Magnetostriction and Crystallographic Texture in Rolled and Annealed Fe-Ga Based Alloys
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Magnetostriction and Crystallographic Texture in Rolled and Annealed Fe-Ga Based Alloys Suok-Min Na and Alison B. Flatau Dept. of Aerospace Engineering, University of Maryland, College Park, MD 20742, U.S.A. ABSTRACT Results that demonstrate the selective development of {100} preferred texture in polycrystalline Fe81.3Ga18.7 plus B (0.5~1.0 at.%) and S (~0.05 at.%) alloys using a conventional rolling and annealing processes are presented in this work. We found that boron improved ductility by enhancing grain boundary cohesion during rolling and sulfur played an important role in controlling the surface energy and formation of the selective growth of {100} grains during annealing. The as-rolled (Fe81.3Ga18.7)+0.5 at.%B+0.005 at.%S sheet had some {100} and near {111} texture corresponding to α-fiber texture parallel to the rolling direction. The near {100} sheet texture was formed in sheet that was annealed at 1200oC for 2h (198 ppm), while the texture of sheet annealed at 1100oC for 4h (165 ppm) was closer to {110}. The maximum observed magnetostriction of 220 ppm was obtained as a result of a double annealed, first at 1000oC for 6h and then at 1200oC for 1h, with the resultant texture closer to the ideal {100} than the less desirable {100}.
INTRODUCTION Fe-Ga alloys have the possibility of being useful in magnetostrictive actuators and sensors due to their large saturation magnetostriction potential (~400 ppm) in low applied fields (~200 Oe), high mechanical strength, and good ductility [1]. Motivation for this study arises from the potential for textured polycrystalline Fe-Ga alloys to provide enhanced mechanical properties and lower cost than single crystal with magnetostrictive strain capabilities that are not significantly reduced. It was recently reported that texture annealing of the Fe85Ga15 alloy with 1 mol% NbC at 1150oC for 2h changed the texture from a strong as-rolled {hkl} texture to a predominant texture that was close to {100} and the anneal at 1150oC for 24 h and 1300oC produced a [001] or near-[001] preferred orientation along the rolling direction [2], however the study did not report values of magnetostriction. It has been also suggested that the ideal recrystallized texture can be governed by the interfacial segregation of sulfur which is contained in the bulk interior, due to facilitating the control of sulfur, rather than by the adsorption using H2S gas [3-5]. Building on results from studies on the selective development of “Goss texture” {110} and “Cube texture”{100} in Fe-Si alloys, an α-iron alloy that is similar to Fe-Ga, results are presented on the introduction of sulfur additions to Fe-Ga arc-melted, as-rolled and texture annealed specimens. Measured magnetostriction results that vary with final annealing time, temperature, and atmosphere are also presented and correlated to changes in texture.
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The raw materials for (Fe81.3Ga18.7)+0.5 at.%B+0.005 at.%S and (Fe81.3Ga18.7)+1.0 at.%B+0.05 at.%S alloy buttons weighing roughly 50 grams ea
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