5 major metal structural materials and 4 major functional materials

Thread Content

I. Advanced metallic structural materials
1. Wrought magnesium alloys
Wrought magnesium alloys exhibit high specific strength, stiffness, and plasticity. They are among the most promising metallic structural materials in the aerospace industry. Components such as cockpit frames, air intake ducts, missile section panels, helicopter skins, and landing gear are mostly made from magnesium-lithium alloys. Studies have shown that using magnesium alloy components in place of aluminum alloys can solve the fatigue problems associated with aluminum alloy wings. At present, research and development on magnesium alloys have reached a relatively advanced stage, with various types of wrought magnesium alloys having been developed, such as heat-resistant magnesium alloys, corrosion-resistant magnesium alloys, flame-retardant magnesium alloys, high-strength and ductile magnesium alloys, as well as ultra-light wrought Mg-Li alloys. Research on Mg-Li alloys is particularly active; the United States, Japan, and Russia have conducted extensive research in both theoretical aspects and practical applications. In China as well, some institutions are carrying out preliminary research, such as Northeastern University and Harbin Institute of Technology. These magnesium alloys are currently mainly used in fighter jets and firearms; for example, jet fighters like the Lockheed F-80 and bombers like the B-36 utilize such heat-resistant magnesium alloys. Current research is mainly focused on rare earth magnesium alloys; for example, the QE22 and WE44 magnesium alloys developed in the United States possess very high high-temperature strength, which enables their use in manufacturing Verrier rocket shells with a diameter of 1 meter, thereby improving their flight performance. Research on flame-retardant magnesium alloys is also moving in the direction of incorporating rare earth elements. The Engineering Research Center for Precision Forming of Light Alloys at Shanghai Jiao Tong University has achieved significant results; the magnesium alloys to which beryllium and rare earth elements have been added have been successfully used in industrial tests for car transmission casings. It is believed that, given the demand for higher performance in military applications, such magnesium alloys hold great potential for use in the military industry. 2. Advanced titanium alloys: Titanium is an important metal that became available for industrial production in the 1980s; it is also a new type of metal that holds great significance for both the economy and national defense. Similar to magnesium alloys, titanium alloys possess advantages such as low density, high strength, good high-temperature resistance, and excellent corrosion resistance. As a result, they are widely used in the aerospace and military fields, including military and commercial aircraft, aviation engines, missiles, ships, nuclear reactors, and light artillery. To expand the military applications of titanium alloys, research has been conducted primarily in the following areas: (1) High strength and toughness. The Ti1023 titanium alloy developed in the United States features high tensile strength, high fracture toughness, good fatigue resistance, and excellent forgeability; it has been used in components such as the landing gear systems of B777 aircraft, as well as in fuel tanks and conduits for rocket engines. Additionally, a new type of oxidation-resistant, ultra-high-strength titanium alloy named 21S, developed by Timet, a division of the American company Titanium Metals Corporation, exhibits excellent oxidation resistance at 690 degrees; it can operate continuously at 540 degrees. It also has good properties for cold and hot working, and can be processed into foil with a thickness of 0.064 mm. This alloy has been selected by the U.S. NASA as a matrix material for silicon/titanium composite materials, and it will be used in the fuselage and wing panels of American space shuttles. (2) High-temperature resistance: Research in this area began in the early 1950s, with the United Kingdom, the United States, and Russia being at the forefront. The IMI829 and IMI834 titanium alloys from the UK, Ti100 from the United States, and BT18, BT36, and BT37 from Russia have been used in military aircraft engines. (3) Flame retardancy: In the 1980s, two companies in the United States developed the titanium alloy Alloy C (Ti-1270), which is insensitive to sustained combustion. It possesses high strength at room temperature, as well as good plasticity, creep resistance, and fatigue resistance at both room and high temperatures. This alloy is used in the F119 engine. The Ti-40 alloy developed in China has flame retardant properties comparable to those of America’s Ti-1270, and it is also used in China’s new fighter engine models. China’s 600 high-temperature titanium alloy, TI60, is still in the development stage. 3. Ultra-high strength steel: Ultra-high strength steel is a type of steel whose yield strength and tensile strength exceed 1200 Mpa and 1400 Mpa respectively. It was developed to meet the needs for materials with high specific strength in aircraft structures. Aermet 100 is a high-alloy, ultra-high-strength steel developed by the American company Carpenter Technology; it has been used in the landing gears of advanced aircraft such as the F-22 and F-18E/F. The U.S. has recently developed a successor to this material, called Aermet 310, which boasts a strength 10% higher than that of Aermet 100, with a KIc value of 70 MPa. SFGHITEN and NANOHITEN are several high-strength steels recently developed by Japan’s JFE Corporation. SFGHITEN is a high-strength IF steel containing Nb, and it is primarily used for exterior panels of automobile bodies. NANOHITEN is a hot-rolled steel sheet with a strength level of 780 MPa; it features good plasticity and a high hole-expansion rate, as well as excellent flanging properties and stable mechanical characteristics, making it suitable for various reinforced components such as arms and beams. ERW and HISTORY are high-strength steel tubes developed by JFE for use in aircraft suspension components, also with a strength level of 780 MPa. These materials exhibit good hydroforming properties and have already begun to be used in arm components of aircraft suspension systems. Stelco has recently developed a high-strength microalloy codenamed SteIR MM, which possesses excellent fracture toughness; tests have shown that its fracture toughness is about 22% higher than that of ordinary steel, and it has already been brought to market. The technology related to transmission materials for engines in China is quite backward, but the Beijing Institute of Aeronautical Materials has independently developed high-strength steel suitable for engines in certain types of aircraft. 4. Intermetallic compounds: The technology related to intermetallic compound materials is still in the exploratory and development stage. The American company GE succeeded in using Ti-48Al-2Nb-2Cr alloys, cast in precision form, for turbine blades in CF6-80CZ engines during ground tests. HP also plans to conduct tests on these alloys in F119 engines as part of the Caesar program. Extensive research is also being carried out on nickel-aluminum intermetallic compounds. In recent years, Russia has developed BKHA-1B and BKHA-2M successfully. The former is based on Nl3Al, while the latter is based on N₃Al+NaAl; they have been used respectively as coating materials for engine stator blades and guide vanes. Abroad, Si has been added to niobium matrices to create Nb-Si composite materials, whose heat resistance is 200–300 higher than that of single-crystal alloys. 5. The development of composite material science has led to the creation of carbon fibers with high strength, high modulus, and low specific weight, thus ushering in an era of advanced composite materials. Japan was the first country to invent polyacrylonitrile (PAN)-based carbon fibers in 1955, and industrial production of these fibers began in the early 1960s. By the mid-1970s, advanced composite materials using carbon fibers as reinforcing agents were developed. Carbon-based reinforcements possess unparalleled high specific strength and high specific stiffness, as well as corrosion and fatigue resistance, making them highly suitable for use in airplanes and space shuttles. PAN-based carbon fibers were initially of the T300 grade and used in military equipment. At the end of the 1960s, the United States developed epoxy resin composites reinforced with boron fibers, which were successfully applied to the tail fins of F-14 fighter jets in 1971. Since then, composite tail fins have been used in aircraft such as the F-15, F-16, MiG-29, Mirage 2000, and A-18. At this time, the vertical and horizontal stabilizers of a military aircraft are usually made entirely of composite materials, which can account for about 5% of the total weight. With further development, the proportion of composite materials used in modern aircraft ranges from 20% to 50%; for example, the U.S. B-2 fighter jet has about 50% of its structure made of composite materials. In addition to making significant contributions in military aircraft, composite materials are also widely used in missile warheads. The first composite materials applied to missile warheads were laminated glass/phenolic composites; however, limitations were identified, which led to the development of molded high-siloxane/phenolic composites. Currently, scientists have developed better carbon/carbon composites, which have a low density (