Efficiency of the Inertia Friction Welding Process and Its Dependence on Process Parameters

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INERTIA friction welding (IFW) is a solid-state process widely used for joining axisymmetric components such as shafts, tubes, disks, etc. In this process, the kinetic energy stored in a rotating flywheel is converted into frictional heat between the contacting surfaces resulting in local material softening and axial (and radial) metal flow under the action of a superimposed axial compression force. By this means, the weld upset moves surface contaminants and oxides into flash, which is later removed by a final machining operation, and brings nascent material from each component into contact, facilitating the formation of a metallurgical bond.[1–3] IFW is a rather simple process inasmuch as only three parameters, the moment of inertia of the flywheel I, its initial angular velocity xo, and the axial

O.N. SENKOV is with the Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, Dayton, OH, 45433, and also with UES Inc., Dayton, OH, 45432. Contact e-mail: [email protected] D.W. MAHAFFEY and S.L. SEMIATIN are with the Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB. D.J. TUNG and W. ZHANG are with the Department of Materials Science and Engineering, The Ohio State University, Columbus, OH, 43221 Manuscript submitted 13 December 2016. Article published online April 28, 2017 3328—VOLUME 48A, JULY 2017

compression force P, need to be properly selected to obtain sound and consistent welds.[2,4] The initial kinetic energy of the flywheel (often called total ‘welding energy’), Eo, is a function of I and xo: Eo ¼ Ix2o =2:

½1

It is generally assumed that this kinetic energy is transformed into heat at the faying surfaces of the two components during IFW. By contrast, the fact that a certain fraction of the initial kinetic energy is also consumed by the rotating parts within the welding machine (due to friction associated with the journal and thrust bearings) is often overlooked. In fact, it is frequently assumed in the literature that the energy losses within the welding machine (denoted as parasitic energy, EM) comprise a relatively small fraction of the initial flywheel energy and that ~70 to 95 pct (denoted as sample energy, ES) is utilized for workpiece heating/ welding per se.[3,5–10] Moreover, during IFW process optimization and modeling, it is frequently assumed that the fractions of the parasitic and sample energies are constant and do not depend on the IFW parameters. With this assumption, the same sample energy is obtained for different combinations of I and xo which provide the same value of Eo.[3,6] However, recent work by Mahaffey et al.[11] has shown that this assumption is not valid. In their study, metal flow and microstructure response during IFW of the dissimilar Ni-based METALLURGICAL AND MATERIALS TRANSACTIONS A

superalloys LSHR and Mar-M247 exhibited a noticeable dependence on the flywheel moment of inertia for fixed values of Eo and P. It was demonstrated that an increase in I for a given Eo reduced the parasitic energ