Achieving High Coercivity and Magnetic Energy in Nd-Fe-B Magnets via Combined Dual-Alloy and Grain Boundary Diffusion Using Tb₈₆Al₇Co₇

Abstract

The dual-alloy approach has been recognized for its efficacy in optimizing grain boundary (GB) distribution within Nd-Fe-B magnets, which in turn enhances their magnetic properties. In this study, we introduce a novel approach that combines a Nd/Cu-rich dual-alloy with a Tb₈₆Al₇Co₇ grain boundary diffusion process (GBDP) to fabricate sintered Nd-Fe-B magnets with improved coercivity (H_cj) and magnetic energy ((BH)_max). The synergistic effect of the dual-alloy and GBDP resulted in a significant increase in coercivity from 1524.34 to 2532.87 kA/m, and a minimal reduction in (BH)_max (0.6%) compared to the traditional method (1.6%). Microstructural analysis revealed that the Nd/Cu-rich dual-alloy treatment led to the enrichment of Nd and Cu at the GBs, forming RE₆Fe₁₃Cu phases. This enrichment dilutes the Fe content at the GBs and decouples the exchange interaction between grains. Additionally, the presence of Cu during the dual-alloy process promotes the transformation of GBs from the hexagonal h-RE₂O₃ to the cubic c-RE₂O₃ phase, which aligns better with the matrix grains. The optimized GBs facilitate the subsequent diffusion of Tb during GBDP, contributing to the remarkable enhancement of coercivity. Furthermore, the incorporation of Nd during the dual-alloy process tends to form a new Nd₂Fe₁₄B phase around the matrix grains, which results in an increase in magnetic energy ((BH)_max). This research presents a promising method for the preparation of Nd-Fe-B permanent magnets with high coercivity and high magnetic energy, offering significant potential for applications in various industrial sectors.