Effect of Process Variables on the Inertia Friction Welding of Superalloys LSHR and Mar-M247
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NICKEL-BASE superalloys are widely used in aerospace applications involving elevated-temperature service but are generally considered difficult to weld. Nevertheless, a number of aerospace applications would benefit from hybrid (dual-/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. Several attempts have been made to join these types of dissimilar alloys using solid-state techniques such as friction welding.[1–4] In friction welding methods, the materials are bonded in the solid state using friction-induced heating of the mating surfaces which are brought together by an applied compression force. By this means, solidification defects associated with fusion welding techniques are avoided. To produce a sound bond in practice, however, extensive plastic deformation and D. W. MAHAFFEY, Materials Research Engineer, S.L. SEMIATIN, Senior Scientist, Materials Processing/Processing Science, are with the Air Force Research Laboratory, Materials and Manufacturing Directorate, AFRL/RXCM, Wright-Patterson Air Force Base, Dayton, OH 45433. Contact e-mail: David.Mahaff[email protected] O.N. SENKOV, Senior Scientist, is with the Air Force Research Laboratory, Materials and Manufacturing Directorate, AFRL/RXCM, Wright-Patterson Air Force Base, and also with UES Inc., 4401 Dayton-Xenia Rd, Dayton, OH 45432 R. SHIVPURI, Professor of Integrated Systems Engineering, is with the College of Engineering, Ohio State University, Columbus, OH 43210. D.W. Mahaffey and S.L. Semiatin are employed by the Air Force Research Laboratory, Materials and Manufacturing Directorate. U.S. Government work is not protected by U.S. Copyright. Manuscript submitted March 2, 2016. Article published online June 8, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
mechanical mixing of the materials at the mating surfaces are required.[5] In the specific process known as inertia friction welding (IFW), the energy is supplied by a rotating flywheel, and the primary process parameters are the flywheel moment of inertia (I), the initial flywheel rotation speed (xo), and the applied axial (forging) force (P). I and xo define the initial kinetic energy of the flywheel Eko (also referred to as the welding energy): Eko ¼
Ix2o : 2
½1
During the IFW process, the kinetic energy of the flywheel is transformed into heat via friction at the weld interface. The energy required to produce a sound weld is generally considered a sufficient criterion for a given material combination and weld geometry.[6] However, Eq. [1] indicates that numerous combinations of I and xo can produce the same value of Eko. Recently, IFW was applied to join the forged, PM superalloy LSHR to coarse-grain, cast Mar-M247.[4] The vario
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