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Volume 50, Issue 1
Displaying 1-12 of 12 articles from this issue
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Kazushige Kamihira, Tadayuki Fujii2003 Volume 50 Issue 1 Pages 3-7
Published: January 15, 2003
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSIn order to understand in detail the secondary recrystallization behavior of dispersion strengthened molybdenum sheet made by adding a certain amount of La2O3 the influence of La2O3 additives on the secondary grain growth behavior was investigated by use of EPMA and chemical analyses. The results obtained were as follows:
(1) Second phase, which are dispersed in the form of La2O3 as a stable oxide at the primary grain boundaries and matrices, plays an important role as inhibitors to the normal grain growth and conversely as promoters of the secondary grain growth at higher temperatures.
(2) At higher temperatures the dissociation and dissolution of second phase consisting of La2O3 are taken place, resulting in development of secondary grain growth.
(3) A single crystal sheet can be easily prepared from La2O3 dispersion strengthened molybdenum sheet.View full abstractDownload PDF (3340K) -
[in Japanese]2003 Volume 50 Issue 1 Pages 10
Published: January 15, 2003
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSDownload PDF (98K) -
Kurima Kobayashi, Mika Nakamura, Takahiro Akiya, Kazuo Hayakawa2003 Volume 50 Issue 1 Pages 11-15
Published: January 15, 2003
Released on J-STAGE: July 12, 2010
JOURNAL FREE ACCESSThe domain wall motion in the multi-domain particles in Sm2Fe17N3(SFN)powder reacted with Zn metal samples was studied.In the samples, 2 wt.% of SFN particles were homogeneously, isotropically distributed in Zn metal powder, and pressed under 20 MPa, followed by heat-treatment at various temperatures. The saturable multi-domain particles (SMDP) in the sample powders were magnetized into the single-domain state after the pulse magnetization in 5 T. The magnetization reversal in SMDP after magnetization became difficult in the heat-treated samples. The reversal behavior, which can be detected by susceptibility measurements, should be the origin of the enhancement of coercivity. For example, the coercivity (μoH) is about 0.4 T larger in the 623 K treated sample than that of the untreated sample. The direct observation of the domain structures before and after the magnetization in untreated SMDP was also curried out using magnetic force microscopy (MFM).View full abstractDownload PDF (3463K) -
Hiroshi Yamamoto, Hironori Iwase2003 Volume 50 Issue 1 Pages 16-21
Published: January 15, 2003
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSExperiments were carried out to investigate the magnetic properties of Sm-Fe-Co-W-Cu system nitriding compounds with TbCu7-type structure. Sm10(Fe0.95Co0.05)89.7-xW0.3Cux(x=0-0.7)alloy ribbons were prepared by the single roller rapid-quenching method, and the effects of alloy composition, and conditions of heat-treatment and nitrogenation, were examined with regards to their magnetic properties. The optimum preparation conditions of the compounds are as follows: Composition: {Sm10(Fe0.95Co0.05)89.4W0.3Cu0.3}85.1N14.9, roller velocity: 50m/s, heat treatment: 675°C×60 min in high-purity Ar gas, and nitriding condition: 420°C×15 h in high-purity N2 gas. The typical magnetic properties of the obtained compound powders are Jr=0.94T, HcJ=716.2 kA/m, HcB=519.2kA/m, (BH)max=138.1 kJ/m3(17.4 MGOe), and Tc=492°C. It was found that this sample was an exchange spring magnet from TEM photographs and recoil loops of the hysteresis curve. The value of(BH)max for the compression-molded isotropic bonded magnet prepared from the {Sm10(Fe0.95Co0.05)89.4W0.3Cu0.3}85.1N14.9 powder is 102.3 kJ/m3(12.9 MGOe), when the density of bonded magnet is 6.07 Mg/m3. The reversible temperature coefficient of Jr is α(Jr)=-0.047%/°C, the temperature coefficient of HcJ in the range from 25°C to 125°C obtained by a linear extrapolation is α(HcJ)=-0.45 %/°C.View full abstractDownload PDF (1722K) -
Mitsuaki Mochizuki, Michihisa Shimizu, Masao Murakawa, Shigeho Tanigaw ...2003 Volume 50 Issue 1 Pages 22-27
Published: January 15, 2003
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSThe magnetic properties and crystal structures of nanocrystalline Sm-Fe-Co-Nb-B compounds were studied using rapid quenching technique and powder x-ray diffraction analysis. As a result, it was found that the TCu7-type structure was able to be obtained even if the B content of the ribbons was around 8at%, and high magnetic properties was obtained. In over-annealing conditions, the TbCu7-type structure transforms to Sm2(Fe, Co)14B1 and α-(Fe, Co) phases. Optimizing the compositions and preparing conditions, the following results have been obtained; compositions: Sm6.2Fe82.8-xCoxNb2.7B8.3(x=12-16); roll surface velocity: 16-18m/s; annealing conditions: 640°C×(1.5-2.5)h; magnetic properties: HCJ, =0.55-0.60 MA/m, Br=0.85-0.95T, (BH)max=100-120kJ/m3; temperature coefficients: -α=0.05-0.06%/°C, -β=0.33-0.35%/°C. Curie temperature: Tc>500°C, Grain size of the ribbon was about 20nm and halo component in x-ray pattern was around 30%. Outside the suitable composition or annealing conditions, Sm3(Fe, Co)62B14, Sm2(Fe, Co)23B3, Sm2(Fe, Co)14B1 or α-(Fe, Co) phases appeared.View full abstractDownload PDF (1754K) -
Katsuhiko Mori, Kazunori Igarashi, Ryoji Nakayama, Koichiro Morimoto2003 Volume 50 Issue 1 Pages 28-33
Published: January 15, 2003
Released on J-STAGE: July 12, 2010
JOURNAL FREE ACCESSNd12.6-xDyxFebal.CoyB6.2Zr0.1Ga0.3(x =0.3-1.9, y =5.8-18.3) alloys were processed by improved HDDR process with intermediate argon treatment and desorption under constant H2 pressure to increase remanence and coercivity, respectively. In this study, we investigated effect of Co and Dy contents on the magnetic properties of the HDDR powders. By the improved process, remanence of HDDR powders containing 0.3 at.% Dy and 12 to 16 at.% Co is increased to a maximum of 0.96 T, and coercivity of them containing 0.9 to 1.6 at.% Dy and 5.8 at.% Co is increased to the maximum of 1570 kA/m. Undecomposed (Nd, Dy)2(Fe, Co)14B phase remains in HDDR powders including Dy above the critical content expressed by the line drawn from 0.6 at.% Dy and 18.3 at.% Co to 1.9 at.% Dy and 7.8 at.% Co. The magnetic properties of the bonded magnets with density of 6.2 Mg/m3 made from the Nd12.0Dy0.6Febal.Co5.8B6.2Zr0.1Ga0.3 anisotropic HDDR powder areas follows: Br =0.87 T, HCJ=1530 kA/m and (BH)max =137 kJ/m3. Its temperature coefficient of remanence is -0.11%/°C and of coercivity is -0.43 %/°C.View full abstractDownload PDF (2082K) -
Hideaki Ono, Tetsuro Tayu, Norihisa Waki, Tatsuo Sugiyama, Munekatsu S ...2003 Volume 50 Issue 1 Pages 34-40
Published: January 15, 2003
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSAnisotropic magnet powders are generally prepared via the usual hydrogenation decomposition desorption recombination.(HDDR) process after heat-treating raw material master alloys for a long time to homogenize them. In this study, the possibility of omitting the homogenization heat treatment, i.e., the applicability of the HDDR process to as-cast Nd-Fe-B system master alloys with segregation, was examined with the aim of reducing the process cost. The HDDR powders made from the as-cast alloy with segregation showed anisotropy, large coercive force, and good magnet characteristics. At the conclusion of the hydrogen decomposition (HD) process, areas having a fine structure composed of NdH2+α-Fe+Fe2B and large-scale areas with α-Fe and Nd-rich parts measuring 30μm in size were observed. However, after the desorption recombination (DR) process was completed, the Nd2Fe14B phase was formed over the whole alloy. The Nd2Fe14B phase after the HDDR process had an almost homogeneous structure, which was composed of recombined crystals with a fine grain size of 300-400nm.View full abstractDownload PDF (3686K) -
Masafumi Fukuzumi, Yuji Kaneko, Kazuhiko Majima2003 Volume 50 Issue 1 Pages 41-44
Published: January 15, 2003
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSEffects of Co addition on improving the corrosion resistance of Nd-Fe-B ternary alloy have been investigated through the measurements of potentiodynamic polarization curves. Nd-Fe-B ternary magnets are easily corroded with contact of wet air because the natural electrode potential (Ecorr) of Nd-rich phase shows almost half level compared with that of 2-14-1 phase. In order to improve reliability of Nd-Fe-B magnets, it is necessary to control the component phases of the magnets as follows; 1) Improvement of the Ecorr, level of main phase to be noble potential, 2) Improvement of the difference of Ecorr between main phase and grain boundary phase to be minimum. Our research shows that Ecorr of Nd11.8Fe82.3-xCoxB5.9(x=0, 5, 10, 20, 50) alloys varies with Co content of the alloy because standard redox potential of Co is higher than that of Fe. In addition, the relation between weight changes by oxidation under 80°C×90%R.H. test and Ecorr of Nd11.8Fe82.3-xCoxB5.9(x=0, 5, 10, 20, 50) alloys shows a linear correlation. This result indicates the corrosion resistance of Nd-Fe-B magnets is estimated by the polarization evaluation.View full abstractDownload PDF (1563K) -
Shigeru Takaki, Ken Makita, Atsuki Okamoto2003 Volume 50 Issue 1 Pages 45-49
Published: January 15, 2003
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSIn order to investigate the texture formation of Nd-Fe-B system sintered magnet, 006 Miller indices pole figures of (Nd⋅Dy)2Fe14B phase were measured for as-compacted sample and for as-sintered one by X-ray diffraction. The degree of preferred orientation P was estimated by the integration of the product between the normalized diffraction intensity IN and cosα, which α is the inclined angle between the direction of the applied magnetic field and that of the magnetic moment in each grain. As a result, P had good corelation with the remanence Br in sintered sample. P in as-compacted sample was always lower than that in as-sintered one. The difference between as-sintered state and as-compacted state was largest when the magnetic field was 0.2T.View full abstractDownload PDF (363K) -
Satoru Ishihara, Wei Zhang, Akihisa Inoue2003 Volume 50 Issue 1 Pages 50-57
Published: January 15, 2003
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSConsolidation of Fe67Co95Nd3Dy0.5B20 glassy powders has been tried by uniaxial hot-pressing in the supercooled liquid state in order to synthesize a hard magnetic bulk material. Effects of hot-press temperature and powder size on the consolidation of the glassy powders were investigated. The powders sieved to 45 -90μm were heated up to temperatures in a range from 783 to 853 K under a pressure of 780 MPa. The glassy powders could be consolidated into bulk forms with relative densities above 99.0% by hot-pressing at 823 K and higher. The structure kept a glassy single phase for the compacts consolidated at 833 K and lower. These as-hot-pressed samples exhibited soft magnetic characteristics, but the soft magnetism changed to a hard type by annealing-induced crystallization. The remanence, coercivity and maximum energy product for the bulk compact consolidated at 833 K, followed by annealing for 600 s at 873 K were 1.03 T, 275 kA/m and 83.8 kJ/m3, respectively. The compact of the 90-150, um powders hotpressed at 833 K showed almost the same results as those made of the 45-90μm powder, while the density and magnetic properties were deduced for the compact of the powders sieved to under 45μm.View full abstractDownload PDF (3934K) -
Toshio Kagotani, Daisuke Fujiwara, Satoshi Sugimoto, Koichiro Inomata, ...2003 Volume 50 Issue 1 Pages 58-62
Published: January 15, 2003
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSMicrowave radiation in the GHz band is increasingly being used in many various communication devices. However, this has brought about the problems of electromagnetic interference (EMI). Now M-type Ba ferrite is expected to be used as a powerful countermeasure to EMI. Our recent works have shown that M-type Ba ferrite is promising material for microwave absorber in the GHz range. The electromagnetic resonance absorption properties depend on the complex permeability μ=μ'-jμ", particularly the imaginary part μ"=Ms/2HAα(Ms: saturation magnetization, HA: anisotropy field, a: extinction coefficient). We investigated the effects of substitution composition (x) of Me for Ba (Me: La) and substitution composition (y) of Me ion (Me: Zn, Zr, Sn) for Fe3+ on the electromagnetic absorption properties of the Ba1-xLaxZnxFe12-x-y(Me0.5Mn0.5)yO19 compound. The c-axis aligned samples were formed into toroidal shapes. The magnetic properties (Ms, HA) and the resonance absorption properties (μr', μr" etc) were measured using a VSM and a network analyzer. The aligned Zr-substituted samples (x=0.0, y=1.4) showed values of HA =0.21 MAm-1, and μ'= 7.5 and μ" =7.1 that were higher than those of (TiMn) substituted samples. The matching thickness dm decreased to 0.8 mm at the matching frequency of 7.6 GHz. In the sample of x=0.0 and y=1.5, μ'=7.7 and μ" = 6.7 were obtained, and the matching thickness dm was 0.98 mm at 5.95 GHz. Also, Sn-substituted samples showed high m' and m" values of 6.3 and 6.3, respectively, and dm of 1.02mm. It is therefore concluded that Sn or Zr substitution is effective in enhancing the electromagnetic wave absorption characteristics of M-type Ba ferrite absorber.View full abstractDownload PDF (419K) -
Toru Maeda, Nobuki Tezuka, Toshio Kagotani, Satoshi Sugimoto, Koichiro ...2003 Volume 50 Issue 1 Pages 63-67
Published: January 15, 2003
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSThe RE-Fe-B (RE=Rare earth) compounds have a possibility to be used as electromagnetic (EM) wave absorption materials in the GHz range, because of their high saturation magnetization and large anisotropy field. This paper describes the natural resonance phenomena and the EM wave absorption properties of Sm-substituted Y2Fe14B resin composites, which were measured in the GHz frequency range. The (Y1-xSmx)2Fe14B powders showed an uniaxial anisotropy in the samples of x=0 to 0.12, and their anisotropy fields decreased with increasing x value. However, the easy axis of magnetization changed to basal plane in the samples of x> 0.15. The natural resonance frequency (fr) of the sample with x=0, was calculated as 51.0 GHz from its anisotropy field. The calculated fr value showed a tendency to decrease with increasing x value and exhibited a minimum value of 20.8 GHz in the sample of x=0.15. The magnetic resonance phenomenon were observed in the epoxy resin composites of these powders, and the resonance frequencies showed a good agreement with their calculated f, values. The x=0.10 sample absorbed the EM wave over 99% at 22 GHz with the thickness of 0.69 mm, which is 30% thinner than that of the M-type ferrite/resin absorber. It can be considered that the sample can function as an electromagnetic wave absorber at frequencies around 22 GHz, where one kind of wireless LANs is now planned.View full abstractDownload PDF (410K)
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