

 

Alumina has high hardness and zirconia has good toughness. ZTA ceramics, a high-strength and high-toughness composite made of two materials, can be used in the production of ceramic tools to realize the processing of cast iron and alloys; Used to make the interface structure of engineering ceramics to prolong the service life of engineering materials; used to make wear-resistant ceramic balls; relying on the excellent biocompatibility of alumina ceramic materials, it can be made into biomedical materials for hard tissues of the body ( Such as teeth) reconstruction and restoration.