Effect of Solidification Texture on the Magnetostrictive Behavior of Galfenol
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Fe-Ga binary alloys are known as a class of smart magnetostrictive materials for mechanically robust actuators and sensor applications.[1,2] These alloys are referred to as ‘‘galfenol.’’ Typical galfenol contains 13 wt pct to 23 wt pct Ga[3] and is a random substitutional solid solution of Fe-Ga possessing body-centered cubic (bcc) crystal symmetry.[4] Single crystals of galfenol exhibit large magnetostrictions approaching 400 ppm at room temperature.[5] Given the disadvantages in preparation of single-crystal material, polycrystalline alloys are preferentially textured by proper methods such as directional solidification, rolling, etc.[6] To improve the potential for improved mechanical robustness in a cost-effective manner, directional solidification is introduced as an efficient and beneficial approach for producing anisotropic materials. It has been reported that crystallographic texture created by directional solidification improves the magnetostrictive behavior remarkably.[7] Directional solidification alters grain boundary arrangement as well, where grain boundary and grain size have mutual effects and are troublesome parameters for magnetostrictive property of these alloys. On the one hand, the finer the grain sizes, the better the mechanical characteristics.[6] On the other hand, grain boundaries may deteriorate the ALI AKBAR EMDADI, Self-funded Researcher, and SYAMAK HOSSEIN NEDJAD, Associate Professor, are with the Faculty of Materials Engineering, Sahand University of Technology, P.O. Box 51335-1996, Tabriz, Iran. Contact e-mail: [email protected] HABIB BADRI GHAVIFEKR, Assistant Professor, is with the Faculty of Electrical Engineering, Sahand University of Technology. Manuscript submitted June 26, 2013. Article published online October 16, 2013 906—VOLUME 45A, FEBRUARY 2014
magnetostrictive performance because of their tendency to impede magnetic domain wall motion.[8–10] In an effort to optimize the magnetostrictive performance of polycrystalline Fe82.4Ga17.6, the authors were motivated to create a preferred crystallographic texture in the material using the directional solidification technique. Studies of the effect of different cooling rates on the magnetostriction of heat-treated galfenol and the magnetic domain structures by magnetic force microscopy (MFM) in those alloys have been reported previously.[11,12] But no report on the effect of solidification texture on the magnetostriction and also on the magnetic domain structures of directionally solidified as-cast galfenol samples has been published. The current work focuses on the influence of the solidification texture on the magnetostrictive behavior of a polycrystalline Fe82.4Ga17.6 alloy. In addition, configurations of the magnetic domain structures in the solidification structure are demonstrated.
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EXPERIMENTAL PROCEDURE
Polycrystalline galfenol with a nominal composition Fe80Ga20 (in at pct) was prepared using appropriate quantities of Fe (commercial purity) and Ga (99.999 pct purity) by button arc melting under the protection of inert argon gas
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