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

Effect of DyF3 and TbF3 additions on the coercivity enhancement in grain boundary diffusion processed Nd-Fe-B permanent magnets

“…Same with the previous investigations [1,5,7], our experiment exhibited that happen increasing the coercivity of sintered Nd-Fe-B permanent magnet after conducting the GBDP using the temperature up to 900°C by both Dy or Tb additions, and then the coercivity decreased if temperatures going up above than 900°C. The diffusion of Dy or Tb into the inside of the magnets was strongly dependent on temperature.…”

“…The coercivity of sintered Nd-Fe-B permanent magnets can be significantly increased by partial substitution of Nd by Dy or Tb elements, because both Dy2Fe14B and Tb2Fe14B phase has much higher magnetocrystalline anisotropy field than that of Nd2Fe14B [1,[4][5][6][7]. Same with the previous investigations [1,5,7], our experiment exhibited that happen increasing the coercivity of sintered Nd-Fe-B permanent magnet after conducting the GBDP using the temperature up to 900°C by both Dy or Tb additions, and then the coercivity decreased if temperatures going up above than 900°C.…”

“…NdFe-B permanent magnets exhibit excellent magnetic properties and currently widely used for some variety applications such as traction motors of electric (hybrid electric) vehicles, generators and transformers [1,2,[3][4][5][6][7]. However, the poor temperature stability of Nd-Fe-B magnets still makes it inapplicable in many potential fields requiring operating temperatures above 150°C [2,5,[7][8]. There are basically two possibilities to improve coercivity at elevated temperatures; either improving the intrinsic temperature dependence of the materials or developing sufficient coercivity at room temperature to guarantee enough coercivity remained at elevated temperatures.…”

“…The core-shell microstructure can be easily obtained through HRE elements diffusion by using different coating methods such as dipping, sputter deposition, vapor deposition and electrophoretic deposition (EPD) [5,7]. However, the HRE elements diffusion method will determine the economics of the procedure.…”

“…With an increase of the RE content in the starting magnets, the fraction of the Nd-rich phase increased, and the grain boundary phase become more continuous [6]. X.J Chao et al [5] reported that when the samples were diffused at 700°C, the grain boundary phase was not continuous. The discontinuous grain boundary phase gives rise to a poor decoupling between the hard-magnetic grains, which corresponds well with the observed low coercivity.…”