Effect Of High-magnetic-field Annealing On Magnetic Properties And Microstructure Of Sintered NdFeB Magnets

The come out of the rare earth NdFeB permanent magnetic material shaked many correlative fields, and its magnetic properties are more excellent than other magnetic materials. It is called "the king of magnetic material" because of its high remanence, coercivity, and (BH)_max. But the thermal stability of sintered NdFeB is weaker than other magnetic materials, which limits the application of the NdFeB in many high and diversified temperature fields. So the research to enhance the magnetic properties and the thermal stability is very important.In 1980s, the technology of low temperature superconduct was developed very fast, and it made more and more application of superconduct high-magnetic-field.High-magnetic-field has effects of alignment , controlling the flow of liquid metals and working on the diversification of material phases. High-magnetic-field can transmit high energy to the atom of materials without touching, and it also can change the alignment , matching and transference of atoms, so the materials' properties would be improved. In high-magnetic-field, non-magnetic materials will get the same effects as magnetic materials.The microstructure of sintered NdFeB has transmissibility. The raw materials and the process of manufacture(smelting, milling, sintering, heat treatment and so on) have effect on its microstructure. Heat treatment is an easy way to improve the microstructure. As we know, for sintered NdFeB, it is necessary to have annealing after sintering to achieve good magnetic properties. The effect of high-magnetic-field annealing process on the microstructure and magnetic properties of sintered NdFeB magnets are studied here, compared with the way of common annealing. The results show that the magnetic properties of magnets is enhanced after High-magnetic-field annealing, and also the microstructure of magnets is ameliorated. Especially on the effect of high magnetic fields, the Nd-rich phase can make batter lattice matching in the interface with the main Nd₂Fe_<sub>14B phase , resulting in smoother grain boundary. The magnets' M-H Loop squareness is enhanced after high-magnetic-field annealing, resulting in better thermal stability.