Application and development of nickel alloy in the field of aviation

R.F. Smith, UK, discusses the development of nickel alloys for new aerospace applications in four areas, firstly, disc alloys; secondly, low expansion superalloys; thirdly, nickel-based superalloys that can be superplasticized (Inconel 718 alloy); and fourthly, low expansion alloys for composite preparation tools (Nilo).

Nickel-based superalloys for aero-engine disks The goal of the development of this type of alloy is to make it have higher service temperature by adding additional elements. A newly developed nickel-based alloy with better creep and fatigue properties is Ni-20Cr-1.5Al-3Ti-4.5Mo-13.5Co. Initially, this alloy was prepared by vacuum induction melting (VIM) and vacuum arc remelting (VAR). Due to the reduced life of the discs due to composition bias white spots and carbide build-up, Specialty Metals Corporation (SMC) switched to VIM and electroslag refining to eliminate these defects, and future newer engines will require higher temperature and strength materials. Initially, Udimet 720 alloy (Ni-16Cr-2.5A1-5Ti-3Mo-14.7Co-1.25W) used for blades required powder metallurgy methods to prepare large disk forgings, but now SMC through the melting and refining process, as well as forging process research and improvement, has successfully prepared φ250mm diameter forging billets, and used in civilian and The forging billets are used in civil and military engines.

Low expansion superalloys The chromium-containing superalloys used in gas turbine engines, such as Inconel 718, are highly expansionary and cause problems such as fit tolerances, which require careful design and expensive mechanical cooling systems and effective clearance between rotating parts and seals to solve these problems. Engine efficiency and low chromium Incoloy903 alloy for compressor cassette and cover development, and later developed Incoloy907 alloy with the addition of niobium and reduced aluminum content, as well as the addition of silicon Incoloy909 alloy, the latter although to improve the longevity and plasticity, but its high temperature oxidation resistance is poor, the need for high temperature coating to use, and stress concentration will accelerate the grain boundary Crack expansion and other problems. For this reason, Inconel 783 alloy with high cobalt content (28.5A13Cr34Co.3Nb5.4A10.1Ti) was developed. This alloy has oxidation resistance and resistance to stress grain boundary crack expansion, and can be used to temperatures below 700°C without coating.

Inconel 718SPF, a superplasticizable nickel-based alloy, has the same composition as the standard (AMS5596) Inconel 718 alloy, containing 50% Ni, 17% Cr, 0.6% A1, 1% Ti, 30% Mo, 5% Nb, and the balance of Fe. Compared with ordinary Inconel 718 alloy, the fatigue life of Inconel 718SPF alloy with fine grain can be superplasticized by 100 times, and it is easier to make use of superplasticizing technology to make components with complex shape, high specific strength at high temperature and low manufacturing cost. This is because the original superplastic forming technology was primarily used for aluminum and titanium alloys. Inconel 718SPF superplastic forming alloy represents the latest advancement in the field of material superplastic forming technology.

Low expansion alloys for composite tooling (Nilo) Recently, as aircraft skin materials have shifted from aluminum to carbon-reinforced thermoset and thermoplastic resin materials, the expansion characteristics of the tooling materials used to manufacture such composite components should be similar to those of the material being processed throughout the composite curing temperature range. Of course, the composite material can be used to make the mold, but its short life, high cost, not conducive to mass production. Therefore, the low expansion characteristics of the Nilo alloy "Invar effect" (Invar effect) can meet this requirement. Since 1985, SMC has produced a number of Ni-Fe solid tile alloys, such as Nilo36 and Nilo42, which were not used in composite tools at the time. Nilo alloys are now available in wide and thick plates, extruded profiles and square bars for the manufacture of composite tools. The Nilo 36 alloy can be easily formed by cold and hot working. One of the main reasons why the use of Nilo alloys in composite processing tools was limited in the early days was the welding problem. Now SMC has developed the filling alloy CF36 and CF42 for welding, they are added to the Nb-C modified alloy, the composition of CF36: 0.2C, 0.4Mn, 36Ni, 1.5Nb, the rest is Fe; CF42: 0.2C, 0.4Mn, 41.5Ni, 1.5Nb, the rest is Fe, these two alloys are used for The welded joints have the same expansion coefficient as the base material, resulting in high quality, crack-free welds. Ni-Fe solid tile alloy made of tools and welding, should be annealed at 760 ℃ for 2h, followed by furnace cooling or air cooling stress relief.

Recently, the United States SMC and developed a better rigidity, higher hardness Nilo365 alloy, can be made into a longer service life of processing tools. The alloy composition is similar to Nilo36 alloy, but with the addition of Nb and Ni (43.5Ni3.3Nb1.4Ti0.2Co balance for Fe).

In conclusion, for engine disc parts, SMC continues to develop and research low expansion alloys for engine castings as requested by engine manufacturers, and to provide manufacturers with newer alloys that can be superplasticized and molded. In the area of processing and manufacturing of composite materials, SMC continues to develop research and supply alloys for processing tools. Nickel-based alloys have played an extremely important role in the aerospace industry since 1940 for aero engines to today's composite structural parts for aircraft.

Our company has advanced special smelting, casting, wire drawing, hydrogen fading and other full production chain equipment to independently produce corrosion resistant alloys (pure nickel wire N4, N6, Monel 400, 500), copper-nickel low resistance heating alloys (NC003-NC050), thermocouple with compensation wire combined (K, N, E, T, J type), high temperature alloys, precision alloys, hydrogen storage alloys and other high performance special Alloy materials such as wire, flat, strand, bar, coil, etc. From upstream raw material procurement to downstream physical property testing of finished products to final product quality tracking, we monitor product quality in all aspects.