Minggang Zhu

Influence of Ce Content on the Rectangularity of Demagnetization Curves and Magnetic Properties of Re-Fe-B Magnets Sintered by Double Main Phase Alloy Method

Research on the application of the most abundant rare-earth elements for permanent magnetic materials has gained intense interest. However, the magnetic properties decrease dramatically with the increase of Ce content due to the traditional Ce substitute for Nd. A double main phase alloy method has been performed to adjust the composition and combination of main phases in the magnets and make a partial main phase without Ce, which can maintain higher remanence. The influence of Ce content on the rectangularity of demagnetization curves and magnetic properties of (Nd1-xCex)30 (Fe,TM)balB1 sintered by the double main phase alloy method has been investigated. When the Ce content was 30% of the total amounts of all the rare earth metals, the maximum energy product of the sintered magnet, was still over 43 MGOe.

The microstructure and magnetic properties of melt-spun CeFeB ribbons with varying Ce content

The microstructural and magnetic properties of melt-spun ribbons with the composition (CexNd100-x)30FebalCo4Ga0.2B0.92 (where x = 50, 60, 70, 80, and 90) were investigated. The ribbons were examined with Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Vibrating Sample Magnetometry (VSM). It was found that the grain size of the ribbons is on the nanometer scale, and the grain size decreases with decreasing Ce content. The magnetic hysteresis loops showed that the magnetic properties of the ribbons gradually deteriorated with increasing Ce content. This is because the magnetic polarization (Js) and magnetocrystalline anisotropy field (HA) of Ce2Fe14B are smaller than those of Nd2Fe14B. Furthermore, from the initial magnetization curve it was found that increasing the Ce content changes the coercive force mechanism to the nucleation mechanism. When Ce content accounts for 90% of total rare earth metals, the coercive force mechanism mainly appears to be a nucleation mechanism.

Effect of Co on the thermal stability and magnetic properties of AlNiCo 8 alloys

The magnetic properties, microstructure, and reversible temperature coefficient of magnetic flux of Alnico 8 alloys with the different Co and Ti have been investigated in this paper. The Alnico alloys containing 34, 36, 38, and 40 mass percent cobalt were fabricated by the conventional casting method including thermomagnetic treatment. The transmission electron microscopy (TEM) testing shows that there are more α1 phases particles with the diameter of less than 10 nm appearing in the matrix with the increasing of the content of Co and Ti. The thermal stability of Alnico 8 alloys deteriorates with the increasing of the content of Co and Ti, which are caused mainly by the decrease of the degree of particle alignment and particle perfection.

Investigation of chemical composition and crystal structure in sintered Ce15Nd15FebalB1 magnet

The substitution of cerium, a more abundant rare-earth element, for sintered Nd-Fe-B magnets has drawn intense interest. In the present work, nominal composition of Ce15Nd15FebalB1 (wt. %), with cerium constitutes increased to 50% of the total rare-earth content, was used. And Ce-free Nd30FebalB1 (wt. %) was prepared by the same preparation process as comparison. The microstructure of the sintered magnets has been investigated by means of X-ray diffraction and transmission electron microscope. The results show that there are three kinds of RE-rich phases in the same magnet, i.e., fcc-(Ce,Nd)Ox (a=0.547nm), hcp-(Ce,Nd)2O3 (a=0.386nm, c=0.604nm) and bcc-(Ce,Nd)2O3 (a=1.113nm). Ors of (140)(Ce,Nd)2Fe14B// (1-21)bcc-(Ce,Nd)2O3(∼3°), [001](Ce,Nd)2Fe14B// [-214]bcc-(Ce,Nd)2O3; (01-1)(Ce,Nd)2Fe14B// (101)fcc- (Ce,Nd)Ox(∼2°), [101](Ce,Nd)2Fe14B// [12-1]fcc-(Ce,Nd)Ox were found through selected area electron diffraction (SAED) analysis. According to the analysis, it can be concluded that cerium has partly substitu...

Magnetic micro-structural uniformity of die-upset Nd-Fe-B magnets

Die-upset Nd13.62Fe75.70Co4.45B5.76Ga0.47 magnets have been prepared with height reduction (h) in the range of 60 to 88%. The energy product as high as 50.4 MGOe was obtained in the sample with h ∼ 70%. The magnetic domains of the samples are revealed by using magnetic force microscopy (MFM). The average domain widths of the die-upset samples with surface normal parallel (//) and perpendicular (⊥) to the loading direction are in the range of w//: 0.4-0.6 μm; w⊥: 0.9-3.8 μm, respectively. These interaction domains are formed due to the strong inter-granular exchange interaction and magnetostatic interaction between grains. It was found that the ratio of φrms// to φrms⊥ is a good indicator for the quality of the magnet, where the φrms// and φrms⊥ are defined as the root-mean-square values of phase shift for the MFM images. The microstructures have been investigated by scanning electron microscopy (SEM), MFM and SEM results indicate the magnetic and crystalline microstructures are uniform for the sample with...

Investigation on microstructure and magnetic properties of Sm2Co17 magnets aged at high temperature

The Sm2Co17 magnet is the most promising candidate for high temperature applications. The microstructure evolutions and losses in the magnetic properties of the magnet in high temperature aging status have been investigated. The Sm(CobalFe0.22Cu0.068Zr0.025)7.75 magnets were prepared using the conventional powder sintering method. The magnet samples were isothermally aged at 500°C, 600 °C, and 700 °C for 72 h, respectively. The magnetic properties and the demagnetization curve were kept invariable for the magnet samples aged at 500 °C. The coercivity Hcj of the magnet samples decreased with increasing aging temperature. The Hcj decreased from 29.2 kOe for the original status samples to 10.8 kOe for the samples aged at 700 °C. The cell structure in the magnet is not destroyed after aging at 700 °C for 72 h. The deterioration of the magnetic properties and the demagnetization-curve squareness was caused by an increasing lattice mismatch between the 2:17R cell phase and the cell-boundary 1:5H phase, and by a...

Quasi-periodic layer structure of die-upset NdFeB magnets

Abstract Isotropic magnets were prepared from melt-spun powders at different hot pressing temperatures from 550 to 700 °C, then upset into fully dense anisotropic magnets at the same die-upsetting temperature of 850 °C. Die-upset magnets had the characteristics of inhomogeneous microstructure, including well-aligned grains structure and nonaligned grains layers transverse to press direction, which was quasi-periodic layer structure with a total length of 5–15 μm. Nonaligned grains layers were mainly made of large grains and had higher Nd content. To clearly understand the formation of layer structure, the microstructure of isotropic precursors with different hot pressing temperatures and their subsequent die-upset magnets was investigated. A new interpretation for the formation of layer structure was proposed in this paper: the layer structure was correlated to the original ribbon interface which was divided into three types based on the contact forms. Because of the incomplete contact of neighboring ribbons, concentration of stress occurred in the contacted points and the Nd-rich phase was squeezed into interspaces at high temperature under stress. Due to the release of interfacial energy and the fluidity of enough Nd-rich liquid phases, the nonaligned layers with large grains formed both in hot compaction and subsequent hot deformation process. The layer structure affected the magnetic properties of die-upset magnets. With increase of the hot pressing temperature, the nonaligned grains layers became thicker, and the magnetic performance of die-upset magnets decreased. It was necessary to reduce the thickness of large grains layers for the preparation of high-performance die-upset magnets.

Optimal design of sintered Ce9Nd21FebalB1 magnets with a low-melting-point (Ce,Nd)-rich phase

A systemic investigation was done on the chemistry and crystal structure of boundary phases in sintered Ce9Nd21FebalB1 (wt%) magnets. Ce2Fe14B is believed to be more soluble in the rare-earth (RE)-rich liquid phase during the sintering process. Thus, the grain size and oxygen content were controlled via low-temperature sintering, resulting in high coercivity and maximum energy products. In addition, Ce formed massive agglomerations at the triple-point junctions, as confirmed by elemental mapping results. Transmission electron microscopy (TEM) images indicated the presence of (Ce,Nd)Ox phases at grain boundaries. By controlling the composition and optimizing the preparation process, we successfully obtained Ce9Nd21FebalB1 sintered magnets; the prepared magnets exhibited a residual induction, coercivity, and energy product of 1.353 T, 759 kA/m, and 342 kJ/m3, respectively.

Relationship between controllable preparation and microstructure of NdFeB sintered magnets

Abstract The double hard magnetic phase magnets with nominal compositions of Nd30–xDyxFe69B1(x=2, and 4) (wt.%) were prepared. The magnetic properties of the magnets were measured with a NIM-2000H hysteresigraph. The crystalline structures of the magnets were identified by X-ray diffraction (XRD). The Rietveld refinement was carried out using the FULLPROF software. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses were carried out in order to investigate the microstructure of the magnets. It showed that the magnets consisted mainly of Nd2Fe14B phase, and some Nd-rich phase. Two types of matrix-phase grains in dark grey and light grey were found in the magnets with x=2 and 4. The Dy content was obviously different in the two types of grains, which proved that the double hard magnetic phases (Dy-rich and Dy-lean phases) coexisted in the magnet. It revealed that the Nd-rich phases in junction regions had fcc structure, with the unit cell parameter of about 0.52–0.56 nm. The weak superlattice spots were found in the SAD patterns of the junction Nd-rich phases with large scale. The double hard magnetic phase structure seemed to improve the magnetic properties of NdFeB magnets with high coercivity, while decrease the consumption of Dy element, compared with the single alloy magnet.

Effect of Die-upset Process on Magnetic Properties and Deformation Behavior of Nanostructured Nd-Fe-B Magnets

Nd-Fe-B high performance magnets were prepared by die-upset forging. The effects of the deformation parameters on magnetic properties and flow stress were studied. Deformation temperatures in the range of 600~900 ℃ enable to achieve an effective anisotropy and temperature 800 ℃ proves to be suitable for deformation of Nd-Fe-B magnets. The amount of c-axis alignment along the press direction seems to depend on the amount of deformation and a saturation behavior is shown at deformation ratio of 75%. Magnetic properties are also related to strain rate, and maximum energy product is attained at an optimum strain rate of Φ= 1 × 10?² s?¹. By analyzing the relationship of stress and strain at different deformation temperature during die-upset forging process, deformation behavior of Nd-Fe-B magnets was studied and parameters for describing plastic deformation were obtained. Nd-rich boundary liquid phase, which is additionally decreasing the flow stress during deformation, is supposed to play the role of diffusion path and enhance the diffusion rate.