Microstructure and magnetic properties of grain boundary modified recycled Nd-Fe-B sintered magnets

Full-density recycled Nd-Fe-B sintered magnets were produced from collected waste Nd-Fe-B magnets with the coercivity, mu H-0(C), of 1.30 T and remanence, mu M-0(r), of 1.37 T. A small fraction of Nd6Dy21Co19Cu2.5Fe powder (Grain Boundary Modified (GBM (TM)) powder) was blended to the powders obtained from the Nd-Fe-B waste magnets. The addition of 5.0 wt% GBM (TM) powder resulted in mu H-0(C) = 2.36 T with, mu M-0(r) = 1.29 T in recycled magnets. The temperature coefficient of intrinsic coercivity, beta, in the recycled magnet was measured to be -0.47%/degrees C. Microstructure studies showed that the addition of the GBM (TM) powder increases the volume fraction of a metallic Nd-rich phase in the recycled magnets. 3D tomography revealed a good interconnection of Nd-rich phases through the grain boundaries of the recycled magnet. Microstructure studies suggested that obtained high coercivity in the recycled magnet with 5.0 wt% addition of GBM (TM) is due to the formation of distinct grain boundary phase combined with the formation of Dy-rich shell in the Nd2Fe14B grains with similar to 0.8 at. % Dy. (C) 2016 Elsevier B.V. All rights reserved.