Shulin Huang

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...

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.

An Enhanced Coercivity for (CeNdPr)–Fe–B Sintered Magnet Prepared by Structure Design

To obtain the excellent magnetic properties for the Ce substitution magnets, we proposed a dual-main-phase method to prepare the high-permanence (CePrNd)-Fe-B magnet with low cost. The main phase in this method means the hard magnetic phase with high anisotropy field. Compared with the traditional sintered method adjusting the composition of the magnet, the dual-main-phase method can also design the distribution of the main phase in the magnet, which makes the structure satisfy the demand of the magnet with outstanding properties. Compared with the magnet prepared by the single-alloy method, the coercivity of the magnet prepared by the dual-main-phase method is dramatically enhanced from 7.7 to 12.1 kOe, which may be due to the distribution of the grain boundary phase between the different kinds of main phases.

Preparation of Sintered (Ce1−x Ndx)30FebalCu0.1B1 Magnets by Blending Powder Method

Magnets with nominal compositions of (Nd1−x Cex)30 Febal Cu0.1 B1 (x = 0, 0. 15, 0.3 and 0.4, mass%) have been fabricated by blending powder method. The remanence (Br), intrinsic coercivity (Hc) and maximum energy product (BH)max of the RE2F14B type magnets deteriorated when Nd was replaced by Ce. The chemical composition and crystal structure of magnet were investigated systemically. Backscattered electron (BSE) and energy dispersive spectroscopy (EDS) results revealed that Ce-rich and Ce-lcan matrix grains coexisted in the magnets. The magnetic coupling mechanism among the double hard magnetic phases was discussed. Low melting point RE-Cu phase was in favor of the formation of uniform continuous grain boundary. Transmission electron microscopy (TEM) investigation showed the presence of fcc (Nd,Ce)Ox phase in the grain boundary. When the Ce content was 15% of the total amounts of all the rare earth, the maximum energy product of the sintered magnet was 359. 8 kJ/m3.

Investigation of Low Melting-Point Boundary Phase in Sintered (Ce,Nd)-Fe-B Magnets

A (Ce,Nd)-Fe boundary phase with low melting-point was obtained in the sintered Ce9Nd21FebalB1 magnets by the two powders blending method. Ce element enriched in the boundary phase and decreased the melting point. The melting-point of the boundary phase decreases with the increase of Ce content. Thus, the high performance magnets with fine grain and low oxygen content can be obtained by low temperature sintering. The sintered Ce9Nd21FebalB1 magnet with 600 PPM oxygen content and magnetic property of Br = 13.5 kGs, Hci =9.5 kOe and (BH)max =42.8 MGOe has been fabricated by the low melting-point phase formation and low temperature sintering method. Microstructure and chemistry composition of the magnet and the low melting-point boundary phase were investigated by SEM and TEM.