Effect of Static Magnetic Field on Recalescence and Surface Velocity Field in Electromagnetically Levitated Molten CuCo
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INCE the binary CuCo system exhibits a metastable miscibility gap in the undercooled state, the homogeneous melt separates into two liquid phases, i.e., Co-rich and Cu-rich phases, once the melt is undercooled below the binodal temperature in this system. The structures formed by such phase separation are commonly determined by the compositions of the two metallic elements, the cooling rate, and the degree of undercooling. Therefore, CuCo alloys with such controlled phase separation structures have attracted attention not only as suitable materials in the fields of electrical and
TSUBASA KITAHARA, Engineer, is with The Yokohama Rubber Co., Ltd., Tokyo, Japan. KOKI TANADA and SHOYA UENO, Students, MASAKI KUBO, Associate Professor, and TAKAO TSUKADA, Professor, are with the Department of Chemical Engineering, Tohoku University, 6-6-07 Aramaki, Aoba-ku, Sendai 980-8579, Japan. Contact e-mail: [email protected] KEN-ICHI SUGIOKA, Associate Professor, is with the Department of Mechanical Systems Engineering, Toyama Prefectural University, Imizu, Toyama 939-0398, Japan. MASAHITO UCHIKOSHI, Assistant Professor, and HIROYUKI FUKUYAMA, Professor, are with the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan. Manuscript submitted June 19, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
magnetic materials, but also as model materials for investigating the kinetics of liquid phase separation.[1–6] In addition to the compositions, cooling rate, and degree of undercooling, the convection in molten CuCo alloys also strongly affects the phase separation structures. The effect of melt convection on the phase separation structures in an electromagnetically levitated molten CuCo droplet in the undercooled state has recently been investigated,[7–10] where the electromagnetic force drives magnetohydrodynamic (MHD) convection in the levitated droplet, in addition to buoyancy convection and Marangoni convection due to thermal inhomogeneity. Kolbe and Gao,[7] Zhang et al.,[8] Gao et al.,[9] and Zhang et al. [10] have performed solidification experiments on an undercooled molten CuCo droplet electromagnetically levitated in a microgravity environment or a static magnetic field. In either environment, the flow velocities in the droplet should be much lower than those without the static magnetic field on the ground. These studies suggested that the flow pattern and its intensity in a levitated droplet affect the phase separation structures of undercooled CuCo alloys. We have also studied the effect of melt convection on phase separation structures in undercooled Cu80Co20 (hereafter referred to as CuCo) alloy using an electromagnetic levitator on which a static magnetic field was imposed.[11] It was revealed that, for a relatively small magnetic field, dispersed structures with relatively fine
Co-rich spheres distributed in the matrix of the Cu-rich phase were observed, while a few large, coalesced Co-rich phases appeared in the Cu-rich matrix above a magnetic
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