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Application and Development of Nickel Alloy in Aviation Field
Release time:
2024-07-03
R.F.Smith of the United Kingdom discusses the development of nickel alloys in four aspects of the recent application of aviation, the first is the disc alloy; the second is the low expansion superalloy; the third is the superplastic molding of nickel-based superalloy (Inconel718 alloy); the fourth is the composite material preparation tool for low expansion alloy (Nilo).
The development goal of nickel-based superalloys for aero-engine discs is to make them have a higher service temperature by adding additional elements. The composition of a newly developed nickel-based alloy with better creep and fatigue properties is Ni-20Cr-1.5Al-3Ti-4.5Mo-13.5Co. The alloy was initially prepared by vacuum induction melting (VIM) and vacuum arc remelting (VAR). Due to the alloy composition segregation white spots and carbide aggregation lead to reduced disc life, the United States Special Metals Company (SMC) switched to VIM and electroslag refining to eliminate these defects, the future of the engine requires the use of materials of higher temperature and strength. Udimet 720 alloy (Ni-16Cr-2.5A1-5Ti-3Mo-14.7Co-1.25W) originally used for blades needs powder metallurgy method to prepare large disc forgings. Now SMC has successfully prepared φ250mm diameter forging blanks through research and improvement of melting and refining process and forging process, and has been used in civil and military engines.
Low-expansion superalloys Chromium-containing superalloys used in gas turbine engines, such as the high expansion of Inconel 718 alloys, can cause difficulties such as fit tolerances, which require careful design and use of expensive mechanical cooling systems and effective clearance between rotating parts and seals, in order to solve the problem from the root, it began to explore the use of new low-expansion superalloys to improve engine efficiency and low-chromium Incoloy903 alloys for the development of compressor casings and covers. Later, Incoloy907 alloys with added niobium and reduced aluminum content and Incoloy909 alloys with added silicon were developed. Although the latter improved the durability and plasticity, it had poor high-temperature oxidation resistance and needed high-temperature coatings to be used, and there are problems such as stress concentration will accelerate grain boundary crack propagation. To this end, a high cobalt-containing Inconel 783 alloy (28.5 A13Cr34Co Nb5.4A10.1Ti) was developed. The alloy has oxidation resistance and stress grain boundary crack propagation resistance, can be used to 700 degrees Celsius temperature, no coating, its stress durability is better than Incoloy 909 alloy, also has a certain low expansion, is the future of aviation materials, the main research object.
Inconel718SPF-a superplastically formable nickel-base alloy of the same composition as a standard (AMS5596)Inconel718 alloy, containing 50% Ni,17% Cr,0.6 Al, 1% Ti,30% Mo,5% Nb, and the balance Fe. However, the alloy also has its own standard AMS5950, the main difference is that it requires the best thermal deformation to obtain fine grain size. Compared with ordinary Inconel 718 alloy, the fatigue life of Inconel 718SPF alloy with fine grain superplastic forming is increased by 100 times, and it is easier to make full use of superplastic forming technology into components with complex shapes, high specific strength at high temperature and low manufacturing cost. Because the original superplastic forming technology is mainly used for aluminum and titanium alloys. Inconel 718SPF superplastic forming alloy represents the latest progress in the field of material superplastic forming technology.
Low Expansion Alloy (Nilo) for Composite Tools Recently, with the change of aircraft skin materials from aluminum to carbon reinforced thermosetting and thermoplastic resin materials, the expansion characteristics of the tool materials used to manufacture such composite components should be similar to those of the processed materials throughout the curing temperature range of the composite materials. Of course, the mold can be made of composite materials, but its short service life and high cost are not conducive to mass production. Therefore, the low expansion characteristics of the "invar effect" of Nilo alloys can meet this requirement. Since 1985, SMC has produced many Ni-Fe solid tile alloys, such as Nilo36 and Nilo42 alloys, when these alloys were not used in composite tools. Now has produced Nilo alloy wide plate, extrusion profiles and square bars, etc., used to manufacture composite processing tools. Nilo alloy is easy to process and manufacture into composite processing tools with complex shapes. Its yield strength is 276MPa, tensile elastic modulus is 138GPa, elongation rate can reach 50%, and the work hardening rate is low, elastic rebound is small, Nilo36 alloy is easy to cold and hot process forming. One of the main reasons for the limitations of earlier Nilo alloys for composite processing tools was welding problems. Now SMC Company has developed filling alloys CF36 and CF42 for welding. They are alloys modified with Nb-C. Their components are CF36:0.2C,0.4Mn,36Ni,1.5Nb and the rest Fe respectively. CF42:0.2C,0.4Mn,41.5Ni,1.5Nb and the rest Fe. These two alloys are respectively used for welding Nilo36 and Nilo42 alloys, the welded joint has the same expansion coefficient as the base material, resulting in a high-quality, crack-free weld. After Ni-Fe the tools made of solid tile alloy and welding, it should be annealed at 760 ℃ for 2h, followed by furnace cooling or air cooling to relieve stress.
Recently, the United States SMC has developed a better rigidity, higher hardness of Nilo365 alloy, can be made into a longer life of processing tools. The alloy composition is similar to the Nilo36 alloy, but with the addition of Nb and Ni(43.5Ni3.3Nb1.4Ti0.2Co balance Fe).
In short, in the engine disc, SMC continues to develop and study low expansion alloys for engine castings in accordance with the requirements of engine manufacturers, and provides manufacturers with newer alloys that can be superplastically formed. In the processing and manufacturing of composite materials, SMC continues to develop, research and supply alloys for processing tools. From the aircraft engine in 1940 to today's aircraft composite structural parts, nickel-based alloys have played an extremely important role in the aviation industry.
The company has advanced special smelting, casting, wire drawing, hydrogen removal and other full production chain equipment, and can independently produce corrosion-resistant alloys (pure nickel wire N4, N6, Monel Monel400, 500), copper-nickel low-resistance heating alloy (NC003-NC050), thermocouple compensation wire combination (K,N,E,T,J-type), high-temperature alloys, precision alloys, hydrogen storage alloys and other high-performance special alloy materials wire, flat, stranded wire, bar, coil, etc. From the upstream procurement of raw materials to the downstream physical characteristics of the finished product testing, to the final product quality tracking, all-round monitoring of product quality.
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