Sandwiched structure of hot-deformed Nd-Fe-B permanent magnets processed by Nd-Cu eutectic alloys diffusion

Abstract

A series of sandwiched structures with different near-surface mass fractions x (x = 3 wt%, 4 wt%, 5 wt%) was employed to develop high-coercivity hot-deformed Nd-Fe-B magnets by the addition of 2 wt% Nd-Cu eutectic alloys via adjusting the middle thickness and near-surface thickness. The designed magnet with a pronounced composite structure shows a 23% increase in coercivity with a 6% loss of remanence by adjusting the sandwiched structure at 4 wt% Nd-Cu eutectic alloys in the near-surface regions. The results indicate that the near-surface Nd-Cu-rich “shell” structure can effectively suppress the magnetization reversal of overall magnets, enhancing the coercivity. With the help of loading stress, Nd-Cu liquid enriched at the near-surface regions of the sample is infiltrated into the Nd-Cu-lean middle region, resulting in a concentration gradient. Microstructure characterizations further demonstrate that the infiltrated Nd–Cu eutectic plays a critical role in inhibiting grain growth and intergranular magnetic interaction. The optimized microstructure features suppress the reversed magnetization process, which makes a positive contribution to coercivity.