Design and preparation of a sintered Nd-Y-Fe-B magnet with high magnetic properties via multi-main-phase process and subsequent grain boundary diffusion

A sintered Nd-Y-Fe-B magnet was designed and manufactured by the multi-main-phase process. Unevenly distributed Y in the magnet decreases the adverse magnetic weakening effect of Y on the coercivity. Grain boundary diffusion process (GBDP) was conducted to further enhance the coercivity of the Nd-Y-Fe-B magnet. The coercivity increases significantly from 884 to 1741 kA/m after GBDP with Pr60Tb10Cu30 alloy. The mechanism of the coercivity enhancement is discussed based on the microstructure analysis. Micromagnetic simulation reveals that when the diffused Tb-rich shell thickness is lower than 12 nm the c-plane shell (perpendicular to the c-axis) is much more effective in enhancing the coercivity than the side plane shell (parallel to the c-axis). But when the Tb-rich shell thickness is above 12 nm the side plane shell contributes more to the coercivity enhancement. The results in this work can help to design and manufacture Nd-Fe-B magnets with low cost and high magnetic properties.