| Summary: | 碩士 === 國立中正大學 === 物理學系暨研究所 === 102 === In this study, we adopted the grain boundary diffusion (GBD) process to improve the iHc of sintered NdFeB magnet. Powder were used as the diffusion source in this process. In order to study the effect of R content on the increment of iHc of sintered NdFeB magnet, film was prepared by screen printing.
At first, the effect of crystallinity and particle size of powders on the magnetic properties of the GBD NdFeB magnets was also studied. It can be found that the powders with semicrystalline structure have to absorb thermal energy for crystallization prior to GBD process, which might degrade the GBD performance. As a result, low temperature, X oC, crystallization of powders before making screen printing film should be necessary. Nevertheless, too high temperature, i.e., Y oC, may cause particle coarsening to degrade the GBD efficiency. The optimum crystallization temperature for B powders is X2,X3 oC and results in the coercivity increment (∆iHc) of 5.9 kOe. In contrast, the best crystallization temperature for C powders is X1 oC and the ∆iHc reaches 8.7 kOe.
At last, the films were adopted to study the controlled R content GBD effect on the sintered NdFeB magnets. It is found that, for 2-mm thickness magnet,A film is sufficient for giving the GBD magnet 6.0 kOe in ΔiHc. For 3.2-mm thickness magnet, the optimal magnetic properties of ΔiHc=6.0 kOe with A film. For 5-mm thickness magnet, the optimal magnetic properties of ΔiHc=4.4 kOe. More attractive results were found in the case of using C film, for 3.2-mm thickness magnet, the optimal magnetic properties of ΔiHc=8.8 kOe by using C µm film. From the above results, it reflects that the C film for GBD process is cost effective in enhancing the coercivity of sintered NdFeB magnets, which might be a suitable solution for mass production of GBD NdFeB magnets.
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