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ABSTRACT: Sintered [Nd 0.45 (La r Dy 1 ) 1/(r+1)*0.55 ] 2.6 Fe 14 B magnets (r = 1 to 3) were studied. Magnetic properties and microstructures of the magnets were investigated by magnetic measurements and electron microprobe analysis. The microstructure of magnets consists of a mixed rare-earth (MRE) 2 Fe 14 B (2: 14: 1) phase matrix having a grain size of ∼8 μm and a rare earth (RE)-rich grain boundary phase. The grain boundaries are rich in La and Nd but depleted in Dy, while the La, Nd, and Dy contents are constant across the 2: 14: 1 grains. The coercivity and temperature stability of magnets are improved with increasing Dy content. A (BH) max of 21.1 MGOe at room temperature is obtained in the magnet with r = 1. Temperature coefficients of α = -0.06 and β = -0.48% °C were also obtained, which is comparable to those of Nd-based magnets with the best temperature stability. Unfortunately, the improvement of coercivity and its temperature coefficient is mainly achieved by adding greater amounts of Dy and DyF 3 , which leads to low (BH) max values and high magnet costs.
Journal of Applied Physics 05/2011; · 2.17 Impact Factor
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ABSTRACT: The grain pinning behavior of TiC particles in a rapidly solidified MRE-Fe-B (MRE = Nd + Y + Dy) nanocrystalline hard magnet was studied using electron tomography (ET). The 3D reconstruction overcomes the inherent 2D nature of conventional transmission electronmicroscopy (TEM) to reveal how this grain boundary phase controls the nanoscale structure in the rapidly solidified alloy. The 3D reconstruction was performed on the optimally annealed alloy (750 °C/15 min) with hard magnetic properties of Mr = 8.1 kGs, Hc = 6.2 kOe, (BH)max = 11.2 MGOe measured at 300 k. The sampled volume, 425 × 425 × 92.5 nm3, contains more than 20 grains of the RE2-14-1 phase and more than 70 TiC nanoparticles. The TiC grains’ shapes depend on their sizes and locations along the grain boundary. Most of the TiC particles are oval or short rod like shapes and range from 5 nm to 10 nm. TiC particles less than 10 nm formed between adjacent 2-14-1 grains, while the largest ones formed at triple junctions. There are ∼1.7 × 108 TiC particles within a 1 mm3 volume in the alloy. This accounts for the strong grain boundary pinning effect, which limits grain growth during annealing.
Journal of Applied Physics 03/2011; 109(7):07A705-07A705-3. · 2.17 Impact Factor
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ABSTRACT: Sintered [ Nd <sub>0.45</sub>( Y <sub>3</sub> Dy <sub>1</sub>)<sub>0.25<sup>*</sup>0.55</sub>]<sub>2.8</sub> Fe <sub>14</sub> B magnets were prepared for the first time. Magnetic properties and microstructures of the magnets were investigated by magnetic measurements and electron microprobe analysis. The microstructure consists of a MRE <sub>2</sub> Fe <sub>14</sub> B (2-14-1) phase matrix having a grain size of ∼10 μ m and a RE-rich grain boundary phase. However, sintering resulted in segregation of Y to the inner and Nd to the outside of the 2-14-1 grains. The magnet has a room temperature ( BH )<sub> max </sub> of 25.4 MGOe, which is two times higher than that of the isotropic melt spun ribbons with similar compositions. The temperature coefficients of Br (α) and Hcj (β) for the magnet are -0.150 and -0.632 % /° C from 27 to 127 ° C , respectively. These temperature coefficients, especially for β , are also much higher than those of melt spun ribbons. The composition segregation in the 2-14-1 grains is believed to be responsible for the higher temperature coefficients.
Journal of Applied Physics 06/2010; · 2.17 Impact Factor
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ABSTRACT: Gas atomization powder with Zr substitutions for the MRE and ZrC additions were systematically studied. The results show that the partial substitutions of Zr and the ZrC additions effectively improved glass formability in the alloys. Scanning electron microscopy (SEM) revealed that the as-atomized powder with a particle size of less than 32 μ m is predominately uniform equiaxed grains with an average grain size of 1.5 μ m . X-ray diffraction and differential thermal analysis measurements detected very tiny amounts of amorphous phase. After annealing at 700 ° C for 15 min, the SEM grain microstructure exhibits a minor change, but magnetic properties are substantially improved. M versus T measurements reveal that the phase composition evolved from 2:14:1 plus a small amount of 2:17 phases to a single 2:14:1 phase during the annealing process. The sieve analysis of the powders showed a particle size distribution with 90 wt % of the powder less than 45 μ m . The magnetic properties of the annealed powder varied with particle size. (BH)<sub> max </sub> first increases with increasing particle size from 5 μ m , reaches the peak value in the size range of 20–25 μ m , and then decreases with increasing particle size. For the 20–25 μ m powder sample annealed at 700 ° C for 15 min, the (BH)<sub> max </sub> of 9.6 MG Oe at room temperature and 5.6 MG</ro-
man> Oe at 200 ° C were obtained, respectively.
Journal of Applied Physics 05/2009; · 2.17 Impact Factor
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ABSTRACT: An MRE <sub>2</sub>( Fe , Co )<sub>14</sub> B alloy with Zr substitution and TiC addition was systematically studied. It was found by means of X-ray diffraction, transmission electron microscopy (TEM) and magnetic measurements that the combination of Zr substitution and TiC addition yields adequate microstructural control in both gas atomization (GA) and melt spinning (MS) techniques. For MS ribbons, an H<sub>cj</sub> of 11.7 kOe and (BH)<sub> max </sub> of 11.9 MG Oe at 27 ° C were obtained in the ribbons spun at 16 m / s and annealed at 700 ° C for 15 min . For GA powders, an H<sub>cj</sub> of 9.1 kOe and (BH)<sub> max </sub> of 9.2 MG Oe at 27 ° C were obtained in 20–25 μ m GA powder annealed at 700 ° C for 15 min . The temperature coefficients of B<sub>r</sub> and H<sub>cj</sub> are 0.06 and 0.36%/° C for the MS ribbon and 0.09 and 0.4%/° C for the GA powder in the temperature range of 27–100 ° C , respectively. TEM images revealed that the MS ribbon consists of a fine and uniform microstructure with an average size of 30 nm </-
formula>, while the GA spherical powder consists of an interior coarsened microstructure with a grain size of 80 nm and a rim area with a grain size of 10 nm .
Journal of Applied Physics 06/2007; · 2.17 Impact Factor
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ABSTRACT: The partitioning behavior of various rare-earth (RE) elements during solidification and their segregation behavior at the grain boundaries were investigated in nanocrystalline ( Y <sub>0.5</sub> Dy <sub>0.5</sub>)<sub>2.2</sub> Fe <sub>14</sub> B and ( Nd <sub>0.5</sub> Y <sub>0.25</sub> Dy <sub>0.25</sub>)<sub>1.8</sub> Zr <sub>0.4</sub> Co <sub>1.5</sub> Fe <sub>12.5</sub> B alloys by transmission electron microscopy and atom probe tomography. The best hard magnetic properties obtained are H<sub>cj</sub>=22 kOe , B<sub>r</sub>=5.10 kG , and (BH)<sub> max </sub>=5.97 MG Oe for the Y–Dy-based alloy and H<sub>cj</sub>=10.6 kOe , B<sub>r</sub>=6.64 kG , and (BH)<sub> max </sub>=9.56 MG Oe for the Y–Nd–Dy based alloy. The grain size of the Y–Dy based alloy was ∼50 nm . The Y–Nd–Dy based alloy had an overall finer, bimodal grain size. An intergranular ( Y <sub>0.36</sub> Dy <sub>0.64</sub>)<sub>6</sub> Fe <sub>23</sub> phase was detected in the Y–Dy based alloy. A uniform distribution of RE elements was found within the 2-14-1 grains in both alloys. The Y :( Dy + Nd ) ratio in the Y–Nd–Dy alloy was lower than its nominal composition, indicating that the Y is segregating to grain boundaries or forming a second phase.
Journal of Applied Physics 05/2006; · 2.17 Impact Factor
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ABSTRACT: Effects of a TiC addition on microstructure and magnetic properties in [ MRE <sub>2.2</sub> Fe <sub>14</sub> B ]<sub>(100-2x)/17.2</sub>+ Ti <sub>x</sub> C <sub>x</sub>( MRE = Nd + Y + Dy ,x=1–5) ribbons, melt spun at a wheel speed of 16 m / s , were systematically studied. X-ray diffraction and differential thermal analysis data revealed that the addition of TiC improves the glass formability in the mixed rare earth alloys without Co, resulting in partially amorphous alloys. TEM observations showed that the average grain size in the as spun samples decreases from 200 to 20 nm with increasing x from 1 to 5, confirming that the addition of TiC can significantly improve microstructure. For an optimized [ MRE <sub>2</sub>( Fe , Co )<sub>14</sub> B ]<sub>(100-2x)/17.2</sub>+ Ti <sub>x</sub> C <sub>x</sub> sample with x=2 , spun at 25 m / s and annealed at 750 °C for 15 min, the room-temperature magnetic properties of H <sub> cj </sub>=11.8 kOe , M<sub>r</sub>=7.2 kGs , and ( BH )<sub> max </sub>=11.3 MGOe were obtained. Temperature coefficients for M<sub>r</sub> and H <sub> cj </sub> of -0.06 and -0.37%/° C , respectively, also were measured in the temperature range of 27–100 °C. The new magnet alloy exhibits more uniform magnet-
ic properties and a usable energy product to nearly 300 °C.
Journal of Applied Physics 05/2006; · 2.17 Impact Factor
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ABSTRACT: A microstructural characterization was performed on 3 iron-based bulk metallic glasses. These alloys were an arc cast Fe 61 Y 2 Zr 8 Co 6 Al 1 Mo 7 B 15 A2 alloy, a twin roll cast Fe 68 Y 2 Zr 2 Nb 2 Cr 1.5 V 4.5 B 20 DarpaQ21 alloy and a vacuum induction melted Fe 50.7 Y 1.5 Cr 14.5 Mo 13 C 14.8 B 5.5 Darva101-Y alloy. The alloys were characterized by scanning electron microscopy and atom probe tomography in the as-cast condition. Some micrometer and nanometer scale precipitates were observed in all 3 alloys indicating that the alloy compositions are not fully optimized in the as-cast state. The Darva101-Y alloy was also characterized after annealing above the onset of crystallization temperature for 1 h at 610 8C. This annealing treatment produced a mixture of crystalline phases: M 6 (BC) and Fe 14 Y 2 B in addition to a high temperature M 23 C 6 phase that is indicated from XRD and previous research.
04/2006;
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ABSTRACT: The effect of Zr substitution on the microstructure and magnetic properties in [ Nd <sub>0.5</sub>( Y Dy )<sub>0.25</sub>]<sub>2.2-x</sub> Zr <sub>x</sub> Co <sub>1.5</sub> Fe <sub>12.5</sub> B (x=0–0.7) ribbons melt spun at a wheel speed of 10 m / s has been systematically studied. For as-spun Zr-free ribbon, a coercivity H<sub> cj </sub> of 15.5 kOe is obtained but the demagnetization curve exhibits a large shoulder, resulting in a very low maximum energy product (BH)<sub> max </sub>(3 MGOe ) . With increasing Zr content (x) , H<sub> cj </sub> first decreases and then increases. When x=0.4 , both H<sub> cj </sub> and (BH)<sub> max </sub> reach their optimized values of 10.6 kOe and 9.6 MGOe , respectively. The H<sub> cj </sub> and (BH)<sub> max </sub> for the sample at 200 ° C are 5 kOe and 4.3 MGOe , respectively. Transmission electron microscopy characterizations show that the average grain size is 200, 65, and 50 nm for x=0 , 0.4, and 0.7, respectively, indicating that the substitution of Zr can effectively inhibit grain growth. However, an excessive substitution of Zr results in the appearance of the 2:17 phase and thus the reduction of magnetic properties.
Journal of Applied Physics 06/2005; · 2.17 Impact Factor
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ABSTRACT: The effect of Nd substitution on microstructure and magnetic properties in [Nd<sub>x</sub>(YDy)<sub>0.5(1-x)</sub>]<sub>2.2</sub>Fe<sub>14</sub>B ribbons melt-spun at 22 m/s has been systematically studied. As-spun ribbons with low Nd content consist of 2 : 17 and 2 : 14 : 1 phases in an amorphous matrix, while as-spun ribbons with high Nd contain 2 : 14 : 1 and Fe phases in the amorphous matrix. After annealing at 700°C for 15 min, all of the ribbons exhibit only a single 2 : 14 : 1 phase in their X-ray diffraction patterns. Nd substitution can improve the maximum energy product of annealed ribbons but deteriorate the temperature stability of the ribbons. Increasing Nd (x) from 0 to 0.8, decreases coercivity from 22 to 13.5 kOe, but increases the maximum energy product from 5.87 to 11.2 MGOe. The temperature coefficients for remanence and coercivity increase from -0.045°C to -0.106 %/°C, and -0.306 to -0.38 %/°C, respectively for the same substitution range. Transmission electron microscope microstructures show that the samples with less Nd content exhibit a more uniform distribution of grains. Their average grain size is about 40 nm. The studied results show that the YDy-based R<sub>2</sub>Fe<sub>14</sub>B magnets are very promising for high-temperature performance.
IEEE Transactions on Magnetics 08/2004; · 1.36 Impact Factor
