Nickel base alloy is one of the most widely used superalloys, especially in aerospace and defense fields, such as aero-engine, missile and other cutting-edge equipment development, plays an important role. Because a variety of alloying elements can be dissolved in nickel-based alloys and the structure stability can be maintained, there are many ways to improve the properties of nickel-based alloys. The development of science and technology has put forward higher requirements for nickel-based superalloy. In order to meet the market demand, it is necessary to accelerate the research of nickel-based superalloy and improve its comprehensive performance. Alloying optimization design is a key point in this research and development work.
First, solid solution strengthening
The main way to strengthen the properties of nickel-based superalloy is to add appropriate solution strengthening elements. The solid solution reinforced alloy has excellent oxidation resistance and fatigue resistance, as well as good plasticity. Its most prominent advantage is organizational stability. Based on these characteristics, nickel-based superalloys can be used to produce metal parts with high working temperatures, such as engine blades. The atomic radius of nickel is close to the atomic radius of tungsten, molybdenum and other alloying elements. Based on these characteristics, nickel can dissolve a large number of alloying elements such as tungsten, molybdenum and cobalt at the same time, but no new phase will appear. The results show that the solution temperature range of common metals is generally between 1050 ℃ and 1560℃. The United States has developed a kind of solid solution strengthening alloy, nickel-based deformation superalloy Haynes280, which has a strength of 165MPa and an elongation of 87% at 1400℃. This is mainly due to the addition of refractory metal elements, such as tungsten and chromium, to the alloy; At the same time, a small amount of carbon is added to form carbides, which can hinder grain growth and strengthen grain boundaries.
The results also show that the strength of the alloy can be improved by adding a large amount of molybdenum and other refractory metal elements. The microstructure stability of the alloy can be improved by adding ruthenium. By adding a certain amount of refractory metals such as tungsten, the corrosion resistance of the alloy can be improved under certain circumstances. The oxidation corrosion resistance can be greatly improved by adding a certain amount of rare earth.
Second, precipitation strengthening and diffusion strengthening
γ'-Ni3(Al,Ti)) phase can be precipitated by adding a certain amount of precipitation strengthening elements to the nickel-based superalloy during aging, which greatly increases the strength of the metal. However, under high temperature working conditions, the precipitated phase is easy to aggregate and grow, and some of it will be dissolved in the matrix again, so as to reduce the high temperature strength. In recent years, the oxide dispersion strengthened nickel-based superalloy has been paid more and more attention. These alloys are usually mechanically alloyed to obtain ultra-fine (less than 50nm) oxides that are stable at high temperature and uniformly dispersed in the alloy matrix. The alloy strength can be maintained close to the melting point of the alloy itself, and it has excellent high-temperature creep properties, excellent high-temperature oxidation resistance and carbon and sulfur corrosion resistance. At present, there are three kinds of nickel-based superalloys that have been commercialized. MA956 alloy has the highest oxidation, carbon and sulfur corrosion resistance of superalloys, which can be used as the lining of combustion chamber of aeroengines. The temperature of MA956 alloy can reach 1350℃ under oxidizing atmosphere. MA754 alloy can be used at temperature up to 1250℃ under oxidized atmosphere and has high temperature strength and resistance to medium alkali glass corrosion. MA754 alloy has been used in manufacturing labyrinth ring and guide blade of aero-engine guide. The tensile strength and yield strength of MA6000 alloy at 1100℃ are 222MPa and 192MPa, respectively. 1100℃/1000 hours durable strength of 127MPa, ranking the first high temperature alloy, can be used for aero-engine blades.