Linear friction welding of Ti-6Al-4V: Processing, microstructure, and mechanical-property inter-relationships
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I. INTRODUCTION
LINEAR FRICTION welding involves solid-state joining of materials through the relative motion of two components under compressive forces.[1,2,3] This pressurized reciprocating motion results in plasticization of the weld interface between two workpieces, one that is stationary and the other that oscillates linearly. During processing, frictional heat and deformation strain is generated and results in continued plasticization of the interfacial region between the workpieces and displacement of plastically deformed material toward the weld edges. Once sufficient plasticization has occurred, a forging force is applied, to produce a consolidated joint seam with a limited thermomechanically affected zone (TMAZ). According to Vairis and Frost,[3] linear friction welding occurs in four distinct phases: the initial phase, the transition phase, the equilibrium phase, and the deceleration (or forging) phase. The joining process begins when two components are brought into pressurized contact in a linear reciprocating motion, resulting in heat and strain generation as well as the wearing of surface asperities on the faying surfaces. For the process to attain plasticization of the interface, the reciprocating motion must generate sufficient heat to overcome losses via conduction to the base or parent metal and radiation and convection to the atmosphere. Wear particles are expelled from the interface as “flash” during the transition phase, and permanent deformation of the soft plasticized layer between the two materials occurs due to high axial loading. The TMAZ begins to expand from the interface into the parent material during this stage of the process. The
P. WANJARA, Research Associate, and M. JAHAZI, Group Leader, are with the National Research Council Canada, IAR-AMTC, Montréal, PQ, Canada H3T 2B2. Contact e-mail: [email protected] Manuscript submitted November 12, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS A
equilibrium phase then involves significant axial shortening of the part as material is expelled from the interface. The TMAZ continues to develop throughout the equilibrium stage as heat is conducted away from the interface. Deceleration involves the rapid cessation of the relative motion and the application of a forging pressure to consolidate the weld. The application of linear friction welding has extended the commercial potential of frictional bonding techniques by allowing for the joining of nonasymmetric parts with precise angular alignment.[4] Although linear friction welding has been available for 15 years, industrial applications have been limited to aircraft engine manufacturing, where the high value-added cost of the components justifies the capital cost of the joining equipment.[5] Nonetheless, linear friction welding has been used successfully to join a range of materials including steel, aluminum, titanium, and intermetallic alloys.[6] Of these materials, the manufacturing costs for titanium-based alloys remain high as compared to aluminum and steel, for example. In addit
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