For the key components of rocket engines, such as gas rudder and nozzle throat liner, their working environment is very harsh. The temperature rise at the moment of ignition is about 2000℃/s, and the working temperature is usually around 3000℃, and they are also subject to oxidation. The continuous scouring of material particles. Therefore, the material is required to be able to withstand high temperature, thermal shock, erosion, and have a certain high temperature strength. The materials used in the early days mainly include refractory metals and their alloys, graphite, etc., but these materials have disadvantages such as difficult processing, inability to resist erosion and poor thermal shock resistance. The sweat cooling technology appeared in the 1960s, which provided an effective way for materials to prevent heat and reduce temperature.
Sweat cooling technology and materials
Sweating cooling, as a bionic technology, is a kind of ability and technology that uses organisms to self-regulate the environment (temperature) in order to survive. That is, when the material is working in a high-temperature environment, it “sweats” by itself to reduce its own temperature, thereby achieving The purpose of thermal protection.
Perspiration cooling can be divided into spontaneous sweating and forced sweating according to its spontaneity. Forced sweating is a composite cooling technology that consists of sweat cooling and air film cooling. Spontaneous sweat cooling is more common in powder metallurgy material products. It is the purpose of cooling by adding low melting point metal in the base material to vaporize and evaporate at high temperature to achieve the purpose of cooling. The base material is generally a material with high melting point, high hardness and high strength , The added low melting point metal generally has good plasticity, and the spontaneous sweat cooling material combines the advantages of the two, and has good ablation resistance, thermal shock resistance and high strength.
Spontaneous sweat cooling materials were originally studied as heat protection materials for aerospace vehicles. Therefore, they are mainly used in the aerospace field. Tungsten-copper and molybdenum-copper materials are widely used in solid rocket engine nozzles, throat linings, gas rudders, guard plates, fasteners, etc. The application on throat linings and gas rudders is relatively mature and has formed corresponding standards. Graphite copper infiltration material is mainly used as a solid rocket motor throat lining material. Ceramic-based sweat cooling material is a very promising high-temperature and ablation-resistant material for aerospace due to its advantages of light weight, wear resistance, and high temperature resistance, but there is no relevant report on its application.
Ceramic base spontaneous sweat cooling material
In recent years, the development of sweating ceramic composite materials has received widespread attention. These ceramic materials not only have high melting points, such as ZrB2, TiB2, ZrC and other melting points have reached nearly 3000 ℃, especially borides have good oxidation resistance at high temperatures. It has been reported in the literature that TiB2/Al sweat cooling material has a high temperature test, because the volatilization of Al not only plays the role of sweat cooling, the Al2O3 oxide film formed at high temperature of Al adheres to the surface of the material, enhancing the oxidation resistance of the substrate. This high-temperature resistant cermet composite material has always been the focus of development in various countries. Because of its light weight, high efficiency, and simple structure, it has great development potential in high-temperature locations such as rocket and missile engine combustion chambers, nozzles, throat linings, and guard plates. , A confidential technology belonging to various countries, rarely seen in public research reports.
At present, materials such as TiC/Cu, TiB2/Cu, TiB2/Al are reported in the literature. Judging from the existing literature, the thermal shock resistance of ceramic-based spontaneous sweating materials is not good, the machining performance is poor, the material system is not perfect, and there is a lack of understanding of the composition, process, organization and performance of existing materials. system Research.
Forced sweat cooling material based on porous ceramic
Compared with spontaneous sweat cooling materials, forced sweat cooling materials use liquid (gas) as the coolant. Coolant is generally a component of propellant, without sacrificing the components of structural materials, it is easier to control heat, and it has a wider application prospect in rocket engines, especially in liquid rocket engines. According to the different formation methods of the coolant transmission channel, forced sweat cooling materials are mainly divided into layered sweat cooling materials and porous sweating materials.
The porous sweating material is mainly obtained by the incomplete densification process in the material preparation process to obtain a porous body with a certain porosity, and uses its effective pore channel (ie, opening) to realize the transmission of the coolant. Porous sweating materials mainly include metal-based and ceramic-based sweating material systems.
Since the 1980s, the porous ceramic-based sweating material has the incomparable performance advantages of metal materials due to its light weight, high temperature resistance and other performance advantages. The research hotspot of cooling materials. Currently, the main material systems are porous C/SiC composites and SiC foam ceramics. Among them, porous SiC foam ceramic material is a new type of sweat cooling material reported in recent years.
Porous SiC foam ceramics have the characteristics of high porosity, low density, high specific surface area and high temperature resistance. Among them, high porosity is conducive to coolant transmission, and high specific surface area is conducive to sufficient heat exchange between the coolant and the solid framework, which improves the cooling effect and reliability of sweat cooling. At present, the research is in its infancy, and the main work includes the preparation of materials, the testing of permeability, and the discussion of fluid flow in porous ceramic foam.