What materials are used for large turbines?

At present, the materials selected for turbine components are basically high-temperature heat-resistant alloys with nickel or cobalt as the main component. Foreign materials with high temperature, high strength and low density have made important progress in the past few years. Intermetallic compounds, composites, carbon-carbon composites, ceramics and ceramic-based composites are being studied and many achievements have been made.

The development of turbine blade materials has experienced the development process from forging superalloy, polycrystalline casting superalloy, directionally solidified columnar crystal, single crystal and directionally solidified superalloy. In the future, intermetallic compounds, man-made fiber reinforced superalloys and directionally recrystallized oxide dispersion strengthened alloys will be further developed, and nonmetallic materials will be used as turbine materials in the future. For decades, the working temperature of superalloys has increased by about 8K per year, which is 300K higher than that of the original alloys.

Directional solidification technology can eliminate the grain boundary perpendicular to the principal stress axis, reduce casting metallurgical defects, and significantly improve thermal strength and thermal stability. The material itself can increase the turbine inlet temperature by 20-60℃, so that the blade has higher strength and creep resistance. The development of directional columnar superalloys, single crystal superalloys, directional * * crystal superalloys and mechanical alloying superalloys has further improved the working temperature of blades.

Single crystal turbine blade is one of the important technologies of aero-engine since 1980s. In the past 15 years, the first generation, the second generation and the third generation single crystal alloys have been developed and applied successively. The temperature resistance of aero-engine turbine blades is 90℃ higher than that of oriented columnar crystals. At present, single crystal technology is widely used in the first-class engine with thrust-to-weight ratio of 8. In general, the alloy working temperature of turbine blades is 880℃, which can reach 940℃-980℃ after directional solidification or single crystal technology is adopted. The working temperature of turbine blades made of directionally solidified * * * crystals is 1040℃, and the service temperature of the first generation single crystals is 25-50℃ higher than that of directionally solidified alloys. The second generation single crystal alloys (PWA/kloc-0 The application temperature of Rene￠N4) The third generation single crystal alloy (CMSX- 10) can further improve the temperature resistance by 28-56℃, reaching 1 100℃, which is a candidate material for engine turbine blades in the next decade.

The material of turbine disk has also been greatly improved. The application of vacuum melting, vacuum casting and powder metallurgy technology can control materials more accurately and eliminate harmful impurities. The material performance is greatly improved and the disk strength is doubled.

At present, the first-stage engine turbine with thrust ratio 10 adopts single crystal blade material and thermal insulation coating. These engines use the third generation single crystal blade material, and its heat resistance reaches 1320- 1370 K. Advanced thermal insulation coating can provide the thermal insulation effect of 100- 150K.

The manufacturing technology of turbine parts has gone through several stages in the past decades, including die forging, casting and no-allowance hollow precision casting. Since 1982 JT9D-7R4D engine first-stage turbine blades used single crystal hollow precision casting blades and put them into use, more than 20 kinds of engines have used hollow precision casting blades. At present, foreign countries are exploring the manufacturing technology of single crystal splitting and diffusion bonding blades and porous laminated blades with higher performance, which can further increase the inlet temperature of the turbine. The casting cooling technology developed for small hole machining makes it possible to cast 0.25 mm gas film holes on turbine blades. The development of single crystal precision casting, vacuum diffusion welding and excellent surface protection and treatment ensure that turbine blades are more and more refined after design.

Great progress has also been made in the manufacturing technology of turbine blades abroad. Pratt & Whitney Company of the United States built an automatic production line of directional solidification precision casting blades controlled by computer from the late 1970s to the early 1980s. This method has been applied in the directional solidification precision casting process of turbine blades of F 100 engine.

The recent development direction of turbine materials is: oriented * * crystal alloy, super single crystal alloy, mechanically alloyed superalloy, and in the future, artificial fiber reinforced superalloy, oriented recrystallization oxide dispersion strengthened alloy, intermetallic compounds and composites, carbon-carbon composites, ceramics, ceramic matrix composites and other new high-temperature resistant materials. Future engines will use a lot of nonmetallic materials. 2 1 century aero-engine turbine inlet temperature is required to be 2000°C, and then the blades will adopt new high-temperature structural materials. High temperature structural ceramics represented by Si3N4 are one of the most promising materials. I hope I can help you.