Abstract
In this study, a pre-treatment process was introduced into the grain boundary diffusion process (GBDP) to improve the diffusion efficiency of the source materials into permanent magnets during GBDP using metal ribbon-type sources. Dysprosium (Dy)-based alloy ribbons manufactured by the melt-spin method were used as source materials for the GBDP of the permanent magnets. The microstructure and magnetic properties of the Nd-Fe-B permanent magnets were analyzed to understand the effects of the pre-treatment process. After the pre-treatment process, the diffusion depth of Dy into magnet slightly increased and the Dy content in the heavy rare earth (HRE)-shell also increased. The core-shell structure with a clearly formed HRE shell was observed at a depth of 300 μm from the magnet surface in both pretreated and unpretreated magnets. However, a slight decrease in coercivity was observed in the pre-treated specimens, which was attributed to the formation of rare-earth (RE) oxide. The oxidation control is needed to apply pre-treatment to GBDP using ribbon type metal sources.
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