Development of thick Nd-Fe-B magnets with high coercivity and resistivity via a sandwich-structured grain boundary diffusion strategy

Abstract

Sandwich-structured grain boundary diffusion (GBD) strategy using a low-melting-point Pr-Cu-Al-Ga (PCAG) alloy is proposed to overcome the diffusion-depth limitation of conventional grain boundary diffusion in Nd-Fe-B magnets. Applying the PCAG-GBD to both the outer surface and internal bonding interface enables the fabrication of thick Nd-Fe-B magnets with high coercivity comparable to that of thin single magnets treated via grain boundary diffusion. Microstructural analysis reveals the formation of Pr-rich shells and continuous grainboundary phases within whole stacked magnets, which effectively improve the coercivity of thick magnets by the GBD process. The diffusion-bonded interface exhibits markedly increased resistivity, reduced eddy-current heating, and improved mechanical strength. Overall, this approach offers a practical and scalable route for producing thick, high-performance Nd-Fe-B magnets suitable for next-generation electric drives and highfrequency applications.