Change of microstructure and magnetic properties of sintered Nd–Fe–B induced by annealing

 The effect of annealing treatment on the magnetic properties and microstructure of Nd12.0Dy2.8Fe74.7Co3.4Cu0.2B6.9 magnets has been investigated. It is found that intrinsic coercivity iHc is improved with the increase of annealing temperature, and the maximum value is attained at 480 °C. iHc is rapidly decreased with a further increase of annealing temperature. For a given annealing temperature of 480 °C, iHc is increased with the increase of annealing time, and the maximum value is achieved at 2 h. It almost remains constant when annealing time is further increased. However, while the annealing treatment has little effect on remanence Br. It is certain that the increase of iHc for the annealed magnets arises from the more smooth grain boundaries of the RE2Fe14B phases and the more continuous/uniform distribution of RE-rich phases. The great change of microstructure in the annealed magnets can be explained using atomic diffusion theory.