Dysprosium-saving improvement of coercivity in Nd-Fe-B sintered magnets by Dy2S3 additions

Abstract

Dysprosium-added sintered magnets were prepared from blends of Nd15.5(Fe,Co,Ga)78.2B6.3 and Dy2S3 powders; their microstructure and magnetic properties were compared to those of the magnets made with Dy2O3 additions or from single (Nd,Dy)-(Fe,Co,Ga)-B alloys. The addition of Dy2S3 leads to replacement of the neodymium oxide phases in the sintered magnets by the Nd2O2S and NdS phases. The magnets prepared with both the Dy2S3 and Dy2O3 powders exhibited inhomogeneous distribution of Dy within the (Nd,Dy)2Fe14B grains with Dy-rich outer grain regions. However, in a marked difference from the Dy2O3-added and single-alloy magnets, where the grain-boundary oxide phases were Dy-rich, the magnets prepared with Dy2S3 had their sulfur-containing grain-boundary phases depleted of Dy. With the larger fraction of Dy atoms available for alloying the main (Nd,Dy)2Fe14B phase, the magnets prepared with Dy2S3 showed the largest coercivity gain per 1 at.% of the added Dy.

Simultaneous application of Dy–X (X= F or H) powder doping and dip-coating processes to Nd–Fe–B sintered magnets

“…In addition, a slight decrease in the relative density of the as-sintered magnet by DyF 3 powder doping also contributes to the improvement in the grain boundary diffusion depth of Dy during the GBDP. The simultaneous application of the dip-coating and doping processes using DyF 3 and DyH 2 results in saving approximately 2.5 wt.% Dy in the magnet's overall contents. …”

“…The development of a core-shell microstructure, formed by targeting Dy to the grain boundary region of the Nd 2 Fe 14 B phase, is one efficient method for reducing the Dy content in sintered Nd-Fe-B magnets [2][3][4][5][6][7][8][9][10][11][12]. The core-shell microstructure can be obtained by a Dy-X (X = F, H, O, S, or N) powder doping process, or by the grain boundary diffusion process (GBDP) using Dy-X dip-coating [2][3][4][5][6][7][8][9][10][11][12]. DyF 3 and DyH 2 compounds are frequently used for powder doping or dip-coating processes [5][6][7][8][9][10][11][12].…”

Coercivity enhancement of sintered Nd–Fe–B magnets by efficiently diffusing DyF3 based on electrophoretic deposition

“…It has been reported that a simple process called grain boundary diffusion process (GBDP) in which HRE elements powders in different forms (oxide, fluoride or pure metal) are used for coating the magnets and through GBDP process, the core-shell microstructure can be easily obtained by Dy-X (X = F, H, O, or S) powder doping [4][5][6][7]. In the DyF 3 -doped magnet, an ordered Dy-free Nd-O-F phase was formed instead of the unnecessary RE-rich phase (Dy-Nd-O) which ineffectively consumes the Dy in the magnet [4,8].…”

Electroplating Dysprosium from IL-Based Solutions: A Promising Electrochemical Step to Produce Stronger High Performance Nd(Dy)-Fe-B Sintered Magnets

“…12 The introduction of Dy as DyF 3 or Dy 2 O 3 has also proved not to be as efficient as that of pure metallic Dy. 13 Therefore, it was expected that using high purity metallic films result in superior magnetic properties for the GBD-treated magnet.…”