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Effect of Ti on structure and soft magnetic properties of Si-rich Finemet-type nanocrystalline Fe73.5Cu1Nb3-xSi17.5B5Tix alloys
Accepted Manuscript Title: Effect of Ti on structure and soft magnetic properties of Si-rich Finemet-type nanocrystalline Fe73.5 Cu1 Nb3−x Si17.5 B5 Tix alloys Authors: Yurong Jia, Zhi Wang, Fang Wang, Li Zhang, Hongjun Duan PII: DOI: Reference:
S0025-5408(17)33717-0 https://doi.org/10.1016/j.materresbull.2018.06.018 MRB 10056
To appear in:
MRB
Received date: Revised date: Accepted date:
25-9-2017 24-3-2018 12-6-2018
Please cite this article as: Jia Y, Wang Z, Wang F, Zhang L, Duan H, Effect of Ti on structure and soft magnetic properties of Si-rich Finemet-type nanocrystalline Fe73.5 Cu1 Nb3−x Si17.5 B5 Tix alloys, Materials Research Bulletin (2018), https://doi.org/10.1016/j.materresbull.2018.06.018 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Effect of Ti on structure and soft magnetic properties of Si-rich Finemet-type nanocrystalline Fe73.5Cu1Nb3-xSi17.5B5Tix alloys Yurong Jiaa, Zhi Wanga,*, Fang Wangb, Li Zhanga, Hongjun Duana School of Science, Tianjin University, Tianjin 300072, P. R.China
b
School of Materials Science and Engineering, Tianjin University, Tianjin 300072, P. R.China
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*Corresponding author. E-mail: [email protected]
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Graphical abstract
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Highlights
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Substitution of Nb by Ti can reduce the Tx1 and enlarge the ΔTx. Fe73.5Cu1Nb2Si17.5B5Ti1 alloy exhibits high μi of 18000 and low Hc of 0.54 Oe. Magnetic properties were analysed in terms of the relationship between Hc and i. Soft magnetic properties will deteriorate when Nb is completely replaced by Ti. The reasons of variation of permeability at high temperature were analyzed.
Abstract
Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) amorphous alloys were prepared by the
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single roller melt spinning method. The effects of Ti substitution for Nb on the
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crystallization behavior, microstructure and soft magnetic properties were investigated.
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Compared to the previously reported Finemet alloy, the onset primary crystallization temperature Tx1 becomes lower which has dropped from 803K to 758K. The
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crystallization temperature interval ΔTx increases from 468K to 488K as the x increases
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from 0 to 3. However, the Curie temperature of amorphous phase shows a downward tendency with the increase of Ti content. Compared to the previously reported Finemet
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alloy, the μi increases obviously to more than 18000 at x=1, the Hc decreases from 0.59Oe to 0.54Oe. When Ti replaces Nb completely, the optimum annealing
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temperature range for precipitating single soft magnetic phase is enlarged, but the permeability at room- and high-temperature is deteriorated, the reason of which was also analysed.
Keywords : Amorphous materials ; Nanocrystalline materials; Soft magnetic 2
properties; Finemet-type alloy; Herzer’s model
1. Introduction Due to excellent soft magnetic properties [1, 2], nanocrystalline soft magnetic
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materials especially Fe73.5Cu1Nb3Si13.5B9 alloy (Finemet) [3] produced by crystallizing its amorphous precursor have a great potential for electromagnetic applications. The
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excellent soft magnetic properties are related primarily to the exchange coupling
between nanocrystalline grains through the amorphous matrix [4], which can make the
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magnetocrystalline anisotropy average out. However, the lower Curie temperature of the
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residual amorphous matrix limited its high temperature applications [5]. The higher
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volume fraction of crystalline phase is beneficial to improve the soft magnetic
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properties at high temperature because of the penetrating effect of strong exchange
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coupling between grains [6, 7]. It has been reported that the larger crystalline volume fraction or thinner intergranular amorphous layer can be obtained in Si-rich Fe-based
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nanocrystalline alloys [8-10]. Proper amount of Ti has similar effect as Nb in inhibiting
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the grain growth [11]. Furthermore, the volume fraction of -Fe(Si) crystalline phase is usually increased with Ti substituting for Nb, which is in favor of enhancing the ferromagnetic exchanging coupling between -Fe(Si) grains of FeCuNbSiB alloy [12].
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The replacement of Nb with Ti can also reduce the cost of materials. Therefore, we investigated the effects of replacement of Nb with Ti on microstructure, crystallization behavior and magnetic properties of Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys.
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2. Experimental procedure Amorphous Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloy ribbons were produced by the melt spinning technique. The width and thickness of the ribbons were approximately 1.5mm and 20m, respectively. The toroidal samples with an outer diameter of about
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18mm and inner diameter of about 16mm were fabricated by winding the ribbons into toroidal cores. In order to obtain the characteristic nanocrystalline structure, the samples
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were submitted to isothermal treatment for 0.5h at 550°C under vacuum atmosphere
(10-3pa) in a tubular argon furnace. The phase structures of annealed ribbons were
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identified by X-ray diffraction (XRD) using D/max-2500/PC with Cu-Kα radiation ( =
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1.54056Å). Rietveld refinements [13] of the structural parameters were carried out
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using the program “FullProf” [14]. The thermal stability of the as-quenched ribbons was
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evaluated using the differential scanning calorimeter (DSC) at a heating rate of 0.67K/s.
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The initial permeability was in situ measured in a furnace with argon atmosphere protection by using an HP4294A impedance analyzer under a field of 0.4 A/m and the
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frequency of 10 kHz. The magnetization hysteresis loops were measured with a
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vibrating sample magnetometer (VSM, Lake Shore 7400).
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3. Results and discussion Fig. 1 shows the DSC curves of the as-quenched Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1,
2, 3) alloys at a heating rate of 0.67K/s. It can be seen that all the curves have two separate exothermic peaks, indicating that the crystallization process includes two stages. The onset primary crystallization temperature and second crystallization 4
temperature are represented as Tx1 and Tx2, respectively. The Tx1 of the first peak corresponding to the precipitation of Fe3Si phase decreases gradually with the increasing of Ti content. Compared to the previously reported Finemet alloy [3], the onset primary crystallization temperature (Tx1) becomes lower which has dropped from
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803K to 758K. According to the previous study, it is known that the precipitation of bcc-Fe (Si) is triggered by the Cu-enriched clusters precipitated during annealing
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process and/or the primary crystals in the as-quenched state [15, 16]. Hence, in this alloy system, the replacement of Nb by Ti is beneficial for the formation of a high
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density of nucleation sites which affects the nanocrystallization and nanostructure [17].
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Therefore, this is favorable to crystallize at a lower temperature. The Tx2 relates to the
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formation of FeB hard magnetic phase [18]. Meanwhile, a slightly change of Tx2 takes
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place, which is 695C for x = 0, 707C for x = 1, 704C for x = 2, and 700C for x = 3,
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respectively. The ΔTx (ΔTx = Tx2 - Tx1) enlarges from 468K to 488K with increasing x from 0 to 3, which is conducive to the precipitation of a single soft magnetic crystalline
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phase in a wide range of temperature [19]. Thus the Ti addition is effective for
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improving the thermal stability of amorphous phase. The onset primary crystallization temperature (Tx1), second crystallization temperature (Tx2) and the interval temperature (ΔTx) for as-quenched Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys and Finemet
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Fe73.5Cu1Nb3Si13.5B9 [20] are shown in the Table 1.
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Fig. 1. DSC curves of as-quenched Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloy ribbons at a heating rate of 0.67K/s Table 1
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The onset primary crystallization temperature Tx1, second crystallization temperature Tx2, the interval
Tx2
Tx
Tcam
635
105
320
500
695
195
320
Fe73.5Cu1Nb2Si17.5B5Ti1 505
707
202
299
Fe73.5Cu1Nb1Si17.5B5Ti2 498
704
206
313
700
215
314
Tx1
Fe73.5Cu1Nb3Si13.5B9
530
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Fe73.5Cu1Nb3Si17.5B5
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Composition
Fe73.5Cu1Si17.5B5Ti3
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Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys.
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temperature Tx and Curie temperature Tcam for as-quenched Fe73.5Cu1Nb3Si13.5B9 [20]and
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Fig. 2 (a) shows the temperature dependence of initial permeability (μi-T) curves of
as-quenched Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys. A sharp Hopkinson peak is observed on all curves at the Curie temperature of amorphous phase, Tcam, which is due to the faster decrease of magnetic anisotropy than that of saturation magnetization with increasing temperature. When temperature is just above Tcam, the μi drops abruptly to 6
zero, which is attributed to the transition from ferromagnetic to paramagnetic state of the amorphous alloy. It can be observed that Tcam ranges from 320C to 299C, showing a downward trend with Ti substitution for Nb overall (see Fig. 2(b)). A number of researches indicated that Tcam was dominated by the interaction of atomic pairs for
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single amorphous alloys [21, 22], and the interaction depends on the distance between the Fe-Fe atoms. Considering the atomic radius of Ti is less than that of Nb, it makes the
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radius of 3d orbitals of Fe decrease from the optimum ferromagnetic exchange between
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Fe-Fe atoms [23]. Therefore, the replacement of Nb by Ti caused the fall of Tcam.
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Fig. 2. (a) μi -T curves and (b) Tcam for as-quenched Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys.
Fig. 3. μi -T curves of 550C-annealed Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys. 7
Fig. 3 shows the μi -T curves of the Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys annealed at 550C for 0.5h. It can be found that the Hopkinson peak of all the samples disappeared at near Tcam, indicating the formation of desired two phase nanocrystal structure [24]. The elevated-temperature μi of the samples with Ti decreased more
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quickly around at Tcam than that with Nb. With the Ti content increasing, the room-temperature μi of the samples first increases to the maximum of about 18000 for x
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= 1, then decreases to about 2000 for x = 3. Therefore, the proper addition of Ti is
beneficial to improve the μi of Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys at room
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temperature. When Ti completely replaces Nb, both room- and high-temperature μi of
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the samples deteriorate, which may be due to the increased magnetic anisotropy
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originated from the increased grain size. It has been reported that the Si-rich Fe-based
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nanocrystalline alloy has a higher μi of about 10000, which can be held up to 420C [10].
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However, the high temperature μi of this kind of alloy is deteriorated after Nb is replaced by Ti completely. The reason of this behavior may be attributed to the role of
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Ti in hindering grain growth far less than that of Nb.
Fig. 4. XRD patterns of Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys annealed at 550C for 0.5h. 8
In order to ascertain the relationship between the microstructure and magnetic properties of 550C-annealed Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys, all samples were identified by XRD as shown in Fig. 4. All the annealed samples show the characteristic (111), (200), (220), (400) and (422) diffraction peaks corresponded to bcc
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Fe3(Si) crystalline phase. It indicates that all the annealed samples partially crystallize after annealing, including the crystalline phase and the residual amorphous phase. With
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the increase of the Ti content, the intensity of (111) and (200) diffraction peaks are
enhanced, indicating the increase of the crystalline volume fraction of Fe3(Si) phase.
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Since the XRD test results show that the as-quenched of x = 2 and x = 3 alloys partially
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crystallized, the relative volume fraction of crystalline phase of each sample has not
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been calculated. On the one hand, it shows that the larger ΔTx do not guarantee the
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enhancement of glass forming ability (GFA). On the other hand, the proper addition of
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Ti is beneficial for improving the GFA, in agreement with the Inoue’s criteria [25]. Rietveld analysis is mainly used to analyze crystalline structure by powder
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diffraction data. FullProf is a very excellent Rietveld analysis software compared with
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other Rietveld analysis programs. Powder diffraction is becoming more and more powerful but FullProf is not an automatic (black-box) program, as is usually found in single crystal structure determination. There are some unavoidable errors because the
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experimental sample is an alloy strip. The XRD patterns of Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) are refined with the cubic structure with the space group of Fm-3m, as shown in Fig. 5. In all the refinements performed, the low values of agreement factors (R - factors) affirm the correctness of fit. The fitting degree of the experimental data and 9
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the calculated data is very high, indicating the high purity of bcc-Fe (Si).
Fig. 5 The XRD pattern of Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) refined with the space group of
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Fm-3m.
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Fig. 6 shows the changes of average grain size (D) and room-temperature initial permeability (i) as a function of Ti content for Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3)
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alloys annealed at 550 for 0.5h. In many references [12, 26, 27], the average grain size is obtained by using Williamson Hall method, so we also use this method. The
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Williamson-Hall method can be described by the following equation [26]: 𝐵𝑠 𝑐𝑜𝑠𝜃 =
𝑘 𝐷
+ 2(𝜀)𝑠𝑖𝑛𝜃
(1)
where 𝐵𝑠 is the full-width at half-maximum (FWHM) of the XRD peaks, 𝑘 is the Scherrer constant, is the wavelength of the incident X-ray, 𝐷 is the crystallite size, ε is the internal microstrain and 𝜃 is the Bragg angle. The values of 𝐵𝑠 𝑐𝑜𝑠𝜃 and 2𝑠𝑖𝑛𝜃 10
for the three -Fe(Si) peaks including (200),
(400) and (422) were calculated for each
sample. According to Eq. (1), the data can be fitted linearly with the least square method. The microstrain ε which reflects the unrelieved internal stress of the sample equals to the slope of the linear correlation between 𝐵𝑠 𝑐𝑜𝑠𝜃 and 2𝑠𝑖𝑛𝜃, while the grain size 𝐷
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is inversely proportional to the intercept of the fitted line on the Y axis. Table 1 lists the average grain size of each sample after annealing for 0.5h at 550C, respectively. The
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grain size 𝐷 calculated by WilliamsonHall method is smaller than that of Scherrer formula, which is due to the latter does not consider the effect of internal stress on the
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grain size 𝐷. Table 2 summarizes the obtained values of the average grain size 𝐷 for
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the samples annealed at 550C. With the increase of Ti content, D decreases from about
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15 for x=0 to the minimum value of 12 for x=1 and then increases to the maximum
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value of about 25 for x=3, which is still smaller than the magnetic exchange length Lex =
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35nm [28]. At the same time, the room-temperature μi increases from about 16000 for x=0 to the maximum value of 18000 for x=1 and then decreases dramatically to the
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minimum value of about 2000 for x=3. The variation of D and room-temperature μi can
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be explained by Herzer’s model [29], which points out that the μi is inversely
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proportional to D6. According to Herzer’s model: Hc=PK14D6/JsA3
(2)
i=PJsA3/0K14D6
(3)
Where P is a dimensionless prefactor and 0 is the vacuum magnetic permeability, K1 is the local anisotropy of the crystallites, A is the exchange constant, Js is average saturation magnetization, D is average grain size. It can be seen that i is inversely 11
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proportional to D6, which is consistent with the experimental results as shown in Fig. 6.
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Fig. 6. The Ti content dependences of initial permeability (μi) and average grain size (D) for Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys annealed at 550C for 0.5h.
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Table 2
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Average grain size of bcc-Fe(Si) phase calculated from X-ray diffraction patterns of
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Average grain size (nm)
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Ti content x at.%
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Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) samples annealed for 0.5h at 550C.
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2
3
12
16
25
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Fig. 7 shows the Ti content dependences of coercivity (Hc) and average grain size
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(D) for 550C-annealed Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys. It can be observed that the Hc decreases from 0.59 Oe for x=0 to the minimum value of about 0.54 Oe for x=1, and then increases to the maximum value of about 0.70 Oe for x=3.
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The variation of Hc and D is also consistent with the Herzer’s model.
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Fig. 7. The Ti content dependence of coercivity (Hc) and average grain size (D) of Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys annealed at 550C for 0.5h.
Therefore, we discuss the reasons for the high temperature permeability changing
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after adding Ti. After vacuum annealing at 550C, Fe-based nanocrystalline alloy is
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composed of the crystalline phase and the remaining amorphous phase. The decrease of
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initial permeability with the increase of temperature can be explained in two aspects. On the one hand, the thermal energy destroys the magnetic ordering state of the grains,
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deflects the magnetic moment orientation of each grain, then decreases the macroscopic
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magnetic moment of the alloy. On the other hand, the magnetic transformation of the residual amorphous phase has played a major role. When the temperature reaches the
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Tcam, residual amorphous phase firstly becomes paramagnetic, and the interaction between adjacent grains is blocked by the paramagnetic amorphous layer, hence the
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initial permeability decreases to almost zero. Another interpretation is the Hernando’s theory of the Curie temperature enhancement effects of Fe-based alloys which can be expressed as [30]: TcA = Tcam + (Tca-Tcam) 2L /
(4)
where TcA is the Curie temperature of intergranular amorphous matrix in two-phase 13
nanocrystalline alloy, Tcam is the Curie temperature of amorphous phase, Tca is the Curie temperature of crystalline phase, L is exchange penetration length and is distance between -Fe(Si) grains. The intersection of the maximum slope tangent in the μi -T curves and T axis is TcA, and the intersection point between the tangent and the T axis at
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the maximum slope of the second drop of high temperature permeability is Tca. By calculation, the value of 2L / is obviously smaller after adding Ti, which indicates that
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the exchange coupling interaction between adjacent grains is weakened, and the serious attenuation of permeability at high temperature is also explained.
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4. Conclusions
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Compared to the previously reported Finemet alloy, replacing Nb with Ti in
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Fe73.5Cu1Nb3Si17.5B5 alloy can decrease the onset primary temperature Tx1 from 803K to
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758K and enlarge the crystallization temperature interval ΔTx from 468K to 488K, which
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is in favor of precipitating a single soft magnetic phase in a wide temperature range. However, the Tcam shows a decreasing trend with Ti substitution for Nb. After annealing
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at 550C, Fe73.5Cu1Nb2Si17.5B5Ti1 alloy exhibits the higher room-temperature μi of about
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18000 and lower Hc of about 0.54 Oe. Such excellent soft magnetic properties of the Fe-based amorphous alloy have further improved the potential industrial applications. The room- and high-temperature properties of Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3)
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alloys deteriorated when Ti completely replaced Nb, indicating that the role of Ti far less than that of Nb in preventing grain growth.
Acknowledgments This work was supported by National Natural Science Foundation of China (Grant 14
No. 51271130).
References [1] A. Kolano-Burian, R. Kolano, L.K. Varga, J. Alloys Compd. 483 (2009) 560. [2] H.A. Shivaee, H.R.M. Hosseini, E.M. Lotfabad, S. Roostaie, J. Alloys Compd. 491
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(2010) 487. [3] Y. Yoshizawa, S. Oguma, K. Yamauchi, J. Appl. Phys. 64 (1988) 6044.
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[4] G. Herzer, Acta Mater. 44 (2013) 718-734.
[5] T. Kulik, J. Ferenc, M. Kowalczyk, J. Mater. Process. Technol. 162 (2005) 215–
U
219.
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[6] X. H. Ma, Z. Wang, X. T. Han, et al., Mater. Sci. Eng. A. 448 (2007) 216.
A
[7] Y. Han, Z. Wang, J. Non-Cryst. Solids 434 (2016) 92.
M
[8] Y. Ueda, S. Ikeda, K. Minami, Mater. Sci. Eng. A. 181 (1994) 992–996.
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[9] D.T. Ngo, et al. J. Magn. Magn. Mater. 322 (2010) 342–347. [10] R. Shi, Z. Wang, Y. Jia, et al. J. Appl. Phys.112 (2012) 252.
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[11] K. Suzuki, A. Makino, A. Inoue, T. Masumoto, Jpn. J. Appl. Phys. 30 (1991) 1729.
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[12] M. Yan, H. Tong, S. Tao, J.H. Liu, J. Alloys Compd. 505 (2010) 264. [13] R.A. Young, The Rietveld Method, IUCr 5, Oxford University Press, Oxford, 1993, pp. 1–39.
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[14] J. Rodriguez-Carvajal, FULLPROF: A Program for Rietveld Refinement and Pattern Matching Analysis, Abstracts of the Satellite Meeting on Powder Diffraction of the XV Congress of the IUCr, p. 127, Toulouse, France. [15] A. D. Wang, H. Men, B. L. Shen, et al. Thin Solid Films, 519 (2011) 8283. 15
[16] J. D. Ayers, V. G. Harris, J. A. Sprague, et al. Appl. Phys. Lett. 64 (1994) 974. [17] M. Ohta., Y. Yoshizawa, J. Magn. Magn. Mater. 321 (2009) 2220. [18] R. Brzozowski, M. Wasiak, H. Piekarski, P. Sovak, P. Uznanski, M.E. Moneta, J. Alloys Compd. 470 (2009) 5.
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[19] K. Suzuki, G. Herzer, Adv. Magn. Nanostruct. (2006) 365. [20] T. H. Noh, M. B. Lee, H. J. Kim, and I. K. Kang, J. Appl. Phys. 67 (1990) 5568.
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[21] I. Orue, M.L. Fdez-Gubieda, F. Plazaola, J.M. Barandiaran, J. Phys. Condens. Mater. 10 (1998) 3807.
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[23] H. Tian. et al. Physica B. 407 (2012) 250-257.
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[22] A. Ghasemi, J. Alloys Compd. 645 (2015) 467.
M
A 304–306 (2001) 1046.
A
[24] Z. Wang, K.Y. He, J. Jin, J. He, L. Zhang, H.W. Zhang, B.G. Shen, Mater. Sci. Eng.
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[25] A. Takeuchi, A. Inoue, Mater. Trans. 46 (2005) 2817. [26] G. K. Williamson, W.H. Hall, Acta Metall. 1 (1953) 22-31.
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[27] C. Wu, H. Chen, H. Lv, et al. J. Alloys Compd. 673 (2016) 278.
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[28] G. Herzer, Mater. Sci. Eng. A 133 (1991) 1. [29] G. Herzer, IEEE Trans. Magn. 26 (1990) 1397-1402.
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[30] C. Kuhrt and G. Herzer. IEEE Trans. Magn. 32 (1996) 4881.
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S0025-5408(17)33717-0 https://doi.org/10.1016/j.materresbull.2018.06.018 MRB 10056
To appear in:
MRB
Received date: Revised date: Accepted date:
25-9-2017 24-3-2018 12-6-2018
Please cite this article as: Jia Y, Wang Z, Wang F, Zhang L, Duan H, Effect of Ti on structure and soft magnetic properties of Si-rich Finemet-type nanocrystalline Fe73.5 Cu1 Nb3−x Si17.5 B5 Tix alloys, Materials Research Bulletin (2018), https://doi.org/10.1016/j.materresbull.2018.06.018 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Effect of Ti on structure and soft magnetic properties of Si-rich Finemet-type nanocrystalline Fe73.5Cu1Nb3-xSi17.5B5Tix alloys Yurong Jiaa, Zhi Wanga,*, Fang Wangb, Li Zhanga, Hongjun Duana School of Science, Tianjin University, Tianjin 300072, P. R.China
b
School of Materials Science and Engineering, Tianjin University, Tianjin 300072, P. R.China
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a
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*Corresponding author. E-mail: [email protected]
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Graphical abstract
1
Highlights
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Substitution of Nb by Ti can reduce the Tx1 and enlarge the ΔTx. Fe73.5Cu1Nb2Si17.5B5Ti1 alloy exhibits high μi of 18000 and low Hc of 0.54 Oe. Magnetic properties were analysed in terms of the relationship between Hc and i. Soft magnetic properties will deteriorate when Nb is completely replaced by Ti. The reasons of variation of permeability at high temperature were analyzed.
Abstract
Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) amorphous alloys were prepared by the
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single roller melt spinning method. The effects of Ti substitution for Nb on the
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crystallization behavior, microstructure and soft magnetic properties were investigated.
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Compared to the previously reported Finemet alloy, the onset primary crystallization temperature Tx1 becomes lower which has dropped from 803K to 758K. The
ED
crystallization temperature interval ΔTx increases from 468K to 488K as the x increases
PT
from 0 to 3. However, the Curie temperature of amorphous phase shows a downward tendency with the increase of Ti content. Compared to the previously reported Finemet
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alloy, the μi increases obviously to more than 18000 at x=1, the Hc decreases from 0.59Oe to 0.54Oe. When Ti replaces Nb completely, the optimum annealing
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temperature range for precipitating single soft magnetic phase is enlarged, but the permeability at room- and high-temperature is deteriorated, the reason of which was also analysed.
Keywords : Amorphous materials ; Nanocrystalline materials; Soft magnetic 2
properties; Finemet-type alloy; Herzer’s model
1. Introduction Due to excellent soft magnetic properties [1, 2], nanocrystalline soft magnetic
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materials especially Fe73.5Cu1Nb3Si13.5B9 alloy (Finemet) [3] produced by crystallizing its amorphous precursor have a great potential for electromagnetic applications. The
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excellent soft magnetic properties are related primarily to the exchange coupling
between nanocrystalline grains through the amorphous matrix [4], which can make the
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magnetocrystalline anisotropy average out. However, the lower Curie temperature of the
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residual amorphous matrix limited its high temperature applications [5]. The higher
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volume fraction of crystalline phase is beneficial to improve the soft magnetic
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properties at high temperature because of the penetrating effect of strong exchange
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coupling between grains [6, 7]. It has been reported that the larger crystalline volume fraction or thinner intergranular amorphous layer can be obtained in Si-rich Fe-based
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nanocrystalline alloys [8-10]. Proper amount of Ti has similar effect as Nb in inhibiting
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the grain growth [11]. Furthermore, the volume fraction of -Fe(Si) crystalline phase is usually increased with Ti substituting for Nb, which is in favor of enhancing the ferromagnetic exchanging coupling between -Fe(Si) grains of FeCuNbSiB alloy [12].
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The replacement of Nb with Ti can also reduce the cost of materials. Therefore, we investigated the effects of replacement of Nb with Ti on microstructure, crystallization behavior and magnetic properties of Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys.
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2. Experimental procedure Amorphous Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloy ribbons were produced by the melt spinning technique. The width and thickness of the ribbons were approximately 1.5mm and 20m, respectively. The toroidal samples with an outer diameter of about
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18mm and inner diameter of about 16mm were fabricated by winding the ribbons into toroidal cores. In order to obtain the characteristic nanocrystalline structure, the samples
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were submitted to isothermal treatment for 0.5h at 550°C under vacuum atmosphere
(10-3pa) in a tubular argon furnace. The phase structures of annealed ribbons were
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identified by X-ray diffraction (XRD) using D/max-2500/PC with Cu-Kα radiation ( =
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1.54056Å). Rietveld refinements [13] of the structural parameters were carried out
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using the program “FullProf” [14]. The thermal stability of the as-quenched ribbons was
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evaluated using the differential scanning calorimeter (DSC) at a heating rate of 0.67K/s.
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The initial permeability was in situ measured in a furnace with argon atmosphere protection by using an HP4294A impedance analyzer under a field of 0.4 A/m and the
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frequency of 10 kHz. The magnetization hysteresis loops were measured with a
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vibrating sample magnetometer (VSM, Lake Shore 7400).
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3. Results and discussion Fig. 1 shows the DSC curves of the as-quenched Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1,
2, 3) alloys at a heating rate of 0.67K/s. It can be seen that all the curves have two separate exothermic peaks, indicating that the crystallization process includes two stages. The onset primary crystallization temperature and second crystallization 4
temperature are represented as Tx1 and Tx2, respectively. The Tx1 of the first peak corresponding to the precipitation of Fe3Si phase decreases gradually with the increasing of Ti content. Compared to the previously reported Finemet alloy [3], the onset primary crystallization temperature (Tx1) becomes lower which has dropped from
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803K to 758K. According to the previous study, it is known that the precipitation of bcc-Fe (Si) is triggered by the Cu-enriched clusters precipitated during annealing
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process and/or the primary crystals in the as-quenched state [15, 16]. Hence, in this alloy system, the replacement of Nb by Ti is beneficial for the formation of a high
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density of nucleation sites which affects the nanocrystallization and nanostructure [17].
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Therefore, this is favorable to crystallize at a lower temperature. The Tx2 relates to the
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formation of FeB hard magnetic phase [18]. Meanwhile, a slightly change of Tx2 takes
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place, which is 695C for x = 0, 707C for x = 1, 704C for x = 2, and 700C for x = 3,
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respectively. The ΔTx (ΔTx = Tx2 - Tx1) enlarges from 468K to 488K with increasing x from 0 to 3, which is conducive to the precipitation of a single soft magnetic crystalline
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phase in a wide range of temperature [19]. Thus the Ti addition is effective for
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improving the thermal stability of amorphous phase. The onset primary crystallization temperature (Tx1), second crystallization temperature (Tx2) and the interval temperature (ΔTx) for as-quenched Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys and Finemet
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Fe73.5Cu1Nb3Si13.5B9 [20] are shown in the Table 1.
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Fig. 1. DSC curves of as-quenched Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloy ribbons at a heating rate of 0.67K/s Table 1
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The onset primary crystallization temperature Tx1, second crystallization temperature Tx2, the interval
Tx2
Tx
Tcam
635
105
320
500
695
195
320
Fe73.5Cu1Nb2Si17.5B5Ti1 505
707
202
299
Fe73.5Cu1Nb1Si17.5B5Ti2 498
704
206
313
700
215
314
Tx1
Fe73.5Cu1Nb3Si13.5B9
530
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Fe73.5Cu1Nb3Si17.5B5
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Composition
Fe73.5Cu1Si17.5B5Ti3
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Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys.
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temperature Tx and Curie temperature Tcam for as-quenched Fe73.5Cu1Nb3Si13.5B9 [20]and
485
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Fig. 2 (a) shows the temperature dependence of initial permeability (μi-T) curves of
as-quenched Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys. A sharp Hopkinson peak is observed on all curves at the Curie temperature of amorphous phase, Tcam, which is due to the faster decrease of magnetic anisotropy than that of saturation magnetization with increasing temperature. When temperature is just above Tcam, the μi drops abruptly to 6
zero, which is attributed to the transition from ferromagnetic to paramagnetic state of the amorphous alloy. It can be observed that Tcam ranges from 320C to 299C, showing a downward trend with Ti substitution for Nb overall (see Fig. 2(b)). A number of researches indicated that Tcam was dominated by the interaction of atomic pairs for
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single amorphous alloys [21, 22], and the interaction depends on the distance between the Fe-Fe atoms. Considering the atomic radius of Ti is less than that of Nb, it makes the
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radius of 3d orbitals of Fe decrease from the optimum ferromagnetic exchange between
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A
N
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Fe-Fe atoms [23]. Therefore, the replacement of Nb by Ti caused the fall of Tcam.
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Fig. 2. (a) μi -T curves and (b) Tcam for as-quenched Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys.
Fig. 3. μi -T curves of 550C-annealed Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys. 7
Fig. 3 shows the μi -T curves of the Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys annealed at 550C for 0.5h. It can be found that the Hopkinson peak of all the samples disappeared at near Tcam, indicating the formation of desired two phase nanocrystal structure [24]. The elevated-temperature μi of the samples with Ti decreased more
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quickly around at Tcam than that with Nb. With the Ti content increasing, the room-temperature μi of the samples first increases to the maximum of about 18000 for x
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= 1, then decreases to about 2000 for x = 3. Therefore, the proper addition of Ti is
beneficial to improve the μi of Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys at room
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temperature. When Ti completely replaces Nb, both room- and high-temperature μi of
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the samples deteriorate, which may be due to the increased magnetic anisotropy
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originated from the increased grain size. It has been reported that the Si-rich Fe-based
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nanocrystalline alloy has a higher μi of about 10000, which can be held up to 420C [10].
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However, the high temperature μi of this kind of alloy is deteriorated after Nb is replaced by Ti completely. The reason of this behavior may be attributed to the role of
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Ti in hindering grain growth far less than that of Nb.
Fig. 4. XRD patterns of Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys annealed at 550C for 0.5h. 8
In order to ascertain the relationship between the microstructure and magnetic properties of 550C-annealed Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys, all samples were identified by XRD as shown in Fig. 4. All the annealed samples show the characteristic (111), (200), (220), (400) and (422) diffraction peaks corresponded to bcc
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Fe3(Si) crystalline phase. It indicates that all the annealed samples partially crystallize after annealing, including the crystalline phase and the residual amorphous phase. With
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the increase of the Ti content, the intensity of (111) and (200) diffraction peaks are
enhanced, indicating the increase of the crystalline volume fraction of Fe3(Si) phase.
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Since the XRD test results show that the as-quenched of x = 2 and x = 3 alloys partially
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crystallized, the relative volume fraction of crystalline phase of each sample has not
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been calculated. On the one hand, it shows that the larger ΔTx do not guarantee the
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enhancement of glass forming ability (GFA). On the other hand, the proper addition of
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Ti is beneficial for improving the GFA, in agreement with the Inoue’s criteria [25]. Rietveld analysis is mainly used to analyze crystalline structure by powder
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diffraction data. FullProf is a very excellent Rietveld analysis software compared with
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other Rietveld analysis programs. Powder diffraction is becoming more and more powerful but FullProf is not an automatic (black-box) program, as is usually found in single crystal structure determination. There are some unavoidable errors because the
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experimental sample is an alloy strip. The XRD patterns of Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) are refined with the cubic structure with the space group of Fm-3m, as shown in Fig. 5. In all the refinements performed, the low values of agreement factors (R - factors) affirm the correctness of fit. The fitting degree of the experimental data and 9
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the calculated data is very high, indicating the high purity of bcc-Fe (Si).
Fig. 5 The XRD pattern of Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) refined with the space group of
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Fm-3m.
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Fig. 6 shows the changes of average grain size (D) and room-temperature initial permeability (i) as a function of Ti content for Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3)
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alloys annealed at 550 for 0.5h. In many references [12, 26, 27], the average grain size is obtained by using Williamson Hall method, so we also use this method. The
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Williamson-Hall method can be described by the following equation [26]: 𝐵𝑠 𝑐𝑜𝑠𝜃 =
𝑘 𝐷
+ 2(𝜀)𝑠𝑖𝑛𝜃
(1)
where 𝐵𝑠 is the full-width at half-maximum (FWHM) of the XRD peaks, 𝑘 is the Scherrer constant, is the wavelength of the incident X-ray, 𝐷 is the crystallite size, ε is the internal microstrain and 𝜃 is the Bragg angle. The values of 𝐵𝑠 𝑐𝑜𝑠𝜃 and 2𝑠𝑖𝑛𝜃 10
for the three -Fe(Si) peaks including (200),
(400) and (422) were calculated for each
sample. According to Eq. (1), the data can be fitted linearly with the least square method. The microstrain ε which reflects the unrelieved internal stress of the sample equals to the slope of the linear correlation between 𝐵𝑠 𝑐𝑜𝑠𝜃 and 2𝑠𝑖𝑛𝜃, while the grain size 𝐷
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is inversely proportional to the intercept of the fitted line on the Y axis. Table 1 lists the average grain size of each sample after annealing for 0.5h at 550C, respectively. The
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grain size 𝐷 calculated by WilliamsonHall method is smaller than that of Scherrer formula, which is due to the latter does not consider the effect of internal stress on the
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grain size 𝐷. Table 2 summarizes the obtained values of the average grain size 𝐷 for
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the samples annealed at 550C. With the increase of Ti content, D decreases from about
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15 for x=0 to the minimum value of 12 for x=1 and then increases to the maximum
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value of about 25 for x=3, which is still smaller than the magnetic exchange length Lex =
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35nm [28]. At the same time, the room-temperature μi increases from about 16000 for x=0 to the maximum value of 18000 for x=1 and then decreases dramatically to the
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minimum value of about 2000 for x=3. The variation of D and room-temperature μi can
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be explained by Herzer’s model [29], which points out that the μi is inversely
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proportional to D6. According to Herzer’s model: Hc=PK14D6/JsA3
(2)
i=PJsA3/0K14D6
(3)
Where P is a dimensionless prefactor and 0 is the vacuum magnetic permeability, K1 is the local anisotropy of the crystallites, A is the exchange constant, Js is average saturation magnetization, D is average grain size. It can be seen that i is inversely 11
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proportional to D6, which is consistent with the experimental results as shown in Fig. 6.
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Fig. 6. The Ti content dependences of initial permeability (μi) and average grain size (D) for Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys annealed at 550C for 0.5h.
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Table 2
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Average grain size of bcc-Fe(Si) phase calculated from X-ray diffraction patterns of
0
Average grain size (nm)
15
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Ti content x at.%
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A
Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) samples annealed for 0.5h at 550C.
1
2
3
12
16
25
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Fig. 7 shows the Ti content dependences of coercivity (Hc) and average grain size
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(D) for 550C-annealed Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys. It can be observed that the Hc decreases from 0.59 Oe for x=0 to the minimum value of about 0.54 Oe for x=1, and then increases to the maximum value of about 0.70 Oe for x=3.
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The variation of Hc and D is also consistent with the Herzer’s model.
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Fig. 7. The Ti content dependence of coercivity (Hc) and average grain size (D) of Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3) alloys annealed at 550C for 0.5h.
Therefore, we discuss the reasons for the high temperature permeability changing
N
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after adding Ti. After vacuum annealing at 550C, Fe-based nanocrystalline alloy is
A
composed of the crystalline phase and the remaining amorphous phase. The decrease of
M
initial permeability with the increase of temperature can be explained in two aspects. On the one hand, the thermal energy destroys the magnetic ordering state of the grains,
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deflects the magnetic moment orientation of each grain, then decreases the macroscopic
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magnetic moment of the alloy. On the other hand, the magnetic transformation of the residual amorphous phase has played a major role. When the temperature reaches the
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Tcam, residual amorphous phase firstly becomes paramagnetic, and the interaction between adjacent grains is blocked by the paramagnetic amorphous layer, hence the
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initial permeability decreases to almost zero. Another interpretation is the Hernando’s theory of the Curie temperature enhancement effects of Fe-based alloys which can be expressed as [30]: TcA = Tcam + (Tca-Tcam) 2L /
(4)
where TcA is the Curie temperature of intergranular amorphous matrix in two-phase 13
nanocrystalline alloy, Tcam is the Curie temperature of amorphous phase, Tca is the Curie temperature of crystalline phase, L is exchange penetration length and is distance between -Fe(Si) grains. The intersection of the maximum slope tangent in the μi -T curves and T axis is TcA, and the intersection point between the tangent and the T axis at
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the maximum slope of the second drop of high temperature permeability is Tca. By calculation, the value of 2L / is obviously smaller after adding Ti, which indicates that
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the exchange coupling interaction between adjacent grains is weakened, and the serious attenuation of permeability at high temperature is also explained.
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4. Conclusions
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Compared to the previously reported Finemet alloy, replacing Nb with Ti in
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Fe73.5Cu1Nb3Si17.5B5 alloy can decrease the onset primary temperature Tx1 from 803K to
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758K and enlarge the crystallization temperature interval ΔTx from 468K to 488K, which
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is in favor of precipitating a single soft magnetic phase in a wide temperature range. However, the Tcam shows a decreasing trend with Ti substitution for Nb. After annealing
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at 550C, Fe73.5Cu1Nb2Si17.5B5Ti1 alloy exhibits the higher room-temperature μi of about
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18000 and lower Hc of about 0.54 Oe. Such excellent soft magnetic properties of the Fe-based amorphous alloy have further improved the potential industrial applications. The room- and high-temperature properties of Fe73.5Cu1Nb3-xSi17.5B5Tix (x=0, 1, 2, 3)
A
alloys deteriorated when Ti completely replaced Nb, indicating that the role of Ti far less than that of Nb in preventing grain growth.
Acknowledgments This work was supported by National Natural Science Foundation of China (Grant 14
No. 51271130).
References [1] A. Kolano-Burian, R. Kolano, L.K. Varga, J. Alloys Compd. 483 (2009) 560. [2] H.A. Shivaee, H.R.M. Hosseini, E.M. Lotfabad, S. Roostaie, J. Alloys Compd. 491
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(2010) 487. [3] Y. Yoshizawa, S. Oguma, K. Yamauchi, J. Appl. Phys. 64 (1988) 6044.
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[4] G. Herzer, Acta Mater. 44 (2013) 718-734.
[5] T. Kulik, J. Ferenc, M. Kowalczyk, J. Mater. Process. Technol. 162 (2005) 215–
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219.
N
[6] X. H. Ma, Z. Wang, X. T. Han, et al., Mater. Sci. Eng. A. 448 (2007) 216.
A
[7] Y. Han, Z. Wang, J. Non-Cryst. Solids 434 (2016) 92.
M
[8] Y. Ueda, S. Ikeda, K. Minami, Mater. Sci. Eng. A. 181 (1994) 992–996.
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[9] D.T. Ngo, et al. J. Magn. Magn. Mater. 322 (2010) 342–347. [10] R. Shi, Z. Wang, Y. Jia, et al. J. Appl. Phys.112 (2012) 252.
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[11] K. Suzuki, A. Makino, A. Inoue, T. Masumoto, Jpn. J. Appl. Phys. 30 (1991) 1729.
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[12] M. Yan, H. Tong, S. Tao, J.H. Liu, J. Alloys Compd. 505 (2010) 264. [13] R.A. Young, The Rietveld Method, IUCr 5, Oxford University Press, Oxford, 1993, pp. 1–39.
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[14] J. Rodriguez-Carvajal, FULLPROF: A Program for Rietveld Refinement and Pattern Matching Analysis, Abstracts of the Satellite Meeting on Powder Diffraction of the XV Congress of the IUCr, p. 127, Toulouse, France. [15] A. D. Wang, H. Men, B. L. Shen, et al. Thin Solid Films, 519 (2011) 8283. 15
[16] J. D. Ayers, V. G. Harris, J. A. Sprague, et al. Appl. Phys. Lett. 64 (1994) 974. [17] M. Ohta., Y. Yoshizawa, J. Magn. Magn. Mater. 321 (2009) 2220. [18] R. Brzozowski, M. Wasiak, H. Piekarski, P. Sovak, P. Uznanski, M.E. Moneta, J. Alloys Compd. 470 (2009) 5.
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[19] K. Suzuki, G. Herzer, Adv. Magn. Nanostruct. (2006) 365. [20] T. H. Noh, M. B. Lee, H. J. Kim, and I. K. Kang, J. Appl. Phys. 67 (1990) 5568.
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[21] I. Orue, M.L. Fdez-Gubieda, F. Plazaola, J.M. Barandiaran, J. Phys. Condens. Mater. 10 (1998) 3807.
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[23] H. Tian. et al. Physica B. 407 (2012) 250-257.
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[22] A. Ghasemi, J. Alloys Compd. 645 (2015) 467.
M
A 304–306 (2001) 1046.
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[24] Z. Wang, K.Y. He, J. Jin, J. He, L. Zhang, H.W. Zhang, B.G. Shen, Mater. Sci. Eng.
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[25] A. Takeuchi, A. Inoue, Mater. Trans. 46 (2005) 2817. [26] G. K. Williamson, W.H. Hall, Acta Metall. 1 (1953) 22-31.
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[27] C. Wu, H. Chen, H. Lv, et al. J. Alloys Compd. 673 (2016) 278.
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[28] G. Herzer, Mater. Sci. Eng. A 133 (1991) 1. [29] G. Herzer, IEEE Trans. Magn. 26 (1990) 1397-1402.
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[30] C. Kuhrt and G. Herzer. IEEE Trans. Magn. 32 (1996) 4881.
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