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Soft magnetic Fe–Co–Zr–W–B bulk glassy alloys
Journal of Alloys and Compounds 423 (2006) 96–98
Soft magnetic Fe–Co–Zr–W–B bulk glassy alloys Piotr Pawlik ∗ Institute of Physics, Cz˛estochowa University of Technology, Al. Armii Krajowej 19, 42-200 Cz˛estochowa, Poland Available online 31 January 2006
Abstract Suction-cast rod samples of the diameters 1 and 2 mm, thin walled tubes of the outer diameters 2, 3 and 4 mm and the melt-spun ribbon samples of various thicknesses up to 350 m were produced for Fe61 Co10+x Zr5 W4−x B20 (x = 0, 2, 3) alloys. XRD analysis revealed fully amorphous structure of the ribbon samples up to the thickness of 220 m for the x = 0 alloy. Those results indicate its good glass forming ability (GFA). The suctioncasting process allowed to produce the bulk glassy samples by die-casting to the copper mould. X-ray diffractometry and M¨ossbauer spectroscopy revealed, that for the Fe61 Co10 Zr5 W4 B20 alloy, up to a diameter of 2 mm rod samples and up to 4 mm outer diameter thin walled tubes, were also fully amorphous. Furthermore, studies of the influence of W contents on the microstructure and glass forming abilities are discussed. © 2005 Elsevier B.V. All rights reserved. Keywords: Metallic glasses; Magnetically ordered materials; Rapid-solidification; Magnetic measurements; M¨ossbauer spectroscopy
1. Introduction
2. Samples preparation and investigation methods
Iron-based bulk glassy alloys are of great interests for their soft magnetic properties and potential magnetic applications. It was reported for the Fe61 Co7 Zr10 Mo5 W2 B15 alloy, that the maximum diameter of fully amorphous rods reaches ∼6 mm [1]. However, prospective applications of this alloy are limited, due to its low Curie temperature TC of ∼300 K, being the result of the large fractions of metalloid and refractory metal elements [2]. Much higher TC were reported for Fe–Ga–Cr–Mo–P–B–C-type alloys, but the maximum diameter of fully amorphous rods for these alloys was limited to 1 mm [3]. The novel bulk glassy Fe61 Co10 Zr5 W4 B20 alloy, with relatively large Js of ∼0.8 T, J Hc ∼ 2 A/m and good glass forming abilities allowing to process 1 mm diameter rods and up to 4 mm outer diameter (o.d.) thin walled tubes, was reported in [4]. Although tungsten atoms have beneficial impact on the GFA of the alloy, they also have a detrimental influence on the Curie temperature TC and the magnetization polarization Js . The aim of this work was to investigate the influence of W substitution by Co on the glass forming abilities for novel Fe61 Co10+x Zr5 W4−x B20 (x = 0, 2, 3) alloys. Such substitution results in the improvement of Js and TC with the decrease of W contents. Furthermore, changes of the thermal stability parameters with the W contents were studied.
Samples of Fe61 Co10+x Zr5 W4−x B20 (x = 0, 2, 3) alloys were produced by arc-melting under an argon atmosphere, the high purity Fe, Co, W and Zr elements and pre-alloyed Fe–B of known composition. The ribbon samples of various thicknesses up to 350 m were produced by controlled atmosphere melt-spinning, varying the speed of the copper roll. Rod and tube samples of various diameters were produced by suction-casting of the melt into a split copper die, using an argon pressure difference between the chambers integrated within the arc-melting unit. X-ray diffractometry (with Co K␣ radiation) and M¨ossbauer spectroscopy were used for the assessment of microstructure of the ribbon and rod samples. Magnetic properties of the rod samples were measured by LakeShore VSM magnetometer operating in an external magnetic fields up to 2 T. The thermal stability parameters (crystallization temperature Tx and melting temperature Tm ), were determined from the DTA traces. Furthermore the DSC calorimetry was used to determine more accurately the glass transition temperature Tg for particular alloy. The reduced glass transition temperatures Trg = Tg /Tm for investigated alloys were also calculated.
∗
Tel.: +48 34 32 50 795; fax: +48 34 32 50 795. E-mail address: [email protected].
0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2005.12.031
3. Results and discussion Examples of SEM secondary electron micrographs for the Fe61 Co12 Zr5 W2 B20 alloy suction-cast rod and tube, are shown in Fig. 1a and c. SEM micrograph of the fracture morphology for a 1 mm rod sample (Fig. 1b) indicates ductile elements in the shear process, consistent with a fully glassy structure. The surface of the fracture is smooth with shiny luster for fully amorphous rod and tube samples, while the fracture surface becomes rough when crystalline phases are present. In order to confirm the glassy state of the samples, further X-ray diffraction measurements were performed. XRD traces
P. Pawlik / Journal of Alloys and Compounds 423 (2006) 96–98
Fig. 1. SEM secondary electrons micrographs for the Fe61 Co12 Zr5 W2 B20 alloy: (a and b) 1 mm diameter rod; (c) 3 mm o.d. tube.
measured for Fe61 Co10+x Zr5 W4−x B20 (x = 0, 2, 3) alloys ribbon, rod and tube samples are shown in Fig. 2. For the x = 0 alloy, specimens not thicker than 220 m were fully amorphous, while thicker ribbons contained a fraction of crystallites embedded within an amorphous matrix. A decrease of the maximum thickness of fully amorphous ribbons was observed with decreasing W content (170 m for the x = 2 alloy and 140 m for the x = 3 alloy). The maximum thickness of fully amorphous samples for unidirectionally cooled ribbon indicated good GFA for the investigated alloy. These results (especially for the x = 0 and 2 alloys) suggested possibility of casting bulk glassy samples of large dimensions. It was demonstrated that for the x = 0 alloy, rods of the diameters up to 2 mm, were fully amorphous (Fig. 1a). A similar decrease of the maximum diameter of fully glassy rods, was observed with decreasing W content. So that fully amorphous 1 mm diameter rods for the x = 2 alloy and partly amorphous rods of 0.5 mm diameter for the x = 3 alloy, were produced. DTA traces measured on a fully amorphous thin ribbon samples for all three alloy compositions are shown in Fig. 3. A two stage crystallization process was observed for all three alloys. A
97
Fig. 2. XRD traces for the Fe61 Co10+x Zr5 W4−x B20 (x = 0, 2, 3) alloys as-cast ribbon samples of various thicknesses and suction-cast rods of the diameter 1 and 2 mm, and 3 mm o.d. tube: (a) x = 0; (b) x = 2; (c) x = 3; φ: the rod diameter, t: the ribbon thickness.
Fig. 3. DTA scans recorded for Fe61 Co10+x Zr5 W4−x B20 (x = 0, 2, 3) alloys under an Ar atmosphere (10 K/min); Tx1 , Tx2 —first and second crystallization temperature, respectively, Tm —melting temperature.
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P. Pawlik / Journal of Alloys and Compounds 423 (2006) 96–98
Fig. 4. M¨ossbauer spectrum for the Fe61 Co10 Zr5 W4 B20 alloy 1 mm as-cast rod (a) and hyperfine field distribution for this spectrum (b), with its deconvolution into low and high field components; P(B), hyperfine field distribution.
gradual increase of the glass transition temperature Tg , as well as both crystallization temperatures Tx1 and Tx2 , were observed with the increase of W content. At the same time, the melting temperature Tm remained almost constant for all three compositions. A value of the reduced glass transition temperature Trg = Tg /Tm is an experimental parameter that determine the glass forming abilities of the particular alloy. For the investigated alloys, Trg increases from 0.58 for the x = 3 alloy to 0.6 for the x = 0 alloy. For the Fe61 Co10 Zr5 W4 B20 alloy rods a low value of coercivity J Hc of ∼2 A/m and high anisotropy field HA ∼ 4000 A/m which reduces the magnetic permeability, were reported by Pawlik et al. in [4]. With increase of the W contents, successive increase of the saturation polarization was observed from ∼0.8 T for the x = 0 alloy to ∼1.24 T for the x = 3 alloy, while low coercivities were measured for all investigated bulk samples. M¨ossbauer spectrum and its hyperfine field distribution for the Fe61 Co10 Zr5 W4 B20 alloy 1 mm as-cast rod samples were shown in Fig. 4. Due to the typical for the amorphous alloys large broadening of the M¨ossbauer lines, the spectrum was not deconvoluted into separate subspectra, instead the hyperfine field distribution was calculated. The hyperfine field distribution was subsequently deconvoluted into two Gaussian distributions. The low and high field components of the hyperfine field distribution indicated the coexistence of two different neighborshell surroundings of the Fe atoms. These neighborshells may contain various volume fractions of Co, Fe and B elements. Similar decomposition of the amorphous structure was observed for the bulk glassy Fe60 Co8 Zr10 Mo5 W2 B15 alloy [5]. Such two amorphous phases were formed simultaneously during rapid solidification process. During spinodal decomposition process
in the crystalline Alnico alloys [6], similar simultaneous formation of crystalline phases was observed. 4. Conclusions Investigation of novel Fe61 Co10+x Zr5 W4−x B20 (x = 0, 2, 3) alloys ribbon, rod and tube samples, revealed remarkably good glass forming abilities together with good soft magnetic properties for the alloys. An increase of W content resulted in considerable change of Tg and Tx up to the higher temperatures, while Tm remained almost constant; thus leading to an increase of Tg /Tm . At the same time the increase of maximum thickness of fully amorphous samples with increasing W content, was observed. For the alloy containing 4 at.% of W, a fully amorphous 220 m thick melt-spun ribbon samples and 2 mm diameter suction-cast rods were produced. Acknowledgment This research was supported by Polish Scientific Research Committee (KBN) (projects no. 3T08A 046 27 and 3T08A028 25). References [1] A. Inoue, T. Zhang, A. Tekeuchi, Appl. Phys. Lett. 71 (1997) 464. [2] P. Pawlik, H.A. Davies, J. Non-Cryst. Sol. 329 (2003) 17–19. [3] M. Stoica, J. Eckert, S. Roth, L. Schultz, Mater. Sci. Eng. A 375–377 (2004) 399. [4] P. Pawlik, H.A. Davies, M.R.J. Gibbs, Appl. Phys. Lett. 83 (2003) 2775. [5] D.Y. Liu, W.S. Sun, A.M. Wang, H.F. Zhang, Z.Q. Hu, J. Alloys Compd. 370 (2004) 249. [6] R.A. McCurrie, in: E.P. Wohlfarth (Ed.), Ferromagnetic Materials, vol. 3, North-Holland Publishing Company, 1982, pp. 107–188.
Soft magnetic Fe–Co–Zr–W–B bulk glassy alloys Piotr Pawlik ∗ Institute of Physics, Cz˛estochowa University of Technology, Al. Armii Krajowej 19, 42-200 Cz˛estochowa, Poland Available online 31 January 2006
Abstract Suction-cast rod samples of the diameters 1 and 2 mm, thin walled tubes of the outer diameters 2, 3 and 4 mm and the melt-spun ribbon samples of various thicknesses up to 350 m were produced for Fe61 Co10+x Zr5 W4−x B20 (x = 0, 2, 3) alloys. XRD analysis revealed fully amorphous structure of the ribbon samples up to the thickness of 220 m for the x = 0 alloy. Those results indicate its good glass forming ability (GFA). The suctioncasting process allowed to produce the bulk glassy samples by die-casting to the copper mould. X-ray diffractometry and M¨ossbauer spectroscopy revealed, that for the Fe61 Co10 Zr5 W4 B20 alloy, up to a diameter of 2 mm rod samples and up to 4 mm outer diameter thin walled tubes, were also fully amorphous. Furthermore, studies of the influence of W contents on the microstructure and glass forming abilities are discussed. © 2005 Elsevier B.V. All rights reserved. Keywords: Metallic glasses; Magnetically ordered materials; Rapid-solidification; Magnetic measurements; M¨ossbauer spectroscopy
1. Introduction
2. Samples preparation and investigation methods
Iron-based bulk glassy alloys are of great interests for their soft magnetic properties and potential magnetic applications. It was reported for the Fe61 Co7 Zr10 Mo5 W2 B15 alloy, that the maximum diameter of fully amorphous rods reaches ∼6 mm [1]. However, prospective applications of this alloy are limited, due to its low Curie temperature TC of ∼300 K, being the result of the large fractions of metalloid and refractory metal elements [2]. Much higher TC were reported for Fe–Ga–Cr–Mo–P–B–C-type alloys, but the maximum diameter of fully amorphous rods for these alloys was limited to 1 mm [3]. The novel bulk glassy Fe61 Co10 Zr5 W4 B20 alloy, with relatively large Js of ∼0.8 T, J Hc ∼ 2 A/m and good glass forming abilities allowing to process 1 mm diameter rods and up to 4 mm outer diameter (o.d.) thin walled tubes, was reported in [4]. Although tungsten atoms have beneficial impact on the GFA of the alloy, they also have a detrimental influence on the Curie temperature TC and the magnetization polarization Js . The aim of this work was to investigate the influence of W substitution by Co on the glass forming abilities for novel Fe61 Co10+x Zr5 W4−x B20 (x = 0, 2, 3) alloys. Such substitution results in the improvement of Js and TC with the decrease of W contents. Furthermore, changes of the thermal stability parameters with the W contents were studied.
Samples of Fe61 Co10+x Zr5 W4−x B20 (x = 0, 2, 3) alloys were produced by arc-melting under an argon atmosphere, the high purity Fe, Co, W and Zr elements and pre-alloyed Fe–B of known composition. The ribbon samples of various thicknesses up to 350 m were produced by controlled atmosphere melt-spinning, varying the speed of the copper roll. Rod and tube samples of various diameters were produced by suction-casting of the melt into a split copper die, using an argon pressure difference between the chambers integrated within the arc-melting unit. X-ray diffractometry (with Co K␣ radiation) and M¨ossbauer spectroscopy were used for the assessment of microstructure of the ribbon and rod samples. Magnetic properties of the rod samples were measured by LakeShore VSM magnetometer operating in an external magnetic fields up to 2 T. The thermal stability parameters (crystallization temperature Tx and melting temperature Tm ), were determined from the DTA traces. Furthermore the DSC calorimetry was used to determine more accurately the glass transition temperature Tg for particular alloy. The reduced glass transition temperatures Trg = Tg /Tm for investigated alloys were also calculated.
∗
Tel.: +48 34 32 50 795; fax: +48 34 32 50 795. E-mail address: [email protected].
0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2005.12.031
3. Results and discussion Examples of SEM secondary electron micrographs for the Fe61 Co12 Zr5 W2 B20 alloy suction-cast rod and tube, are shown in Fig. 1a and c. SEM micrograph of the fracture morphology for a 1 mm rod sample (Fig. 1b) indicates ductile elements in the shear process, consistent with a fully glassy structure. The surface of the fracture is smooth with shiny luster for fully amorphous rod and tube samples, while the fracture surface becomes rough when crystalline phases are present. In order to confirm the glassy state of the samples, further X-ray diffraction measurements were performed. XRD traces
P. Pawlik / Journal of Alloys and Compounds 423 (2006) 96–98
Fig. 1. SEM secondary electrons micrographs for the Fe61 Co12 Zr5 W2 B20 alloy: (a and b) 1 mm diameter rod; (c) 3 mm o.d. tube.
measured for Fe61 Co10+x Zr5 W4−x B20 (x = 0, 2, 3) alloys ribbon, rod and tube samples are shown in Fig. 2. For the x = 0 alloy, specimens not thicker than 220 m were fully amorphous, while thicker ribbons contained a fraction of crystallites embedded within an amorphous matrix. A decrease of the maximum thickness of fully amorphous ribbons was observed with decreasing W content (170 m for the x = 2 alloy and 140 m for the x = 3 alloy). The maximum thickness of fully amorphous samples for unidirectionally cooled ribbon indicated good GFA for the investigated alloy. These results (especially for the x = 0 and 2 alloys) suggested possibility of casting bulk glassy samples of large dimensions. It was demonstrated that for the x = 0 alloy, rods of the diameters up to 2 mm, were fully amorphous (Fig. 1a). A similar decrease of the maximum diameter of fully glassy rods, was observed with decreasing W content. So that fully amorphous 1 mm diameter rods for the x = 2 alloy and partly amorphous rods of 0.5 mm diameter for the x = 3 alloy, were produced. DTA traces measured on a fully amorphous thin ribbon samples for all three alloy compositions are shown in Fig. 3. A two stage crystallization process was observed for all three alloys. A
97
Fig. 2. XRD traces for the Fe61 Co10+x Zr5 W4−x B20 (x = 0, 2, 3) alloys as-cast ribbon samples of various thicknesses and suction-cast rods of the diameter 1 and 2 mm, and 3 mm o.d. tube: (a) x = 0; (b) x = 2; (c) x = 3; φ: the rod diameter, t: the ribbon thickness.
Fig. 3. DTA scans recorded for Fe61 Co10+x Zr5 W4−x B20 (x = 0, 2, 3) alloys under an Ar atmosphere (10 K/min); Tx1 , Tx2 —first and second crystallization temperature, respectively, Tm —melting temperature.
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P. Pawlik / Journal of Alloys and Compounds 423 (2006) 96–98
Fig. 4. M¨ossbauer spectrum for the Fe61 Co10 Zr5 W4 B20 alloy 1 mm as-cast rod (a) and hyperfine field distribution for this spectrum (b), with its deconvolution into low and high field components; P(B), hyperfine field distribution.
gradual increase of the glass transition temperature Tg , as well as both crystallization temperatures Tx1 and Tx2 , were observed with the increase of W content. At the same time, the melting temperature Tm remained almost constant for all three compositions. A value of the reduced glass transition temperature Trg = Tg /Tm is an experimental parameter that determine the glass forming abilities of the particular alloy. For the investigated alloys, Trg increases from 0.58 for the x = 3 alloy to 0.6 for the x = 0 alloy. For the Fe61 Co10 Zr5 W4 B20 alloy rods a low value of coercivity J Hc of ∼2 A/m and high anisotropy field HA ∼ 4000 A/m which reduces the magnetic permeability, were reported by Pawlik et al. in [4]. With increase of the W contents, successive increase of the saturation polarization was observed from ∼0.8 T for the x = 0 alloy to ∼1.24 T for the x = 3 alloy, while low coercivities were measured for all investigated bulk samples. M¨ossbauer spectrum and its hyperfine field distribution for the Fe61 Co10 Zr5 W4 B20 alloy 1 mm as-cast rod samples were shown in Fig. 4. Due to the typical for the amorphous alloys large broadening of the M¨ossbauer lines, the spectrum was not deconvoluted into separate subspectra, instead the hyperfine field distribution was calculated. The hyperfine field distribution was subsequently deconvoluted into two Gaussian distributions. The low and high field components of the hyperfine field distribution indicated the coexistence of two different neighborshell surroundings of the Fe atoms. These neighborshells may contain various volume fractions of Co, Fe and B elements. Similar decomposition of the amorphous structure was observed for the bulk glassy Fe60 Co8 Zr10 Mo5 W2 B15 alloy [5]. Such two amorphous phases were formed simultaneously during rapid solidification process. During spinodal decomposition process
in the crystalline Alnico alloys [6], similar simultaneous formation of crystalline phases was observed. 4. Conclusions Investigation of novel Fe61 Co10+x Zr5 W4−x B20 (x = 0, 2, 3) alloys ribbon, rod and tube samples, revealed remarkably good glass forming abilities together with good soft magnetic properties for the alloys. An increase of W content resulted in considerable change of Tg and Tx up to the higher temperatures, while Tm remained almost constant; thus leading to an increase of Tg /Tm . At the same time the increase of maximum thickness of fully amorphous samples with increasing W content, was observed. For the alloy containing 4 at.% of W, a fully amorphous 220 m thick melt-spun ribbon samples and 2 mm diameter suction-cast rods were produced. Acknowledgment This research was supported by Polish Scientific Research Committee (KBN) (projects no. 3T08A 046 27 and 3T08A028 25). References [1] A. Inoue, T. Zhang, A. Tekeuchi, Appl. Phys. Lett. 71 (1997) 464. [2] P. Pawlik, H.A. Davies, J. Non-Cryst. Sol. 329 (2003) 17–19. [3] M. Stoica, J. Eckert, S. Roth, L. Schultz, Mater. Sci. Eng. A 375–377 (2004) 399. [4] P. Pawlik, H.A. Davies, M.R.J. Gibbs, Appl. Phys. Lett. 83 (2003) 2775. [5] D.Y. Liu, W.S. Sun, A.M. Wang, H.F. Zhang, Z.Q. Hu, J. Alloys Compd. 370 (2004) 249. [6] R.A. McCurrie, in: E.P. Wohlfarth (Ed.), Ferromagnetic Materials, vol. 3, North-Holland Publishing Company, 1982, pp. 107–188.