Enhanced magnetic performance of sintered Nd-Fe-B magnets by Dy-Co film grain boundary diffusion

High magnetic performances are achieved using limited amount of heavy rare earth. The high coercivity of Nd-Fe-B-type magnets are obtained by magnetron sputtering heavy rare earth and cobalt on their surface, followed by vacuum heat treatments. It means that limited heavy rare earth can be used to achieve the higher performance of magnets to meet the demanding requirements. Dy-Co film was successfully deposited on the surface of commercial sintered Nd-Fe-B magnets with direct current (DC) magnetron sputtering, and the elements entered into NdFeB – type magnets through grain boundary diffusion process (GBDP). The maximum energy product, (BH)max, 423.07 kJ/m3 is achieved after the processing. The coercivity, Hcj is increased by 25.7 %, while the remanence, Br, declines slightly. Microstructural investigations indicate that the main phase grain is surrounded by a well-formed (NdxDy1-x)2Fe14B shell. The higher magnetic anisotropy field, HA, of (NdxDy1-x)2Fe14B hard magnetic phases and the optimized grain boundary structure with Dy-Co diffusion contribute to the increase of Hcj. The temperature stability of Dy-Co diffused magnets is improved.