Carbon / carbon composites refer to carbon matrix composites reinforced with carbon fibers and their fabrics. Carbon fiber as a reinforcement can be used in a variety of forms and types, either chopped fiber, continuous long fiber and braid. The carbon matrix may be pyrolytic carbon prepared by chemical vapor deposition, or solid carbon formed by pyrolysis of a polymer material. Carbon / carbon composite materials have the advantages of low density (<2.0g / cm3), high strength, high specific modulus, high thermal conductivity, low expansion coefficient, good friction performance, good thermal shock resistance and high dimensional stability. Today, the few candidate materials used above 1650 ° C have a maximum theoretical temperature of up to 2600 ° C, so they are considered to be one of the most promising high-temperature materials.
Carbon / carbon composite
The preparation process of carbon / carbon composite materials mainly includes chemical vapor phase method and liquid phase impregnation method. The former is based on organic low-molecular gas, and the latter is based on thermoplastic resins such as asphalt or thermosetting resins such as phenolic resin. These raw materials undergo a series of complex chemical changes at high temperature to be converted into matrix carbon. Among them, the chemical vapor method is to deposit carbon directly in the pores of the green body. The physical and mechanical properties of the product can be better, but the production cycle is longer. The liquid-phase impregnation method is to immerse a preform made of carbon fiber in a liquid impregnating agent, and then cycle through a series of processes such as curing, carbonization, and graphitization to finally obtain a carbon / carbon composite material. Among them, the composition and structure of the impregnating agent are very important, which not only affects the densification efficiency, but also affects the mechanical and physical properties of the product. The high viscosity and low carbonization yield of the impregnating agent are one of the important reasons for the higher cost of carbon / carbon composites. In order to obtain a better densification effect, two methods are usually combined to prepare a carbon / carbon composite material with an ideal density.
Chemical vapor deposition furnace
Carbon / carbon composite materials are excellent thermal structure and functional integrated engineering materials. Since their birth in 1958, they have made considerable progress in military industry. The most important use of them is in the manufacture of warhead components for missiles. Because of its high temperature resistance and good friction, it has been widely used in solid rocket engine nozzles, space shuttle structural parts, brake devices for aircrafts and racing cars, thermal elements and mechanical fasteners, heat exchangers, hot end parts of aero engines Wait. Among them, at present, solid rocket motor nozzles and brake discs are the two main application areas of carbon / carbon composite materials.
Rocket engine nozzle
In the application of solid rocket engine nozzles, carbon / carbon composite materials have greatly promoted the development of SRM nozzle materials since the first successful flight as a solid rocket engine (SRM) throat lining in the 1970s. The throat lining, expansion section, and extension outlet cone of carbon / carbon composite materials have extremely low ablation rate and good ablation profile, which can greatly improve the specific impact of SRM, and the nozzle efficiency can be improved by 1% to 3%. In the field of braking, experimental research on carbon / carbon composite brake discs was first used in aircraft braking in 1973. Currently, more than half of the carbon / carbon composite materials are used as aircraft brakes. Aircraft brake discs made of carbon / carbon composite materials are light weight, high temperature resistance, and 2.5 times higher heat capacity than steel; compared with metal brake materials, they can save 40% of the structural weight, service life can be increased by 5 to 7 times, and braking torque Stable, low noise when braking. Therefore, the advent of carbon brake discs is considered to be a major technological advancement in the development history of brake materials.
Aircraft carbon brake prefabricated parts
Since being invented in the 1960s, carbon / carbon composite materials have received great attention in the fields of military, aerospace, nuclear energy, and many civil industries. However, due to the complex manufacturing process of carbon / carbon composite materials, technical difficulties, expensive raw materials, and long-term product costs, its use is still limited to some parts with harsh working conditions, and other aerospace and military fields that cannot be replaced by other materials . At present, in the field of carbon / carbon composite materials research, the most important problems to be solved are: research on high-efficiency, low-cost, and rapid preparation methods; research on anti-oxidation coatings that can be used for long-term use above 1800 ° C; Carbon composite materials are also used in solid rocket throat lining materials; improve the friction and wear performance of carbon / carbon composite materials, making them more satisfied with the application of brake materials.