Hard-to-deform superalloys usually refer to a type of deformed superalloys with a strengthening phase mass fraction of more than 40%. This type of alloy generally has the following typical characteristics: high degree of alloying, large number of strengthening phases, large deformation resistance, poor thermal conductivity, and narrow thermal processing range. Under existing equipment conditions, some special thermal processing techniques are required to obtain relatively uniform organization.
Due to the high content of strengthening phases and excellent high-temperature microstructure stability, difficult-to-deform superalloys have comprehensive mechanical properties that can reach the level of powder superalloys, and their temperature-bearing capacity is higher than that of traditional deformed superalloys. At present, it has become a key material for high thrust-to-weight ratio aerospace engine components, mainly used to manufacture aerospace engine turbine discs, compressor discs, casings, blades and other parts.
1. Development of difficult-to-deform superalloy materials
Superalloys were born in the 1930s and were affected by the Second World War, and their research and application have developed rapidly. Since the 1970s, in order to meet the requirements of higher service performance of engines, breakthroughs have been made in the development of difficult-to-deform superalloys with better comprehensive performance. There have been alloys such as Udimet 710, Udimet 720, Udimet 720Li, and Russia ЭК79 and ЭК151. The representative hard-to-deform superalloy (see Figure 1) meets the demand for high-performance turbine disk materials for aerospace engines. In the 21st century, the new alloy ВЖ175 has been successfully developed, and its long-term service temperature can reach 800 ℃, and it inherits the advantages of the high thermal strength of Russian superalloys. In order to achieve low cost control, General Electric has developed René65 hard-to-deform superalloy based on the chemical composition of René88DT, which has a lower temperature bearing capacity than ВЖ175 alloy, but has good hot workability. The mechanical properties of AD730 alloy developed in France are equivalent to Udimet 720Li alloy, but the hot workability and welding properties are better than Udimet 720Li alloy, and it is expected to be used to prepare lower cost aero engine parts. In general, the current international development of new hard-to-deform superalloys has shifted from focusing solely on high-temperature mechanical properties of materials to a balance between service performance and preparation technology.
2. Development of difficult-to-deform superalloy technology
Compared with the traditional double or triple smelting of superalloy turbine discs + forging billeting + die forging/rolling, as a hard-to-deform superalloy with a strengthening phase over 40%, the successful implementation of the casting and forging process needs to be solved There are a series of technical problems such as the composition control of large-size steel ingots and the prevention of metallurgical defects, the fracture of as-cast structure and the preparation of large-size fine-grained bars, and the efficient control of the structure and performance of disc forgings. In recent years, key technologies such as triple large ingot smelting of difficult-to-deform superalloys, homogenization treatment, repeated upsetting + diameter forging billets of large-size fine-grained bars, plate forging and microstructure and performance control have been gradually broken in the world. And with the improvement of metallurgical technology and equipment level, continuous breakthroughs in the limit preparation level of difficult-to-deform superalloys have been achieved, meeting the needs of advanced aeroengines.
3. Development and application of difficult-to-deform superalloys in China
China`s first furnace of superalloys was successfully tested on March 26, 1956. From imitating foreign countries to gradually possessing independent research and development capabilities, the research, production and application of domestic superalloys in China has experienced 64 years of development and has formed The superalloy system with Chinese characteristics, in which the manufacturing process and application achievements of the difficult-to-deform superalloy materials are remarkable.
Since the 1980s, with the development of aerospace engines, China has begun tracking research on difficult-to-deform superalloys, and has overcome the composition control of various grades of steel ingots, the prevention of metallurgical defects, the preparation of fine-grained rods, and the organization of plate forgings. A series of technical difficulties, such as performance control, have successfully developed GH4710, GH4079, GH4720Li, GH4096 and other difficult-to-deform superalloys to meet the needs of Chinese aerospace engines. At present, China is carrying out research on a variety of new difficult-to-deform superalloys to provide more reliable material guarantee for the development of advanced aerospace engines in China in the future.
4. Prospects of difficult-to-deform superalloy materials
In recent years, China's domestic special metallurgy and thermal processing technology has been rapidly improved, laying a solid foundation for the successful development of China's difficult-to-deform superalloys. In order to ensure the higher thrust-to-weight ratio of the engine for the use of materials, China and abroad are still exploring the development potential of difficult-to-deform superalloys, moving towards higher alloying, higher mechanical properties, better processing performance and low-cost manufacturing. , Lay the foundation for the final formation of a hard-to-deform superalloy material system with independent intellectual property rights.