Aviation manufacturing is the most concentrated field of high-tech and belongs to advanced manufacturing technology. For example, the F119 engine developed by Pratt & Whitney of the United States, the F120 engine of General Electric Company, the M88-2 engine of SNECMA Company of France, and the EJ200 engine jointly developed by the United Kingdom, Germany, Italy and Spain. It is worth mentioning that these aero-engines representing the world's most advanced level have a common feature of using new materials, new processes and new technologies. The seven new materials used are introduced respectively as follows:
1
Carbon/Carbon Composite
What are carbon/carbon composites? It is a carbon matrix composite material reinforced by carbon fiber and its fabric, with low density (<2.0g/cm3), high strength, high specific modulus, high thermal conductivity, low expansion coefficient, good friction performance, and good thermal shock resistance , high dimensional stability, etc., especially the few candidate materials used above 1650 °C, the highest theoretical temperature is as high as 2600 °C, so it is considered to be one of the most promising high-temperature materials in the world.
Although carbon/carbon composites have many excellent high-temperature properties, they undergo oxidation reactions in an aerobic environment with a temperature higher than 400 °C, resulting in a sharp decline in the properties of the material. Therefore, the application of carbon/carbon composites in high-temperature aerobic environments must have oxidation protection measures. The oxidation protection of carbon/carbon composites is mainly through the following two ways, that is, the matrix modification and the passivation of surface active points can be used to protect carbon/carbon composites at lower temperatures; as the temperature increases, The method of coating must be used to isolate the carbon/carbon composite material from direct contact with oxygen, so as to achieve the purpose of oxidation protection. At present, the method of coating is the most used method. With the continuous advancement of science and technology, there is more and more reliance on the ultra-high temperature performance of carbon/carbon composite materials, and the only feasible oxidation protection solution under ultra-high temperature conditions can only be coating protection. .
It is worth mentioning that C/C-based composite materials are a new material with higher temperature resistance that has received the most attention in the world in recent years. Because only C/C composite materials are considered to be the only successor materials for turbine rotor blades with a thrust-to-weight ratio of more than 20 and an engine inlet temperature of 1930-2227°C. The highest strategic goal pursued by advanced industrial countries.
The so-called C/C-based composite material is a carbon fiber-reinforced carbon basic composite material, which combines the refractory properties of carbon with the high strength and high rigidity of carbon fiber, making it non-brittle. Because C/C-based composite materials have light weight, high strength, superior thermal stability and excellent thermal conductivity, they are the most ideal high-temperature-resistant materials today, especially in high-temperature environments of 1000-1300 ° C. Not only did the strength not decrease, but it was able to increase. Especially when it is below 1650°C, it still maintains the strength and grace at room temperature. Therefore, C/C-based composites have great development potential in aerospace manufacturing.
It is worth mentioning that one of the main problems of C/C-based composite materials in the application of aero-engines is poor oxidation resistance. Therefore, in recent years, the United States has adopted a series of technological measures to solve this problem, and gradually Applied to the new engine. For example, the tail nozzle of the afterburner on the American F119 engine, the nozzle and combustion chamber nozzle of the F100 engine, and some parts of the combustion chamber of the F120 verification machine have been made of C/C-based composite materials. Another example is the French M88-2 engine, and the afterburner fuel injection rod, heat shield, and nozzle of the Mirage 2000 engine also use C/C-based composite materials.
2
New material of ultra-high strength steel
What is Ultra High Strength Steel? In the mid-1940s, the United States developed Cr-Mo steel (AISI4130) and Cr-Ni-Mo steel (AISI 4340). After quenching and low-temperature tempering, the tensile strengths were 170 and 190kgf/mm2 respectively. In the early 1950s, Si and V were added to AISI 4340 steel to make 300M with a tensile strength of 190~210kgf/mm2. In 1960, the International Nickel Company made maraging steel with a tensile strength of about 180kgf/mm2, fracture toughness up to 390kgf/mm. In the 1970s, the United States reduced C and increased Si on the basis of 300M, improved toughness, and developed into HP310 steel; on the basis of maraging steel, it developed into AF1410 steel, with a tensile strength of 170kgf/mm2 and a fracture toughness of 400kgf/mm2 mm.
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It is worth noting that ultra-high-strength steel must have high tensile strength and maintain sufficient toughness. It also requires a large specific strength (ratio of strength to density) and a high yield ratio (σs/σb) to reduce the weight of the component , and must have good weldability and formability and other process properties. Ultra-high-strength steel has very high requirements on metallurgical quality, and is often smelted by electric arc furnace and electroslag remelting. Steel types requiring high purity are mostly smelted in vacuum induction furnaces or vacuum consumable electric arc furnaces. Medium- and low-alloy ultra-high-strength steels should be prevented from decarburization during heat treatment; maraging steels and precipitation-hardening stainless steels can be solid-solution treated in ordinary heating furnaces. Shielding gas welding or argon tungsten arc welding must be used for welding. Some low-alloy ultra-high-strength steels with high carbon content (about 0.4%) should be stress-relieved annealed immediately after welding.
It is worth mentioning that ultra-high-strength steel is used as a material for landing gear on aircraft. For example, the landing gear used in the second-generation aircraft is made of 30CrMnSiNi2A steel with a tensile strength of 1700MPa. This kind of landing gear has a short service life of about 2000 flight hours.
Another example is that the design of the third-generation fighter jet requires the life of the landing gear to exceed 5,000 flight hours. At the same time, due to the increase in airborne equipment, the weight coefficient of the aircraft structure decreases, and higher requirements are placed on the selection of landing gear materials and manufacturing technology. Both the US and our third-generation fighters use 300M steel (tensile strength 1950MPa) landing gear manufacturing technology.
In fact, the improvement of material application technology is promoting the further extension of the life of the landing gear and the expansion of adaptability. For example, the landing gear of the European Airbus A380 aircraft adopts super-large integral forging forging technology, new atmosphere protection heat treatment technology and high-speed flame spraying technology, so that the life of the landing gear can meet the design requirements. Therefore, the introduction of new materials and manufacturing techniques ensured the replacement of aircraft.
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As we all know, the long-life design of aircraft in a corrosion-resistant environment puts forward higher requirements for materials. For example, AerMet100 steel has the same strength level as 300M steel, but its general corrosion resistance and stress corrosion resistance are significantly better than 300M steel. The matching landing gear manufacturing technology has been applied to advanced aircraft such as F/A-18E/F, F-22, and F-35. Higher strength Aermet310 steel has lower fracture toughness and is being continuously developed and improved. The crack growth rate of the damage-tolerant ultra-high-strength steel AF1410 is extremely slow, which can be used as the joint of the actuator of the wing of the B-1 aircraft, which is 10.6% lighter than Ti-6Al-4V, with a 60% increase in processing performance and a 30.3% reduction in cost . For example, the amount of high-strength stainless steel used in Russia's Smig-1.42 is as high as 30%. PH13-8Mo is the only high-strength martensitic precipitation-hardening stainless steel widely used as corrosion-resistant components. Ultra-high-strength gear (bearing) steels have also been developed internationally, such as CSS-42L, Gearmet C69, etc., and have been used in engines, helicopters and aerospace.
3
High temperature alloy material
What are superalloy materials? High-temperature alloys are actually divided into three types of materials: 760°C high-temperature materials, 1200°C high-temperature materials and 1500°C high-temperature materials, with a tensile strength of 800MPa. In other words, it refers to high-temperature metal materials that work for a long time under 760-1500°C and certain stress conditions. Its important features: it has excellent high temperature strength, good oxidation resistance and thermal corrosion resistance, good fatigue performance, fracture toughness and other comprehensive properties, and has become an irreplaceable key material for the hot end parts of gas turbine engines for military and civilian use worldwide.
760°C high-temperature materials Since the late 1930s, Britain, Germany, the United States and other countries began to study superalloys. During World War II, in order to meet the needs of new aero-engines, the research and use of superalloys entered a period of rapid development. In the early 1940s, the United Kingdom first added a small amount of aluminum and titanium to the 80Ni-20Cr alloy to form a γ' phase (gamma prime) for strengthening, and developed the first nickel-based alloy with high high-temperature strength. During this period, in order to meet the needs of the development of turbochargers for piston aeroengines, the United States began to use Vitallium cobalt-based alloys to make blades.
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It is worth mentioning that the United States has also developed Inconel nickel-based alloys to make combustion chambers for jet engines. Later, in order to further improve the high-temperature strength of the alloy, metallurgists added elements such as tungsten, molybdenum, and cobalt to the nickel-based alloy to increase the content of aluminum and titanium, and developed a series of alloys, such as "Nimonic" in the United Kingdom, and "Nimonic" in the United States. "Mar-M" and "IN", etc.; adding nickel, tungsten and other elements to the cobalt-based alloys to develop a variety of high-temperature alloys, such as X-45, HA-188, FSX-414, etc. Due to the lack of cobalt resources, the development of cobalt-based superalloys is limited.
In the 1940s, iron-based superalloys were also developed. In the 1950s, grades such as A-286 and Incoloy901 appeared, but due to poor high temperature stability, the development was slow. The former Soviet Union began to produce "ЭИ" brand nickel-based superalloys in 1950, and later produced "ЭП" series of deformed superalloys and ЖС series of cast superalloys. In the 1970s, the United States also adopted a new production process to manufacture directional crystallization blades and powder metallurgy turbine disks, and developed high-temperature alloy components such as single crystal blades to meet the needs of the continuous increase in the inlet temperature of aero-engine turbines.
Superalloys are developed to meet the very demanding requirements of jet engines on materials, and have become an irreplaceable key material for military and civilian gas turbine engine hot end components. In advanced aero-engines, the proportion of high-temperature alloys has reached more than 50%.
The development of high-temperature alloys is closely related to the technological progress of aero-engines, especially the turbine disk, turbine blade material and manufacturing process of the hot-end parts of the engine are important symbols of engine development. Due to the high requirements for the high temperature resistance and stress bearing capacity of the material, the Ni3 (Al, Ti) strengthened Nimonic80 alloy was developed in the early days in the UK, which was used as the material for the turbine blade of the turbojet engine. In addition, the Nimonic series alloy was continuously developed . The United States has developed dispersion-strengthened nickel-based alloys containing aluminum and titanium, such as the Inconel, Mar-M and Udmit alloy series developed by the famous Pratt & Whitney Company, GE Company and Special Metals Company respectively.
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In the development process of superalloys, the manufacturing process plays a great role in promoting the development of alloys. Due to the emergence of vacuum melting technology, the removal of harmful impurities and gases in alloys, especially the precise control of alloy composition, has continuously improved the performance of superalloys. In particular, the successful research of new technologies such as directional solidification, single crystal growth, powder metallurgy, mechanical alloying, ceramic core, ceramic filtration, and isothermal forging has promoted the rapid development of superalloys. Among them, the directional solidification technology is the most prominent. The directional and single crystal alloy produced by the directional solidification process has a service temperature close to 90% of the initial melting point. Therefore, advanced aero-engine blades around the world use directional, single-crystal alloys to manufacture turbine blades. From a global perspective, nickel-based cast superalloys have formed equiaxed crystals, directionally solidified columnar crystals and single crystal alloy systems. Powder superalloys have also been developed from the first generation of 650°C to 750°C, 850°C powder turbine disks and dual-performance powder disks for those advanced high-performance engines.
4
ceramic matrix composites
What are Ceramic Matrix Composites? It is a type of composite material that uses ceramics as a matrix and various fibers. The ceramic matrix can be high-temperature structural ceramics such as silicon nitride and silicon carbide. These advanced ceramics have excellent properties such as high temperature resistance, high strength and rigidity, relatively light weight, and corrosion resistance. The fatal weakness is that they are brittle. When they are under stress, they will crack or even break to cause material failure. The use of high-strength, high-elastic fiber and matrix composite is an effective method to improve the toughness and reliability of ceramics. Fibers can prevent cracks from expanding, thus obtaining fiber-reinforced ceramic matrix composites with excellent toughness.
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Ceramic matrix composites have been used as liquid rocket engine nozzles, missile radomes, space shuttle nose cones, aircraft brake discs and high-end automobile brake discs, etc., becoming an important branch of high-tech new materials.
Because ceramic materials have excellent wear resistance, high hardness and good corrosion resistance, they have been widely used. However, the biggest disadvantage of ceramics is that they are brittle and sensitive to cracks and pores. Since the 1980s, ceramic matrix composites obtained by adding particles, whiskers, and fibers to ceramic materials have greatly improved the toughness of ceramics.
Ceramic matrix composites have high strength, high modulus, low density, high temperature resistance, wear resistance and corrosion resistance, and good toughness, and have been used in high-speed cutting tools and internal combustion engine components. However, the development of this type of material is relatively late, and its potential has yet to be further developed. The focus of research is to apply it to high-temperature materials and wear-resistant and corrosion-resistant materials, such as enhanced turbines for high-power internal combustion engines, thermal components for aerospace vehicles, and vehicle engines instead of metals, petrochemical containers, waste incineration equipment, etc.
When it comes to ceramics, people naturally think of its brittleness. More than ten years ago, if it was used as a load-bearing part in the engineering field, it was impossible for anyone to accept it. Until now, when it comes to ceramic composite materials, some people may not be clear, thinking that ceramics and metals are originally two irrelevant materials. However, since people cleverly combined ceramics and metals, people's concept of this material has undergone a fundamental change, which is ceramic matrix composites.
Ceramic matrix composite material is a very promising new structural material in the field of aviation industry, especially in the application of aero-engine manufacturing, it is increasingly showing its uniqueness. In addition to the advantages of light weight and high hardness, ceramic matrix composites also have excellent high temperature resistance and high temperature corrosion resistance. At present, ceramic matrix composites have surpassed metal heat-resistant materials in terms of high temperature resistance, and have good mechanical properties and chemical stability. They are ideal and excellent materials for high-temperature areas of high-performance turbine engines.
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Countries around the world are focusing on research on silicon nitride and silicon carbide reinforced ceramics to meet the material requirements of the next generation of advanced engines
materials, and has made great progress, especially in modern aero-engines. For example, the F120 engine of the American verification machine, its high-pressure turbine sealing device, and some high-temperature parts of the combustion chamber are all made of ceramic materials. For another example, the combustion chamber and nozzle of the French M88-2 engine also use ceramic matrix composites.
5
New materials of intermetallic compounds
What are intermetallic compounds? Compounds of metals and metals or metals and metalloids (such as H, B, N, S, P, C, Si, etc.). The atoms of the two metals are combined in a certain proportion to form an alloy composition that is different from the original two crystal lattices. Intermetallic compounds are new types of materials that have received widespread attention.
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In fact, the development of high-performance, high-thrust-to-weight ratio aeroengines has promoted the development and application of intermetallic compounds. Intermetallic compounds are generally compounds composed of binary, ternary or multi-element metal elements. Intermetallic compounds have great potential in high-temperature structural applications. It has high service temperature, specific strength, thermal conductivity, and especially at high temperature, it also has good oxidation resistance, corrosion resistance and high creep strength. . In addition, because the intermetallic compound is a new material between the superalloy and the ceramic material, it fills the gap between the two materials, so it becomes one of the ideal materials for high-temperature components of aero-engines.
In the global aero-engine structure, research and development are mainly focused on intermetallic compounds such as titanium-aluminum and nickel-aluminum. These titanium aluminum compounds have basically the same density as titanium, but have a higher service temperature. For example, the operating temperatures of TiAl are 816°C and 982°C respectively. The intermetallic compound has a strong bond between atoms and a complex crystal structure, which makes it difficult to deform, and it is hard and brittle at room temperature. After years of experimental research, a new type of alloy with high temperature strength, room temperature plasticity and toughness has been successfully developed, and it has been installed and used, and the effect is very good. For example, the high-performance F119 engine in the United States uses intermetallic compounds in the casing and turbine disks, and the compressor blades and disks of the verification machine F120 engine use new titanium-aluminum intermetallic compounds.
6
resin matrix composites
What are resin matrix composites? It is a fiber-reinforced material based on an organic polymer, usually using fiber reinforcements such as glass fiber, carbon fiber, basalt fiber or aramid fiber. Resin-based composite materials are widely used in aviation, automobile and marine industries.
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The resin matrix of composite materials is mainly thermosetting resin. As early as the 1940s, fiberglass reinforced plastics were used as radomes on fighter jets and bombers. In the 1960s, the United States used boron fiber reinforced epoxy resin as rudders, horizontal stabilizers, wing trailing edges, rudder doors, etc. on military aircraft such as F-4 and F-111. In terms of missile manufacturing, in the late 1950s, the casing of the second-stage solid rocket motor of the U.S. medium-range submarine missile "Polaris A-2" used glass fiber reinforced epoxy resin winding parts, which are better than steel casings. 27% lighter; later, high-performance glass fiber was used instead of ordinary glass fiber to make "Polaris A-3", which made the shell weight 50% lighter than that of steel shell, so that the range of "Polaris A-3" missile was changed from 2700 thousand meters increased to 4500 km. In the 1970s, aramid fiber was used instead of glass fiber to reinforce epoxy resin, and the strength was greatly improved, while the weight was reduced. Carbon fiber reinforced epoxy resin composites are widely used in aircraft, missiles, satellites and other structures.
The research on the application of resin-based composite materials in aviation turbofan engines began in the 1950s. After more than 60 years of development, GE, PW, RR, MTU, SNECMA and other companies have invested a lot of energy in the research and development of resin-based composite materials, and achieved Great progress has been made, and its engineering has been applied to active aviation turbofan engines, and there is a tendency to further expand its application.
The service temperature of resin matrix composites generally does not exceed 350°C. Therefore, resin matrix composites are mainly used in the cold end of aero-engines.
7
metal matrix composites
What are metal matrix composites? It is a composite material that is artificially combined with metal and its alloy as the matrix and one or several metal or non-metal reinforcements. Most of its reinforcing materials are inorganic non-metals, such as ceramics, carbon, graphite and boron, etc., and metal wires can also be used. Together with polymer matrix composites, ceramic matrix composites and carbon/carbon composites, it forms a modern composite system.
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The characteristics of metal matrix composite materials: in terms of mechanics, they have high transverse and shear strength, good comprehensive mechanical properties such as toughness and fatigue, and also have thermal conductivity, electrical conductivity, wear resistance, small thermal expansion coefficient, good damping, no moisture absorption, and no corrosion resistance. Advantages such as aging and no pollution. For example, the specific strength of carbon fiber reinforced aluminum composite materials is 3~4×107mm, and the specific modulus is 6~8×109mm. For example, the specific modulus of graphite fiber reinforced magnesium can reach 1.5×1010mm, and its thermal expansion coefficient is almost zero.
It is worth mentioning that, compared with resin-based composite materials, metal-based composite materials have good toughness, do not absorb moisture, and can withstand relatively high temperatures. The reinforcing fibers of metal matrix composites include metal fibers, such as stainless steel, tungsten, lead, nickel-aluminum intermetallic compounds, etc.; ceramic fibers, such as alumina, silicon oxide, carbon, boron, silicon carbide, etc.
The matrix materials of metal matrix composites include aluminum, aluminum alloy, magnesium, Chin and Chin alloys, heat-resistant alloys, diamond alloys, etc. Among them, composite materials based on aluminum alloys, aluminum alloys and iron alloys are currently the main choices. For example, SiC fiber-reinforced Chin alloy matrix composites can be used to make compressor blades. Carbon fiber or alumina fiber reinforced magnesium or magnesium alloy matrix composites can be used to manufacture turbofan blades. Another example is that nickel-chromium-aluminum-iridium fiber-reinforced nickel-based alloy matrix composites can be used to manufacture sealing elements for turbines and compressors.
In addition, fan casings, rotors, compressor disks and other parts are all made of metal matrix composites abroad. But one of the biggest problems with this kind of composite material is that it is easy to react between the reinforcing fiber and the matrix metal to produce a brittle phase, which deteriorates the performance of the material. Especially when it is used for a long time at a higher temperature, the reaction of the interface is more prominent. The current solution is to add appropriate coatings on the fiber surface and alloy the matrix metal according to different fibers and different substrates, so as to slow down the interface reaction and maintain the reliability of composite material performance.
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Materials used in engine fan blades
The engine fan blade is the most representative and very important part of the turbofan engine, and the performance of the turbofan engine is closely related to its development. Compared with titanium alloy fan blades, resin matrix composite material fan blades have a very obvious advantage in weight reduction. In addition to the obvious advantages of weight reduction, the resin-based composite fan blades have less impact on the fan case after impact, so it is beneficial to improve the containment of the fan case.
The main representatives of composite fan blades for commercial application in foreign countries are: GE90 series engines for B777, GEnx engines for B787, and LEAP-X engines for COMAC C919. As early as 1995, the GE90-94B engine equipped with resin-based composite material fan blades was officially put into commercial operation, marking the official realization of the engineering application of resin-based composite materials in modern high-performance aeroengines. On the basis of comprehensive consideration of aerodynamics, high and low cycle fatigue cycles and other factors, GE has developed a new composite fan blade for the subsequent GE90-115B engine.
In the 21st century, the strong demand of aero-engines for high damage-tolerant composite materials drives the further development of composite material technology, and it is difficult to meet the requirements of high damage-tolerant materials by continuously improving the toughness of carbon fiber/epoxy resin prepregs. As a result, 3D woven structure composite fan blades began to appear.
Materials used in engine fan case
The engine fan casing is the largest stationary part of an aero-engine, and its weight reduction will directly affect the thrust-to-weight ratio and efficiency of an aero-engine. Therefore, foreign advanced aero-engine OEMs have always been committed to the weight reduction and structural optimization of the fan casing.
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Materials used for engine fan cowls
Because it is a non-main load-bearing component, the fan cowl is one of the first parts made of composite materials on an aero-engine. The fan cowl made of composite materials can provide lighter weight, simplified anti-icing structure, better Corrosion resistance and better fatigue resistance. Such as the famous R.R company's RB211 engine, PW company's PW1000G, and PW4000 use resin-based composite materials to prepare fan caps.
Compared with aero-engine mainframes, resin-based composite materials have a very broad application space in aero-engine nacelles. Global manufacturers have used resin-based composite materials on a large scale in nacelle inlets, fairings, thrust reversers, and noise reduction linings. Material. In terms of other parts, resin-based composite materials are also applied to varying degrees in aero-engine fan runner plates, bearing sealing covers, and cover plates.
