烧结Nd-Fe-B磁体晶界扩散TbH2高温稳定性及其机理

采用涂敷方式，在烧结钕铁硼表面均匀涂敷TbH₂粉末，经过不同的扩散温度处理，制备出晶界扩散磁体。研究了晶界扩散TbH₂对烧结Nd-Fe-B磁体常温磁性能及高温稳定性的影响，并分析了磁体矫顽力提升的机理。常温磁性能研究表明，扩散磁体经过890 ℃+490 ℃工艺处理后性能达到最优，矫顽力从1 383 kA/m提升到1 988 kA/m。高温磁性能结果显示，扩散磁体200 ℃的矫顽力温度系数|β|比原始磁体降低0.032%/℃，磁通不可损失hirr比原始磁体降低21.47%，扩散TbH₂明显提高了烧结Nd-Fe-B磁体的热稳定性。分析得出，晶界扩散TbH₂磁体矫顽力提升的机理是Nd₂Fe₁₄B晶粒外延层形成了（Tb, Nd）₂Fe₁₄B核壳结构，提高了磁晶各向异性场；同时改善了磁体的微观组织结构，有效地隔绝了晶粒之间的磁交换耦合作用。 

Study on the high-temperature stability and mechanism of sintered Nd-Fe-B magnet by the grain boundary diffusion of TbH2

The Nd-Fe-B magnet was prepared by the grain boundary diffusion process in which TbH₂ power was evenly coated on the surface of Nd-Fe-B and then diffused at different temperatures in the ground boundary of Nd-Fe-B. The effects of the diffusion of TbH₂ power in the grain boundary of Nd-Fe-B magnet on the magnetic properties at room temperature and thermal stability at high temperature were investigated, and the mechanism of coercivity enhancement was analyzed. The study of magnetic properties at room temperature showed that the performance of the magnet reached the best after 890 ℃+490 ℃ process and its coercivity increased from 1 383 kA/m to 1 988 kA/m. The study of high-temperature magnetic performance showed that the temperature coefficient of coercivity |β| of the magnet at 200 ℃ was reduced by 0.032% /℃ and the irreversible loss of magnetic flux (hirr) was reduced by 21.47% compared with the original one, and the thermal stability of sintered Nd-Fe-B magnet was significantly increased. Through analysis, it can be concluded that the mechanism of coercivity enhancement of the magnet caused by the diffusion of TbH₂ powder in its grain boundary lies in that the epitaxial layer of Nd₂Fe₁₄B grain forms a (Tb, Nd)₂Fe₁₄B core-shell structure which enhances the magnetocrystalline anisotropy field and that the microstructure of the magnet is improved so that the magnetic exchange coupling between the grains is effectively avoided.