Several Issues on the Development of Grain Boundary Diffusion Process for Nd-Fe-B Permanent Magnets

Nd-Fe-B based permanent magnets have been widely used in many industries, including renewable energy, information and communication, and intelligent manufacturing. The applications in the electric vehicle drive motors and wind power system generators set high requirements on the elevated temperature performance and coercivity for Nd-Fe-B magnets. Heavy rare earth (HRE) of Tb and Dy have been frequently used to substitute Nd to enhance the anisotropy field of the magnets. However, introducing these HRE elements reduces the remanence of magnets and increases the total price of end-products. The grain boundary diffusion (GBD) process, invented at the beginning of this century, is a significant progress in the field of rare earth permanent magnet manufacturing. The coercivity can be significantly improved by diffusing HRE elements or rare earth alloys into the magnet along the grain boundary. Simultaneously, the reduced heavy rare earth consumption and enhanced performance-cost ratio can also be realized. Although the GBD process has attracted much attention and has been quickly industrialized since its appearance, some key issues still exist on technical and theoretical levels. Based on the latest domestic and overseas developments and the research results from the authors' group, this paper summarizes the urgent problems and feasible solutions for the GBD process. Several issues are described in this report, including the GBD process for thick magnets, utilization of anisotropic behavior of GBD, selection of low-cost diffusion sources, combination of GBD with the existing process, influence of GBD on the service performance, and advancement of GBD related theories. The challenges and opportunities in the future development of the GBD process for Nd-Fe-B based magnets are also highlighted.

Automated summary

Nd-Fe-B based permanent magnets are widely used in various industries, such as renewable energy, information and communication, and intelligent manufacturing. The introduction of heavy rare earth elements through the grain boundary diffusion process has led to significant improvements in coercivity and reduced consumption of heavy rare earth, enhancing the performance-cost ratio. However, technical and theoretical challenges still exist, including issues related to thick magnets, anisotropic behavior, diffusion sources, combination with existing processes, service performance, and theoretical advancements. Opportunities and challenges in the future development of the GBD process for Nd-Fe-B based magnets are also highlighted.