Effect of Preheating on the Inertia Friction Welding of the Dissimilar Superalloys Mar-M247 and LSHR
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ASED superalloys are broadly used in hightemperature applications because of their unique properties such as high strength and creep resistance.[1–3] A number of aerospace applications operating in a gradient temperature field would benefit from hybrid (multi-alloy) structures comprising superalloys with dissimilar mechanical properties. For example, high-strength powder metallurgy (PM) or wrought superalloys are often beneficial in locations that require high strength levels at moderate temperatures. Likewise, heat-resistant, coarsegrain or single-crystal cast superalloys are typically preferred in sections operating at higher temperatures or when creep resistance is critical. Successful development of processing techniques to join dissimilar alloys would therefore increase the service-temperature and load-bearing capabilities of hybrid structures. Fusion welding techniques are generally not acceptable to join highly alloyed Ni-based superalloys that contain a high volume fraction of second-phase particles due to hot cracking during post-weld solidification.[4] By O.N. SENKOV, Senior Scientist, is with the Air Force Research Laboratory, Materials and Manufacturing Directorate Wright-Patterson AFB, Dayton, OH 45433, and also with UES Inc., 4401 DaytonXenia Rd, Dayton, OH 45432. D.W. MAHAFFEY, Materials Research Engineer and S.L. SEMIATIN, Senior Scientist, Materials Processing/Processing Science, are with Air Force Research Laboratory, Materials and Manufacturing Directorate Wright-Patterson AFB. Contact e-mail: david.mahaff[email protected] D.W. Mahaffey and S.L. Semiatin are employed by the Air Force Research Laboratory. U.S. Government work is not protected by U.S. Copyright. Manuscript submitted June 15, 2016. Article published online September 23, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
contrast, solid-state joining techniques, such as diffusion bonding and friction welding, can be applied to join these materials.[4–10] In particular, inertia friction welding (IFW) is used widely to join axisymmetric components. In this process, one of the workpieces to be joined is attached to a flywheel with a known moment of inertia, rotated to a specific velocity, and then brought into contact with its mating workpiece under an applied axial compressive load. The friction between the contacting surfaces converts the kinetic energy of the flywheel into heat, thereby producing a rapid temperature increase in a relatively narrow region at the interface that can approach the solidus temperatures of the workpiece materials. This temperature transient reduces the flow stress substantially, resulting in considerable plasticity at and near the weld interface and substantial radial flow leading to the formation of flash due to the applied axial load. Under optimal conditions, the radial flow of material moves oxides, particulates, and other contaminants from the weld interface into the flash, thus bringing nascent surfaces together and producing a sound metallurgical bond.[4] For the case involving dissimilar superalloys with significantly diff
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