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Advancements of Superplastic Forming and Diffusion Bonding of Titanium Alloys for Heat Critical Aerospace Applications
ISSN: 0148-7191, e-ISSN: 2688-3627
Published March 10, 2020 by SAE International in United States
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Titanium’s high strength-to-weight ratio and corrosion resistance makes it ideal for many aerospace applications, especially in heat critical zones. Superplastic Forming (SPF) can be used to form titanium into near-net, complex shapes without springback. The process uses a machined die where inert gas is applied uniformly to the metal sheet, forming the part into the die cavity. Standard titanium alpha-beta alloys, such as 6Al-4V, form at temperatures between 900 and 925°C (1650-1700°F). Recent efforts have demonstrated alloys that form at lower temperatures ranging between 760 and 790°C (1400-1450°F). Lowering the forming temperature reduces the amount of alpha case that forms on the part, which must be removed. This provides an opportunity of starting with a lower gauge material. Lower forming temperatures also limit the amount of oxidation and wear on the tool and increase the life of certain press components, such as heaters and platens. A variation of this process is SPF combined with Diffusion Bonding (SPF/DB) of two or more titanium sheets to produce integrally stiffened structures with limited fasteners and less weight than comparable components. The four sheet process utilizes two core sheets with a welded cell pattern and two face sheets that are welded together along the periphery. Inert gas pressure is then applied at elevated temperature to form the sandwich structure. Recent studies have shown that dissimilar alloys with different grain sizes and flow stresses can be sufficiently diffusion bonded together. Using lower temperature alloys as the core sheet material allows the entire structure to be formed and bonded at a lower temperature regardless of the flow stress of the face sheets.
CitationBurkhart, E. and Hefti, L., "Advancements of Superplastic Forming and Diffusion Bonding of Titanium Alloys for Heat Critical Aerospace Applications," SAE Technical Paper 2020-01-0033, 2020.
- Koehler, W., Plege, K., and Sahm, K.F. , “Metal Forming Specialized Procedures for the Aircraft Industry,” Encyclopedia of Materials: Science and Technology 2:5427-5433, 2001.
- Ridley, N. , “Metals for Superplastic Forming,” Superplastic Forming of Advanced Metallic Materials: Methods and Applications (Philadelphia: Woodhead Publishing Limited, 2011).
- Lee, H.S. , “Diffusion Bonding of Metal Alloys in Aerospace and Other Applications,” Welding and Joining of Aerospace Materials 320-344, 2012.
- Dieter, G.E. , “The Tension Test,” Mechanical Metallurgy (New York: McGraw Hill Education, 1986).
- Hefti, L.D. , “Advances in the Superplastically Formed and Diffusion Bonded Process,” Materials Science Forum 551-552:87-92, 2007.
- Comley, P.N. and Hefti, L.D. , “Superplastic Forming and Diffusion Bonding of Fine Grain Titanium,” U.S. Patent 7,533,794, May 19, 2009.
- Porter, R.L. and Crist, E. , “Development of RTI Ti-6Al-2Sn-4Zr-2Mo Production-Scale Fine Grain Size Sheets for Low-Temperature Superplastic Forming Applications,” in Aeromat Conference, 2013.
- Runyan, M.R., Sanders, D.G., Hefti, L.D., Papenfuss, D.R. et al. , “SPF/DB Structure for Attenuation of Noise from Air Flow,” U.S. Patent 10,294,815, May 21, 2019.