Nickel-based alloys are the most widely used alloys in superalloys, especially in the aerospace and defense fields, such as the development of cutting-edge equipment such as aero engines and missiles. Since nickel-based alloys can dissolve a variety of alloying elements and maintain good structural stability, this provides many ways to improve their performance. The development of science and technology puts higher requirements on nickel-base superalloys. In order to meet market demand, it is necessary to speed up research on nickel-based superalloys and improve their comprehensive performance. Alloying optimization design is a key point in this research and development work.
First, solid solution strengthening
The main means of strengthening the performance of nickel-based superalloys is to add an appropriate amount of solid solution strengthening elements. Solid solution strengthened alloys have excellent oxidation and fatigue resistance and good plasticity; their most prominent advantage is structural stability. Based on these characteristics, nickel-based superalloys can be used to produce metal parts with higher operating temperatures, such as engine blades. The atomic radius of nickel is close to the atomic radius of alloying elements such as tungsten and molybdenum. Based on these characteristics, nickel can simultaneously dissolve a large amount of alloying elements such as tungsten, molybdenum and cobalt without a new phase. Studies have shown that the solid solution temperature range of common metals is generally between 1050 and 1560 °C. The United States has developed a high-performance solid solution strengthening alloy, the nickel-based deformed superalloy Haynes 280, which has a strength of up to 165 MPa and an elongation of 87% at a high temperature of 1400 °C. It is mainly because refractory metal elements such as tungsten and chromium are added to the alloy; at the same time, a small amount of carbon is added during the development to form carbides, which hinders grain growth and strengthens grain boundaries.
Studies have also shown that the strength of the alloy can be improved by adding a large amount of refractory metal elements such as molybdenum; the structural stability of the alloy can be improved by adding niobium; by adding a certain amount of refractory metal such as tungsten, it can be improved under certain conditions. The corrosion resistance of the alloy; the corrosion resistance can be greatly improved by adding a certain amount of rare earth.
Second, precipitation strengthening and dispersion strengthening
Adding a certain amount of precipitation strengthening element to the nickel-based superalloy can precipitate the γ'-Ni3(Al, Ti) phase during aging, greatly increasing the strength of the metal. However, under high temperature working conditions, the precipitated phase tends to aggregate and grow, and some will be re-solidified in the matrix, thereby reducing the high temperature strength. In recent years, oxide-dispersed nickel-base superalloys have received attention. Such alloys are typically subjected to a mechanical alloying process to obtain an ultrafine (less than 50 nm) microstructure that is uniformly dispersed in the alloy matrix at a high temperature. The alloy strength can be maintained close to the melting point of the alloy itself, with excellent high temperature creep properties, superior high temperature oxidation resistance and resistance to carbon and sulfur corrosion. At present, there are mainly three kinds of oxide-strengthened nickel-based superalloys that have been commercialized: MA956 alloy can be used in an oxidizing atmosphere at a temperature of up to 1350 °C, which is the first place in the high-temperature alloy for oxidation, carbon and sulfur corrosion. Engine combustion chamber lining. MA754 alloy is used in the oxidizing atmosphere at temperatures up to 1250 ° C and maintains a relatively high temperature strength and resistance to alkali - alkali glass corrosion. It has been used to make aero-engine guide ring and guide vanes. MA6000 alloy has a tensile strength of 222 MPa at 1100 °C, a yield strength of 192 MPa, and a permanent strength of 127 MPa at 1100 °C/1000 hours, which is the first place in high-temperature alloys and can be used in aero-engine blades.
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