The Research Of The Microstructure And Magnetic Properties Of Ce-containing Magnets

Sintered Nd-Fe-B magnets exhibit superior magnetic properties. Hence, the production and applications of sintered Nd-Fe-B magnets have increased enormously. Interests in reducing the amount of neodymium in Nd-Fe-B magnets by partial substitution of cerium have recently been revived due to the economic and environmental pressures arising from the large scale consumption of neodymium. If cerium, a more abundant rare earth element, is widely applied to the commercial magnets, it would conduce to the comprehensive utilization of rare earth resources.The Ce-Nd-Fe-B magnets have been prepared by double main phase method. By optimizing the composition and preparation technology, the magnetic performance gradually improved. The composition and crystal structure of the RE-rich intergranular phases were observed and analyzed among the magnets with different Ce content. The effects of different intergranular phase on coervicity were discussed. In addition, the industrialization of low cost Ce-containing magnets was realized. The main results are showed as below:By adjusting the amount of total rare earths and optimizing the process parameters, sintered Nd3oFebalB1M (M= Cu, Co, Nb and Ga) magnets with the energy product of 52.8 MGOe and intrinsic coercivity of 12.28 kOe were prepared. A series of (CexNd1-x)3oFeba1B]M (x=0、0.1、0.2、0.3、0.4 and 0.5) magnets were prepared using the double main phase method. For Ce9Nd21FebalB1M magnet, the corecivity of the magnet fabricated by double main phase method were higher than that fabricated by single main phase method.The Ce6.4(PrNd)25.6FebaiB1M magnets with the the magnetic properties of Br=1.3 T, Hcj=12 kOe, and (BH)max=42 MGOe were successfully obtained via double main phase method. It is believed that the change of the difference among the magneto-crystalline anisotropy constant K1 of different grains and the microstructure of the interfaces between fcc-(Ce,Nd,Fe)Ox grain boundary phase and the matrix could influence the coercivity of the as-sintered magnet, which were the main reasons causing that the coercivity of the magnet fabricated by double main phase method was bigger than that of magnet fabricated by single matrix phase method.The Curie temperature Tc, the eutectic temperature and the melting point all reduced with the increase of the Ce substitute amount. Thus, the sintering temperature decreased monotonously with the increase of Ce content. When Ce substitute amount reached 30 wt.% to 50 wt.%, the best annealing temperatures were 480℃. The grain-boundary structure could be improved by adding moderate amount of Ce element.With the Ce content increasing, the magnetic properties declined slowly. The (BH)max and Hcj of the Ce9Nd21Feba1B1M magnets were 42.5 MGOe and 9.53 kOe. The (BH)max and Hcj of the Ce15Nd15FebalB1M magnets decreased to 28 MGOe and 3.67 kOe.The RE-rich phases of the Ce-containing magnets were mainly fcc-fcc-(Ce,Nd,Fe)Ox phase. The formation of this phase was related to the oxidation during preparation process of the TEM sample. Besides, there was hcp-(Ce,Nd)2O3 phase in Ce15Nd15FebalB1M magnet. The hcp-(Ce,Nd)2O3 phase is sTab with high melting point. Hence it would imply poor wettability at the annealing temperature and is to the disadvantage of the coercivity.