Carbon/ceramic material-ideal material for high temperature resistance

Carbon/ceramic composite material is made of carbon fiber, ceramic fiber and its fabric as a reinforcing phase, quartz, feldspar, silicon carbide and other ceramics as the matrix phase of a class of composite materials in general.

(Atmosphere Deposition Furnace)

Carbon/ceramic materials not only have the advantages of high strength, high modulus, high hardness, impact resistance, oxidation resistance, high temperature resistance, acid and alkali resistance, corrosion resistance of all chemical substances, small thermal expansion coefficient, light specific gravity, etc., but also completely overcome the brittleness and single function of general ceramic materials. It is recognized as an ideal high-temperature structural material, friction material and cryogenic material in the world, it is an excellent material for manufacturing mechanical seals, bearings, molds and other components. It is currently widely used in many fields such as aerospace, automotive, metallurgy, semiconductor and construction industries.
With the dual advantages of carbon and ceramics, it can be used as heating elements, electrodes, heat exchangers, crucibles, bearings, mechanical seals and hot-pressing molds and other materials, and is used in the fields of machinery, electronics, chemistry, metallurgy and aerospace.

01
King of Brake Materials

At present, the brake materials widely used in high-speed trains, automobiles and airplanes are mainly powder metallurgy and C/C composite materials. However, powder metallurgy brake materials have the disadvantages of easy bonding at high temperature, easy deterioration of friction performance, significant decrease of high temperature strength, poor thermal shock resistance, short service life, etc. However, C/C brake materials have problems such as low static and wet friction coefficients (wet state is attenuated by about 50% relative to dry state), large volume of thermal storage, long production cycle (about 1200h) and high production cost, restrict its further development and application.
Development history of high-performance brake materials

Carbon/ceramic brake material is a kind of high performance brake material developed after powder metallurgy material and C/C composite material in recent years. Compared with traditional metal and semi-metal brake materials, it has the advantages of low density, high strength, stable friction performance, low friction, large braking ratio, high temperature resistance, and long service life. Compared with C/C composite materials, due to the introduction of the appropriate amount of SiC ceramic hard material as the matrix, the oxidation resistance and friction coefficient of the material can be improved, and the friction performance is not sensitive to the external environment medium (mold and oil, moisture, etc.). Therefore, C/SiC brake materials have broad application prospects in high-speed trains, automobiles, aircraft and other fields.

02

Ultra-high temperature oxidation resistance thermal protection materials-key technologies for aerospace

Hypersonic aircraft unique "long flight, atmospheric re-entry, cross-atmospheric flight" working conditions, making its wing leading edge, nose cone and combustion chamber and other key components of the thermal protection requirements are extremely harsh, so ultra-high temperature anti-oxidation thermal protection structure materials become one of the main key technologies restricting hypersonic aircraft.

At present, three types of commonly used high-temperature materials are difficult to meet the requirements of use. C/C composites still have high strength, high modulus, good fracture toughness and wear resistance at high temperature, and are ideal high-temperature engineering structural materials. But its oxidation resistance is poor, and oxidation will occur in the oxidation environment above 370 ℃. Existing refractory metal materials are used at low temperatures and their strength drops sharply at high temperatures. Ceramic materials have high melting point and good oxidation resistance, but they are brittle and difficult to produce complex thermal structural components.

The oxidation resistance of C/C composites can be improved by using ceramic materials to modify C/C composites, and the oxidation resistance temperature of C/C composites after ceramic modification is mainly determined by the melting point of the modified ceramic material itself and the melting point of its oxide. SiC, ZrC, ZrB2, HfC, HfB2 and other ceramics have high melting point and low density, which is an ideal choice for high temperature oxidation modification of C/C composites above 2300K, and can solve the problems that plague the development of new weapon technologies such as hypersonic vehicles.

Because the thermal expansion coefficient of SiC and C/C composites is relatively matched, SiC has become the most commonly used ceramic material for oxidation resistance modification of C/C composite matrix, and the resulting composite material is called C/C-SiC carbon ceramic composite material. The main function of the SiC matrix in the material is to form a dense SiO2 based vitreous layer, which can effectively protect the carbon fiber from oxidation. At the same time, the preparation technology of SiC ceramic matrix is mature, the source of raw materials is wide and the cost is low, so it is widely used.

03
Sealing material

Graphite material has many characteristics such as high temperature resistance, corrosion resistance and self-lubrication, so it is widely used in the field of fluid sealing, but its application is limited by its low mechanical strength and easy oxidation at high temperature. In aerospace, aviation and other high-temperature engineering, the materials used for mechanical seals often have to withstand high speed, high specific pressure and high friction rate and the resulting high friction heat, and the temperature value of the friction surface can be as high as 700 ℃ ~ 1000 ℃. Ordinary graphite materials are difficult to adapt to such harsh working conditions.

In order to develop fluid mechanical seal materials that can meet the requirements of aerospace, aviation and modern high temperature technology, scholars at home and abroad have carried out a lot of exploratory research over the years, and achieved remarkable results. Among them, SiC, B4C, CrC and other ceramic particles are dispersed to strengthen the graphite material, which is very effective in improving the mechanical strength, wear resistance and high temperature air oxidation resistance of the composite material. Among them, BN has similar high temperature (air) oxidation resistance to B4C, can reduce the reaction power of carbon and oxygen, has a hexagonal crystal structure similar to graphite, and also has excellent self-lubricating properties. And the self-lubricating performance is not as dependent on the existence of gas and liquid media as graphite materials, and can adapt to high temperature dry grinding conditions. In addition, the similar hexagonal crystal structure BN has good structural compatibility with graphite composites, and makes such composites combine their respective advantages.

04
insulator second-change conductive material

Among ceramic materials, except for ZrO2, which has a conductive function under high temperature conditions, other ceramics such as Al2O3, MgO, SiO2, CaO, etc. are all electrical insulators, and the application of these materials is limited. If these materials can be electrically conductive through a certain process, plus the excellent characteristics of the ceramic material itself, then the application range of ceramic materials will be further expanded. Carbon/ceramic composite conductive material is a new type of inorganic non-metallic material developed in this context. It is widely used in electric spark electrode materials, industrial heating, school drying systems, home heating and other fields.

The ceramic base material mainly includes diopside, quartz and feldspar, and the conductive filler mainly includes carbon-based conductive filler, metal conductive filler and metal compound conductive filler. The carbon-based conductive filler mainly includes carbon black, graphite, carbon fiber, carbon nanotube, etc.

5, diffusion welding heating element, heating induction heating, resistance heating, long-term use temperature of 600-800 ℃, good thermal conductivity, high hardness, and graphite material than the production efficiency of each mold more than doubled, the service life of more than 2 times.

6, electronic components sintering mold, long-term use temperature of 600 ℃, good oxidation resistance, no powder, no pollution of electronic components, good thermal conductivity, dimensional stability, thermal stability and chemical stability.

7, hot bending glass mold, particle size below 3μm, compact and uniform organization, good thermal conductivity, small coefficient of thermal expansion, long-term use temperature of 600 ℃, good oxidation resistance, no powder, easy processing.
Preparation method of carbon/ceramic composite material

In the preparation process of C/C-SiC carbon ceramic composite materials, the C/C embryo with certain porosity is prepared by chemical vapor deposition (CVD) or resin impregnation/cracking method, and then the SiC matrix is introduced to replace part of the C matrix by other methods. There are usually four ways to introduce SiC matrix:
(1) Gas phase method, such as chemical vapor infiltration method (CVI);
(2) Liquid phase methods, such as precursor impregnation cracking (PIP) and reaction melt infiltration (RMI);
(3) ceramic method, such as mud impregnation-hot pressing sintering process;
(4) Combined processes, such as CVI PIP, CVI RMI, PIP RMI, etc.