1 Introduction.
1.1 Introduction.
High-temperature alloys, also known as heat-resistant alloys, superalloys, or heat-strength alloys, are a class of alloys that can withstand complex stresses and work reliably for long periods of time at high temperatures ranging from 600°C to 1100°C and under gas oxidation and corrosion conditions. High-temperature alloy is a kind of alloy developed for high-temperature (>600℃) service under the environment of quite severe mechanical stress and good surface stability. High-temperature alloys originated in the 1940s during the Second World War. Since then such alloys have developed rapidly, and their service temperatures have increased at an average rate of 10°C per year. At present, the gas inlet temperature of advanced aviation engines has reached 1370℃, and the thrust of the engine has been increased from 363kg in the 1940s to 55 tonnes at present.
High-temperature alloys are widely used in high-temperature components such as turbine blades, guide vanes, turbine discs, high-pressure compressor discs and combustion chambers of aerospace engines, ships and industrial gas turbines, as well as heat-resistant parts of nuclear power systems due to their good organisational stability, excellent high-temperature strength, good oxidation and corrosion resistance, and good thermal fatigue and fracture toughness, with a wide range of applications involving Aviation, aerospace, nuclear industry, petrochemical and other fields. The earliest high-temperature alloys are based on 80Ni – 20Cr electrical alloy with a small amount of Ti and AI to improve creep strength. With the development of high-temperature alloys, its composition is more and more complex, the matrix from a single nickel-based development of iron-based and cobalt-based, alloying elements have reached more than 10 kinds of, in addition to AI, Ti, there are Nb, C, W, Mo, Ta, Co, Zr, B, Ce, La, Hf, Mn, N, etc.. High-temperature alloy organisation has changed from a single austenite to a complex organisation containing intracrystalline and grain boundary strengthening phases, and even harmful phases. High-temperature alloy production process development is also very fast, greatly promoting the development of high-temperature alloys. From the 40′s high temperature alloys after the birth of ten years, mainly through the adjustment of the chemical composition of the alloy to improve the performance of the alloy. 50′s, the vacuum induction melting technology began to develop, can effectively remove harmful impurities and gases in the alloy, especially can be accurately control the chemical composition of the alloy, so that the development of high temperature alloys has made further breakthroughs. 60′s, after some new process research began to Development, such as directional solidification, single-crystal alloys, powder metallurgy, mechanical alloying, and so on, vigorously promote the development of high-temperature alloys, in which the single-crystal alloys made by directional solidification process, the use of its temperature up to the melting point of the alloy of about 90%. The matrix of high-temperature alloys is mainly iron-based, nickel-based, cobalt-based and intermetallic compound-based. Nickel-based alloys are the most complex of all high-temperature alloys and are most widely used in high-temperature components in the range of 600°C to 1100°C. The nickel-based alloys are used in a wide range of applications. Nickel-based alloys can be made to have high high-temperature strength by adding elements with different strengthening effects. Such as
(1) solid solution strengthening austenite matrix elements W, Mo, Co, Nb, Ta, etc., produce lattice distortion: reduce the stacking dislocation energy, so that dislocations through the difficult; reduce the diffusion capacity.
(2) the formation of y (Ni3X) precipitation phase elements Al, Ti, Nb, Ta, precipitation of the second phase of the strengthening effect of the second phase and the nature of the second phase (type, crystal structure, composition and its degree of cooperation with the matrix), size, number and stability are closely related.
(3) Strengthening of grain boundary elements B, Zr, Hf, Ce, La, Mg, etc., to reduce the energy of the grain boundary and purify the grain boundary. In addition, at high temperatures, the alloy will react with the oxygen in the environmental medium (oxidation) or interact with the salt and ash etc. deposited on it (thermal corrosion). Improving the resistance of high temperature alloys to oxidation and thermal corrosion will extend their service life. It can be solved by alloying or surface coating, and the commonly used alloying elements are Cr, Al, Si and so on. By adding different strengthening elements, as well as alloying or surface coating, to improve the comprehensive performance of nickel-based alloys such as strength and heat resistance. China since 1956 imitation of the Soviet Union’s ЭN435 (named GH3030) alloy, the beginning of China’s high-temperature alloy production era. Imitation of GH3030 (ЭN435), GH4033 (ЭN437), GH3039 (ЭN602), GH3044 (ЭN868), GH4049 (ЭH929) alloys such as nickel-based high-temperature alloys, and then imitated the iron-nickel-based high-temperature alloys. The birth of China’s high-temperature alloys, starting from nickel-based high-temperature alloys, laying the foundation for its development of the earliest, the widest range of applications, and the most dosage. In the world’s advanced engine development, nickel-based high-temperature alloy material usage has accounted for 40-60% of the total number of engines, high-temperature alloy production and development, determines the technology and progress of the aviation engine.
Post time: Jul-29-2023
