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Presents information on a study which conducts a microstructural analysis of strip cast Nd-Fe-B allowys for high (BH) max magnets. Information on the use of sintered Nd-Fe-B-type permanent magnets; Investigation of the orientation relationship between Nd-rich intragranular platelets and hard magnetic matrix grains using transmission electron microscopy; Advantages of using strip cast alloys as a staring material for high performance Nd-Fe-B magnets.

Presents information on a study which investigated the demagnetization process of sintered rare-earth-iron-boron magnets for various configuration grains. Methodology of the study; Results and discussion.

Presents information on a study which observed the microstructure of grain-boundary regions in sintered neodymium iron boron magnets under a high resolution transmission electron microscope. Methodology of the study; Results and discussion.

Nd-Fe-B sintered magnets are used for motors of hybrid or electric vehicles due to their high energy products. Dy is added to Nd-Fe-B sintered magnets to work in a high temperature environment. Although the addition of Dy decreases the magnetization of Nd-Fe-B magnets, it increases coercivity; a decrease in the amount of Dy is strongly required. Recently, Nd-Fe-B sintered magnets with a grain size of 1 μm achieved high coercivity of ∼20 kOe without the addition of Dy or other heavy rare earth elements. In this paper, the microstructure of their magnets was observed and compared to magnets with a grain size of ∼3 μm. The coercivity of magnets consisting of larger particles was 17 kOe. Microstructures were observed by the scanning electron microscope and the shapes of grains and the distribution of the Nd-rich phase were evaluated. The observation was promoted in two directions. One direction is the plane perpendicular to the magnetically aligned direction (c plane side) and the other is the side parallel to the magnetically aligned direction (c axis side). For magnets consisting of smaller particles, the shapes of grains are isotropic for the c plane side and elongated for the c axis side. The angle of minor axis prefers to be parallel to magnetically aligned direction. The distribution of the Nd-rich phase for magnets was also evaluated for both magnets. The distribution of the Nd-rich phase at triple junctions for the magnets with smaller particles becomes homogeneous compared to that for magnets with larger particles. It is considered that Dy-free magnets with high coercivity were realized by the achievement of homogeneous distribution of Nd-rich phase besides decreasing grain size. [ABSTRACT FROM AUTHOR]

Abstract: An influence of a 140kOe magnetic field applied during the last-stage annealing process was investigated in Dy-free Nd-Fe-B sintered magnets. When a sample containing small amount of Cu and Al was annealed at and under a magnetic field of , the coercivity increased by 20% and 16%, respectively, as compared with the control sample annealed at zero field. DSC data of this sample showed anomalies around 500 and . These results were discussed in terms of a field-induced change in interface matching between Nd2Fe14B and intergranular phases. [Copyright &y& Elsevier]

Microstructures of Ga-doped ultra-fine-grained (UFG) Nd-Fe-B magnets processed from press-less sintering of He-jet-milled powder and hydrogenation-disproportionation-desorption-recombination (HDDR) powder have been investigated to understand the large coercivity difference in the two magnets with nearly the same grain size. While the sintered magnet processed from the jet-milled powder showed a very high coercivity of 2.14 T, the sintered magnet made from HDDR powder showed a low coercivity of only 1.31 T regardless of the similar grain size. Microstructure observations by scanning electron microscopy (SEM) and scanning transmission electron microscope (STEM) combined with energy-dispersive X-ray (EDS) analysis revealed that the Nd-rich grain boundary (GB) phase in the magnet produced from HDDR powder exhibits thickness of 1–2 nm with large variations in their chemical compositions, while the Nd-rich GB phase in the magnet made from He-jet-milled powder displays larger thickness variations (1–7 nm) along with significant increase of nonferromagnetic elements (Nd, Pr, Cu, Ga) in the GB phase after optimal annealing. The possible reasons for these differences in GB phases are discussed based on quantitative microstructure characterization results. [ABSTRACT FROM AUTHOR]

We have investigated the effect of carbon on the coercivity and microstructure in fine-grained Nd–Fe–B sintered magnets fabricated by the pressless sintering method. The coercivity of the sample with the carbon content of 730 ppm (low-C) was 1.59 T while that of the sample with 1500 ppm (high-C) was 1.44 T in the as-sintered state. The low-C sample exhibited a larger coercivity increase by a post-sinter annealing, reaching the highest coercivity of 1.85 T, while the high-C sample reached a lower coercivity of 1.54 T. Detailed microstructure investigations using scanning electron microscopy, scanning transmission electron microscopy and atom probe tomography revealed that the high carbon content resulted in the formation of a Nd-carbide with a tetragonal structure and the reduction in the volume fraction of an α-Nd phase at triple junctions. This in turn decreased the Nd + Pr concentration in thin Nd-rich grain boundary phase, resulting in the lower coercivity. [ABSTRACT FROM AUTHOR]

Abstract: The Nd-rich phases in pressless processed fine grained Nd–Fe–B sintered magnets have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and three dimensional atom probe tomography (3DAP). The combination of the backscattered electron (BSE) and in-lens secondary electron (IL-SE) images in SEM led to an unambiguous identification of four types of Nd-rich phases, NdO x , type phase, which is isostructural to Nd2O3, dhcp-Nd and Nd1Fe4B4. In addition, the 3DAP analysis of thin Nd-rich grain boundary layer indicate that the coercivity has a close correlation with the chemistry of the grain boundary phase. [Copyright &y& Elsevier]

Abstract: Microstructures of fine grained Nd–Fe–B sintered magnets that were produced by the pressless process were investigated to understand the origin of the sudden coercivity decrease below a certain grain size. The intrinsic coercivity is inversely proportional to ln D 2 with the highest coercivity of 17kOe at D∼4.5μm, below which the coercivity drops as the grain size decreases. We found that the degradation of the coercivity of the magnet with a grain size of 3μm was mainly caused by the inhomogeneous distribution of fcc-Nd oxide whose volume fraction increased with respect to the dhcp Nd-rich phase. [Copyright &y& Elsevier]

• Low coercivity is found in HDDR sintered magnets despite the small grain size. • Magnetic domain observation by soft X-ray magnetic circular dichroism microscopy. • The nucleation field for HDDR sintered magnet is greatly reduced. The demagnetization process of a variety of Nd-Fe-B-based magnets produced using different manufacturing techniques are studied by soft X-ray magnetic circular dichroism microscopy. The four magnets studied include a hot deformed magnet, sintered magnets produced from either a N 2 jet-milled or a He jet-milled fine powder, and a magnet produced by hydrogenation-disproportionation-desorption-recombination (HDDR) followed by He jet-milling. The coercivity of the HDDR processed magnet is lower than the magnets produced with N 2 jet-milled powder even though the size of the grains is smaller. By following the magnetic domain reversal behavior during the demagnetization process, it was found that, while the magnets produced with N 2 jet-milled powder and the hot deformed magnet presents a predominance of the reversed magnetic domain propagation, in the HDDR processed magnet the nucleation of individual grains occurs before the reversed magnetic domains propagate. This behavior is associated with a decreased nucleation field of each grain. [ABSTRACT FROM AUTHOR]

Abstract: Temperature dependences of remanences in imperfectly, partially, magnetized Dy-free Nd2Fe14B sintered magnets were measured. The domain structures in demagnetized and magnetized states were observed by Kerr effect microscopy and by magneto-force microscopy. The remanences in the samples after measurements of minor loops with applying of 0.1–1.6T static and of 5T pulse fields are mainly composed of the magnetized grains into single-domain state that are originally multi-domain grains in thermally demagnetized state. A specific temperature of about 500K that corresponds to domain structure re-formation in the magnetized grains was detected in the measurements in this study. [Copyright &y& Elsevier]