Investigation for the Impact of Grain Boundary Diffusion Direction on the Magnetic Properties of Nd–Fe–B Permanent Magnets

In this study, we investigated the effects of grain boundary diffusion direction on the magnetic properties of Nd–Fe–B permanent magnets, which are crucial for high-coercivity applications such as traction motors and automotive generators. A-plane diffusion resulted in a significant increase in coercivity, consistently higher than that observed in C-plane diffusion. Additionally, A-plane diffusion exhibited a notable reduction in irreversible flux loss at high temperatures when appropriate diffusion conditions were applied. Especially, in the case of A-plane diffused magnet, microstructural examinations revealed that very fast lattice diffusion caused inhomogeneous Tb distributions in all of the magnets and reduced the effect of improving magnetic properties. We also suggest that an appropriate choice of diffusion temperatures can effectively reduce thermal late flux loss while maintaining the same coercivity, thereby offering insights into optimizing the grain boundary diffusion processes for enhanced Nd–Fe–B magnet performance in various applications.