- Email: [email protected]
Microstructure and magnetic properties of Fe–50%Ni alloy fabricated by powder injection molding
Journal of Magnetism and Magnetic Materials 329 (2013) 24–29
Contents lists available at SciVerse ScienceDirect
Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm
Microstructure and magnetic properties of Fe–50%Ni alloy fabricated by powder injection molding Jidong Ma, Mingli Qin n, Lin Zhang, Ruijie Zhang, Xuanhui Qu School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 April 2012 Received in revised form 9 October 2012 Available online 23 October 2012
Fe–50%Ni soft magnetic alloys were produced by powder injection molding using carbonyl iron and carbonyl nickel as raw materials. The effects of sintering temperature and time on the microstructure and magnetic properties of the alloys were investigated. The results indicate that the magnetic properties are dependent on the microstructure. The densification and grain size of the alloys increase with increasing sintering temperature and time, facilitating the enhancement of permeability and saturation induction, as well as the decrease of coercive force. In the case of the sintering temperature of 1360 1C for 10 h, the relative density of 97% and grain size of 200 mm were obtained, and the maximum permeability of 43,541, saturation induction of 1.48 T and coercive force of 6.8 A/m were achieved. Further elongation of sintering time did not bring about any increase of densification and grain size. & 2012 Elsevier B.V. All rights reserved.
Keywords: Fe–50%Ni alloy Powder injection molding Magnetic properties Microstructure Density
1. Introduction Fe–50%Ni alloy exhibits excellent magnetic performances of high permeability, high saturation induction, and low coercive force, which was widely used in computer, printer, disk drive components, and automobile fuel injection system components and so on [1–4]. With the development of magnetic devices toward microminiaturization and multifunction, the size of the soft magnetic parts becomes smaller while the shape of the components becomes more complex [5]. Conventional soft magnetic alloys were fabricated by the methods of casting and machining. The Fe–50%Ni alloy fabricated by casting, whose maximum permeability (mm) is 70,000; saturation induction (Bs) is 1.6 T, in the case of the relative density of 100% [6]. The magnetic properties is high, however, mass production of the miniaturization parts with complex shape was greatly limited due to the long production period, low efficiency and high cost. Powder injection molding (PIM) is a near-net shaping technique that is particularly advantageous for the applications where complex shape with high dimensional accuracy and high density are required [7–9]. Numerous researchers have studied the magnetic properties of Fe–50%Ni fabricated by PIM. However, data dispersibility of magnetic performances is large. For example, according to Tasovac and Baum [10], the highest value of maximum permeability of Fe–50%Ni is 17,800 and the corresponding value of saturation induction is 1.33 T. Miura et al. [11] have
n
Corresponding author. Tel.: þ86 10 62332700; fax: þ 86 10 62334321. E-mail address: [email protected] (M. Qin).
0304-8853/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jmmm.2012.10.019
reported the maximum permeability and saturation induction of Fe–50%Ni as 27,000 and 1.37 T, respectively. Duan et al. [12] have obtained the sample whose maximum permeability is 33,830 and saturation induction is 1.52 T. Until now, there is little systematic research on the relationship between microstructure, density and magnetic properties. This work provides a comparatively systematic study on the correlation between microstructural characteristics (porosity and grain size) and magnetic properties of Fe–50%Ni alloy fabricated by PIM. High magnetic performance of Fe–50%Ni with the maximum permeability of 43,541, saturation induction of 1.48 T and coercive force of 6.8 A/m was obtained.
2. Experimental The mixture of carbonyl iron and carbonyl nickel with the weight rate of 1:1 was used as the raw materials. The characteristics of the powders are given in Table 1. The mean particle sizes of carbonyl iron and carbonyl nickel are 4.33 and 4.45 mm, respectively. The morphologies of the two kinds of powder are shown in Fig. 1 Hydroxyl iron is mainly regular spherical particles without severe agglomeration, as shown in Fig. 1(a). It is displayed in Fig. 1(b) that carbonyl nickel has branched chain and obvious agglomeration is observed. Metal powder mixture and binder were mixed using a PSJ32 type mixer at the temperature range of 140–150 1C for 60–90 min. The wax-based as binder was composed of 60 wt% paraffin, 15 wt% high density polyethylene, 10 wt% polypropylene, 10 wt% polystyrene and 5 wt% stearic acid. The powder loading of the obtained feedstock was 60 vol%.
J. Ma et al. / Journal of Magnetism and Magnetic Materials 329 (2013) 24–29
The feedstock was injected into ring-shaped samples with a CJ-80E type injection molding machine at 150–160 1C. The injected preforms were subjected to solvent debinding and thermal debinding. Solvent debinding was carried out in trichloroethylene solvent at room temperature for 360 min, and 58 wt% of the binder was removed. Thermal debinding and pre-sintering was performed under hydrogen atmosphere with the top temperature of 800 1C with a total cycle of 900 min (Fig. 2). Subsequently, the debound samples were sintered at the temperature range of 1300–1380 1C for varied times. Optical microstructure was observed on MeF3A metallurgical microscope. Observation of the morphology of the starting elemental powder was conducted on S-360 scanning electronic microscope (SEM). The densities of the samples were measured by the Archimedes method. The magnetic properties such as saturation induction (Bs), coercive force (Hc) and maximum permeability (mm) were tested on the NIM-2000S dc soft magnetic properties measuring device. The static measurement was tested on the condition that the saturated magnetic field was 1600 A/m.
25
diffusion at high temperature. However, further increasing of temperature would induce the partial melt of the samples. As for soft magnetic, saturation induction belongs to the microstructure insensitive parameters, which depends on the chemical composition and density of the specimens. For a given alloy system, saturation induction is merely related to the density [13–16]. Thus, the
3. Results and discussion 3.1. Effect of sintering temperature Density is the key factor that affects the magnetic properties of PIM parts. Higher sintering temperature generates higher sintered density, which improves magnetic properties and microstructure. The effects of sintering temperature on density, microstructure and magnetic properties of Fe–50%Ni alloy were studied in the temperature range of 1300–1380 1C. Fig. 3 shows the effect of sintering temperature on the relative density and saturation induction of the specimens sintered at varied temperature for 2 h. The relative densities of the samples increase from 93.8% to 94.7% in the temperature range of 1300–1380 1C, and corresponding saturation induction increases from 1.315 T to 1.398 T. The densification is improved due to the enhancement of solid state
Fig. 2. Diagram of thermal debinding and pre-sintering process.
Table 1 Characteristics of the powders. Powder
Fe Ni
Mean particle size (mm)
4.33 4.45
rtap/ (g cm 3)
3.97 1.95
Impurity (wt%) C
O
N
0.63 0.06
0.27 0.049
o 0.001 o 0.001
Fig. 3. Effect of sintering temperature on the relative density and saturation induction.
Fig. 1. SEM images of powders: (a) hydroxyl iron; and (b) hydroxyl nickel.
26
J. Ma et al. / Journal of Magnetism and Magnetic Materials 329 (2013) 24–29
Fig. 4. Effect of sintering temperature on microstructures: (a) 1320 1C; (b) 1340 1C; (c) 1360 1C; and (d) 1380 1C.
reaches 21,890 and coercive force is 11.06 A/m at the sintering temperature of 1360 1C. Compared to the magnetic property of saturation induction, the maximum permeability and coercive force are microstructure sensitive parameters, which are influenced by the density, porosity and grain size [13,16,17]. As indicated in Figs. 3 and 4, higher sintering temperature generally results in higher sintered density as well as larger grain sizes, which improves the magnetic performance of Fe–50%Ni alloy. 3.2. Effect of sintering time
Fig. 5. Effect of coercive force.
sintering
temperature
on
maximum
permeability
and
saturation induction increases with the improvement of density, as shown in Fig. 3. Fig. 4 shows the effect of sintering temperature on the microstructures. It can be seen in Fig. 4(a) that the mean grain size is about 30 mm at the temperature of 1320 1C. The grains grow as the temperature increases. The black dots existing in the figure are porosities. It is obvious that the amount of porosity decreases when the temperature ranged between 1320 1C and 1360 1C. At the same time, coarsening of the grains occurs. The mean grain size grows to 100 mm when the temperature reaches 1360 1C. Fig. 5 shows the relationship between maximum permeability, coercive force and the sintering temperature. The maximum permeability increases while the coercive force decreases gradually with increasing temperature. The maximum permeability
In order to obtain higher magnetic performance of Fe–50%Ni, the effects of sintering time on microstructure, density and magnetic properties were investigated. Fig. 6 shows the microstructures of the specimens sintered at 1360 1C for 2–14 h. With the prolongation of sintering time, it is demonstrated in Fig. 6(a–c) that the porosity decreases with increasing sintering time, and the grain size increases from 100 mm to 200 mm in the sintering time range of 2–10 h. In the case of 10 h, the grain size reaches 200 mm and the grain boundary becomes straight (Fig. 6d). When the sintering time increased to 12 h and 14 h, minor changes in the microstructure can be observed, as shown in Fig. 6(e) and (f), respectively. Fig. 7 shows the effect of sintering time on the relative density and magnetic properties. It can be seen that the relative density, saturation induction and maximum permeability increases while the coercive force decreases with the elongation of sintering time. Relative density increases significantly in the sintering time range of 2–6 h. After sintered for 6 h, relative density of the specimen reaches 96.5–97% and saturation induction reaches 1.46–1.48 T. Relative density and saturation induction keep nearly constant after sintered for 6 h. It also can be seen that maximum permeability increases from 21,890 to 43,541, when the sintering time increases from 2 h to 10 h. It is noted that the density keeps almost the same after sintered for more than 6 h,
J. Ma et al. / Journal of Magnetism and Magnetic Materials 329 (2013) 24–29
27
Fig. 6. Effect of sintering time on microstructures at 1360 1C: (a) 2 h; (b) 4 h; (c) 6 h; (d) 10 h; (e) 12 h; and (f) 14 h.
but the maximum permeability shows noticeable increase. It is inferred that the increased maximum permeability is mainly attributed to the continued grain growth. This is corroborated by the fact that both the grain size and the maximum permeability exhibit minor change for the specimens sintered for more than 10 h. Fig. 8(a) and (b) are the hysteresis loop of the samples sintered at 2 h and 10 h, respectively. The small picture at the top corner is the larger version of the hysteresis loop. From Fig. 8(b), it can be seen that the hysteresis loop is long and narrow, which could quickly reach saturation state under the small external magnetic field, reflecting the characteristics of high permeability. Table 2 shows the dimensional changes of samples at different sintering time. The distortions of samples grow with increasing sintering time. The sample dimension keep constant after sintered for 6 h, which is consistent with the change of relative density. Table 3 shows the contents of impurities of different sintering time. It can be seen that the impurity levels reduce with the elongation of sintering time. It is well known that impurity content in the material can greatly influence magnetic performance [10,11]. Minimizing the impurity to the lowest possible level will result in improved magnetic performance.
3.3. Application The maximum permeability exceeds the reported value (17,800–33,830) of Fe–50%Ni produced by PIM. Fig. 9 shows the microcomplex shaped parts fabricated by PIM, which have been used as a component in the hearing aid. The conventional fabrication methods of casting and machining are very difficult to realize the mass production due to the long production period, low efficiency and high cost. As the permeability of the soft magnetic alloy is improved, the volume of the components can be reduced. This is meaningful for saving resource and energy, which is a firm foundation of the realization of miniaturization and highproperty of magnetic devices.
4. Conclusions Using carbonyl iron and carbonyl nickel as raw materials, Fe–50%Ni soft magnetic alloy was fabricated by PIM. The influence of sintering temperature and time on the microstructure and magnetic properties of the alloys was investigated. The results show that the performance of the injection molded Fe–50Ni alloy is closely associated with the microstructure. The densification
28
J. Ma et al. / Journal of Magnetism and Magnetic Materials 329 (2013) 24–29
and grain size of the alloys increase with increasing sintering temperature and time, leading to the enhancement of the maximum permeability and saturation induction, as well as the decrease of coercive force. In case of the sintering temperature of 1360 1C for 10 h, densification of 97% and grain size of 200 mm were obtained, and the maximum permeability of 43,541, saturation induction of 1.48 T and coercive force of 6.8 A/m were
Table 3 Contents of impurities of different sintering time. Sintering time (h)
C (%)
N (%)
O (%)
2 6 10
0.0025 0.0020 0.0015
0.0003 0.0002 0.0002
0.0084 0.0080 0.0077
Fig. 7. Effect of sintering time on the relative density and magnetic properties at 1360 1C.
Fig. 9. Photographs of minisize soft magnetic components.
Fig. 8. Hysteresis loop of samples at 1360 1C: (a) 2 h; and (b) 10 h.
Table 2 Testing results of samples distortions at 1360 1C for different sintering time. Sintering time (h)
2 6 10
Outside diameter (mm)
Inside diameter (mm)
Height (mm)
Absolute deformation
Relative deformation
Absolute deformation
Relative deformation
Absolute deformation
Relative deformation
5.03 5.13 5.13
0.132 0.135 0.135
3.12 3.22 3.22
0.125 0.129 0.129
0.70 0.71 0.71
0.140 0.142 0.142
J. Ma et al. / Journal of Magnetism and Magnetic Materials 329 (2013) 24–29
achieved. Further elongation of sintering time did not bring about the increase of densification and grain size, and minor changes in magnetic performance were observed.
Acknowledgments This work is financially supported by the Fundamental Research Funds for the Central Universities (FRF-TP-11-004A), the Program for New Century Excellent Talents in University (NCET-10–0226), and the Fok Ying Tung Education Foundation Fund for Young College Teachers (122016). References [1] J.A. Bas, J.A. Calero, M.J. Dougan, Journal of Magnetism and Magnetic Materials 254–255 (2003) 391–398. ¨ [2] D. Olekˇsa´kova´, S. Roth, P. Kolla´r, J. Fuzer, Journal of Magnetism and Magnetic Materials 304 (2006) 730–732. [3] K. Kusaka, T. Itoh, Y. Wanibe, Journal of the Japan Society of Powder and Powder Metallurgy 49 (2002) 430–437.
29
[4] G. Bodo, Journal of Magnetism and Magnetic Materials 290–291 (2005) 1419–1422. [5] D.C. Jiles, Acta Materialia 51 (2003) 5907–5939. [6] M. Tasovac, W. Louis, Baum Jr., Advances in Powder Metallurgy, MPIF, Princeton, 1988, pp. 189. [7] J.L. Johnson, R.M. German, Advanced Materials and Processes 161 (2003) 35–39. [8] R.M. German, Materials Research 7 (1998) 355–364. [9] G.J. Shu, K.S. Hwang, Y.T. Pan, Acta Materialia 54 (2006) 1335–1342. [10] M. Tasovac, L.W. Baum, Advances in Powder Metallurgy and Particulate Materials 48 (1993) 189–204. [11] H. Miura, S. Fujita, M. Fujita, R. Ninomiya, Journal of the Japan Society of Powder and Powder Metallurgy 47 (2000) 1261–1266. [12] B.H. Duan, X.H. Qu, M.L. Qin, Risk Management 25 (2006) 440–444. [13] R. Hamzaoui, O. Elkedim, N. Fenineche, E. Gaffet, J. Craven, Materials Science & Engineering, A 360 (2003) 299–305. [14] H. Shokrollahi, K. Janghorban, Journal of Materials Processing Technology 189 (2007) 1–12. [15] T. Waeckerle, H. Fraisse, Q. Furnemont, Journal of Magnetism and Magnetic Materials 290–291 (2005) 391–398. [16] H.H. Stadelmaier, Materials Science & Engineering, A 287 (2000) 138–145. [17] H. Miura, M. Yonetsu, M. Nakai, Y. Kawakami, Journal of the Japan Society of Powder and Powder Metallurgy 43 (1996) 858–862.
Contents lists available at SciVerse ScienceDirect
Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm
Microstructure and magnetic properties of Fe–50%Ni alloy fabricated by powder injection molding Jidong Ma, Mingli Qin n, Lin Zhang, Ruijie Zhang, Xuanhui Qu School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 April 2012 Received in revised form 9 October 2012 Available online 23 October 2012
Fe–50%Ni soft magnetic alloys were produced by powder injection molding using carbonyl iron and carbonyl nickel as raw materials. The effects of sintering temperature and time on the microstructure and magnetic properties of the alloys were investigated. The results indicate that the magnetic properties are dependent on the microstructure. The densification and grain size of the alloys increase with increasing sintering temperature and time, facilitating the enhancement of permeability and saturation induction, as well as the decrease of coercive force. In the case of the sintering temperature of 1360 1C for 10 h, the relative density of 97% and grain size of 200 mm were obtained, and the maximum permeability of 43,541, saturation induction of 1.48 T and coercive force of 6.8 A/m were achieved. Further elongation of sintering time did not bring about any increase of densification and grain size. & 2012 Elsevier B.V. All rights reserved.
Keywords: Fe–50%Ni alloy Powder injection molding Magnetic properties Microstructure Density
1. Introduction Fe–50%Ni alloy exhibits excellent magnetic performances of high permeability, high saturation induction, and low coercive force, which was widely used in computer, printer, disk drive components, and automobile fuel injection system components and so on [1–4]. With the development of magnetic devices toward microminiaturization and multifunction, the size of the soft magnetic parts becomes smaller while the shape of the components becomes more complex [5]. Conventional soft magnetic alloys were fabricated by the methods of casting and machining. The Fe–50%Ni alloy fabricated by casting, whose maximum permeability (mm) is 70,000; saturation induction (Bs) is 1.6 T, in the case of the relative density of 100% [6]. The magnetic properties is high, however, mass production of the miniaturization parts with complex shape was greatly limited due to the long production period, low efficiency and high cost. Powder injection molding (PIM) is a near-net shaping technique that is particularly advantageous for the applications where complex shape with high dimensional accuracy and high density are required [7–9]. Numerous researchers have studied the magnetic properties of Fe–50%Ni fabricated by PIM. However, data dispersibility of magnetic performances is large. For example, according to Tasovac and Baum [10], the highest value of maximum permeability of Fe–50%Ni is 17,800 and the corresponding value of saturation induction is 1.33 T. Miura et al. [11] have
n
Corresponding author. Tel.: þ86 10 62332700; fax: þ 86 10 62334321. E-mail address: [email protected] (M. Qin).
0304-8853/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jmmm.2012.10.019
reported the maximum permeability and saturation induction of Fe–50%Ni as 27,000 and 1.37 T, respectively. Duan et al. [12] have obtained the sample whose maximum permeability is 33,830 and saturation induction is 1.52 T. Until now, there is little systematic research on the relationship between microstructure, density and magnetic properties. This work provides a comparatively systematic study on the correlation between microstructural characteristics (porosity and grain size) and magnetic properties of Fe–50%Ni alloy fabricated by PIM. High magnetic performance of Fe–50%Ni with the maximum permeability of 43,541, saturation induction of 1.48 T and coercive force of 6.8 A/m was obtained.
2. Experimental The mixture of carbonyl iron and carbonyl nickel with the weight rate of 1:1 was used as the raw materials. The characteristics of the powders are given in Table 1. The mean particle sizes of carbonyl iron and carbonyl nickel are 4.33 and 4.45 mm, respectively. The morphologies of the two kinds of powder are shown in Fig. 1 Hydroxyl iron is mainly regular spherical particles without severe agglomeration, as shown in Fig. 1(a). It is displayed in Fig. 1(b) that carbonyl nickel has branched chain and obvious agglomeration is observed. Metal powder mixture and binder were mixed using a PSJ32 type mixer at the temperature range of 140–150 1C for 60–90 min. The wax-based as binder was composed of 60 wt% paraffin, 15 wt% high density polyethylene, 10 wt% polypropylene, 10 wt% polystyrene and 5 wt% stearic acid. The powder loading of the obtained feedstock was 60 vol%.
J. Ma et al. / Journal of Magnetism and Magnetic Materials 329 (2013) 24–29
The feedstock was injected into ring-shaped samples with a CJ-80E type injection molding machine at 150–160 1C. The injected preforms were subjected to solvent debinding and thermal debinding. Solvent debinding was carried out in trichloroethylene solvent at room temperature for 360 min, and 58 wt% of the binder was removed. Thermal debinding and pre-sintering was performed under hydrogen atmosphere with the top temperature of 800 1C with a total cycle of 900 min (Fig. 2). Subsequently, the debound samples were sintered at the temperature range of 1300–1380 1C for varied times. Optical microstructure was observed on MeF3A metallurgical microscope. Observation of the morphology of the starting elemental powder was conducted on S-360 scanning electronic microscope (SEM). The densities of the samples were measured by the Archimedes method. The magnetic properties such as saturation induction (Bs), coercive force (Hc) and maximum permeability (mm) were tested on the NIM-2000S dc soft magnetic properties measuring device. The static measurement was tested on the condition that the saturated magnetic field was 1600 A/m.
25
diffusion at high temperature. However, further increasing of temperature would induce the partial melt of the samples. As for soft magnetic, saturation induction belongs to the microstructure insensitive parameters, which depends on the chemical composition and density of the specimens. For a given alloy system, saturation induction is merely related to the density [13–16]. Thus, the
3. Results and discussion 3.1. Effect of sintering temperature Density is the key factor that affects the magnetic properties of PIM parts. Higher sintering temperature generates higher sintered density, which improves magnetic properties and microstructure. The effects of sintering temperature on density, microstructure and magnetic properties of Fe–50%Ni alloy were studied in the temperature range of 1300–1380 1C. Fig. 3 shows the effect of sintering temperature on the relative density and saturation induction of the specimens sintered at varied temperature for 2 h. The relative densities of the samples increase from 93.8% to 94.7% in the temperature range of 1300–1380 1C, and corresponding saturation induction increases from 1.315 T to 1.398 T. The densification is improved due to the enhancement of solid state
Fig. 2. Diagram of thermal debinding and pre-sintering process.
Table 1 Characteristics of the powders. Powder
Fe Ni
Mean particle size (mm)
4.33 4.45
rtap/ (g cm 3)
3.97 1.95
Impurity (wt%) C
O
N
0.63 0.06
0.27 0.049
o 0.001 o 0.001
Fig. 3. Effect of sintering temperature on the relative density and saturation induction.
Fig. 1. SEM images of powders: (a) hydroxyl iron; and (b) hydroxyl nickel.
26
J. Ma et al. / Journal of Magnetism and Magnetic Materials 329 (2013) 24–29
Fig. 4. Effect of sintering temperature on microstructures: (a) 1320 1C; (b) 1340 1C; (c) 1360 1C; and (d) 1380 1C.
reaches 21,890 and coercive force is 11.06 A/m at the sintering temperature of 1360 1C. Compared to the magnetic property of saturation induction, the maximum permeability and coercive force are microstructure sensitive parameters, which are influenced by the density, porosity and grain size [13,16,17]. As indicated in Figs. 3 and 4, higher sintering temperature generally results in higher sintered density as well as larger grain sizes, which improves the magnetic performance of Fe–50%Ni alloy. 3.2. Effect of sintering time
Fig. 5. Effect of coercive force.
sintering
temperature
on
maximum
permeability
and
saturation induction increases with the improvement of density, as shown in Fig. 3. Fig. 4 shows the effect of sintering temperature on the microstructures. It can be seen in Fig. 4(a) that the mean grain size is about 30 mm at the temperature of 1320 1C. The grains grow as the temperature increases. The black dots existing in the figure are porosities. It is obvious that the amount of porosity decreases when the temperature ranged between 1320 1C and 1360 1C. At the same time, coarsening of the grains occurs. The mean grain size grows to 100 mm when the temperature reaches 1360 1C. Fig. 5 shows the relationship between maximum permeability, coercive force and the sintering temperature. The maximum permeability increases while the coercive force decreases gradually with increasing temperature. The maximum permeability
In order to obtain higher magnetic performance of Fe–50%Ni, the effects of sintering time on microstructure, density and magnetic properties were investigated. Fig. 6 shows the microstructures of the specimens sintered at 1360 1C for 2–14 h. With the prolongation of sintering time, it is demonstrated in Fig. 6(a–c) that the porosity decreases with increasing sintering time, and the grain size increases from 100 mm to 200 mm in the sintering time range of 2–10 h. In the case of 10 h, the grain size reaches 200 mm and the grain boundary becomes straight (Fig. 6d). When the sintering time increased to 12 h and 14 h, minor changes in the microstructure can be observed, as shown in Fig. 6(e) and (f), respectively. Fig. 7 shows the effect of sintering time on the relative density and magnetic properties. It can be seen that the relative density, saturation induction and maximum permeability increases while the coercive force decreases with the elongation of sintering time. Relative density increases significantly in the sintering time range of 2–6 h. After sintered for 6 h, relative density of the specimen reaches 96.5–97% and saturation induction reaches 1.46–1.48 T. Relative density and saturation induction keep nearly constant after sintered for 6 h. It also can be seen that maximum permeability increases from 21,890 to 43,541, when the sintering time increases from 2 h to 10 h. It is noted that the density keeps almost the same after sintered for more than 6 h,
J. Ma et al. / Journal of Magnetism and Magnetic Materials 329 (2013) 24–29
27
Fig. 6. Effect of sintering time on microstructures at 1360 1C: (a) 2 h; (b) 4 h; (c) 6 h; (d) 10 h; (e) 12 h; and (f) 14 h.
but the maximum permeability shows noticeable increase. It is inferred that the increased maximum permeability is mainly attributed to the continued grain growth. This is corroborated by the fact that both the grain size and the maximum permeability exhibit minor change for the specimens sintered for more than 10 h. Fig. 8(a) and (b) are the hysteresis loop of the samples sintered at 2 h and 10 h, respectively. The small picture at the top corner is the larger version of the hysteresis loop. From Fig. 8(b), it can be seen that the hysteresis loop is long and narrow, which could quickly reach saturation state under the small external magnetic field, reflecting the characteristics of high permeability. Table 2 shows the dimensional changes of samples at different sintering time. The distortions of samples grow with increasing sintering time. The sample dimension keep constant after sintered for 6 h, which is consistent with the change of relative density. Table 3 shows the contents of impurities of different sintering time. It can be seen that the impurity levels reduce with the elongation of sintering time. It is well known that impurity content in the material can greatly influence magnetic performance [10,11]. Minimizing the impurity to the lowest possible level will result in improved magnetic performance.
3.3. Application The maximum permeability exceeds the reported value (17,800–33,830) of Fe–50%Ni produced by PIM. Fig. 9 shows the microcomplex shaped parts fabricated by PIM, which have been used as a component in the hearing aid. The conventional fabrication methods of casting and machining are very difficult to realize the mass production due to the long production period, low efficiency and high cost. As the permeability of the soft magnetic alloy is improved, the volume of the components can be reduced. This is meaningful for saving resource and energy, which is a firm foundation of the realization of miniaturization and highproperty of magnetic devices.
4. Conclusions Using carbonyl iron and carbonyl nickel as raw materials, Fe–50%Ni soft magnetic alloy was fabricated by PIM. The influence of sintering temperature and time on the microstructure and magnetic properties of the alloys was investigated. The results show that the performance of the injection molded Fe–50Ni alloy is closely associated with the microstructure. The densification
28
J. Ma et al. / Journal of Magnetism and Magnetic Materials 329 (2013) 24–29
and grain size of the alloys increase with increasing sintering temperature and time, leading to the enhancement of the maximum permeability and saturation induction, as well as the decrease of coercive force. In case of the sintering temperature of 1360 1C for 10 h, densification of 97% and grain size of 200 mm were obtained, and the maximum permeability of 43,541, saturation induction of 1.48 T and coercive force of 6.8 A/m were
Table 3 Contents of impurities of different sintering time. Sintering time (h)
C (%)
N (%)
O (%)
2 6 10
0.0025 0.0020 0.0015
0.0003 0.0002 0.0002
0.0084 0.0080 0.0077
Fig. 7. Effect of sintering time on the relative density and magnetic properties at 1360 1C.
Fig. 9. Photographs of minisize soft magnetic components.
Fig. 8. Hysteresis loop of samples at 1360 1C: (a) 2 h; and (b) 10 h.
Table 2 Testing results of samples distortions at 1360 1C for different sintering time. Sintering time (h)
2 6 10
Outside diameter (mm)
Inside diameter (mm)
Height (mm)
Absolute deformation
Relative deformation
Absolute deformation
Relative deformation
Absolute deformation
Relative deformation
5.03 5.13 5.13
0.132 0.135 0.135
3.12 3.22 3.22
0.125 0.129 0.129
0.70 0.71 0.71
0.140 0.142 0.142
J. Ma et al. / Journal of Magnetism and Magnetic Materials 329 (2013) 24–29
achieved. Further elongation of sintering time did not bring about the increase of densification and grain size, and minor changes in magnetic performance were observed.
Acknowledgments This work is financially supported by the Fundamental Research Funds for the Central Universities (FRF-TP-11-004A), the Program for New Century Excellent Talents in University (NCET-10–0226), and the Fok Ying Tung Education Foundation Fund for Young College Teachers (122016). References [1] J.A. Bas, J.A. Calero, M.J. Dougan, Journal of Magnetism and Magnetic Materials 254–255 (2003) 391–398. ¨ [2] D. Olekˇsa´kova´, S. Roth, P. Kolla´r, J. Fuzer, Journal of Magnetism and Magnetic Materials 304 (2006) 730–732. [3] K. Kusaka, T. Itoh, Y. Wanibe, Journal of the Japan Society of Powder and Powder Metallurgy 49 (2002) 430–437.
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