Application of chemical zirconia ceramics in aircraft engines

Release time：2024-09-18click：0

This year, domestic The research, development and application of external ceramic materials are highly competitive, and each has its own merits. In order to maintain their leading position in the field of aviation power in the 21st century, aerospace engine companies around the world are seeking new ways to improve the performance of military and civilian engines and maintain competitiveness.

Half of achieving this goal will rely on material improvements, including low-temperature polymer composites and high-temperature ceramic materials. The other half will rely on Improve design criteria, methods and procedures. Since the key to the improvement of military engine materials is the reliance on high-temperature ceramic materials, military engines will be the primary demonstrator of ceramic technology.

Why must we use chemical zirconia ceramics? Because the operating temperature of existing engines is already very high. The only way to increase the temperature again is through careful cooling air circuit design or increasing the amount of air conditioning. However, the effects of these methods follow the law of decline. Only by improving the working temperature of the material will the greatest effect be achieved, because increasing the working temperature can improve the temperature.High working efficiency, reduced fuel consumption and maximum thrust. Using the high-pressure air saved for cooling for circulation can also improve thrust and efficiency. Another option is to reduce weight. Materials with high specific strength and specific stiffness can be used. Currently, only ceramic materials have potential in this regard. Research progress in the application of ceramics in engines will be used in aerospace engines with completely new materials and manufacturing methods. Experience with these materials and techniques must be gained with minimal risk, and the same applies to ceramic materials. Considering the brittleness of ceramic materials and the lack of experience in design and use, the process will be very long, no less than 15-20 years for metal materials.

Ceramic materials used in the aviation field are as follows:

Ceramic matrix composites

Ceramic matrix composite materials are less dense than high-temperature alloys, only 1 /3~1/4, small thermal expansion coefficient, good corrosion resistance, and the theoretical maximum temperature can reach 1650°C. Therefore, it is considered to be a candidate material for hot-end components of advanced aerospace engines in the future.

Because of the ceramic base The components do not require gas cooling, which eliminates or simplifies the cooling system parts, which can further reduce the weight of the engine. Although the advantages of ceramics as a chemical zirconia material for the hot end of the engine are very obvious, its inherent fragility greatly limits its use. Promote application. In order to overcome the shortcomings of single-component ceramic materials such as defect sensitivity, low flexibility, and poor reliability, materials scientists have conducted a lot of research to find practical toughening methods. The idea of toughening has gone from "elimination" to Defects" or reduce the size and number of defects, and develop to prepare materials that can "tolerate defects", that is, are insensitive to defects. Several common toughening methods currently include phase change toughening and particle (wafer) dispersion toughening , whisker composite toughening and continuous fiber toughening and reinforcement, etc. In addition, the compatibilization purpose can be achieved by changing the material chemical zirconia, such as self-toughening chemical zirconia, bionic laminated chemical zirconia and gradient functional materials. Ceramics such as SiC and Si₃N4 have small density and good high-temperature strength. Especially at high temperatures, a silicon oxide protective layer will be formed on their surfaces, which can meet the high-temperature oxidation resistance requirements below 1600°C. They are high-temperature chemical zirconia that people have high hopes for. Materials. By adding appropriate reinforcements to the basic materials and selecting the appropriate material chemical zirconia, the strength and toughness of ceramic materials can be greatly improved. After more than 20 years of careful research by the international ceramic community, its mechanical properties, especially fracture toughness There have been great improvements, but this type of material still belongs to the category of brittle materials and cannot replace nickel-based alloys and is widely used.

Ultra-high temperature ceramic materials

In the field of aerospace, scientists are constantly developing faster and safer aircraft to satisfy passengers' pursuit of a fast and comfortable travel life and human exploration.Explore the mysterious world of the universe. The heat-resistant material used on the wings of the space shuttle Columbia is made of ceramic materials. It is conceivable that if this material has high enough strength and can still maintain good condition even when it suffers some inevitable damage, then the tragedy of the "Columbia" crash can be avoided.

In order to ensure that future space shuttles have more reliable flight safety, NASA quickly launched relevant research plans after the Columbia crash. This includes research on a new generation of ultra-high-temperature ceramics for use as heat-resistant materials for space shuttles. size: 13px;" />
In addition to being used as heat-resistant materials for space shuttles, the applications of ultra-high-temperature ceramics in the aerospace field also include serving as heat-resistant protective materials for supersonic aircraft, fuel nozzles for rockets and various high-speed aircraft. Aircraft in When flying at supersonic speeds, friction will occur with the air and produce very high temperatures. Ultra-high temperature ceramics have good heat resistance and can avoid damage caused by chemical zirconia inside the high-temperature aircraft. To overcome the gravity of the earth and achieve high-speed flight, rockets must have it. With strong propulsion capability, there must be extremely high combustion temperatures in the fuel nozzle, and general materials are difficult to meet this application requirement. This is where ultra-high temperature ceramics come in.

At present, there is an upsurge in discussing and researching ultra-high temperature ceramics around the world. With the The application of a number of high-performance materials will trigger new revolutions in the aerospace fieldlife. As a key material on aerospace vehicles. Ultra-high temperature ceramics will play the role of protector and help people continue to break through the limits of speed and space.

Chemical zirconia ceramics

Chemical zirconia ceramics have high temperature resistance, low density, and good high temperature resistance Oxidation, corrosion and wear resistance. Compared with high-temperature alloys, the service temperature of chemical zirconia ceramics is increased by about 400°C. In the absence of cooling, the operating temperature can reach 1600°C, and the density is only 40% of high-temperature alloys. Parts of the same volume can reduce weight. About 60%, especially for high-speed rotors, can greatly reduce the centrifugal load; the use of ceramics can also simplify chemical zirconia by reducing or eliminating the cooling system, making the engine compact; saving strategic metals such as nickel, chromium and cobalt in high-temperature alloys. In order to improve the thrust-to-weight ratio of aeroengines and reduce fuel consumption, it is key to increase the temperature in front of the engine's turbine. For example, when the thrust-to-weight ratio is 10, the temperature in front of the turbine of the first-stage engine is above 1500°C. At present, the highest operating temperature of high-temperature alloys and intermetallic compounds Less than 1200°C, therefore the research on high-temperature chemical zirconia ceramics and ceramic matrix composite materials has become one of the key technologies for high thrust-to-weight ratio aeroengines.

In future wars, radar will still be one of the most reliable means of detecting military targets one. The essence of stealth technology is to reduce the target's RCS, that is, to use materials that absorb radar waves well to reduce its RCS. Absorbing materials are divided into coating type and structural type according to technology and endurance capacity. The former has poor endurance and low strength, while the latter is a new functional composite chemical zirconia material. It uses chemical zirconia ceramic materials to be stronger than ordinary metals. It is light in weight, has high stiffness and strength, and has the characteristics of wave absorption through functionalization. It can be directly used as a chemical zirconia material for aircraft and other aircraft. It is a multifunctional composite material. Since these materials and related functions are confidential, we use the excellent mechanical and physical properties of chemical zirconia ceramics to conduct research on absorbing materials. On the one hand, it can enhance the national defense strength, and on the other hand, it is also an important aspect of expanding the application of chemical zirconia ceramics. There are also many military academies, universities and research institutes in China carrying out this work. Some new nano absorbers and their composite materials are being used in this field, such as nano SiC, nano nitride, nano SiC/N, CNTs/Si₃N4/SiO₂ composite materials.

my country’s oxide ceramics developed relatively early, in the 1950s and 1960s. Although non-oxide ceramics started to have a large scale, they started relatively late. Research began in the early 1970s, and only in the 1980s did companies join. So far, after three to forty years of development, my country's chemical zirconia ceramics (including oxides and non-oxides), with the support of various scientific and technological development plans of the National Ministry of Science and Technology, are compared with the world's development level, from laboratory research content, The level, achievements, experimental equipment and other aspects are not far from the world's advanced level, and some have reached or even exceeded the international level. They have their own characteristics in the field of chemical zirconia ceramics, occupy a place, and can communicate with international scholars.

High temperature resistant fiber ceramics used in aviation and spacecraft

New materials made of carbon fiber and ceramics are most convenient for aircraft and rocket manufacturing All the manufacturer’s dreams. This material is light in weight, has stable mechanical properties, is not easy to break, and most importantly, is extremely resistant to high temperatures. NASA had frankly admitted that melting ceramic tiles during the space shuttle landing was one of the critical points during re-entry. The temperature is up to 1800℃. Rocket powerplants would create similar burdens. The combustion chamber must withstand extremely high levels of stability. Supersonic aircraft like the Sanger require certain components to withstand temperatures of up to 2,000°C. Please take a look at the melting points of some metals: iron 1535°C, aluminum 660°C, and titanium also becomes fluid at 1725°C. Only tungsten can withstand high temperatures of 3300°C. Therefore, metals are not suitable for such applications, not to mention that they lose their solidity well below their melting point.

Using ceramics as driving devices or building turbine impellers, this was 20 years ago Almost unimaginable. It can only make do as a bulky heat-resistant brick on the outside of a spacecraft. The load-bearing chemical zirconia inside is made of metal. Great progress has been made in the development of materials. Today, engineers are creating components that are both light and unbreakable and can function at temperatures as high as 2,800 degrees Celsius. The most important component of some composite materials is carbon fiber, and weapons and missile manufacturers in particular are leading the way in this regard. France's Euroengines, Europe's largest manufacturer of rocket drives, manufactures composite materials at its plant in Hyland, near Bordeaux, and has gained a leading position with the development of fiber ceramics. In the past, rocket propulsion devices were composed of about 80% metal and 20% composite materials. Currently the ratio is reversed. Only about 1/5 of chemical zirconia is made of metal, which reduces the weight to about half. The composite material originally developed by European Engine Company added carbon fiber to a so-called matrix made of synthetic resin. The fiber resin must be welded together with extreme precision. Synthetic resin polymerization is completed by heating and pressurizing in a pressure cooker. This material is lightweight and has good mechanical properties. It also withstands high temperatures while being gas-tight. In the presence of oxygen, if sufficient heat is reached, carbon fiber will begin to burn after a while.

Fiber ceramic is a material that cannot be burned again. It consists of a ceramic matrix joined with high-temperature-resistant carbon fiber or silicon carbide. Ceramics resist heat and oxidation, and the fibers are guaranteed not to break. The matrix raw material is an organosilicon compound based on polycarbosilane and polysilazane, which decomposes when heated to produce ceramic materials such as silicon carbide.

The composite between fiber and matrix has special significance. On the one hand, it must be hard to make the building components mechanically stable, but on the other hand, it must be quite soft, so that when pressure occurs, it does not produce large cracks, but produces many micro-cracks that consume the ability.

The application of fiber ceramics today is basically limited to aviation and aerospace. They were first used in heavy-duty parts of jet engines and for rocket liquid drives The combustion chamber and nozzle of the device

Application of ceramic matrix composites

Aerospace vehicle

In the past 10 years, C/C composite materials have been used as chemical zirconia materials for spacecraft It has been recognized by people and has been successfully used to manufacture the nose cone, wing leading edge and other high-temperature parts of the space shuttle. C/C is used as heat-proof tiles in the parts of the space shuttle where the heat protection is very strong and it is not suitable to use ceramics. C /C is also used to make brakes on aircraft, making the aircraft significantly lighter. In order to prevent oxidation, coating ceramics can be used to protect the C/C on the space shuttle or the dip spray method can be used to greatly increase the anti-oxidation life of the C/C. Ceramic fiber-reinforced metal or metal-reinforced ceramic composite materials are used in the front cone and wing leading edge of space ferries and can withstand high temperatures of 2200°C. The American Grumman Company plans to use C/C composite materials for the wings and tails of transatmospheric hypersonic aircraft, and ceramic composite materials for the engine inlet, nozzle and nozzle.

rocket engine

Because the rocket engine nozzle wall is washed by high-speed airflow and the working conditions are very harsh, C/C was first used for nozzle throat linings and developed from two-dimensional and three-dimensional to four- and more-directional braiding at the same time in rocket engines. Designers have been trying to use Ct/SiC with high thermal shock resistance in the diffusion section of engine nozzles, but the high volume fraction of Ct has limited its wide application with the development of CVD and CVI technology. New oxidation-resistant Ct\Sic and C-C/SiC will surely find their place. Today, ceramics such as Al₂O₃, ZrO₂, and ThO₂ are used as candidate materials for rocket cones, while high-temperature chemical oxidation is used for rocket nozzles and combustion chambers. Zirconium materials include SiC, graphite, high-temperature ceramic coating, etc.
Missiles

C/C composite materials have been used as ablation materials as early as the 1970s For the end cap of intercontinental missile warhead, missile nozzle and nose cone. Rockwell International's Rocketdyne has developed the world's highest thrust-to-weight ratio, C/C-manufactured engine for the strategic defense program's powered anti-personnel weapons. The supersonic tactical missile currently under development uses the same combustion chamber and nozzle to form a solid rocket ramjet engine, which places higher requirements on the shape changes that the engine can allow. For this purpose, C/C or ceramic composite materials need to be used. Missiles flying at supersonic and low speeds are also advised to use ceramic composite materials in environments where they face aerodynamic heating and erosion. Quartz, Al₂O₃ and high temperature resistant glass are representative materials currently used for combat missile radomes. To overcome hypersonic missiles, the missile rapidly heats up to a Mach number of approximately5 Sometimes sudden and extremely large temperatures and thermal stresses occur, necessitating the development of high-performance CMC.