Microstructure optimization and magnetic properties enhancement of hot pressed Nd-Fe-B magnets via grain boundary diffusion of NdCu powder

• Published in: Journal of magnetism and magnetic materials Vol. 567; p. 170325
• Main Authors: Li, Wei, Feng, Qing, Chen, Cheng, Zhang, Xiaosong, Fu, Zhenglin, Hou, Yuhua, Huang, Youlin
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.02.2023
• Subjects: Coercivity; Grain boundary diffusion; Hot pressing sintering; NdFeB magnet; Thermal stability; Hot pressing sintering; NdFeB magnet; Grain boundary diffusion; Thermal stability; Coercivity
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2022.170325

•The coercivity of the powder diffused with 20 wt% NdCu increases to 21.42 kOe, increasing by 184%.•Magnets with high density and good magnetic properties are prepared by hot pressing.•The diffusion of Nd70Cu30 can significantly improve the thermal stability of the magnets, including the Curie temperature, the temperature coefficient of remanence and coercivity.•Elemental metallurgical behavior and the intergranular phase structure of hot pressed magnets are investigated. Microstructure modification of Nd-Fe-B magnets plays a key role in regulating magnetic properties. In this work, low melting point NdCu alloy was added to improve the coercivity of NdFeB ribbons, and then high coercivity nanocrystalline NdFeB magnets were prepared by hot pressing sintering (HPS). The result shows that the coercivity of NdFeB powders blending with 15 wt% Nd-Cu powders obtained a maximum increment, as high as 12.69 kOe. After HPS, the fully dense magnets with excellent magnetic properties are obtained. Microstructure analysis confirmed that the Nd-Cu alloy has diffused into the interior of hard magnetic grains along the grain boundary during heat treatment. The enrichment of Nd, Pr, and Cu in the grain boundary phase weakens the magnetism of the grain boundary phase and reduces the intergranular exchange coupling. This is the main reason for the coercivity enhancement. In addition, the diffusion of Nd70Cu30 can significantly improve the thermal stability of the magnets.