Investigation and Analytical Description of Acoustic Production by Magneto-Acoustic Mixing Technology
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INTRODUCTION
WITH increased demands for high-performance materials, there is a need for new fabrication methods that can create microstructures optimizing unique structure–property relationships.[1] Both magnetic and acoustic treatments of metals are gaining industrial relevance, as evidenced by the European Union-sponsored ExoMet Project that aims to improve the use of external fields in materials processing.[2–4] Processing materials under high magnetic fields have been shown to alter particle orientation and dispersion,[5,6] change solidification microtexture,[7,8] and modify microstructure and solute distribution through damped convection.[9–11] Acoustic processing, on the other hand, has been shown to improve reactivity,[12,13] disperse nanoparticles,[14–16] and refine solidification microstructures.[17,18] This work focuses on Magneto-Acoustic Mixing Technology (MAMT), which has the potential to effect material structures through the simultaneous application and coupling of magnetic and induction fields to produce strong, yet, controlled acoustic waves in a melt.[19,20] Full utilization of the technology requires a fundamental understanding of inherent, operant mechanisms and associated interactions, as well as careful design of system components. This work provides a fundamental understanding of the underlying physics that control the HUNTER B. HENDERSON, Postdoctoral Associate, and MICHELE V. MANUEL, Associate Professor, are with the Department of Materials Science and Engineering, University of Florida, 100 Rhines Hall, P.O. Box 116400, Gainesville, FL 32611. Contact e-mail: [email protected]fl.edu ORLANDO RIOS, Associate Research Staff, is with the Deposition Sciences Group, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN, and also Adjunct Professor, with the Department of Materials Science and Engineering, University of Tennessee, Oak Ridge National Laboratory. GERARD M. LUDTKA, Distinguished R&D Staff, is with the Materials Science & Technology Division, Oak Ridge National Laboratory. Manuscript submitted May 4, 2014. Article published online May 7, 2015. 2020—VOLUME 46B, OCTOBER 2015
performance of the system and the materials that are processed by it. The key components of an MAMT system are the presence of a strong static magnetic field and an induction coil assembly. When combined in an orthogonal geometry, this system provides both heating and acoustic power to a metallic melt housed in an internal crucible. An illustration is shown in Figure 1(a). The induction system induces electric eddy currents in the liquid metal and crucible. These currents (blue) increase the temperature by Joule heating, a primary mechanism of induction heating.[21] Additionally, these eddy currents couple with the static magnetic field (red) to produce an alternating Lorentz force (green) that displaces the liquid, generating acoustic waves at the induction frequency. If the system is configured in a cylindrical configuration, the acoustic waves propagate in a radial direction in the crucible wall and sample. Photographs
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