With the development of science and technology, there are more and more kinds of mechanical engineering materials. Engineering ceramics is a new kind of materials used in precision machining. This material is formed by combining metals with elements such as carbon, silicon, nitrogen and boron. It becomes three solid materials together with metal materials and polymer materials.
The properties of engineering ceramics are determined by chemical bond and crystal structure. General ceramics have high hardness, high wear resistance and high corrosion resistance. By improving the sintering process and composition, and changing its microstructure, the properties of ceramics can be improved and the toughness of ceramics can be increased.
1. Alumina ceramics
This kind of ceramics can be sintered under normal pressure because of its good sintering performance. The hardness of alumina ceramics is high, and it is still 80hra when the temperature is up to 1200 ℃. It has good wear resistance but high brittleness. It is the first ceramic used to make cutting tools. It can be used for the processing of hard alloy and hard alloy. The impact toughness and bending strength of alumina ceramics can be improved by hot pressing sintering, such as isostatic pressing sintering. The addition of tic, tin and SiC compounds to alumina ceramics can improve the impact toughness, bending strength and thermal shock resistance of the ceramics, and expand the application range of the cutting tools.
2. Silicon nitride ceramics
The bonding energy of silicon nitride ceramics is very high, and it is difficult to sinter at high temperature. The results show that the reaction sintering products have high precision and complex shape parts; the hot pressed sintered products are dense, with high strength, hardness and good toughness.
Silicon nitride ceramics have high bending strength, hardness, low friction coefficient and self lubrication, which can work without lubricant. It not only has good meningeal properties, but also has little wear to matching materials. It is an excellent wear-resistant material. The wear resistance, high temperature resistance and seismic resistance are also good.
3. Silicon carbide ceramics
The technology of reaction sintering and hot pressing roast chicken is commonly used in silicon carbide ceramics. Compared with other ceramics, it is characterized by high strength at high temperature and good thermal conductivity. It is mainly used for nozzle of rocket exhaust nozzle, gate for burning metal, thermowell, gas turbine blade, heat exchange material under high temperature, encapsulation material of nuclear fuel and abrasives, etc.
4. Partially stabilized zirconia
There are three kinds of structure of zirconia crystal, namely monoclinic phase and tetragonal phase cubic phase. When pure zirconia is cooled at high temperature, the crystal structure will change, which is easy to cause ceramic cracking. In order to avoid this phase transformation in high temperature use, adding a certain amount of MgO and yttrium oxide into pure zirconia, and properly controlling the heating and cooling conditions, the high temperature phase is partially stable and zirconium is formed Zirconia, which is partially stable, has good toughness. It can be used for piston crown, valve guide, etc.
5. Boron nitride
Dahuabang crystal is a hexagonal crystal system. Its products include powder, bar and various manufactured products, such as high temperature bearing, glass mold, lubricant, release agent, etc. Hexagonal boron nitride can be converted into cubic boron nitride under high temperature and high pressure with catalyst. The hardness of cubic boron nitride is close to that of diamond, so it is a good abrasive material.
In the future development, engineering ceramics will be widely used in machining industry, such as abrasive jet machining technology, magnetic levitation polishing technology, liquid floating grinding and polishing technology and so on. Based on the characteristics of engineering ceramics, the development trend of engineering ceramics processing technology is summarized.