Papers by Keyword: Nd-Fe-B

Abstract: In this paper, the effect of the grain size on sintered Nd-Fe-B based permanent magnets was investigated. In order, the magnets were produced by different milling times at 200 rpm and then vacuum sintered at 1373 K for 60 minutes followed by cooling outside the furnace. The magnets either produced by lower and higher milling times (30 and 75 minutes) exhibited lower remanence and coercivity, due the inhomogeneous distribution of the grain sizes. The magnet produced by intermediary milling time (45 minutes) exhibited the highest properties among all samples, with remanence of 1.06 T, coercivity of 891.3 KA.m^-1, maximum energy product of 211 KJ.m³ and a squareness factor equal 0.92.

Abstract: In this study, Nanocrystalline Nd8Pr2Fe79-xCo5B6Alx (x= 0, 1, 2, 3) magnets were prepared by mechanical alloying method and respective heat treatment in a constant time and temperature. Afterward, the effects of the Al addition on the microstructure and magnetic properties of Nd-Fe-Co-B alloy were studied. The changes in the nanostructure and magnetic properties were examined by X-Ray diffraction (XRD), combined with Field Emission Scanning electron microscopy (FeSEM) and vibrating sample magnetometer (VSM). Addition of Al was found to be effective for improving the coercivity parameter and the hysteresis squareness in Nd–Fe–Co–B magnets without decreasing much the remanent magnetization.

Abstract: As a rapid solidification technology, strip casting (SC) technology is one of importance method in the production of Nd₂Fe₁₄B-based rare-earth permanent magnets. (Nd_1-2xPr_xY_x)_2.28Fe_13.58B_1.14 (x=0.05, 0.10, 0.15, 0.20) alloys prepared by arc melting method under an argon atmosphere were annealed at 1173 K for 360 hrs and then were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Differential Scanning Calorimetry (DSC). Magnetic properties of the ribbons prepared by melt-spinning method with high cooling rate were measured by Physical Property Measurement System (PPMS). The XRD and SEM results showed that the annealed (Nd_1-2xPr_xY_x)_2.28Fe_13.58B_1.14 (x=0.10, 0.15, 0.20) alloys had a single phase with tetragonal Nd2Fe14B-tpyed structure, while the annealed (Nd_0.90Pr_0.05Y_0.05)_2.28Fe_13.58B_1.14 alloy contained Nd2Fe14B phase and α-Fe secondary phase. On the other hand, the coercivities (H_cj) of (Nd_1-2xPr_xY_x)_2.28Fe_13.58B_1.14 (x=0.05, 0.10, 0.15, 0.20) melt-spun alloys were about 13.42 kOe, 13.49 kOe, 7.97 kOe and 8.36 kOe, respectively, while the remanences (B_r) of the alloys were 7.52 kGs, 7.48 kGs, 9.14 kGs and 7.48 kGs, respectively. In addition, The Curie temperature (Tc) of the annealed (Nd_1-2xPr_xY_x)_2.28Fe_13.58B_1.14 (x=0.05, 0.10, 0.15, 0.20) alloys were determined to be 573 K, 574 K, 579 K and 580 K, respectively.

Abstract: Anisotropic bulk nanocrystal Nd-lean Nd-Fe-B magnets were prepared by hot-pressing the mixture of Nd_11.5Fe_81.5Nb₁B₆ melt-spun ribbons and pure Zn powder and subsequent hot-deforming. The effects of deformation on the magnetic properties and microstructure were also studied. The magnetic properties increased significantly for hot-deformed (HD) samples due to the formation of good c-axis texture with increasing deformation. The remanence M_r and maximal energy product (BH)_m increased and reached their maximal values at 65% deformation due to the increasing orientation. On the other hand, the grains increased and were elongated normal to the press direction gradually with increasing deformation. The variation trend was similar to that of traditional Nd-Fe-B magnets. However, there was an obvious improvement for coercivity in the initial stage of hot-deformation resulting from the adequate Zn diffusion into grain-boundary. When the deformation was larger than 65%, the magnetic properties were deteriorated due to abnormal grain growth. In order to improve further the coercivity Hci, the samples with Dy addition were prepared. The coercivity of 12300 Oe could be obtained for anisotropic bulk Nd_9.5Dy₂Fe_81.5Nb₁B₆.

Abstract: In this work, the effects of substitution of Nd by Gd on the magnetic properties of Nd-Fe-B magnets were investigated. The results demonstrate that the size of grain decreases with the addition of Gd element. The Curie temperatures (Tc) are found to improve with the increase in Gd content, which means that the thermal stability of the magnets is enhanced. The coercivity and saturation magnetization decrease with the increase in Gd content due to the low magnetocrystalline anisotropy and saturation magnetization of Gd₂Fe₁₄B.

Abstract: In this work, the microstructure, crystal structure and magnetic properties of (Nd_0.7Pr_0.15RE_0.15)_2.28Fe_13.58B_1.14 (RE=La, Ce, Y) alloys prepared by arc-melting were investigated experimentally. The experimental results show that all alloys annealed at 1173 K for 360 hrs contain the isotropic Nd₂Fe₁₄B structure phase. The coercivities (H_c) of (Nd_0.7Pr_0.15RE_0.15)_2.28Fe_13.58B_1.14 (RE=La, Ce, Y) melt-spun ribbons are 12.3 kOe, 13.2 kOe, 8.5 kOe, and the Curie temperatures (T_c) of annealed (Nd_0.7Pr_0.15RE_0.15)_2.28Fe_13.58B_1.14 (RE=La, Ce, Y) alloys are 569 K, 552 K and 576 K, respectively. Meanwhile, the remanences (Br) of (Nd_0.7Pr_0.15RE_0.15)_2.28Fe_13.58B_1.14 (RE=La, Ce, Y) melt-spun ribbons are about 67 emu/g, 74 emu/g and 72 emu/g, respectively. It was indicated that the coercivity, remanence and Curie temperatures of (Nd_0.7Pr_0.15RE_0.15)_2.28Fe_13.58B_1.14 alloys are dependent on light rare earth elements.

Abstract: The rare-earth (RE) permanent magnets based on Nd₂Fe₁₄B with excellent magnetic properties have been widely used in industrial applications. In this work, the crystal structure, microstructure and magnetic properties of Nd_2.28Fe_13.58B_1.14, Ce_2.28Fe_13.58B_1.14 and Pr_2.28Fe_13.58B_1.14 alloys prepared by arc-melting were investigated. The results show that all alloys are single phase with tetragonal Nd₂Fe₁₄B-type (space group P42/mnm). The Curie temperatures (T_c) of RE_2.28Fe_13.58B_1.14 (RE=Nd, Ce, Pr) alloys are 583 K, 423 K and 557 K, respectively. On the other hand, the coercivities of Nd_2.28Fe_13.58B_1.14 and Pr_2.28Fe_13.58B_1.14 alloys are about 1.05 T and 1.23 T, respectively, while that of Ce_2.28Fe_13.58B_1.14 alloy is only about 0.25 T due to the poor squareness of hysteresis loop. Meanwhile, the saturation magnetizations of Nd_2.28Fe_13.58B_1.14 and Pr_2.28Fe_13.58B_1.14 alloys are about 135 emu/g and 113 emu/g, respectively, while that of Ce_2.28Fe_13.58B_1.14 alloy is about 97 emu/g. It was indicated that the Curie temperatures and magnetic properties of RE_2.28Fe_13.58B_1.14 alloys with the same crystal structure are dependent on light rare earth elements.

Abstract: The Nd-Fe-B powder was prepared to bulk by cold pressing, and then was hot-deformed by the vacuum hot-pressing machine. Effects of hot-deformation temperature and rate on the density, anisotropy, performance and microstructure were studied. The results showed that the grain size was small, but the density and orientation degree was low, thus leading to poor performance when the deformation temperature was too low or deformation rate was too large. When the temperature was higher than 750 °C or the rate was lower than 0.1mm/s, the anisotropic magnets with good density and texture could be obtained. However, the magnetic properties of hot-deformed magnets deteriorated due to the present of coarse grains. From the microstructure of hot-deformed magnets it could be seen that there were plenty of coarse and irregular grains, which have a higher Nd content than the plate-like grains. The optimum magnetic properties could be obtained at deformation temperature of 700 °C and rate of 0.1 mm/s.