Grain boundary diffusion method is usually applied on the sintered Nd–Fe–B magnets via surface attachment of compounds by Dy or Tb or other heavy rare earth elements. These elements could penetrate into the magnet through the grain boundary under the diffusion treatment at high temperatures above the melting point of the Nd-rich magnet phase. In this investigation the surface attachment method, the diffusion condition, the depth distribution of the diffusion element and the microstructure of the magnet were investigated. On the basis of the results and discussion, it is proposed that the sintered Nd–Fe–B magnets can be utilized to synthesize gradient changing materials chip by a heat treatment process in a single sample. The reasons are that that during the grain boundary diffusion process, there are in parallel the diffusion process of heavy rare earth elements at the grain boundary and the diffusion and substitution process within the main phase grains. The difference of the diffusion rates between the two processes can be adjusted by changing the temperature and time of the diffusion treatment. The thickness, type and combination of the rare earth/non rare earth element compounds attached to the sample surface can be decided accordingly. Finally, the micro-region units at different depth are along the diffusion direction exhibit gradient or different composition-structure-properties, hence the aim to achieve high-throughput synthesis the Nd–Fe–B materials chip by the grain boundary diffusion method could be realized.
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This research was supported by the National Key Research and Development Program of China (No. 2016YFB0700203).
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