Influence of direct electric current on wetting behavior during brazing
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RESEARCH ARTICLE
Kirsten BOBZIN, Wolfgang WIETHEGER, Julian HEBING, Lidong ZHAO, Alexander SCHMIDT Riza ISKANDAR, Joachim MAYER
Influence of direct electric current on wetting behavior during brazing
© The Author(s) 2020. This article is published with open access at link.springer.com and journal.hep.com.cn
Abstract The wetting behavior of liquid metals is of great importance for many processes. For brazing, however, a targeted modification beyond the adjustment of conventional process parameters or the actual set-up was not possible in the past. Therefore, the effect of direct electric current along the surface of a steel substrate on the wetting behavior and the formation of the spreading pattern of an industrial nickel-based filler metal was investigated at a temperature above T = 1000 °C in a vacuum brazing furnace. By applying direct current up to I = 60 A the wetted surface area could be increased and the spreading of the molten filler metal could be controlled in dependence of the polarity of the electric current. The electric component of the Lorentz force is supposed to be feasible reasons for the observed dependence of the electrical polarity on the filler metal spreading direction. To evaluate the influence of the electric current on the phase formation subsequent selective electron microscope analyses of the spreading pattern were carried out. Keywords brazing, electric current assisted wetting, Lorentz force
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Introduction
The wetting behavior of metallic substrates by liquid metals is decisive for many technical manufacturing
Received November 25, 2019; accepted December 11, 2019 Kirsten BOBZIN, Wolfgang WIETHEGER, Julian HEBING, Lidong ZHAO, Alexander SCHMIDT ( ) Surface Engineering Institute (IOT), RWTH Aachen University, 52072 Aachen, Germany E-mail: [email protected]
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Riza ISKANDAR, Joachim MAYER Central Facility for Electron Microscopy, RWTH Aachen University, 52074 Aachen, Germany
processes. As an example, processes like welding, brazing, casting, thermal spraying and their many variations can be mentioned [1–4]. The conventional methods to influence the wetting behavior in such processes are either adjusting the process parameters like temperature of the liquid metal and the substrate, the use of fluxes, or modifying the chemical composition of the liquid metal by adding alloying elements. Another already established and often used method is the modification of the solid interface by applying wettable coatings via thermal spraying or physical vapor deposition technology [1,5,6]. Regarding technical production processes a remarkable approach is the application of electric current at the interface between the substrate and the liquid metal. This approach is based on the effect of electrowetting, which can be described as modifying the surface tension between a solid and a liquid phase due to electric current at the interface. By this the wetting angle can be improved. This effect is applied in a wide range of applications like microfluid transport, lab on a chip devices, electronic dis
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