Titanium is an important structural metal widely used in the aerospace field. The specific strength of titanium is the highest among commonly used metal materials, so it was quickly used in the aviation industry. The aviation industry has always been the largest user of titanium in the world market for 50 years. The figure below shows the main parts and components of titanium and titanium alloy used in aircraft.
At present, the weight of titanium material on advanced aircraft has reached 30% ~ 35% of the total weight of aircraft structure, and titanium material has become an indispensable structural material for modern aircraft. In recent years, the aviation industry is in urgent need of new structural materials with high strength, high elastic modulus, high-temperature resistance and low density, which greatly promotes the rapid development of titanium manufacturing industry.
Titanium alloy of high strength and toughness
Titanium alloy of high strength and toughness has good processing performance, it is easy to forge, rolling, welding, and can obtain higher strength and fracture toughness through the solution of aging treatment.
For example, Ti-l5-3 high-strength titanium alloy is gear-type high-strength corrosion resistant alloy developed in the 1970s with funding from the U.S. Air Force. The alloy has excellent cold deformation, aging hardening, and weldability, and its cold working performance is better than that of industrial pure titanium. The alloy is particularly suitable for making components such as propellant tanks and conduits for rocket engines and has been applied to control system piping and fire extinguishing tanks for Boeing 777.
β-21S alloy is a super high strength titanium alloy developed by Timet in 1989. The alloy has good oxidation resistance and can work under 540 ℃ in the long-term. The alloy, suitable for engine bushing and nozzle, has been used as the matrix material of silicon carbide/titanium composite by NASA.
High-temperature titanium alloy
High-temperature titanium alloy is one of the key materials of modern aero-engine. High-temperature titanium alloy is mainly used as compressor disc, blade and casing of aircraft engine to reduce engine quality and improve the thrust-to-weight ratio. The engine is very demanding on the high-temperature titanium alloy, which requires the material to have a good match of room temperature performance, high-temperature strength, creep performance, thermal stability, fatigue performance, and fracture toughness.
IMI834 Alloy is a kind of titanium alloy close to α developed in Britain in 1984. After heat treatment, the sigma b of the alloy is 930MPa. It is already used on the Trent700, a large engine used in Boeing 777s.
The Ti-1100 alloy was developed in the USA in 1988. The alloy has good high temperature creep property, low toughness, and high fatigue crack growth rate. It is already used in parts such as high-pressure compressor discs and low-pressure turbine blades for Lycoming T55-712 variant engines.
Damage-tolerance titanium alloy
Currently, there are two typical types of damage tolerance titanium alloys, one is the damage-tolerance titanium alloy TC21 with high strength and toughness, and the other is the damage-tolerance titanium alloy TC4-DT with medium strength and high toughness.
The TC21 alloy is a two-phase titanium alloy with high strength, high toughness and damage tolerance developed by Northwest Nonferrous Metal Research Institute in China in 2001. The microstructure of the alloy in general service state is net basket or tri-state, which has good matching of strength, plasticity, toughness and low crack growth rate. Compared with the titanium alloy BT20 (Russia) widely used in the F-22 and SU-27 series aircraft in the United States, the comprehensive mechanical properties of the titanium alloy are better, especially the electron beam welding performance, which is suitable for manufacturing large integral frame, engine hanging frame, beam, joint, landing gear parts, and other important bearing components.
The TC4-DT alloy is a weldable titanium alloy with medium strength, high toughness, damage tolerance and based on Ti-6Al-4VELI alloy in the United States, which is jointly developed by Northwest Nonferrous Institute and Beijing Institute of Aeronautical Materials. The alloy has the characteristics of medium strength, high fracture toughness and high damage tolerance, and has been used in the stabilizer joint of Boeing 777 aircraft and the airframe of F/ A-22 aircraft.
Burn resistant titanium alloy
Common titanium alloys may produce “titanium fire” when used as aero-engine materials. Many countries developed flame retardant titanium alloys to solve this problem.
For example, Alloy C is a type of titanium alloy developed by P&W in the 1980s. The molybdenum yield of this alloy is 47.5, which is the highest industrial alloy at present. It has good plastic, creep and fatigue properties at room temperature and high temperature can be made into a sheet, strip, bar and forging etc. This alloy has been used in the high-pressure compressor casing, guide vane and vectored tail nozzles of the F119 engine (the power unit of the F/ A-22 fighter) and was successfully tested in flight in January 1993.
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