烧结(Nd,Dy)-Fe-B双主相磁体稀土元素扩散的控制和磁性能的研究

The dual-main-phase magnets could be prepared by mixing Nd2Fe14B and Dy2Fe14B powders. However, the substitution of Nd for Dy leads to a decrease in the magnetocrystalline anisotropy of Dy2Fe14B due to Nd element diffusion in sintering at high temperature, so the coercivity doesn’t increase largely. The Project aims to restrain element diffusion according to the difference of activation energy of atomic diffusion between the main phase and the intergranular phase. It is expected to decrease the degree of Nd diffusion in the intergranular phase via decreasing the content of Nd in Nd-Fe-B alloy and increasing Dy content in Dy-Fe-B alloy. The element distribution in the main phase and the intergranular phase as well as the variation of the magnetic properties would be investigated by varying the relative content of Nd and Dy in Nd-Fe-B and Dy-Fe-B alloys. The atomic diffusion and the distribution of rare-earth elements would be further regulated by the doping of refractory metals of Nb and Zr or low melt point elements of Cu and Ga as well as by adjusting the sintering process. Through investigating the effects of the element diffusion and distribution on the magnetization reversal and coercivity, optimize the microstructure, so that the high magnetocrystalline anisotropy could be kept in Dy2Fe14B phase and that Nd2Fe14B grains are well surrounded by Dy2Fe14B phase. It is expected to improve the coercivity significantly by adding a little amount of Dy-Fe-B fine powders and build a theoretical basis for the designs of the composition and the preparation technology of the dual-main-phase rare-earth magnets.

Nd2Fe14B与Dy2Fe14B混合可制备烧结双主相磁体，但高温烧结时Nd元素扩散会取代Dy，导致Dy2Fe14B相磁晶各向异性场降低，磁体矫顽力提高程度不太显著。本项目依据磁体主相、晶间相中元素扩散激活能和扩散机制的不同来控制元素的扩散。拟降低Nd-Fe-B粉末中Nd含量，适当提高Dy-Fe-B细粉的Dy含量，期望减少Nd元素在晶间相中的扩散途径。重点研究Nd和Dy相对含量的变化对主相、晶间相中元素扩散分布以及对磁性能的影响。添加高熔点元素Nb、Zr或低熔点元素Cu、Ga和优化烧结温度时间，进一步控制稀土元素的扩散。在研究元素扩散和非均匀分布对反磁化过程和矫顽力影响的基础上，进一步优化双主相磁体的结构，使Dy2Fe14B相保持高磁晶各向异性场并均匀分布在Nd2Fe14B晶粒边界，期望Dy-Fe-B细粉少量添加能显著提高矫顽力，为优化双主相稀土永磁体的成分和制备工艺建立理论基础。

Nd-Fe-B粉末和Dy-Fe-B粉末混合、压制、烧结制成双主相磁体，调制稀土元素在烧结过程扩散和磁体微结构，提高磁体矫顽力等磁性能。研究不同质量配比合金Dy原子迁移规律，优化低Nd含量Nd-Fe-B粉末成分和少量元素添加工艺，发展晶粒边界相结构调制技术。建立晶粒内部、边界、晶间相中稀土元素Nd、Dy的扩散和分布规律，从成相的稳定性、元素浓度差异揭示烧结(Nd,Dy)-Fe-B双主相复合磁体Nd、Dy等元素的扩散机制。探讨磁体热激活反磁化过程，发现双主相磁体由于晶间交换耦合作用导致反磁化磁畴壁增大的现象。证实除了晶粒壳层能提高反磁化畴壁形核场和磁体矫顽力外，Dy-Fe-B晶粒也能通过晶间耦合作用提高磁体矫顽力。揭示Nd、Dy元素非均匀分布与双主相局部各向异性场变化和矫顽力之间的关系，从成分设计、元素分布工艺调制、结构控制等方面为提高稀土永磁体磁性能建立理论和实验基础。

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