表层磁硬化提高稀土永磁材料矫顽力及其反磁化过程研究

In order to exploit the coercivity potential of rare earth permanent magnet materials and clarify the effect of surface layer magnetic hardening on the coercivity and magnetization reversal process, this study introduces the heavy rare-earth elements to the surface layer of magnets and grain boundaries, respectively. The distribution of heavy rare-earth elements and the modification of microstructure on the impact of the anti-demagnetization ability are evaluated and analyzed. Through forming the surface magnetic hardening of magnet and regulating the phase structure of grain boundaries, the coercivity of magnet and the stability of microstructure can be improved. The rules of phase-transformation of the grain boundaries and the grains are studied, and the influence of microstructure changes on the magnetic domain structure is investigated. Further, the influence of surface magnetic hardening on the magnetization and magnetization reversal process are clarified. Establish a finite element model to simulate the demagnetization process of the magnet surface layer for clarifying the effect of surface magnetic hardening on the coercivity and its temperature coefficients, and reveal the mechanism of coercivity enhancement by the surface magnetic hardening of the magnet. The interfacial structure and temperature stability of the magnet modified by surface magnetic hardening will be investigated for providing a theoretical basis to the preparation of high-performance and high-stability magnet.

为了充分挖掘稀土永磁材料的矫顽力潜力，澄清表层磁硬化对矫顽力及其反磁化过程影响的机理，本研究分别将重稀土元素引入磁体的宏观表层和晶粒表层，以元素在磁体内的分布状态为出发点，对比分析重稀土元素分布及微观结构变化对磁体抗退磁能力的影响。通过重稀土的表面磁硬化及元素晶界调控，提高矫顽力，增加微观组织稳定性，研究晶界与晶粒外层结构的成相规律及其对磁畴结构影响，进而深入研究表面磁硬化对材料的磁化和反磁化过程的影响。利用有限元模拟磁体表面退磁过程及磁畴结构演化表征，澄清表面磁硬化对磁体矫顽力及温度系数的影响，揭示表面磁硬化对磁体矫顽力的增强机制，探讨界面结构与提高磁体温度稳定的规律，为制备高性能高稳定性磁体提供理论依据。

为了充分挖掘稀土永磁材料的矫顽力潜力，澄清表层磁硬化对矫顽力及其反磁化过程影响，本文采用磁体表面晶界扩散和磁粉溶液包覆法进一步探索晶界扩散工艺。研究了不同稀土种类扩散对矫顽力增强效应的影响。在磁体表面均匀涂覆低成本低熔点合金重稀土粉末，扩散过程中，低熔点金属降低了晶界相熔点，增大了元素在晶界相的扩散系数，辅助重稀土元素沿晶界扩散到磁体内部，实现了微观的表层磁硬化。通过调控重稀土元素Dy与Tb在磁体晶界处的分布，改善了晶界相成分，优化了磁体微观结构。同时发展了一种粉末颗粒化学浴的方法对磁粉颗粒进行表面改性，控制元素的分布及晶粒和晶界结构，并对表面改性后磁体的磁性能、耐腐蚀性进行了深入地分析。溶液包覆法将重稀土化合物粉末均匀包裹在磁粉颗粒表面，经烧结和回火热处理，获得了微观晶粒表层的磁硬化结构，突破了常规扩散的磁体厚度限制；系统研究了从晶粒表层到内部，重稀土元素浓度的梯度分布对烧结Nd-Fe-B磁体性能的影响。表层磁硬化结构的研究对制备高性能高温度稳定性磁体具有重要的指导意义。