alumina ceramics strengthening process
The technique of densification of granular alumina ceramic body and forming solid material is called sintering. Sintering is to eliminate the voids between the particles in the green body, to eliminate a small amount of gas and impurities, so that the particles grow and combine with each other to form a new material.
Electric furnace is the most widely used heating device for firing. Besides pressureless sintering, there are also hot pressing sintering and hot isostatic pressing sintering. Although continuous hot pressing sintering increases the output, the cost of equipment and mould is too high. In addition, due to axial heating, the length of products is limited. Hot isostatic pressing (hip) sintering uses high temperature and high pressure gas as pressure transfer medium, which has the advantage of uniform heating in all directions, and is suitable for sintering of products with complex shapes. Because of its uniform structure, the properties of the material are improved by 30-50% compared with that of cold pressing sintering. 10-15% higher than that of conventional hot pressing sintering. Therefore, some high value-added alumina ceramic products or special parts for national defense and military industry, such as ceramic bearings, mirrors, nuclear fuel and gun barrel, are fired by hip method.
In addition, microwave sintering, arc plasma sintering and self propagating sintering are also under development. Some alumina ceramic materials need to be finished after sintering. If it can be used as artificial bone products, the surface should have a very high finish, such as mirror, in order to increase the lubricity. Due to the high hardness of alumina ceramic materials, it is necessary to finish it with harder grinding and polishing brick materials. SiC, such as diamond, etc. Generally, the coarse to fine abrasive is used step by step, and the final surface is polished. Generally, Al203 micro powder with < 1 μ m μ m or diamond paste can be used for grinding and polishing. In addition, laser processing and ultrasonic machining, grinding and polishing methods can also be used.
Strengthening process of alumina ceramics
In order to improve the mechanical strength of alumina ceramics, a new strengthening process of alumina ceramics was developed abroad. The process is novel and simple. The technical means adopted is to coat a layer of silicon compound film on the surface of alumina ceramic by electron ray vacuum coating, sputtering vacuum coating or chemical vapor deposition method, and then heat treatment at 1200 ℃ ~ 1580 ℃. The mechanical strength of the strengthened alumina ceramics can be greatly increased on the original basis High strength alumina ceramics.