Mechanical Property and Microstructure of Linear Friction Welded WASPALOY
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NICKEL-BASE superalloys have long been used in aerospace, power generation, chemical, and petroleum industries because of their superior mechanical properties and corrosion resistance at elevated temperature.[1,2] To join these alloys, mechanical fastening and fusion welding are usually employed. However, these conventional methods impair the properties of the joint. For example, mechanical joining of slotted blade/disk is associated with fretting fatigue damage;[3] melting and re-solidification processes in gas-tungsten arc, laser, or electron beam welding techniques result in welding defects such as microcracking, grain coarsening, and, consequently, the deterioration of mechanical properties such as ductility and fatigue strength.[4–8] Furthermore, conventional welding methods need filler wire, flux, or shielding gas during welding, which increase the complexity of the manufacturing as well as the costs.[9,10] To address these concerns, friction welding has been studied as an alternative joining method. Linear friction welding (LFW) is solid state joining technology aimed at extending the current application of A. CHAMANFAR, PhD Candidate, is with the Department of Mining and Materials Engineering, McGill University, Montreal, QC, Canada H3A 2B2 and is also a Visiting Worker, Aerospace Manufacturing Technology Center (AMTC), Institute for Aerospace Research (IAR), National Research Council of Canada (NRC), Montreal, QC, Canada H3T 2B2. Contact e-mail: [email protected] M. JAHAZI, Adjunct Professor and S. YUE, Professor, are with the Department of Mining and Materials Engineering, McGill University. J. GHOLIPOUR, Research Officer and P. WANJARA, Group Leader, are with the AMTC, IAR, NRC. Reproduced by Permission of Minister of Supply and Services Canada Manuscript submitted June 10, 2010. Article published online November 25, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
rotary friction welding to nonaxisymmetric components.[8] In friction welding, the temperature during the process does not reach the fusion point of the alloy;[11] thus, microcracking does not occur,[5] and filler metal addition or protective gas shielding are not necessary. LFW relies on the development of frictional heat at the interface by linear oscillation of one part relative to another while subjected to a pressure. This process consists of four distinct phases known as the contact phase, the conditioning phase (or friction), the burn-off phase, and the forge phase.[12] Once the components to be joined have been heated to a temperature that plasticizes the material at the interface, the oscillating part is stopped in an aligned position with the stationary part. Then, the axial load is maintained or increased to consolidate and bond the two parts together. During the process, some of the plasticized material is expelled to the sides as flash. The bonding mechanisms in the LFW process can be summarized as follows: (a) viscoplastic flow and intermixing of the interface material from two weld halves as a result of under pressure osc
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