Microstructure improvement related coercivity enhancement for sintered NdFeB magnets after optimized additional heat treatment

Qing Zhou^1,2，Wei Li¹，Yuan Hong¹，Lizhong Zhao¹，Xichun Zhong¹，Hongya Yu¹，Lili Huang²，Zhongwu Liu¹

1. School of Materials Science and Engineering,South China University of Technology2. Guangdong Research Institute of Rare Metals

摘 要：The micro structure, especially the Nd-rich phase and the grain boundary, in sintered NdFeB magnets plays an important role in magnetic reversal and coercivity mechanism. To better understand the effects of the microstructure on the coercivity, we investigated the microstructure and properties improvements of a commercial sintered NdFeB magnet after optimized additional heat treatment. The coercivity is enhanced from 1399 to 1560 kA/m. This enhancement has been explained in terms of the evolution of the grain boundary structure, and the formation of continuous thin layers of Nd-rich phase is important for high coercivity. The micromagnetic simulation together with the numerical analysis based on the nucleation model suggest that the reversed magnetic domains nucleate mainly at the interface of multijunctions of Nd₂ Fe₁₄B grains with high stray fields during the demagnetization process. Both improved anisotropy fields at grain boundaries and reduced stray fields at multi-junction Nd-rich phases contribute to the coercivity enhancement. This work has importance in understanding the crucial micro structure parameters and enhancing the obtainable properties for sintered NdFeB magnets.

关键词：