Shengji Gao

Preparation of isotropic Sm2Fe17Nx magnetic powders and their bonded magnets

Abstract The isotropic Sm 2 Fe 17 N x magnetic powders were prepared by Hydrogenation-Disproportion-Desorption-Recombination (HDDR) process. The phase and microstructure evolutionary process of Sm-Fe alloy during the solidification, homogenization, HDDR and nitration processes were investigated by means of XRD, SEM, EDX and AFM. The results show that the homogeneous Sm 2 Fe 17 alloy was successfully obtained and the impurity phases and residual stress were well removed by heated at 1050 °C for 24 h. When heated at 800 °C for 1h in H 2 of 0.1 MPa, the alloy turns into SmH x and α-Fe with plenty of nanocrystals. After vacuumized at 800 °C for 2 h the alloy recombines into Sm 2 Fe 17 with a crystal grain size of about 85 nm. The lattice constant of the alloy increases and the expanding of the crystal cell reaches 6.28% after nitrified at 500 °C for 5 h. The magnetic property of isotropic bonded Sm 2 Fe 17 N x magnets is B r = 0.6704 T, H cj = 1015 kA·m −1 , ( BH ) max = 73.7 kJ·m −3 with a density of 6.04 g·cm −3 .

Influence of dynamic crystallization on exchange-coupled NdFeB nanocrystalline permanent magnets

Abstract Dynamic crystallization was introduced to improve the magnetic properties of NdFeB nanocrystalline permanent magnets by optimizing microstructure. The microstructure was studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It has been determined that, compared with the conventional heat treatment, dynamic crystallization can shorten the crystallization time. Moreover, dynamic crystallization can refine grains, enhance the exchange-coupled interaction among grains, and promote the magnetic properties. As a result, the optimal magnetic properties of Nd 10.5 (FeCoZr) 83.4 B 6.1 ( B r = 0.685T, H ci = 732 kA·m −1 , H cb = 429 kA·m −1 , (BH) m = 75 kJ·m −3 ) are obtained after dynamic crystallization heat treatment at 700 °C for 10 min.