Is There a Better Superalloy?
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Whilst, 34% of the total weight of GE Aircraft Engines' CF6 engine is comprised of nickel alloy N07718... |
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| ...about 54% of the total weight of Pratt & Whitney's PW4000 engine is attributable to the
nickel-base superalloy |
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More efficient aircraft engines will require new nickel base superalloys
Nickel magazine, Sep. 01 -- Two of the largest aircraft engine manufacturers in the U.S.,
Pratt & Whitney and GE Aircraft Engines, are supporting a 5-year, industry-wide research effort. Financed
partially by government, the project is designed to improve the temperature capabilities of nickel-base
superalloys.
The most widely used superalloy in the aerospace industry today is
N07718 (Alloy 718), which contains 52% nickel. At GE Aircraft Engines, it is used for critical rotating
parts, airfoils, supporting structures and pressurized vessels, according to Robert Schafrik, general manager
of the Cincinnati, Ohio-based company.
For example, N07718 comprises 34% of the total weight of GE Aircraft Engine's CF6 engine and N07718 was also used in 56% of all of the company's rotating and structural forgings in 2000.
N07718 has been the alloy of choice in the aerospace industry since its introduction in 1963. Key advantages include favorable precipitation kinetics, improved weldability and castability, low cost, and ease of manufacture.
A similar story was told by Daniel Paulonis of Pratt & Whitney at the fifth international symposium on superalloys 718, 625 and 706 which was held in Pittsburgh, June 17-20, 2001. N07718 accounts for about 57% (or 760 kilograms) of the weight of that company's PW4000 engine.
However, designers want to increase compressor and turbine efficiencies by driving operating temperatures higher. Therefore to retain the nickel-base alloy's dominant market position, the temperature capability and time dependent fracture behaviour of the alloy must be improved. Numerous attempts have been made through the addition of cobalt and tantalum, but none has been entirely successful.
"Finding a suitable higher temperature counterpart to Alloy 718 has proven to be a daunting task," says Schafrik.
Both he and Paulonis says that in order to make a better high-temperature alloy, several conditions are required. These include the effective use of increasingly sophisticated materials and process modeling tools, good physical models and control of time-dependent crack growth.
Proceedings Available
A 756-page volume containing the proceedings of the International Symposium on Superalloys 718, 625, 706 and Various Derivatives is available at a cost of US$192 by contacting:
The Minerals, Metals and Materials Society
184 Thorn Hill Road
Warrendale, PA 15086-7228 U.S.A.
Tel: 724-776-9000
E-mail: weissp@tms.org
Web site: www.tms.org
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GE Aircraft Engines: |
