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Crystal growth of high magnetostrictive polycrystalline Fe81Ga19 alloys
Journal of Magnetism and Magnetic Materials 324 (2012) 1177–1181
Contents lists available at SciVerse ScienceDirect
Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm
Crystal growth of high magnetostrictive polycrystalline Fe81Ga19 alloys Chuan Li, Jinghua Liu, Zhibin Wang, Chengbao Jiang n School of Materials Science and Engineering, Beihang University, Beijing 100191, China
a r t i c l e i n f o
abstract
Article history: Received 24 July 2011 Received in revised form 12 October 2011 Available online 12 November 2011
High magnetostrictive Fe81Ga19 alloy was prepared by induction heating zone melting method. The microstructure, solute partition behaviour, orientation evolution and magnetostriction are investigated. During the crystal growth process, the initial small grains gradually grow into large columnar crystals, and the solid–liquid interface shows slightly concave morphology. The equilibrium solute partition coefficient (k0), effective solute partition coefficient (ke) and solution diffusion coefficient (D) are calculated to be 0.74, 0.76 and 1.04 10 9 m2/s, respectively. In the steady growth stage, the composition distribution of the FeGa rod is uniform with average level about 18.50 at% Ga, which is close to the nominal composition. The deviation of the /001S orientation from the axial direction evolves from about 81 to 31 along the growth direction, and the corresponding magnetostriction increases from the initial 180 ppm to the final 305 ppm. Crown Copyright & 2011 Published by Elsevier B.V. All rights reserved.
Keywords: Directional solidification Compositional distribution FeGa alloys Crystallographic orientation Magnetostriction
1. Introduction FeGa alloys are a new type of magnetostrictive materials with high magnetostriction, low hysteresis, high tensile strength and good machinability [1–4]. These advantages make FeGa alloys promising in extensive applications such as sensors and actuators. It is known that the magnetostriction of FeGa alloys is sensitive to Ga content [5–11], and the magnetostriction of quenched FeGa single crystals can reach the maximum level at about 19 at% Ga [6]. The magnetostriction increases with Ga increasing when Ga is below 19 at%, which is attributed to an increase in the magneto-elastic coupling, resulting from the formation of shortrange Ga pairs along the /001S direction of A2 structure [12,13]. And the magnetostriction decreases with Ga increasing when Ga is between 19 and 23 at%, due to the A2þD03 phase mixture [12]. Therefore, controlling accurately composition is a key issue to obtain high magnetostriction in FeGa alloys. In addition, striking magneto-elastic anisotropy is found in FeGa alloys [10,14,15]. The magnetostriction of Fe81Ga19 alloys along the /001S crystallographic direction can reach the maximum about 320 ppm [14], and the magnetostrictions along the /110S and /111S directions are about 220 ppm [10] and 13 ppm [15], respectively. Accordingly, another key issue to obtain good magnetostrictive properties is controlling the formation of /001S crystallographic orientation during the crystal growth process. In this paper, the induction heating zone melting method is employed to prepare Fe81Ga19 /001S oriented crystals. /001S
n
Corresponding author. Tel.: þ86 10 82338780; fax: þ86 10 82338200. E-mail address: [email protected] (C. Jiang).
seed crystal of Fe81Ga19 is applied to encourage the growth along the /001S orientation. The basic solute partition behaviour, the orientation evolution and the change of the magnetostriction along the axis of the Fe81Ga19 grown crystal are investigated. And eventually, high magnetostrictive bulk polycrystalline Fe81Ga19 with uniform composition and /001S preferred orientation is achieved.
2. Experimental The Fe81Ga19 ingot was prepared by arc melting furnace using high purity elements (99.99% pure) under a protective argon atmosphere. The raw materials were re-melted 4 times in order to be homogenised, and then suction cast into the water chilled copper mould to form a rod with 7 mm diameter and about 80 mm length. The rough rod was put in an alumina crucible, and a Fe81Ga19 single crystal /001S oriented with 10 mm length was used as a seed. The oriented Fe81Ga19 was prepared by directional solidification using induction heating zone melting with liquid metal cooling. According to our previous work [16,17], the optimum magnetostriction up to 300 ppm could be obtained at low growth rate and decreases obviously with increasing the growth rate. Therefore, the growth rate of 10 mm/h was adopted. Finally, the rod was pulled into the liquid metal to keep the solid–liquid interface at the position of about 65 mm from the starting point. The axial magnetostrictions of as-grown Fe81Ga19 paralleled to external magnetic field were measured at different positions along the growth direction by resistance strain gauge, and the gauge size is 3 mm 2 mm. Then, the sample was cut into five parts (as shown in Fig. 1), and 2 mm thick slices at the
0304-8853/$ - see front matter Crown Copyright & 2011 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2011.11.004
1178
C. Li et al. / Journal of Magnetism and Magnetic Materials 324 (2012) 1177–1181
cross-section I, II and IV were obtained for the subsequent measurements. The microstructure and solid–liquid interface morphology were observed by optical microscopy. The composition distribution of the sample was determined by electron probe microanalysis (EPMA)
(JXA-8100) with a characteristic X-ray wave dispersive spectrum (WDS). A Rigaku D/max-RB X-ray diffractometer with Cu Ka radiation was employed to determine the crystallographic orientation of the cross-section I, II and IV.
3. Results and discussion 3.1. Microstructure and solid–liquid interface Fig. 2a shows the longitudinal microstructure of the as-grown Fe81Ga19 alloy, and the competitive growth of grains is observed along the growth direction from the initial to the end part. The seed crystal is partly melted during the growth processing, and only a few large columnar grains are observed in the initial part of about 5 mm, the binding site between the master rod and the seed can also be seen clearly. Above the binding site, i.e. the starting position of the master rod, several columnar grains are observed due to the structural heredity of the seed. With the crystal growth, large columnar grains form gradually, and finally only three main large columnar grains exist at the end part. The microstructure at the cross-section I (about 55 mm from the starting point) is shown in Fig. 2b. Due to the competitive growth, there are only three main grains remaining in the centre
Growth direction
Fig. 1. Schematic of the processed Fe81Ga19 rod for measuring.
Cast rod
Seed Fig. 2. Morphologies of grains along the growth direction (a), at cross-section I (b) and the solid–liquid interface (c).
Fig. 3. Ga content distribution at solid–liquid interface (a), and composition distribution of Fe81Ga19 rod along the growth direction (b).
C. Li et al. / Journal of Magnetism and Magnetic Materials 324 (2012) 1177–1181
and a few small grains distributing at the edge. The quenched solid–liquid interface shows slightly concave morphology as shown in Fig. 2c, which is advantageous to form large columnar grains along the growth direction.
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the interface till the liquid phase reaching about 23.40 at% ðC L Þ. The critical Ga content in the solid ðC nS Þ and liquid ðC nL Þ phases are about 18.02 at% and 24.28 at%, respectively. And the solute diffusion boundary layer thickness (dN) is about 55 mm. The equilibrium solute partition coefficient (k0) and the effective solute partition coefficient (ke) are defined as follows [18]:
3.2. Solute partition behaviour and composition distribution Fig. 3a shows the composition distribution near the solid– liquid interface, and solute partition behaviour of Ga content around the interface is studied. The average Ga content is about 17.89 at% in the solid phase, and then steeply increases crossing
k0 ¼
ke ¼
C nS C nL C nS CL
Fig. 4. Pole figures of Fe81Ga19 rod at cross-section I (a), II (b) and IV (c) ({200} at left and {110} at right).
ð1Þ
ð2Þ
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C. Li et al. / Journal of Magnetism and Magnetic Materials 324 (2012) 1177–1181
According to the results above, the values of k0 and ke are calculated to be 0.74 and 0.76, respectively, which shows k0 oke o1 and ke-k0. The result reveals that the composition should be relatively uniform and the composition gradient is gentle in the liquid phase, which is beneficial to control and obtain accurate composition of Fe81Ga19 alloys. In this work, due to magnetic induction heating, the convection in the molten liquid is dominated by the magnetic stirring. In addition, the solid–liquid interface morphology is planar. Therefore, the formula of the solute distribution proposed by Burton [19] et al. is adopted: ke ¼
C nS CL
¼
k0 k0 þð1k0 ÞexpððV=DÞdN Þ
ð3Þ
where D, V and dN represent the solute diffusion coefficient, growth rate and solute diffusion boundary layer thickness, respectively. By substituting the values above, the solute diffusion coefficient D in the liquid phase in front of the interface is calculated to be about 1.04 10 9 m2/s. The result of the composition distribution along the growth direction is shown in Fig. 3b. It is a Ga poor region in the initial unsteady stage, and the Ga content increases from about 16 at% to 21 at% along the growth direction till the location of about 16 mm. Then the crystal growth process reaches a steady stage from about 23 mm to 55 mm, and the Ga content reaches an average value of 18.50 at%. Due to subsequently by quenching, the Ga content decreases firstly, and then enriches sharply at the solid–liquid interface in the end part. The result illustrates that the Ga content close to the nominal composition is achieved in the steady growth stage. 3.3. Evolution of the preferred orientation The preferred orientation of Fe81Ga19 alloy is determined at different parts to investigate the evolution during the crystal growth process. The {200} and {110} pole figures of the crosssection I, II and IV are illustrated in Fig. 4, and the location of I, II and IV from the starting point are about 55 mm, 27 mm and 14 mm, respectively. The pole figure of the cross-section IV as shown in Fig. 4a illustrates /001S preferred orientation texture, and the deviation angle between /001S direction and the axial direction is about 81. The pole figure of the cross-section II is shown in Fig. 4b, it also shows /001S preferred orientation texture, and /001S direction deviates about 51 away from the axial direction. Fig. 4c shows the pole figure at cross-section I, and /001S preferred orientation texture with the deviation angle of about 31 is observed. The result demonstrates that the deviation angle of the /001S orientation from the axial direction evolves from 81 to 31 gradually along the growth direction. 3.4. Magnetostriction of the as-grown Fe81Ga19 alloy Magnetostriction curves along the growth direction are measured every 10 mm intervals from the starting point, which is shown in Fig. 5. The magnetostriction increases from 180 ppm at about 10 mm to 305 ppm at about 50 mm, and the saturation magnetic field strength is about 200 to 300 Oe. It can be classified into three stages according to the experimental results mentioned above. The first stage is in the initial 23 mm, it is an unsteady stage, large orientated columnar grains are not formed yet, the Ga content increases from about 16 at% to 21 at% along the growth direction, and the deviation angle of /001S orientation is about 81, therefore, the magnetostriction is only 180 ppm. The second stage is about 20 mm to 40 mm, with the crystal growth of Fe81Ga19 alloy, the Ga content is stable to be about 18.5 at%, large /001S orientated columnar grains form gradually, and the
Fig. 5. Magnetosriction curves of Fe81Ga19 alloy at different positions.
deviation angle of /001S orientation decreases to about 51, as a result, the magnetostriction increases remarkably to about 280 ppm. The magnetostriction performs best in the third stage (from about 40 mm to 55 mm), the crystal growth continues steadily, the deviation angle of /001S orientation decreases to the minimum about 31, and the magnetostriction maintains the maximum value about 305 ppm. The result reveals that, in the steady growth stage, the magnetostriction of Fe81Ga19 alloys is mainly influenced by the crystallographic orientation rather than the composition. And the magnetostriction of the orientated Fe81Ga19 alloy becomes higher, with the /001S direction being closer to the axial direction.
4. Conclusion 1. During the growth process of Fe81Ga19 alloy, the small grains gradually grow into large columnar grains and the solid–liquid interface exhibits slightly concave morphology. 2. The basic solute partition behaviour (k0 ¼0.74, ke ¼0.76 and ke-k0) is beneficial to control and obtain accurate composition of Fe81Ga19 alloys. And actually, the Ga content keeps an average value of 18.50 at% in the steady growth stage, which is close to the nominal original composition. 3. /001S oriented polycrystalline Fe81Ga19 is obtained by induction zone melting method at the growth rate of 10 mm/h, and the deviation angle of /001S orientation evolves from about 81 to 31 along the growth direction. 4. High magnetostrictive polycrystalline Fe81Ga19 up to 305 ppm is achieved, and the magnetostriction increases from the initial 180 ppm to the final 305 ppm, with the /001S direction being closer to the axial direction.
Acknowledgements This work is supported by National Natural Science Foundation of China (Grant nos. 50971008, 50925101, 50921003 and 91016006), and the Fundamental Research Funds for the Central Universities. References [1] A.E. Clark, J.B. Restorff, M. Wun-Fogle, T.A. Lograsso, D.L. Schlagel, IEEE Transactions on Magnetism 36 (2000) 3283.
C. Li et al. / Journal of Magnetism and Magnetic Materials 324 (2012) 1177–1181
[2] A.E. Clark, M. Wun-Fogle, J.B. Restorff, T.A. Lograsso, J.R. Cullen, IEEE Transactions on Magnetism 37 (2001) 2678. [3] T.A. Lograsso, A.R. Ross, D.L. Schlagel, A.E. Clark, M. Wun-Fogle, Journal of Alloys and Compounds 350 (2003) 95. [4] R.A. Kellogg, A.M. Russell, T.A. Lograsso, A.B. Flatau, A.E. Clark, M. Wun-Fogle, Acta Materialia 52 (2004) 5043. [5] Q. Xing, Y. Du, R.J. McQueeney, T.A. Lograsso, Acta Materialia 56 (2008) 4536. [6] A.E. Clark, K.B. Hathaway, M Wun-Fogle, J.B. Restorff, T.A. Lograsso, V.M. Keppens, G. Petculescu, R.A. Taylor, Journal of Applied Physics 93 (2003) 8621. ¨ [7] R. Grossinger, R.S. Turtelli, N. Mehmood, IEEE Transactions on Magnetism 44 (2008) 3001. [8] M. Wuttig, L. Dai, J. Cullen, Applied Physics Letters 80 (2002) 1135. [9] N. Srisukhumbowornchai, S. Guruswamy, Journal of Applied Physics 90 (2001) 5680. [10] E. Summers, T.A. Lograsso, J.D. Snodgrass, Smart Materials and Structures 5387 (2004) 448.
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[11] S. Guruswamy, N. Srisukhumbowornchai, A.E. Clark, J.B. Restorff, M. WunFogle, Scripta Materialia 43 (2000) 239. [12] Q. Xing, T.A. Lograsso, Scripta Materialia 65 (2011) 359. [13] H. Cao, P.M. Gehring, C.P. Devreugd, J.A. Rodriguez-Rivera, J. Li, D. Viehland, Physics Review Letters 102 (2009) 127201. [14] R.A. Kellogg, A.B. Flatau, A.E. Clark, M. Wun-Fogle, T.A. Lograsso, Journal of Applied Physics 91 (2002) 7821. [15] E.M. Summers, T.A. Lograsso, M. Wun-Fogle, Journal of Materials Science 42 (2007) 9582. [16] C.B. Jiang, J.H. Liu, F. Gao, H.B. Xu, Materials Science Forum 561 (2007) 1117. [17] C. Li, J.H. Liu, Z.B. Wang, C.B. Jiang, Material Science Engineering B (submitted for publication). [18] H.Z. Fu, J.J. Guo, L. Liu, J.S. Li, Directional Solidification and Processing of Advanced Materials, Science press, Beijing, 2008. [19] J.A. Burton, R.C. Prim, W.P. Slichter, Journal of Chemical Physics 21 (1953) 1987.
Contents lists available at SciVerse ScienceDirect
Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm
Crystal growth of high magnetostrictive polycrystalline Fe81Ga19 alloys Chuan Li, Jinghua Liu, Zhibin Wang, Chengbao Jiang n School of Materials Science and Engineering, Beihang University, Beijing 100191, China
a r t i c l e i n f o
abstract
Article history: Received 24 July 2011 Received in revised form 12 October 2011 Available online 12 November 2011
High magnetostrictive Fe81Ga19 alloy was prepared by induction heating zone melting method. The microstructure, solute partition behaviour, orientation evolution and magnetostriction are investigated. During the crystal growth process, the initial small grains gradually grow into large columnar crystals, and the solid–liquid interface shows slightly concave morphology. The equilibrium solute partition coefficient (k0), effective solute partition coefficient (ke) and solution diffusion coefficient (D) are calculated to be 0.74, 0.76 and 1.04 10 9 m2/s, respectively. In the steady growth stage, the composition distribution of the FeGa rod is uniform with average level about 18.50 at% Ga, which is close to the nominal composition. The deviation of the /001S orientation from the axial direction evolves from about 81 to 31 along the growth direction, and the corresponding magnetostriction increases from the initial 180 ppm to the final 305 ppm. Crown Copyright & 2011 Published by Elsevier B.V. All rights reserved.
Keywords: Directional solidification Compositional distribution FeGa alloys Crystallographic orientation Magnetostriction
1. Introduction FeGa alloys are a new type of magnetostrictive materials with high magnetostriction, low hysteresis, high tensile strength and good machinability [1–4]. These advantages make FeGa alloys promising in extensive applications such as sensors and actuators. It is known that the magnetostriction of FeGa alloys is sensitive to Ga content [5–11], and the magnetostriction of quenched FeGa single crystals can reach the maximum level at about 19 at% Ga [6]. The magnetostriction increases with Ga increasing when Ga is below 19 at%, which is attributed to an increase in the magneto-elastic coupling, resulting from the formation of shortrange Ga pairs along the /001S direction of A2 structure [12,13]. And the magnetostriction decreases with Ga increasing when Ga is between 19 and 23 at%, due to the A2þD03 phase mixture [12]. Therefore, controlling accurately composition is a key issue to obtain high magnetostriction in FeGa alloys. In addition, striking magneto-elastic anisotropy is found in FeGa alloys [10,14,15]. The magnetostriction of Fe81Ga19 alloys along the /001S crystallographic direction can reach the maximum about 320 ppm [14], and the magnetostrictions along the /110S and /111S directions are about 220 ppm [10] and 13 ppm [15], respectively. Accordingly, another key issue to obtain good magnetostrictive properties is controlling the formation of /001S crystallographic orientation during the crystal growth process. In this paper, the induction heating zone melting method is employed to prepare Fe81Ga19 /001S oriented crystals. /001S
n
Corresponding author. Tel.: þ86 10 82338780; fax: þ86 10 82338200. E-mail address: [email protected] (C. Jiang).
seed crystal of Fe81Ga19 is applied to encourage the growth along the /001S orientation. The basic solute partition behaviour, the orientation evolution and the change of the magnetostriction along the axis of the Fe81Ga19 grown crystal are investigated. And eventually, high magnetostrictive bulk polycrystalline Fe81Ga19 with uniform composition and /001S preferred orientation is achieved.
2. Experimental The Fe81Ga19 ingot was prepared by arc melting furnace using high purity elements (99.99% pure) under a protective argon atmosphere. The raw materials were re-melted 4 times in order to be homogenised, and then suction cast into the water chilled copper mould to form a rod with 7 mm diameter and about 80 mm length. The rough rod was put in an alumina crucible, and a Fe81Ga19 single crystal /001S oriented with 10 mm length was used as a seed. The oriented Fe81Ga19 was prepared by directional solidification using induction heating zone melting with liquid metal cooling. According to our previous work [16,17], the optimum magnetostriction up to 300 ppm could be obtained at low growth rate and decreases obviously with increasing the growth rate. Therefore, the growth rate of 10 mm/h was adopted. Finally, the rod was pulled into the liquid metal to keep the solid–liquid interface at the position of about 65 mm from the starting point. The axial magnetostrictions of as-grown Fe81Ga19 paralleled to external magnetic field were measured at different positions along the growth direction by resistance strain gauge, and the gauge size is 3 mm 2 mm. Then, the sample was cut into five parts (as shown in Fig. 1), and 2 mm thick slices at the
0304-8853/$ - see front matter Crown Copyright & 2011 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2011.11.004
1178
C. Li et al. / Journal of Magnetism and Magnetic Materials 324 (2012) 1177–1181
cross-section I, II and IV were obtained for the subsequent measurements. The microstructure and solid–liquid interface morphology were observed by optical microscopy. The composition distribution of the sample was determined by electron probe microanalysis (EPMA)
(JXA-8100) with a characteristic X-ray wave dispersive spectrum (WDS). A Rigaku D/max-RB X-ray diffractometer with Cu Ka radiation was employed to determine the crystallographic orientation of the cross-section I, II and IV.
3. Results and discussion 3.1. Microstructure and solid–liquid interface Fig. 2a shows the longitudinal microstructure of the as-grown Fe81Ga19 alloy, and the competitive growth of grains is observed along the growth direction from the initial to the end part. The seed crystal is partly melted during the growth processing, and only a few large columnar grains are observed in the initial part of about 5 mm, the binding site between the master rod and the seed can also be seen clearly. Above the binding site, i.e. the starting position of the master rod, several columnar grains are observed due to the structural heredity of the seed. With the crystal growth, large columnar grains form gradually, and finally only three main large columnar grains exist at the end part. The microstructure at the cross-section I (about 55 mm from the starting point) is shown in Fig. 2b. Due to the competitive growth, there are only three main grains remaining in the centre
Growth direction
Fig. 1. Schematic of the processed Fe81Ga19 rod for measuring.
Cast rod
Seed Fig. 2. Morphologies of grains along the growth direction (a), at cross-section I (b) and the solid–liquid interface (c).
Fig. 3. Ga content distribution at solid–liquid interface (a), and composition distribution of Fe81Ga19 rod along the growth direction (b).
C. Li et al. / Journal of Magnetism and Magnetic Materials 324 (2012) 1177–1181
and a few small grains distributing at the edge. The quenched solid–liquid interface shows slightly concave morphology as shown in Fig. 2c, which is advantageous to form large columnar grains along the growth direction.
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the interface till the liquid phase reaching about 23.40 at% ðC L Þ. The critical Ga content in the solid ðC nS Þ and liquid ðC nL Þ phases are about 18.02 at% and 24.28 at%, respectively. And the solute diffusion boundary layer thickness (dN) is about 55 mm. The equilibrium solute partition coefficient (k0) and the effective solute partition coefficient (ke) are defined as follows [18]:
3.2. Solute partition behaviour and composition distribution Fig. 3a shows the composition distribution near the solid– liquid interface, and solute partition behaviour of Ga content around the interface is studied. The average Ga content is about 17.89 at% in the solid phase, and then steeply increases crossing
k0 ¼
ke ¼
C nS C nL C nS CL
Fig. 4. Pole figures of Fe81Ga19 rod at cross-section I (a), II (b) and IV (c) ({200} at left and {110} at right).
ð1Þ
ð2Þ
1180
C. Li et al. / Journal of Magnetism and Magnetic Materials 324 (2012) 1177–1181
According to the results above, the values of k0 and ke are calculated to be 0.74 and 0.76, respectively, which shows k0 oke o1 and ke-k0. The result reveals that the composition should be relatively uniform and the composition gradient is gentle in the liquid phase, which is beneficial to control and obtain accurate composition of Fe81Ga19 alloys. In this work, due to magnetic induction heating, the convection in the molten liquid is dominated by the magnetic stirring. In addition, the solid–liquid interface morphology is planar. Therefore, the formula of the solute distribution proposed by Burton [19] et al. is adopted: ke ¼
C nS CL
¼
k0 k0 þð1k0 ÞexpððV=DÞdN Þ
ð3Þ
where D, V and dN represent the solute diffusion coefficient, growth rate and solute diffusion boundary layer thickness, respectively. By substituting the values above, the solute diffusion coefficient D in the liquid phase in front of the interface is calculated to be about 1.04 10 9 m2/s. The result of the composition distribution along the growth direction is shown in Fig. 3b. It is a Ga poor region in the initial unsteady stage, and the Ga content increases from about 16 at% to 21 at% along the growth direction till the location of about 16 mm. Then the crystal growth process reaches a steady stage from about 23 mm to 55 mm, and the Ga content reaches an average value of 18.50 at%. Due to subsequently by quenching, the Ga content decreases firstly, and then enriches sharply at the solid–liquid interface in the end part. The result illustrates that the Ga content close to the nominal composition is achieved in the steady growth stage. 3.3. Evolution of the preferred orientation The preferred orientation of Fe81Ga19 alloy is determined at different parts to investigate the evolution during the crystal growth process. The {200} and {110} pole figures of the crosssection I, II and IV are illustrated in Fig. 4, and the location of I, II and IV from the starting point are about 55 mm, 27 mm and 14 mm, respectively. The pole figure of the cross-section IV as shown in Fig. 4a illustrates /001S preferred orientation texture, and the deviation angle between /001S direction and the axial direction is about 81. The pole figure of the cross-section II is shown in Fig. 4b, it also shows /001S preferred orientation texture, and /001S direction deviates about 51 away from the axial direction. Fig. 4c shows the pole figure at cross-section I, and /001S preferred orientation texture with the deviation angle of about 31 is observed. The result demonstrates that the deviation angle of the /001S orientation from the axial direction evolves from 81 to 31 gradually along the growth direction. 3.4. Magnetostriction of the as-grown Fe81Ga19 alloy Magnetostriction curves along the growth direction are measured every 10 mm intervals from the starting point, which is shown in Fig. 5. The magnetostriction increases from 180 ppm at about 10 mm to 305 ppm at about 50 mm, and the saturation magnetic field strength is about 200 to 300 Oe. It can be classified into three stages according to the experimental results mentioned above. The first stage is in the initial 23 mm, it is an unsteady stage, large orientated columnar grains are not formed yet, the Ga content increases from about 16 at% to 21 at% along the growth direction, and the deviation angle of /001S orientation is about 81, therefore, the magnetostriction is only 180 ppm. The second stage is about 20 mm to 40 mm, with the crystal growth of Fe81Ga19 alloy, the Ga content is stable to be about 18.5 at%, large /001S orientated columnar grains form gradually, and the
Fig. 5. Magnetosriction curves of Fe81Ga19 alloy at different positions.
deviation angle of /001S orientation decreases to about 51, as a result, the magnetostriction increases remarkably to about 280 ppm. The magnetostriction performs best in the third stage (from about 40 mm to 55 mm), the crystal growth continues steadily, the deviation angle of /001S orientation decreases to the minimum about 31, and the magnetostriction maintains the maximum value about 305 ppm. The result reveals that, in the steady growth stage, the magnetostriction of Fe81Ga19 alloys is mainly influenced by the crystallographic orientation rather than the composition. And the magnetostriction of the orientated Fe81Ga19 alloy becomes higher, with the /001S direction being closer to the axial direction.
4. Conclusion 1. During the growth process of Fe81Ga19 alloy, the small grains gradually grow into large columnar grains and the solid–liquid interface exhibits slightly concave morphology. 2. The basic solute partition behaviour (k0 ¼0.74, ke ¼0.76 and ke-k0) is beneficial to control and obtain accurate composition of Fe81Ga19 alloys. And actually, the Ga content keeps an average value of 18.50 at% in the steady growth stage, which is close to the nominal original composition. 3. /001S oriented polycrystalline Fe81Ga19 is obtained by induction zone melting method at the growth rate of 10 mm/h, and the deviation angle of /001S orientation evolves from about 81 to 31 along the growth direction. 4. High magnetostrictive polycrystalline Fe81Ga19 up to 305 ppm is achieved, and the magnetostriction increases from the initial 180 ppm to the final 305 ppm, with the /001S direction being closer to the axial direction.
Acknowledgements This work is supported by National Natural Science Foundation of China (Grant nos. 50971008, 50925101, 50921003 and 91016006), and the Fundamental Research Funds for the Central Universities. References [1] A.E. Clark, J.B. Restorff, M. Wun-Fogle, T.A. Lograsso, D.L. Schlagel, IEEE Transactions on Magnetism 36 (2000) 3283.
C. Li et al. / Journal of Magnetism and Magnetic Materials 324 (2012) 1177–1181
[2] A.E. Clark, M. Wun-Fogle, J.B. Restorff, T.A. Lograsso, J.R. Cullen, IEEE Transactions on Magnetism 37 (2001) 2678. [3] T.A. Lograsso, A.R. Ross, D.L. Schlagel, A.E. Clark, M. Wun-Fogle, Journal of Alloys and Compounds 350 (2003) 95. [4] R.A. Kellogg, A.M. Russell, T.A. Lograsso, A.B. Flatau, A.E. Clark, M. Wun-Fogle, Acta Materialia 52 (2004) 5043. [5] Q. Xing, Y. Du, R.J. McQueeney, T.A. Lograsso, Acta Materialia 56 (2008) 4536. [6] A.E. Clark, K.B. Hathaway, M Wun-Fogle, J.B. Restorff, T.A. Lograsso, V.M. Keppens, G. Petculescu, R.A. Taylor, Journal of Applied Physics 93 (2003) 8621. ¨ [7] R. Grossinger, R.S. Turtelli, N. Mehmood, IEEE Transactions on Magnetism 44 (2008) 3001. [8] M. Wuttig, L. Dai, J. Cullen, Applied Physics Letters 80 (2002) 1135. [9] N. Srisukhumbowornchai, S. Guruswamy, Journal of Applied Physics 90 (2001) 5680. [10] E. Summers, T.A. Lograsso, J.D. Snodgrass, Smart Materials and Structures 5387 (2004) 448.
1181
[11] S. Guruswamy, N. Srisukhumbowornchai, A.E. Clark, J.B. Restorff, M. WunFogle, Scripta Materialia 43 (2000) 239. [12] Q. Xing, T.A. Lograsso, Scripta Materialia 65 (2011) 359. [13] H. Cao, P.M. Gehring, C.P. Devreugd, J.A. Rodriguez-Rivera, J. Li, D. Viehland, Physics Review Letters 102 (2009) 127201. [14] R.A. Kellogg, A.B. Flatau, A.E. Clark, M. Wun-Fogle, T.A. Lograsso, Journal of Applied Physics 91 (2002) 7821. [15] E.M. Summers, T.A. Lograsso, M. Wun-Fogle, Journal of Materials Science 42 (2007) 9582. [16] C.B. Jiang, J.H. Liu, F. Gao, H.B. Xu, Materials Science Forum 561 (2007) 1117. [17] C. Li, J.H. Liu, Z.B. Wang, C.B. Jiang, Material Science Engineering B (submitted for publication). [18] H.Z. Fu, J.J. Guo, L. Liu, J.S. Li, Directional Solidification and Processing of Advanced Materials, Science press, Beijing, 2008. [19] J.A. Burton, R.C. Prim, W.P. Slichter, Journal of Chemical Physics 21 (1953) 1987.