Significantly improved magnetic properties and thermal stability for sintered Nd-Fe-B magnets via grain boundary diffusion of DyCo alloy

Improving the coercivity in high temperature applications is one of the critical issues of NdFeB-based magnets. In this work, DyCo alloy is selected as the diffusion source for grain boundary infiltration to prepare high coercivity NdFeB magnets with excellent thermal stability. Increasing the diffusion temperature until 950 degrees C is beneficial in elevating the coercivity. Magnetic hardening enhancement of interfacial region contributed by the formation of (Nd, Dy)2Fe14B shell and the elevated magnetic isolation effect between adjacent matrix phase grains are responsible to the coercivity improvement. The optimum magnetic properties with the coercivity of 1573 kA/m, the remanence of 1.33 T, and the maximum magnetic energy product of 338 kJ/m3 can be achieved at 900 degrees C. The significant increase of Curie temperature to 51 K is attributed to the higher exchange energy between Co-Co and Fe-Co. Moreover, the thermal stability including the temperature coefficient of remanence alpha and coercivity beta are all improved considerably.