The Outlook of Nickel Alloy Application in Aviation Industry
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Thanks to the advancement of new technology, an increasing amount of newly developed nickel alloys materials now become accessible, bringing benefits to aviation industry.
Nickel-based Super Alloy for Aviation Engine Disc
Nickel-based super alloy is developed to increase the operation temperature through the addition of some elements. The Udimet 720 alloy (Ni-16Cr-2.5Al-5Ti-3Mo-14.7Co-1.25W), originally used for the blade, involves powder metallurgy to make large disc forgings. Thanks to the smelting & refining technique, as well as the improved forging process, φ250mm diameter forging billets have been successfully developed and used on engines for civil and military aircrafts.
Low Expansion Super Alloy-- from Incoloy 718, 903, 907, 909 to Inconel 783
Chromium-containing super alloys used on gas turbine engines, such as Inconel 718 alloys, feature high expansion properties causing difficulties in fit tolerances. Hence, to solve the problem, it entails thoughtful design beforehand, use of expensive mechanical cooling systems, and leaving effective gap between the rotating parts and the seals. To tackle this problem at its source, new super alloy with low expansion properties, known as Incoloy 903 has been developed. Incoloy 903 featuring low chromium content, is developed to improve engine efficiency and used to make compressor boring and cover. Then come Incoloy 907 with added niobium and reduced aluminum and Incoloy 909 alloy with added silicon. Incoloy 909 features improved durability and plasticity but poor performance of high temperature oxidation resistance which requires high temperature coating for use. Also, intergranular crack expansion can happen when it is subjected to concentrated stress. To solve this issue, a high cobalt-containing Inconel 783 alloy (28.5Al, 3Cr, 34Co, 0.3Nb, 5.4Al, 0.1Ti) is developed. This alloy, with resistance to oxidation and intergranular crack expansion, can be used at temperatures below 700 °C without coating. Inconel 783 alloy features better stress durability than Incoloy 909 alloy and low expansion properties, hence, it is the main research topic of future aviation materials.
