Nickel-based cast high-temperature alloys
Nickel-based cast high-temperature alloys are cast high-temperature alloys with nickel as the main component. With the increase in service temperature and strength, high temperature alloys are alloyed (see high temperature alloy strengthening) to a higher and higher degree, and hot work forming is becoming more and more difficult, and must be produced using the casting process. In addition, the complex internal cavity of the hollow blade using cooling technology can only be produced using the precision casting process. In this way, nickel-based deformed high-temperature alloys are transformed into nickel-based cast high-temperature alloys.
Nickel-based cast high-temperature alloy with γ phase as the matrix, add aluminum, titanium, niobium, tantalum, etc. to form γ 'phase (see intermetallic compound phase of high-temperature alloy materials) for strengthening, γ 'phase number is high, some alloys up to 60%; adding cobalt can improve the dissolution temperature of the γ 'phase, thereby increasing the alloy Use temperature; molybdenum, tungsten, chromium has the effect of strengthening the solid solution, chromium, molybdenum, tantalum can also form a series of carbides on the grain boundaries have a strengthening effect; aluminum and chromium help oxidation resistance, but chromium reduces the dissolution temperature of the γ 'phase and high-temperature strength, so the chromium content should be made lower; add hafnium to improve the medium-temperature plasticity and strength of the alloy; in order to strengthen the grain boundaries, add the right amount of boron, zirconium and other elements .
Industrial gas turbines use fuel containing sulfur, vanadium is high, long-term work on the alloy produces serious thermal corrosion. If the gas turbine is used on a ship, the sodium salt in the marine atmosphere will accelerate sulfide corrosion. Therefore, to take the appropriate increase in chromium content and the proportion of titanium and aluminum, as well as the content of refractory metal elements, developed a series of both to maintain high creep strength and enhance the resistance to heat corrosion resistance of the alloy, such as the United States IN738, IN792, Rene '80, MarM432 and China's K4537, etc.
According to the corrosion performance is divided into two kinds of hot corrosion resistant and non-hot corrosion resistant alloys. The former has a chromium content of 12-16%, and the latter has a chromium content of about 9%, and is widely used in the manufacture of aviation jet engines and the hottest parts of various industrial gas turbines, such as turbine blades, guide blades, superchargers, etc.
Between 700-1000℃, the fracture strength is significantly superior to cobalt-based and iron-based cast high-temperature alloys or nickel-based deformation alloys.
Nickel-based cast high-temperature alloys also have some disadvantages, such as slightly worse fatigue performance, lower plasticity, tissue stability has decreased; due to the presence of sparse, performance fluctuations. In order to alleviate these shortcomings, the United States in 1968 first developed a high boron low carbon nickel-based casting high temperature alloy. In the case of nickel-based cast high-temperature alloy other elements remain unchanged, only the boron content increased by 10 to 20 times, the carbon content decreased to 0.01% to 0.03%, while the alloy's strength and plasticity increased, sparseness reduced, improved long-term stability of the organization, etc.. This kind of alloy has been practical application in the United States
Nickel-based cast high-temperature alloys are used for the most critical high-temperature components of gas turbines for aircraft, ships, industry and vehicles, such as turbine blades, guide blades and integral turbines
Nickel-based cast high-temperature alloy with γ phase as the matrix, add aluminum, titanium, niobium, tantalum, etc. to form γ 'phase (see intermetallic compound phase of high-temperature alloy materials) for strengthening, γ 'phase number is high, some alloys up to 60%; adding cobalt can improve the dissolution temperature of the γ 'phase, thereby increasing the alloy Use temperature; molybdenum, tungsten, chromium has the effect of strengthening the solid solution, chromium, molybdenum, tantalum can also form a series of carbides on the grain boundaries have a strengthening effect; aluminum and chromium help oxidation resistance, but chromium reduces the dissolution temperature of the γ 'phase and high-temperature strength, so the chromium content should be made lower; add hafnium to improve the medium-temperature plasticity and strength of the alloy; in order to strengthen the grain boundaries, add the right amount of boron, zirconium and other elements .
Industrial gas turbines use fuel containing sulfur, vanadium is high, long-term work on the alloy produces serious thermal corrosion. If the gas turbine is used on a ship, the sodium salt in the marine atmosphere will accelerate sulfide corrosion. Therefore, to take the appropriate increase in chromium content and the proportion of titanium and aluminum, as well as the content of refractory metal elements, developed a series of both to maintain high creep strength and enhance the resistance to heat corrosion resistance of the alloy, such as the United States IN738, IN792, Rene '80, MarM432 and China's K4537, etc.
According to the corrosion performance is divided into two kinds of hot corrosion resistant and non-hot corrosion resistant alloys. The former has a chromium content of 12-16%, and the latter has a chromium content of about 9%, and is widely used in the manufacture of aviation jet engines and the hottest parts of various industrial gas turbines, such as turbine blades, guide blades, superchargers, etc.
Between 700-1000℃, the fracture strength is significantly superior to cobalt-based and iron-based cast high-temperature alloys or nickel-based deformation alloys.
Nickel-based cast high-temperature alloys also have some disadvantages, such as slightly worse fatigue performance, lower plasticity, tissue stability has decreased; due to the presence of sparse, performance fluctuations. In order to alleviate these shortcomings, the United States in 1968 first developed a high boron low carbon nickel-based casting high temperature alloy. In the case of nickel-based cast high-temperature alloy other elements remain unchanged, only the boron content increased by 10 to 20 times, the carbon content decreased to 0.01% to 0.03%, while the alloy's strength and plasticity increased, sparseness reduced, improved long-term stability of the organization, etc.. This kind of alloy has been practical application in the United States
Nickel-based cast high-temperature alloys are used for the most critical high-temperature components of gas turbines for aircraft, ships, industry and vehicles, such as turbine blades, guide blades and integral turbines
Cobalt-based high-temperature alloys
Solid solution reinforced alloys
Casting alloys
Single crystal alloy
Nickel-based single crystal alloy
Directional crystalline high temperature alloys
Deformed high temperature alloys
Powder Metallurgy High Temperature Alloys
Iron-based cast high-temperature alloys