Large market of new materials for military industry (一)
New materials, also known as advanced materials, refer to new materials that have been successfully researched and are being developed and have excellent characteristics and functions and can meet the needs of high technology. The development of human history shows that materials are the material basis and guide of social development, while new materials are the milestone of social progress.
Materials technology has always been a very important field in the scientific and technological development planning of all countries in the world. Together with information technology, biotechnology and energy technology, it is recognized as a high technology that will dominate the overall human situation in today’s society and for a long time in the future. The high technology of materials is also the key technology of modern industry supporting human civilization today, and is also the most important material foundation of a country’s national defense force. National defense industry is often the priority user of new material technology achievements. The research and development of new material technology plays a decisive role in the development of national defense industry and weapons and equipment.
Strategic significance of new military materials
New military materials are the material basis of the new generation of weapons and equipment, and also the key technology in the military field of the world today. The military new material technology is the new material technology used in the military field, is the key of modern sophisticated weapons and equipment, and is an important component of military high technology. Countries all over the world have attached great importance to the development of military new material technology. Accelerating the development of military new material technology is an important prerequisite for maintaining military leadership.
Current situation and development of new military materials
New military materials can be divided into structural materials and functional materials according to their uses, which are mainly used in aviation industry, aerospace industry, weapons industry and ship industry.
Military structural materials
1. Aluminum alloy
Aluminum alloy has been the most widely used metal structural material in military industry. Aluminum alloy has the characteristics of low density, high strength and good processing performance. As a structural material, because of its excellent processing performance, it can be made into various sections of profiles, pipes, high-ribbed plates, etc., to give full play to the potential of materials and improve the rigidity and strength of components. Therefore, aluminum alloy is the preferred lightweight structural material for weapon lightweight.
In the aviation industry, aluminum alloy is mainly used to manufacture aircraft skin, partition frame, long beam and honing strip; In the aerospace industry, aluminum alloy is an important material for the structural parts of launch vehicles and spacecraft. In the field of weapons, aluminum alloy has been successfully used in infantry combat vehicles and armored transport vehicles. Recently developed howitzer turrets also use a large number of new aluminum alloy materials.
In recent years, the consumption of aluminum alloy in the aerospace industry has decreased, but it is still one of the main structural materials in the military industry. The development trend of aluminum alloys is to pursue high purity, high strength, high toughness and high temperature resistance. The aluminum alloys used in military industry mainly include aluminum lithium alloy, aluminum copper alloy (2000 series) and aluminum zinc magnesium alloy (7000 series).
The new Al-Li alloy is applied in the aviation industry, and it is predicted that the aircraft weight will decrease by 8~15%; Al-Li alloy will also become a candidate structural material for aerospace vehicles and thin-walled missile shells. With the rapid development of aerospace industry, the research focus of Al-Li alloy is still to solve the problems of poor toughness in thickness direction and cost reduction.
2. Magnesium alloy
As the lightest engineering metal material, magnesium alloy has a series of unique properties, such as light specific gravity, high specific strength and specific stiffness, good damping and thermal conductivity, strong electromagnetic shielding ability, and good shock absorption, which greatly meets the needs of aerospace, modern weapons and other military fields.
Magnesium alloy has many applications in military equipment, such as tank seat frame, commander’s mirror, gunner’s mirror, gearbox box, engine filter base, inlet and outlet pipes, air distributor base, oil pump housing, water pump housing, oil heat exchanger, oil filter housing, valve cover, respirator and other vehicle parts; Support cabin and aileron skin, wall panel, stiffening frame, rudder plate, partition frame and other missile and missile components of tactical air defense missile; Fighters, bombers, helicopters, transport aircraft, airborne radar, ground-to-air missiles, carrier rockets, satellites and other spacecraft components. Magnesium alloy has the characteristics of light weight, good specific strength and stiffness, good damping performance, electromagnetic interference and strong shielding ability, which can meet the requirements of military products for weight reduction, noise absorption, shock absorption and radiation protection. It plays a very important role in the construction of aerospace and national defense, and is the key structural material required for weapons and equipment such as aircraft, satellites, missiles, fighter planes and combat vehicles.
3. Titanium alloy
Titanium alloy has high tensile strength (441~1470MPa), low density (4.5g/cm3), excellent corrosion resistance, high temperature endurance strength and good low-temperature impact toughness at 300~550 ℃, and is an ideal lightweight structural material. Titanium alloy has the functional characteristics of superplasticity. Using superplastic formation-diffusion bonding technology, the alloy can be made into products with complex shape and precise size with little energy consumption and material consumption.
The application of titanium alloy in aviation industry is mainly to make aircraft fuselage structural parts, landing gear, support beams, engine compressor discs, blades and joints, etc; In the aerospace industry, titanium alloys are mainly used to make load-bearing components, frames, gas cylinders, pressure vessels, turbopump shells, solid rocket motor shells, nozzles and other components.
Among the existing titanium alloys for aerospace, the most widely used is a+b type Ti-6Al-4V alloy. In recent years, the West and Russia have successively developed two new titanium alloys, which are titanium alloys with high strength, high toughness, weldability and good formability, and high-temperature, high-strength and flame-retardant titanium alloys. These two advanced titanium alloys have good application prospects in the future aerospace industry.
With the development of modern war, the army forces need advanced howitzer systems with powerful, long range, high accuracy and fast response capability. One of the key technologies of advanced howitzer system is new material technology. The lightweight of self-propelled gun turret, components and materials for light metal armored vehicles is an inevitable trend of weapon development. On the premise of ensuring dynamic and protective performance, titanium alloys are widely used in military weapons.
In the past quite a long time, titanium alloy has been greatly limited in application due to its high manufacturing cost. In recent years, countries around the world are actively developing low-cost titanium alloys. While reducing costs, they also need to improve the properties of titanium alloys.
4. Composite materials
4.1 Resin matrix composites
Resin-based composites are widely used in military industry due to their good formability, high specific strength, high specific modulus, low density, fatigue resistance, shock absorption, chemical corrosion resistance, good dielectric properties and low thermal conductivity.
In the aviation industry, resin matrix composites are used to manufacture aircraft wings, fuselage, canards, flat tails and engine external culverts; In the aerospace field, resin matrix composites are not only important materials for rudder, radar and inlet, but also can be used to manufacture the thermal insulation shell of the combustion chamber of solid rocket motor, and also can be used as the ablative heat protection material of the engine nozzle. The new cyanate resin composite developed in recent years has the advantages of strong moisture resistance, good microwave dielectric property and good dimensional stability, and is widely used to make aerospace structures, aircraft primary and secondary load-bearing structures and radar radomes.
4.2 Metal matrix composites
Metal matrix composites have been widely used in military industry due to their high specific strength, high specific modulus, good high temperature performance, low thermal expansion coefficient, good dimensional stability, and excellent thermal conductivity.
Aluminum, magnesium and titanium are the main substrates of metal matrix composites, and reinforcement materials can generally be divided into three categories: fiber, particle and whisker. Among them, particle reinforced aluminum matrix composites have entered the model verification. For example, when used as the belly fin of F-16 fighter aircraft to replace aluminum alloy, its stiffness and life have been greatly improved.
Carbon fiber reinforced aluminum and magnesium matrix composites have high specific strength, close to zero thermal expansion coefficient and good dimensional stability, and have been successfully used to make satellite support, L-band plane antenna, space telescope, satellite paraboloid antenna, etc; Silicon carbide particle reinforced aluminum matrix composites have good high temperature performance and wear resistance, and can be used to make rocket and missile components, infrared and laser guidance system components, precision avionics components, etc;
Silicon carbide fiber reinforced titanium matrix composite has good high temperature resistance and oxidation resistance. It is an ideal structural material for high thrust-weight ratio engines. At present, it has entered the testing stage of advanced engines.
In the field of weapon industry, metal matrix composite materials can be used for parts such as sabot of large caliber tail fin stabilized shelling penetrator, solid motor shell of anti-helicopter/anti-tank multi-purpose missile, to reduce the weight of warhead and improve combat capability.
4.3 Ceramic matrix composites
Ceramic matrix composites are the general term of materials composed of fibers, whiskers or particles as reinforcements and ceramic matrix through certain composite processes. It can be seen that ceramic matrix composites are multiphase materials composed of introducing the second phase component into the ceramic matrix, which overcomes the inherent brittleness of ceramic materials, and has become the most active aspect of current material science research.
Ceramic matrix composites are characterized by low density, high specific strength, good thermal mechanical properties and thermal shock resistance, and are one of the key supporting materials for the development of military industry in the future.
Although ceramic materials have good high-temperature performance, they are brittle. The methods to improve the brittleness of ceramic materials include phase transformation toughening, microcrack toughening, dispersed metal toughening and continuous fiber toughening.
Ceramic matrix composites are mainly used to make nozzle valves for aircraft gas turbine engines. They play an important role in improving the thrust weight ratio of engines and reducing fuel consumption.
4.4 Carbon-carbon composite
Carbon-carbon composite is a composite material composed of carbon fiber reinforcing agent and carbon matrix. Carbon-carbon composites have a series of advantages, such as high specific strength, good thermal shock resistance, strong ablation resistance, and designable performance. The development of carbon-carbon composites is closely related to the stringent requirements of aerospace technology. Since the 1980s, the research of carbon-carbon composites has entered a stage of improving performance and expanding application.
In the military industry, the most noticeable application of carbon-carbon composites is the anti-oxidation carbon-carbon nose cone cap and wing leading edge of the space shuttle, and the largest amount of carbon-carbon products is the brake pads of supersonic aircraft.
The carbon-carbon composite material is mainly used as ablative material and thermal structural material in aerospace. Specifically, it is used as nose cone cap of intercontinental missile warhead, solid rocket nozzle and leading edge of aerospace aircraft wing.
At present, the density of advanced carbon-carbon nozzle material is 1.87~1.97 g/cm3, and the hoop tensile strength is 75~115 MPa. The recently developed long-range intercontinental missile end caps almost all use carbon-carbon composite materials.
With the development of modern aviation technology, the loading quality of aircraft is increasing and the landing speed is increasing, which puts forward higher requirements for emergency braking of aircraft. The carbon-carbon composite material has light weight, high temperature resistance, large energy absorption and good friction performance. It is widely used in high-speed military aircraft to make brake pads.
5. Ultra-high strength steel
Ultra-high strength steel is a steel with yield strength and tensile strength exceeding 1200 MPa and 1400 MPa respectively. It is researched and developed to meet the requirements of materials with high specific strength in aircraft structure. Due to the expansion of the application of titanium alloy and composite materials in aircraft, the amount of steel used in aircraft has decreased, but the key load-bearing components in aircraft are still made of ultra-high strength steel.
At present, the representative low alloy ultra-high strength steel 300M in the world is a typical steel for aircraft landing gear. In addition, low alloy ultra-high strength steel D6AC is a typical solid rocket motor shell material. The development trend of ultra-high strength steel is to continuously improve toughness and stress corrosion resistance while ensuring ultra-high strength.
6. Advanced superalloy
Superalloy is the key material of aerospace power system. The superalloy is an alloy that can bear certain stress at high temperature of 600~1200oC and has the ability of oxidation resistance and corrosion resistance. It is the preferred material for the turbine disk of aerospace engine. According to the different matrix components, superalloys can be divided into three categories: iron-based, nickel-based and cobalt-based.
The engine turbine disk was made of forged superalloy before the 1960s, with typical brands of A286 and Inconel 718. In the 1970s, GE made CFM56 engine turbine disc with rapidly solidified powder Rene95 alloy, which greatly increased its thrust-weight ratio and significantly increased its service temperature. Since then, powder metallurgy turbine discs have developed rapidly.
Recently, the superalloy turbine disk manufactured by spray deposition rapid solidification process in the United States is a preparation technology with great development potential because of its simple process, low cost and good forging processing performance compared with powder superalloy.
7. Tungsten alloy
Tungsten has the highest melting point among metals. Its outstanding advantage is that the high melting point brings good high temperature strength and corrosion resistance of materials, and it shows excellent characteristics in military industry, especially in weapons manufacturing. In the weapon industry, it is mainly used to make warheads of various armor-piercing projectiles.
Through powder pretreatment technology and large deformation strengthening technology, tungsten alloy can refine the grain of the material and elongate the grain orientation, so as to improve the strength, toughness and penetration power of the material. At present, tungsten alloy is widely used as the core material for the main battle tank armor-piercing projectile with large length-diameter ratio, small and medium-calibre antiaircraft armor-piercing projectile and hypervelocity kinetic energy armor-piercing projectile, which makes all kinds of armor-piercing projectiles more powerful.
8. Intermetallic compounds
Intermetallic compounds have long range ordered superlattice structure and maintain strong metal bonding, which makes them have many special physical and chemical properties and mechanical properties.
In the military industry, intermetallic compounds have been used to manufacture parts that bear heat loads, such as the JT90 gas turbine engine blades manufactured by the United States Puo Company, the rotor blades of small aircraft engines manufactured by the United States Air Force with titanium and aluminum, and the Russian titanium and aluminum intermetallic compounds have been used to replace heat-resistant alloys as the plug top, greatly improving the performance of the engine.
In the field of weapon industry, K18 nickel-base superalloy is used as the turbine material of tank engine supercharger. Because of its large ratio and large starting inertia, the acceleration performance of the tank is affected. The application of titanium-aluminum intermetallic compound and its composite lightweight heat-resistant new material reinforced by aluminum oxide and silicon carbide fiber can greatly improve the starting performance of the tank and improve its viability in the battlefield.
In addition, intermetallic compounds can also be used in a variety of heat-resistant components to reduce weight, improve reliability and combat technical indicators.
9. Structural ceramics
Ceramic material is the fastest developing high-tech material in the world today. It has developed from single-phase ceramics to multiphase composite ceramics. Structural ceramic materials have good application prospects in military industry due to their excellent properties such as high temperature resistance, low density, wear resistance and low thermal expansion coefficient.
In recent years, a wide range of research work has been carried out on structural ceramics for military engines at home and abroad.
For example, the small turbine of engine supercharger has been applied; The United States inlays ceramic plates on the top of the piston, which greatly improves the service life of the piston and also improves the thermal efficiency of the engine. Germany inlays ceramic components in the exhaust port to improve the use efficiency of the exhaust port. The piston sleeve and cylinder sleeve of the miniature Stirling refrigerator on the foreign infrared thermal imager are made of ceramic materials, and their service life is up to 2000 hours; The power of the missile gyroscope is supplied by gunpowder gas, but the gunpowder residue in the gas has serious damage to the gyroscope.
In order to eliminate the residue in the gas and improve the hit accuracy of the missile, it is necessary to study the ceramic filter material suitable for the missile gunpowder gas to work at 2000oC. In the field of weapon industry, structural ceramics are widely used in the turbocharger turbine, piston crown, exhaust port inlay, etc. of the main battle tank engine, and are the key materials of new weapons and equipment. At present, the radio frequency requirement of the 20-30mm caliber machine gun is more than 1200 rounds/minute, which makes the barrel erosion extremely serious. The high melting point and high temperature chemical stability of ceramics can effectively inhibit the serious gun tube erosion. The ceramic material has high compression and creep resistance characteristics. Through reasonable design, the ceramic material can maintain the three-dimensional compression state, overcome its brittleness, and ensure the safe use of the ceramic liner.