Motion of Crystal Particles by the Electromagnetic Vibrations in Mg-Cu-Y Bulk Metallic Glasses
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INTRODUCTION
DIFFERENT combinations of stationary or alternating electric and magnetic fields have been used for a wide range of purposes, including stirring, shaping, etc.[1] Among these combinations, it was reported that electromagnetic vibrations induced by the interaction between alternating electric and stationary magnetic fields can act as a powerful vibrating force in melts and affect microstructural refinements in the usual crystalline alloys.[2–11] The simultaneous imposition of a stationary magnetic field with a magnetic flux density B and an alternating electric field with a current density J and a frequency f on a conducting liquid results in the induction of a vibrating electromagnetic body force with a density of F = J · B inside the liquid. This force, which has a frequency equal to that of the applied electric field, vibrates in a direction perpendicular to the plane of the two fields and results in vibrational motion of the conducting liquid. The present authors reported that a new method for producing Mg-Cu-Y bulk metallic glasses using electromagnetic vibrations is effective in forming the metallic glass phase, and that disappearance or decrement of clusters by the electromagnetic vibrations applied to the liquid state is considered to cause suppression of crystal TAKUYA TAMURA and NAOKI OMURA, Researchers, YUUKI MAEHARA, Post-doctoral Researcher, and KENJI MIWA, Principal Research Scientist, are with the Solidification Processing Group, Materials Research Institute for Sustainable Development, National Institute of Advanced Industrial Science and Technology (AIST), Nagoya 463-8560, Japan. Contact e-mail: takuya-tamura@ aist.go.jp This article is based on a presentation given in the symposium entitled ‘‘Bulk Metallic Glasses IV,’’ which occurred February 25– March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee. Article published online April 1, 2008 METALLURGICAL AND MATERIALS TRANSACTIONS A
nucleation.[12–14] Moreover, the present authors reported that the glass-forming ability of Fe-Co-B-Si-Nb alloys also increases with increasing intensity of electromagnetic vibrations. The effects of the electromagnetic vibrations were found to be twofold. The first effect was the decrease in the number of crystal nuclei. The second effect was the increase in the cooling rate. However, this increase in the cooling rate disappears with electromagnetic vibrational frequencies of more than 10 kHz.[15–17] It was found that the absence of macroscopic stirring resulted in the disappearance of the increase in the cooling rate because of the nanometer-sized amplitudes at higher frequencies. When particles in the liquid metal have lower electric resistance than the liquid metal, these particles are considered to vibrate vigorously in the liquid metal by Lorentz force, because the electric current concentrates in those. It was suggested that this phenomenon is the reason electromagnetic vibrations decrease the number of crystal nuclei, because
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