Journal
ACTA MATERIALIA
Volume 115, Issue -, Pages 278-284Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2016.06.003
Keywords
High-coercivity; Nd-Fe-B magnets; Low heavy-rare-earth concentration; Electrophoretic deposition; Induction coupled plasma with optical electron spectroscope; Core-shell-type microstructure
Funding
- European Project ROMEO (Replacement and Original Magnet Engineering options) [FP7-NMP-2012-SMALL-6]
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Using a grain-boundary diffusion process (GBDP) involving the electrophoretic deposition (EPD) of submicron TbF3 powder, we substantially increased the coercivity of sintered Nd-Fe-B permanent magnets. The experiments used magnets with low heavy-rare-earth (HRE) content (HRE = 1.2 wt%) and a coercivity of 790 kA/m (at 75 degrees C). After experiencing optimized conditions at 875 degrees C for 10 h and subsequent annealing at 500 degrees C for 1 h, the coercivity was increased to 1536 kA/m (at 75 degrees C). This value is 1.94 times higher than that for a sintered magnet, without post-sintering heat treatment. Furthermore, a vibration test revealed satisfactory adhesion of the TbF3 powder to the surface of the magnet with no detected reduction in coercivity. Using field emission gun scanning electron microscopy (FEG-SEM) with an energy dispersive spectroscope (EDS), we confirmed the formation of various secondary intergranular phases and the core-shell-type microstructure, which increases the coercivity. The Tb content in the magnet, exposed to the EPD-based GBDP, was controlled by inductively coupled plasma optical electron spectroscopy (ICP-OES). The additional Tb detected in the magnet due to the described technology was only 0.12 wt%. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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