Superalloy refers to a class of metal materials based on elements (iron, cobalt, nickel), adding a large number of strengthening elements, which can work at high temperature above 600℃ and under certain stress for a long time. Superalloy has high high temperature strength and good oxidation resistance, thermal corrosion resistance, fatigue resistance, good organizational stability and service reliability at high temperature, so it is also known as heat strength alloy, heat resistance alloy or super alloy.
superalloys basic overview
Superalloy is a new type of aviation metal material developed in the 1940s. It can withstand complex stress and work reliably for a long time under oxidation and gas corrosion conditions at 600–1100℃. Superalloys are mainly used in the hot end parts of aeroengines, and are also widely used in aerospace, energy, transportation and chemical industries.
From the perspective of the subdivided industries, superalloy materials belong to the high-end metal structural materials in the field of new materials. It has excellent comprehensive performance, excellent high temperature strength and plasticity, good oxidation resistance and thermal corrosion resistance, excellent creep resistance, fracture resistance and good organizational stability, and has become the key special materials for the development of many important industrial fields
Performance characteristics of superalloy materials:
- Excellent high temperature strength and plasticity
- Good oxidation resistance and heat corrosion resistance
- Excellent creep resistance and fission resistance
- Good organizational stability
- Deformation machining is difficult
- Good performance-price ratio
Classification of superalloys
With the continuous progress of technology and materials, superalloy products are constantly iterated, temperature bearing capacity is constantly improved, and comprehensive performance is constantly enhanced. They have been changed from traditional casting superalloy and deformation superalloy. A series of new superalloy materials such as powder superalloy, titanium and aluminum intermetallic compounds, oxide dispersion strengthening superalloy, corrosion resistant superalloy, powder metallurgy and nanomaterials have been developed.
Superalloy Classification
Superalloys can be classified according to a variety of classification methods.
- Iron base or iron nickel superalloy
- Nickel-based superalloy
- Cobalt base superalloy
- Solid solution strengthened superalloy
- Precipitation-strengthened superalloy
- Deformed superalloy
- Cast superalloy
- Powder superalloy
- Hot corrosion resistant superalloy
- Low expansion superalloy
- High yield strength superalloy
- Superalloy for turbine blades
- Superalloy for turbine guide blades
- Superalloy for combustion chamber
Preparation technology of superalloy
During the development of superalloy, the technology plays a great role in promoting the development of superalloy. The production and preparation process of superalloy is complicated, with melting, casting and heat treatment as the main processes. The stability of production process and technology has direct influence on the mechanical properties of superalloy materials. The rapid development of economy and science and technology for the development and promotion of a variety of new superalloy materials provide a large space for development, in the case of higher and higher requirements for alloy properties, it is necessary to constantly improve and optimize a variety of processes, to ensure that a variety of processes and superalloy materials adapt to the changes. The continuous improvement of the process can realize the continuous improvement of performance, the development of new superalloy, and then promote the development of related products and industries.
• Smelting process
Strict control of chemical composition is the basis of ensuring excellent performance of superalloy. The melting process can effectively eliminate inclusions larger than the critical size, reduce the content of oxygen, nitrogen and sulfur, and improve the purity of superalloy from the source. Therefore, the melting process is in the first position in the preparation process of superalloy.
At present, the main melting methods of superalloy in the world are vacuum induction furnace (VIM), vacuum consumable furnace (VAR), electroslag remelting furnace (ESR). In recent years, the application of new superalloys represented by powder superalloys has become more and more extensive, and the melting process of powder superalloys has become a cutting-edge research technology. Internationally, Russian powder superalloys adopt VIM or VIM+VAR dual melting process, and American powder superalloys adopt VIM+ESR+VAR triple process. However, the domestic powder superalloy basically adopts VIM single refining process, resulting in the purity of Chinese powder superalloy material is lower than the advanced level of foreign countries.
• casting
The precision casting technology of superalloy is mainly investment casting, which has developed into equiaxed crystal type, directional cylindrical crystal type and single crystal type. At present, superalloy castings have begun to develop in the direction of complexity, large scale and high precision, which poses certain challenges to the casting process and process, and also promotes the continuous progress of investment precision casting technology, from vacuum smelting technology to non-residual casting technology, directional solidification technology, single crystal technology and other aspects.
There is also a direct connection between the improvement of casting technology and the production and manufacturing of superalloy raw materials. It is necessary to combine the characteristics of superalloy materials and the use of castings, improve the corresponding technological mode and mechanism, control the performance of materials, and ensure the stability of production process. At present, in the process of production, there are difficulties in the control of composition parameters and solidification parameters of superalloy, and it is easy to appear defects such as freckles, hot cracking and loose during directional solidification production or single crystal production, which seriously affect the high temperature performance of products. In the process of research in the United States, high gradient directional solidification technology is used to produce aero-engine blades, which effectively reduces the incidence of freckles, strictly controls the temperature gradient parameters under the condition of each part size, and plays a certain role in production optimization and improvement.
Classification of precision casting: mainly investment casting, ceramic casting, metal casting, pressure casting, lost casting.
• Heat treatment
With the application of new superalloy materials and the high requirements on the properties of alloys, heat treatment is an essential process. Heat treatment process of superalloy refers to a kind of metal hot working process in which superalloy materials are heated, insulated and cooled in solid state to obtain expected microstructure and properties. In recent years, solid solution heat treatment and aging heat treatment have been studied systematically in superalloy.
⁎ Solid solution heat treatment means that the precipitation phase with uneven distribution in the alloy is fully dissolved into the matrix phase at a temperature higher than the total solution temperature of the precipitated phase in the superalloy structure, so as to strengthen the solid solution, improve the toughness and corrosion resistance, and eliminate the residual stress, so as to continue processing and forming, and prepare for the precipitation phase with uniform distribution in the subsequent aging treatment.
⁎ Aging heat treatment refers to heating and holding for a certain time within the temperature interval of the precipitation of the strengthened phase, so that the strengthened phase of the superalloy precipitates evenly and the carbide is evenly distributed, so as to realize the role of hardening the alloy and improving its strength.
Application of superalloy
The global superalloy market continues to grow, with China becoming a major incremental market. In the Chinese superalloy market, deformed superalloy and nickel-based superalloy account for the largest proportion. According to the manufacturing process, deformed superalloy accounts for about 70% of the whole superalloy market, followed by casting superalloy (20%) and powder superalloy (10%). According to the matrix elements of the alloy, the nickel base superalloy accounts for about 80%, the nickel – iron superalloy and cobalt base superalloy account for about 14% and 6%, respectively.
The largest application scenario of superalloy is the aerospace field, with a demand share of 55%. Superalloy material is an important raw material for aerospace engine manufacturing. It is mainly used in engine combustion chamber, guide, turbine blade, turbine disc, tail nozzle, casing and other components. Second, superalloy has excellent properties such as high temperature resistance and corrosion resistance, and is also widely used in gas turbine, petrochemical, industrial and automotive fields.
1) Aeroengine
Superalloy has been applied to aero engines since its birth. In modern aero engines, superalloy materials are mainly used in four main hot end components: combustion chamber, guide chamber, turbine blade and turbine disc, as well as in casing, ring parts, afterburner and tail nozzle.
2) Automotive turbochargers
Automobile exhaust gas supercharger turbine is also an important application field of superalloy materials. Nowadays, most of the turbochargers manufacturers in our country are nickel base superalloy turbochargers, which form a rotor with the vortex shaft and compressor impeller. According to the superalloy consumption of turbocharger for every 10,000 vehicles is about 3.5 tons, the automobile production industry needs about 9,128.7 tons of superalloy materials in 2021, and the market size is about 1.83 billion yuan. Considering the increase in the number of cars in the future and the assembly rate in China, it is estimated that the total demand for superalloy materials in the Chinese automobile market will be about 106,000 tons by 2030, assuming an average annual growth rate of 5% in the future.
3) Nuclear power
Superalloys for nuclear power include: fuel element cladding materials, structural materials, fuel rod positioning grids, heat exchangers for high temperature gas furnaces, etc., which are difficult to be replaced by other materials.
The nuclear fuel report released by the World Nuclear Energy Association predicts that the global installed nuclear power capacity is expected to grow at an annual rate of 2.6%, and by 2040 the global installed nuclear power capacity will reach 615 million kilowatts, and the installed capacity growth will mainly come from China, Russia and other countries. In January 2022, with Fuqing Nuclear Power Plant Unit 6 connected to the grid, the Chinese mainland had 53 grid-connected nuclear power units with a total installed capacity of 5,4636,695 kw, ranking third in the world after the US and France. The National Energy Administration estimates that China’s installed nuclear power capacity will reach 120 million to 150 million kw in 2030, so it is estimated that China will complete about 80 million kw of new nuclear power units by 2030. Each 600,000-kilowatt nuclear power plant requires about 600 tons of superalloy materials, so the total demand for superalloy materials is about 80,000 tons. Considering that the domestic production rate of nuclear power plant construction is about 80%, it is expected that the average annual domestic demand for superalloy will be about 7,111 tons in the future.
4) Other areas
Superalloy materials are also widely used in glass manufacturing, metallurgy, medical instruments and other fields
