Nickel-based alloys are the most widely used alloys in high-temperature alloys, especially in the aerospace and defense fields, such as the development of cutting-edge equipment such as aero engines and missiles. Because nickel-based alloys can dissolve a variety of alloying elements and can maintain good tissue stability, this provides many ways to improve their performance. The development of science and technology has put forward higher requirements for nickel-based superalloys. In order to meet market demand, it is necessary to accelerate research on nickel-based superalloys and improve their comprehensive properties. The optimized design of alloying is one of the key points in this research and development work.

1. 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. The solid solution strengthened alloy has excellent oxidation resistance and fatigue resistance, as well as good plasticity; its most prominent advantage is tissue 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 alloy elements such as tungsten and molybdenum. Based on these characteristics, nickel can dissolve a large amount of alloy elements such as tungsten, molybdenum and cobalt at the same time, but no new phase will appear. Studies have shown that the solid solution temperature range of common metals is generally between 1050 ~ 1560 ℃. The United States has developed a solid solution strengthening alloy with excellent properties-Nickel-based deformed superalloy Haynes280. This alloy has a strength of 165 MPa and an elongation of 87% at 1400°C. The main reason is that 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 process to form carbides, which hinders the growth of grains and strengthens the grain boundaries.

The research also shows that by adding a large amount of refractory metal elements such as molybdenum, the strength of the alloy can be improved; by adding ruthenium elements, the structural stability of the alloy can be improved; by adding a certain amount of refractory metals such as tungsten, it can be improved under certain circumstances. The corrosion resistance of the alloy; by adding a certain amount of rare earth can greatly improve the resistance to oxidation corrosion.

Second, precipitation strengthening and dispersion strengthening

Adding a certain amount of precipitation strengthening elements to the nickel-based superalloy can make the alloy precipitate γ'-Ni3(Al,Ti)) phase during aging, greatly improving the strength of the metal. However, under high-temperature working conditions, the precipitated phases tend to aggregate and grow, and some will also re-dissolve in the matrix, thereby reducing the high-temperature strength. In recent years, the oxide dispersion-strengthened nickel-based superalloys have received attention. This type of alloy usually uses a mechanical alloying process to obtain an ultra-fine (less than 50nm) microstructure of oxides that are stable at high temperatures and evenly dispersed in the alloy matrix. Its alloy strength can be maintained under the condition of close to the melting point of the alloy itself, and it has excellent high temperature creep performance, excellent high temperature oxidation resistance and carbon and sulfur corrosion resistance. At present, there are mainly three kinds of oxide dispersion-strengthened nickel-based high-temperature alloys that have been commercially produced: MA956 alloy can be used in an oxidizing atmosphere at a temperature of up to 1350°C, ranking first in the oxidation resistance, carbon resistance, and sulfur corrosion of high-temperature alloys, and can be used in aviation Lining in the engine combustion chamber. The MA754 alloy can be used in an oxidizing atmosphere at a temperature of up to 1250°C and maintains a relatively high high-temperature strength and is resistant to corrosion by medium-alkali glass. It has now been used to make aero-engine guide tooth rings and guide blades. The tensile strength of MA6000 alloy at 1100℃ is 222MPa and the yield strength is 192MPa; the endurance strength at 1100℃/1000 hours is 127MPa, ranking first among high-temperature alloys, and it can be used for aeroengine blades.