High temperature alloy investment casting technology

High temperature alloy precision casting is widely used in advanced weapon equipment, such as turbine case of aircraft engine, interstage case, front diffuser, regulating plate and large gas turbine impeller. The application of investment casting technology in superalloy production began in the 1970s. With the development of hip and filtration purification technology, the metallurgical defects of castings were greatly reduced, and the properties were significantly improved. It mainly includes ultra-high temperature material precision casting technology, ultra-high temperature composite material precision casting technology and directional solidification complex hollow blade precision casting technology.

In foreign countries, the whole precision casting technology of large-scale and complex superalloy components has been regarded as the supporting point for improving the performance and competitiveness of aeroengine. A large number of large-scale high temperature alloy integral precision castings have been successfully used in many kinds of civil and military aeroengines, such as CFM56 series, jt90d, PW4000, rb211, ej200, etc. The outer dimension of intake gearbox of CFM56 engine is 1024mm × 209mm, and the minimum wall thickness is 2mm; PW4000 engine intake gearbox is equipped with 15 hollow support plates, with the outer dimension of 1360mm × 310mm. Since the 1980s, the structure, material and manufacturing technology of turbine working blades and guide vanes, which are the key hot end components of engines, have been deeply studied abroad. The blade cooling system, material and manufacturing technology with high efficiency air cooling effect have been developed successively. Howmet, Rolls Royce and other companies have carried out research on dual energy integral bladed disk materials and precision casting technology, and successfully developed a complete set of precision casting and purification smelting technology at the end of the 20th century. The integral bladed disk with directional columnar crystal blade and equiaxed fine crystal wheel disk has been completely poured out, which improves the service life of existing gas turbine engine by 2-3 times, Engine power increased by 7.3% ~ 9.2%. In the middle and late 1990s, Al lision company developed the manufacturing technology of cooling holes, precision casting and material preparation technology of assembled porous laminates, and cast a single crystal La Milloy alloy turbine blade with high cooling efficiency. Russia has added cooling channels to the existing high-pressure turbine blade wall, and obtained the precision casting technology of high-efficiency single crystal hollow blade.

In 2003, GE company successfully used the arc melting and drop casting technology to cast the blade simulation piece in the aluminum base ceramic shell with low reaction coating. The length is about 150 mm and the thickness is 3 ~ 8 mm, which can meet the needs of gas turbine engine with thrust weight ratio of 15 or more. At present, the first generation of Nb Si series ultra-high temperature material precision casting developed by GE company has completed the engine test, and plans to launch a more complex high-pressure turbine blade in 2015. The technical maturity of Nb Si series alloy preparation and forming process has reached level 4-5.

In recent years, some progress has been made in the key technology of large-scale complex ultra-high temperature material precision casting in China, and the engine turbine case with an overall dimension of 1080mm and a minimum wall thickness of 2mm has been successfully developed. The key technology of double wall high efficiency gas cooled single crystal blade precision casting is broken through, and the high efficiency gas cooled single crystal blade is developed. A large number of researches have been carried out in the melting, alloying, preparation process, heat treatment, coating and other aspects of Nb SI system ultra-high temperature materials, and the relevant process equipment has been established, initially realizing the organization optimization and control.