Microstructure and Magnetostriction of Rapidly-solidified Fe-Ga System Alloy
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D12.4.1
Microstructure and Magnetostriction of Rapidly-solidified Fe-Ga System Alloy Teiko Okazaki1, Yasubumi Furuya1, Chihiro Saito1, Takashi Matsuzaki2, Tadao Watanabe2, and Manfred Wuttig3 1 Faculty of Science and Technology, Hirosaki University, Hirosaki 036-8651, Japan 2 Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan 3 Department of Materials and Nuculear Engineering, University of Maryland, College Park, MD 20742-2115, USA ABSTRACT Rapid-solidification method was applied to make Fe-15at%Ga and Fe-17at%Ga ribbons of 100 µm thickness. These ribbons have large magnetostriction of 270 ppm, where the coercive force exhibits a maximum value. The phenomenon is related to special metallic texture, that is, the ribbon has strongly [001]-oriented textured fine columnar microstructure with grain size of 2~5 µm. The ribbon has little-hysteresis loop of magnetostriction and a good ductility (i.e., full bending is possible). Rapid-solidified Fe-Ga alloy has a promising possibility as a new magnetic-induced sensor/actuator material. INTRODUCTION Inexpensive magnetostrictive materials which exhibit reversible strains for applied magnetic field are demanded for sensor /actuators. Terfenol-D [1] and ferromagnetic shape memory alloys [2,3] have large magnetostriction. Clark et al. demonstrated that a large magnetostriction of 300 ppm (10-6) in Fe-17at%Ga single crystal [4] and of 271 ppm in polycrystalline Fe-27.5at%Ga rods [5] occur at room temperature. However, many of those materials are brittle polycrystals or expensive single crystals. Furthermore, the shape of rod type has a limit in applicability owing to the loss caused by eddy current. In our previous study [6,7], we showed that polycrystalline Fe-29.6at%Pd ribbons prepared by rapid-solidification melt-spinning method with simple, one processing technique have fine columnar microstructure with strong [100]-oriented texture and exhibit giant magnetostriction of 1000-1800 ppm with good shape memory effect. Recently, the melt-spinning method was applied to Fe-Ga alloy system[8,9]. In this study, we analyze the texture of rapidly solidified Fe1-xGax (x=0.137, 0.151, 0.173) ribbons by using XRD and SEM-EBSP/OIM. The short-annealed ribbon has a strong [001]-oriented texture which induces magnetic anisotropy and large magnetostriction.
D12.4.2
EXPERIMENT METHOD (a)
(b)
Ar Gas
Quartz Nozzle
Work Coil
Ribbon
High-speed Roller
(c) Thickness Direction
Molten Metal
15 μm
Figure 1. (a) Schematic diagram of melt-spinning single roll method, (b) ribbon and (c) laser microscope cross-section image for ribbon.
Ingots of three kinds of composition, Fe-13.7at%Ga, Fe-15.1at%Ga and Fe-17.3at%Ga were prepared from electrolytic iron (4N) and gallium (5N) by using arc-melting method in Ar atmosphere. They were annealed at 1173 K for 24 hours in order to make the alloys homogeneous. The ribbon samples of about 100µm in thickness were produced from these ingots by using original designed melt-spinning apparatus with iron single roll in Ar atmosphere, as
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