Motion of Solid Grains During Magnetic Field-Assisted Directional Solidification
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Motion of Solid Grains During Magnetic FieldAssisted Directional Solidification JIANG WANG, XIN LIN, YVES FAUTRELLE, HENRI NGUYEN-THI, and ZHONGMING REN In this paper, we report the visible evidence for thermoelectric magnetic forces (TEMFs) during magnetic field-assisted directional solidification, and their potential to control the motion of solid grains(dendrite fragments or equiaxed grains). These motions are observed by means of synchrotron X-ray radiography and compared with analytic calculations for a spherical particle’s motion driven only by TEMFs, which confirms that the observed solid grain motions are the combined result of the TEMFs and gravity. We also carried out corresponding 3D numerical simulations to validate the calculations and further prove our conclusion that TEMF acts on the solid grain and affects its motion trajectory. https://doi.org/10.1007/s11663-018-1199-6 The Minerals, Metals & Materials Society and ASM International 2018
I.
INTRODUCTION
MAGNETIC field can influence the flow of a conducting liquid without direct contact in accordance with the theory of magnetohydrodynamics, therefore applying magnetic fields to control flows in the melt during solidification of metals has gained increasing attention over the last half a century.[1] Although extensive experimental and theoretical studies[2,3] have yielded widely accepted conclusions that applying static magnetic fields to solidification processes can shift the liquid-to-solid phase-transformation temperature,[4] align crystal/grain orientation,[5] redistribute the solute,[6] primary phase or inclusion[7] and damp flows in the melt,[8,9] our understanding of magnetic field-assisted solidification is still far from complete. For instance, contrary to damping the melt flows, Shercliff[10] pointed out that applying a static magnetic field can also induce flows in the melt by interacting with thermoelectric currents at the vicinity of the solid–liquid interface during solidification. Such flows, named thermoelectric magnetohydrodynamic flows (TEMHDFs), have been extensively studied in the context of pumping
JIANG WANG and ZHONGMING REN are with the State Key Laboratory of Advanced Special Steel, Shanghai University, 200072 Shanghai, P.R. China. Contact e-mail: [email protected] YVES FAUTRELLE is with the SIMAP/EPM, 1130 rue de la Piscine BP 75 ENSEEG, 38402 St-Martin d Heres, France. HENRI NGUYEN-THI is with the Aix Marseille University, Campus Saint-Jerome, Case 142, 13397 Marseille Cedex 20, France. XIN LIN is with the State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, P.R. China. Manuscript submitted August 22, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
or stirring liquid metal coolants in nuclear reactors.[11] Research on the role of TEMHDFs in solidification process began shortly after Shercliff’s study, because it had been already known[12] that thermoelectric currents inherently exist at the solid–liquid interface. Initially in crystal growth[13] and secondly in solidification of metals,[
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