As we all know, the most important performance indicator of an aero engine is its thrust-to-weight ratio, which is also the ratio of the thrust generated by the engine to its mass, and the continuous improvement of the engine's thrust-to-weight ratio has also made the aircraft's performance continuously leap. The early jet engine had a thrust-to-weight ratio of only 2 to 3, and now it can reach more than 10, and the maximum speed of the aircraft has grown from no more than the speed of sound to the current speed of 2 to 3 times, and it can cruise without supercharged supersonic for a long time. Flight, this is the contribution of aero engine's increasing weight-to-weight ratio. To increase the thrust-to-weight ratio, in addition to continuously increasing the engine's turbine operating temperature, it is also an important way to continuously reduce the weight of the engine. The density of titanium is about 40% lighter than that of steel, and its strength is comparable. The melting point is 1668 ° C, which should be a very good high-temperature metal material for aero engines. However, in practical applications, titanium alloy materials can only be used in lower temperature aero engine front-end fans and low-pressure compressors. The operating temperature range of blades, disks, and casings made from them is generally 350 to 400 ° C. Not more than 600 ° C.
When the surface temperature of titanium exceeds 600 ° C, an extremely fast oxidation reaction will occur in the air environment, and the oxide film on the outer layer that inhibits combustion will fall off rapidly, causing its high-temperature performance to be significantly damaged, and even a fatal "titanium fire" phenomenon . In order to increase the operating temperature of titanium alloys, the development of new high-temperature resistant titanium alloys or titaniumized aluminum alloys, the use of new high-efficiency air-cooled blade technology, and the development of new high-temperature oxidation-resistant coatings have become the three major tasks in the field of high-temperature resistant titanium alloys. The operating temperature of the main high temperature titanium alloys used in aviation engines in China and in research is continuously increasing. The titanium alloys used in active engines are mainly TC-4, TC-11, TC-14, etc., which are mainly used for engine fans and The working temperature range of blades, disks, casings and other parts working in the low temperature section of the compressor is 400-500 ℃. In the 1990s, for the newly developed turbofan engine at that time, a high-temperature-resistant titanium alloy TA-12 at 550 ° C was developed. However, it encountered major technical problems during engineering. After optimization of the composition, the rare earth element neodymium was removed and renamed. It's TA-32.
In recent years, with the urgent demand for high-temperature titanium alloys from the new generation of engines such as 10, 600 ° C high-temperature titanium alloys, flame-retardant titanium alloys, titanium alloys, and silicon carbide fiber-reinforced titanium composites have become the development of new high-temperature titanium alloys. Focus. Several domestic research institutes have carried out a lot of research on 600 ℃ high temperature titanium alloys. For example, the new-generation 600 ° C high-temperature titanium alloy TA-29 developed by the Beijing Institute of Aeronautical Materials has made titanium alloy integral disc parts that have passed high-temperature over-rotation cracking, low cycle fatigue, and blade vibration fatigue strength assessment. TA-29 titanium alloy large-sized bars, integral leaf disk forgings and parts have been produced in small batches. TA-29 titanium alloy has very good high temperature properties. When other properties meet the design requirements, it can also be extended to about 620 ° C for long-term use. In addition to its good application potential in the field of aero-engines, TA-29 titanium alloy can still maintain a high tensile strength at 750 to 800 ° C, which can be used for a short time in this temperature range. High-speed missiles, rockets, aircraft, spacecraft and other equipment body components, skins, and high-temperature components of space engines.
Aluminum titanide (TiAl) alloy has become one of the most potential high-temperature structural materials due to its high melting point, high specific strength, good high-temperature creep performance, and good high-temperature oxidation resistance. In the temperature range of 700 to 850 ° C, the specific strength of titanium alloys is significantly higher than that of ordinary titanium alloys and nickel-based superalloys. The GEnx engine developed by the United States GE company and the LEAP engine newly developed and produced by the French-American joint venture CFM company use aluminum titanium turbine blades. The test proves that it can significantly reduce the engine weight, improve engine performance and save about 15% of fuel consumption. The domestic γ-TiAl alloy low-pressure turbine blades made by the centrifugal precision casting method of the Shenyang Institute of Metal Research of the Chinese Academy of Sciences have completed 1,750 simulated flights covering a major overhaul cycle on the Trent XWB high thrust and high bypass ratio engine of the British Rolls-Royce. Cycle assessment test. Relevant experts said that the γ-TiAl alloy developed by Shenyang Metals has a wide application prospect in high-temperature structural components such as low-pressure turbine blades and high-pressure compressor blades for automotive aerospace engines, automotive turbochargers and exhaust valves.
Relevant researchers at Huazhong University of Science and Technology have adopted a new technology of laser alloying to prepare 1000 ° C high temperature silicon nitride / aluminum titanium composite coatings on the surface of ordinary titanium alloy plates. The high temperature oxidation resistance is higher than that of ordinary titanium materials and titanium alloys. The substrate has been increased by 12.3 times, and the problem of high temperature oxidation resistance and easy to produce "titanium fire" is effectively solved while maintaining the inherent performance advantages of the titanium alloy.