Inertia Friction Welding Dissimilar Nickel-Based Superalloys Alloy 720Li to IN718
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INERTIA friction welding (IFW) is a solid-state welding process, which allows joining nickel-base superalloys with a high c¢ volume fraction or different types of nickel-base superalloys. During IFW, one part is attached to a rotating flywheel, while the second, nonrotating part is forced into contact with the rotating one under hydraulic pressure. The kinetic energy stored in the rotating flywheel is then transformed into heat at the interface of the two parts. In this way, a sufficiently high temperature is produced at the interface, which, together with the torsional forces and axial pressure, results in material being ejected, and a bond is formed. The IFW is considered an attractive manufacturing process because of its suitability for mass production. More importantly, unlike electron beam welding, laser welding, and other welding technologies, the IFW process is a solid-state joining process. As a result, problems related to liquation such as occurrence of microfissures,[1,2,3] precipitation of detrimental phases, Z.W. HUANG, Senior Research Fellow, H.Y. LI, Research Fellow, and P. BOWEN, Professor, are with the Department of Metallurgy and Materials, School of Engineering, The University of Birmingham, Birmingham B15 2TT, United Kingdom. Contact e-mail: z.w.huang@ bham.ac.uk M. PREUSS, Lecturer in Materials Performance, and M. KARADGE, Research Fellow, are with the School of Materials, University of Manchester, Manchester, M1 7HS, United Kingdom. S. BRAY, Friction Welding Sprcialist and G. BAXTER, Intertia Welding Sprcialist, are with Rolls-Royce plc., Elton Road, Derby DE24 8BJ, United Kingdom. Manuscript submitted June 15, 2006. Article published online June 26, 2007. 1608—VOLUME 38A, JULY 2007
intergranular hot cracking,[4–7] and porosity[8] can be either avoided or diminished. As a consequence, high c¢ volume fraction nickel-base superalloys, considered to be unweldable by fusion welding techniques, can be joined by IFW. The IFW is widely used in the automotive and power generation industry.[9,10] In the aeroengine industry, it is mainly used to join high-temperature materials such as titanium and nickel-base superalloys.[11,12] The IFW of two different types of nickel-base superalloys, namely, alloy 720Li to IN718, has been undertaken in this study. Such dissimilar joints are highly attractive for the aeroengine industry as they result in significant weight reductions while maintaining the mechanical properties and required temperature capability. The aim of this study is to improve the understanding of inertia friction joining two types of high-temperature alloys by mapping microhardness and microstructure variations across the weld region of the dissimilar material combination. Previous microstructural characterization of similar friction-welded nickel-base superalloys has demonstrated that, due to the thermal history and heavy plastic deformation in the near weld region, a dramatic variation of the microstructure is observed, resulting in partial or full dissolution of c¢ precipitates in this region.[12,13]
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