Microstructure Characterization and Mechanical Properties in Individual Zones of Linear Friction Welded Ti-6Al-4V Alloy
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LINEAR friction welding is a solid-state welding process involving two workpieces that are in direct contact and subjected to compressive forces[1,2] across their area of contact. During the typical process, one workpiece is stationary while the other one is in motion, creating friction that is localized to the interface between the two workpieces and that generates heat and strain which plasticizes the contact zone, after which point in the process a final forging pressure is applied to consolidate the joint.[3] Vairis and Frost[4,5] describe
MICHAEL Y. MENDOZA is with the Department of Materials Science and Engineering, Iowa State University, Ames, IA 50011 and with the Center for Advanced Non-Ferrous Structural Alloys (CANFSA), and with the Institute of Naval and Maritime Science, Universidad Austral de Chile, Los Rios XIV, 5110566 Valdivia, Chile. MARIA J. QUINTANA is with the Department of Materials Science and Engineering, Iowa State University and with the Center for Advanced Non-Ferrous Structural Alloys (CANFSA) and with the Universidad Panamericana. Facultad de Ingenierı´ a. Augusto Rodin 498, 03920 Mexico, Mexico. PETER C. COLLINS is with the Department of Materials Science and Engineering, Iowa State University and with the Center for Advanced Non-Ferrous Structural Alloys (CANFSA) and with the Ames Laboratory, Iowa State University, Ames, IA 50011. Contact e-mail: [email protected] Manuscript submitted July 13, 2020; accepted September 24, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS A
the process according to four distinct phases. During Phase I, the two workpieces are put into contact under a specific pressure. The real contact area is increased as topological asperities are reduced. Concurrently, heat is generated due to friction. In Phase II, the heat generation is sufficiently high so as to decrease the flow stress, enhancing plastic deformation which further reduces the asperities and increases the area of real contact to 100 pct and extrudes highly plastic material from the interface (i.e. initial flash formation). In the specific case of Ti-6Al-4V, it has been reported that Phase I is reached when the interface reaches the b-transus temperature.[6] During Phase III, the process is said to be in equilibrium, the flash formation is more visible, and the axial shortening proceeds at a constant rate.[7] Phase IV is known as the deceleration and forging phase where in less than 0.1 second the two workpieces are brought to rest and a final forging pressure is applied to finish the joint. An important and defining technical advantage of LFW over regular welding or any additive manufacturing technique is the solid-state nature of the process. Therefore, all problems associated with solidification are avoided (e.g., porosity, hot cracking, segregation, etc.) while the benefits of solid-state processes are realized. For example, dissimilar materials can be welded due to lower peak temperatures[8] and the avoidance of liquid-state interactions. The thermal excursions are short, and the severe deformation at the
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