Microstructure Optimization and Magnetic Properties Enhancement of Hot Deformed Nd-Fe-B Magnets via Grain Boundary Diffusion and Secondary Hot Deformation

Abstract

Based on spark plasma sintered (SPS) Nd-Fe-B magnets with PrCu sintering aid, hot deformed (HD) magnets are prepared through hot deformation technique. After that, using PrCu as the diffusion source, grain boundary diffusion (GBD) is implemented on HD magnet. Eventually, GBD magnet is subjected to hot deformation to regulate the distribution of RE-rich phase and increase <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$c$ </tex-math></inline-formula> -axis orientation, referred to as the secondary deformation (SD). The results show that hot deformation processes have an important influence on magnetic properties and microstructure, among which the deformation condition of 700 °C/0.5 h is the most favorable to obtain optimal magnetic properties. Through GBD, the coercivity, as high as 2117 kA/m, can be obtained, increasing by 7.5% comparing with that of the initial SPS sample. Moreover, it is found that the SD can effectively optimize the distribution of RE-rich phase, and improve <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$c$ </tex-math></inline-formula> -axis orientation of grains. Eventually, a good balance between coercivity and remanence is achieved. In addition, both GBD and SD can increase the thermal stability of HD magnets.