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 H-i(c) is improved with the increase of annealing temperature, and the maximum value is attained at 480 degrees C. H-i(c) is rapidly decreased with a further increase of annealing temperature. For it given annealing temperature of 480 degrees C, H-i(c) 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 B-r. It is certain that the increase of H-i(c) 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. (c) 2005 Elsevier B.V. All rights reserved.