Microstructure modification and coercivity enhancement of Nd-Ce-Fe-B sintered magnets by grain boundary diffusing Nd-Dy-Al alloy

Grain boundary diffusing process was applied to Nd-Ce-Fe-B sintered magnets using Nd80-xDyxAl20 (x = 0, 20, 40, 60, 80 at.%) ribbons. After diffusion treatment at 900 °C for 13 h and annealing at 470 °C for 2 h, the coercivities of processed samples were 12.5, 17.2, 14.9, 15.2 and 14.3 kOe, respectively. The highest coercivity, with a 70% increasement compared to original sample, was achieved using Nd60Dy20Al20 with the least Dy content. Microstructural investigations show that the coercivity enhancement of these diffused samples is mainly attributed to the magnetic hardening extensive layers along (Nd,Ce)2Fe14B grains and weakening magnetic coupling between adjacent grains by continuous intergranular phases. Nd60Dy20Al20 is a promising diffusion source for producing high-coercivity Nd-Ce-Fe-B sintered magnets with effective Dy utilization.