New Materials for Next-Generation Commercial Transports (1996) / Chapter Skim
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3 Metallic Materials and Processes
3 Metallic Materials and Processes
Pages 26-35
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From page 26... ...
The tighter controls on chemistry and processing parameters may cause an increase in the cost of the material, but production 26 applications of improved alloys show that this cost can be offset by benefits in performance or durability. Improved Strength and Corrosion Resistance The conventional T76 and T73 tempers used to develop high resistance to exfoliation corrosion and to stress corrosion cracking in the short transverse direction of 7XXX alloys are associated with a 1~15 percent reduction in strength compared with the peak-aged T6 temper.
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From page 27... ...
Finally, strain localization in the PFZ and associated void nucleation at grain boundary precipitates cannot be eliminated by alloying additions. However, this problem can be minimized by stretching the material and then aging the material at low temperatures, both of which accelerate precipitation in the matrix and lead to decreased grain boundary precipitation, a smaller PFZ, and improve combined strength and fracture toughness.
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From page 28... ...
TITANIUM ALLOYS Titanium and titanium alloys are widely used in aircraft applications because of their high strenath-to-wei:,ht ratio and excellent corrosion resistance. Titanium use is, however,
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From page 29... ...
Alloy Ti-6-6-2 was used extensively in the landing gear support structure of the Boeing 747 because of its superior corrosion resistance to the low-alloy steels. One ~ alloy, Ti- 1 OV-2Fe-3A1 (Ti- 10-2-3)
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From page 30... ...
The most significant application of Ti-10-2-3 is on the landing gear of the Boeing 777, which results in a significant weight savings compared with 4340 steel and eliminates the potential for stress corrosion cracking associated with steel. Timetal 21 S has good high-temperature properties, with creep properties superior to that of Ti-6-4 (Fanning, 1993~.
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From page 31... ...
Stress relaxation occurs during the age-formin:, process to convert elastic strain into retained deformation for simple and compound contour shapes. Production use of age forming has occurred primarily on wing skins and stnngers, with experience on B-1B upper and lower skin panels, Gulfstream IV compound curvature upper wing panels, Airbus A330 and A340 upper wing panels, and iso- and ortho-gnd patterns for Titan IV booster skirts.
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From page 32... ...
The advances in casting processes, particularly HIP, the improving performance database, and prior history in engine applications led the Boeina,/Lockheed team to commit to produce the F-22 side-of-body rib assembly (figure 3-1) , a primary structure/fracture critical part, from two Ti-6-4 castinas with a casting factor of 1.0.
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From page 33... ...
Biaxially stiffened concepts with integral web channels produced by hiah-speed machining show encouraging structural efficiencies at affordable manufacturing costs. Superplastic Forming and Diffusion Bonding Superplastic forming (SPF)
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From page 34... ...
Based on these service experiences, SPF of aluminum components should see increased use in commercial aircraft. Fabrication methods that combine SPF and DB, as used for titanium alloys, are not commercially available for aluminum alloys.
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From page 35... ...
The primary reasons for using titanium for aircraft applications include weight savings, high operating temperature, space limitation, corrosion resistance, and composite compatibility. The committee believes that titanium alloys will continue to be developed with improved performance in terms of temperature resistance and strength/toughness combinations.
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