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 Nd2Fe14 B 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.
In this paper, the magnetic Nd–Fe–B particles of different sizes were conducted under vacuum by the hot pressing, then cooled quickly to room temperature. Finally hot deformation was performed to get the anisotropy Nd–Fe–B magnet at a deformation rate of 70 % in the protection of argon atmosphere. NIM-2000 was used for the measurement of hysteresis loop of the samples. Meanwhile, scanning electron microscopy(SEM) was used to observe the surface morphology of the magnetic particles with different sizes and hot-deformed magnets, energy spectrum analyzer to analyze the composition of magnetic particles. The effect of magnetic particle sizes on the microstructure and magnetic properties of the hot-deformed anisotropic magnet was investigated. Anisotropic hot-deformed magnets produced from the maximum particle size of 200–350 lm have the highest magnetic properties of Br= 1.465 T, Hcj=1,157 k Aám-1,(BH)max= 425 k Jám-3.
Xu-Chao WangMing-Gang ZhuWei LiYan-Feng LiBin LaiAn Du
通过中性盐雾(NSS)腐蚀试验,对比分析了烧结Nd Fe B磁体和热变形Nd Fe B磁体在NSS腐蚀环境中的耐蚀行为。研究结果表明,Nd Fe B永磁体的盐雾腐蚀进程可分为两个阶段:腐蚀增重期和失重期,并给出了相应的腐蚀反应速率方程。在NSS腐蚀环境中,热变形Nd Fe B磁体表现出更好的耐蚀性,其失重比高矫顽力烧结磁体降低了30%,认为热变形Nd Fe B磁体具有特殊的片状纳米晶组织结构,富Nd相的晶粒更加细小,分布更加均匀,使得发生晶间腐蚀的通道更窄,从而抑制了腐蚀速率,提高了磁体基体的耐蚀性。
